Displacement and mass sensing device and method based on CrPS4 thin film mechanical oscillator

Abstract

This invention discloses a displacement and mass sensing device and method based on a CrPS4 thin-film mechanical oscillator, comprising: a substrate, a CrPS4 thin film, the substrate including a Si substrate, a SiO2 layer, a Si3N4 layer, and a Ti and Au composite layer; a groove is provided in the middle of the Ti and Au composite layer, the Si3N4 layer, and the SiO2 layer, and an electrode composed of the Ti and Au composite layer is provided at the bottom of the groove; the middle part of the CrPS4 thin film is suspended above the groove; at a temperature of 4K, the CrPS4 thin-film mechanical oscillator has a wide dynamic range of up to 85-93dB and a quality factor of up to 3000-4500, and the displacement and mass sensitivities of the sensing device are 14-18 fm / Hz, respectively. 1 / 2 With a mass of 0.9–1.7 μg, equivalent to the mass of a proton or a hydrogen atom, this opens up possibilities for distinguishing different chemical elements in future inertial mass spectrometry measurements. The ultra-high mass sensitivity CrPS4 mechanical oscillator offers new opportunities for mass spectrometry, magnetometers, and adsorption experiments.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of mass sensing, nanoelectromechanical resonators and the like, and particularly relates to a method for performing ultra-high sensitivity displacement and mass sensing by using a novel two-dimensional material CrPS4 film mechanical vibrator. BACKGROUND

[0002] The emerging technology revolution is driving the miniaturization and diversification of devices. Integrating mechanical and electronic components at very small scales to perform specific functions has become an important technical field, which is widely used in people's daily life as sensors, actuators, microstructure electronic devices. Nanoelectromechanical systems (NEMS) based on semiconductor technology, due to its ultra-small size, material selection and ultra-strong flexibility of design, and inherent multi-physical field characteristics, makes such devices applied to many basic scientific researches. In NEMS, small displacement and mass change can be monitored by small resonance frequency shift, thereby realizing an ultra-high sensitivity displacement mass sensor. Resonant sensors with high sensitivity have been widely used in various fields of science and technology. At present, the sensitivity is higher, which is based on crystal, thin film and micro-sized cantilever beam NEMS. Among them, the effective mass, dynamic range and quality factor of the resonator are the core of the mass sensitivity. We designed the first CrPS4 film mechanical vibrator based on CrPS4 film, which works at a very high frequency band (up to 80 MHz), has excellent electrically tunable and dynamic range. Through deterministic measurement and calibration, we found that the CrPS4 film mechanical vibrator based on CrPS4 film has a very wide DR (up to 85-93 dB) and a higher quality factor (up to 3000-4500). Therefore, the CrPS4 film mechanical vibrator based on a new type of two-dimensional material can realize ultra-high sensitivity mass detection of 0.9-1.7 yg, which is equivalent to the mass of one proton (1.67 yg), and can reach a displacement sensitivity of 14-18 fm / Hz 1 / 2 , which is much higher than other two-dimensional material-based NEMS. The high mass and displacement resolution of the CrPS4 mechanical vibrator provides hope for various scientific and technological applications. SUMMARY

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

[0004] The displacement and mass sensing device based on CrPS4 thin film mechanical oscillator comprises a substrate and a CrPS4 thin film above the substrate, wherein the substrate comprises a Si substrate 5, a SiO2 layer 4 above the Si substrate 5, a Si3N4 layer 3 above the SiO2 layer 4, and a Ti and Au composite layer 2 above the Si3N4 layer 3; a recess is arranged in the middle of the Ti and Au composite layer 2, the Si3N4 layer 3 and the SiO2 layer 4, and an electrode 6 composed of the Ti and Au composite layer is arranged at the bottom of the recess; the CrPS4 thin film is fixed on the upper surface of the uppermost Ti and Au composite layer 2 at both sides and suspended above the recess in the middle.

[0005] As a preferred mode, the suspended CrPS4 thin film is regarded as a mechanical oscillator, and mechanical vibration occurs when the CrPS4 thin film mechanical oscillator is subjected to force or the mass loaded on the thin film changes; when laser irradiates the CrPS4 thin film, part of the laser is reflected back, and the other part penetrates the CrPS4 thin film and is reflected on the bottom substrate surface, and then the two parts of reflected signals generate interference patterns, and the interference signals change with the change of the depth of the vacuum gap between the CrPS4 thin film and the substrate; the change of the reflected light intensity generated thereby is detected by a photodetector, and a lock-in amplifier is used for recording; the laser detects the resonance frequency and the quality factor of the CrPS4 thin film mechanical oscillator by regulating the light field, and realizes the sensing of the displacement caused by the mass or force through the frequency shift response of the CrPS4 thin film mechanical oscillator; the principle of sensing is that the mechanical characteristics of the CrPS4 thin film mechanical oscillator change due to the force or the change of the mass loaded on the thin film, thereby causing the resonance frequency of the mechanical oscillator to shift to a certain extent, i.e. frequency shift, and through the establishment of the relationship between the small mass disturbance and the frequency shift response, the small displacement and mass sensing and detection are realized.

[0006] As a preferred mode, the small mass is 10 -24 grams.

[0007] As a preferred mode, the laser source is a He-Ne laser with a wavelength of 633 nm.

[0008] As a preferred mode, the sensing device works at a bottom temperature of 4k-100k.

[0009] As a preferred mode, at a temperature of 4k, the displacement and mass sensitivity of the sensing device are 14-18 fm / Hz 1 / 2 and 0.9-1.7 yg respectively, and the CrPS4 thin film mechanical oscillator has a wide dynamic range of up to 85-93 dB and a quality factor of up to 3000-4500.

[0010] As a preferred mode, in the Ti and Au composite layer, the thickness of Ti is 5 nm and the thickness of Au is 20 nm.

[0011] As a preferred mode, the thickness of the CrPS4 film is 20-50 nm, and the suspension height between the CrPS4 film and the bottom substrate is 250-300 nm.

[0012] The application also provides a preparation method of the displacement and mass sensing device based on the CrPS4 film mechanical resonator.

[0013] The substrate structure is prepared by using a semiconductor patterning process, an etching method and an electron beam evaporation coating method; the CrPS4 is obtained by mechanical peeling and transferred to the substrate structure by using a two-dimensional material dry transfer technology, so as to form the CrPS4 film mechanical resonator.

[0014] As a preferred mode, the preparation method comprises the following steps:

[0015] (1) Pretreatment: including cutting of a silicon wafer, surface cleaning and drying;

[0016] (2) First photoetching: the silicon wafer is subjected to a gluing operation, and an adhesion aid and a reverse glue are sequentially spin-coated, and then is placed on a sample table of a photoetching machine to perform exposure, development and fixation treatment to obtain a gate pattern;

[0017] (3) Inductive coupling plasma etching: the wafer after the first photoetching is placed in a reaction coupling plasma device to perform etching, so as to obtain a groove with a depth of about 80 nm;

[0018] (4) Hydrofluoric acid wet etching: the wafer after the inductive coupling plasma etching is subjected to wet etching in a hydrofluoric acid solution with a certain concentration, so as to etch downward to a certain depth on the SiO2 layer, so that the CrPS4 film structure is suspended to form a mechanical resonator;

[0019] (5) Cleaning of photoresist on the wafer surface: the photoresist on the wafer surface with a pattern structure is removed, and the wafer is soaked in a photoresist removing solution acetone, ultrasonic cleaning, nitrogen blowing dry, and the remaining moisture on the wafer surface is baked on a heating table; after the above process, the gate pattern and under-cut structure etched on the wafer surface are observed under an optical microscope and a scanning electron microscope;

[0020] (6) Second photoetching: a layer of photoresist is re-coated on the wafer surface after the photoresist removing, the wafer after the coating is placed on the sample table of the photoetching machine to perform alignment, exposure, reverse baking, general exposure, development, fixation, nitrogen blowing dry and finally baking to achieve the purpose of hardening the film;

[0021] (7) Electron beam evaporation coating: after the second photoetching, the wafer is fixed on a sample table of an electron beam evaporation coating machine, a layer of 5 nm titanium is first coated, and then a layer of 20 nm gold is coated to serve as an electrode;

[0022] (8) De-glue: After the end of plating, the sample is taken out, and is sequentially cleaned in acetone solution, alcohol and deionized water by ultrasonic cleaning, and finally is dried by nitrogen blowing, and the surface is dried by heating, and thus the substrate of the CrPS4 thin film mechanical vibrator is prepared;

[0023] (9) CrPS4 thin film dry transfer: a few layers of CrPS4 thin film are torn by using a polydimethylsiloxane (PDMS) tape, and the CrPS4 thin film is transferred to the substrate structure by using a two-dimensional material dry transfer platform, and thus the sample of the CrPS4 thin film mechanical vibrator is prepared.

[0024] The CrPS4 thin film mechanical vibrator has a wide dynamic range of up to 85-93 dB and a quality factor of up to 3000-4500. The CrPS4 mechanical vibrator with ultra-high mass sensitivity provides new opportunities for mass spectrometry, magnetometers and adsorption experiments, and opens up the possibility of distinguishing different chemical elements in future inertial mass spectrometry. 1 / 2 BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a perspective view of the device of the present application;

[0026] Figure 2 is a detection principle diagram of the present application.

[0027] Figure 3 is a preparation method flowchart of the device of the present application.

[0028] 1 is a CrPS4 thin film; 2 is a Ti and Au composite layer; 3 is a Si3N4 layer; 4 is a SiO2 layer; 5 is a Si substrate; and 6 is an electrode. DETAILED DESCRIPTION

[0029] The embodiments of the present application will be described in detail below with specific reference to the drawings. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the present specification. The present application can also be implemented or applied by using different specific embodiments, and the details in the present specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present application.

[0030] ​The embodiment provides a displacement and mass sensing device based on a CrPS4 thin film mechanical oscillator, comprising a substrate and a CrPS4 thin film above the substrate, wherein the substrate comprises a Si substrate 5, a SiO2 layer 4 above the Si substrate 5, a Si3N4 layer 3 above the SiO2 layer 4, and a Ti and Au composite layer 2 above the Si3N4 layer 3; a recess is arranged in the middle of the Ti and Au composite layer 2, the Si3N4 layer 3 and the SiO2 layer 4, and an electrode 6 composed of the Ti and Au composite layer is arranged at the bottom of the recess; and the CrPS4 thin film is fixed to the upper surface of the uppermost Ti and Au composite layer 2 at both sides and suspended above the recess in the middle.

[0031] In some embodiments, the suspended CrPS4 thin film is regarded as a mechanical oscillator, and mechanical vibration occurs when the CrPS4 thin film mechanical oscillator is subjected to force or the mass loaded on the thin film changes; when laser irradiates the CrPS4 thin film, part of the laser is reflected back, and the other part penetrates the CrPS4 thin film and is reflected on the bottom substrate surface, and then the two parts of reflected signals generate interference patterns, and the interference signals change with the change of the depth of the vacuum gap between the CrPS4 thin film and the substrate; the change of the reflected light intensity generated thereby is detected by a photodetector, and a lock-in amplifier is used for recording; the laser detects the resonance frequency and the quality factor of the CrPS4 thin film mechanical oscillator by regulating the light field, and realizes the sensing of the displacement caused by the mass or force through the frequency shift response of the CrPS4 thin film mechanical oscillator; the principle of sensing is that the mechanical characteristics of the CrPS4 thin film mechanical oscillator change due to the force or the change of the mass loaded on the thin film, thereby causing the resonance frequency of the mechanical oscillator to shift to a certain extent, i.e. frequency shift, and through the establishment of the relationship between the small mass disturbance and the frequency shift response, the small displacement and mass sensing and detection are realized.

[0032] In some embodiments, the small mass is 10 -24 grams (1yg).

[0033] In some embodiments, the laser source is a 633nm He-Ne laser.

[0034] In some embodiments, the sensing device works at a bottom temperature of 4k-100k.

[0035] In some embodiments, at a temperature of 4k, the displacement and mass sensitivity of the sensing device are 14-18fm / Hz 1 / 2 and 0.9-1.7yg, respectively, and the CrPS4 thin film mechanical oscillator has a wide dynamic range of up to 85-93dB and a quality factor of up to 3000-4500.

[0036] In some embodiments, in the Ti and Au composite layer, the thickness of Ti is 5nm, and the thickness of Au is 20nm.

[0037] In some embodiments, the thickness of the CrPS4 film is 20-50 nm, and the suspension height between the CrPS4 film and the bottom substrate is 250-300 nm.

[0038] The embodiment also provides a method for fabricating the displacement and mass sensing device based on the CrPS4 thin film mechanical oscillator, wherein a substrate structure is fabricated using semiconductor patterning process, etching method and electron beam evaporation deposition method; CrPS4 is obtained by mechanical peeling and transferred to the substrate structure using two-dimensional material dry transfer technology to form the CrPS4 thin film mechanical oscillator.

[0039] Specifically, in some embodiments, the preparation method includes the following steps:

[0040] (1) Pre-treatment: including silicon wafer cutting, surface cleaning, and drying; corresponding to Figure 3 ① in the middle;

[0041] (2) Single-stage photolithography: The silicon wafer is coated with adhesive, followed by spin-coating of a bonding agent and a reversal adhesive. It is then placed on the sample stage of the photolithography machine for exposure, development, and fixing to obtain the gate pattern; corresponding to... Figure 3 ② in the middle;

[0042] (3) Inductively Coupled Plasma Etching: The wafer after photolithography is placed in a reactive plasma etching apparatus for etching to obtain a groove with a depth of approximately 80 nm; corresponding to Figure 3 ③ in the middle;

[0043] (4) Hydrofluoric acid wet etching: The wafer etched by inductively coupled plasma is wet-etched in a hydrofluoric acid solution of a certain concentration. The purpose is to etch a certain depth into the SiO2 layer, so that the CrPS4 thin film structure is suspended and forms a mechanical oscillator; corresponding to Figure 3 ④ in the middle;

[0044] (5) Cleaning the photoresist on the wafer surface: Remove the photoresist on the wafer surface with the patterned structure, soak it in acetone stripper, ultrasonically clean it, blow it dry with nitrogen, and bake the remaining moisture on the silicon wafer surface on a heating stage; after the above process, observe the gate pattern etched on the silicon wafer surface and the drilled under-cut structure under an optical microscope and a scanning electron microscope.

[0045] (6) Second photolithography: A new layer of photoresist is applied to the surface of the silicon wafer after the photoresist has been removed. The coated silicon wafer is then placed on the sample stage of the photolithography machine for alignment, exposure, reverse baking, general exposure, development, fixing, nitrogen drying, and finally baking to achieve the purpose of hardening the film; corresponding to Figure 3 ⑤ in the middle;

[0046] (7) Electron beam evaporation film coating: after completing the secondary photoetching, the silicon wafer is fixed to the sample table of the electron beam evaporation film coating machine, a layer of 5 nm titanium is coated first, and then 20 nm gold is coated, which is used as an electrode; corresponding to Figure 3 (6) in the

[0047] (8) Debinding: after the film coating is completed, the sample is taken out, and ultrasonic cleaning is sequentially performed in the acetone solution, alcohol and deionized water, and finally nitrogen blowing drying is performed, and the surface excess moisture is dried by heating, and thus the substrate preparation of the CrPS4 thin film mechanical vibrator is completed;

[0048] (9) CrPS4 thin film dry transfer: a few layers of CrPS4 thin film are torn by using a polydimethylsiloxane (PDMS) tape, the CrPS4 thin film is transferred to the substrate structure by using a two-dimensional material dry transfer platform, and thus the CrPS4 thin film mechanical vibrator sample is prepared; corresponding to Figure 3 (7) in the

[0049] The above examples only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A displacement and mass sensing device based on a CrPS4 thin film mechanical resonator, characterized in that, The substrate includes a Si substrate (5), a SiO2 layer (4) above the Si substrate (5), a Si3N4 layer (3) above the SiO2 layer (4), and a Ti and Au composite layer (2) above the Si3N4 layer (3); a recess is arranged in the middle of the Ti and Au composite layer (2), the Si3N4 layer (3), and the SiO2 layer (4), and an electrode (6) composed of the Ti and Au composite layer is arranged at the bottom of the recess; the CrPS4 thin film is fixed to the upper surface of the uppermost Ti and Au composite layer (2) on both sides and suspended above the recess in the middle. The suspended CrPS4 thin film is regarded as a mechanical vibrator, and mechanical vibration occurs when the mechanical vibrator is forced or the mass loaded on the thin film changes; when laser irradiates the CrPS4 thin film, part of the laser is reflected back, and the other part penetrates the CrPS4 thin film and is reflected on the bottom substrate surface, and then the two parts of reflected signals generate interference patterns, and the interference signals change with the change of the depth of the vacuum gap between the CrPS4 thin film and the substrate; the change of the reflected light intensity generated thereby is detected by a photodetector, and a lock-in amplifier is used for recording; the laser detects the resonance frequency and quality factor of the CrPS4 thin film mechanical vibrator by regulating the light field, and realizes the sensing of the displacement caused by the mass or force through the frequency shift response of the CrPS4 thin film mechanical vibrator; the principle of sensing is that the mechanical characteristics of the CrPS4 thin film mechanical vibrator change due to the force or the change of the mass loaded on the thin film, thereby causing the resonance frequency of the mechanical vibrator to shift to a certain extent, i.e. frequency shift, and by establishing the relationship between the small mass disturbance and the frequency shift response, the small displacement and mass sensing and detection are realized.

2. The displacement and mass sensing device based on CrPS4 thin film mechanical resonator of claim 1, wherein: The micro-amount is 10 -24 grams.

3. The displacement and mass sensing device based on CrPS4 thin film mechanical resonator of claim 1, wherein: The laser source is a 633 nm He-Ne laser.

4. The displacement and mass sensing device based on CrPS4 thin film mechanical resonator of claim 1, wherein: The sensing device works at a low temperature of 4k-100k.

5. The displacement and mass sensing device based on CrPS4 thin film mechanical resonator of claim 1, wherein: The displacement and mass sensitivities of the sensing device are 14-18 fm / Hz and 0.9-1.7 yg, respectively, at a temperature of 4K 1 / 2 The CrPS4 thin film mechanical resonator has a wide dynamic range of up to 85-93 dB and a quality factor of up to 3000-4500.

6. The displacement and mass sensing device based on CrPS4 thin film mechanical resonator of claim 1, wherein: In the Ti and Au composite layer, the thickness of Ti is 5 nm, and the thickness of Au is 20 nm.

7. The displacement and mass sensing device based on CrPS4 thin film mechanical resonator of claim 1, wherein: The thickness of the CrPS4 thin film is 20-50 nm, and the suspended height between the CrPS4 thin film and the bottom substrate is 250-300 nm.

8. A preparation method of the displacement and mass sensing device based on the CrPS4 thin film mechanical vibrator according to any one of claims 1 to 7, characterized in that: The substrate structure is prepared by using a semiconductor patterning process, an etching method, and an electron beam evaporation coating method; the CrPS4 is obtained by mechanical peeling and transferred to the substrate structure by using a two-dimensional material dry transfer technology to form a CrPS4 thin film mechanical vibrator; Specifically, the method comprises the following steps: (1) Pretreatment: including cutting, surface cleaning, and drying of the silicon wafer; (2) First photoetching: the silicon wafer is subjected to a gluing operation, and then spin-coated with an adhesion agent and a reverse adhesive in sequence, and then placed on a sample stage of a photoetching machine for exposure, development, and fixation to obtain a gate pattern; (3) Inductively coupled plasma etching: the wafer after the first photoetching is placed in a reaction coupled plasma device for etching to obtain a recess with a depth of about 80 nm; (4) Hydrofluoric acid wet etching: the wafer etched by inductively coupled plasma etching is placed in a solution of hydrofluoric acid with a certain concentration for wet etching. The purpose is to etch the SiO2 layer downward to a certain depth, so that the CrPS4 thin film structure is suspended, forming a mechanical vibrator; (5) Cleaning the photoresist on the wafer surface: remove the photoresist on the wafer surface with a pattern structure, soak in a degreasing solution of acetone, ultrasonic cleaning, nitrogen blowing dry, and bake the wafer surface to dry the remaining moisture on the heating table. After the above process, the gate pattern etched on the wafer surface and the under-cut structure are observed under an optical microscope and a scanning electron microscope; (6) Second lithography: re-coat a layer of photoresist on the wafer surface after degreasing, place the wafer with coated photoresist on the sample stage of the lithography machine, align, expose, reverse bake, flood exposure, develop, fix, dry with nitrogen, and finally bake to achieve the purpose of hardening the film; (7) Electron beam evaporation coating: after completing the second lithography, fix the wafer to the sample stage of the electron beam evaporation coating machine, first coat a layer of 5 nm titanium, then coat 20 nm gold, which serves as the electrode; (8) Degreasing: after coating is completed, remove the sample, soak in acetone solution, alcohol, and deionized water for ultrasonic cleaning, and finally dry with nitrogen, heat to dry the excess moisture on the surface. At this point, the substrate preparation of the CrPS4 thin film mechanical vibrator is completed; (9) CrPS4 thin film dry transfer: tear off a few layers of CrPS4 thin film with polydimethylsiloxane (PDMS) tape, and transfer the CrPS4 thin film to the substrate structure using a two-dimensional material dry transfer platform. Thus, the CrPS4 thin film mechanical vibrator sample is prepared.

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