Piezoelectric resonant MEMS spectroscopic chip for gas component analysis

Abstract

The present invention relates to the fields of micro-electromechanical technology and gas detection technology, specifically a piezoelectric resonant MEMS spectroscopy chip for gas component analysis, including a silicon substrate, the silicon substrate is a hollowed-out flat plate, a first support beam and a second support beam are formed thereon, the first support beam and the second support beam are cross-arranged in a cross shape, wherein two TPoS resonators are arranged on the first support beam, the two TPoS resonators are symmetrical about the intersection of the cross, and both include a doped silicon layer, a piezoelectric film, and a top electrode arranged in sequence from bottom to top, a self-assembled gold nanoparticle array is arranged on the top electrode, and the gold nanoparticles in the array are self-assembled particles modified by functional groups. The present invention realizes the quantitative analysis of the mass of the gas to be detected and the accurate analysis of the components of the gas to be detected by setting two resonances and the self-assembled gold nanoparticle array.

Description

Technical Field

[0001] The present invention relates to the fields of micro-electro-mechanical systems (MEMS) technology and gas detection technology, and in particular to a piezoelectric resonant MEMS spectroscopy chip for gas component analysis. Background Art

[0002] Various gases are ubiquitous in human society's living, production and daily life. In view of this, the detection of these gases has become a common concern of today's industry and academia, especially the detection of toxic, harmful or flammable and explosive gases, which is crucial to ensure daily safe production, healthy life and comfortable living. Traditional gas analysis technologies, such as gas chromatography and mass spectrometry, although their detection accuracy is high, often have problems such as large equipment, high cost and inconvenient rapid deployment and use on site.

[0003] In recent years, micro-electro-mechanical systems (MEMS) based on micro-machining technology have achieved rapid development. MEMS micro-machining technology is developed on the basis of microelectronics processing technology, and is mainly realized by photolithography, diffusion, oxidation, thin film growth, etching, evaporation and sputtering and other process technologies. Since MEMS sensors have the advantages of small sensing volume, light weight, and low power consumption, gas sensors prepared by micro-machining technology have become an important branch of the sensor field.

[0004] According to their working principles, MEMS gas sensors can be divided into MEMS fiber optic gas sensors, MEMS conductivity gas sensors, MEMS resonant gas sensors, etc. Among them:

[0005] Fiber optic gas sensors detect gas by coating a layer of special chemical material on the exposed surface of the fiber core. When the material comes into contact with the gas, it causes changes in parameters such as the coupling degree and reflection coefficient of the fiber, thereby achieving the purpose of detecting the gas composition. However, the sensor has disadvantages such as high cost, susceptibility to light source fluctuations, and inability to perform quantitative analysis of gas quality.

[0006] Conductivity gas sensors work by utilizing the mechanism that when gas molecules are adsorbed on the surface of a semiconductor material, the conductivity of the semiconductor material changes. However, their stability is usually poor, and they also do not have the ability to quantitatively analyze gas quality.

[0007] Resonant MEMS gas sensors utilize the mass load effect of the resonant unit. When an external mass load is applied to the surface of the resonator, it will affect the resonant frequency of the resonator. In addition, the resonant units of this type of sensor are rich in various forms, including beams, tuning forks, diaphragms of various shapes, etc. At the same time, with the help of a variety of different excitation and vibration pickup devices, it can convert frequency changes into electrical signals that are easier to detect and process, thereby accurately realizing quantitative analysis of gas quality. However, resonant MEMS sensors have problems such as complex manufacturing process, low sensitivity, and inability to simultaneously realize gas component analysis functions. Summary of the invention

[0008] The purpose of the present invention is to provide a piezoelectric resonant MEMS spectroscopy chip for gas component analysis, in view of the problems of the above-mentioned existing MEMS gas sensors, such as the inability to simultaneously detect gas components and mass, and low sensitivity. The chip utilizes the mass loading effect of a resonant unit based on a thin film piezoelectric-on-silicon (TPoS) structure to achieve quantitative mass analysis of the gas to be detected. At the same time, a gold nanoparticle array capable of adsorbing specific gases is formed on the surface of the resonant unit using a nanoparticle self-assembly method. Finally, the gas component analysis can be achieved through the SERS technology.

[0009] To achieve the above object, the present invention adopts the following technical solution:

[0010] A piezoelectric resonant MEMS spectroscopic chip for gas component analysis, including a silicon substrate;

[0011] The silicon substrate is a hollowed-out flat plate, on which a first support beam and a second support beam are formed, and the first support beam and the second support beam are cross-arranged to form a cross-shaped structure; an input excitation TPoS resonator and an output detection TPoS resonator are arranged on the first support beam, and the two TPoS resonators have the same structure and are symmetrically distributed about the intersection of the cross-shaped structure; the two TPoS resonators include doped silicon, a piezoelectric film, and a top electrode arranged in sequence from bottom to top; a self-assembled metal nanoparticle array is arranged on the top electrode, and the self-assembled metal nanoparticle array is tightly attached to the top electrode;

[0012] On the upper surface of the non-hollowed-out area of ​​the silicon substrate, a first electrical connection and conduction structure is provided at a position corresponding to one end of the second support beam, and a second electrical connection and conduction structure is provided at a position corresponding to the other end of the second support beam. The first electrical connection and conduction structure is connected to the top electrode of the input excitation TPoS resonator, and the second electrical connection and conduction structure is connected to the top electrode of the output detection TPoS resonator.

[0013] Furthermore, the first electrical connection and conduction structure includes an input metal electrode plate, a first grounded metal electrode plate and an input metal transmission line. The first grounded metal electrode plate and the input metal electrode plate are arranged side by side, one end of the input metal transmission line is connected to the top electrode of the input excitation TPoS resonator, and the other end is connected to the input metal electrode plate; the second electrical connection and conduction structure includes an output metal electrode plate, a second grounded metal electrode plate and an output metal transmission line; the second grounded metal electrode plate and the output metal electrode plate are also arranged side by side, one end of the output metal transmission line is connected to the top electrode of the output detection TPoS resonator, and the other end is connected to the output metal electrode plate.

[0014] Furthermore, the input excitation TPoS resonator and the output detection TPoS resonator are both regular hexagonal structures.

[0015] Furthermore, an isolation oxide layer is provided between the input metal transmission line, the output metal transmission line, the input metal electrode plate, the output metal electrode plate and the support beam to prevent the electrical signal from leaking into the cross beam.

[0016] Furthermore, the isolation oxide layer material is silicon dioxide, and the thickness is 0.3 μm to 1.5 μm;

[0017] The metal transmission line, metal electrode disk and top electrode are made of gold, silver, copper, aluminum, nickel or platinum and have a thickness of 0.2 μm to 2 μm.

[0018] The piezoelectric film is made of LiNbO3, PZT, AlN, ZnO, PVDF, LiTaO3 or other piezoelectric materials, and has a thickness of 0.1 μm to 1 μm.

[0019] Furthermore, the metal nanoparticles are gold nanoparticles with a two-dimensional or three-dimensional size between 1-100 nm.

[0020] Furthermore, the gold nanoparticles in the gold nanoparticle array are self-assembled particles modified with functional groups, and the functional group modification method adopted is to form Au-S bonds with thiol compounds and gold.

[0021] Furthermore, the input excitation TPoS resonator and the output detection TPoS resonator are both suspended structures formed by etching the silicon substrate thereunder using a deep reactive ion etching process, so as to utilize the difference in acoustic impedance between the resonator and air to improve the quality factor (Q value) of the device.

[0022] After adopting the above technical solution, the present invention has the following beneficial effects:

[0023] 1. The piezoelectric resonant spectral chip in the present invention realizes the mutual conversion of mechanical energy and electrical energy through piezoelectric transduction, and can still work stably and normally even without additional vacuum packaging conditions. It not only has the ability of direct frequency output, but also can realize gas component analysis and gas quality quantitative analysis at the same time, with high functional integration and strong practicality. In terms of production and preparation, it has the advantages of compatibility with CMOS technology, easy large-scale batch processing and preparation, and low manufacturing cost, showing significant economic benefits and industrial application value.

[0024] 2. The two TPoS resonators in the present invention work based on the modal coupling principle. Input excitation and output detection are respectively completed by two resonator bodies. The two resonator bodies are connected only by a cross beam and do not share the same piezoelectric film. Compared with the traditional structure in which one resonator simultaneously completes input excitation and output detection, this structure has a top electrode with a larger surface area that can be used to deposit self-assembled gold nanoparticles. Therefore, it has the characteristics of strong output signal and high detection sensitivity.

[0025] 3. The present invention utilizes nanoparticle self-assembly technology to form a gold nanoparticle array on the surface of the top electrode of the resonator. The gold nanoparticles in the array are self-assembled particles modified with functional groups. The functional group modification method adopted is to use thiol compounds and gold to form Au-S bonds. After functional group modification, the chip can strongly adsorb methane, formaldehyde, carbon monoxide, and sulfur dioxide gases. The self-assembly technology and functional group modification technology can enable the chip to have gas adsorption capacity without affecting the normal operation of the main body of the resonator chip. Finally, the quantitative analysis of gas components and quality can be achieved by detecting the frequency change of the resonator output signal and the SERS technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A three-dimensional structure diagram of a piezoelectric resonant MEMS spectroscopic chip for gas component analysis in an embodiment;

[0027] Figure 2 A top view of a piezoelectric resonant MEMS spectroscopic chip for gas component analysis in an embodiment;

[0028] Figure 3 A bottom view of a piezoelectric resonant MEMS spectroscopy chip for gas component analysis in an embodiment;

[0029] Figure 4 This is a diagram of a gold nanoparticle array after using nanoparticle self-assembly technology and functional group surface modification in the embodiment;

[0030] Figure 5 is a graph showing the shift of the resonance frequency of the TPoS resonator due to the change of the load mass in the embodiment;

[0031] Reference numerals:

[0032] 1. Input excitation TPoS resonator; 2. Piezoelectric film; 3. Input excitation TPoS resonator top electrode; 301. First grounded metal electrode disk; 302. Input metal electrode disk; 303. Input metal transmission line; 4. Doped silicon; 5. Isolation oxide layer; 6. Silicon substrate; 7. Output detection TPoS resonator; 8. Output detection TPoS resonator top electrode; 801. Second grounded metal electrode disk; 802. Output metal electrode disk; 803. Output metal transmission line; 9. Output detection TPoS resonator piezoelectric film; 10. Gold nanoparticle array; 1002. Surface functional group. DETAILED DESCRIPTION

[0033] Hereinafter, the term "include" or "may include" used in various embodiments of the present invention indicates the presence of the invented function, operation or element, and does not limit the addition of one or more functions, operations or elements. In addition, as used in various embodiments of the present invention, the terms "include", "have" and their cognates are intended only to indicate specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be understood as first excluding the presence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or the possibility of adding one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0034] In various embodiments of the present invention, the expression "or" or "at least one of A or / and B" includes any combination or all combinations of the words listed at the same time. For example, the expression "A or B" or "at least one of A or / and B" may include A, may include B, or may include both A and B.

[0035] The expressions (such as "first", "second", etc.) used in various embodiments of the present invention may modify the various constituent elements in various embodiments, but may not limit the corresponding constituent elements. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only used for the purpose of distinguishing an element from other elements. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, without departing from the scope of various embodiments of the present invention, the first element may be referred to as the second element, and similarly, the second element may also be referred to as the first element.

[0036] It should be noted that if it is described that one component element is “connected” to another component element, the first component element may be directly connected to the second component element, and a third component element may be “connected” between the first component element and the second component element. Conversely, when one component element is “directly connected” to another component element, it can be understood that there is no third component element between the first component element and the second component element.

[0037] The terms used in various embodiments of the present invention are only used for the purpose of describing specific embodiments and are not intended to limit various embodiments of the present invention. As used herein, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. Unless otherwise limited, all terms used here (including technical terms and scientific terms) have the same meaning as the meaning generally understood by those of ordinary skill in the art to which the various embodiments of the present invention belong. The terms (such as the terms defined in the dictionary generally used) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized meaning or an overly formal meaning, unless clearly defined in various embodiments of the present invention.

[0038] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention. The technical scheme of the present invention is described in detail below in conjunction with the accompanying drawings.

[0039] Example 1, such as Figure 1-Figure 3 As shown, the piezoelectric resonant MEMS spectroscopy chip for gas component analysis provided in this example includes a silicon substrate 6. The silicon substrate 6 is a hollow flat plate, on which a first support beam and a second support beam are formed, and the first support beam and the second support beam are cross-arranged to form a cross-shaped structure. Two TPoS resonators are arranged on the first support beam, and the two TPoS resonators have the same structure and are symmetrically distributed about the intersection of the cross-shaped structure. The two TPoS resonators are respectively an input excitation TPoS resonator 1 and an output detection TPoS resonator 7.

[0040] The input excitation TPoS resonator 1 includes doped silicon 4, a piezoelectric film 2, and a top electrode arranged in sequence from bottom to top, and a self-assembled gold nanoparticle array 10 is provided on the top electrode, and the self-assembled gold nanoparticle array 10 is tightly attached to the top electrode. The output detection TPoS resonator 7 has the same structure as the input excitation TPoS resonator 1.

[0041] The upper surface of the non-hollowed-out area of ​​the silicon substrate is provided with a first electrical connection and conduction structure at one end of the second support beam, and a second electrical connection and conduction structure is provided at the other end of the second support beam. The first electrical connection and conduction structure is connected to the input excitation TPoS resonator top electrode 3, and the second electrical connection and conduction structure is connected to the output detection TPoS resonator top electrode 8.

[0042] The first electrical connection and conduction structure includes an input metal electrode disk 302, a first grounded metal electrode disk 301 and an input metal transmission line 303. The first grounded metal electrode disk 301 is arranged on the left side of the input metal electrode disk 302 to realize the GS electrode structure; one end of the input metal transmission line 303 is connected to the input excitation TPoS resonator top electrode 3, and the other end is connected to the input metal electrode disk 302. The second electrical connection and conduction structure includes an output metal electrode disk 802, a second grounded metal electrode disk 801 and an output metal transmission line 803; the second grounded metal electrode disk 801 is arranged on the right side of the output metal electrode disk 802, and is also used to realize the GS electrode structure; one end of the output metal transmission line 803 is connected to the output detection TPoS resonator top electrode 8, and the other end is connected to the output metal electrode disk 802.

[0043] In this embodiment, the input excitation TPoS resonator 1 and the output detection TPoS resonator 7 are both regular hexagonal structures. After adopting this structure, the internal stress and strain caused by structural asymmetry can be reduced, and the stability and reliability of the resonator can be improved. An isolation oxide layer 5 is provided between the input metal transmission line 303, the input metal electrode disk 302, the output metal transmission line 803, the output metal electrode disk 802 and the support beam to prevent the electrical signal from leaking into the cross-shaped structure. The isolation oxide layer 5 is made of silicon dioxide with a thickness of 0.3μm~1.5μm. The input metal transmission line 303, the input metal electrode disk 302, the output metal transmission line 803, the output metal electrode disk 802, the input excitation TPoS resonator top electrode 3, and the output detection TPoS resonator top electrode 8 are made of metals such as gold, silver, copper, aluminum, nickel or platinum. In this embodiment, the preferred material is gold with a thickness of 0.2μm~2μm.

[0044] In the piezoelectric resonant MEMS spectroscopy chip of this embodiment, the characteristic frequencies of the two TPoS resonators are sensitive to the mass of the gas loaded on the surface. When the self-assembled gold nanoparticles on the surface of the TPoS resonator adsorb the gas in the surrounding environment, a mass load will be formed on the surface of the TPoS resonator, and the overall mass of the TPoS resonator will increase, resulting in a decrease in the resonant frequency. Since the self-assembled gold nanoparticles will uniformly adsorb the gas and the load mass is a rigid material, the load mass can be equivalent to an increase in the thickness of the piezoelectric film 2. Figure 5As shown, the resonant frequency of the resonator without a load layer f 0 for:

[0045] ;

[0046] The frequency shift with the load mass Δf With the original resonant frequency f 0 The ratio is:

[0047] ;

[0048] Substituting equation (1-1) into equation (1-2) yields the change in resonance shift:

[0049] ;

[0050] in, v is the phase velocity of acoustic wave propagation in the TPoS resonator, c To resonate the Young's modulus of the entire material, d is the TPoS resonator thickness, A is the effective area of ​​the TPoS resonator, is the density of the piezoelectric material, E 0 is the Young's modulus of the piezoelectric material , Δm is the mass of adsorbed gas, f 1 for f 0 The frequency after the offset occurs.

[0051] According to the above formula, it can be found that the frequency response of the TPoS resonator shows a linear shift with the mass of the adsorbed gas. Therefore, by utilizing the characteristic that the resonant frequency of the resonator changes linearly with the mass of the adsorbed gas, the mass of the adsorbed gas can be known by simply measuring the change in the resonant frequency of the TPoS resonator.

[0052] The TPoS resonator is an acoustic device that relies on piezoelectric and inverse piezoelectric phenomena. In this two-terminal resonant device, the input excitation TPoS resonator and the output detection TPoS resonator serve as its input and output terminals. When a voltage is applied to the input terminal for excitation, the inverse piezoelectric effect causes the piezoelectric material to produce mechanical strain, thereby driving the entire input excitation TPoS resonator to oscillate according to a specific vibration mode, completing the conversion of electrical energy into mechanical energy. At the same time, the output terminal uses the piezoelectric effect to capture the charge changes generated by the piezoelectric film under stress. Since the polarity of the charge changes periodically over time, the metal electrode at the output terminal generates a periodic current output. In this embodiment, the two TPoS resonators are connected by a first cross-shaped support beam and a second cross-shaped support beam. When the input excitation TPoS resonator is excited to oscillate under the action of an electrical signal, the output detection TPoS resonator will also oscillate through the coupling effect of the first cross-shaped support beam and the second cross-shaped support beam, thereby detecting the electrical signal output on the output electrode.

[0053] Self-assembly refers to the process by which nanoparticles or other discrete components spontaneously form organizations through direct interactions or indirect interactions through the environment. Figure 4 As shown, in this embodiment, a gold nanoparticle array 10 is arranged on the top electrode 3 of the input excitation TPoS resonator and the top electrode 8 of the output detection TPoS resonator. The gold nanoparticles in the array are self-assembled particles modified with surface functional groups 1002, thereby achieving uniform and effective adsorption of gas on the surfaces of the two TPoS resonators. Using the nanoparticle self-assembly technology, the gold nanoparticles are spontaneously and orderly arranged above the top electrode of the TPoS resonator. In this way, the characteristics of the large specific surface area of ​​the nanoparticles are retained, and their high reactivity is maintained. The modification of the surface functional group 1002 is achieved by forming an Au-S bond with gold by means of a thiol compound. Through the modification of the surface functional group 1002, chemical bonds that can react chemically with specific gases such as methane, sulfur dioxide, carbon monoxide, and formaldehyde are introduced on the surface of the self-assembled nanoparticles to achieve surface modification of the nanoparticles. In addition, gold, as the most commonly used metal substrate in SERS technology, can significantly improve the intensity of the Raman scattering signal and accurately detect the components of the gas to be analyzed.

[0054] In summary, the piezoelectric resonant MEMS spectroscopy chip of this embodiment realizes quantitative analysis of gas components and quality while having a relatively simple device structure design. The chip also has the advantages of small size, good mechanical stability and direct frequency output.

[0055] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A piezoelectric resonant MEMS spectroscopic chip for gas component analysis, comprising a silicon substrate, characterized in that: The silicon substrate is a hollowed-out flat plate, on which a first support beam and a second support beam are formed, the first support beam and the second support beam are cross-arranged to form a cross-shaped structure, and an input excitation TPoS resonator and an output detection TPoS resonator are provided on the first support beam; The input excitation TPoS resonator and the output detection TPoS resonator have the same structure, and the two are symmetrically distributed about the intersection of the cross-shaped structure; the two TPoS resonators include doped silicon, piezoelectric film, and top electrode arranged in sequence from bottom to top; a self-assembled metal nanoparticle array is provided on the top electrode, and the self-assembled metal nanoparticle array is tightly attached to the top of the top electrode; On the upper surface of the non-hollowed-out area of ​​the silicon substrate, a first electrical connection and conduction structure is provided at a position corresponding to one end of the second support beam, and a second electrical connection and conduction structure is provided at a position corresponding to the other end of the second support beam, wherein the first electrical connection and conduction structure comprises an input metal electrode disk, a first grounded metal electrode disk and an input metal transmission line, wherein the first grounded metal electrode disk and the input metal electrode disk are arranged side by side, and one end of the input metal transmission line is connected to the top electrode of the input excitation TPoS resonator, and the other end is connected to the input metal electrode disk; The second electrical connection and conduction structure includes an output metal electrode plate, a second grounded metal electrode plate, and an output metal transmission line; The second grounded metal electrode disk is also arranged side by side with the output metal electrode disk. One end of the output metal transmission line is connected to the top electrode of the output detection TPoS resonator, and the other end is connected to the output metal electrode disk.

2. The piezoelectric resonant MEMS spectroscopy chip according to claim 1, characterized in that: The input excitation TPoS resonator and the output detection TPoS resonator are both regular hexagonal structures.

3. The piezoelectric resonant MEMS spectroscopy chip according to claim 1, characterized in that: An isolation oxide layer is provided between the input metal transmission line, the output metal transmission line, the input metal electrode disk, the output metal electrode disk and the support beam to prevent the electrical signal from leaking into the cross-shaped structure.

4. The piezoelectric resonant MEMS spectroscopy chip according to claim 3, characterized in that: The isolation oxide layer material is silicon dioxide with a thickness of 0.3μm to 1.5μm; the metal transmission line, metal electrode disk, and top electrode are made of gold, silver, copper, aluminum, nickel or platinum with a thickness of 0.2μm to 2μm; the piezoelectric film is LiNbO3, PZT, AlN, ZnO, PVDF or LiTaO3 with a thickness of 0.1μm to 1μm.

5. The piezoelectric resonant MEMS spectroscopy chip according to claim 1, characterized in that: The metal nanoparticles are gold nanoparticles with a two-dimensional or three-dimensional size between 1 and 100 nm.

6. The piezoelectric resonant MEMS spectroscopy chip according to claim 5, characterized in that: The gold nanoparticles in the gold nanoparticle array are self-assembled particles modified with functional groups, and the functional group modification method adopted is to form Au-S bonds with thiol compounds and gold.

7. The piezoelectric resonant MEMS spectroscopy chip according to claim 1, characterized in that: The input excitation TPoS resonator and the output detection TPoS resonator are suspended structures formed by etching the silicon substrate thereunder using a deep reactive ion etching process.

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