JP2002543625A - Minimal patterned semiconductor devices for display applications - Google Patents

Abstract

(57) Abstract A thin film transistor array includes at least a first transistor and a second transistor. Each transistor includes a source electrode, a drain electrode, a semiconductor electrode, a gate electrode, and a semiconductor layer. The semiconductor layer is continuous between the first transistor and the second transistor. The semiconductor layer is preferably unpatterned. In various display applications, the transistor geometry is selected to provide an acceptable leakage current. In a preferred embodiment, the transistor array is used in an encapsulated electrophoretic display.

Description

DETAILED DESCRIPTION OF THE INVENTION

(Related Application) The present application is based on US Provisional Application No. USSN60 / filed May 5, 1999.
132,642, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION [0002] The present invention relates generally to electronic displays and methods for manufacturing electronic displays, and more particularly, to semiconductor devices for electronic display applications and methods for manufacturing semiconductor devices.

BACKGROUND OF THE INVENTION [0003] Encapsulated particle-based displays provide a useful means for creating electronic displays. There are many types of encapsulated particle-based displays, including encapsulated electrophoretic displays, encapsulated suspended particle displays, and rotating ball displays.

[0004] Encapsulated particle-based displays can be manufactured with high reflectivity, bistable, and optically and electrically efficient. However, obtaining a high resolution display requires that the individual pixels of the display be addressable from adjacent pixels without interference. One way to achieve this goal is to provide an array of non-linear elements, such as transistors or diodes, where each transistor or diode is associated with each pixel. The address electrode is connected to each pixel via a transistor or a diode.

[0005] Processes for manufacturing active matrix arrays of thin film transistors and diodes are well established in display technology. For example, thin film transistors can be manufactured using various deposition and photolithography techniques. The transistor includes a gate electrode, an insulating dielectric layer, a semiconductor layer, and a source electrode and a drain electrode. Applying a voltage to the gate electrode provides an electric field across the semiconductor layer, which dramatically increases the source-to-drain conductivity of the semiconductor layer. This change allows for electrical conduction between the source and gate electrodes.
The gate, source and drain electrodes are usually patterned. Generally, the semiconductor layer and the gate dielectric layer also have stray conduction between adjacent circuit elements (ie,
Patterning to minimize crosstalk). Following these steps, thin film transistors can be manufactured to provide high performance. However, these processes can result in significant costs.

[0006] The high costs in manufacturing thin film transistors result in part from the patterning process. This is because this step requires the use of expensive masks in the photolithography configuration and etching steps. The trend to produce higher performance devices has made precision patterning even more important, further increasing manufacturing costs.

However, for some electronic devices, while cost is still very important,
Does not require high performance. For such devices, it is still desirable to have a means to achieve better yields and reduced manufacturing costs.

SUMMARY OF THE INVENTION In one aspect, the invention features an electronic circuit having lower manufacturing costs, and in another aspect, the invention provides a method of manufacturing an electronic circuit that includes simpler processing steps. It is characterized by. In particular, the circuit has an application in a display device. In a preferred embodiment, the circuit comprises a thin film transistor with a continuous semiconductor layer that mediates current between the source and the drain. In a preferred embodiment, the semiconductor layer is not patterned. Optionally, the circuit may include an unpatterned dielectric layer.

[0009] In one alternative embodiment, the spacing between the transistors is selected to achieve an acceptable leakage current. The geometry of the transistor can be selected to obtain an acceptable leakage current between the first data line and the second data line. Alternatively, the spacing between the first data line and the first pixel electrode may be selected to provide an acceptable leakage current between the first data line and the first pixel electrode.

In one aspect, an array of thin film transistors includes at least first and second transistors, each of the transistors including a source electrode, a drain electrode spaced from the source electrode, a source electrode and a drain electrode. A semiconductor layer electrically connected to both electrodes, and a gate disposed adjacent to the semiconductor layer such that the resistance of the semiconductor layer between the source electrode and the drain electrode can be changed by changing the potential of the gate electrode. Electrodes. The semiconductor layer extends continuously from the first transistor to the second transistor.

In another aspect, an electronic display includes a display medium, a first pixel electrode and a second pixel electrode provided adjacent to the display medium, and a first pixel electrode electrically connected to the first pixel electrode. A second electronic device electrically connected to the electronic device and the second pixel electrode, a first electronic device including a first electrode and a second electronic device including a second electrode, And a semiconductor layer electrically connected to the second electrode and the second electrode. The semiconductor layer continuously extends from the first electrode to the second electrode.

In yet another aspect, an array of thin film transistors that includes at least a first transistor and a second transistor is manufactured by a method that includes the following steps. Providing a substrate, forming an unpatterned semiconductor layer adjacent to the substrate, and forming at least one patterned drain electrode for each of the transistors, the drain comprising: Forming an at least one patterned source electrode for each of the transistors, wherein the source electrode is electrically connected to the semiconductor layer; Forming at least one gate electrode for each of the transistors, wherein the resistance of the semiconductor layer between one source electrode and the drain electrode of the transistor is changed by changing the potential of the gate electrode. The gate electrode is adjacent to the semiconductor layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing and other objects, features and advantages of the present invention, as well as the invention itself, are read from the following description of the preferred embodiments, when read in conjunction with the accompanying drawings. More fully understood.

In one aspect, the invention features a minimally patterned semiconductor device for a display application. In a preferred embodiment,
Semiconductor devices are arrays of thin film transistors. Referring to FIG. 1, an array of transistors 10 includes a substrate 12, a gate electrode 14 for each transistor provided adjacent to the substrate 12, and a gate dielectric layer provided adjacent to the substrate 12 and the gate electrode 14. 16, a semiconductor layer 18 provided adjacent to the gate dielectric layer 16, and a source electrode 20 and a drain electrode 22 for each transistor provided adjacent to the semiconductor layer 18.

For the manufacture of a thin film transistor, the substrate 12 can be, for example, a silicon wafer, a glass substrate, a steel foil, or a plastic sheet. Gate electrode 14
Can be any conductive material such as, for example, a metal or a conductive polymer. The material for use as the semiconductor layer 18 can be, for example, an inorganic material such as amorphous silicon or polysilicon. Alternatively, the semiconductor layer 18 can be formed of an organic semiconductor such as polythiophene and its derivatives, oligothiophene, and pentacene. In general, any semiconductor material useful in creating a conventional thin film transistor can be used in this embodiment. The material for the gate dielectric layer 16 can be an organic or inorganic material. Examples of suitable materials include, but are not limited to, polyimide, silicon oxide, and various inorganic coatings and glasses. Source electrode 20 and drain electrode 22 may be made of any conductive material, such as a metal or a conductive polymer.

The array of transistors shown in FIG. 1 may be manufactured using any one of many suitable methods. For example, vacuum-based methods such as evaporation or sputtering can be used to deposit the necessary materials to form a transistor, after which the deposited material can be patterned. Alternatively, a wet print or transfer method can be used to deposit the necessary materials to form the transistor.

In one embodiment of FIG. 1, the electrodes 14, 20, 22 (ie, the gate electrodes,
The source and drain electrodes) are patterned while the semiconductor layer 18 is being patterned.
And the gate dielectric layer 16 is not patterned, resulting in a significant reduction in processing effort and cost. This circuit design may show some crosstalk between adjacent transistors. However, the degree of crosstalk can be reduced to an acceptable level for some applications.

For some applications, some crosstalk may be tolerated. For example, if only a few gray level states of the display are addressed, a small stray voltage will not significantly affect the overall appearance of the display. In addition, if the display is designed for moderate resolution or over a large area, neighboring circuit elements are far apart from each other, reducing the effects of crosstalk.

In general, crosstalk errors are significant in a display only if they cause unwanted optical changes in the pixel area surrounding any one particular pixel element. Specifically, only two pixels
If there are only two possible switching states, dark or light, slight variations in the electronic signal due to crosstalk will not substantially change the optical appearance of the pixel. However, if an intermediate optical state, i.e., a gray level, is addressed, the display pixel elements are more sensitive to errors. In this situation, it is more likely that incorrect gray levels will be displayed by the pixels.

[0020] Depending on the particular display type and application, smaller or larger error tolerances may be preferred. For example, a monochrome display may be able to tolerate more than 10% leakage current, while a 256 level display generally requires a much lower leakage level. In a preferred embodiment, the display incorporates pixels having a limited number of gray levels. In this case, a given pixel is less sensitive to crosstalk-induced voltage errors. Because it is switched between a limited number of optical states.

For a particular display, the acceptable leakage depends on the degree of error in the electrical signal seen by the pixel and how it affects the optical state of the pixel. This depends on the display medium. For display electrophoresis and rotating ball displays, including ferroelectric liquid crystal displays, which depend on the DC signal being switched, the switching of the electronic signal depends on both the magnitude and duration of the applied voltage. The allowable leak corresponds to the maximum allowable error in the optical state of the display pixel.

The array of transistors described with reference to FIG. 1 can be used to address an electronic display. This embodiment is applicable to various electronic displays, including: Electrophoretic displays, liquid crystal displays, emissive displays (including organic light emitting materials), and rotating ball displays. For liquid crystal displays, error limiting requires a time averaged square of the voltage across the pixel. For current driven emissive displays, the acceptable tolerance for voltage variations depends on how the emission varies with the current through the pixel. In general, display types with switching elements that have a threshold associated with switching, rather than gradually changing in optical state, are more tolerant of errors.

An array of transistors having acceptable crosstalk can be prepared by following the design rules provided herein with reference to FIG. FIG. 2 shows a plan view of conductive leads and elements for driving a display. The array includes: Data lines 30, 32, select lines 36, 46, and pixel electrode 3
4, 38, 40, 42. Voltages are applied to the appropriate data lines 30, 32 and select lines 36, 46 to address the pixel electrodes 34, 38, 40, 42. For example, voltages are applied to data lines 46 and select lines 36 to address a particular pixel electrode 34. Changes in the optical properties of the display element are achieved by addressing the pixel electrodes 34, 38, 40, 42 associated with the display element.

The preferred embodiment includes two design criteria for a properly functioning display. Referring first to FIG. 2, resistance leakage between adjacent data lines 30, 32 is such that the voltage applied to each data line 30, 32 can be controlled within a desired tolerance by the associated driver element. Must be small. Leakage of resistance between adjacent data lines is very large if it leads to an unacceptable voltage drop across the driver circuit or data line. Second, when the corresponding transistor is turned off, two pixels adjacent to the pixel electrode 34 having the pixel electrode 34
Current leakage from each of the three data lines 30 or 32 must be small enough to avoid unacceptable optical artifacts.

In displays where the optical properties are primarily determined by the time-varying voltage profile on the pixel electrodes, such as electrophoresis and twisted nematic displays, current leakage can cause the pixels to maintain a given optical state. It must be small enough over the required period (frame time), so that the pixel voltage does not change by an unacceptable amount for a period of time. The large current leakage between the data line 30 and the pixel electrode 34 causes an unintended shift in the pixel voltage, thus changing the optical state of the pixel. In displays that use luminescent materials, such parasitic leakage currents can cause unwanted light emission from the pixels.

The following description shows how the above two design criteria can be calculated. Because the semiconductor layer is much thinner than the lateral gap between the electrical elements, the calculation of resistance may use a thin film approximation.

(First Design Criteria) The conductivity between adjacent data lines 30, 32 is greatly facilitated by the presence of column pixel electrodes 34, 40. An efficient conduction path can be approximated as: Current can leak through the first data line 30 to the pixel electrodes 34, 40 in the column next to the data line 30. Note that the display has a first row of pixel electrodes 34, 38 and a second row of pixel electrodes 40, 42. More generally, if there are N rows in a particular display, where N is an integer, there are N parallel conductive paths between adjacent data lines 30, 32 and a resistive path between adjacent data lines 30, 32. Can be approximated by the resistance element shown in FIG.

Referring to FIG. 3, R _TFT is the resistance between the first data line 30 and the pixel electrode 34 via the thin film transistor channel in the “off” state, and R ₁ is the first data line the resistance through the remaining gap between the 30 and the pixel electrode 34, R ₂ is the resistance through the gap between the pixel electrode 34 and the second data line 32. The adjacent data lines 30, 3 along the area between the adjacent electrodes 34, 40
The resistance path provided directly between the two can be ignored as insignificant compared to the path provided by the pixel electrodes 34,40. That is, the pixel electrodes 34, 4
0 is a good conductor. Using this model, adjacent data lines 30, 32
The resistance across (R _dd ) can be expressed as: R _dd = 1 / N [R ₂ + (1 / R _TFT + 1 / R ₁ ) ⁻¹ ] where R _TFT = ρL / Wh R _{1 = ρL 1 / (Y p -W} ) h R 2 = ρL 2 / Y p h N is the number of wax of the pixel electrodes, [rho is the bulk resistance of the semiconductor layer, L is the source electrode and the drain electrode L ₁ is the distance between the data line and the adjacent pixel electrode, L ₂ is the distance between the pixel electrode and the adjacent data line, and Y _p is the width of the pixel electrode. Where W is the width of the channel and h is the thickness of the continuous semiconductor layer.

A properly functioning display has a resistance voltage source (R _d ) between adjacent data lines 30, 32 that is much larger than the resistance between the data lines 30, 32. In an approximation where the width of the thin film transistor channel is much smaller than the pixel width (Y _p ),
This condition can be achieved by a display that obeys two inequalities: R ₁ + R ₂ >> NR _d and R _TFT >> NR _{d The} data lines are also adjacent while the select line is off (no array selected). There is no need to charge the pixel. This requirement can be translated as follows: R _TFT >> R _p and R ₂ >> R _p R _p is the resistance through the pixel.

For amorphous silicon, the (undoped) resistivity is approximately 10 ⁸ ohm-cm. A typical semiconductor thickness is about 500 angstroms.
You. This information and pixel dimensions are used to calculate the associated resistance
obtain.

(Second Design Criteria) The minimum distance between the pixel electrode 34 and the data line 30, L _ms Can be obtained by considering the effect of leakage on the pixel voltage. Pi
The following conditions need to be met to avoid unwanted voltage changes on the cell
There is: I_leakT_f≤C_pδV_p I_leakIs the pixel from the data line through the unpatterned semiconductor layer
The leakage current to the electrode, T_fIs the frame time, and C_pIs the pixel
Total capacitance. δV_pIs the voltage induced by the leak on the pixel electrode
Maximum tolerance for shift. This value indicates that the change in voltage is the optical state of the
And what is the effect on the tolerance specified by the display parameters?
It depends on what you give.

I _leak at the maximum spacing can be represented by: I _leak = σwh (V _p −V _d ) / L _ms σ is the conductivity of the semiconductor material, w is the width of the leak path, h Is the thickness of the underlying semiconductor material, and V _d is the data line voltage.

Combining the above two equations gives the following relationship that defines the minimum spacing L _ms : L _ms ≧ σ wh (V _p −V _d ) / C _pix δV _p Applies to embodiments with leak sources. If there are multiple leak sources, I _leak includes the leak current from each leak source, and the minimum spacing L _ms for each leak path needs to be obtained accordingly.

A preferred embodiment of a thin film transistor for use in a capsule electrophoretic display is shown in FIG. 4a. Referring to FIG. 4a, this preferred embodiment includes a data line 30 ', 32', a select line 36 ', a pixel electrode 34', and a capacitor 9 '.
2 '. Various physical dimensions are indicated in microns.

The embodiment of FIG. 4a is shown in cross section in FIG. 4b, but without the scale. Referring to FIG. 4b, an embodiment includes a gate electrode 53 ', a SiN dielectric layer 54', an amorphous silicon layer 56 ', an amorphous silicon contact 58' drain and pixel electrode 59 ', and a capacitor 92'.

To illustrate the operating characteristics of the embodiment of FIG. 4, the samples were conditioned through either a two-mask process as appropriate or a three-mask process for comparison. In the two mask process, the SiN dielectric layer 54 'and the amorphous silicon layer 56' were not patterned, while in the three mask process, both the SiN dielectric layer 54 'and the amorphous silicon layer 56' were patterned. Was. The physical and experimentally measured electrical properties for these two samples are given in the table below.

[0037]

[Table 1] As expected, the leakage current and on / off ratio for the unpatterned sample is inferior to the patterned sample. However, unpatterned samples are both appropriate and suitable for many display applications, as explained above. Referring to FIG. 5, the drain current vs. gate voltage characteristics of the two mask samples are shown. The drain current can vary in magnitude by more than five orders of magnitude by changing the gate voltage from zero to 30 volts. In this large range, the transistor is suitable for many display applications.

Another embodiment of a thin film transistor array will now be given. Referring to FIG. 6, an array of bottom gate transistors 50 includes a substrate 52, a patterned gate electrode 53 for each transistor disposed adjacent to the substrate 52,
Dielectric layer 54 and dielectric layer 5 provided adjacent to gate electrode 53 and substrate 52
4, a boron-doped amorphous silicon layer 56 provided adjacent the amorphous silicon-doped amorphous silicon contact 58, and a plurality of patterned n ⁺ -doped amorphous silicon contacts 58 provided adjacent the amorphous silicon-doped layer 56; A patterned source electrode, drain electrode or pixel electrode 59 disposed adjacent to the doped n ⁺ -doped amorphous silicon contact 58. Each patterned n ⁺ doped amorphous silicon contact 58 is provided between the amorphous silicon layer 56 and the patterned electrode 60 to provide better electrical contact. The contact 58 at the metal-semiconductor interface ensures ohmic behavior. Contact 58, a PH ₃ in the gas phase can be deposited by adding to the SiH _4. Contact 5
8 can also be achieved by high temperature annealing, as an alternative to directly implanting n-type dopants into selected regions of the intrinsic amorphous silicon layer 56, followed by an additional n ⁺ amorphous silicon deposition step. However, contact 58
Is not essential for producing a fully functioning transistor.

Referring to FIG. 7, an array of upper gate transistors 60 includes a substrate 62 and a substrate 6
2, a patterned source electrode, a drain electrode, and / or a pixel electrode 64 for each transistor provided adjacent to each other, a patterned n ⁺ amorphous silicon contact 66 provided adjacent to each electrode 64 , A boron-doped amorphous silicon layer 68 provided adjacent to the contact 66 and the substrate 62, a dielectric layer 70 provided adjacent to the boron-doped amorphous silicon layer 68, and an adjacent to the dielectric layer 70. And a gate electrode 72 for each transistor provided.

Referring to FIG. 8, an array of bottom gate transistors 80 is substantially similar to transistor 50 of FIG. The transistor 80 of FIG. 8 includes an inactive layer 82 provided over the exposed regions of the boron-doped amorphous silicon layer 56. Inert layer 82 may be deposited after patterning of electrode 59. For example, the inert layer 82 can be made of silicon nitride. In one embodiment, a light blocking layer is incorporated into the array of transistors to protect any exposed silicon layer 56. The light blocking layer can be either light absorbing or light reflecting.

Referring to FIG. 9, an array of bottom gate transistors 90 is substantially similar to the array of transistors 80 of FIG. The array of transistors 90 further incorporates a substrate capacitor 92. Substrate capacitor 92 may be formed by simply extending pixel electrode 94 over previous gate line 53. Capacitance is directly proportional to the area of overlap.

In one alternative embodiment, an inexpensive display can be manufactured by minimizing the number of patterning steps. Such displays may take different forms and include, but are not limited to, large area displays, displays having low to medium pixel densities, or microencapsulated electrophoretic display devices. In a preferred embodiment, the semiconductor layers 18, 5
6, or 68 is not patterned. Alternatively, the dielectric layers 16, 54,
Or 70 is not patterned. Alternatively, both the semiconductor layer 18, 56, or 68 and the dielectric layer 16, 54, or 70 are not patterned.

An electronic display may incorporate an array of transistors as described above.
Referring to FIG. 10, electronic display 100 includes a substrate 10 supporting electrodes 102.
1, a display medium 106 provided adjacent to the electrode 102, a plurality of pixel electrodes 104 provided adjacent to the display medium 106, and a separate (d
includes a plurality of discrete electronic devices (e.g., transistors) adjacent and electrically connected to the pixel electrodes 104 supported by a substrate 110 adjacent and electrically connected to the electronic devices. . In this embodiment, the separate electronic device is a transistor. The gate electrode 112, the gate dielectric layer 100, the semiconductor layer 118, and the source electrode 120 of the transistor are shown in this cross section.

The substrate 101 can be made from a transparent material. Substrate 101 can also be a flexible substrate. For example, the substrate 101 can be made of polyester. The electrode 102 can be a normal electrode. Alternatively, electrode 102 may be a multiple array of electrodes. The electrode 102 can be made of a transparent conductive material. For example, an indium tin oxide (ITO), polyaniline, or polythiophene coating may be applied to the substrate 1
01 may be provided on the inner surface.

The display medium 106 may include a plurality of microcapsules 124 dispersed in a binder 126. Each microcapsule 124 may include an electro-optic material. Electro-optical materials are materials that display optical properties in response to electrical signals. The electro-optic material can be, for example, electrophoretic particles or a liquid crystal dispersed in a solvent. Electro-optical materials also include bichroma spheres dispersed in a solvent.
l sphere). Details of the electro-optic material in the microcapsule 124 will be described below. An important property of the electro-optic material within the microcapsule 124 is that the material can display one visible state when an electric field is applied and a different visible state when a different electric field is applied.

In one embodiment, display medium 106 includes a particle-based display medium. In one detailed embodiment, the particle-based display media includes electronic ink. Electronic inks are optoelectronically active materials that include at least two phases: the phase of the electrophoretic control medium and the coating / binding phase. The electrophoretic phase may, in some embodiments, be a single type of electrophoretic particles dispersed in a transparent or colored medium, or different physical properties and electrical properties dispersed in a transparent or colored medium. Including two or more types of electrophoretic particles having specific properties. In some embodiments, the electrophoretic phase is capsule-shaped, ie, there is a phase of the capsule wall between the two phases. The coating / binding phase, in one embodiment, comprises a polymer matrix surrounding the electrophoretic phase. In this embodiment, the polymer in the polymerized binder can be dried, cross-linked, or otherwise cured, similar to a conventional ink, so that the printing process is performed to deposit the electronic ink on the substrate. Can be used for

The optical properties of electronic inks are quite different from other electronic display materials. The most notable difference is that electronic inks provide both high reflectivity and contrast because they are pigment-based (as are normal printing inks). Light scattered from the electronic ink results from a very thin layer of pigment close to the top of the viewing surface. In this respect, it resembles a normal printed image. In addition, electronic inks are easily seen from a wide range of viewing angles in the same manner as printed pages, and such inks come closer to Lambert's contrast curve than any other electronic display material. Because electronic inks can be printed, they can be included on the same surface with all other printing materials, including conventional inks. Electronic ink can be optically stable in all display configurations. That is, the ink can be set to a persistent optical state. The manufacture of displays by printing electronic ink is particularly useful for low power applications due to this stability.

[0048] Electronic ink displays are novel in that they can be addressed by a DC voltage and draw little current. The conductive leads and electrodes used to deliver voltage to the electronic ink display can be of relatively high resistivity. The ability to use resistive conductors substantially expands the number and type of materials that can be used as conductors in electronic ink displays. In particular, no expensive vacuum sputtered indium tin oxide (ITO) conductor, a standard material for liquid crystal devices, is required. Apart from saving costs,
Replacing ITO with other materials may provide benefits in appearance, throughput (printed conductors), flexibility, and durability. In addition, the printed electrodes are in contact only with a solid binder, not with a fluid layer (like a liquid crystal). This means that some conductive materials that would otherwise melt and degrade in contact with the liquid crystal could be used in electronic ink applications. These include opaque metallic inks (eg, silver and graphite inks) for the back electrode, and conductive transparent inks for any substrate. These conductive coatings include conductive or semiconductive colloids, examples being indium tin oxide and antimony doped tin oxide. Organic conductors (polymerizable and molecular organic conductors) can also be used. Polymers include polyaniline and its derivatives, polythiophene and its derivatives, poly (3,4-ethylenedioxythiophene) (PEDOT) and its derivatives, polypyrrole and its derivatives, and polyphenylenevinylene (PPV) and its derivatives. However, the present invention is not limited to these. Organic molecular conductors include, but are not limited to, derivatives of naphthalene, phthalocyanine and pentacene. Because the conductivity requirements are not stringent, the polymer layer can be made thinner and more transparent than conventional displays.

The pixel electrode 104 can be adhered to the display medium 106 through a binder. For example, the binder can be a pressure sensitive adhesive. Pixel electrode 104 can be made of any conductive material. Pixel electrode 104 may be transparent or opaque. For example, pixel electrodes 104 can be made of solder paste, copper, copper clad polyimide, graphite ink, silver ink, and other metal-containing conductive inks. Pixel electrode 104 may be formed on substrate 110 and then coupled to display medium 106.

The individual electrode device can be a non-linear device such as a transistor for addressing the pixels of the display. Alternatively, the non-linear device can be a diode.

The electrodes 112, 120 can be made of any conductive material, either transparent or opaque. The conductive material can be printed, coated, or vacuum sputtered. For example, electrodes 102, 112, 120 can also be made using a transparent material, such as indium tin oxide, and a conductive polymer, such as polyaniline or polythiophene. Alternatively, electrodes 102, 112, 120 may be made of an opaque material such as solder paste, copper, copper clad polyimide, graphite ink, silver ink, and other metal-containing conductive inks.

The architecture of electronic display 100 shown in FIG. 10 is exemplary only, and other architectures for electronic displays may be used in accordance with the present invention.

Materials for Use in Electrophoretic Displays Useful materials for making the above-described capsule electrophoretic displays are described in detail below. Many of these materials are well known to those skilled in the art of manufacturing conventional electrophoretic displays or of microencapsulation. The combination of these materials and processes, together with other necessary components found in a capsule electrophoretic display, make up the invention described herein.

A. Particles As explained above, there is much flexibility in selecting particles for use in an electrophoretic display. For the purposes of the present invention, a particle is any component that can be charged or acquire a charge (ie, has or is capable of electrophoretic mobility), and In some cases, this mobility is
It can be zero or close to zero (ie, the particles do not move). The particles can be neat pigments, or pigmented (lake) or pigment / polymer complexes, or any other component that is charged or acquires a charge. Typical considerations for electrophoretic particles include their optical, electrical,
And surface chemistry. The particles can be organic or inorganic compounds and can either absorb light or scatter light. Particles for use in the present invention can further include scattering pigments, absorbing pigments, and luminescent pigments. The particles may be retroreflected, such as a corner cube, or may be electroluminescent, such as zinc sulfide particles that emit light when excited by an AC electric field, or may be photoluminescent. Finally, the particles can be surface treated to improve charging or interaction with the charging agent, ie to improve dispersibility.

A preferred particle for use in the electrophoretic display of the present invention is titania. The titania particles can be coated with a metal oxide such as, for example, aluminum oxide or silicon oxide. For example, the titania particles can have one or two or more metal oxide coating layers. For example, titania particles for use in the electrophoretic display of the present invention can have an aluminum oxide coating and a silicon oxide coating. The coating can be added to the particles in any order.

The electrophoretic particles are usually pigments, polymers, laked pigments, or some combination of the above. The neat pigment can be any pigment, and for particles of usually light color, pigments such as, for example, rutile (titania), anatase (titania), barium sulfate, kaolin, or zinc oxide are useful. Some typical particles have a high refractive index, a high scattering coefficient, and a low absorption coefficient. Other particles are absorbent, such as carbon black or color pigments used in paints and inks. The pigment must also be insoluble in the suspending fluid. Yellow pigments such as Diarylide Yellow, Hansa Yellow, and Benzidine Yellow also find use in similar displays. Any other reflective material may be used for light colored particles, including non-pigmented materials such as metal particles.

Useful neat pigments are PbCrO ₄ , Cyan Blue GT 55-32
95 (American Cyanamid Company, Wayne, N.
J), Cibacron Black BG (Ciba Company I)
nc. , Newport, DE), Cibacron Turquoise
, Blue G (Ciba), Cibalon Black BGL (Cib
a), Orasol Black BRG (Ciba), Orasol B
rack RBL (Ciba), Acetamine Blac, CBS (
E. FIG. I. du Pont de Nemours and Company,
Inc. , Wilmington, DE), Crossin Scarl
et N Ex (du Pont) (27290), Fiber Black
VF (DuPont) (30235), Luxol Fast Black
L (DuPont) (Solv. Black 17), Nirosine
Base No. 424 (DuPont) (50415B), Oil Bl
ack BG (DuPont) (Solv. Black 16), Rota
lin Black RM (DuPont), Sevron Brillia
nt Red 3 B (DuPont); Basic Black DSC (
Dye Specialties, Inc. ), Hectone Bl
ack (Dye Specialties, Inc.), Azosol B
illiant Blue B (GAF, Diestuff and Ch
electronic Division, Wayne, NJ) (Solv. Blu
e 9), Azosol Brilliant Green BA (GAF)
(Solv. Green 2), Azosol Fast Brillian.
t Red B (GAF), Azosol Fast Orange RA
Conc. (GAF) (Solv. Orange 20), Azosol
Fast Yellow GRA Conc. (GAF) (13900A),
Basic Black KMPA (GAF), Benzofix Bla
ck CW-CF (GAF) (35435), Cellitazol BNF
V Ex Soluble CF (GAF) (Disp. Black 9),
Celliton Fast Blue AF Ex Conc (GAF) (
Disp. Blue 9), Hyper Black IA (GAF) (B
asic Blk. 3), Diamond Black CAP Ex C
onc (GAF) (30235), Diamond Black EAN H
i Con. CF (GAF) (15710), Diamond Black
PBBA Ex (GAF) (16505); Direct Deep Bl
ack EA Ex CF (GAF) (30235), Hansa Yell
ow G (GAF) (11680); Indianthrene Black
BBK Powder. (GAF) (59850), Indocarbon CL
GS Conc. CF (GAF) (53295), Katigen Dee
p Black NND Hi Conc. CF (GAF) (15711),
Rapidogen Black 3G (GAF) (Azoic Blk.
4); Sulfone Cyanine Black BA-CF (GA
F) (26370), Zambezi Black VD Ex Conc.
(GAF) (30015); Rubanox Red CP-1495 (T
he Shewin-Williams Company, Clevela
nd, OH) (15630); Raven 11 (Columbian C)
arbon Company, Atlanta, GA), (carbon black aggregates with a particle size of about 25 μm), Statex B-12 (Co
lumbian Carbon Co. ) (Furnace black with an average particle size of 33 μm), and chrome green, but may also include laked or pigmented pigments. Laked pigments are particles that have a precipitated dye or are dyed. Lakes are easily soluble metal salts of anionic dyes. These are dyes of the azotriphenylmethane or anthraquinone structure containing one or more sulfonate or carboxylic acid groups. These are usually precipitated on the substrate by calcium, barium or aluminum salts. A typical example is Peacock Blue Lake (C
I Pigment Blue 24) and Persian orange, (CI Ac
id Orange 7 rake), Black M Toner (GAF) (
A mixture of carbon black and black dye precipitated on the lake).

The colored particles of the colored type may be composed of any light absorbing material, such as carbon black or inorganic black material. Darker materials can also be selectively absorbent. For example, a dark green pigment may be used. The black particles also include butadiene, styrene, isoprene, methacrylic acid, methyl methyl methacrylate, acrylonitrile, vinyl chloride, acrylic acid, sodium styrene sulfonate, vinyl acetate,
Latex copolymer consisting of chlorostyrene, dimethylaminopropyl methacrylamide, isocyanoethyl methacrylate, and N- (isobutoxymethacrylamide), and optionally containing conjugated diene compounds such as diacrylate, triacrylate, dimethyl acrylate and trimethacrylate For example, it can be formed by dyeing a latex with a metal oxide such as. Black particles can also be formed by dispersion polymerization techniques.

In systems that include pigments and polymers, the pigments and polymers may form multiple domains within the electrophoretic particles, or may be a collection of smaller pigment / polymer bound particles. Alternatively, the central pigment core may be surrounded by a polymer shell. The pigment, the polymer, or both, may include a dye. The optical purpose of the particles can be to scatter light, absorb light, or both. Useful sizes can range from 1 nm to about 100 μm, as long as the particles are smaller than the bounding capsule. In a preferred embodiment, the density of the electrophoretic particles can be substantially matched to the density of the suspended (ie, electrophoretic) fluid. As defined herein, the suspending fluid has a density that is “substantially matched” to the density of the particles when the respective density difference is about 0 to about 2 g / ml. The difference is preferably between about 0 and about 0.5 g.
/ Ml.

Useful polymers for the particles include polystyrene, polyethylene, polypropylene, phenolic resin, DuPont Elvax resin (ethylene-vinyl acetate copolymer), polyester, polyacrylate, polymethacrylate, ethylene acrylic acid copolymer Or methacrylic acid copolymer (Nucrel Resins)
-DuPont, Primacor Resins-Dow Chemical
l), acrylic copolymers and terpolymers (Elvacite Resin)
s, DuPont), and PMMA. Useful materials for homopolymer / pigment phase separation in high shear melts include polyethylene, polypropylene, polymethyl methacrylate,
Polyisobutyl methacrylate, polystyrene, polybutadiene, polyisoprene, polyisobutylene, polyauryl methacrylate,
Polystearyl methacrylate, polyisobornyl (polyisoborn)
yl) including, but not limited to, methacrylate, poly-t-butyl methacrylate, polyethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylonitrile, and copolymers of two or more of these materials. Some useful pigment / polymer complexes that are commercially available are Process Magenta PM 1776 (from Magruder Co.).
lor Company, Inc. , Elizabeth, NJ), Meth
yl Violet PMA VM6223 (Magruder Color
Company, Inc. , Elizabeth, NJ), and Napht.
hol FGR RF6257 (Magruder Color Company)
y, Inc. , Elizabeth, NJ).

The pigment-polymer composite is subjected to a physical treatment (eg, attrition)
Or ball milling), chemical treatment (eg, microencapsulation or dispersion polymerization), or any other treatment known in the art of particle production. From the following non-limiting examples, it can be seen that processes and materials for both particle production and particle charge generally come from the field of liquid toner or liquid immersion development. Thus, the known processes from any liquid development are particularly, but not exclusively, relevant.

Although new and useful electrophoretic particles may still be discovered, some particles already known to those skilled in electrophoretic displays and liquid toners may also prove useful. In general, the demand for polymers for liquid toners and encapsulated electrophoretic inks is that pigments or dyes need to be easily incorporated into that demand, either by physical, chemical, or physico-chemical processing. Similarly, it may promote the stability of the colloid, may include charged sites, or may be capable of incorporating materials that include charged sites. One general requirement from the liquid toner industry that is not shared by encapsulated electrophoretic inks is that the toner must be able to "fix" the image, i.e., heat melt together and produce a uniform film after the deposition of the toner particles. That is.

Typical manufacturing techniques for particles come from liquid toners and other techniques, and include ball milling, friction, jet milling, and the like. The process is illustrated for the case of colored polymer particles. In such cases, the pigment is synthesized in the polymer, usually in some high shear mechanism such as a screw extruder. The composite is then polished (wet or dry) to a starting size of about 10 μm. The material is then, for example, ISOPAR® (Exxon
(Houston, Tex.) With some conductivity controlling material and ground with high shear for several hours to final particle size and / or size distribution.

Another manufacturing technique for particles resulting from the liquid toner field is to add polymers, pigments, and suspending fluids to a media mill. The mill is started and at the same time,
The polymer is heated to a temperature at which the polymer expands substantially with the solvent. This temperature is usually 100
It is around ° C. In this state, the pigment is easily sealed to the swollen polymer. After a suitable time, usually a few hours, the mill is gradually cooled to ambient temperature while stirring. Milling can be continued for some time to achieve a sufficiently small particle size, usually a few microns in diameter. A charging agent may be added at this point. Optionally, more suspending fluid can be added.

[0065] Dispersion polymerization, miniemulsion polymerization or microemulsion polymerization, suspension polymerization precipitation, phase separation, solvent evaporation, in situ polymerization, seeded emulsion polymerization, or any process falling within the general category of microencapsulation. Chemical treatments such as can be used. A typical process of this type is a phase separation process in which the dissolved polymeric material is precipitated from solution onto the dispersed pigment surface through solvent dilution, evaporation, or temperature change. Other treatments include, for example, chemical means for dyeing the polymerized latex with metal oxides or dyes.

B. Suspension Fluid A suspension fluid containing particles can be selected based on properties such as density, refractive index, and solubility. Suitable suspending fluids have low dielectric constant (about 2) and high volume resistivity (about 10 ¹⁵ o
hm-cm), low viscosity (less than 5 cst), low toxicity and low environmental impact, low water solubility (less than 10 ppm), high specific gravity (more than 1.5), high boiling point (more than 90 ° C)
, And low refractive index (less than 1.2).

The choice of the suspending fluid may be based on chemical inertness, density compatible with the electrophoretic particles, or chemical compatibility with both electrophoresis and binding capsules. The viscosity of the fluid is
If you want to move particles, it needs to be low. The refractive index of the suspending fluid may also be substantially compatible with the pain index of the particles. As used herein, the refractive index of a suspending fluid is such that the difference between the respective refractive indices is from 0 to about 0.3, preferably from about 0.05 to about 0.2. "Substantially matches" the refractive index of the particles.

In addition, the fluid may select a weak solvent for some polymers, which is advantageous for use in producing microparticles. Because it increases the range of polymeric materials useful in producing polymer and pigment particles. Organic solvents, such as halogenated organic solvents, saturated linear or branched hydrocarbons, silicone oils, and low molecular weight halogen-containing polymers are some useful suspending fluids. The suspending fluid may include a single fluid. However, fluids are often mixtures of two or more fluids to adjust their chemical and physical properties. In addition, the fluid
It may include a surface modifier to modify the surface energy or charge of the electrophoretic particles or boundary capsule. Reactants or solvents for the microencapsulation process, such as oil-soluble monomers, can also be included in the suspending fluid. Charge control agents can also be added to the suspending fluid.

Useful organic solvents are, for example, epoxides such as decane epoxide and dodecane epoxide; for example, cyclohexyl vinyl ether and Decave® (International Flavors & Fragrance)
s, Inc. , New York, NY); and aromatic carbohydrates such as, for example, toluene and naphthalene. Useful halogenated organic solvents include, but are not limited to, tetrafluorodibromoethylene, tetrachloroethylene, trifluorochloroethylene, 1,2,4-trichlorobenzene, carbon tetrachloride. These materials have a high density. Useful carbohydrates are found in the Isopar® series (E
xxon, Houston, TX), Norpar® (normal paraffinic liquid series), Shell-Sol® (Shell,
Houston, TX), and Sol-Trol® (Shel)
Including, but not limited to, dodecane, tetradecane, aliphatic carbohydrates, naphtha, and other petroleum solvents in l). These materials usually have a low density. Useful examples of silicone oils include, but are not limited to, octamethylcyclosiloxane and higher molecular weight cyclic siloxanes, poly (methylphenylsiloxane), hexamethyldisiloxane, and polydimethylsiloxane. These materials usually have a low density. Useful low molecular weight halogen containing polymers are poly (chlorotrifluoroethylene) polymers (Halogenated hydro).
rocarbon Inc. , River Edge, NJ), Galden
(Registered trademark) (perfluorinated ether from Ausimont, Morristown, NJ) or Dupont (Wi
(Krytox (R) from Lincoln, DE). In a preferred embodiment, the suspending fluid is a poly (chlorotrifluoroethylene) polymer. In a particularly preferred embodiment, the polymer is
It has a degree of polymerization from about 2 to about 10. Many of the above materials are available in a range of viscosities, densities, and boiling points.

The fluid needs to be able to form into small droplets before the capsule is formed. Processes for forming droplets include flow-through jets, membranes, nozzles, or orifices, and shear-based emulsification schemes. Droplet formation may be facilitated by an electric or sonic field. Surfactants and polymers can be used to promote droplet stabilization and emulsification in the case of emulsion type encapsulation. A preferred surfactant for use in the displays of the present invention is sodium dodecyl sulfate.

[0071] It may be advantageous for some displays that the suspending fluid contains a light absorbing dye. The dye needs to be soluble in the fluid, but is generally insoluble in the other components of the capsule. There is much flexibility in choosing the dye material. Dyes can be pure compounds or mixtures of dyes to achieve a particular color, including black. Dyes can be fluorescent, thereby producing a display whose fluorescent properties depend on the location of the particles. Dyes can be photoactive, change to another color, or become colourless upon emission of either visible or ultraviolet light, providing another means for obtaining an optical response. Dyes are also polymerizable and can form solids that absorb the polymer inside the boundary shell.

There are many dyes that can be selected for use in a capsule electrophoretic display. Important properties herein are light fixability, solubility in suspension, color, and cost. These are a class of dyes of the azo, anthraquinone, and triphenylmethane type, which can be chemically modified to increase solubility in the oil phase and reduce absorption by the particle surface.

Some dyes already known to those skilled in the art of electrophoretic displays have proven useful. Useful azo dyes are Oil Red dyes, as well as Sudan
Including, but not limited to, Red and Sudan Black series dyes. Useful anthraquinone dyes are Oil Blue dyes, and Macr
Includes, but is not limited to, the olex Blue series of dyes. Useful triphenylmethane dyes include Michler's Hydrol, Malachit
e Green, Crystal Violet, and Auramine O
Including, but not limited to.

C. Charge Control Agents and Particle Stabilizers Charge control agents are used to provide good electrophoretic mobility to electrophoretic particles. Stabilizers are used to prevent clumping of the electrophoretic particles and to prevent the electrophoretic particles from irreversibly depositing on the capsule wall. Either component can be composed of materials that span a wide range of molecular weights (low molecular weight, oligomeric, or polymeric) and can be pure or a mixture. In particular, suitable charge control agents are generally adapted from liquid toner technology. Charge control agents used to modulate and / or stabilize the charge on the particle surface include liquid toners, electrophoretic displays,
It is applied as generally known in the art of water-insoluble paint dispersion and engine oil additives. In all of these techniques, charged species can be added to a water-insoluble medium to increase electrophoretic mobility or increase electrostatic stabilization. The material may also improve steric stabilization. The different theory of charge is
It is hypothesized, including selective ion adsorption, proton transfer, and contact charging.

[0075] An optional charge control agent or charge director may be used. These components typically comprise a low molecular weight surfactant, a polymerizing agent, or a mixture of one or more components,
It then acts to stabilize or otherwise adjust the sign and / or magnitude of the charge on the electrophoretic particles. The charge properties of the pigment itself can be explained by taking into account the acidic or basic surface properties of the pigment, or
It can occur at the carrier resin surface (if present), or a combination of the two. Other pigment properties that may be relevant are particle size distribution, chemical composition, and light fixability.
Charge control agents used to modulate and / or stabilize the surface charge of particles include those commonly known in the fields of liquid toners, electrophoretic displays, water-insoluble paint dispersions, and engine oil additives. The same applies. In all of these techniques, charged species can be added to a water-insoluble medium to increase electrophoretic mobility or increase electrostatic stabilization. The material may also improve steric stabilization. Different theories of charge have been postulated, including selective ion adsorption, proton transfer, and catalytic charging.

[0076] Charge adjuvants may also be added. These materials increase the effectiveness of the charge control agent or charge director. The charge adjuvant may be a polyhydroxy compound or an amino alcohol compound, which are suitably soluble in the suspending fluid in an amount of at least 2% by weight. Examples of polyhydroxy compounds containing at least two hydroxyl groups are ethylene glycol, 2,4,7,9-teramethyl-decine-4
, 7-diol, poly (propylene glycol), pentaethylene glycol,
Including, but not limited to, tripropylene glycol, triethylene glycol, glycerol, pentaerythritol, glycerol tris (12 hydroxystearate), propylene glycerol monohydroxysterate, and ethylene glycol monohydroxysterate. At least one in the same molecule
Examples of amino alcohol compounds containing one alcohol action and one amino action are triisopropanolamine, triethanolamine, ethanolamine,
Including but not limited to 3-amino-1-propanol, o-aminophenol, 5-amino-1-pentanol, and tetrakis (2-hydroxyethyl) ethylenediamine. The charge adjuvant comprises from about 1 mg / g to about 1 mg of the mass of the particles.
Preferably at 00 mg / g and more preferably at about 50 mg / g to about 200 mg / g in the suspending fluid.

The particle surface can also be chemically modified, for example, to promote dispersion, improve surface charge, and improve dispersion stability. The surface conditioner is an organic siloxane,
Organohalogen silanes and silane binders with other functional groups (Dow C
orning® Z-6070, Z-6124, and three additives, Mi
organic titanates and zirconates (Tyzor® TOT, TBT, and TE Series, DuPont, Wilm)
inton, DE); hydrophobic agents such as alkyl and alkyl benzene sulfonic acids of long atomic chains (C12 to C50), fatty amines or diamines, and salts or quaternary derivatives thereof; and can be covalently attached to the particle surface. Includes an amphipathic polymer.

Generally, it is believed that the charge is caused by an acid-base reaction between certain parts present in the continuous phase and the particle surface. Thus, useful materials are those that can cooperate with reactions similar to those known in the art or any other charge reactions.

Useful different non-limiting classes of charge control agents are organic sulfates or sulfonates, metal soaps, block or comb copolymers, organic amides,
Includes organic zwitterions, as well as organic phosphates and phosphites. Useful organic sulfates and sulfonates are sodium bis (2-ethylhexyl) sulfosuccinate, calcium dodecylbenzenesulfonate, calcium petroleum sulfonate, barium basic or neutral dinonylnaphthalenesulfonate , Neutral or basic calcium dinonylnaphthalenesulfonate, sodium dodecylbenzenesulfonate, and ammonium lauryl sulfate. Useful metal soaps include neutral or basic petronate barium,
Petronate calcium, Co-, Ca-, Cu-, Mn-, Ni of naphthenic acid
-, Zn- and Fe- salts, Ba-, Al-, Zn-, Cu- stearic acid
, Pb-, and Fe-salts and aluminum tristearate, aluminum octanoate, lithium heptanoate, iron stearate, iron distearate, barium stearate, chromium stearate, magnesium octanoate, calcium stearate, iron naphthenate, And trivalent metal carboxylic acids, such as zinc and naphthenate, Mn- and Zn-heptanoates, and Ba-, Al-
, Co-, Mn-, and Zn-octanoate. Useful block or comb copolymers are (A) 2- (N, N) -dimethylaminoethyl methacrylate polymer, quartered with methyl-p-toluene sulfate, and (B) poly-2- AB diblock copolymer of ethylhexyl methacrylate and the soluble end of poly (12-hydroxystearic acid) (
and a comb graft copolymer having a molecular weight of about 1800 and a pendant on a group of petroleum soluble anchors of poly (methyl methacrylate methacrylic acid). Useful organic amides are OLOA 12
00, and polyisobutylene succinimides, such as, but not limited to, N-vinyl pyrrolidone polymers. Useful organic zwitterions include, but are not limited to, retin. Useful organic phosphates and phosphites include, but are not limited to, sodium salts of phosphorylated mono- and diglycerides having saturated and unsaturated acid substituents.

A particle dispersion stabilizer may be added to prevent flocculation or sticking of the particles to the capsule wall. For typical high resistivity liquids used as suspending fluids in electrophoretic displays, water-insoluble surfactants can be used. These are glycol ethers, acetylene glycols, alkanolamides, sorbitol derivatives,
Including but not limited to alkylamines, quaternary amines, imidazolines, dialkyl oxides, and sulfosuccinates.

D. Encapsulation Encapsulation has a long and rich history, and many processes and polymers have been shown to be useful in making capsules. Encapsulation of the internal phase can be achieved in many different ways. Many suitable procedures for microencapsulation are described in Microencapsulation, Processes.
and Application, (IE Vandegaer, ed.)
And Plenum, Press, New York, NY (1974) and Gutcho, Microcapsules and Microenca.
Pulsation Technologies, Nuyes Data Cor
p. Park Ridge N .; J. (1976). The process falls into several general categories, all of which can be applied to the present invention. These are physical processes such as interfacial polymerization, in-situ polymerization, coextrusion and other phase separation processes, in-liquid curing, and simple / complex coacervation.

It should be noted that a number of materials and processes are useful to clearly describe the displays of the present invention. Materials useful for simple coacervation processes include, but are not limited to, gelatin, polyvinyl alcohol, polyvinyl acetate, cellulose derivatives (eg, carboxymethyl cellulose). Materials useful for complex coacervation processes include gelatin, acacia, carrageenan, carboxymethylcellulose, hydrolyzed styrene anhydride copolymer, agar, alginate, casein, albumin, methyl vinyl ether-co-maleic anhydride and cellulose phthalate. However, it is not limited to these. Useful materials for the phase separation process are polystyrene, PM
MA includes, but is not limited to, MA, polyethyl methacrylate, polybutyl methacrylate, ethyl cellulose, polyvinyl pyridine, polyacrylonitrile.
Materials useful for the in-situ polymerization process include aldehydes, polyhydroxyamides having melamine or urea and formaldehyde, water-soluble oligomers of condensates of melamine or urea and formaldehyde, vinyl monomers (e.g., styrene,
MMA, acrylonitrile, etc.). Finally, useful materials for the interfacial polymerization process include, but are not limited to, diacyl chlorides, for example, sebacoyl, adipoly, di- or poly-amines or alcohols and isocyanates. Useful emulsion polymerization materials are
Including, but not limited to, styrene, vinyl acetate, acrylic acid, butyl acrylate, t-butyl acrylate, methyl acrylate, butyl methacrylate.

The resulting capsules can be dispersed in a curable carrier and the resulting inks can be printed on large and arbitrarily shaped or curved surfaces using conventional printing and coating techniques, May be coated.

In view of the present invention, one skilled in the art will select an encapsulation procedure and wall material based on the desired encapsulation properties. These characteristics include the distribution of the capsule radius,
It includes the electrical, mechanical, diffusion and optical properties of the capsule wall and its chemical compatibility with the internal phase of the capsule.

The capsule wall generally has a high electrical resistivity. Walls with relatively low resistivity can be used, but this limits performance when relatively high address voltages are required. The capsule wall should also be mechanically strong (but mechanical strength is not critical if the finished capsule powder is dispersed in a curable polymer binder for coating). The capsule wall should generally not be porous. However, if it is desired to use a capsule procedure that produces porous capsules, they can be overcoated (ie, a second encapsulation) in a post-processing step. Further, when the capsules are dispersed in a curable binder, the binder functions to close the pores.
The capsule wall should be optically transparent. However, the wall material can be selected to match the refractive index of the internal phase of the capsule (ie, the suspending fluid) or the binder in which the capsule is dispersed. In some applications (eg, insertion between two fixed electrodes), a monodisperse capsule radius is desirable.

The encapsulation procedure involves the polymerization between urea and formaldehyde in the aqueous phase of an oil-in-water emulsion in the presence of a negatively charged, carboxy-substituted, linear hydrocarbon polyelectrolyte material. About. The resulting capsule wall is a urea / formaldehyde copolymer that individually surrounds the internal phase. The capsule is transparent, mechanically strong and has good resistivity properties.

A related technique for in situ polymerization uses oil-in-water emulsions. Oil-in-water emulsions are formed by dispersing an electrophoretic component (ie, a dielectric liquid containing a suspension of dye particles) in an aqueous environment. The monomers are polymerized to form a polymer having a higher affinity for the inner layer than for the aqueous phase. Thereby,
Condenses around the emulsified oily droplets. In one particularly useful in situ polymerization process, urea and formaldehyde condense in the presence of poly (acrylic acid) (see, for example, US Pat. No. 4,001,140). In another useful process, any of a variety of cross-linking reagents generated in the aqueous solution accumulate around the microscopic oily droplets. Such crosslinking agents are aldehydes, especially formaldehyde, glyoxal or glutaraldehyde; alum;
Zirconium salt; including polyisocyanate. U.S. Pat. No. 4,001, shown above.
No. 4,140, and U.S. Pat. No. 4,273,672, the entire disclosures of which are incorporated herein by reference.

The coacervation approach also uses an oil-in-water emulsion. One or more colloids are coacervated (ie, agglomerated) from the aqueous phase;
As a shell around the oily droplet, it is deposited via control of temperature, pH and / or relative concentration, thereby producing microcapsules. Suitable materials for coacervation include gelatin and gum arabic.

The interfacial polymerization approach relies on the presence of an oil-soluble monomer of the electrophoretic component. The oil-soluble monomer reappears as an emulsion in the aqueous phase. The monomer within the slightly hydrophobic droplet reacts with the monomer introduced into the aqueous phase and polymerizes at the interface between the droplet and the surrounding aqueous medium, forming a shell around the droplet. The resulting wall may be relatively thin and permeable, but this process does not require the elevated temperature characteristics of some other processes. Therefore, from the viewpoint of selecting a dielectric liquid, there is room for greater flexibility.

The coating aid can be used to improve the uniformity and quality of the coated or printed electrophoretic ink material. Generally, wetting agents are added to adjust the interfacial tension at the coating / substrate interface and adjust the liquid / gas interfacial tension.
Wetting agents include, but are not limited to, anionic or cationic surfactants and non-ionic species such as silicone or fluoropolymer based materials. Dispersants can be used to modify the interfacial tension between the capsule and the binder, providing control over aggregation and particle settling.

A surface tension modifier can be added to adjust the air / ink interfacial tension. In general, polysiloxanes can be used in such applications to minimize surface defects while improving other defects in the coating. The surface tension modifier is, for example, D
uPont (Wilmington, DE) to Zonyl® series (series), 3M (St. Paul, MN) to Fluorod (
Registered trademark) series and AutoChem (Glen Rock)
Fluorinated surfactants, such as fluoroalkyl series from NJ); for example, Union Carbride (Danbury, CT)
Siloxanes, such as, for example, Silwet®, and polyethoxy and polypropoxy alcohols. Defoamers (eg, silicone and silicone-free polymeric materials) can be added to enhance the movement of air from inside the ink to the surface and to facilitate the destruction of air bubbles at the coating surface. Other useful defoamers are made from combinations of glyceryl esters, polyhydric alcohols, synthetic defoamers such as alkylbenzenes, natural fats, fatty acids and oil solutions of metal soaps, and dimethylsiloxane polymers and silica. But not limited thereto. Stabilizers such as uv-absorbers and antioxidants may also be added to increase the life of the ink.

[0092] Other additives may be used in the coating fluid to control properties such as coating viscosity and foaming. Stabilizers (UV-absorbers, antioxidants) and other additives may show utility in practical materials.

(E. Binder Material) A binder is used as a non-conductive, adhesion medium that binds the electrode material to the capsule dispersion and supports and protects the capsule. Binders are available in many forms and chemical forms. These include, among water-soluble polymers, water-borne polymers, oil-soluble polymers, thermoset and thermoplastic polymers, and radiation-curable polymers.

Water-soluble polymers include various polysaccharides, polyvinyl alcohol,
N-methylpyrrolidone, N-vinylpyrrolidone, various Carbowax (
(Registered trademark) series (Union Carbide, Danbu)
ry, CT) and poly-2-hydroxyethyl acrylate.

[0095] The aqueous dispersion or drinking water vehicle system is generally a latex composition. This is N
eorez® and Neocryl® resins (Zeneca®)
Resins, Wilmington, MA), Acrysol®
(Rohm and Haas, Philadelphia, PA), Bayh
hydrol® (Bayer, Pittsburgh, PA) and C
ytec Industries (West Paterson, NJ) HP 1
ine. These are generally latexes of polyurethane, sometimes one or more acrylic, polyester, polycarbonate, or silicone compounds, each of which has a glass transition temperature, "tack"
Final set with a specific set of properties defined by the degree of softness, clarity, flexibility, water permeability, solvent durability, elongation modulus, tensile strength, thermoplastic flow, and solids level Contributes to resin. Certain water-borne systems can be mixed with reactive monomers and catalyzed to form more complex resins. For example, some can be further cross-linked by the use of a cross-linking reagent such as aziridine that reacts with a carboxyl group.

Typical applications of waterborne resins and of water-soluble capsules are as follows. The particle mass is centrifuged to separate excess water. After a given centrifugation process, for example 10 minutes at 60 × G, capsules are found at the bottom of the centrifuge tube and the water part is found at the top. The water portion is carefully removed (by decanting or pipetting). The mass of the remaining capsule is measured and the mass of the resin is added, whereby the mass of the resin is one eighth to one tenth of the weight of the capsule. The mixture is mixed gently and gently in a vibrating mixer, suitably for one and a half hours. 1
After half an hour, the mixture is ready to be coated on a suitable substrate.

[0097] Thermosetting resin systems are exemplified by epoxy systems. These two-component systems vary greatly in viscosity, and the reactivity of the pair determines the "pot life" of the mixture. If the pot life is long enough to allow the coating operation, the capsules can be coated in an ordered configuration in the coating process before resin curing and solidification.

[0098] Thermoplastic polymers (often polyesters) are melted at elevated temperatures.
A common application for this type of product is hot melt adhesives.
The dispersion of the heat-resistant capsule can be coated in such a medium. The solidification process begins upon cooling, and the final hardness, clarity, and flexibility are affected by polymer branching and molecular weight.

Oily or solvent-soluble polymers are often similar in construction to water-borne resin systems, except for the water itself. The tolerance in solvent-based formulations is great and is limited only by solvent choice and polymer solubility. The viability of the capsule itself is quite important in solvent based systems. The integrity of the capsule wall cannot be compromised in any way by the solvent.

[0100] Radiation curable resins are generally found among solvent-based systems. Capsules can be dispersed and coated in such a medium. The resin may then be cured by timed exposure to a threshold level of ultraviolet radiation. The wavelength of the radiation is long or short. In all cases of curing the polymer resin, the ultimate properties are branching,
It is determined by the molecular weight of monomers and oligomers, and crosslinking.

However, many water reducing monomers and oligomers are commercially available. In the strict sense, they are not water-soluble, but water is an acceptable diluent at low concentrations and can be dispersed relatively easily into the mixture. Under these circumstances, water is used to reduce viscosity (initially thousands to hundreds of thousands of centipoise). Water-based capsules (such as those formed from protein or polysaccharide materials) can be dispersed and coated in such media if the viscosity can be sufficiently low. Curing of such systems is generally by ultraviolet radiation.

Referring to FIG. 11a, an embodiment of an electrophoretic display using the thin film transistor array of the present invention is shown. FIG. 11a shows a cross-sectional view of an electrophoretic display 130 constructed using electronic ink. Binder 132 includes at least one capsule. The capsule is filled with a plurality of particles 136 and a suspension fluid 138
It is dyed. In some embodiments, particles 136 are titania particles. When a DC field of the appropriate polarity is applied to the capsule 134, the particles 136 move to the display surface of the display and scatter light. When reversing the applied electric field, the particles 136 move to the back of the display, which then darkens the display surface of the display.

FIG. 11b shows another electrophoretic display 140 constructed using electronic ink.
2 shows a cross section of FIG. The display includes a first particle set 1 in a capsule 141.
42 and a second set of particles 144. First particle set 142 and second particle set
Of particles 144 have symmetric optical properties. For example, the first particle set 1
42 and the second set of particles 144 may have different electrophoretic mobilities. Further, the first particle set 142 and the second particle set 144 can have symmetric colors. For example, the first set of particles 142 may be white, while the second set of particles 144 may be black. Capsule 141 further includes a substantially transparent fluid. The capsule 141 has an electrode 146 and an electrode 146 ′ arranged close to the capsule 141. Electrodes 146 and 146 'are connected to a voltage source 148. The voltage source 148 supplies an electric field to the capsule 141. In some embodiments,
When an electric field is applied to the electrodes 146 and 146 ', the first set of particles 142
Move toward electrode 146 ′, while the second set of particles 144 moves toward electrode 146. In another embodiment, when an electric field is applied to the electrodes 146 and 146 ′, the first set of particles 142 moves rapidly toward the electrodes 146 ′,
On the other hand, the second set of particles 144 moves slowly toward the electrode 146 or does not move at all. Thereby, the first set of particles is preferentially clustered at the microcapsule surface adjacent to the electrode 146 '.

FIG. 11 c shows a cross-sectional view of the suspended particle display 150. Suspended particle display 150 includes needle-like particles 152 within transparent fluid 154. The particles 152 change their orientation when an AC field is applied to the electrodes 156 and 156 '. When applying an AC field, the particles 152 are oriented perpendicular to the display surface and the display appears transparent. When removing the AC field, particles 152
Are randomly oriented and the display 150 appears opaque.

The electrophoretic and suspended particle displays provided in FIGS. 9a-9c are merely exemplary, and other electrophoretic displays can be used in accordance with the present invention.

In another detailed embodiment, the display medium 106 may include a plurality of bichromal spheres as shown in FIG. 11d. Bichromal sphere 1
60 generally includes a positive hemisphere 162 of a first color and a negative hemisphere 164 of a second color within a liquid medium 166. The ball 16 via the pair of electrodes 168, 168 '
When an electric field is applied to zero, the sphere 160 rotates and displays one color of the two hemispheres 162, 164.

In an alternative embodiment, an array of transistors with reduced crosstalk is created by increasing the resistivity of the semiconductor layer. For example, if the semiconductor layer is amorphous silicon, which is slightly n-type, the semiconductor may be slightly doped with boron or an equivalent p-type dopant to increase the resistivity of the semiconductor layer.
If too much boron is doped into the semiconductor layer, the semiconductor layer becomes p-type and the resistivity decreases. For example, in display applications, the minimum "on" required to adjust the boron doping to drive the display pixels
Current is supplied to the transistor while at the same time maintaining sufficient isolation between adjacent elements or signals. As discussed, the space between the adjacent source and drain electrodes of the transistor and the metal signal line must in this embodiment be large enough to suppress charge leakage through the underlying semiconductor layer. Must. Knowing the leakage current, electrode potential, semiconductor conductivity and thickness of the various materials, this minimum space can be derived through resistance calculations.

The present invention has been particularly shown and described with reference to certain preferred embodiments, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood by those skilled in the art that various changes in form and detail may be made. For example, an array of active or passive elements can be made in accordance with the present invention. Arrays of elements can be used in devices other than displays.

[Brief description of the drawings]

FIG. 1 is a sectional view of a thin film transistor array according to an embodiment of the present invention.

FIG. 2 shows a plan view of one embodiment of an electronic display with the display media removed.

FIG. 3 shows the location of a resistive leak path of the display of FIG. 2;

FIG. 4a shows a plan view of one embodiment of a thin film transistor.

FIG. 4b shows a schematic representation of a cross-sectional view corresponding to the embodiment of the transistor shown in FIG. 4a.

FIG. 5 shows a graph of drain current versus gate voltage for one sample of a two mask transistor of the type shown in FIG. 4a.

FIG. 6 shows a cross-sectional view of a thin film transistor array according to one embodiment of the present invention.

FIG. 7 is a sectional view of a thin film transistor array according to an embodiment of the present invention.

FIG. 8 shows a cross-sectional view of a thin film transistor array according to one embodiment of the present invention.

FIG. 9 is a sectional view of a thin film transistor array according to an embodiment of the present invention.

FIG. 10 shows a cross-sectional view of an electronic display according to one embodiment of the present invention.

FIG. 11a shows a schematic diagram of a cross-sectional view of an electronic display according to one embodiment of the present invention.

FIG. 11b shows a schematic diagram of a cross-sectional view of an electronic display according to one embodiment of the present invention.

FIG. 11c shows a schematic diagram of a cross-sectional view of an electronic display according to one embodiment of the present invention.

FIG. 11d shows a schematic diagram of a cross-sectional view of an electronic display according to one embodiment of the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR , HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, UZ, VN, YU, ZA, ZW (72) Inventors Dazzler, Greg M. United States Massachusetts 02146, Cambridge, Beacon Street 1243, Apartment 6E (72) Inventor Kazulas, Peter Tee. United States Massachusetts 01776, Sudbury, Dutton Road 405 (72) Inventor Chen, United States Massachusetts 02138, Cambridge, Troveridge Street 77 F-term (reference) 5C094 AA42 AA43 BA03 BA43 BA75 BA76 CA19 EA04 EA07 5F110 AA16 BB08 CC01 CC05 CC01 DD02 DD05 EE01 EE02 FF01 FF02 FF03 GG02 GG05 GG13 GG15 GG32 GG35 HJ13 HJ23 HK01 HK02 HK09 HK16 HK21 HK34 NN02 NN24 NN41 NN72

Claims (13)

[Claims] At least a first transistor, a second transistor, and a third transistor
A thin film transistor array (10) comprising: a source electrode (20); a drain electrode (22) spaced from the source electrode (20); and a source electrode (20). A semiconductor layer (18) electrically connected to both the drain electrode (22) and a gate electrode (14) arranged close to the semiconductor layer (18), wherein the gate electrode (14) Of the source electrode (20)
) And a gate electrode (14) that can change the resistance of the semiconductor layer between the drain electrode (22) and the transistor array (10). A first data line (32) connected to one of the source electrode (20) and the drain electrode (22) of each of the two transistors.
), A second data line (32) connected to a corresponding one of the source electrode (20) and the drain electrode (22) of the third transistor, and a gate electrode of the first transistor and the third transistor. A first selection line (36) connected to (14), and a second selection line (46) connected to the gate electrode (14) of the second transistor.
And the array further comprises: the semiconductor layer (18) is a first transistor, a second transistor,
A thin-film transistor array extending continuously between the third transistors. 2. The thin film transistor array according to claim 1, wherein the semiconductor layer is non-patterned. 3. The thin-film transistor array according to claim 1, wherein the non-patterned dielectric layer (16) is adjacent to the semiconductor layer (18). 4. The first transistor further comprises a first pixel electrode (34) of an electronic display, the first pixel electrode (34) being connected to the drain electrode (22) of the first transistor. , The second transistor further comprises a second pixel electrode (40) of the electronic display, the second pixel electrode (40) being connected to the drain electrode (22) of the second transistor, The third transistor further comprises a third pixel electrode (38) of the electronic display;
Is connected to the drain electrode (22) of the third transistor, and is connected to the source electrode (2) of the first transistor and the second transistor.
0) is connected to the first data line, and the source electrode (20) of the third transistor is connected to the second data line. Thin film transistor array. 5. The thin film transistor array according to claim 1, wherein the semiconductor layer includes an organic semiconductor material or silicon. 6. The thin film transistor array according to claim 5, wherein said semiconductor layer comprises amorphous silicon. 7. The thin film transistor array according to claim 6, wherein the semiconductor layer includes amorphous silicon having a p-type dopant. 8. At least one transistor comprising: (a) a patterned n-doped silicon layer provided between said semiconductor layer (18) and at least one of a source electrode (20) and a drain electrode of said transistor; The thin film transistor array according to any one of claims 1 to 7, further comprising: (b) a passivation layer provided close to the semiconductor layer (18). 9. An electronic display (100) characterized by a thin film transistor array (10) according to any of the preceding claims and a display medium (106). 10. The medium (106) is electrophoretic,
An electronic display according to claim 9. 11. The electronic display according to claim 10, wherein the electrophoretic medium comprises at least one type of particles and a suspending fluid. 12. The electronic display according to claim 10, wherein the electrophoretic medium is encapsulated. 13. The electronic display according to claim 9, characterized by a light blocking layer proximate to the semiconductor layer of the transistor array.