FR3125891A1 - Matrix photosensitive detector and method of making the photosensitive detector - Google Patents

Abstract

The invention relates to a matrix photosensitive detector comprising a substrate (12a), several photosensitive elements (30) organized in rows and columns, line conductors (22, 24) making it possible to drive the photosensitive elements (30) and columns (26, 28) allowing the photosensitive elements (30) to be read, the conductors being carried by the substrate (12a) of the photosensitive detector (10a) in which the photosensitive elements (30), individually or in groups, are made each carried on one or more micro-substrates independent of the substrate of the photosensitive detector, the photosensitive elements (30) being individually connected to the conductors. The invention also relates to a method for producing a Figure detector for the abstract: Fig. 1a

Description

Matrix photosensitive detector and method of making the photosensitive detector

The invention relates to a photosensitive detector and its method of production. The invention finds a particular utility for the realization of a photosensitive detector used to elaborate visible images. The invention is not limited to the production of this type of detector. The invention can be implemented to produce a detector making it possible to produce pressure or temperature maps or even two-dimensional representations of chemical or electrical potentials. These maps or representations form images of physical magnitudes.

The invention applies in particular to the production of active matrix detectors used for example for detection purposes in imaging devices by ionizing radiation, for example by X or gamma rays.

In a matrix detector, a pixel represents the elementary sensitive element of the detector. Each pixel converts a physical phenomenon to which it is subjected into an electrical signal. The electrical signals from the different pixels are collected during a matrix reading phase and then digitized so that they can be processed and stored to form an image. The pixels are formed of a zone sensitive to the physical phenomenon and deliver, for example, a current of electric charges. The physical phenomenon may be electromagnetic radiation conveying a flux of photons and subsequently, the invention will be explained by means of this type of radiation and the charging current is a function of the flux of photons received by the sensitive zone. The generalization to any matrix detector will be easy.

A matrix image detector comprises row conductors, each connecting the pixels of the same row, and column conductors, each connecting the pixels of the same column. The column conductors are connected to conversion circuits generally arranged on an edge of the matrix which can be called the “column foot”. It is understood that the designations “rows” and “columns” are purely conventional and can be reversed.

Each pixel generally comprises a photosensitive component, or photodetector, which can for example be a photodiode, a photoresistor or a phototransistor. There are large photosensitive matrices which can have several million pixels organized in rows and columns. Each pixel further comprises an electronic circuit comprising at least one actuator. The electronic circuit may also include other switches, capacitors, resistors, downstream of which the actuator is placed. The assembly formed by the photosensitive component and the electronic circuit makes it possible to generate electrical signals and to collect them. The electronic circuit generally allows the reinitialization of the signal collected in each pixel after a transfer for the reading of the pixel. The role of the actuator is to transfer or copy, in a column conductor, the signals collected by the electronic circuit according to the information received from the photosensitive component. This transfer is carried out when the actuator receives the instruction from a line driver. The output of the actuator corresponds to the output of the pixel.

X-ray detectors are subject to a size constraint. Indeed, there is no simple way to deflect this type of radiation. The detector must therefore have the dimensions of the image to be produced. For example in medical radiology, a detector can exceed 400 mm on a side. The realization of detector having such dimensions is not easy.

To date, there are two main families of X-ray matrix detectors. The first family uses materials such as silicon in the amorphous, polycrystalline or microcrystalline state. These materials are deposited in thin layers on substrates such as, for example, glass or polyimide. A second family implements monocrystalline materials. The second family achieves much better performance than the first family. On the other hand, the second family is limited in size due to the silicon substrates used. To produce large detectors, in the second family, it is necessary to butt together several substrates on which parts of the detector are produced.

Moreover, in the two families of detectors, the scrap rate can be high during the manufacture of the detector. Indeed, the greater the number of pixels, the greater the risk that at least one pixel is defective. it is possible to accept that a few isolated pixels are defective by means of image correction, but this remains an imperfect palliative.

The invention seeks first of all to take advantage of the advantages of the two families, that is to say to allow the widening of the choice of the type of pixels arranged on large-sized substrates such as substrates based on glass or polyimide. . More generally, the invention seeks to dissociate the choice of the substrate of the photosensitive detector and the substrate on which the various pixels are made. In addition, the invention seeks to reduce the defects of current detectors, in particular by making it possible to individually test each pixel or each group of pixels before implanting it on the substrate of the detector.

To this end, the subject of the invention is a matrix photosensitive detector comprising a substrate, several photosensitive elements organized in rows and columns, row conductors making it possible to drive the photosensitive elements and column conductors making it possible to read the photosensitive elements, the conductors being carried by the substrate of the photosensitive detector, in which the photosensitive elements, individually or in groups, are each carried by one or more micro-substrates independent of the substrate of the photosensitive detector, the photosensitive elements being individually connected to the conductors.

The photosensitive elements are advantageously arranged edge to edge, within a manufacturing tolerance, this tolerance including dimensional tolerances and possible deformations of the photosensitive detector.

The photosensitive detector can be configured to detect ionizing radiation of the X or gamma type, the photosensitive detector advantageously comprising two scintillators, one placed in contact with the photosensitive elements and the other placed on a face of the substrate of the photosensitive detector opposite that receiving the photosensitive elements.

The invention also relates to a method for producing a matrix photosensitive detector comprising a substrate, several photosensitive elements organized in rows and columns, row conductors making it possible to drive the photosensitive elements and column conductors making it possible to read the photosensitive elements, the method comprising:
- produce on the substrate of the photosensitive detector, the row and column conductors,
- produce the photosensitive elements on one or more micro-substrates independent of the substrate of the photosensitive detector,
- transfer each photosensitive element onto the substrate of the photosensitive device.

Advantageously, the method consists in testing the photosensitive elements before transferring them onto the substrate of the photosensitive detector.

The photosensitive detector can be configured to detect ionizing radiation of the X or gamma type, a scintillator configured to convert the ionizing radiation into radiation to which the photosensitive elements are sensitive being advantageously produced on each of the photosensitive elements before being transferred onto the substrate of the photosensitive detector.

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, description illustrated by the attached drawing in which:

FIGS. 1a, 1b, 1c and 1d represent several examples of pieces of photosensitive detectors according to the invention;

FIGS. 2 and 3 represent in partial section examples of photosensitive detectors according to the invention.

For the sake of clarity, the same elements will bear the same references in the different figures.

FIGS. 1a to 1d each represent four pixels of a matrix photosensitive detector marked 10a, 10b, 10c and 10d respectively. In practice, photosensitive detectors can have a larger number of pixels, typically several million. The invention is all the more advantageous the greater the number of pixels.

Each photosensitive detector 10a, 10b, 10c and 10d comprises a substrate, respectively 12a, 12b, 12c and 12d which can be of any kind such as for example glass or an organic material such as polyimide. An advantage of the invention is to allow the use of substrates having very diverse mechanical properties, such as for example a flexible substrate and/or a substrate that cannot withstand high temperatures. For example, polyimide-based substrates cannot withstand temperatures typically above 200°C. It is of course possible to implement a substrate that is mechanically more rigid and/or that can withstand higher temperatures.

Each photosensitive detector 10a, 10b, 10c and 10d comprises several pixels organized in a matrix of rows and columns. The pixels are evenly distributed on the detector substrate, each occupying an area of the substrate. The areas are considered adjacent and are shown in Figures 1a through 1d as dotted squares. Four pixels 14, 16, 18 and 20 are shown in each of Figures 1a to 1d. The pattern of these four pixels is repeated to form the photosensitive surface of the respective detector.

Each pixel comprises at least one photosensitive component, for example a photodiode, a phototransistor, a photoresistor, a photoconductor, etc. Each pixel can also comprise other electronic components such as transistors allowing in particular the selection of the pixel for its reading, its reset to zero, an amplification of the signal from the photosensitive component. More advanced functions can also be integrated into each pixel, such as an analog-to-digital converter, a counter charge injection circuit, etc. For example, patent applications WO 2015/063156, and WO 2020 can be cited. /127180, both filed in the name of the applicant, where different types of pixels are described.

Each pixel also comprises portions of electrical tracks making it possible to supply and control the pixel considered and making it possible to extract the useful signal which can be analog or already digitized in the pixel. In the case of an analog signal, the value of this signal can be carried by a voltage, a current or an electrical charge. In the detector, the track portions of the pixels of the same row, line or column are continuous and are connected either to driving modules or to reading modules generally located outside the photosensitive surface of the detector. More precisely, the driving modules making it possible in particular to drive the pixels are for example arranged at the end of the rows of pixels and the reading modules are for example arranged at the end of the columns of pixels. The names rows and columns are purely conventional and it is quite possible to reverse these names. Some row or column tracks may carry pixel supply voltages. Any other arrangement of the control and reading modules is of course possible. It is for example possible to place the two types of module on the same side or on opposite sides of the photosensitive area

For the implementation of the invention, for each pixel, one distinguishes on the one hand the portions of tracks and on the other hand the photosensitive elements. The tracks are made directly on the substrate considered, 12a, 12b, 12c or 12d. The photosensitive elements comprising photosensitive components and possibly other electronic components are made separately on one or more substrates independent of the substrate of the detector. This or these independent substrates will be called hereinafter, micro-substrate. After production of the photosensitive components on their micro-substrate, these are transferred to the substrate of the detector by connecting them to the tracks present on the substrate of the detector.

On the , two tracks 22 and 24 are associated with each row of pixels and two tracks 26 and 28 are associated with each column of pixels. Each pixel 14, 16, 18 and 20 comprises a photosensitive element formed of a photosensitive component arranged on its own micro-substrate. On the , the four photosensitive elements are identical and carry the reference 30. As mentioned above, in addition to the photosensitive component, other components can be arranged on the micro-substrate of each pixel. Tracks 22 and 24 circulate in the upper part of their respective line of pixels and tracks 26 and 28 circulate in the right part of their respective line of pixels. Electrical connections between the tracks and the photosensitive elements 30 are provided between the rows and the respective columns.

FIGS. 1b, 1c and 1d represent a particular case where a photosensitive element 32 carries four photosensitive components each belonging to a pixel and possibly other components directly associated with the photosensitive components. The association of the other components can be individual, i.e. each photosensitive component is associated with its own components, or collective, i.e. the other components are pooled for several photosensitive components, in this case for four components. In the example shown in the , the tracks 22 and 24 circulate in the upper part of the photosensitive element 32 and the tracks 26 and 28 circulate in the right part of the micro-substrate 32. In the example represented on the , track 22 runs in the upper part of the photosensitive element 32 and track 24 runs in the lower part of the photosensitive element 32. Track 26 runs in the right part of the photosensitive element 32 and track 28 runs in the left part of the photosensitive element 32. In the example represented on the , there are the two tracks 22 and 24 circulating in the upper part of the photosensitive element 32 and the tracks 26 and 28 circulating in the right part of the photosensitive element 32. In addition, two tracks 34 and 36 circulate in the lower part of the photosensitive element 32 and two tracks 38 and 40 circulate in the left part of the photosensitive element 32.

There represents the photosensitive detector 10a in partial section in a plane perpendicular to the substrate 12a. Several photosensitive elements 30 appear there. On the , the photosensitive elements can be arranged practically edge to edge on the substrate 12a. The proximity limit of the photosensitive elements 30 can be given by the stacking of dimensional tolerances allowing the correct positioning of the photosensitive elements 30 on the substrate 12a, in particular to allow their connection to the tracks. It is also possible to take account of the possible deformations of the photosensitive detector 10a as a whole, including the differential thermal expansion and the general flexibility that it is desired to obtain for the substrate 12a. The edge-to-edge arrangement of the photosensitive elements 30 makes it possible to increase the useful photosensitive detection surface by maximizing the surface of each photosensitive component.

The photosensitive elements 30 are electrically connected to the tracks circulating on the substrate 12a each by means of pads: 42 and 44. The pads 42 are connected to a track 22 passing in the cutting plane. The studs 44 behind the cutting plane are connected to another track, for example 44 also located behind the cutting plane. The tracks 26 and 28 are for example arranged on a face 46 of the substrate 12a opposite the face 48 bearing the tracks 22 and 24 and the photosensitive elements 30. The tracks 26 and 28 are also connected to the photosensitive elements 30 via metallized holes passing through the substrate 12a and studs located behind the cutting plane. The substrate 12a can carry directly, without micro-substrate, some electronic components, as illustrated in the by the component 50. These may be isolated components or more complex modules such as modules for driving the pixels and emitting signals transmitted to the pixels by the tracks, for example 22 and 24. The driving modules can comprise shift registers allowing sequential control for example of the lines of pixels. The substrate 12a can also carry directly, without micro-substrate, circuits for reading the different pixels.

Alternatively, to the direct production of the driving and reading modules directly on the substrate 12a, the modules can also be produced each on a micro-substrate which is specific to it. These modules are transferred onto the substrate 12a in the same way as the photosensitive elements 30.

The variant of the can of course be adapted to the other examples of photosensitive detectors 10b, 10c and 10d.

The photosensitive detector according to the invention can be configured to directly detect the incident radiation to which it is sensitive. The photosensitive components are then chosen to be directly sensitive to the wavelength of the incident radiation. For example, in the case of X imaging detector, it is possible to implement photoconductors directly sensitive to X radiation. Still in X imaging, it is possible to implement photosensitive components sensitive to another band of length waveform, such as in visible light and inserting a scintillator between the incident radiation and the photosensitive components. The scintillator converts the received X photons into visible photons. The scintillator is for example made from cesium iodide, recognized for its conversion properties.

It is for example possible to produce a scintillator 60 on a dedicated substrate 62. The cesium iodide 64 is then deposited on the substrate 62. The scintillator 60 is then attached to the photosensitive elements 30 after they have been placed on the substrate 12a .

There represents a particular configuration of the detector implementing a second scintillator 66 placed on the face 46 of the substrate 12a of the photosensitive detector. The scintillator 66 can be made on a dedicated substrate 68 on which the active material 70 carrying out the conversion is grown. Alternatively, it is possible to grow the active material 70 directly on the substrate 12a.

This arrangement with two scintillators associated with a transparent substrate 12a and also transparent photosensitive elements 30 makes it possible to recover X photons having passed through the first scintillator 60 without being converted into visible light in order to convert them in the second scintillator 66 and return the light therefrom. converted to the photosensitive elements by crossing the substrate 12a and the micro-substrates of the photosensitive elements 30. This configuration makes it possible to improve the absorption/spatial resolution compromise. This configuration is also of particular interest in spectroscopy by operating a spectral separation by means of photosensitive elements oriented either towards the first scintillator 60 or towards the second 66.

By implementing the invention, the choice of the substrate 12a can be made independently of that of the photosensitive elements 30 specially adapted for the production of the photosensitive elements. It is possible, for example, to make the substrate 12a in a thin material that is transparent both to the incident X-ray radiation and to the light radiation emitted by the second scintillator 66.

There represents a photosensitive detector variant in which each photosensitive element 30 is equipped with its own scintillator 72. A scintillator 72 is produced on each of the photosensitive elements 30 before being transferred onto the substrate 12a.

Claims (6)

Matrix photosensitive detector comprising a substrate (12a, 12b, 12c, 12d), several photosensitive elements (30, 32) organized in rows and columns, line conductors (22, 24, 34, 36) allowing the photosensitive elements to be driven (30, 32) and column conductors (26, 28, 38, 40) allowing the photosensitive elements (30, 32) to be read, the conductors being carried by the substrate (12a, 12b, 12c, 12d) of the photosensitive detector (10a, 10b, 10c, 10d) in which the photosensitive elements (30, 32), individually or in groups, are each carried on one or more micro-substrates independent of the substrate of the photosensitive detector, the photosensitive elements (30, 32) being individually connected to the conductors. Photosensitive detector according to Claim 1, in which the photosensitive elements (30, 32) are arranged edge to edge, within a manufacturing tolerance, this tolerance including dimensional tolerances and possible deformations of the photosensitive detector (10a, 10b, 10c, 10d). Photosensitive detector according to one of the preceding claims, the photosensitive detector (10a, 10b, 10c, 10d) being configured to detect ionizing radiation of the X or gamma type, the photosensitive detector further comprising two scintillators (60, 66), the one disposed in contact with the photosensitive elements (30, 32) and the other disposed on a face (46) of the substrate (12a, 12b, 12c, 12d) of the photosensitive detector (10a, 10b, 10c, 10d) opposite to that (48) receiving the photosensitive elements (30, 32). Method for producing a matrix photosensitive detector comprising a substrate (12a, 12b, 12c, 12d), several photosensitive elements (30, 32) organized in rows and columns, row conductors (22, 24, 34, 36) for driving the photosensitive elements and column conductors (26, 28, 38, 40) for reading the photosensitive elements, the method comprising:
- produce on the substrate (12a, 12b, 12c, 12d) of the photosensitive detector (10a, 10b, 10c, 10d), the row and column conductors,
- making the photosensitive elements (30, 32) on one or more micro-substrates independent of the substrate of the photosensitive detector,
- transfer each photosensitive element onto the substrate of the photosensitive device. Method according to claim 4, consisting in testing the photosensitive elements (30, 32) before transferring them onto the substrate (12a, 12b, 12c, 12d) of the photosensitive detector (10a, 10b, 10c, 10d). Method according to one of Claims 4 or 5, the photosensitive detector (10a, 10b, 10c, 10d) being configured to detect ionizing radiation of the X or gamma type, in which a scintillator (72) configured to convert the ionizing radiation into radiation to which the photosensitive elements (30, 32) are sensitive is produced on each of the photosensitive elements (30, 32) before being transferred to the substrate (12a, 12b, 12c, 12d) of the photosensitive detector (10a, 10b, 10c, 10d).