Graphene-lithium tantalate transistor long-wave infrared detector and preparation method thereof

Abstract

The application belongs to the technical field of semiconductor photoelectric device process, and particularly relates to a graphene-lithium tantalate transistor long-wave infrared detector and a preparation method thereof. The infrared detector comprises a substrate, a lithium tantalate film, a graphene layer, a source metal electrode, a drain metal electrode and a passivation layer; the lithium tantalate film is located on the substrate; the source metal electrode and the drain metal electrode are arranged on the lithium tantalate film; the graphene layer is arranged on the lithium tantalate film between the source metal electrode and the drain metal electrode; and the passivation layer is arranged on the graphene layer. The application introduces graphene into the lithium tantalate film to form a ferroelectric field effect transistor structure, constructs a vertical heterostructure of "silicon substrate-lithium tantalate film-graphene channel", utilizes the excellent conductivity of graphene and the pyroelectricity of lithium tantalate, significantly improves the signal reading and amplification capacity and the pyroelectricity response characteristic of the detector, and successfully prepares an infrared detection unit device with high sensitivity and rapid response capacity.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic device technology, and in particular to a graphene-lithium tantalate transistor long-wave infrared detector and its fabrication method. Background Technology

[0002] Uncooled infrared detection technology has significant application value in the field of infrared detection, and is widely used in civilian applications such as environmental monitoring, smart homes, and medical testing. It also plays an important role in key fields such as aerospace and military, including infrared guidance, target recognition, and space environment monitoring. Among these technologies, pyroelectric detectors are one of the important technical solutions for long-wave infrared detection.

[0003] Currently, pyroelectric detectors typically employ a capacitor-type structure, generating an electrical charge signal through temperature changes caused by infrared radiation. However, this structure suffers from a weak readout current, resulting in insufficient signal strength and limiting the detector's sensitivity.

[0004] Therefore, a new type of uncooled infrared detector is needed. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a graphene-lithium tantalate transistor long-wave infrared detector and its fabrication method. This long-wave infrared detector amplifies and reads signals using a ferroelectric field-effect transistor structure, overcoming the weakness of signals in traditional capacitive structures. The introduction of graphene improves the device's electron transport performance and enhances the pyroelectric response of the lithium tantalate material, resulting in higher sensitivity of the detector in the infrared band.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A graphene-lithium tantalate transistor long-wave infrared detector, comprising a substrate, a lithium tantalate thin film, a graphene layer, a source metal electrode, a drain metal electrode, and a passivation layer;

[0008] The lithium tantalate film is located on the substrate; the source metal electrode and the drain metal electrode are disposed on the lithium tantalate film; a graphene layer is disposed on the lithium tantalate film between the source metal electrode and the drain metal electrode; and a passivation layer is disposed on the graphene layer.

[0009] The portion of the substrate in contact with the lithium tantalate film has a cavity, which allows the graphene-lithium tantalate transistor long-wave infrared detector to form a suspended structure.

[0010] The length of the cavity is 0.5% of the length of the substrate; the depth of the cavity is 0.2% of the depth of the substrate.

[0011] The thickness of the lithium tantalate film is 3~5μm; the thickness of the passivation layer is 6~30nm.

[0012] Wherein, the graphene layer is a single layer of graphene; the substrate is a silicon substrate; the source metal electrode is a chromium electrode; the drain metal electrode is a gold electrode; and the passivation layer is a zinc sulfide layer.

[0013] The above-mentioned method for fabricating a graphene-lithium tantalate transistor long-wave infrared detector includes the following steps:

[0014] Lithium tantalate thin films were prepared on a substrate;

[0015] A source metal electrode and a drain metal electrode are fabricated on the lithium tantalate film;

[0016] A graphene layer is prepared on a lithium tantalate film between the source metal electrode and the drain metal electrode;

[0017] A passivation layer is prepared on the graphene layer.

[0018] The process includes a step of improving the surface morphology of the lithium tantalate film by plasma etching before preparing the source metal electrode and the drain metal electrode.

[0019] The graphene layer is prepared by wet transfer of monolayer graphene, which is transferred from the copper growth substrate to the lithium tantalate film and baked on a hot plate at 100-150 degrees Celsius for 30-60 minutes.

[0020] The preparation method further includes the step of forming a cavity on the substrate, specifically:

[0021] Thermal insulation trenches are etched into the lithium tantalate film to expose the substrate;

[0022] The substrate is etched using XeF2 gas through the heat-insulating trench until a cavity is formed.

[0023] The source metal electrode and the drain metal electrode are fabricated based on photolithography mask and metal thermal evaporation deposition process;

[0024] The passivation layer is prepared using electron beam evaporation deposition technology.

[0025] The physical basis of the graphene-lithium tantalate transistor long-wave infrared detector of the present invention lies in the ferroelectric-semiconductor coupling mechanism constructed by the high pyroelectric effect of lithium tantalate film and the high mobility of graphene, combined with the suspended thermal isolation structure, so that the device can achieve synergistic enhancement of optical-thermal-electric multi-physics fields in the 6-25 micrometer long-wave infrared band, providing a high-sensitivity solution for long-wave infrared imaging.

[0026] The beneficial effects of this invention are as follows:

[0027] (1) This invention introduces graphene onto a lithium tantalate film to form a ferroelectric field-effect transistor structure. By utilizing the excellent conductivity of graphene and the pyroelectric properties of lithium tantalate, the signal readout and amplification capabilities and pyroelectric response characteristics of the detector are significantly improved, and an infrared detection unit device with high sensitivity and fast response capability is successfully fabricated.

[0028] (2) The graphene-lithium tantalate transistor long-wave infrared detector of the present invention makes full use of the excellent electron transport performance of graphene and the ferroelectric polarization regulation and pyroelectric characteristics of lithium tantalate, which significantly enhances the infrared detection performance of the device.

[0029] (3) The graphene-lithium tantalate transistor long-wave infrared detector of the present invention significantly improves the signal amplification and readout capability of the detector by applying the field effect transistor structure, thereby improving the sensitivity, signal-to-noise ratio and detection rate of the detector.

[0030] (4) The graphene-lithium tantalate transistor long-wave infrared detector of the present invention utilizes the ferroelectric field-effect transistor structure and MEMS suspension technology to construct a vertical heterostructure of "silicon substrate-cavity-lithium tantalate thin film-graphene channel". Among them, the suspended cavity effectively blocks the conduction of heat to the substrate, significantly improving the temperature response of the lithium tantalate pyroelectric thin film; at the same time, the efficient control of the carrier concentration of the graphene channel by the polarization electric field of lithium tantalate realizes the in-situ amplification and readout of the infrared radiation signal.

[0031] (5) The graphene-lithium tantalate transistor long-wave infrared detector of the present invention also has the characteristics of compact structure, strong stability and suitability for mass production, providing a new technical solution for the development of high-performance infrared detectors. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the graphene-lithium tantalate transistor long-wave infrared detector of the present invention.

[0033] Figure 2 This is a schematic diagram showing the response of the graphene-lithium tantalate transistor long-wave infrared detector of the present invention under 638 nm laser chopping.

[0034] Figure 3 This is a schematic diagram showing the test results of the detectivity of the graphene-lithium tantalate transistor long-wave infrared detector of the present invention under a bias voltage of 1 volt and at different blackbody radiation temperatures.

[0035] Figure 4 This is a schematic diagram showing the test results of the response time of the graphene-lithium tantalate transistor long-wave infrared detector of the present invention under a 1-volt bias voltage and at different blackbody radiation temperatures.

[0036] Figure 5 The thermal field distribution simulation diagram is obtained by simulating the graphene-lithium tantalate transistor long-wave infrared detector of the present invention using the finite element simulation software (COMSOL).

[0037] In the attached figures, the reference numerals are: 1-substrate, 2-cavity, 3-lithium tantalate film, 4-graphene layer, 5-source metal electrode, 6-passivation layer, and 7-drain metal electrode. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] See Figure 1 The present invention provides a graphene-lithium tantalate transistor long-wave infrared detector, which includes a substrate 1, a lithium tantalate thin film 3, a graphene layer 4, a source metal electrode 5, a drain metal electrode 7, and a passivation layer 6.

[0040] The lithium tantalate film 3 is located on the substrate 1; the source metal electrode 5 and the drain metal electrode 7 are disposed on the lithium tantalate film 3; the graphene layer 4 is disposed on the lithium tantalate film 3 between the source metal electrode 5 and the drain metal electrode 7; and the passivation layer 6 is disposed on the graphene layer 4.

[0041] The graphene-lithium tantalate transistor long-wave infrared detector of the present invention introduces a graphene layer 4 onto a lithium tantalate thin film 3 to form a ferroelectric field-effect transistor structure. The ferroelectric field-effect transistor structure amplifies and reads out signals, improves the readout current intensity of the device, and overcomes the problem of weak signals in traditional capacitive structures. The introduction of graphene improves the electron transport performance of the device and enhances the pyroelectric response of lithium tantalate material, giving the detector higher sensitivity in the infrared band. By utilizing the excellent conductivity of graphene and the pyroelectric properties of lithium tantalate, the signal readout and amplification capability and pyroelectric response characteristics of the detector are significantly improved, and an infrared detection unit device with high sensitivity and fast response capability is successfully fabricated.

[0042] In one embodiment, see Figure 1A cavity 2 is provided at the portion of the substrate 1 that contacts the lithium tantalate film 3, forming a suspended structure for the graphene-lithium tantalate transistor long-wave infrared detector. In this embodiment, the cavity is obtained by etching the substrate. The purpose of the cavity is to block heat conduction to the silicon substrate to achieve excellent thermal isolation, thereby maximizing the temperature response of the pyroelectric film under infrared radiation and improving the detector's sensitivity. To verify the effect of the suspended structure on improving the device's temperature response, the thermal field distribution of the device with the suspended structure was simulated using finite element simulation software (COMSOL). The simulation results are as follows: Figure 5 As shown, from Figure 5 As can be seen, the cavity, i.e., the suspended structure of the present invention, effectively blocks the conduction of heat to the silicon substrate, so that the heat is highly concentrated in the central sensing area of ​​the device, thereby significantly improving the temperature response of the lithium tantalate film.

[0043] Preferably, the length of the cavity 2 is 0.5% of the length of the substrate 1; and the depth of the cavity 2 is 0.2% of the depth of the substrate 1.

[0044] Preferably, the thickness of the lithium tantalate film 3 is 3~5μm; and the thickness of the passivation layer 6 is 6~30nm.

[0045] Preferably, the graphene layer 4 is a single layer of graphene; the substrate 1 is a silicon substrate; the source metal electrode 5 is a chromium electrode; the drain metal electrode 7 is a gold electrode; and the passivation layer 6 is a zinc sulfide layer.

[0046] The above-mentioned method for fabricating a graphene-lithium tantalate transistor long-wave infrared detector includes the following steps:

[0047] (1) A lithium tantalate film 3 is prepared on substrate 1; in this embodiment, substrate 1 is a 0.4 mm silicon substrate and lithium tantalate film 3 is a 5 μm silicon-based lithium tantalate film.

[0048] (2) Improve the surface morphology of lithium tantalate film; specifically, use oxygen plasma etching machine to bombard the surface of silicon-based lithium tantalate film for 1 minute.

[0049] (3) A source metal electrode 5 and a drain metal electrode 7 are prepared on the lithium tantalate film 3. Specifically, the source and drain electrode patterns are first prepared by laser direct writing method; then the metal electrodes are prepared by thermal evaporation technology, with chromium 15 nm and gold 15 nm; then the metal film is peeled off by peeling method to obtain the patterned source metal electrode 5 and drain metal electrode 7.

[0050] (4) A graphene layer 4 is prepared on the lithium tantalate film 3 between the source metal electrode 5 and the drain metal electrode 7. Specifically, a wet transfer method is used to transfer monolayer graphene from the growth substrate copper to the lithium tantalate film 3 and bake it on a hot plate at 100 degrees Celsius for 30 minutes to improve the adhesion between the graphene layer 4 and the lithium tantalate film 3. Then, the graphene layer 4 is patterned at the micrometer level by photolithography and oxygen plasma etching.

[0051] (5) A passivation layer 6 is prepared on the graphene layer 4. Specifically, a zinc sulfide film with a thickness of 30 nanometers is prepared by electron beam evaporation coating technology to protect the graphene structure.

[0052] (6) Etch thermal insulation trenches on the lithium tantalate film 3 and expose the substrate 1. Specifically, the thermal insulation trenches are etched on the lithium tantalate film 3 using reactive ion etching (RIE) method. The lithium tantalate film 3 with a thickness of 5 micrometers needs to be etched through to expose the silicon substrate and ensure the thermal insulation of the device.

[0053] (7) Forming cavity 2: Using XeF2 gas to etch the substrate 1 through the heat insulation trench until cavity 2 is formed.

[0054] (8) Photoelectric performance testing:

[0055] The prepared device was placed in the probe station, and the source metal electrode 5 and drain metal electrode 7 of the sample were connected to the two ends of the picoammeter, respectively. The laser beam was directed onto the device through the optical path. A constant voltage of 1 volt and a square wave frequency of 0.5 Hz were applied between the source and drain electrodes. Figure 2 As shown, the device exhibits a periodic and clear response when illuminated by a laser with a wavelength of 638 nanometers.

[0056] like Figure 3 and Figure 4 As shown, in the blackbody light source test, with the room temperature controlled at 19°C and the blackbody-device distance at 12 cm, the detectivity of the graphene-lithium tantalate transistor long-wave infrared detector of this invention reached 1.4 × 10⁻⁶. 9 Jones achieved a response time of 38 milliseconds, demonstrating excellent far-infrared detection capabilities.

[0057] This invention first improves the surface cleanliness of a thin film on a silicon-based lithium tantalate substrate through oxygen plasma surface treatment; then, source and drain metal electrodes are fabricated using photolithography and metal thermal evaporation deposition processes; to establish carrier transport channels, monolayer graphene is transferred onto the lithium tantalate film with the prepared electrodes, and micron-level patterning is achieved through photolithography and oxygen plasma etching; to address the environmental sensitivity of graphene, zinc sulfide is deposited by electron beam evaporation for surface encapsulation; to achieve thermal isolation, a 5-micron-deep thermal insulation trench is formed on the lithium tantalate film using reactive ion etching (RIE); finally, the underlying silicon substrate is removed by dry etching with xenon difluoride to form an infrared long-wave pyroelectric device with a suspended structure and polarization field modulation.

[0058] The physical basis of the graphene-lithium tantalate transistor long-wave infrared detector of the present invention lies in the ferroelectric-semiconductor coupling mechanism constructed by the high pyroelectric effect of lithium tantalate film and the high mobility of graphene, combined with the suspended thermal isolation structure, so that the device can achieve synergistic enhancement of optical-thermal-electric multi-physics fields in the 6-25 micrometer long-wave infrared band, providing a high-sensitivity solution for long-wave infrared imaging.

[0059] The graphene-lithium tantalate transistor long-wave infrared detector of this invention utilizes a ferroelectric field-effect transistor structure and MEMS suspension technology to construct a vertical heterostructure of "silicon substrate-cavity-lithium tantalate thin film-graphene channel". The cavity effectively blocks heat conduction to the substrate, significantly improving the temperature response of the lithium tantalate pyroelectric thin film; simultaneously, the efficient control of carrier concentration in the graphene channel by the polarized electric field of lithium tantalate enables in-situ amplification and readout of the infrared radiation signal.

[0060] The graphene-lithium tantalate transistor long-wave infrared detector of the present invention achieves synergistic enhancement of optical-thermal-electric multi-physics fields in the 6-25 micrometer long-wave infrared band, solving the problems of low sensitivity, severe thermal crosstalk and slow response speed of traditional pyroelectric detectors. It has high sensitivity and millisecond-level fast response capability, providing a high-performance solution for uncooled infrared imaging.

[0061] It should be understood that the sequence number of each step in the above invention does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the invention in this application.

[0062] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0063] The parts of this invention not described in detail are well-known in the art. The above embodiments are provided merely for the purpose of describing the invention and are not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principles of the invention should be covered within the scope of the invention.

Claims

1. A graphene-lithium tantalate transistor long-wave infrared detector, characterized in that, The infrared detector includes a substrate, a lithium tantalate thin film, a graphene layer, a source metal electrode, a drain metal electrode, and a passivation layer. The lithium tantalate film is located on the substrate; the source metal electrode and the drain metal electrode are disposed on the lithium tantalate film; a graphene layer is disposed on the lithium tantalate film between the source metal electrode and the drain metal electrode; and a passivation layer is disposed on the graphene layer.

2. The graphene-lithium tantalate transistor long-wave infrared detector according to claim 1, characterized in that, A cavity is provided in the portion of the substrate that contacts the lithium tantalate film, and the cavity enables the graphene-lithium tantalate transistor long-wave infrared detector to form a suspended structure.

3. The graphene-lithium tantalate transistor long-wave infrared detector according to claim 2, characterized in that, The length of the cavity is 0.5% of the length of the substrate; the depth of the cavity is 0.2% of the depth of the substrate.

4. The graphene-lithium tantalate transistor long-wave infrared detector according to claim 1, characterized in that, The thickness of the lithium tantalate film is 3~5μm; the thickness of the passivation layer is 6~30nm.

5. The graphene-lithium tantalate transistor long-wave infrared detector according to claim 1, characterized in that, The graphene layer is a single-layer graphene; the substrate is a silicon substrate; the source metal electrode is a chromium electrode; the drain metal electrode is a gold electrode; and the passivation layer is a zinc sulfide layer.

6. The method for fabricating the graphene-lithium tantalate transistor long-wave infrared detector according to any one of claims 1 to 5, characterized in that, Includes the following steps: Lithium tantalate thin films were prepared on a substrate; A source metal electrode and a drain metal electrode are fabricated on the lithium tantalate film; A graphene layer is prepared on a lithium tantalate film between the source metal electrode and the drain metal electrode; A passivation layer is prepared on the graphene layer.

7. The method for fabricating a graphene-lithium tantalate transistor long-wave infrared detector according to claim 6, characterized in that, The process includes a step of improving the surface morphology of the lithium tantalate film by plasma etching before the preparation of the source metal electrode and the drain metal electrode.

8. The method for fabricating a graphene-lithium tantalate transistor long-wave infrared detector according to claim 6, characterized in that, The graphene layer is prepared by wet transfer of monolayer graphene, which is transferred from the copper growth substrate to the lithium tantalate film and baked on a hot plate at 100-150 degrees Celsius for 30-60 minutes.

9. The method for fabricating a graphene-lithium tantalate transistor long-wave infrared detector according to claim 6, characterized in that, The preparation method further includes the step of forming a cavity on the substrate, specifically: Thermal insulation trenches are etched into the lithium tantalate film to expose the substrate; The substrate is etched using XeF2 gas through the heat-insulating trench until a cavity is formed.

10. The method for fabricating a graphene-lithium tantalate transistor long-wave infrared detector according to claim 6, characterized in that, The source metal electrode and drain metal electrode are fabricated based on photolithography mask and metal thermal evaporation deposition process; The passivation layer is prepared using electron beam evaporation deposition technology.

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