Photosensitive material detector and pixel structure for flexible infrared image sensor

Abstract

The present invention relates to a photosensitive material detector and a pixel structure for a flexible infrared image sensor, comprising: an infrared photosensitive material structure, an insulating layer and a flexible substrate; wherein the insulating layer is arranged above the flexible substrate; the infrared photosensitive material structure is arranged above the insulating layer; the infrared photosensitive material structure is a Schottky heterojunction; the Schottky heterojunction is formed by hexagonal boron nitride, twisted graphene and a two-dimensional material structure; the hexagonal boron nitride, twisted graphene and the two-dimensional material structure are all connected to electrodes. The beneficial effects of the present invention are: the present invention introduces twisted graphene into the pixel structure, and since the twisted graphene contains a zero band gap and the work function of the twisted graphene can be adjusted by voltage, the pixel structure can respond to a very wide wavelength range and can achieve selectivity for the response wavelength.

Description

Technical Field

[0001] The present invention relates to the technical field of pixel structures, and more specifically, to a photosensitive material detector and a pixel structure for a flexible infrared image sensor. Background Art

[0002] Infrared image sensors are used to detect infrared radiation from target objects, and convert the temperature distribution image of the target object surface into a video image through photoelectric conversion, electrical signal processing, etc. The basic principle of infrared image sensors is that the infrared radiation emitted by an object is focused on a flexible infrared detector through an optical lens, the detector converts the infrared radiation into an electrical signal, and the hardware circuit processes the electrical signal and translates the data sent by the detector into an image that can be viewed in a viewfinder, a standard video monitor or an LCD display.

[0003] Infrared photodetectors use the voltaic effect produced by light to convert infrared light signals into electrical signals. Based on the minority carrier extraction effect of the reverse bias junction (PN junction, Schottky junction). Illumination generates unbalanced carriers, which are drifted by the built-in electric field and the reverse bias electric field to form a large reverse current, i.e., photocurrent. The photocurrent is proportional to the intensity of the incident light and is closely related to the frequency of the incident light. Therefore, the infrared signal can be converted into an electrical signal, thereby achieving the purpose of light detection.

[0004] The avalanche effect is that under the action of a strong electric field, the carriers in the semiconductor will be heated by the electric field, and some carriers can obtain sufficiently high energy. These carriers may transfer energy to the electrons in the valence band through collision, causing them to ionize, thereby generating electron-hole pairs. This process is called impact ionization. The generated electron-hole pairs move in opposite directions in the electric field, are heated by the electric field again, and generate new electron-hole pairs. In this way, a large number of carriers can be multiplied, and this phenomenon is called the avalanche multiplication effect.

[0005] Photosensitive materials: Currently commercial infrared and terahertz detectors are based on photosensitive materials such as silicon (Si), germanium (Ge), indium gallium arsenide (InGaAs), and mercury cadmium telluride (HgCdTe). They cannot respond to very wide wavelengths and have weak infrared absorption capabilities, making it difficult to meet the current demand for detectors in many fields. Commercial wearable devices are made of discrete rigid semiconductor material photodiodes, which cannot fit closely to the skin, thereby reducing the accuracy of the data and limiting the body position of the wearable device.

[0006] CN202210277241.5 discloses a novel pixel structure and manufacturing method for infrared image sensors. The invention relates to a novel pixel structure for infrared image sensors, including the following steps: active area photolithography positioning; formation of insulating isolation grooves STI at shallow trenches; formation of N-wells and P-wells; formation of gates; formation of shallowly doped drain regions LDD; formation of gate sidewalls; formation of source and drain regions of novel pixel structures; and coverage of metal wiring and passivation layers. The invention uses graphene as a photosensitive material. Due to the thermal electron scattering and multiplication effect in graphene, as well as its zero-bandgap energy band structure, the photosensitive material made of graphene can generate a photoelectric response and can respond to a very wide wavelength. The invention optimizes existing infrared image sensors with low cost and simplified processes, so that the response wavelength of silicon CMOS image sensors is extended to a farther distance in the near-infrared, and the response wavelength is electrically adjustable.

[0007] However, the photosensitive material of the prior art pixel structure does not have a Schottky barrier with adjustable gate voltage, so the absorption wavelength and photocurrent cannot be adjusted by gate voltage. In addition, the prior art pixel structure does not have the support of ballistic avalanche effect, and its gain and sensitivity are limited. In addition, the prior art pixel structure contains rigid materials, which makes it impossible to fit closely to the skin, thereby reducing the accuracy of the data and limiting the body position of the wearable device. Summary of the invention

[0008] The purpose of the present invention is to address the deficiencies of the prior art and to propose a photosensitive material detector and a pixel structure for a flexible infrared image sensor.

[0009] In a first aspect, a photosensitive material detector for a flexible infrared image sensor is provided, comprising: an infrared photosensitive material structure, an insulating layer and a flexible substrate;

[0010] Among them, the insulating layer is arranged above the flexible substrate; an infrared sensitive material structure is arranged above the insulating layer; the infrared sensitive material structure is a Schottky heterojunction; the Schottky heterojunction is formed by hexagonal boron nitride, twisted graphene and a two-dimensional material structure; the hexagonal boron nitride, twisted graphene and the two-dimensional material structure are all connected to electrodes.

[0011] Preferably, the two-dimensional material structure is integrated with semiconductor quantum dots.

[0012] Preferably, the material of the flexible substrate is any one of polyvinyl alcohol, polyester, polyimide or polyethylene naphthalate.

[0013] Preferably, in the infrared photosensitive material structure, the twisted graphene is a photosensitive material for infrared light, and the hexagonal boron nitride is a protective material and a gate dielectric.

[0014] Preferably, the Fermi level of the twisted graphene is adjusted by a gate voltage, and the barrier height of the Schottky heterojunction is adjustable.

[0015] Preferably, the electrodes are flexible interdigitated electrodes.

[0016] In a second aspect, a method for preparing a photosensitive material detector for a flexible infrared image sensor as described in any one of the first aspects is provided, comprising:

[0017] Step 1, preparing an insulating layer of a flexible substrate;

[0018] Step 2, spin-coating photoresist on the insulating layer of the flexible substrate, and performing photolithography and development of a gold electrode pattern on the photoresist coating; placing the developed substrate into an electron beam evaporation device, performing evaporation growth of metal chromium and gold electrodes respectively, and then removing the photoresist to form an electrode;

[0019] Step 3, forming a two-dimensional material structure on an electrode on one side of the flexible substrate insulating layer;

[0020] Step 4: forming a twisted graphene on the two-dimensional material structure, wherein the two-dimensional material structure and the twisted graphene have an overlapping region;

[0021] Step 5, spin-coating a photoresist on the surface of the corner graphene, and performing photolithography and development of a gold electrode pattern on the photoresist coating; placing the developed substrate into an electron beam evaporation device, performing evaporation growth of metal chromium and gold electrodes respectively, and then removing the photoresist to form an electrode;

[0022] Step 6, forming hexagonal boron nitride on the twisted graphene, wherein the hexagonal boron nitride and the twisted graphene form an overlapping region;

[0023] Step 7: Spin-coat photoresist on hexagonal boron nitride, and perform photolithography and development of a gold electrode pattern on the photoresist coating; and place the developed substrate into an electron beam evaporation device to perform vapor deposition growth of metal chromium and gold electrodes respectively, and then remove the photoresist to form an electrode.

[0024] Preferably, in step 2, step 5 and step 7, the spin coating of the photoresist includes a low-speed spin coating stage and a high-speed spin coating stage, and the duration of the high-speed spin coating stage is longer than the duration of the low-speed spin coating stage.

[0025] In a third aspect, a photosensitive material pixel structure for a flexible infrared image sensor is provided, comprising the detector, reset transistor T1, amplifier transistor T2 and switch transistor T3 described in any one of the first aspects; the detector is connected to the reset transistor T1, amplifier transistor T2 and switch transistor T3. In a fourth aspect, a flexible infrared image sensor is provided, comprising the photosensitive material pixel structure described in the third aspect and a readout circuit corresponding to the photosensitive material pixel structure; the readout circuit is connected to the photosensitive material pixel structure.

[0026] The beneficial effects of the present invention are:

[0027] 1. The present invention utilizes a Schottky heterojunction formed by hexagonal boron nitride, twisted graphene and a two-dimensional material structure as an infrared photosensitive material to solve the problem of narrow photoelectric response bandwidth of the pixel structure of the infrared image sensor, further improve the speed and sensitivity, and realize electrically adjustable photogenerated current.

[0028] 2. The present invention utilizes flexible materials to realize a wearable infrared image sensor device, thereby solving the problem of lack of data accuracy caused by poor skin fit.

[0029] 3. The present invention introduces twisted graphene into the pixel structure. Since twisted graphene contains zero band gap and the work function of twisted graphene can be adjusted by voltage, the pixel structure can respond to a very wide wavelength range and can achieve selectivity for the response wavelength. In addition, the present invention integrates semiconductor quantum dots into the two-dimensional material structure, which can further improve the gain and sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the structure of a photosensitive material detector for a flexible infrared image sensor;

[0031] Figure 2 Schematic diagram of SEM test results of graphene and two-dimensional material structures;

[0032] Figure 3 It is an IV curve diagram of a composite material composed of graphene and a two-dimensional material structure;

[0033] Figure 4 A schematic diagram of a pixel structure of a photosensitive material for a flexible infrared image sensor;

[0034] Explanation of the reference numerals: flexible substrate 1 , insulating layer 2 , hexagonal boron nitride 3 , twisted graphene 4 , two-dimensional material structure 5 , electrode 6 . DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for ordinary persons in the art, without departing from the principle of the present invention, the present invention can also be modified in some ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0036] Embodiment 1:

[0037] As a zero-gap semiconductor, twisted graphene is an ideal model structure to study carrier relaxation channels, which are inefficient in conventional semiconductors. These scattering channels bridge the valence and conduction bands for carrier multiplication—a process that generates multiple charges by absorbing a single photon. The remarkable gapless and linear band structure of twisted graphene opens new carrier relaxation channels that connect the valence and conduction bands. These Auger scattering processes change the population of charge carriers and can lead to significant multiplication of optically excited carriers in twisted graphene.

[0038] To solve the problems of the prior art, such as Figure 1 As shown, the present application introduces twisted graphene, which can absorb 1550nm light and has an adjustable Fermi level, thereby achieving low current at the twisted graphene's own PN junction.

[0039] Specifically, Embodiment 1 of the present application provides a photosensitive material detector for a flexible infrared image sensor, comprising: an infrared photosensitive material structure, an insulating layer 2 and a flexible substrate 1;

[0040] Among them, the insulating layer 2 is arranged above the flexible substrate 1; an infrared sensitive material structure is arranged above the insulating layer 2; the infrared sensitive material structure is a Schottky heterojunction; the Schottky heterojunction is formed by hexagonal boron nitride 3, twisted graphene 4 and a two-dimensional material structure 5, which can achieve a wider absorption band, and the gate voltage applied thereto can adjust the Schottky barrier and thus adjust the photocurrent; the hexagonal boron nitride 3, twisted graphene 4 and the two-dimensional material structure 5 are all connected to the electrode 6.

[0041] The avalanche photomultiplier tube formed by the corner graphene-two-dimensional material contains a ballistic avalanche effect. The two-dimensional material structure is silicene and is integrated with semiconductor quantum dots, which is beneficial to improving sensitivity and gain and reducing dark current.

[0042] The material of the flexible substrate 1 is selected from any one of polyvinyl alcohol (PVA), polyester (PET), polyimide (PI) or polyethylene naphthalate (PEN), paper, textile materials, etc., and has bendable and stretchable properties, which can improve the skin fit and data accuracy of wearable devices. In addition, by attaching inorganic / organic devices to the flexible substrate 1, thin-film electronic devices can be bent, folded, twisted, compressed, stretched, and even deformed into any shape, while still maintaining high-efficiency optoelectronic performance, reliability and integration.

[0043] In the infrared photosensitive material structure, Figure 2 and Figure 3 As shown, the corner graphene 4 is a photosensitive material for infrared light and a full-spectrum material that can absorb light of all wavelengths. The corner graphene 4 with only a few atomic layers (one layer is about 0.34 nanometers) and a two-dimensional material structure (one layer is about 0.4 nanometers) has the advantages of being thin, having a small capacitance and having a fast response, and is the preferred photosensitive material for high-speed avalanche photodetectors, while the hexagonal boron nitride 3 is a protective material and a gate dielectric.

[0044] Moreover, the Fermi level of the twisted graphene 4 can be adjusted by the gate voltage, resulting in adjustable photocurrent, which can reduce dark current, resulting in relatively small noise and higher sensitivity. The infrared photosensitive materials of the prior art cannot adjust their Fermi level in real time by voltage, so their Schottky barriers cannot be adjusted, so the photocurrent cannot be adjusted in real time. In addition, the thermal electron scattering and multiplication effect in the twisted graphene 4, as well as its zero-bandgap energy band structure, are the reasons for responding to infrared light. The infrared photosensitive materials of the prior art only respond to infrared light through their intrinsic bandgap size, while the twisted graphene 4 increases the low-energy infrared photogenerated electrons to an energy height detectable by the device through the scattering effect of electrons, and has the effect of current enhancement.

[0045] The electrode 6 is a flexible interdigitated electrode, which is based on PI and PET respectively. By utilizing the bendable and stretchable properties of PI / PET, the produced electrode 6 can fit closely to human skin.

[0046] Embodiment 2:

[0047] On the basis of Example 1, Example 2 of the present application provides a method for preparing a photosensitive material detector for a flexible infrared image sensor, comprising:

[0048] Step 1, preparing an insulating layer 2 of a flexible substrate 1;

[0049] Step 2, spin-coating photoresist on the flexible substrate insulating layer 2, and performing photolithography and development of the gold electrode pattern on the photoresist coating; and placing the developed substrate into an electron beam evaporation device, performing evaporation growth of metal chromium and gold electrodes respectively, and then removing the photoresist to form an electrode 6;

[0050] Step 3, forming a two-dimensional material structure 5 on one side electrode of the flexible substrate insulating layer 2;

[0051] Step 4, forming a twisted graphene 4 on the two-dimensional material structure 5, wherein the two-dimensional material structure 5 and the twisted graphene 4 have an overlapping area;

[0052] Step 5, spin-coating a photoresist on the surface of the corner graphene 4, and performing photolithography and development of a gold electrode pattern on the photoresist coating; placing the developed substrate into an electron beam evaporation device, performing evaporation growth of metal chromium and gold electrodes respectively, and then removing the photoresist to form an electrode 6;

[0053] Step 6: forming hexagonal boron nitride 3 on the twisted graphene 4, wherein the hexagonal boron nitride 3 and the twisted graphene 4 form an overlapping region.

[0054] Step 7, spin-coating a photoresist on the hexagonal boron nitride 3, and performing photolithography and development of a gold electrode pattern on the photoresist coating; placing the developed substrate into an electron beam evaporation device, performing evaporation growth of metal chromium and gold electrodes respectively, and then removing the photoresist to form an electrode 6;

[0055] In steps 2, 5 and 7, the spin coating of the photoresist includes a low-speed spin coating stage and a high-speed spin coating stage, and the duration of the high-speed spin coating stage is longer than the duration of the low-speed spin coating stage.

[0056] Specifically, the method provided in this embodiment is a preparation method corresponding to the detector provided in Example 1. Therefore, the parts in this embodiment that are the same or similar to those in Example 1 can be referenced to each other and will not be repeated in this application.

[0057] Embodiment 3:

[0058] Based on Example 1, Example 3 of the present application provides a photosensitive material pixel structure for a flexible infrared image sensor, such as Figure 4As shown, it includes: a corner graphene-two-dimensional material avalanche photomultiplier tube P1 (i.e., the detector in Example 1), a reset transistor T1, an amplifying transistor T2, and a switching transistor T3; the corner graphene-two-dimensional material avalanche photomultiplier tube P1 includes boron nitride, corner graphene, a two-dimensional material heterojunction, and a flexible substrate, the corner graphene and the two-dimensional material structure constitute a Schottky heterojunction, and the boron nitride, the corner graphene, and the two-dimensional material heterojunction are bonded to the CMOS image sensor as pixels. The substrate of the corner graphene-two-dimensional material avalanche photomultiplier tube P1 is respectively provided with an insulating isolation groove STI at a shallow channel, an N well, a P well, a gate, and a shallowly doped drain region LDD; a pair of gate sidewalls are provided around the gate; a source region of a new pixel structure is provided in the N well, and a drain region of a new pixel structure is provided in the P well; the insulating isolation groove STI at a shallow channel, the N well, the P well, the gate, the shallowly doped drain region LDD, the source region, and the drain region are connected by metal wiring to form a circuit; and the surface of the circuit is covered with a passivation layer.

[0059] It should be noted that the parts in this embodiment that are the same or similar to those in Embodiment 1 can be referenced to each other and will not be described in detail in this application.

[0060] Embodiment 4:

[0061] On the basis of Example 3, Example 4 of the present application provides a method for preparing a photosensitive material pixel structure for a flexible infrared image sensor, comprising:

[0062] Step 1, prepare a flexible substrate 1; grow a layer of hexagonal boron nitride (h-BN) on the surface of the flexible substrate 1, and then define the active area through photolithography technology; the active area is the part protected by photoresist, and the active area is also the working area of ​​the device.

[0063] In step 1, the embodiment of the present application uses polyimide material to prepare a flexible substrate 1.

[0064] Step 2: Etch a groove in the area not covered by the photoresist, fill the groove with hexagonal boron nitride, and then chemically mechanically polish the surface of the hexagonal boron nitride to smooth it. Finally, remove the hexagonal boron nitride on the surface of the active area to form a shallow trench isolation (STL) area at the original groove.

[0065] Specifically, a shallow trench is formed by dry etching technology, the part covered by the photoresist is protected, and the area without photoresist protection is etched into a shallow groove, and finally the photoresist is removed. In addition, through the shallow trench isolation area, each device in the integrated circuit plays its own role and blocks the influence between each other.

[0066] Step 3: Form a P-well and an N-well in a specific area; deposit hexagonal boron nitride and heavily doped polysilicon on the surface, define the gate position by photolithography, and obtain the gate after dry etching; form a shallow doped drain (LDD) by ion implantation in the P-well and N-well, respectively.

[0067] The specific process of forming the P-well and N-well is as follows: using photolithography technology to expose the area where ions need to be injected, covering other areas with photoresist, and injecting boron (B) ions into the surface of the flexible substrate 1. The area without photoresist protection forms a P-well. Then, ion injection is performed in the channel area with a relatively small energy to adjust the turn-on voltage. Finally, the photoresist is removed. In the same way as the above steps, phosphorus (P) ions are injected into a specific area to form an N-well.

[0068] In addition, after the gate is formed, the above steps of forming the N-well and P-well are used to ion-implant arsenic (As) in the P-well and boron fluoride (BF2) in the N-well to form LDD. LDD is used to reduce the hot carrier effect.

[0069] Step 4: forming a gate sidewall around the gate by dry etching; and forming a source region and a drain region by ion implantation in the P-well and N-well.

[0070] Specifically, after the gate and the shallowly doped drain are formed, a layer of hexagonal boron nitride is deposited on the surface of the silicon wafer by chemical vapor deposition, and then dry etching is performed. No photolithography is required before etching, and direct etching is performed. A pair of side walls are left around the gate by utilizing the deposition height difference and the anisotropy of dry etching to isolate the source (drain) from the gate.

[0071] In addition, similar to the steps of forming the N-well and P-well above, high concentration As is injected into the N-well and high concentration BF2 is injected into the P-well, thereby forming the source and drain regions of the device. After the above steps, both NMOS and PMOS have been completed, and the next step is to make the connections between the various devices to complete the function of the entire integrated circuit.

[0072] Step 5: Use deposition, dry etching, photolithography and chemical mechanical polishing techniques to make metal connections to connect the entire circuit; cover the entire circuit surface with a passivation layer to prevent mechanical scratches and contamination on the surface.

[0073] Specifically, the method provided in this embodiment is a preparation method corresponding to the pixel structure provided in Embodiment 3. Therefore, the parts in this embodiment that are the same or similar to those in Embodiment 3 can be referenced to each other and will not be repeated in this application.

Claims

1. A photosensitive material detector for a flexible infrared image sensor, characterized in that: include: Infrared sensitive material structure, insulating layer (2) and flexible substrate (1); The insulating layer (2) is arranged above the flexible substrate (1); an infrared sensitive material structure is arranged above the insulating layer (2); the infrared sensitive material structure is a Schottky heterojunction; the Schottky heterojunction is formed by hexagonal boron nitride (3), twisted graphene (4) and a two-dimensional material structure (5); the hexagonal boron nitride (3), twisted graphene (4) and the two-dimensional material structure (5) are all connected to an electrode (6); the two-dimensional material structure (5) is silicene and is integrated with semiconductor quantum dots.

2. The photosensitive material detector for a flexible infrared image sensor according to claim 1, characterized in that: The material of the flexible substrate (1) is selected from any one of polyvinyl alcohol, polyester, polyimide or polyethylene naphthalate.

3. The photosensitive material detector for a flexible infrared image sensor according to claim 2, characterized in that: In the infrared photosensitive material structure, the twisted graphene (4) is a photosensitive material for infrared light, and the hexagonal boron nitride (3) is a protective material and a gate dielectric.

4. The photosensitive material detector for a flexible infrared image sensor according to claim 3, characterized in that: The Fermi level of the twisted graphene (4) is adjusted by gate voltage, and the barrier height of the Schottky heterojunction is adjustable.

5. The photosensitive material detector for a flexible infrared image sensor according to claim 4, characterized in that: The electrode (6) is a flexible interdigitated electrode.

6. A method for preparing a photosensitive material detector for a flexible infrared image sensor according to any one of claims 1 to 5, characterized in that: include: Step 1: preparing an insulating layer (2) of a flexible substrate (1); Step 2, spin-coating a photoresist on the flexible substrate insulating layer (2), and performing photolithography and development of a gold electrode pattern on the photoresist coating; placing the developed substrate into an electron beam evaporation device, performing evaporation growth of metal chromium and gold electrodes respectively, and then removing the photoresist to form an electrode (6); Step 3, forming a two-dimensional material structure (5) on one side electrode of the flexible substrate insulating layer (2); Step 4: forming a twisted graphene (4) on the two-dimensional material structure (5), wherein the two-dimensional material structure (5) and the twisted graphene (4) have an overlapping region; Step 5, spin-coating a photoresist on the surface of the corner graphene (4), and performing photolithography and development of a gold electrode pattern on the photoresist coating; placing the developed substrate into an electron beam evaporation device, performing evaporation growth of metal chromium and gold electrodes respectively, and then removing the photoresist to form an electrode (6); Step 6: forming hexagonal boron nitride (3) on the twisted graphene (4), wherein the hexagonal boron nitride (3) and the twisted graphene (4) form an overlapping region; Step 7, spin-coating a photoresist on the hexagonal boron nitride (3), and performing photolithography and development of a gold electrode pattern on the photoresist coating; placing the developed substrate into an electron beam evaporation device, performing vapor deposition growth of metal chromium and gold electrodes respectively, and then removing the photoresist to form an electrode (6).

7. The method for preparing a photosensitive material detector for a flexible infrared image sensor according to claim 6, characterized in that: In step 2, step 5 and step 7, the spin coating of the photoresist includes a low-speed spin coating stage and a high-speed spin coating stage, and the duration of the high-speed spin coating stage is longer than the duration of the low-speed spin coating stage.

8. A photosensitive material pixel structure for a flexible infrared image sensor, characterized in that: It comprises the detector according to any one of claims 1 to 5, a reset transistor T1, an amplifying transistor T2 and a switching transistor T3; the detector is connected to the reset transistor T1, the amplifying transistor T2 and the switching transistor T3.

9. A flexible infrared image sensor, characterized in that: It comprises the photosensitive material pixel structure as described in claim 8 and a readout circuit corresponding to the photosensitive material pixel structure; the readout circuit is connected to the photosensitive material pixel structure.

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