阅读说明：本技术 基于石墨烯电荷耦合器件的辐射探测器 (Radiation detector based on graphene charge-coupled device ) 是由 徐杨 董云帆 吕建杭 刘亦伦 俞滨 于 2021-07-12 设计创作，主要内容包括：本发明公开了一种基于石墨烯电荷耦合器件的辐射探测器,由若干像素组成阵列,单个像素包括栅极、半导体衬底、绝缘层、源极、漏极、石墨烯薄膜和隔离。辐射粒子由背部入射后被半导体衬底吸收,产生与入射能量成正比的电子空穴对,其中少子积累到由脉冲栅压产生的深耗尽势阱中,石墨烯耦合出与势阱中空穴对应的等量电子,通过监测石墨烯电流读出势阱中的载流子数量,像素间设有隔离防止串扰。由于石墨烯薄膜的特殊性质,其通过电容性耦合有效收集载流子,产生的电流信号直接从单个像素结构输出,实现随机无损读出,无需采用传统电荷耦合器件的像素之间横向转移电荷方式,且石墨烯本身具有增益效应,从而提高辐射探测灵敏度和探测极限。(The invention discloses a radiation detector based on a graphene charge-coupled device, which is formed by a plurality of pixels into an array, wherein each pixel comprises a grid, a semiconductor substrate, an insulating layer, a source electrode, a drain electrode, a graphene film and an isolation. Radiation particles are absorbed by the semiconductor substrate after being incident from the back, electron hole pairs in direct proportion to incident energy are generated, minority carriers are accumulated in a deep depletion potential well generated by pulse grid voltage, equal-quantity electrons corresponding to holes in the potential well are coupled out by graphene, the number of carriers in the potential well is read by monitoring current of the graphene, and isolation is arranged among pixels to prevent crosstalk. Due to the special properties of the graphene film, carriers are effectively collected through capacitive coupling, generated current signals are directly output from a single pixel structure, random lossless reading is achieved, a mode of transversely transferring charges among pixels of a traditional charge coupling device is not needed, and the graphene has a gain effect, so that the radiation detection sensitivity and the detection limit are improved.)

1. A radiation detector based on a graphene charge-coupled device is characterized in that a radiation detector array is formed by a plurality of detector pixels; the single pixel is provided with a grid (1), a semiconductor substrate (2) and an insulating layer (3) from bottom to top, a drain electrode (4) and a source electrode (5) are horizontally arranged on the upper surface of the insulating layer (3) at intervals, a graphene film (6) covers the upper surfaces of the insulating layer (3), the drain electrode (4) and the source electrode (5), and isolation (7) are arranged on two sides of the insulating layer (3); and the radiation detector array and the reading circuit interface are packaged in a lead bonding mode.

2. The radiation detector based on the graphene charge-coupled device according to claim 1, wherein the isolation (7) is formed by a deep trench isolation technology and is vertically slotted downwards to a semiconductor substrate (2) region, and a deep trench region is used for isolating different pixels, so that crosstalk between pixels in radiation detection of the detector array is reduced.

3. The radiation detector of claim 1, wherein the graphene film (6) covers the upper surfaces of the insulating layer (3), the drain electrode (4) and the source electrode (5), and does not exceed the range defined by the drain electrode (4) and the source electrode (5).

4. The graphene charge-coupled device-based radiation detector according to claim 1, wherein the semiconductor substrate (2) material is one of silicon, germanium, silicon carbide, gallium arsenide, cadmium telluride or indium gallium arsenide.

5. The radiation detector based on the graphene charge-coupled device according to claim 1, wherein the insulating layer (3) is made of one of silicon oxide, aluminum oxide or silicon nitride and has a thickness of 5nm to 100 nm.

6. The graphene charge-coupled device-based radiation detector according to claim 1, wherein the graphene thin film (6) is a single-layer CVD graphene thin film.

7. The radiation detector according to claim 1, wherein a pulsed gate voltage V is applied between the gate (1) and the source (5) when the single pixel is operated_gsDriving the semiconductor substrate (2) into a deep depletion state; while applying a fixed bias voltage V between the drain (4) and source (5)_dsBy reading the current I between the source and drain_dsAnd judging the radiation dose.

8. The radiation detector based on the graphene charge-coupled device of claim 1, wherein a detection object of the radiation detector is ionizing radiation, and the ionizing radiation comprises one or more of photon radiation and sub-atomic particles, wherein the photon radiation comprises X-rays and gamma-rays, and the sub-atomic particles comprise alpha particles, beta particles and neutrons; the detector works in a back incidence mode, and damage of high-energy radiation to the insulating layer is reduced.

9. The radiation detector based on the graphene charge-coupled device as claimed in claim 1, wherein after the particles enter the radiation detector, the particles cause the accumulation of charges in the deeply depleted potential well, and meanwhile, the equal amount of electrons corresponding to holes in the potential well are coupled out from the graphene thin film (6), which causes the concentration of carriers of the graphene thin film to change, thereby changing the conductivity of the graphene thin film; the radiation information is randomly read without damage by monitoring the current change at two ends of the graphene film in real time.

10. The radiation detector based on the graphene charge-coupled device according to claim 1, wherein the readout circuit performs amplification, filtering and analog-to-digital conversion on multiple output signals, so as to realize high-quality and low-noise array signal output.

Technical Field

The invention belongs to the technical field of radiation detection, relates to an ionizing radiation detector structure, and particularly relates to a radiation detector based on a graphene charge-coupled device.

Background

The radiation detector has important application value in the fields of medical diagnosis, industrial detection, national defense safety and the like. Among them, the solid detector can be classified into an indirect detector and a direct detector. The indirect detector firstly utilizes the scintillator to absorb ionizing radiation and convert the ionizing radiation into visible light, and then utilizes the photoelectric detection array to detect signals. The advantages of indirect detection by using the scintillator are fast response speed and low cost. But the spatial resolution is low due to the cross-talk effect caused by optical refraction and scattering. The direct detector utilizes a photosensitive semiconductor material to absorb high-energy rays to generate electron-hole pairs and directly convert particles into electric signals, can realize better spatial resolution and minimum detection limit, but is generally expensive, harsh in working conditions and low in detectable radiation energy. Therefore, it is very important to improve the detection sensitivity of the radiation detector and reduce the radiation detection limit by adopting a new device structure.

The Charge Coupled Device (CCD) image sensor can directly convert an optical signal into an analog current signal, and the signal current can be amplified and subjected to analog-to-digital conversion to realize the acquisition, transmission and processing of an image. As a photoelectric detector, the CCD image array system is applied to a photosensitive component of a camera, a scanner, or the like, and has good photosensitive efficiency and imaging quality.

Graphene is a novel two-dimensional material consisting of a single layer of sp²The hybridized carbon atoms form a honeycomb two-dimensional planar crystal film and have excellent force, heat, light, electricity and other properties. Graphene is currently the thinnest and hardest nanomaterial in the world. Unlike common metals, graphene is a novel two-dimensional conductive material having transparency and flexibility. The graphene covered on the semiconductor oxide chip can form a simple graphene Field Effect Transistor (FET), and the preparation process is simple and is easy to transfer to any substrate.

Disclosure of Invention

The invention aims to provide a radiation detector based on a graphene charge-coupled device, aiming at the defects of the prior art.

The purpose of the invention is realized by the following technical scheme: a radiation detector based on a graphene charge-coupled device comprises a radiation detector array formed by a plurality of detector pixels; the single pixel is provided with a grid electrode, a semiconductor substrate and an insulating layer from bottom to top, the upper surface of the insulating layer is horizontally provided with a drain electrode and a source electrode at intervals, the upper surfaces of the insulating layer, the drain electrode and the source electrode are covered with a graphene film, and two sides of the insulating layer are provided with isolation; and the radiation detector array and the reading circuit interface are packaged in a lead bonding mode.

Furthermore, the isolation adopts a deep groove isolation technology, grooves are formed vertically downwards until reaching the semiconductor substrate area, different pixels are isolated by utilizing the deep groove area, and crosstalk between the pixels in radiation detection of the detector array is reduced.

Furthermore, the graphene film covers the insulating layer and the upper surfaces of the drain electrode and the source electrode, and the graphene film does not exceed the range defined by the drain electrode and the source electrode.

Further, the semiconductor substrate material is one of silicon, germanium, silicon carbide, gallium arsenide, cadmium telluride or indium gallium arsenide.

Further, the insulating layer is made of one of silicon oxide, aluminum oxide or silicon nitride, and the thickness of the insulating layer is 5 nm-100 nm.

Further, the graphene film is a single-layer CVD graphene film.

Further, when a single pixel is operated, a pulse gate voltage V is applied between the gate and the source_gsDriving the semiconductor substrate into a deep depletion state; while applying a fixed bias voltage V between the drain and source_dsBy reading the current I between the source and drain_dsAnd judging the radiation dose.

Further, the detection object of the radiation detector is ionizing radiation, and comprises one or more of photon radiation and subatomic particles, wherein the photon radiation comprises X rays and gamma rays, and the subatomic particles comprise alpha particles, beta particles and neutrons; the detector works in a back incidence mode, and damage of high-energy radiation to the insulating layer is reduced.

Further, after the particles enter the radiation detector, charge accumulation in the deeply depleted potential well is caused, and meanwhile, equal-quantity electrons corresponding to holes in the potential well are coupled out of the graphene film, so that the carrier concentration of the graphene film is changed, and the conductivity of the graphene film is changed. The radiation information is randomly read without damage by monitoring the current change at two ends of the graphene film in real time.

Furthermore, the readout circuit performs amplification, filtering, analog-to-digital conversion and other processing on the multi-path output signals, so as to realize high-quality and low-noise array signal output.

The working principle of the radiation detector provided by the invention is as follows:

(1) when a single pixel works, a pulse grid voltage with a certain frequency is applied between the grid electrode and the source electrode, and a positive electrode of voltage is applied to the grid electrode. The graphene film, the insulating layer and the semiconductor substrate form an MIS junction, and the semiconductor substrate enters a depletion state along with the gradual increase of the gate voltage. When the gate voltage is sufficiently large, an inversion layer is formed at the semiconductor substrate-insulating layer interface. Since the gate voltage is a pulse signal and the generation of minority carriers requires a certain lifetime, an inversion layer does not occur immediately and remains in a depletion state, i.e., a deep depletion region is formed in the semiconductor substrate.

(2) The detector works in a back incidence mode to reduce the damage of high-energy radiation to the insulating layer, when particles enter a depletion region of the semiconductor substrate after entering the device from the back, the depletion region absorbs photons to generate electron-hole pairs, the electron-hole pairs are separated under the action of an electric field of the substrate, the holes are stored in a deep depletion potential well and are continuously accumulated along with time, and the accumulation rate reflects the energy of the incident particles.

(3) The surface graphene couples out the equivalent electrons corresponding to the holes in the potential well, so that the carrier concentration of the graphene film is changed, and the conductivity of the graphene film is changed. And applying a fixed bias voltage between the drain electrode and the source electrode, and monitoring the current change on the graphene film to calculate the quantity of carriers accumulated in the deep depletion potential well so as to judge the radiation energy.

(4) When the array device works, the radiation detector array and the read-out circuit interface are packaged in a lead bonding mode, and the read-out circuit performs amplification, filtering, analog-to-digital conversion and other processing on multi-path output signals to realize high-quality and low-noise array signal output.

The invention has the following beneficial effects:

1. according to the invention, a pulse bias voltage with a certain frequency is applied to the CCD back gate electrode, so that the semiconductor substrate enters a deep depletion state, and particles are absorbed by the semiconductor substrate after being incident from the back. The electron-hole pairs generated in the depletion region are separated under the action of an internal electric field, and electrons are collected by the graphene, so that a large current signal is formed.

2. The device has simple structure, is easy to manufacture in large scale and is compatible with the CMOS process. The preparation process of the graphene is mature, the manufacturing cost is relatively low, and the preparation and production are easy.

3. Due to the special properties of graphene, carriers can be effectively collected through capacitive coupling, generated current signals are directly output from a single pixel structure, random, lossless and high-speed reading is achieved, a mode of transversely transferring charges among pixels of a traditional CCD device is not needed, and response speed and sensitivity of radiation detection are improved.

4. The invention has the advantages that the deep groove isolation is arranged between the pixels, thereby reducing the crosstalk influence of array detection and improving the reliability of radiation detection.

5. According to the invention, the graphene has higher gain, so that an integration function similar to that of a traditional CCD (charge coupled device) is realized, a larger response can be obtained even under a low-dose environment, and the lowest detection limit of radiation is improved.

Drawings

Fig. 1 is a structural diagram of a radiation detector based on a graphene charge-coupled device according to the present invention, in which: the grid electrode 1, the semiconductor substrate 2, the insulating layer 3, the drain electrode 4, the source electrode 5, the graphene film 6 and the isolation 7;

FIG. 2 shows that the radiation detector prepared by the embodiment of the invention works under the 0.2Hz pulse grid voltage of 0 to-30V and the duty ratio of 90 percent, and the dark field and the dose rate are 85nGy_air s^-1Response curve under X-ray;

fig. 3 is a schematic diagram of the 2 × 2 array integration of the radiation detector based on the graphene charge-coupled device according to the present invention.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, the present invention is described in further detail below with reference to the accompanying drawings and examples. The specific embodiments described herein are merely illustrative of the invention and do not limit the scope of the invention.

As shown in fig. 1, the radiation detector based on the graphene charge coupled device provided in this embodiment includes a plurality of pixels forming an array, where the pixels include a gate 1, a semiconductor substrate 2, an insulating layer 3, a drain 4, a source 5, a graphene film 6, and an isolator 7.

Wherein, the isolation 7 is positioned at two sides of the insulating layer 3 and is vertically slotted downwards until reaching the area of the semiconductor substrate 2; the upper surfaces of the insulating layer 3 are horizontally provided with a drain electrode 4 and a source electrode 5 at intervals, the upper surfaces of the insulating layer 3, the drain electrode 4 and the source electrode 5 are covered with a graphene film 6, and the area of the graphene film 6 does not exceed the range defined by the drain electrode 4 and the source electrode 5; the graphene film 6, the insulating layer 3 and the semiconductor substrate 2 form an MIS structure.

The grid electrode 1 is composed of a heavily doped region and contact metal, the contact metal is made of aluminum, the semiconductor substrate 2 is made of n-type lightly doped silicon and 500 mu m in thickness, the resistivity is 1K-10K omega cm, the insulating layer 3 is made of silicon dioxide and 100nm in thickness, the drain electrode 4 and the source electrode 5 are made of chromium/gold alloy, the graphene film 6 is 2mm multiplied by 2mm in size, and the isolation 7 is made of silicon oxide.

The preparation method of the radiation detector based on the graphene charge-coupled device comprises the following steps:

(1) preparing a silicon wafer comprising a substrate and an insulating layer;

(2) photoetching and injecting doped ions into the back surface to form a grid electrode heavily doped region, annealing at high temperature to activate doping, photoetching to form a grid electrode metal pattern, and depositing an aluminum metal layer;

(3) manufacturing an isolation pattern on the surface by using a photoetching technology, filling silicon dioxide in the groove by using chemical vapor deposition after etching, and forming isolation by using chemical mechanical polishing;

(4) etching the surface to form source and drain patterns, and growing a chromium adhesion layer with a thickness of about 15nm and a gold layer with a thickness of 80nm as an electrode by adopting an electron beam evaporation or thermal evaporation technology;

(5) covering the upper surfaces of the source electrode, the drain electrode and the silicon dioxide insulating layer with a single-layer graphene film; graphene transfer using a wet process: uniformly spin-coating a layer of polymethyl methacrylate (PMMA) film on the surface of the single-layer graphene, then putting the single-layer graphene into an acidic etching solution, soaking for about 6 hours, and corroding to remove the copper foil, so that the single-layer graphene film supported by the PMMA is left; washing a graphene film supported by PMMA (polymethyl methacrylate) with deionized water, and transferring the washed graphene film to the upper surfaces of a silicon dioxide insulating layer, a source electrode and a drain electrode; finally, soaking the sample in acetone and isopropanol to remove PMMA;

(6) the device is again photolithographically etched, covering defined areas of the desired single layer graphene pattern with photoresist. Then, the power and the etching time are respectively 75W and 3min by using an Oxygen plasma reactive ion etching technology (Oxygen plasma ICP-RIE). And etching the redundant graphene outside the photoresist, and after etching is finished, cleaning with acetone and isopropanol to remove the residual photoresist.

As shown in fig. 1, a pulse gate voltage is applied to the radiation detector based on the graphene charge-coupled device to drive the substrate to enter a deep depletion operating state, so as to realize photon absorption and charge accumulation. And applying fixed bias voltage to two ends of the graphene, and monitoring the current change of the graphene to realize the nondestructive reading of charges in the potential well. One end of the grid voltage is connected to the grid electrode of the device, the other end of the grid voltage is connected to the source electrode of the device, and a fixed bias voltage is strengthened between the source electrode and the drain electrode.

The radiation detector prepared by the embodiment of the invention uses an n-type silicon substrate, the device works under 0-30V, the duty ratio is 0.2Hz pulse grid pressure of 90%, and the fixed bias voltage between the source and the drain is 0.01V. In the dark field and dose rate of 85nG_yairs^-1The response curve under X-ray is shown in fig. 2. As can be seen from fig. 2, the prepared device has good linesThe linearity, the response photocurrent is large, and the device can be applied to X-ray detection.

Radiation detector arrays have a wide range of applications, including medical imaging, dose detection, and the like. The radiation detector based on the graphene charge-coupled device can be used for manufacturing a detector array by using a standard semiconductor process. Meanwhile, different pixels are isolated among the pixels by adopting a deep groove isolation technology, so that crosstalk among the pixels of the detector array in radiation detection is reduced. The detector array is connected with the read-out circuit in an on-chip integration or off-chip connection mode to complete packaging, a 2 x 2 array integration schematic diagram is shown in fig. 3, and the read-out circuit is used for carrying out amplification, filtering, analog-to-digital conversion and other processing on multi-path output signals to realize high-quality and low-noise array signal output.

The foregoing is only a preferred embodiment of the present invention, and although the present invention has been disclosed in the preferred embodiments, it is not intended to limit the present invention. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify equivalent embodiments to equivalent variations, without departing from the scope of the present teachings, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.