Liquid phase sensor based on longitudinal surface acoustic wave as well as preparation method and application of liquid phase sensor

Abstract

The invention belongs to the technical field of sensors, and particularly relates to a liquid phase sensor based on longitudinal surface acoustic waves and a preparation method and application thereof. The liquid phase sensor based on the longitudinal surface acoustic wave comprises a delay line type surface acoustic wave device and a sensitive element, the delay line type surface acoustic wave device comprises a substrate, a temperature compensation layer and a piezoelectric layer which are arranged in a stacked mode, an interdigital transducer is arranged on the surface of the piezoelectric layer, and the piezoelectric layer is made of tangential lithium niobate or lithium tantalate single crystals. A high-speed longitudinal surface acoustic wave (LSAW) mode without body wave leakage is excited by adopting a heterogeneous acoustic layer structure of an interdigital electrode / a piezoelectric thin layer / a temperature compensation layer / a high-sound-velocity substrate, and a delay line type low-loss and high-sensitivity sensor for a liquid phase is constructed by utilizing the LSAW. Compared with a traditional rayleigh and love mode SAW sensor, the LSAW-based sensor has the advantages that the attenuation coefficient is greatly reduced, the sensitivity is greatly improved, and the LSAW-based sensor has a good application prospect in a liquid phase environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular relates to a liquid phase sensor based on longitudinal acoustic surface waves and a preparation method and application thereof. Background Art

[0002] A surface acoustic wave device is a device that transmits and processes signals by converting surface acoustic waves into electrical signals. It is mainly composed of two parts: a piezoelectric substrate and an interdigital transducer (IDT). Surface acoustic waves mainly propagate on the shallow surface of the piezoelectric substrate. By utilizing its piezoelectric properties, the surface acoustic wave device can realize the conversion between the electrical and acoustic states of the transmission signal.

[0003] Liquid-phase surface acoustic wave sensors usually use liquid as their main working environment. Their functions include not only the detection of biological or chemical components in liquids, but also the detection of liquid level, flow rate, liquid temperature and viscosity, etc. When surface acoustic wave devices are used in liquid-phase sensing, the dielectric and mass load characteristics of the liquid will change the boundary conditions for surface acoustic wave propagation; at the same time, the components to be measured in the liquid environment can also combine with the sensitive film in the sensitive area of ​​the device, affecting the changes in the density, elastic modulus, and conductivity of the sensitive film, changing the propagation of surface acoustic waves on the piezoelectric substrate, and affecting the center frequency. Therefore, surface acoustic wave devices can be used to sense liquid parameters.

[0004] At present, the commonly used acoustic transmission modes of surface acoustic wave devices are mainly Rayleigh wave type and Love wave type. Rayleigh wave has two polarization directions during propagation, one parallel to the propagation direction of the wave and the other perpendicular to the substrate surface. The components of the two directions can be combined into an elliptical trajectory during propagation. The component perpendicular to the substrate surface makes Rayleigh wave have a large attenuation in the liquid environment, so Rayleigh wave is mostly used in gas phase detection. During the propagation of Love wave, its surface particles only have shear displacement parallel to the substrate surface, which makes the Love wave device have less signal attenuation in the liquid and can be used in liquid phase sensors. However, the piezoelectric single crystal substrate materials used in traditional acoustic devices are lithium tantalate and lithium niobate. The sound speed of its Love wave mode is close to that of Rayleigh wave (about 3300m / s and 3900m / s respectively), making it difficult to achieve high frequency, which makes the sensitivity of sensor devices based on Love wave low. Surface acoustic wave liquid phase sensors based on Rayleigh wave and Love wave still have problems of large loss and low sensitivity, and their application in liquid phase detection is limited. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a liquid phase sensor based on longitudinal surface acoustic wave and its preparation method and application. The liquid phase sensor of the present invention is based on the longitudinal surface acoustic wave with low loss and high sensitivity.

[0006] The present invention provides a liquid phase sensor based on longitudinal surface acoustic wave, comprising a delay line type surface acoustic wave device, and a sensitive element arranged in the delay region of the delay line type surface acoustic wave device;

[0007] The delay line type surface acoustic wave device includes a stacked substrate, a temperature compensation layer and a piezoelectric layer, an interdigital transducer is arranged on the surface of the piezoelectric layer, the material of the piezoelectric layer is lithium niobate single crystal or lithium tantalate single crystal, the lithium niobate single crystal is a y-cut x-lithium niobate single crystal, the rotation angle is φ, the propagation angle is ψ, 15°≤φ≤50°, 30°≤ψ≤70°.

[0008] Preferably, φ=37°, ψ=47°.

[0009] Preferably, the substrate is made of silicon carbide or diamond.

[0010] Preferably, the temperature compensation layer is made of silicon dioxide.

[0011] Preferably, the thickness of the temperature compensation layer is 0.2λ-4λ.

[0012] Preferably, the thickness of the piezoelectric layer is 0.2λ to 0.42λ.

[0013] Preferably, the IDT is a metal electrode, and the metal electrode includes an aluminum electrode.

[0014] Preferably, the thickness of the metal electrode is 0.06λ to 0.08λ, and the metallization rate is 0.48 to 0.56.

[0015] The present invention also provides a method for preparing a liquid phase sensor based on longitudinal surface acoustic waves according to the above technical solution, comprising the following steps:

[0016] Plasma enhanced chemical vapor deposition is performed on one surface of the substrate to obtain a temperature compensation layer;

[0017] Bonding the piezoelectric layer to the temperature compensation layer, depositing an interdigital transducer on the surface of the piezoelectric layer, and obtaining a delay line type surface acoustic wave device;

[0018] A sensitive element is arranged in the delay region of a delay line type surface acoustic wave device to obtain a liquid phase sensor based on longitudinal surface acoustic waves.

[0019] The present invention also provides the application of the liquid phase sensor based on longitudinal surface acoustic waves described in the above technical solution or the liquid phase sensor based on longitudinal surface acoustic waves obtained by the above preparation method in liquid phase detection.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a liquid phase sensor based on longitudinal surface acoustic waves, comprising a delay line surface acoustic wave device and a sensitive element arranged in a delay zone of the delay line surface acoustic wave device; the delay line surface acoustic wave device comprises a stacked substrate, a temperature compensation layer and a piezoelectric layer, an interdigital transducer is arranged on the surface of the piezoelectric layer, the material of the piezoelectric layer is lithium niobate single crystal or lithium tantalate single crystal, the lithium niobate single crystal is a y-cut x-lithium niobate single crystal, the rotary cutting angle is φ, the propagation angle is ψ, 15°≤φ≤50°, 30°≤ψ≤70°.

[0022] In view of the problem that the current surface acoustic wave sensor has large propagation loss and low sensitivity when used in liquid, the present invention provides a longitudinal surface acoustic wave (LSAW) sensor suitable for liquid phase, by optimizing the tangent direction of the piezoelectric thin layer, exciting the LSAW in the piezoelectric medium, and utilizing its high sound velocity, large electromechanical coupling coefficient and no energy leakage, y-cut x lithium niobate single crystal, 15°≤rotation angle φ≤50°, 30°≤propagation angle ψ≤70°, the corresponding Euler angle is (0°, -75°~-40°, 30°~70°), within this Euler angle range, the electromechanical coupling coefficient can reach 12%~15%, thereby solving the problem that the existing surface acoustic wave sensor is limited in application in liquid phase detection.

[0023] The particles of LSAW vibrate longitudinally. During the propagation along the substrate surface, the vibration energy of the medium particles is mainly concentrated in the propagation direction of the surface acoustic wave, and there is almost no vibration component in the normal direction of the substrate surface, so that it radiates almost no energy to the liquid during the propagation process. At the same time, the phase velocity of LSAW is higher than that of traditional Rayleigh waves and Love waves. Under a specific substrate tangent, its phase velocity is closer to the longitudinal body wave. The operating frequency of the surface acoustic wave sensor using this acoustic wave mode is easier to reach a higher operating frequency than the sensor using conventional surface acoustic waves, so the sensitivity is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 Schematic diagram of the structure of the LSAW acoustic device in an embodiment of the present invention;

[0026] Figure 2 is a schematic structural diagram of a delayed linear LSAW acoustic sensor (including a microfluidic liquid pool) in an embodiment of the present invention;

[0027] Figure 3 is the electromechanical coupling coefficient (K 2 ) and the two-dimensional relationship diagram of the Euler angle (0°, θ°, ψ°);

[0028] Figure 4 It is a two-dimensional relationship diagram between phase velocity (Vp) and Euler angle (0°, θ°, ψ°);

[0029] Figure 5 is the electrode thickness, LiNbO 3 Two-dimensional relationship between film thickness and LSAW electromechanical coupling coefficient characteristics (a) and two-dimensional relationship between film thickness and LSAW phase velocity characteristics (b);

[0030] Figure 6 The two-dimensional relationship between the metallization rate η, the aluminum electrode film thickness and the LSAW electromechanical coupling coefficient characteristics (a) and the two-dimensional relationship with the LSAW phase velocity characteristics (b);

[0031] Description of reference numerals:

[0032] 1-substrate; 2-temperature compensation layer; 3-piezoelectric thin layer; 4-interdigital transducer. DETAILED DESCRIPTION

[0033] The present invention provides a liquid phase sensor based on longitudinal surface acoustic wave, comprising a delay line type surface acoustic wave device, and a sensitive element arranged in the delay region of the delay line type surface acoustic wave device;

[0034] The delay line type surface acoustic wave device comprises a stacked substrate, a temperature compensation layer and a piezoelectric layer, an interdigital transducer is arranged on the surface of the piezoelectric layer, the material of the piezoelectric layer is lithium niobate single crystal or lithium tantalate single crystal, the lithium niobate single crystal is a y-cut x-cut lithium niobate single crystal, and the spin cutting angle is The propagation angle is ψ, 30°≤ψ≤70°.

[0035] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0036] In the present invention, λ is the wavelength of the wave generated by the IDT.

[0037] The liquid phase sensor of the present invention works using the (longitudinal surface acoustic wave) LSAW mode. This surface acoustic wave mode can be achieved by bonding a single crystal thin layer of lithium niobate or lithium tantalate with a film thickness less than one SAW wavelength to a high acoustic velocity substrate deposited with a temperature compensation layer to obtain a "forked electrode / piezoelectric thin layer / temperature compensation layer / high acoustic velocity substrate" heterogeneous acoustic layer structure.

[0038] In the present invention, the material of the substrate is preferably silicon carbide or diamond, which are high-sound-velocity materials. The high-sound-velocity substrate guides the sound waves to propagate in the low-sound-velocity layer, reducing the loss of sound energy. The present invention has no special requirements for the thickness of the substrate.

[0039] In the present invention, the material of the temperature compensation layer is preferably silicon dioxide, and the temperature compensation layer is a material with a positive temperature coefficient. Adding a silicon dioxide temperature compensation layer with a positive temperature coefficient on a silicon carbide single crystal substrate or a diamond substrate can reduce the frequency temperature coefficient of the acoustic device, thereby achieving higher temperature stability and preventing the acoustic device from being affected by temperature changes in the sensing environment.

[0040] In the present invention, the thickness of the temperature compensation layer is preferably 0.2λ to 4λ, and specifically may be 0.2λ, 0.5λ or 4λ.

[0041] In the present invention, the material of the piezoelectric layer is preferably lithium niobate single crystal, and the electromechanical coupling coefficient is not less than 12.47%. Preferably, φ=37°, ψ=47°, that is, the lithium niobate single crystal is cut 37° and rotated in the Y direction, and propagated 47° in the X direction, and the corresponding Euler angle is (0°, -53°, 47°), and the electromechanical coupling coefficient reaches a maximum of 14.98%.

[0042] In the present invention, the thickness of the piezoelectric layer is preferably 0.2λ to 0.42λ, the sound velocity of the excited LSAW is 5943m / s to 6258m / s, and the thickness of the piezoelectric layer can specifically be 0.2λ, 0.28λ, 0.3λ, 0.34λ or 0.42λ.

[0043] In the present invention, the interdigital transducer (IDT) is preferably a metal electrode, the metal electrode preferably includes an aluminum electrode, the thickness of the metal electrode is preferably 0.06λ to 0.08λ, more preferably 0.064λ to 0.066λ, specifically 0.065λ; the metallization rate is preferably 0.48 to 0.56, specifically 0.5, the thickness and metallization rate of the metal electrode of the present invention have a large electromechanical coupling coefficient. The period of the IDT is 4μm.

[0044] In the present invention, the delay area of ​​the delay line type surface acoustic wave device is a sensitive area. The delay line type surface acoustic wave device is preferably composed of two interdigital transducers and a piezoelectric substrate, the input end interdigital transducer converts the electrical signal into an acoustic signal, the acoustic signal is transmitted to the output end interdigital transducer through the delay area, and the output end interdigital transducer converts the acoustic signal into an electrical signal.

[0045] In the present invention, the sensitive element is arranged in the delay region of the delay line type surface acoustic wave device. The sensitive element is used to sense liquid parameters, and the sensitive element is preferably a sensitive film.

[0046] In the present invention, the liquid phase sensor preferably also includes a microfluidic liquid pool, the material of the microfluidic liquid pool is preferably polydimethylsiloxane (PDMS), and the drip channel of the microfluidic liquid pool preferably adopts a confocal fluid design. A peristaltic pump is connected at the drip channel interface to control and adjust the flow rate and flow rate ratio, and control the size of droplets generated inside the flow channel.

[0047] In the present invention, two cavities are provided on both sides of the microfluidic liquid pool so that the interdigital transducer is not in close contact with the PDMS. PDMS has a strong absorption effect on sound waves. The present invention reserves cavities to avoid the problem that the PDMS is in too close contact with the interdigital transducer of the delay line device, which will cause some sound waves to leak and increase signal loss.

[0048] The present invention also provides a method for preparing a liquid phase sensor based on longitudinal surface acoustic waves according to the above technical solution, comprising the following steps:

[0049] Plasma enhanced chemical vapor deposition is performed on one surface of the substrate to obtain a temperature compensation layer;

[0050] Bonding the piezoelectric layer to the temperature compensation layer, depositing an interdigital transducer on the surface of the piezoelectric layer, and obtaining a delay line type surface acoustic wave device;

[0051] A sensitive element is arranged in the delay region of a delay line type surface acoustic wave device to obtain a liquid phase sensor based on longitudinal surface acoustic waves.

[0052] The present invention has no special requirements for the conditions of the plasma enhanced chemical vapor deposition (PECVD) and the bonding process, and the common conditions used by those skilled in the art can be used.

[0053] In the present invention, before depositing the interdigital transducer on the surface of the piezoelectric layer, the method further includes: photolithography micromachining to obtain a photolithography pattern; and the deposition is performed by metal evaporation.

[0054] The present invention also provides the application of the liquid phase sensor based on longitudinal surface acoustic waves described in the above technical solution or the liquid phase sensor based on longitudinal surface acoustic waves obtained by the above preparation method in liquid phase detection.

[0055] In the present invention, the liquid phase detection preferably includes liquid level detection, flow rate detection, liquid temperature detection, viscosity measurement or component detection.

[0056] In order to further illustrate the present invention, the liquid phase sensor based on longitudinal surface acoustic waves and its preparation method and application provided by the present invention are described in detail below in combination with the accompanying drawings and embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] Surface acoustic wave devices based on longitudinal surface acoustic wave (LSAW), such as Figure 1 As shown, it includes a substrate 1, a temperature compensation layer 2, a piezoelectric thin layer 3 and an interdigital transducer (IDT) 4 arranged on the surface of the piezoelectric thin layer, which are stacked in sequence, wherein the substrate 1 adopts a silicon carbide single crystal substrate, and the piezoelectric thin layer 3 adopts a lithium niobate single crystal piezoelectric thin layer.

[0059] The lithium niobate single crystal piezoelectric thin layer is tangentially rotated 37° in the Y direction and propagates in the Z direction, with a thickness of 0.42λ, a thickness of 0.065λ for the interdigital electrode, and a metallization ratio of 0.5. The temperature compensation layer uses silicon dioxide with a thickness of 0.2λ.

[0060] The slow shear body wave sound velocity of the silicon carbide single crystal substrate is about 7200m / s, and the LSAW sound velocity in the lithium niobate single crystal piezoelectric thin layer is as high as 6300m / s. The lithium niobate single crystal piezoelectric thin layer is bonded to the temperature compensation layer. By adjusting the cut angle and film thickness of the lithium niobate single crystal piezoelectric thin layer, the sound velocities of the longitudinal leakage wave short-circuit gate and the open-circuit gate are made smaller than the slow shear body wave sound velocity in the substrate. The sound wave can be guided to propagate in the low sound velocity area (piezoelectric surface area), reducing the sound energy loss and improving the performance of the sensor.

[0061] Fabrication of delay line SAW devices, such as Figure 2 As shown, first, a temperature compensation layer is deposited on one side of the substrate by PECVD; then, the piezoelectric thin layer is combined with the temperature compensation layer by a bonding process; and through photolithography micromachining, interdigital electrodes are deposited on the photolithography pattern by metal evaporation.

[0062] Polydimethylsiloxane (PDMS) is used to make microfluidic cells suitable for sensing tests, such as Figure 2 As shown, the droplet channel adopts a confocal fluid design, including a bifurcation, and a peristaltic pump is connected at the channel interface to control and adjust the flow rate and flow rate ratio to control the size of droplets generated inside the flow channel.

[0063] Delay line surface acoustic wave devices can sense liquid parameters through changes in LSAW propagation boundary conditions caused by the dielectric, mass load and other characteristics of the liquid. The delay zone of the device serves as a sensitive area, combined with a sensitive film for combining with the substance to be tested, and can sense changes in the biological or chemical composition of the liquid.

[0064] The present invention provides a surface acoustic wave liquid phase sensor, comprising a high sound velocity substrate (silicon carbide or diamond), a temperature compensation layer, a piezoelectric thin layer on the substrate, and an interdigital electrode. The substrate adopts a silicon carbide single crystal substrate or a diamond substrate with a high sound velocity, and the piezoelectric thin layer adopts a cut lithium niobate single crystal or a lithium tantalate single crystal piezoelectric thin layer. By combining the lithium niobate or lithium carbonate single crystal piezoelectric thin layer with the temperature compensation layer by a bonding process, a "interdigital electrode / piezoelectric thin layer / temperature compensation layer / high sound velocity substrate" heterogeneous acoustic layer structure is obtained, which guides the propagation of sound waves in the piezoelectric surface area, stimulates LSAW without body wave leakage, and thus reduces the sound energy loss.

[0065] In the above structure, the condition for stimulating leakage-free LSAW is to make the acoustic velocity of the longitudinal leakage surface wave stimulated inside the lithium niobate or lithium tantalate in a specific tangential direction lower than the slow shear acoustic velocity of the high acoustic velocity substrate silicon carbide (or diamond), and the thickness of the piezoelectric layer at this time is the cut-off film thickness. When the piezoelectric layer thickness exceeds the cut-off film thickness and gradually increases, the LSAW attenuation coefficient will decrease rapidly.

[0066] Traditional Rayleigh waves are formed by coupling longitudinal waves in the form of compression and vertical shear waves in the form of shear. Rayleigh waves generally do not leak energy into the dielectric body, but the polarization component perpendicular to the substrate surface will be greatly attenuated in the liquid environment, increasing the loss. Traditional Love waves have less loss in liquids, but are limited by the speed of sound and are difficult to achieve high frequencies. However, the IDT / LiNbO surface acoustic wave device in the embodiment of the present invention 3 / SiO 2 The heterogeneous acoustic layer structure of SiC / SiC can guide the sound waves to propagate in the low sound velocity region under a specific substrate tangent, and the LSAW excited by it is a non-leakage high sound guided wave mode.

[0067] The present invention converts LiTaO 3 or LiNbO 3 The single crystal film is bonded to a high-acoustic-velocity SiC or diamond substrate, effectively suppressing the slow shear body wave and the fast shear body wave that are simultaneously radiated into the dielectric body during the propagation of the leaky surface wave, greatly reducing the acoustic energy loss. The particles of LSAW vibrate longitudinally, and the phase velocity is higher than the traditional structure that excites Rayleigh waves and Love waves, and is closer to the phase velocity of longitudinal body waves, which can reach 6363-6442 m / s.

[0068] Using the stiffness matrix method and the effective dielectric constant method, in h LN When / λ=0.28 (the thickness of lithium niobate layer is 0.28λ) and the electrode is ignored, the different LiNbO 3 Two-dimensional optimization of the electromechanical coupling coefficient and phase velocity under tangential conditions. Figure 3 and Figure 4 is the simulation result diagram, where Figure 3 is the electromechanical coupling coefficient (K2 ) and the two-dimensional relationship diagram of the Euler angle (0°, θ°, ψ°), Figure 4 The two-dimensional relationship between phase velocity (Vp) and Euler angle (0°, θ°, ψ°) shows the Y-cut LiNbO 3 / SiC structure LSAW excitation, from these two figures, we can see that when θ<-10°, ψ>10°, the electromechanical coupling coefficient can reach more than 9%. 3 The / SiC structure can achieve an electromechanical coupling coefficient of 12% to 15% within the Euler angle range of (0°, -75° to -40°, 30° to 70°), and can reach a maximum of 14.98% at (0°, -53°, 47°), at which time the phase velocity can reach 6288m / s; within the Euler angle range of (0°, -50° to -30°, 85° to 90°), the electromechanical coupling coefficient can reach 10% to 12.5%, and can reach a maximum of 12.47% at (0°, 35°, 90°), which is smaller than that at (0°, -53°, 47°).

[0069] Figure 5 is the electrode thickness, LiNbO 3 Two-dimensional relationship between film thickness and LSAW electromechanical coupling coefficient characteristics (a) and two-dimensional relationship between film thickness and LSAW phase velocity characteristics (b). Figure 6 The two-dimensional relationship between the metallization rate η, the aluminum electrode film thickness and the LSAW electromechanical coupling coefficient characteristics (a) and the two-dimensional relationship with the LSAW phase velocity characteristics (b).

[0070] like Figure 5 In (a), at (aluminum electrode thickness) h Al / λ is 0.046~0.07, (lithium niobate layer thickness)h LN When / λ is in the range of 0.3 to 0.4, the electromechanical coupling coefficient can reach more than 18.75%. Al / λ is 0.06, h LN When / λ is 0.34, the electromechanical coupling coefficient reaches its extreme value of 19.38%. Figure 5 (b) shows the electrode thickness and LiNbO 3 The increase of film thickness will reduce the phase velocity of LSAW.

[0071] exist Figure 5 Based on the results, LiNbO 3 The film thickness is set to 0.34λ, Figure 6 is the relationship between the metallization rate and the aluminum electrode film thickness and the propagation characteristics of LSAW, Figure 6In (a), it can be concluded that when the metallization rate η is 0.5 and the electrode film thickness is 0.065λ, the electromechanical coupling coefficient of LSAW is the largest. Too large or too small a metallization rate η will reduce the electromechanical coupling coefficient of LSAW. Figure 6 From (b), it can be seen that the phase velocity of LSAW decreases with the increase of metallization rate η and aluminum electrode film thickness.

[0072] Although the above-mentioned embodiments have made a detailed description of the present invention, they are only some embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on the embodiments of the present invention without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A liquid phase sensor based on longitudinal acoustic surface waves, characterized in that: It comprises a delay line type surface acoustic wave device, and a sensitive element arranged in a delay region of the delay line type surface acoustic wave device; The delay line type surface acoustic wave device includes a stacked substrate, a temperature compensation layer and a piezoelectric layer, an interdigital transducer is arranged on the surface of the piezoelectric layer, the material of the piezoelectric layer is lithium niobate single crystal or lithium tantalate single crystal, the lithium niobate single crystal is a y-cut x-lithium niobate single crystal, the rotation angle is φ, the propagation angle is ψ, 15°≤φ≤50°, 30°≤ψ≤70°.

2. The liquid phase sensor according to claim 1, characterized in that: φ=37°, ψ=47°.

3. The liquid phase sensor according to claim 1 or 2, characterized in that: The substrate is made of silicon carbide or diamond.

4. The liquid phase sensor according to claim 1, characterized in that: The material of the temperature compensation layer is silicon dioxide.

5. The liquid phase sensor according to claim 1 or 4, characterized in that: The thickness of the temperature compensation layer is 0.2λ-4λ.

6. The liquid phase sensor according to claim 1, characterized in that: The thickness of the piezoelectric layer is 0.2λ to 0.42λ.

7. The liquid phase sensor according to claim 1, characterized in that: The interdigital transducer is a metal electrode, and the metal electrode includes an aluminum electrode.

8. The liquid phase sensor according to claim 7, characterized in that: The thickness of the metal electrode is 0.06λ to 0.08λ, and the metallization rate is 0.48 to 0.

56.

9. The method for preparing a liquid phase sensor based on longitudinal surface acoustic waves according to any one of claims 1 to 8, characterized in that: The following steps are involved: Plasma enhanced chemical vapor deposition is performed on one surface of the substrate to obtain a temperature compensation layer; Bonding the piezoelectric layer to the temperature compensation layer, depositing an interdigital transducer on the surface of the piezoelectric layer, and obtaining a delay line type surface acoustic wave device; A sensitive element is arranged in the delay region of a delay line type surface acoustic wave device to obtain a liquid phase sensor based on longitudinal surface acoustic waves.

10. Use of the liquid phase sensor based on longitudinal surface acoustic waves according to any one of claims 1 to 8 or the liquid phase sensor based on longitudinal surface acoustic waves obtained by the preparation method according to claim 9 in liquid phase detection.

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