A Graphene Terahertz Detector under Ferroelectric Regulation and Its Preparation Method

Abstract

The present invention discloses a ferroelectrically regulated graphene terahertz detector and a preparation method thereof. The device preparation steps are as follows: transfer mechanically exfoliated graphene onto an intrinsic high-resistance silicon substrate, fabricate source and drain electrodes by using ultraviolet lithography technology and electron beam evaporation, transfer mechanically exfoliated CuInP2S6 from polydimethylsiloxane (PDMS) onto the high-resistance silicon substrate by using a dry fixed-point transfer technology, fabricate a gate electrode by using electron beam lithography technology and electron beam evaporation, and prepare a ferroelectrically regulated graphene terahertz detector by using processes such as ultrasonic wire bonding. By constructing a metal structure antenna with a butterfly shape, under the regulation of the ferroelectric material, high-sensitivity terahertz broadband absorption at room temperature is achieved, thereby significantly enhancing the source-drain current of the detector and greatly improving the signal-to-noise ratio and detection ability of the device. The ferroelectrically regulated graphene terahertz detector exhibits high sensitivity in the terahertz band. The advantages of the present invention are high responsivity, fast response, low power consumption, and easy integration.

Description

Technical Field

[0001] The present invention relates to the antenna structure design, preparation method and performance research of a graphene terahertz detection device under ferroelectric regulation. By constructing a metal structure antenna with a butterfly shape and using the ferroelectric material CuInP2S6 (CIPS) as the top gate, the source-drain current of the detector is significantly enhanced, realizing the conversion of optoelectronic signals, and greatly improving the detection sensitivity and signal-to-noise ratio of the device in the terahertz band. Background Art

[0002] Terahertz waves are electromagnetic waves with a frequency range between 0.1 THz and 10 THz, whose wavelengths correspond to 3 mm to 30 μm, and the characteristic value of the photon corresponding energy is at the millielectronvolt level. This energy range matches the vibrational and rotational energies of molecules, is much smaller than the energy gap of general semiconductors, and exhibits different characteristics in terms of propagation, scattering, and absorption compared with microwaves, infrared rays, and visible light, providing a large free space for information transmission, characterization, and manipulation of material materials. The terahertz band is located in the cross-field of electronics and photonics, and related research can promote the integration and development of these two disciplines. Currently, the research and development of terahertz are not yet mature, lacking efficient terahertz sources, terahertz detectors, and terahertz modulators, so it is called the "terahertz gap".

[0003] Developing high-speed, high-response-rate, and room-temperature-operable terahertz detection technology is the key to realizing the development and application of terahertz technology. Improving the coupling ability between light and the device and the optoelectronic conversion efficiency is the breakthrough point of terahertz detection. Current commercial terahertz detectors include pyroelectric terahertz detectors, bolometers, and Schottky diodes. Generally, the response speed of pyroelectric detectors is relatively slow; the operating frequency of Schottky diodes is relatively low, and the process is complex; bolometers need to work under low-temperature conditions. Therefore, realizing terahertz detection by changing the gate material of the terahertz detector field of field-effect transistors has become a hot topic in the terahertz detection field and has received extensive attention.

[0004] Ferroelectric materials have characteristics such as large dielectric constant, spontaneous polarization, and strong inverse piezoelectric effect. By using the spontaneous polarization characteristics of ferroelectric materials, the carrier concentration and mobility of graphene can be regulated, thereby realizing the regulation of the optoelectronic properties of graphene. Nowadays, terahertz frequency-related technologies are widely applied in fields such as homeland security, quality inspection, biology, medicine, spectroscopy, data communication, and imaging. Therefore, using the ferroelectric material CuInP2S6 (CIPS) as the top gate to regulate the optoelectronic properties of graphene is still one of the most important technical challenges and a key priority task for a new generation of optoelectronic technology. Summary of the Invention

[0005] The present invention provides an antenna structure design, a preparation method and a performance study of a graphene terahertz detection device under room-temperature ferroelectric regulation. By constructing a metal structure antenna with a butterfly shape and using the ferroelectric material CuInP2S6 (CIPS) as the top gate, the source-drain current of the detector is significantly enhanced, realizing the photoelectric signal conversion and achieving fast and highly sensitive room-temperature terahertz detection.

[0006] The structure of the detector is as follows: on the intrinsic high-resistivity silicon substrate 1 is a silicon dioxide layer 2, on the silicon dioxide layer 2 is graphene 3, at both ends of the graphene 3 are a source electrode 4 and a drain electrode 5, on the source electrode 4 and the drain electrode 5 is a two-dimensional ferroelectric material CuInP2S66, and on the two-dimensional ferroelectric material CuInP2S66 is a gate electrode 7.

[0007] The substrate 1 is intrinsic high-resistivity silicon with a resistivity of 10000 Ω·cm and a thickness of 500 μm; covered on it is silicon dioxide 2 with a thickness of 300 nm;

[0008] The graphene 3 has a thickness of approximately 4 nm;

[0009] The source electrode 4 and the drain electrode 5 are metal composite electrodes. The lower-layer metal is chromium, serving as an adhesion layer with a thickness of 10 nm, and the upper-layer metal is gold with a thickness of 90 nm.

[0010] The two-dimensional ferroelectric material CuInP2S66 has a thickness of approximately 110 nm;

[0011] The gate electrode 7 is a metal composite electrode. The lower-layer metal is chromium, serving as an adhesion layer with a thickness of 10 nm, and the upper-layer metal is gold with a thickness of 90 nm.

[0012] The preparation method of a graphene terahertz detection device under room-temperature ferroelectric regulation of the present invention is as follows: an oxide layer is prepared on the intrinsic high-resistivity silicon by thermal oxidation method as the substrate; graphene is simply mechanically exfoliated using blue tape to obtain nanometer-thick graphene; then the graphene is transferred to the substrate surface; ultraviolet lithography technology is adopted, combined with electron beam evaporation and traditional lift-off process to prepare the source and drain of the butterfly antenna structure; the mechanically exfoliated CuInP2S6 is transferred from polydimethylsiloxane (PDMS) to the high-resistivity silicon substrate by dry fixed-point transfer technology, and then electron beam lithography technology is used, combined with electron beam evaporation and traditional lift-off process to prepare the gate of the butterfly antenna structure; the device is attached to the PCB base, wired, and simply packaged to complete the preparation of the ferroelectric-regulated graphene terahertz detector.

[0013] Advantages of this invention patent:

[0014] 1 Our experiment is based on graphene, which has excellent properties such as low defect density, easy large-area transfer, and high carrier mobility.

[0015] 2 When the graphene device is at zero bias voltage, it can achieve a room-temperature terahertz photosensitivity of 0.13 A / W, which is superior to many similar two-dimensional materials. At the same time, under a bias voltage of 40 mV and a gate voltage of 2.12 V, the device responsivity will increase to 0.5 A / W.

[0016] 3 Generally, terahertz detector materials require complex nanofabrication processes and proper encapsulation of the active channel region. Relatively speaking, our graphene device has the advantage of a simple structure and excellent cost-effectiveness.

[0017] 4 Under the gate voltage, the signal-to-noise ratio of the device is improved, but the response time hardly changes, showing the potential of graphene devices in terahertz technology.

[0018] 5 The noise equivalent power is low, generally reaching 0.81 nW / HZ in the terahertz band 0.5 ; We have successfully realized room-temperature terahertz imaging applications. We placed a metal object in an invisible envelope and obtained a clear high-contrast imaging map under 0.3 THz radiation. Brief Description of the Drawings

[0019] Figure 1 is a schematic cross-sectional structure diagram of a graphene terahertz detection device under ferroelectric regulation.

[0020] Figure 2 is a schematic structure diagram of the butterfly antenna used for the source and drain electrodes.

[0021] Figure 3 is a block diagram of the detection device responsivity test system.

[0022] Figure 4 is the transfer characteristic curve of the device at a bias voltage of 0.1 V.

[0023] Figure 5 is the change in the optical responsivity under 0.12 THz terahertz band radiation at different gate voltages.

[0024] Figure 6 is the change in the optical responsivity under radiation of different bands at different bias voltages.

[0025] Figure 7 is to evaluate the noise equivalent power (NEP) of the device at two frequency bands. The NEP is the incident signal radiation power required to make the signal output by the detector equal to the noise voltage or current. Detailed Implementation Modes

[0026] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings:

[0027] The present invention relates to the antenna structure design, preparation method and performance research of graphene terahertz detection devices under ferroelectric control. By constructing a butterfly-shaped metal structure antenna and using the ferroelectric material CuInP2S6 (CIPS) as the top gate, the source-drain current of the detector is significantly enhanced, the photoelectric signal conversion is realized, and the detection sensitivity and signal-to-noise ratio of the device in the terahertz band are greatly improved.

[0028] The specific steps are as follows:

[0029] 1. Substrate selection

[0030] Intrinsic high-resistance silicon 1 and silicon dioxide 2 covering the intrinsic high-resistance silicon 1 are selected as substrates.

[0031] 2. Graphene preparation

[0032] Simple mechanical exfoliation using blue tape can yield graphene at a thickness of a few nanometers.

[0033] 3. Direct transfer of graphene 3 to substrate surface 2;

[0034] 4. Using ultraviolet lithography technology, combined with electron beam evaporation and traditional stripping process to prepare the butterfly antenna source electrode 4 and drain electrode 5;

[0035] 5. The mechanically peeled CuInP2S6 was transferred from polydimethylsiloxane (PDMS) to a high-resistance silicon substrate using dry method spot transfer technology, and then the gate of the butterfly antenna structure was prepared by electron beam exposure technology combined with electron beam evaporation and traditional peeling process;

[0036] 6. Stick the device to the PCB base, wire it, and simply package it to complete the preparation of the graphene terahertz detector under ferroelectric control.

[0037] 7. Test the photoelectric response of the prepared ferroelectrically controlled graphene terahertz detector. Figure 3 The photoelectric response test system shown in the figure is mainly based on a microwave source (E8257D) (frequency band 0.02-0.04THz), and uses a frequency multiplier to increase the frequency to 0.12THz and 0.3THz; the terahertz radiation light is irradiated to the entire surface of the detection device, and the detector converts the AC electromagnetic wave signal into a DC signal, amplifies the signal through a current amplifier (SR570), and inputs it into an oscilloscope and a phase-locked amplifier (SR830) respectively. The built-in modulation frequency signal of the microwave source (E8257D) is used as a reference signal and input into the oscilloscope and the phase-locked amplifier respectively. During the test, the device showed ultra-high response rate and rapid detection capabilities. Specific steps: a) According to Figure 2Connect the test system and perform system presetting; b) Adjust the test system, apply the specified gate voltage and bias voltage to the device under test to make the device in a normal working state; c) Place the device at the position perpendicular to the microwave source radiation, ensure that the power density of the outgoing electromagnetic wave is constant within the aperture range of the power meter, measure the total power P0 incident on the power meter window and the area S1 of the power meter window using the power meter model AV2434; d) Place the detector at the position of the power meter window, the pixel area of the detector is S2, measure the response voltage signal V through the lock-in amplifier, and the received power of the detector is P in = P0*S2 / S1; e) Calculate the responsivity of the device as R = V / P in .

[0038] 8. Figure 4 is the transfer characteristic curve of the device at a bias voltage of 0.1V. When the ferroelectric gate voltage is scanned from a negative voltage to a positive voltage and then back to a negative voltage, the conductance of the graphene channel can be effectively regulated with a stable hysteresis behavior. The observed hysteresis behavior can be regarded as a reflection of the CIPS ferroelectric hysteresis characteristic.

[0039] 9. Figure 5 shows the variation of the optical responsivity under 0.12THz terahertz band radiation at different gate voltages. When the bias voltage and the gate voltage are zero, the responsivity reaches 0.13 A / W in the 0.12THz band. At the same time, at a bias voltage of 40 mV and a gate voltage of 2.12 V, the device responsivity increases to 0.5 A / W. The results show that the method of using two-dimensional ferroelectric materials as the top gate to increase the graphene response current and improve the detection ability of the device is reasonable and effective.

[0040] 10. Figure 6 shows the optical response current with variable bias voltage at different bands. The square icon represents the value of the responsivity varying with the bias voltage under 0.12THz light illumination; the circular icon represents the photocurrent value of the responsivity varying with the bias voltage under 0.29THz light illumination. When the bias voltage is zero, the responsivity reaches 0.43 A / W in the 0.12THz band; the responsivity reaches 0.18 A / W in the 0.30THz band.

[0041] 11. Figure 7 shows the noise equivalent power value (NEP) with variable bias voltage at different bands. The noise equivalent power refers to the incident radiation power required when the signal-to-noise ratio is 1. The square icon represents the value of the NEP varying with the bias voltage under 0.12THz light illumination; the circular icon represents the photocurrent value of the NEP varying with the bias voltage under 0.29THz light illumination. When the bias voltage is zero, the responsivity reaches 0.81 nW / HZ in the 0.12THz band 0.5 ; the responsivity reaches 1.78 nW / HZ in the 0.29THz band 0.5。The results show that the method of using two-dimensional ferroelectric materials as the top gate to improve the signal-to-noise ratio is reasonable and effective.

Claims

1. A graphene terahertz detector under ferroelectric regulation, characterized in that: The structure of the detector is as follows: a silicon dioxide layer (2) is provided on a substrate (1), a graphene (3) is provided on the silicon dioxide layer (2), source electrode (4) and drain electrode (5) are at both ends of the graphene (3), a two-dimensional ferroelectric material CuInP2S6 (6) is on the source electrode (4) and the drain electrode (5), and a gate electrode (7) is on the two-dimensional ferroelectric material CuInP2S6 (6); The substrate (1) is an intrinsic high-resistance silicon with a resistivity of 10,000 Ω·cm and a thickness of 500 μm; The thickness of the silicon dioxide layer (2) is 300 nm; The thickness of the graphene (3) is 4 nm; The source electrode (4) and the drain electrode (5) are metal composite electrodes. The lower-layer metal of the metal composite electrode is chromium, serving as an adhesion layer with a thickness of 10 nm, and the upper-layer metal of the metal composite electrode is gold with a thickness of 90 nm; The thickness of the two-dimensional ferroelectric material CuInP2S6 (6) is 110 nm; The gate electrode (7) is a metal composite electrode. The lower-layer metal of the metal composite electrode is chromium, serving as an adhesion layer with a thickness of 10 nm, and the upper-layer metal of the metal composite electrode is gold with a thickness of 90 nm.

2. A method for preparing the graphene terahertz detector under ferroelectric regulation as claimed in claim 1, characterized in that The method is as follows: An oxide layer is prepared on the intrinsic high-resistance silicon by thermal oxidation as the substrate; the graphene is mechanically exfoliated using blue tape to obtain graphene at the nanometer-thick level; then the graphene is transferred to the substrate surface; ultraviolet lithography technology is adopted, combined with electron beam evaporation and traditional lift-off process to prepare the source and drain of the butterfly antenna structure; the mechanically exfoliated CuInP2S6 is transferred from polydimethylsiloxane to the high-resistance silicon substrate by dry fixed-point transfer technology, and then electron beam lithography technology is used, combined with electron beam evaporation and traditional lift-off process to prepare the gate of the butterfly antenna structure; The device is attached to the PCB base, wired, and simply packaged to complete the preparation of the graphene terahertz detector under ferroelectric regulation.

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