JP2006004966A - Electrostatic discharge protection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive electrostatic discharge protection device where voltage change to low impedance can be stabilized and a protection function operates on low voltage. <P>SOLUTION: A pair of electrodes 3 and 4 which are disposed through a gap 2 and are insulated by the gap 2 and carbon nanotubes 8 projected from the surface of the gap 2-side of at least one electrode 3 are installed in the electrostatic discharge protection device 1 for setting a charge generated by electrostatic discharge free. Thus, the carbon nanotubes 8 are used as field emission elements of a spark gap. Consequently, the electrostatic discharge protection device 1 can be supplied whose cost is made low, in which voltage change to low impedance can be stabilized, and in which the protection function operates on low voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrostatic discharge protection device that protects an integrated circuit (IC), an optical device, and the like from a transient voltage due to static electricity.

  Electrostatic discharge (ESD) stores information such as integrated circuits (ICs) using Si, SiGe, compound semiconductors, etc., optical devices using compound semiconductors, and network communication devices using them, or computers. It is detrimental to magnetic disk drives and so on. In order to protect them from electrostatic discharge, various ESD protection circuits have been proposed. In particular, Patent Document 1 (Integrated Circuit), Patent Document 2 (Network Communication Device), and Patent Document 3 (Magnetic Disk Drive) use a spark gap. ESD protection has been proposed. However, the spark gap used in these is described as forming a concentrated structure for concentrating the electric field, that is, manufacturing the tip of the member so as to be sharpened to a radius of less than 1 μm (see Patent Document 3). It has been.

  On the other hand, semiconductor lasers and photodiodes using compound semiconductors typified by GaAs, etc. used light not only from trunk-line networks, but also from LANs, network terminals and electronic devices, between boards, and between LSI chips. It is used for information transmission. In particular, optical interconnections connecting electronic devices, boards, and LSI chips will become increasingly important in the future. Among them, with compound semiconductors, it is very difficult to form an ESD protection device using diodes and transistors that have been used in semiconductors such as CMOS, SOI, and SiGe. Therefore, in Non-Patent Document 1, a conical protrusion is formed on GaAs by etching, and a spark gap is formed so as to face an electrode with a small gap. This is because when an electrostatic discharge voltage is applied, an extremely strong electric field is applied to the tip of the GaAs protrusion, causing a spark in the gap, and a current due to the electrostatic discharge flows, and the current flows to the device and necessary circuit side. Can be prevented from flowing, and thus acts as an ESD protection device. Such an ESD protection device based on field emission has an advantage that it has a small capacitance and does not significantly affect the normal function of the circuit as compared with a protection element using a diode or a transistor. Further, since a very large current can be discharged, the ESD protection capability is also high.

  On the other hand, carbon nanotubes (CNT) have a fibrous structure in which one or several to several tens of cylinders with rounded graphite-like carbon atomic surfaces are arranged in a nested manner, and the diameter is extremely fine on the order of nanometers. It is a serious substance. This tube with a rounded graphite-like carbon atom surface is called a single-walled carbon nanotube (SWNT), and a fiber in which several to several tens of cylinders with a rounded graphite-like carbon atom surface are arranged in a nested manner The tube having the structure is called a multi-walled carbon nanotube (MWNT). Since these have a very stable bond obtained by rounding the graphite-like carbon atom face, they have excellent mechanical strength and are chemically stable. Carbon nanotubes have a wide range of electrical properties from metals to semiconductors depending on their structures, and have unique shapes such as being minute and having a large surface area, a large aspect ratio (length / diameter ratio), and hollow. Furthermore, since carbon nanotubes have special characteristics derived from their shapes, they are expected to be applied to industries as new carbon materials. In particular, the tip of the carbon nanotube has a hemispherical shape with a diameter on the order of nanometers, and electric field concentration can be easily obtained by applying a voltage. In fact, Non-Patent Document 2 reports field emission from a single multi-walled carbon nanotube (MWNT) for the first time experimentally. Thereafter, carbon nanotubes are employed as electron emission sources in electron emission elements used in display devices such as Patent Document 1, Patent Document 2, and Non-Patent Document 3.

JP-A-7-263666 Japanese Patent Laid-Open No. 11-26185 JP-A-8-335305 Japanese Patent Laid-Open No. 10-12124 JP-A-11-111158 JP 2000-44216 A Nikkei Science January 2003 P84 Science 269, 1550 (1995) Appl. Phys. Lett. , Vol 72, No. 22 (1998) P2912

  However, Patent Document 3 and the like describe that a concentrated structure for concentrating the electric field is formed, that is, the tip of the member is manufactured so as to be sharpened to a radius of less than 1 μm. It is used to manufacture on a wafer plane, and there is a limit to sharpening the tip, and an expensive process such as photolithography is required.

  In Non-Patent Document 1, a conical protrusion is formed on GaAs by etching, and a spark gap is formed to face an electrode with a minute gap. Thus, in order to form a conical protrusion from a semiconductor such as GaAs or Si, fine processing such as etching is generally required, and the electric field emission voltage value is likely to change depending on the shape. Further, this microfabrication requires a relatively expensive process such as photolithography and etching a plurality of times, and is expensive.

  Patent Document 6 proposes a method for purifying carbon nanotubes. Among them, ESD countermeasures using antistatic materials are cited. This is to prevent electrostatic discharge by preventing electrification with a conductive material, and suggests the possibility of carbon nanotubes with unique electrical characteristics from semiconductors to metals as antistatic materials. However, this does not suggest an ESD protection device using the field emission characteristics of carbon nanotubes such as a spark gap.

  An object of the present invention is to provide an electrostatic discharge protection device capable of realizing a low cost, stabilizing a voltage changing to a low impedance, and having a protective function even for a lower voltage.

  According to a first aspect of the present invention, there is provided an electrostatic discharge protection device for releasing charges generated by electrostatic discharge, each of which is provided via a gap and insulated by the gap, and a gap between at least one of the electrodes And a carbon nanotube protruding from the surface on the side.

  According to a second aspect of the present invention, in the electrostatic discharge protection device according to the first aspect, the carbon nanotube protrudes from both gap-side surfaces of the pair of electrodes.

  According to a third aspect of the present invention, in the electrostatic discharge protection device according to the first or second aspect, the gap is in a state filled with an inert gas or nitrogen, or in a vacuum state.

  According to a fourth aspect of the present invention, in the electrostatic discharge protection device according to the first, second, or third aspect, the carbon nanotube is a multi-walled carbon nanotube.

  According to a fifth aspect of the present invention, in the electrostatic discharge protection device according to the first, second, or third aspect, the carbon nanotube is a single-walled carbon nanotube.

  A sixth aspect of the present invention is the electrostatic discharge protection device according to any one of the first to fifth aspects, wherein the carbon nanotube is a tube whose tip is opened.

  A seventh aspect of the present invention is the electrostatic discharge protection device according to any one of the first to sixth aspects, wherein a plurality of the carbon nanotubes are provided.

  The invention according to claim 8 is the electrostatic discharge protection device according to any one of claims 1 to 7, wherein the carbon nanotube is held by the carbon nanotube holding layer provided on the electrode. It is provided on the surface.

  According to the first aspect of the present invention, by using carbon nanotubes (CNT) as the spark gap field emission device, it is possible to achieve low cost and stabilize the voltage that changes to low impedance, Since the voltage value can be lowered, it is possible to provide an electrostatic discharge protection device in which a protection function works even for a low voltage.

  According to the second aspect of the present invention, the carbon nanotubes are projected from either surface of the pair of electrodes, thereby realizing low cost and stabilizing the voltage that changes to low impedance, while maintaining the positive potential and the negative potential. It is possible to provide an electrostatic discharge protection device capable of making the voltage value changing to low impedance the same for both electrical overvoltages.

  According to the third aspect of the invention, the gap between the pair of electrodes is reduced to a low impedance by being filled with an inert gas such as He, Ne, Ar, Kr, Xe or nitrogen, or in a vacuum state. While stabilizing the changing voltage, it is possible to prevent the deterioration of the carbon nanotube, and it is possible to provide an electrostatic discharge protection device having a longer life and higher reliability.

  According to the invention of claim 4, by projecting the multi-walled carbon nanotube from the electrode, the voltage changing to low impedance is stabilized, and the field emission characteristic is high and the cost is reduced by utilizing the metallic conductivity. An electrostatic discharge protection device can be provided.

  According to the invention of claim 5, by causing the single-walled carbon nanotube to protrude from the electrode, the voltage changing to low impedance can be further lowered while stabilizing the voltage changing to low impedance, It is possible to provide an electrostatic discharge protection device in which a protection function works even for a low voltage.

  According to the invention of claim 6, by using the carbon nanotube whose tip is opened, the voltage changing to low impedance can be further reduced while stabilizing the voltage changing to low impedance, It is possible to provide an electrostatic discharge protection device in which a protection function works even for a low voltage.

  According to the seventh aspect of the present invention, since the plurality of carbon nanotubes protrude from the surface of the electrode, field emission from the plurality of carbon nanotubes occurs, and charge due to electrostatic discharge can be increased in a short time. Therefore, it is possible to provide an electrostatic discharge protection device with a high protection capability.

  According to the eighth aspect of the present invention, the carbon nanotube protruding from the electrode surface is held on the electrode through the carbon nanotube holding layer, so that the voltage changing to low impedance is stabilized and the electrode is strongly turned into the electrode. By being held, it is possible to prevent detachment of the carbon nanotube, and it is possible to provide a highly reliable electrostatic discharge protection device.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a longitudinal side view schematically showing a basic configuration of an ESD protection device (electrostatic discharge protection device) of the present embodiment.

  As shown in FIG. 1, the ESD protection device 1 includes a pair of electrodes 3 and 4 provided with a gap 2 for generating field emission, and substrates 5 and 6 holding the electrodes 3 and 4, respectively. A spacer 7 provided between the pair of electrodes 3 and 4 to form the gap 2, a carbon nanotube (CNT) 8 protruding from the surface of the one electrode 3, and a shield (not shown) that blocks the gap 2 from the atmosphere. Etc. Such an ESD protection device 1 is provided between a signal line and a ground line (GND line), and destroys an IC or an optical device from a transient voltage caused by electrostatic discharge that has entered the IC (integrated circuit) or the optical device. To prevent.

  As the substrates 5 and 6, a Si substrate, a GaAs substrate, or the like is used. The pair of electrodes 3 and 4 are provided so as to face each other with the gap 2 therebetween, and are insulated by the gap 2. The pair of electrodes 3 and 4 are connected to a signal line such as an IC or an optical device and a ground line. Carbon nanotubes 8 protrude from the surface of one electrode 3 on the gap 2 side. The spacer 7 is formed of an insulator or the like and has an insulating property.

  The carbon nanotube 8 is provided on the electrode 3 by a CNT holding layer (carbon nanotube holding layer) 9 for holding it. The CNT holding layer 9 is provided on the surface of the electrode 3. That is, the carbon nanotube 8 is formed by forming a CNT epoxy resin matrix composed of an epoxy resin and the carbon nanotube 8 on the electrode 3 as the CNT holding layer 9 and polishing the surface of the CNT holding layer 9 to thereby obtain the surface of the electrode 3. It is formed so as to protrude from. Here, FIG. 2 is a photograph of the surface of the CNT holding layer 9 taken obliquely from above with a scanning electron microscope. As shown in FIG. 2, the portion (white portion) that appears to shine in a rod shape is the carbon nanotube 8 that protrudes from the surface of the electrode 3 (the surface of the CNT holding layer 9).

  Since the carbon nanotube 8 has metallic electrical conductivity, the CNT holding layer 9 formed by mixing the epoxy resin and the carbon nanotube 8 also has electrical conductivity. Therefore, since the voltage applied to the electrode 3 is applied to the tip of the carbon nanotube 8 via the CNT holding layer 9, a very large electric field can be formed.

  The carbon nanotube 8 has excellent mechanical strength, is chemically stable, exhibits field emission characteristics at a low voltage, and has a Fowler-Nordheim equation.

Is known to follow.

  In such a configuration, when a negative transient voltage due to electrostatic discharge enters the ESD protection device 1, a negative voltage is applied to the carbon nanotubes 8 protruding from the surface of the electrode 3 through the electrode 3, and the tip thereof is several nm to several nm. Due to the sharpness of 10 nm, a very strong electric field is locally formed, and a current due to field emission is generated instantaneously according to the above formula, and a transient voltage can be avoided by the ground line through the ESD protection device 1. it can.

In the electric field at this time, in the case of field emission using a parallel plate type metal electrode on the order of 10 ⁷ V / cm, for example, the field emission is not made until a very large voltage of 10 ⁴ V is applied with a 10 μm gap, for example. Begins. Actually, field emission starts at a lower voltage due to fine irregularities such as grain boundaries on the electrode surface. However, in order to operate at a lower voltage, a protrusion is formed to operate at a lower voltage due to electric field concentration. I have to. Such protrusions are formed by photolithography and etching microfabrication techniques well known in the semiconductor process, but it is difficult to stably form the shape. On the other hand, the carbon nanotubes 8 can be manufactured to have a finer tip and a relatively uniform diameter. Further, by projecting a large number of carbon nanotubes 8 from the surface of the electrode 3, a local electric field can be obtained. Depends on the diameter of the carbon nanotube 8 and the gap 2, and more stable characteristics can be obtained.

  As described above, according to the present embodiment, the ESD protection device 1 can prevent destruction of the IC, the optical device, etc. from the transient voltage caused by the electrostatic discharge entering the IC (integrated circuit), the optical device, etc. even when a low voltage is applied. it can. In addition, by causing the carbon nanotubes 8 to protrude from the surface of the electrode 3, it is possible to stabilize the voltage that changes to low impedance. In particular, since a large number of carbon nanotubes 8 protrude, field emission from the plurality of carbon nanotubes 8 occurs, and a larger amount of current can flow in a short time due to electrostatic discharge. Furthermore, by using the multi-walled carbon nanotube 8, it is possible to form a CNT holding layer 9 having electrical conductivity using a resin by utilizing its metallic conductivity, and the ESD protection device 1 with a lower cost can be obtained. Can be provided. Further, since the carbon nanotube 8 is held on the electrode 3 through the CNT holding layer 9 made of a CNT resin matrix in which an epoxy resin and the carbon nanotube 8 are mixed, it is possible to prevent the carbon nanotube 8 from being detached. Thus, the ESD protection device 1 having sufficient mechanical strength and high reliability can be provided. Furthermore, it is possible to form the ESD protection device 1 that maintains the small capacitance and the large discharge current, which are the characteristics of the field emission element.

In the present embodiment, the carbon nanotubes 8 are dispersed on the epoxy resin to form a CNT resin matrix as the CNT holding layer 9 and the CNT holding layer 9 is polished, so that the carbon nanotubes 8 are formed on the surface of the electrode 3. Although protruding, the carbon nanotubes 8 may protrude from the surface of the electrode 3 by etching the CNT holding layer 9. Further, the carbon nanotubes 8 may be directly grown on the surface of the electrode 3 by CVD, or the carbon nanotubes 8 may be fixed to the surface of the electrode 3 via a conductive adhesive.
A second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a longitudinal side view schematically showing a basic configuration of the ESD protection device (electrostatic discharge protection device) of the present embodiment.

  The ESD protection device 1A of the present embodiment has substantially the same configuration as the ESD protection device 1 of the first embodiment. Here, differences between the ESD protection device 1A of the present embodiment and the ESD protection device 1 of the first embodiment will be described. In addition, the same part as 1st embodiment is shown with the same code | symbol, and the description is also abbreviate | omitted.

  As shown in FIG. 3, carbon nanotubes (CNT) 8 protrude from both surfaces of the pair of electrodes 3 and 4 that face each other. Thus, even when a transient voltage due to positive or negative electrostatic discharge is applied, a current due to field emission is generated from the carbon nanotubes 8 protruding from the surfaces of the electrodes 3 and 4 having a relatively low voltage, and ESD protection is performed. Transient voltages can be avoided on the ground line through the device 1A.

  In addition, the gap 2 formed by the pair of electrodes 3 and 4 which are protruded and opposed to each other by the carbon nanotube 8 is filled with Ar which is an inert gas. In the atmosphere in which oxygen is present, the carbon nanotubes 8 are deteriorated due to field emission. However, in the Ar atmosphere, the deterioration of the carbon nanotubes 8 due to field emission is suppressed, so that the ESD protection has a longer lifetime and higher reliability. A device 1A can be provided. Note that although Ar is used as the gas to be filled, the present invention is not limited to this, and for example, an inert gas such as He, Ne, Kr, or Xe, or nitrogen may be used. Thus, the gap 2 may be filled with an inert gas or nitrogen, or may be in a vacuum state.

  In such a configuration, when either a positive or negative transient voltage due to electrostatic discharge enters the ESD protection device 1A, a negative voltage or a positive voltage is applied to the carbon nanotube 8 protruding from the surface of the electrode 3 or 4 through the electrode 3 or 4. Is applied, and the tip thereof is sharp, from several nanometers to several tens of nanometers. Therefore, a very strong electric field is locally generated, current is generated by field emission instantaneously, and a transient voltage is grounded through the ESD protection device 1A. The line can be avoided.

  As described above, according to the present embodiment, the ESD protection device 1A can prevent destruction of the IC or the optical device from the transient voltage caused by the electrostatic discharge that enters the IC (integrated circuit) or the optical device even when the low voltage is applied. it can. In particular, the ESD protection device 1A acts as a protection device against electrostatic discharge at a low voltage regardless of whether a positive or negative voltage is applied. Furthermore, by filling the gap 2 with Ar, there is no deterioration of the carbon nanotubes 8 due to field emission, and it is possible to provide a longer-life ESD protection device 1A. Further, by causing the carbon nanotubes 8 to protrude from the surfaces of the electrodes 3 and 4, it is possible to stabilize the voltage that changes to low impedance. In particular, since a large number of carbon nanotubes 8 protrude, field emission from the plurality of carbon nanotubes 8 occurs, and a larger amount of current can flow in a short time due to electrostatic discharge. Furthermore, by using the multi-walled carbon nanotubes 8, it is possible to form the electrically conductive CNT holding layer 9 using a resin using metallic conductivity, and to provide a lower cost ESD protection device 1A. can do. In addition, since the carbon nanotubes 8 are held on the electrodes 3 and 4 via the CNT holding layer 9 made of a CNT resin matrix in which an epoxy resin and a carbon nanotube are mixed, the separation of the carbon nanotubes 8 can be prevented. Therefore, the ESD protection device 1A having sufficient mechanical strength and high reliability can be provided. Furthermore, the ESD protection device 1A that maintains the small capacitance and the large discharge current, which are the characteristics of the field emission element, can be formed.

  A third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a longitudinal side view schematically showing a basic configuration of the ESD protection device (electrostatic discharge protection device) of the present embodiment.

  The ESD protection device 1B of the present embodiment is a surface mount type device (SMD: Surface-Mountable Device) mounted on the surface of a printed circuit board (not shown). In addition, the same part as 1st embodiment is shown with the same code | symbol, and the description is also abbreviate | omitted.

  As shown in FIG. 4, the ESD protection device 1 </ b> B includes a base material 11 that holds components, and a pair of lower electrodes 4 a and 4 b that are provided on the base material 11 and are connected to a signal line and a ground line of a printed circuit board, respectively. The pair of upper electrodes 3a and 3b provided on the base material 11 with the gap 2 interposed therebetween, the carbon nanotubes (CNT) 8 protruding from the surfaces of the upper electrodes 3a and 3b, and the sealing material 12 on the upper electrodes 3a and 3b It is comprised from the protective layer 13 etc. which were provided through.

  The lower electrodes 4a and 4b and the upper electrodes 3a and 3b are electrically connected to each other by a terminate electrode 14. Further, the carbon nanotubes 8 and the gap 2 protruding from the surfaces of the upper electrodes 3a and 3b are shielded from the atmosphere by the insulating sealing material 12 and the protective layer 13.

  As the base material 11, a glass substrate or the like is used. The pair of upper electrodes 3 a and 3 b are provided so as to face each other with the gap 2 interposed therebetween, and are insulated by the gap 2. Carbon nanotubes 8 protrude from the surface of the pair of upper electrodes 3a, 3b on the gap 2 side. Further, the tips of the carbon nanotubes 8 protruding from the surfaces of the upper electrodes 3a and 3b are opened. Normally, the tip of the carbon nanotube 8 has a closed shape by a 5-membered ring and a 6-membered ring of carbon. However, by opening the tip, it is possible to cause field emission at a lower voltage. The operating voltage can be lowered.

  The carbon nanotubes 8 are provided on the upper electrodes 3a and 3b by a CNT holding layer (carbon nanotube holding layer) 9 that holds the carbon nanotubes 8. The CNT holding layer 9 is provided on the surfaces of the upper electrodes 3a and 3b so that the carbon nanotubes 8 of the pair of upper electrodes 3a and 3b face each other. The carbon nanotube 8 is formed by forming a CNT epoxy resin matrix composed of an epoxy resin and a carbon nanotube 8 between the upper electrodes 3a and 3b, and forming a gap 2 in the CNT epoxy resin matrix using lithography and ashing. The upper electrodes 3a and 3b are formed so as to protrude from the surface. When forming the gap 2, only the epoxy resin is removed, so that the carbon nanotubes 8 protrude from the surface of the CNT holding layer 9.

  The gap 2 is filled with nitrogen. In the atmosphere in which oxygen is present, the carbon nanotubes 8 are deteriorated due to field emission. However, in the nitrogen atmosphere, the deterioration of the carbon nanotubes 8 due to field emission is suppressed, so that the ESD protection has a longer lifetime and higher reliability. Device 1B can be provided. Note that nitrogen is used as the gas to be filled, but is not limited thereto, and for example, an inert gas such as He, Ne, Kr, or Xe may be used. Thus, the gap 2 may be filled with an inert gas or nitrogen, or may be in a vacuum state.

  In such a configuration, when either a positive or negative transient voltage due to electrostatic discharge enters the ESD protection device 1B, the negative voltage is negatively applied to the carbon nanotubes 8 protruding from the upper electrode 3a or the upper electrode 3b through the upper electrode 3a or the upper electrode 3b. A voltage or positive voltage is applied, and the tip thereof is sharp, from several nanometers to several tens of nanometers. Therefore, a very strong electric field is locally generated, and a current due to field emission is instantaneously generated through the ESD protection device 1B. Transient voltage can be avoided on the ground line.

  As described above, according to the present embodiment, the ESD protection device 1B is caused by electrostatic discharge that intrudes into an IC (integrated circuit) or an optical device even when a lower voltage is applied as compared with the case of the multi-walled carbon nanotube 8 that does not open the ring. It is possible to prevent destruction of ICs and optical devices from the transient voltage. Furthermore, by filling the gap 2 with nitrogen, it is possible to provide an ESD protection device 1B having a longer life without deterioration of the carbon nanotubes 8 due to field emission. Further, the operation voltage can be stabilized by projecting the carbon nanotube 8 from the upper electrodes 3a and 3b. In particular, since a large number of carbon nanotubes 8 protrude, field emission from the plurality of carbon nanotubes 8 occurs, and a larger amount of current can flow in a short time due to electrostatic discharge. Furthermore, by using the multi-walled carbon nanotubes 8, it is possible to form the electrically conductive CNT holding layer 9 using a resin by utilizing metallic conductivity, and to provide a lower cost ESD protection device 1 </ b> B. it can. Further, since the carbon nanotubes 8 are held by the upper electrodes 3a and 3b via the CNT holding layer 9 made of a CNT resin matrix in which an epoxy resin and the carbon nanotubes 8 are mixed, the separation of the carbon nanotubes 8 is prevented. Therefore, the ESD protection device 1B having sufficient mechanical strength and high reliability can be provided. Further, it is possible to form the ESD protection device 1B that maintains the small capacitance and the large discharge current, which are the characteristics of the field emission element.

  In the present embodiment, multi-walled carbon nanotubes (MWNT) are used as the carbon nanotubes 8. However, the present invention is not limited to this, and for example, single-walled carbon nanotubes (SWNT) may be used. In this case, the single-walled carbon nanotube 8 has a single-layer graphene sheet, has a smaller radius of curvature at the tip than the multi-walled carbon nanotube 8, and emits electric field at a lower voltage. For example, as the single-walled carbon nanotube 8, a tube whose average diameter is 1.5 nm and whose tip is not opened is used.

<Example 1>
The ESD protection device 1 according to the first embodiment of the present invention is manufactured (see FIG. 1). First, the electrodes 3 and 4 are formed on the substrates 5 and 6 which are Si substrates by a known technique such as plating or sputtering. Next, multi-walled carbon nanotubes (NWNT) 8 having an average diameter of 10 nm, an average length of 1 μm, and an unopened tip are dispersed in an epoxy resin, which is applied onto the substrate 5 and thermally cured. A CNT epoxy resin matrix composed of the thermoset epoxy resin and the carbon nanotubes 8 is used as a CNT holding layer 9. Next, the surface of the CNT holding layer 9 is polished using an alumina abrasive (particle size: 0.3 μm) and a urethane foam polishing pad, and the carbon nanotubes 8 are projected from the surface of the electrode 3.

  The carbon nanotubes 8 are mechanically and chemically stable, only the epoxy resin is removed by polishing, and a large number of multi-walled carbon nanotubes 8 protrude from the surface of the electrode 3 through the conductive CNT holding layer 9. . The CNT epoxy resin matrix functions as a CNT holding layer 9 that holds the carbon nanotubes 8 protruding from the surface of the electrode 3. Moreover, since the multi-walled carbon nanotube 8 has metallic electrical conductivity, the CNT holding layer 9 formed by mixing the epoxy resin and the carbon nanotube 8 also has electrical conductivity. Therefore, since the voltage applied to the electrode is applied to the tip of the carbon nanotube 8 via the CNT holding layer 9, a very large electric field can be formed.

  Finally, the substrate 5 on which the electrode 3 having the carbon nanotubes 8 is formed and the substrate 6 on which the electrode 4 is formed are bonded together via an insulating spacer 7. Here, a mylar having a thickness of 12 μm is used as the spacer 7, and a gap 2 of 12 μm is formed between the electrodes 3 and 4 facing the CNT holding layer 9.

  When the minimum operating voltage of the ESD protection device 1 thus formed was measured, it was confirmed that the ESD protection device 1 acts as a protection device against electrostatic discharge even when a low voltage of −110 V was applied. It was also confirmed that the voltage that changes to low impedance can be stabilized by causing the carbon nanotubes 8 to protrude from the surface of the electrode 3. On the other hand, it was also confirmed that it works sufficiently as a protection device against electrostatic discharge even for the conventional contact discharge 8 kV test defined by IEC61000-4-2 Level 4.

  In such an ESD protection device 1, in particular, since a large number of carbon nanotubes 8 protrude, field emission from the plurality of carbon nanotubes 8 occurs, and a large amount of current can flow in a short time due to electrostatic discharge. Furthermore, by using the multi-walled carbon nanotube 8, it is possible to form a CNT holding layer 9 having electrical conductivity using a resin by utilizing its metallic conductivity, and the ESD protection device 1 with a lower cost can be obtained. Can be provided. Further, since the carbon nanotube 8 is held on the electrode 3 through the CNT holding layer 9 made of a CNT resin matrix in which an epoxy resin and the carbon nanotube 8 are mixed, it is possible to prevent the carbon nanotube 8 from being detached. Thus, the ESD protection device 1 having sufficient mechanical strength and high reliability can be provided. Furthermore, it is possible to form the ESD protection device 1 that maintains the small capacitance and the large discharge current, which are the characteristics of the field emission element.

<Example 2>
The ESD protection device 1A according to the second embodiment of the present invention is manufactured (see FIG. 3). First, the electrodes 3 and 4 are formed on the substrates 5 and 6 which are Si substrates by a known technique such as plating or sputtering. Next, the multi-walled carbon nanotubes 8 having an average diameter of 10 nm, an average length of 1 μm, and an unopened tip are dispersed in an epoxy resin, which is coated on the substrates 5 and 6 and thermally cured. The CNT resin matrix matrix composed of the thermosetting epoxy resin and the carbon nanotubes 8 is used as the CNT holding layer 9. Next, the surface of the CNT holding layer 9 is polished using an alumina abrasive (particle size: 0.3 μm) and a urethane foam polishing pad, and the carbon nanotubes 8 are projected from the surfaces of the electrodes 3 and 4.

  The carbon nanotubes 8 are mechanically and chemically stable, only the epoxy resin is removed by polishing, and a large number of multi-walled carbon nanotubes 8 protrude from the surface of the electrode 3 through the conductive CNT holding layer 9. . The CNT epoxy resin matrix functions as a CNT holding layer 9 that holds the carbon nanotubes 8 protruding from the surface of the electrode 3.

  Finally, the substrate 5 on which the electrode 3 having the carbon nanotube 8 on the surface is formed and the substrate 6 on which the electrode 4 having the carbon nanotube 8 on the surface are bonded to each other through the insulating spacer 7. Here, a mylar having a film thickness of 12 μm is used as the spacer 7, a gap 2 of 12 μm is formed between the electrodes 3 and 4 facing the CNT holding layer 9, the atmosphere is exhausted in a vacuum apparatus, and then the gap 2 After Ar is filled with Ar gas, it is bonded and sealed. Note that although Ar is used as the gas to be filled, the present invention is not limited to this, and for example, an inert gas such as He, Ne, Kr, or Xe, or nitrogen may be used. Thus, the gap 2 may be filled with an inert gas or nitrogen, or may be in a vacuum state. Thus, when oxygen does not exist in the gap 2, the deterioration of the carbon nanotube 8 due to field emission can be prevented.

  When the minimum operating voltage of the ESD protection device 1A formed in this way was measured, it was confirmed that the ESD protection device 1A acts as a protection device against electrostatic discharge at a low voltage when a voltage of either ± 110 V or any polarity is applied. It was done. The ESD protection device 1A also has the same effect as that of the first embodiment. In addition, by filling the gap 2 with Ar, the carbon nanotubes 8 are not deteriorated by field emission, and a longer-lifetime ESD protection device 1A can be provided.

<Example 3>
The ESD protection device 1B according to the third embodiment of the present invention is manufactured (see FIG. 4). First, multi-walled carbon nanotubes 8 having an average diameter of 10 nm, an average length of 1 μm, and no open ends are dispersed in sulfuric acid, heated to 150 ° C., added with potassium permanganate, and refluxed for several hours. The ring is opened by oxidizing the tip of the multi-walled carbon nanotube 8. A glass substrate is used as the base material 11, and the upper electrodes 3a and 3b are formed on the base material 11 by a known technique such as plating or sputtering. Next, the multi-walled carbon nanotubes 8 whose ends are opened are dispersed in an epoxy resin, which is applied between the upper electrodes 3a and 3b and thermally cured. The CNT epoxy resin matrix composed of this thermoset epoxy resin and carbon nanotubes is used as the CNT holding layer 9.

  Next, the CNT holding layer 9 is patterned using lithography and ashing to form a gap 2 having a width of 10 μm. The patterning used here is very rough and low cost. At this time, since only the epoxy resin is removed, the carbon nanotubes 8 protrude from the surface of the CNT holding layer 9. That is, the carbon nanotubes 8 protrude from the surfaces of the electrodes 3a and 3b. Thereafter, cleaning is performed to remove the carbon nanotubes 8 released between the gaps 2. After exhausting the atmosphere in a vacuum apparatus, filling with nitrogen gas, the carbon nanotubes 8 are filled with an insulating sealing material 12. The base material 11 on which the upper electrodes 3a and 3b having the surface are formed and the protective layer 13 are bonded together and sealed. Finally, the lower electrodes 4a and 4b and the terminate electrode 14 are formed to form the ESD protection device 1B.

Here, the tip of the carbon nanotube 8 is opened by wet oxidation, but the present invention is not limited to this. For example, the tip of the carbon nanotube 8 is opened by heating from 700 ° C. to 850 ° C. in the air or CO _2. Also good. Moreover, although nitrogen is used as the gas to be filled, the present invention is not limited to this. For example, an inert gas such as He, Ne, Ar, Kr, or Xe may be used. Thus, the gap 2 may be filled with an inert gas or nitrogen, or may be in a vacuum state. Thus, when oxygen does not exist in the gap 2, the deterioration of the carbon nanotube 8 due to field emission can be prevented.

  When the minimum operating voltage of the ESD protection device 1B formed in this way was measured, the ESD protection device 1B is ± 80 V, which is less susceptible to electrostatic discharge even when a lower voltage is applied than in the case of the multi-walled carbon nanotube 8 that does not open. It has been confirmed that it acts as a protective device. Furthermore, it was also confirmed that it works sufficiently as a protection device against electrostatic discharge even for the conventional contact discharge 8 kV test defined by IEC61000-4-2 Level 4. The ESD protection device 1B also has the same effect as that of the first embodiment. In addition, by filling the gap 2 with nitrogen, there is no deterioration of the carbon nanotube 8 due to field emission, and the ESD protection device 1B having a longer life can be provided.

<Example 4>
By using single-walled carbon nanotubes instead of multi-walled carbon nanotubes as the carbon nanotubes 8, the ESD protection device 1B of the third embodiment of the present invention is manufactured in the same manner as in Example 3 (see FIG. 4). The single-walled carbon nanotube 8 to be used is a tube whose average diameter is 1.5 nm and whose tip is not opened.

  When the minimum operating voltage of the ESD protection device 1B formed in this way was measured, the ESD protection device 1B is ± 80 V, which is less susceptible to electrostatic discharge even when a lower voltage is applied than in the case of the multi-walled carbon nanotube 8 that does not open. It has been confirmed that it acts as a protective device. Furthermore, it was also confirmed that it works sufficiently as a protection device against electrostatic discharge even for the conventional contact discharge 8 kV test defined by IEC61000-4-2 Level 4. Further, the ESD protection device 1B has the same effect as that of the third embodiment.

It is a vertical side view which shows roughly the basic composition of the ESD protection device (electrostatic discharge protection device) of 1st embodiment of this invention. It is the photograph which image | photographed the surface of the CNT holding layer from diagonally upward with the scanning electron microscope. It is a vertical side view which shows roughly the basic composition of the ESD protection device (electrostatic discharge protection device) of 2nd embodiment of this invention. It is a vertical side view which shows roughly the basic composition of the ESD protection device (electrostatic discharge protection device) of 3rd embodiment of this invention.

Explanation of symbols

1,1A, 1B Electrostatic discharge protection device (ESD protection device)
2 Gap 3, 4 electrode 3a, 3b electrode (upper electrode)
8 Carbon nanotubes 9 Carbon nanotube holding layer (CNT holding layer)

Claims (8)

In the electrostatic discharge protection device for releasing the charge generated by electrostatic discharge,
A pair of electrodes each provided via a gap and insulated by the gap;
Carbon nanotubes protruding from the gap-side surface of at least one of the electrodes,
An electrostatic discharge protection device comprising:   The electrostatic discharge protection device according to claim 1, wherein the carbon nanotube protrudes from the surface of the gap side of both of the pair of electrodes.   The electrostatic discharge protection device according to claim 1, wherein the gap is in a state filled with an inert gas or nitrogen, or in a vacuum state.   The electrostatic discharge protection device according to claim 1, wherein the carbon nanotube is a multi-walled carbon nanotube.   The electrostatic discharge protection device according to claim 1, wherein the carbon nanotube is a single-walled carbon nanotube.   The electrostatic discharge protection device according to any one of claims 1 to 5, wherein the carbon nanotube is a tube whose tip is opened.   The electrostatic discharge protection device according to any one of claims 1 to 6, wherein a plurality of the carbon nanotubes are provided. The electrostatic discharge according to any one of claims 1 to 7, wherein the carbon nanotube is provided on a surface of the electrode by a carbon nanotube holding layer provided on the electrode to hold the carbon nanotube. Protective device.

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