Room temperature infrared detection device and method based on si3n4 thin film mechanical resonator

Abstract

The application provides a room temperature infrared detection device based on a silicon nitride film mechanical oscillator and a working method and a preparation method thereof; the device comprises a rectangular substrate and a trampoline structure; the rectangular substrate comprises a Si3N4 layer, a SiO2 layer and a Si substrate from top to bottom; the trampoline structure is formed by etching in the center of the rectangular substrate, and the trampoline structure comprises a circular arc-shaped quadrilateral in the middle and arc-shaped strips extending out of the four corners; and a PdSe2 rectangular film is fixed on the upper surface center of the trampoline structure; due to the strong absorption characteristics of PdSe2 to infrared light at room temperature and the characteristics of the Si3N4 mechanical oscillator capable of providing a high quality factor, the application combines the advantages of the two to provide a device capable of detecting a mid-infrared band at room temperature, and the device can realize high responsivity and high sensitivity, and can bridge the gap between the low performance level of a non-refrigeration infrared detector and the limited application scenarios of a low-temperature cooling infrared detector due to the small portability.

Description

TECHNICAL FIELD

[0001] The application relates to the technical fields of non-refrigeration infrared detection and micro-electromechanical resonator, and particularly relates to a method and device for infrared detection at room temperature by using a Si3N4 thin film mechanical vibrator. BACKGROUND

[0002] Infrared radiation is a common form of energy exchange in nature. The information carried in infrared radiation can be received by a detector and transmitted in the form of a corresponding signal through conversion, so infrared detection technology has become a research hotspot in the world. At present, infrared detection technology has important applications in the fields of laser radar, night vision imaging, fluorescence microscopy and the like. Infrared detectors can be divided into light-sensitive and heat-sensitive types according to the sensing mechanism. The light-sensitive infrared detector uses the quantum effect of light to realize precise measurement of the intensity of a light source, so it needs extremely high monochromaticity of the light source and is equipped with an expensive cooling device for low-temperature detection, which greatly restricts the development and application of the light-sensitive infrared detector due to high cost and difficulty in miniaturization. In order to accelerate the commercial application process of infrared detection, the research on low-cost non-refrigeration infrared detection technology has attracted attention of countries in the world. The main technology is the thermal infrared detector based on thermal effect, including a radiation thermometer, a pyroelectric infrared detector and a thermopile. In the new century, the micro-electromechanical system (MEMS) with high processing precision and low integration cost develops vigorously as a new microfabrication technology. The use of the MEMS technology in the development of non-refrigeration infrared detectors can make the device develop towards miniaturization, high integration and process compatibility. At present, the Si3N4 thin film resonator prepared based on the MEMS processing technology has super-high quality factor and extraordinary thermodynamic characteristics, which effectively improves the response time and sensitivity of the infrared detector at room temperature, but the lack of infrared absorption capacity needs to be solved. Two-dimensional materials have strong light-matter interaction and can realize strong absorption of infrared light. PdSe2 as a narrow-bandgap semiconductor two-dimensional material has a very wide response spectrum for infrared radiation, and the detection range is from visible light to mid-infrared band, so it has great application potential in the field of non-refrigeration infrared detectors. Based on the advantages of the above materials and structures, we invent a detector combining the advantages of the materials, aiming to monitor infrared radiation by using the coupling of heat conduction and mechanical vibration, so as to realize super-high quality factor sensitive infrared detection at room temperature. The application is a device combining the characteristics of PdSe2 and the micro-mechanical resonator. The device comprises a PdSe2 layer and a controllable mechanical vibration structure. The mechanical vibration part adopts a trampoline type thin film structure with high resonant frequency, so that the super-high quality factor resonant mode and sensitive infrared detection can be effectively combined. SUMMARY

[0003] To achieve the above-mentioned application purposes, the technical scheme of the application is as follows:

[0004] A room temperature infrared detection device based on a Si3N4 thin film mechanical oscillator includes a rectangular substrate 6 and a trampoline structure 1 at the center of the rectangular substrate 6. The rectangular substrate 6 consists of a Si3N4 layer 3, a SiO2 layer 4, and a Si substrate 5 from top to bottom. The trampoline structure is formed at the center of the rectangular substrate 6 by etching. The trampoline structure includes a central arc-shaped quadrilateral 11 and arc-shaped strips 12 extending from the four corners. The trampoline structure is obtained by etching four identical arcs from the four sides of the central square towards the center. The etching depth penetrates the entire Si3N4 layer 3 and SiO2 layer 4. A PdSe2 rectangular thin film 2 is fixed at the center of the upper surface of the trampoline structure 1.

[0005] The trampoline structure is equivalent to a Si3N4 mechanical oscillator suspended above the rectangular substrate 6. When the Si3N4 mechanical oscillator is subjected to temperature changes, it will vibrate mechanically. The PdSe2 rectangular thin film 2 acts as an infrared radiation absorbing material to conduct heat and is used to drive and regulate the Si3N4 mechanical oscillator. The infrared detection device detects the resonant frequency and quality factor of the Si3N4 mechanical oscillator by controlling the light field at room temperature. It uses the frequency shift response of the Si3N4 mechanical oscillator under infrared radiation intensity to realize the detection of the corresponding infrared band.

[0006] As a preferred embodiment, the trampoline structure is suspended 250–300 nm above the rectangular substrate 6.

[0007] As a preferred embodiment, the thickness of the Si3N4 layer 3 is 100 nm.

[0008] As a preferred method, the Si3N4 mechanical oscillator can reach a maximum strength of 10 at room temperature. 9 The quality factor.

[0009] As a preferred embodiment, the length d of the diagonal of the central square of the trampoline structure is the length of the trampoline structure, where d = 10 μm.

[0010] As a preferred embodiment, the width a of the arc-shaped strip 12 is 2 μm.

[0011] The present invention also provides a method for operating the room temperature infrared detection device based on the Si3N4 thin film mechanical oscillator, which is as follows:

[0012] At room temperature, when infrared light is incident on the PdSe2 rectangular thin film 2, due to the absorption characteristics of the PdSe2 rectangular thin film 2, the PdSe2 rectangular thin film 2 absorbs most of the infrared radiation and converts it into heat energy. The heat energy can only be transferred out through the Si3N4 mechanical oscillator below the PdSe2 rectangular thin film 2. The Si3N4 mechanical oscillator will undergo mechanical vibration under heating, and the heat energy will be dissipated in the form of vibration. This causes a change in the mechanical characteristics of the Si3N4 mechanical oscillator, which in turn causes a certain degree of shift in the resonant frequency of the oscillator, i.e., frequency shift. At this time, the incident infrared light can be regarded as the driving light that drives the mechanical oscillator to vibrate.

[0013] Another beam of light is then used to strike the Si3N4 mechanical oscillator in the trampoline structure as a probe light. When the probe light shines on the Si3N4 mechanical oscillator, part of it is reflected back, and the other part penetrates the Si3N4 layer and is reflected on the bottom substrate surface. The two reflected signals then produce an interference pattern. Finally, a photodetector is used to capture the reflected signal, thereby detecting the vibration mode of the Si3N4 mechanical oscillator. By establishing the relationship between the intensity of the incident infrared radiation and the frequency shift response, the sensing and detection of the incident infrared light can be achieved.

[0014] The present invention also provides a method for fabricating the room temperature infrared detection device based on the Si3N4 thin film mechanical oscillator, which is as follows:

[0015] A Si3N4 mechanical oscillator with a trampoline structure was fabricated using a contact ultraviolet exposure, reaction-coupled plasma etching system, hydrofluoric acid etching, and electron beam evaporation coating system. A few layers of PdSe2 were obtained by mechanical peeling and then transferred and fixed to the center of the upper surface of the trampoline structure using a two-dimensional material dry transfer technique.

[0016] As a preferred embodiment, the preparation method includes the following steps:

[0017] (1) Pre-treatment: including wafer cutting, surface ultrasonic cleaning, and drying;

[0018] (2) Dry transfer of PdSe2: The few-layer PdSe2 film was peeled off with polydimethylsiloxane PDMS tape and transferred to the center of Si3N4 using a two-dimensional material dry transfer platform.

[0019] (3) One-time photolithography: The PdSe2 thin layer film is sequentially spin-coated with reverse adhesive, pre-baked, exposed to ultraviolet light, reverse baked, exposed to light, developed and fixed to obtain the pattern of the electrode system;

[0020] (4) Reactive-coupled plasma etching: The wafer after photolithography is placed in a reactive-coupled plasma device for etching, so that the Si3N4 layer is etched through, and the purpose is to transfer the trampoline structure pattern to the Si3N4 layer.

[0021] (5) Hydrofluoric acid wet etching: The wafer that has been etched by reaction-coupled plasma is wet etched in hydrofluoric acid solution. The purpose is to etch a certain depth down the SiO2 layer so that the trampoline structure is suspended and forms a mechanical oscillator.

[0022] (6) Cleaning the photoresist on the wafer surface: Remove the photoresist on the wafer surface with the patterned structure to finally obtain a room temperature infrared detection device based on a Si3N4 thin film mechanical oscillator.

[0023] The beneficial effects of this invention are as follows: Due to the strong absorption characteristics of PdSe2 for infrared light at room temperature and the high quality factor provided by the Si3N4 mechanical oscillator, this invention combines the advantages of both to propose a device that can be used to detect the mid-infrared band at room temperature, attempting to achieve a value higher than 10. 3 The peak response of nm and sensitivity of around 700 A / W bridge the gap between the low performance of uncooled infrared detectors and the limited application scenarios of cryogenically cooled infrared detectors due to their small portability. This invention combines the characteristics of PdSe2 with a micromechanical resonator, where the mechanical vibration part adopts a high-resonance-frequency trampoline-type thin-film structure, which can effectively combine ultra-high quality factor resonance modes with sensitive infrared detection. Attached Figure Description

[0024] Figure 1 This is a perspective view of the device of the present invention;

[0025] Figure 2 This is a schematic diagram of the PdSe2 structure of the present invention;

[0026] Figure 3 This is a cross-sectional view of the overall structure of the present invention; wherein (b) is a cross-sectional view of (a) along the black dashed line;

[0027] Figure 4 This is a schematic diagram of the detection principle of the present invention.

[0028] Figure 5 This is a dimensional schematic diagram of the trampoline structure of the present invention.

[0029] Figure 6 This is a flowchart of the fabrication method of the device of the present invention.

[0030] 1 is a trampoline structure; 2 is a PdSe2 rectangular thin film; 3 is a Si3N4 layer; 4 is a SiO2 layer; 5 is a Si substrate; 6 is a rectangular substrate; 11 is an arc-shaped quadrilateral; 12 is an arc-shaped strip. Detailed Implementation

[0031] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0032] Example

[0033] This embodiment provides a room temperature infrared detection device based on a Si3N4 thin film mechanical oscillator, including a rectangular substrate 6 and a trampoline structure 1 at the center of the rectangular substrate 6; the rectangular substrate 6 consists of a Si3N4 layer 3, a SiO2 layer 4, and a Si substrate 5 from top to bottom; the trampoline structure is formed at the center of the rectangular substrate 6 by etching, the trampoline structure includes a central arc-shaped quadrilateral 11 and arc-shaped strips 12 extending from the four corners, the trampoline structure is obtained by etching away four identical arcs from the four sides of the central square towards the center, the etching depth penetrates the entire Si3N4 layer 3 and SiO2 layer 4, and a PdSe2 rectangular thin film 2 is fixed at the center of the upper surface of the trampoline structure 1;

[0034] The trampoline structure is equivalent to a Si3N4 mechanical oscillator suspended above the rectangular substrate 6. When the Si3N4 mechanical oscillator is subjected to temperature changes, it will vibrate mechanically. The PdSe2 rectangular thin film 2 acts as an infrared radiation absorbing material to conduct heat and is used to drive and regulate the Si3N4 mechanical oscillator. The infrared detection device detects the resonant frequency and quality factor of the Si3N4 mechanical oscillator by controlling the light field at room temperature. It uses the frequency shift response of the Si3N4 mechanical oscillator under infrared radiation intensity to realize the detection of the corresponding infrared band.

[0035] The trampoline structure is suspended 250–300 nm above the rectangular substrate 6, i.e. Figure 3 h in the figure is 250–300 nm.

[0036] The thickness of Si3N4 layer 3 is 100nm.

[0037] At room temperature, the maximum energy of Si3N4 mechanical oscillators can reach 10 9 The quality factor.

[0038] The length d of the diagonal of the central square of the trampoline structure is the length of the trampoline structure, where d = 10 μm.

[0039] The width of the arc-shaped strip 12 is a = 2 μm.

[0040] This embodiment also provides a method for operating the room temperature infrared detection device based on the Si3N4 thin film mechanical oscillator, which is as follows:

[0041] At room temperature, when infrared light is incident on the PdSe2 rectangular thin film 2, due to the absorption characteristics of the PdSe2 rectangular thin film 2, the PdSe2 rectangular thin film 2 absorbs most of the infrared radiation and converts it into heat energy. The heat energy can only be transferred out through the Si3N4 mechanical oscillator below the PdSe2 rectangular thin film 2. The Si3N4 mechanical oscillator will undergo mechanical vibration under heating, and the heat energy will be dissipated in the form of vibration. This causes a change in the mechanical characteristics of the Si3N4 mechanical oscillator, which in turn causes a certain degree of shift in the resonant frequency of the oscillator, i.e., frequency shift. At this time, the incident infrared light can be regarded as the driving light that drives the mechanical oscillator to vibrate.

[0042] Another beam of light is then used to strike the Si3N4 mechanical oscillator in the trampoline structure as a probe light. When the probe light shines on the Si3N4 mechanical oscillator, part of it is reflected back, and the other part penetrates the Si3N4 layer and is reflected on the bottom substrate surface. The two reflected signals then produce an interference pattern. Finally, a photodetector is used to capture the reflected signal, thereby detecting the vibration mode of the Si3N4 mechanical oscillator. By establishing the relationship between the intensity of the incident infrared radiation and the frequency shift response, the sensing and detection of the incident infrared light can be achieved.

[0043] This embodiment also provides a method for fabricating the room temperature infrared detection device based on the Si3N4 thin film mechanical oscillator, which is as follows:

[0044] A Si3N4 mechanical oscillator with a trampoline structure was fabricated using a contact ultraviolet exposure, reaction-coupled plasma etching system, hydrofluoric acid etching, and electron beam evaporation coating system. A few layers of PdSe2 were obtained by mechanical peeling and then transferred and fixed to the center of the upper surface of the trampoline structure using a two-dimensional material dry transfer technique.

[0045] As a preferred embodiment, the preparation method includes the following steps:

[0046] (1) Pre-treatment: including wafer dicing, surface ultrasonic cleaning, and drying; corresponding to Figure 6 ① in the middle;

[0047] (2) Dry transfer of PdSe2: A few-layer PdSe2 film was peeled off using polydimethylsiloxane PDMS tape and transferred to the center of Si3N4 using a two-dimensional material dry transfer platform; corresponding to Figure 6 ② and ③ in the middle;

[0048] (3) Single-stage photolithography: The wafer with the transferred PdSe2 thin layer is sequentially subjected to spin-coating of reverse adhesive, pre-baking, UV exposure, reverse baking, overexposure, development, and fixing to obtain the pattern of the electrode system; corresponding to Figure 6 ④ and ⑤ in the middle;

[0049] (4) Reactive-coupled plasma etching: The wafer after photolithography is placed in a reactive-coupled plasma device for etching, which etches through the Si3N4 layer. The purpose is to transfer the trampoline structure pattern to the Si3N4 layer; corresponding to Figure 6 ⑥ in the middle;

[0050] (5) Hydrofluoric acid wet etching: The wafer, after reaction-coupled plasma etching, is wet-etched in a hydrofluoric acid solution. The purpose is to etch a certain depth into the SiO2 layer, causing the trampoline structure to levitate and form a mechanical oscillator; corresponding to Figure 6 ⑦ in the middle;

[0051] (6) Cleaning the photoresist on the wafer surface: The photoresist on the patterned wafer surface is removed, ultimately yielding a room-temperature infrared detector based on a Si3N4 thin-film mechanical oscillator. Corresponding to Figure 6 ⑧ in the middle.

[0052] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A room-temperature infrared detection device based on a Si3N4 thin-film mechanical oscillator, characterized in that: The rectangular substrate (6) includes a rectangular substrate (6) and a trampoline structure (1) at the center of the rectangular substrate (6). The rectangular substrate (6) consists of a Si3N4 layer (3), a SiO2 layer (4), and a Si substrate (5) from top to bottom. The center of the rectangular substrate (6) is formed by etching to create a trampoline structure. The trampoline structure includes a central arc-shaped quadrilateral (11) and arc-shaped strips (12) extending from the four corners. The trampoline structure is obtained by etching four identical arcs from the four sides of the central square towards the center. The etching depth penetrates the entire Si3N4 layer (3) and SiO2 layer (4). A PdSe2 rectangular thin film (2) is fixed at the center of the upper surface of the trampoline structure (1). The trampoline structure is equivalent to a Si3N4 mechanical oscillator suspended above a rectangular substrate (6). When the Si3N4 mechanical oscillator is subjected to temperature changes, it will vibrate mechanically. The PdSe2 rectangular thin film (2) acts as an infrared radiation absorbing material to conduct heat and is used to drive and regulate the Si3N4 mechanical oscillator. The infrared detection device detects the resonant frequency and quality factor of the Si3N4 mechanical oscillator by regulating the light field at room temperature. The detection of the corresponding infrared band is achieved by measuring the frequency shift response of the Si3N4 mechanical oscillator under the infrared radiation intensity.

2. The room temperature infrared detection device based on a Si3N4 thin-film mechanical oscillator according to claim 1, characterized in that: The trampoline structure is suspended 250-300 nm above the rectangular substrate (6).

3. The room temperature infrared detection device based on a Si3N4 thin-film mechanical oscillator according to claim 1, characterized in that: The thickness of the Si3N4 layer (3) is 100 nm.

4. The room temperature infrared detection device based on a Si3N4 thin-film mechanical oscillator according to claim 1, characterized in that: At room temperature, the maximum energy of Si3N4 mechanical oscillators can reach 10 9 The quality factor.

5. The room temperature infrared detection device based on a Si3N4 thin-film mechanical oscillator according to claim 1, characterized in that: The length d of the diagonal of the central square of the trampoline structure is the length of the trampoline structure, where d = 10 μm.

6. The room temperature infrared detection device based on a Si3N4 thin-film mechanical oscillator according to claim 1, characterized in that: The width of the arc-shaped strip (12) is a = 2 μm.

7. The operating method of the room temperature infrared detection device based on a Si3N4 thin-film mechanical oscillator according to any one of claims 1 to 6, characterized in that: At room temperature, when infrared light is incident on the PdSe2 rectangular film (2), due to the absorption characteristics of infrared light by the PdSe2 rectangular film (2), the PdSe2 rectangular film (2) absorbs most of the infrared radiation and converts it into heat energy. The heat energy can only be transferred out through the Si3N4 mechanical oscillator below the PdSe2 rectangular film (2). The Si3N4 mechanical oscillator will undergo mechanical vibration under the heat, and the heat energy will be dissipated in the form of vibration. This causes the mechanical characteristics of the Si3N4 mechanical oscillator to change, thereby causing the resonant frequency of the oscillator to shift to a certain extent, i.e., frequency shift. At this time, the incident infrared light can be regarded as the driving light that drives the mechanical oscillator to vibrate. Another beam of light is then used to strike the Si3N4 mechanical oscillator in the trampoline structure as a probe light. When the probe light shines on the Si3N4 mechanical oscillator, part of it is reflected back, and the other part penetrates the Si3N4 layer and is reflected on the bottom substrate surface. The two reflected signals then produce an interference pattern. Finally, a photodetector is used to capture the reflected signal, thereby detecting the vibration mode of the Si3N4 mechanical oscillator. By establishing the relationship between the intensity of the incident infrared radiation and the frequency shift response, the sensing and detection of the incident infrared light can be achieved.

8. The method for fabricating the room temperature infrared detection device based on a Si3N4 thin-film mechanical oscillator according to any one of claims 1 to 6, characterized in that: A Si3N4 mechanical oscillator with a trampoline structure was fabricated using a contact ultraviolet exposure, reaction-coupled plasma etching system, hydrofluoric acid etching, and electron beam evaporation coating system. A few layers of PdSe2 were obtained by mechanical peeling and then transferred and fixed to the center of the upper surface of the trampoline structure using a two-dimensional material dry transfer technique.

9. The method for fabricating a room-temperature infrared detection device based on a Si3N4 thin-film mechanical oscillator according to claim 8, characterized in that... Includes the following steps: (1) Pre-treatment: including wafer cutting, surface ultrasonic cleaning, and drying; (2) Dry transfer of PdSe2: The few-layer PdSe2 film was peeled off with polydimethylsiloxane PDMS tape and transferred to the center of Si3N4 using a two-dimensional material dry transfer platform. (3) One-time photolithography: The PdSe2 thin layer film is sequentially spin-coated with reverse adhesive, pre-baked, exposed to ultraviolet light, reverse baked, exposed to light, developed and fixed to obtain the pattern of the electrode system; (4) Reactive-coupled plasma etching: The wafer after photolithography is placed in a reactive-coupled plasma device for etching, so that the Si3N4 layer is etched through, and the purpose is to transfer the trampoline structure pattern to the Si3N4 layer. (5) Hydrofluoric acid wet etching: The wafer that has been etched by reaction-coupled plasma is wet etched in hydrofluoric acid solution. The purpose is to etch a certain depth down the SiO2 layer so that the trampoline structure is suspended and forms a mechanical oscillator. (6) Cleaning the photoresist on the wafer surface: Remove the photoresist on the wafer surface with the patterned structure to finally obtain a room temperature infrared detection device based on a Si3N4 thin film mechanical oscillator.

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