阅读说明：本技术 一种基于单层石墨烯/绝缘层/硅/多层石墨烯结构的电荷注入器件 (Charge injection device based on single-layer graphene/insulating layer/silicon/multi-layer graphene structure ) 是由 徐杨 刘晨 刘威 吕建杭 刘亦伦 俞滨 于 2020-05-08 设计创作，主要内容包括：本发明公开了一种基于单层石墨烯/绝缘层/硅/多层石墨烯结构的电荷注入器件,自下而上设有栅极、多层石墨烯、硅衬底、氧化物绝缘层,氧化物绝缘层上表面设有源极和漏极,并覆盖单层石墨烯薄膜；入射光照射到器件表面时,可见光被半导体硅吸收,其产生的少数载流子积累到硅衬底中的深耗尽势阱；红外光穿过硅层被异质结吸收,产生的少数载流子注入到体硅的深耗尽势阱中。器件表面的石墨烯会耦合出与势阱中的空穴对应的等量电子,从石墨烯的电流中能够实时读出硅势阱中的电荷。本发明通过使用多层石墨烯,拓展了传统CCD器件的光谱响应范围,提高了传统CCD器件在红外波段的吸收效果；同时保持了硅基CCD噪声小、可靠性高、工艺成熟、成本低廉等特点。(The invention discloses a charge injection device based on a single-layer graphene/insulating layer/silicon/multi-layer graphene structure, which is provided with a grid, multi-layer graphene, a silicon substrate and an oxide insulating layer from bottom to top, wherein the upper surface of the oxide insulating layer is provided with a source electrode and a drain electrode and covers a single-layer graphene film; when incident light irradiates the surface of the device, visible light is absorbed by the semiconductor silicon, and minority carriers generated by the visible light are accumulated in a deep depletion potential well in the silicon substrate; the infrared light is absorbed by the heterojunction through the silicon layer and the minority carriers generated are injected into the deeply depleted potential well of the bulk silicon. The graphene on the surface of the device can couple out equivalent electrons corresponding to holes in the potential well, and charges in the silicon potential well can be read out in real time from the current of the graphene. According to the invention, by using the multilayer graphene, the spectral response range of the traditional CCD device is expanded, and the absorption effect of the traditional CCD device in an infrared band is improved; meanwhile, the characteristics of small noise, high reliability, mature process, low cost and the like of the silicon-based CCD are maintained.)

1. The charge injection device based on the single-layer graphene/insulating layer/silicon/multi-layer graphene structure is characterized in that a grid (1), a multi-layer graphene (2), a semiconductor silicon substrate (3), an oxide insulating layer (4) and the like are arranged from bottom to top, a source electrode (5) and a drain electrode (6) are arranged on the upper surface of the oxide insulating layer (4), a single-layer graphene film (7) covers the upper surfaces of the oxide insulating layer (4), the source electrode (5) and the drain electrode (6), the single-layer graphene film (7) is in contact with the source electrode (3) and the drain electrode (4) and does not exceed the range defined by the source electrode (3) and the drain electrode (4), and the range of the single-layer graphene film (7) corresponds to the range defined by the multi-layer graphene (2).

2. Charge injection device according to claim 1, based on a single-layer graphene/insulating layer/silicon/multilayer graphene structure, characterized in that said semiconductor silicon substrate (2) is n-type lightly doped silicon, with a doping concentration of less than 10^12cm^-3。

3. The charge injection device according to claim 1, characterized in that said insulating oxide layer (4) is silicon dioxide and has a thickness of between 5nm and 100 nm.

4. The charge injection device according to claim 1, characterized in that the multilayer graphene (2) has a thickness of 10nm to 40 nm.

5. The device of claim 1, wherein the multilayer graphene (2) is identical in size and shape to the single-layer graphene thin film (7), is located directly below the single-layer graphene thin film (7), and is aligned with the single-layer graphene thin film (7).

6. The charge injection device of claim 1, wherein the single-layer graphene film (7) forms a MIS structure with the oxide insulator (4) and the semiconductor silicon substrate (3), and the multilayer graphene (2) is in close contact with the semiconductor silicon substrate (3) to form a schottky junction.

7. Charge injection device according to claim 1, characterised in that, during operation of the device, a pulsed gate voltage V greater than 1V is applied between the source (5) and the gate (1)_gsThe semiconductor silicon substrate (3) is driven into a deep depletion state. While being applied between the source (5) and the drain (6)A fixed bias voltage V of 10mV_dsThe intensity of the incident light is determined by measuring the current passing between the source (5) and drain (6).

8. The charge injection device of claim 1, wherein when light enters the device, minority carriers generated in the semiconductor silicon substrate (3) and minority carriers generated in the schottky junction formed between the multilayer graphene (2) and the semiconductor silicon substrate (3) are injected into the deep depletion potential well.

9. The charge injection device based on the single-layer graphene/insulating layer/silicon/multi-layer graphene structure of claim 1, wherein when a deeply depleted potential well in the semiconductor silicon substrate (3) has a charge accumulation, a charge opposite to an equal amount of signal charge in the potential well is transferred from the semiconductor silicon substrate (3) into the single-layer graphene thin film (7).

Technical Field

The invention belongs to the technical field of image sensors, relates to an image sensor device structure, and particularly relates to a charge injection device based on a single-layer graphene/insulating layer/silicon/multi-layer graphene structure.

Background

A Charge Coupled Device (CCD), an integrated circuit, is composed of many capacitors arranged in order, and can sense light and convert it into analog signal current, which is amplified and analog-to-digital converted to obtain, transmit and process image. Each small capacitor can transfer its charged charge to its neighboring capacitor under the control of an external circuit. When the CCD device is applied to a photosensitive component of equipment such as a camera, a scanner and the like. The CCD has good light sensing efficiency and imaging quality, but because the CCD outputs data by using a charge transfer mode, the data of the whole row cannot be normally transferred as long as a certain pixel in a row array fails to transfer, and therefore the yield of the CCD is not high.

Graphene (Graphene) is a novel two-dimensional material consisting of carbon atoms in sp²The hybrid orbitals constitute a planar thin film of hexagonal lattice, only one carbon atom thick. Graphene is currently the thinnest and hardest nanomaterial in the world. The transparency of the transparent film is extremely high, and the visible light absorption rate is only 2.3 percent; the thermal conductivity coefficient of the graphene is as high as 5300W/m.K, and the electron mobility exceeds 15000cm at normal temperature²V.s, and a resistivity of only about 10^-6Omega cm. Due to the flexibility and good physical properties of graphene, graphene can be coated on a semiconductor oxide sheet by a simple method to form a graphene Field Effect Transistor (FET) with excellent performance.

Disclosure of Invention

The invention aims to provide a charge injection device based on a single-layer graphene/insulating layer/silicon/multi-layer graphene structure aiming at the defects of the prior art.

The purpose of the invention is realized by the following technical scheme: a Charge Injection Device (CID) based on a single-layer graphene/insulating layer/silicon/multi-layer graphene structure is provided with a grid electrode, multi-layer graphene, a semiconductor silicon substrate and an oxide insulating layer from bottom to top, wherein a source electrode and a drain electrode are arranged on the upper surface of the oxide insulating layer, single-layer graphene films cover the upper surfaces of the oxide insulating layer, the source electrode and the drain electrode, the single-layer graphene films are in contact with the source electrode and the drain electrode and do not exceed the range defined by the source electrode and the drain electrode, and the range of the single-layer graphene films corresponds to that of the multi-layer graphene.

Furthermore, the semiconductor silicon substrate is n-type lightly doped silicon with the doping concentration less than 10^12cm^-3。

Furthermore, the oxide insulating layer is silicon dioxide and has a thickness of 5nm to 100 nm.

Further, the thickness of the multilayer graphene is 10nm to 40 nm.

Further, the multi-layer graphene is identical to the single-layer graphene film in size and shape, is positioned right below the single-layer graphene film, and is aligned with the single-layer graphene film.

Furthermore, the single-layer graphene film, the oxide insulating layer and the semiconductor silicon substrate form an MIS structure, and the multi-layer graphene and the semiconductor silicon substrate are in close contact to form a Schottky junction.

Further, when the device is in operation, a pulse grid voltage V larger than 1V is applied between the source electrode and the grid electrode_gsDriving the semiconductor silicon substrate into a deep depletion state; while a fixed bias voltage V of 10mV is applied between the source and the drain_dsAnd judging the intensity of the incident light by measuring the current passing between the source electrode and the drain electrode.

Further, when light enters the device, minority carriers generated in the semiconductor silicon substrate and minority carriers generated in a schottky junction formed between the multilayer graphene and the semiconductor silicon substrate are injected into the deep depletion potential well.

Further, when a deeply depleted potential well in the semiconductor silicon substrate has a charge build-up, there is a charge transfer from the semiconductor silicon substrate into the single layer graphene film that is opposite in magnitude to the signal charge in the potential well.

The working principle of the charge injection device is as follows:

(1) applying pulse voltage with certain frequency between the grid and the source of the charge injection device to form a deep depletion region in the semiconductor substrate. If the semiconductor substrate used is n-type, a positive voltage is applied to the gate.

(2) When light is incident on the device from the top, visible light enters a depletion region in the silicon, the depletion region absorbs photons to generate electron-hole pairs, and the electron-hole pairs are separated under the action of an electric field of the silicon substrate, wherein minority carriers are stored in a deep depletion potential well; infrared light passes through the silicon layer and is absorbed by a schottky barrier formed by the multilayer graphene and the silicon, and minority carriers generated are injected into the deep depletion potential well under the action of an electric field. Meanwhile, the opposite charges which are equal to the charges generated in the semiconductor potential well are transferred to the single-layer graphene film under the action of the gate electric field, so that the carrier concentration of the single-layer graphene film is changed, and the conductivity of the single-layer graphene film is changed.

(3) And applying a fixed bias voltage between the drain electrode and the source electrode, and monitoring the current variation on the graphene film to calculate the quantity of carriers accumulated in the deep depletion potential well.

The invention has the following beneficial effects:

1. according to the invention, multilayer graphene is integrated on the back of silicon as an infrared photosensitive layer material, a heterojunction between the infrared photosensitive layer and the silicon is formed, infrared light is absorbed in the heterojunction and generates electron-hole pairs, wherein minority carriers are injected into a deep depletion potential well of the silicon under the action of an electric field. Visible light is absorbed in silicon and excites electron-hole pairs, photogenerated charges in the electron-hole pairs are directly generated in a deep depletion potential well and integrated with infrared photogenerated holes, so that the spectral response range of the traditional CCD device is widened, and the absorption efficiency of an infrared band is increased.

2. The device has simple structure, is easy to manufacture in large scale and can be compatible with CMOS process.

3. The preparation process of the graphene is mature, the manufacturing cost is relatively low, and the preparation and production are easy.

4. The transfer method of the multilayer graphene is simple and easy to process.

5. The device has an integral function similar to that of the traditional CCD device, and can obtain great response under the environment of weak light.

Drawings

Fig. 1 is a schematic structural diagram of a charge injection device based on a single-layer graphene/insulating layer/silicon/multi-layer graphene structure according to the present invention, which includes a gate 1, a multi-layer graphene 2, a semiconductor silicon substrate 3, an oxide insulating layer 4, a source 5, a drain 6, and a single-layer graphene film 7;

FIG. 2 is a graph showing the optical response of a CID device prepared in the present invention under 0.2Hz pulse grid voltage of 0 to-5V and 50% duty cycle under dark field and laser with wavelength of 633nm and power of 5 nW;

fig. 3 is a schematic diagram of a charge injection device pixel array of single layer graphene/insulator layer/silicon/multilayer graphene structure.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

The working principle of the Charge Injection Device (CID) based on the single-layer graphene/insulating layer/silicon/multi-layer graphene structure provided by the invention is as follows:

the single-layer graphene, the oxide insulating layer and the semiconductor substrate form an MIS structure, and the multi-layer graphene and the semiconductor substrate form a heterojunction. A high-speed pulse signal is applied to two ends of a grid source, a certain time is needed for generating minority carriers, an inversion layer does not appear in a semiconductor immediately, and the semiconductor is in a depletion state. When the semiconductor enters a deep depletion state, the depletion region width increases. When incident light irradiates the device region, the silicon depletion region absorbs incident visible light, the heterojunction absorbs infrared light, and both parts generate electron-hole pairs; if the semiconductor substrate is n-type, electrons flow into the graphene under the action of the gate electric field, so that the fermi level of the graphene is increased. Due to the specific energy band structure of graphene, the increase of the fermi level causes a proportional change of the conductivity of graphene. After fixed bias voltage is applied to the graphene, the electric charge stored in the potential well can be reflected synchronously by measuring the current of the graphene, direct reading can be achieved, and multiple transfer is not needed.

As shown in fig. 1, the charge injection device based on the single-layer graphene/insulating layer/silicon/multi-layer graphene structure is provided with a gate 1, a multi-layer graphene 2, a semiconductor silicon substrate 3 and an oxide insulating layer 4 from bottom to top, wherein a source 5 and a drain 6 are arranged on the upper surface of the oxide insulating layer 4, a single-layer graphene film 7 covers the upper surfaces of the oxide insulating layer 4, the source 5 and the drain 6, the single-layer graphene film 7 is in contact with the source 3 and the drain 4 and does not exceed the range defined by the source 3 and the drain 4, and the range of the single-layer graphene film 7 corresponds to the range defined by the multi-layer graphene 2.

Further, the multi-layer graphene 2 has the same size and shape as the single-layer graphene film 7, and is located right below the single-layer graphene film 7 and aligned with the single-layer graphene film 7.

The method for preparing the charge injection device based on the single-layer graphene/insulating layer/silicon/multi-layer graphene structure comprises the following steps:

(1) growing a silicon dioxide insulating layer on the upper surface of the lightly doped silicon substrate, wherein the resistivity of the silicon substrate is 1 k-10 k omega cm; the thickness of the silicon dioxide insulating layer is 5 nm-100 nm, and the growth temperature is 900-1200 ℃;

(2) producing source electrode and drain electrode patterns on the surface of the silicon dioxide insulating layer by using a photoetching technology, and then growing a chromium adhesion layer with the thickness of about 15nm and then growing a gold layer with the thickness of 80nm as an electrode by using an electron beam evaporation or thermal evaporation technology;

(3) 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; wherein the acid etching solution consists of CuSO4, HCl and water, and the ratio of CuSO 4: HCl: H2O-10 g:45ml:50 ml;

(4) and carrying out secondary photoetching on the device, and covering the defined area of the needed single-layer graphene pattern by using 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). Etching off redundant graphene outside the photoresist, and after etching is finished, cleaning with acetone and isopropanol to remove residual photoresist;

(5) taking multilayer graphene with the thickness of 10-40 nm, soaking one surface of the multilayer graphene with acetone, transferring the multilayer graphene to the back surface of a silicon substrate, and ventilating and airing;

(6) and photoetching is carried out on the multilayer graphene, and a photoresist is used for covering a defined area of a required multilayer graphene pattern. Then, etching the redundant part by using an oxygen plasma reactive ion etching technology, wherein the power and the etching time are respectively 90W and 15 min;

(7) and coating gallium-indium slurry at the bottom of the multilayer graphene, preparing a grid, and forming ohmic contact with the multilayer graphene.

And (3) applying high-speed pulse gate voltage to the charge injection device based on the single-layer graphene/insulating layer/silicon/multi-layer graphene structure to drive the silicon substrate to enter deep depletion and the heterojunction to enter positive bias, thereby realizing light absorption and charge accumulation. Wherein one terminal of the gate voltage is connected to the gate 1 of the device and the other terminal is connected to the source 5. And a fixed bias voltage of 10mV is applied between the source electrode 5 and the drain electrode 6, so that the charge in the potential well can be read on the graphene without damage. As shown in fig. 1.

The CID device prepared by the embodiment of the invention works under 0-5V and 0.2Hz pulse grid voltage with 50% duty ratio, and the optical response curve under dark field and 5nW laser with 633nm wavelength is shown in figure 2. As can be seen from fig. 2, the prepared photocurrent is large and integration of the photocurrent can be achieved, confirming that the device can be applied to an image sensor array.

Photodetector arrays have wide applications in imaging and monitoring fields. The charge injection device based on the single-layer graphene/insulating layer/silicon/multi-layer graphene structure of the present invention can be used to fabricate the photodetector array as shown in fig. 3 using the standard semiconductor process described in the examples. Conventional signal processing methods can be used to obtain data in each pixel by connecting the top electrode of each element in the photodetector array to the signal processing circuit with gold wires using wire bonding to complete the package.

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.