Matrix photosensitive detector and method for making the photosensitive detector

Abstract

The invention relates to a matrix photosensitive detector comprising a substrate (12a), several photosensitive elements (30) arranged in rows and columns, row conductors (22, 24) for driving the photosensitive elements (30), and column conductors (26, 28) for reading the photosensitive elements (30). The conductors are 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) are individually connected to the conductors. The invention also relates to a method for implementing a detector. Figure for the abstract: Fig. 1a

Description

Title of the invention: Matrix photosensitive detector and method for implementing the photosensitive detector

[0001] The invention relates to a photosensitive detector and a method for its fabrication. The invention is particularly useful for the fabrication of a photosensitive detector used to create visible images. The invention is not limited to the fabrication of this type of detector. The invention can be implemented to create a detector capable of producing pressure or temperature maps, or two-dimensional representations of chemical or electrical potentials. These maps or representations form images of physical quantities.

[0002] The invention applies in particular to the production of active matrix detectors used for example for detection purposes in ionizing radiation imaging devices, for example by X-rays or gamma rays.

[0003] 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 readout phase of the matrix and then digitized so that they can be processed and stored to form an image. The pixels are formed of an area sensitive to the physical phenomenon and deliver, for example, a current of electrical charge. The physical phenomenon can be electromagnetic radiation carrying a flux of photons, and hereafter, the invention will be explained using this type of radiation, and the charge current is a function of the photon flux received by the sensitive area. Generalization to any matrix detector will be straightforward.

[0004] 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 terms "rows" and "columns" are purely conventional and can be reversed.

[0005] Each pixel generally comprises a photosensitive component, or photodetector, which may, for example, be a photodiode, a photoresistor, or a phototransistor. Large photosensitive arrays exist that can have several million pixels arranged in rows and columns. Each pixel further comprises an electronic circuit including at least one actuator. The electronic circuit may also include other switches, capacitors, and resistors, downstream of which the actuator is placed. The assembly constituted by the The photosensitive component and the electronic circuit generate and collect electrical signals. The electronic circuit typically resets the collected signal in each pixel after a transfer for pixel reading. The actuator's role is to transfer or copy the signals collected by the electronic circuit into a column conductor, based on information received from the photosensitive component. This transfer occurs when the actuator receives the instruction from a line conductor. The actuator's output corresponds to the pixel's output.

[0006] 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 may exceed 400 mm on each side. Manufacturing detectors with such dimensions is not easy.

[0007] To date, there are two main families of X-ray matrix detectors. The first family uses materials such as silicon in amorphous, polycrystalline, or microcrystalline form. These materials are deposited as thin films on substrates such as glass or polyimide. A second family uses single-crystal materials. The second family achieves significantly better performance than the first. However, the second family is limited in size due to the silicon substrates used. To create large detectors in the second family, it is necessary to join several substrates on which parts of the detector are fabricated.

[0008] Furthermore, in both detector families, the rejection rate can be significant during detector manufacturing. Indeed, the greater the number of pixels, the higher the risk that at least one pixel will be defective. It is possible to accept that a few isolated pixels may be defective by means of image correction, but this remains an imperfect solution.

[0009] The invention first seeks to take advantage of the benefits of both families, that is, to allow for a wider choice of pixel types arranged on large substrates such as glass-based or polyimide substrates. More generally, the invention seeks to separate the choice of substrate for the photosensitive detector from the substrate on which the individual pixels are fabricated. Furthermore, the invention seeks to reduce the shortcomings of current detectors, in particular by allowing each pixel or group of pixels to be tested individually before being implanted onto the detector substrate.

[0010] To this end, the invention relates to a matrix photosensitive detector comprising a substrate, several photosensitive elements arranged in rows and columns, line conductors for driving the photosensitive elements, and column conductors enabling the reading of the photosensitive elements, the conductors being carried by the substrate of the photosensitive detector, in which the photosensitive elements, individually or in groups, are carried each by one or more micro-substrates independent of the substrate of the photosensitive detector, the photosensitive elements being individually connected to the conductors.

[0011] 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.

[0012] The photosensitive detector can be configured to detect ionizing radiation of type X or gamma, the photosensitive detector advantageously comprising two scintillators, one disposed in contact with the photosensitive elements and the other disposed on a face of the substrate of the photosensitive detector opposite to that receiving the photosensitive elements.

[0013] The invention also relates to a method for implementing a matrix photosensitive detector comprising a substrate, several photosensitive elements arranged in rows and columns, row conductors for driving the photosensitive elements, and column conductors for reading the photosensitive elements, the method consisting of: - to create the line and column conductors on the substrate of the photosensitive detector, - to fabricate 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.

[0014] Advantageously, the method consists of testing the photosensitive elements before transferring them onto the substrate of the photosensitive detector.

[0015] The photosensitive detector can be configured to detect ionizing radiation of type X or gamma, a scintillator configured to convert the ionizing radiation into radiation to which the photosensitive elements are sensitive being advantageously made on each of the photosensitive elements before being transferred to the substrate of the photosensitive detector.

[0016] The invention will be better understood and other advantages will become apparent upon reading the detailed description of an embodiment given by way of example, a description illustrated by the accompanying drawing in which:

[0017] [Fig. la]

[0018] [Fig.lb]

[0019] [Fig. the]

[0020] [Fig.ld] Figures aa, 1b, le and Id represent several examples of pieces of photosensitive detectors according to the invention;

[0021] [Fig.2]

[0022] [Fig.3] Figures 2 and 3 show partial cross-sections of examples of photosensitive detectors according to the invention.

[0023] For the sake of clarity, the same elements will bear the same references in the different figures.

[0024] Figures 1a to 1d each represent four pixels of a matrix photosensitive detector, respectively labeled 10a, 10b, 10c and 10d. In practice, photosensitive detectors can have a larger number of pixels, typically several million. The invention is of greater interest the larger the number of pixels.

[0025] Each photosensitive detector 10a, 10b, 10c, and 10d comprises a substrate, respectively 12a, 12b, 12c, and 12d, which can be of any nature, such as glass or an organic material like polyimide. An advantage of the invention is that it allows the use of substrates with very diverse mechanical properties, such as a flexible substrate and / or a substrate that cannot withstand high temperatures. For example, polyimide-based substrates cannot typically withstand temperatures above 200°C. It is, of course, possible to use a mechanically more rigid substrate and / or one that can withstand higher temperatures.

[0026] Each photosensitive detector 10a, 10b, 10c and 10d comprises several pixels arranged in a matrix of rows and columns. The pixels are distributed regularly on the detector substrate, each occupying a zone of the substrate. The zones are considered adjacent and are represented in Figures 1a to 1d as dashed 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.

[0027] Each pixel comprises at least one photosensitive component, for example a photodiode, a phototransistor, a photoresistor, a photoconductor, etc. Each pixel may also comprise other electronic components such as transistors, enabling, in particular, pixel selection for reading, resetting, and amplification of the signal from the photosensitive component. More advanced functions may also be integrated into each pixel, such as an analog-to-digital converter, a counter-charge injection circuit, etc. As an example, patent applications WO 2015 / 063156 and WO 2020 / 127180, both filed in the name of the applicant, describe different types of pixels.

[0028] Each pixel further comprises portions of electrical tracks for powering and driving the pixel in question and for extracting the useful signal, which may be analog or already digitized within the pixel. In the case of a signal In analog signals, the value of this signal can be carried by a voltage, a current, or an electrical charge. Within the detector, the pixel track sections of the same row, line, or column are continuous and are connected either to driver modules or to readout modules, generally located outside the detector's photosensitive surface. More specifically, driver modules, which control the pixels, are typically placed at the ends of pixel lines, while readout modules are typically placed at the ends of pixel columns. The terms "rows" and "columns" are purely conventional, and it is perfectly acceptable to reverse them. Some row or column tracks may carry the power supply voltages for the pixels. Any other arrangement of driver and readout modules is, of course, possible.For example, it is possible to place the two types of module on the same side or on opposite sides of the photosensitive area.

[0029] For the implementation of the invention, for each pixel, a distinction is made between the track portions and the photosensitive elements. The tracks are fabricated directly on the substrate in question, 12a, 12b, 12c, or 12d. The photosensitive elements, comprising photosensitive components and possibly other electronic components, are fabricated separately on one or more substrates independent of the detector substrate. These independent substrates will be referred to hereafter as micro-substrates. After the photosensitive components have been fabricated on their micro-substrates, they are transferred to the detector substrate by connecting them to the tracks present on the detector substrate.

[0030] In [Fig. 1a], 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 consisting of a photosensitive component arranged on its own micro-substrate. In [Fig. 1a], the four photosensitive elements are identical and are marked with the symbol 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 run along the upper part of their respective rows of pixels, and tracks 26 and 28 run along the right part of their respective rows of pixels. Electrical connections between the tracks and the photosensitive elements 30 are provided between the respective rows and columns.

[0031] Figures 1b, 1a, 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 shared by several photosensitive components, in this case, four components. In the example shown in [Fig. 1b], the Tracks 22 and 24 run in the upper part of the photosensitive element 32, and tracks 26 and 28 run in the right part of the micro-substrate 32. In the example shown in [Fig. 1e], 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 shown in [Fig. 1d], tracks 22 and 24 run in the upper part of the photosensitive element 32, and tracks 26 and 28 run in the right part of the photosensitive element 32. In addition, tracks 34 and 36 run in the lower part of the photosensitive element 32, and tracks 38 and 40 circulate in the left part of the photosensitive element 32.

[0032] Figure 2 shows a partial cross-section of the photosensitive detector 10a in a plane perpendicular to the substrate 12a. Several photosensitive elements 30 are visible. In Figure 2, the photosensitive elements can be arranged practically edge to edge on the substrate 12a. The proximity limit of the photosensitive elements 30 can be determined by the stacking of dimensional tolerances that allow for the correct positioning of the photosensitive elements 30 on the substrate 12a, particularly to enable their connection to the tracks. Possible deformations of the photosensitive detector 10a as a whole, including differential thermal expansion and the general flexibility desired for the substrate 12a, can also be taken into account. The edge-to-edge arrangement of the photosensitive elements 30 increases the effective photosensitive detection area by maximizing the surface area of ​​each photosensitive component.

[0033] The photosensitive elements 30 are electrically connected to the tracks running on the substrate 12a by means of pads 42 and 44. Pads 42 are connected to a track 22 passing through the cutting plane. Pads 44, behind the cutting plane, are connected to another track, for example 44 also located behind the cutting plane. Tracks 26 and 28 are, for example, arranged on a face 46 of the substrate 12a opposite the face 48 carrying tracks 22 and 24 and the photosensitive elements 30. Tracks 26 and 28 are also connected to the photosensitive elements 30 via plated holes through the substrate 12a and pads located behind the cutting plane. The substrate 12a can directly carry, without a micro-substrate, some electronic components, as illustrated in [Fig. 2] by component 50.These can be isolated components or more complex modules such as pixel driver modules that emit signals transmitted to the pixels via tracks, for example 22 and 24. The driver modules may include shift registers allowing sequential control of pixel rows, for example. The substrate 12a can also directly carry, without a micro-substrate, circuits for reading the individual pixels.

[0034] Alternatively, in addition to directly implementing the control and reading modules on the substrate 12a, the modules can also each be implemented on its own micro-substrate. These modules are transferred to the substrate 12a in the same way as the photosensitive elements 30.

[0035] The variant of [Fig.2] can of course be adapted to the other examples of photosensitive detectors 10b, 10c and lOd.

[0036] 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 an X-ray imaging detector, it is possible to use photoconductors directly sensitive to X-rays. Also in X-ray imaging, it is possible to use photosensitive components sensitive to another wavelength band, such as visible light, and to interpose a scintillator between the incident radiation and the photosensitive components. The scintillator converts the received X-ray photons into visible photons. The scintillator is, for example, made from cesium iodide, which is known for its conversion properties.

[0037] For example, it is possible to make a scintillator 60 on a dedicated substrate 62. Cesium iodide 64 is then deposited on the substrate 62. The scintillator 60 is then attached to the photosensitive elements 30 after their placement on the substrate 12a.

[0038] Figure 2 shows a particular configuration of the detector incorporating a second scintillator 66 arranged on face 46 of the substrate 12a of the photosensitive detector. The scintillator 66 can be fabricated on a dedicated substrate 68 on which the active material 70, which performs the conversion, is grown. Alternatively, it is possible to grow the active material 70 directly on the substrate 12a.

[0039] This arrangement of two scintillators associated with a transparent substrate 12a and equally transparent photosensitive elements 30 allows X-ray photons that have passed through the first scintillator 60 without being converted into visible light to be recovered and converted in the second scintillator 66. The converted light is then reflected back to the photosensitive elements by passing through the substrate 12a and the micro-substrates of the photosensitive elements 30. This configuration improves the trade-off between absorption and spatial resolution. This configuration is also of particular interest in spectroscopy by performing spectral separation using photosensitive elements oriented either towards the first scintillator 60 or towards the second scintillator 66.

[0040] By implementing the invention, the choice of substrate 12a can be made independently of that of the photosensitive elements 30 specially adapted for the production of the photosensitive elements. It is, for example, possible to make the substrate 12a from a thin material that is transparent to both incident X-ray radiation and to light radiation emitted by the second scintillator 66.

[0041] Figure 3 represents a variant of a photosensitive detector in which each Photosensitive element 30 is equipped with its own scintillator 72. A scintillator 72 is made on each of the photosensitive elements 30 before being transferred to the substrate 12a.

Claims

Demands

1. A matrix photosensitive detector comprising: - several pixels arranged in rows and columns, each forming an elementary sensitive element of the detector, each pixel comprising a photosensitive element (30, 32), - a substrate (12a, 12b, 12c, 12d) comprising row conductors (22, 24, 34, 36) for driving the photosensitive elements (30, 32) and column conductors (26, 28, 38, 40) for reading the photosensitive elements (30, 32), the conductors being carried by the substrate (12a, 12b, 12c, 12d) of the photosensitive detector (10a, 10b, 10c, 10d) - several micro-substrates independent of the substrate of the photosensitive detector, each carrying one or more photosensitive elements (30, 32), in which the photosensitive elements (30, 32) are individually connected to the conductors.

2. Photosensitive detector according to claim 1, the photosensitive detector (10a, 10b, 10c, 1Od) being configured to detect ionizing radiation of type X or gamma, in which each photosensitive element (30) is equipped with its own scintillator (72).

3. Photosensitive detector according to any one of the preceding claims, wherein 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).

4. Photosensitive detector according to any one of the preceding claims, the photosensitive detector (10a, 10b, 10c, 1Od) being configured to detect ionizing radiation of type X or gamma, the photosensitive detector further comprising two scintillators (60, 66), 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, 1Od) opposite to that (48) receiving the photosensitive elements (30, 32).

5. A method for making a matrix photosensitive detector according to any one of the preceding claims, the method consisting of: - making the row and column conductors on the substrate (12a, 12b, 12c, 12d) of the photosensitive detector (10a, 10b, 10c, 10d), - produce the photosensitive elements (30, 32) on one or more microsubstrates independent of the substrate of the photosensitive detector, - transfer each photosensitive element onto the substrate of the photosensitive device.

6. Method according to claim 5, consisting of testing the photosensitive elements (30, 32) before transferring them onto the substrate (12a, 12b, 12c, 12d) of the photosensitive detector (10a, 10b, 10c, 10d).

7. A method according to any one of claims 5 or 6, the photosensitive detector (10a, 10b, 10c, 1Od) being configured to detect ionizing radiation of type X or gamma, wherein a scintillator (72) configured to convert the ionizing radiation into radiation to which the photosensitive elements (30, 32) are sensitive is made 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, 1Od).

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