General-purpose smr gas sensor structure

Abstract

The present application relates to the technical field of micro-electro-mechanical system (MEMS) sensor, and particularly relates to a universal SMR (Solidly Mounted Resonator, SMR) gas sensor structure based on a BAW bulk acoustic wave resonator, which can be used for detecting hydrogen, volatile organic compounds (VOC), ammonia, nitrogen dioxide, carbon monoxide, humidity and other industrial or environmental gases, and comprises an SMR resonant structure arranged on a substrate, wherein a sensitive layer is arranged on the SMR resonant structure, and the material of the sensitive layer is replaced and adjusted according to the type of the required detection gas; the present sensor platform structure is universal, the same SMR structure can be adapted to sensitive materials of different sensitive layers, a plurality of gases can be detected, the detection function is convenient to quickly adjust, the sensor can be mass-produced, and is compatible with a MEMS process.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS) sensor technology, and in particular to a general-purpose SMR (Solidly Mounted Resonator) gas sensor structure based on a BAW bulk acoustic resonator, which can be used to detect hydrogen, volatile organic compounds (VOCs), ammonia, nitrogen dioxide, carbon monoxide, humidity and other industrial or environmental gases. Background Technology

[0002] Gas sensors are widely used in industrial gas monitoring, petrochemical industry safety monitoring, and ambient air quality detection. Existing gas sensors mainly include electrochemical, metal oxide, and optical sensors, and they generally suffer from the following problems:

[0003] (1) A sensor structure is designed only for a specific gas, and the platform structure is not universal for the detection of other gases.

[0004] (2) Slow response speed and limited sensitivity.

[0005] (3) High power consumption.

[0006] Bulk acoustic wave resonators (BAW / SMR) have been used in the communications field for many years due to their high quality factor, high frequency, and high stability. However, for specific gas sensors, existing technologies employ different device structures and technical approaches depending on the gas composition. Current technology lacks a universal SMR sensor platform with a general sensor structure, replaceable sensitive detection materials, and applicability to multiple gases.

[0007] Therefore, there is an urgent need for an SMR gas sensor platform with a universal sensor structure, replaceable universal sensor structure materials, and applicability to the detection of various gases, in order to overcome the limitations of existing technologies. Summary of the Invention

[0008] The purpose of this invention is to provide an SMR gas sensor platform with a universal sensor structure, replaceable universal sensor structure materials, and applicability to the detection of various gases, in order to overcome the shortcomings of the prior art and to solve the limitations of the prior art.

[0009] A general-purpose SMR gas sensor structure includes an SMR resonant structure disposed on a substrate, characterized in that: a sensitive layer is disposed on the SMR resonant structure.

[0010] In a further optimization, the SMR resonant structure comprises, from bottom to top, a substrate, an acoustic reflection layer, a lower electrode, a piezoelectric layer, and an upper electrode stacked sequentially, with the sensitive layer deposited on the surface of the upper electrode.

[0011] Further optimization involves changing or adjusting the material of the sensitive layer according to the type of gas to be detected.

[0012] Further optimization is achieved by using materials such as metals, metal oxides, composite metals, and non-metallic materials for the sensitive layer.

[0013] Further optimization is made to include the following metals, metal oxides, composite metals and non-metallic materials: Pd, Pt, Au, Ag, Ni, Cu; ZnO, SnO2, WO3, Al2O3, TiO2, In2O3; MOFs, COFs, carbon nanotubes (CNTs), and graphene (rGo).

[0014] Further optimization is achieved by using substrate materials including Si, glass, AlN / Si, SOI, and SiC.

[0015] The acoustic reflective layer is constructed by alternating layers of high acoustic impedance material and low acoustic impedance material, and the combination of high acoustic impedance material and low acoustic impedance material includes W / SiO2, Mo / SiO2, Ru / SiO2, Pt / SiO2, W / AlN, and Ta / SiN.

[0016] The piezoelectric layer is made of AlN, ScAlN, or ZnO.

[0017] The materials of the lower electrode and the upper electrode include Mo, Pt, Al, Au, and Wu.

[0018] An adhesion layer is also disposed on the substrate, and the adhesion layer material includes Ti, Cr, and Ta.

[0019] Further optimization involves detecting gases including H2, VOC, NH3, NO2, CO, and air humidity.

[0020] The present invention has the following beneficial effects:

[0021] (1) Sensor platform structure: The same SMR structure can be adapted to different sensitive materials of different sensitive layers.

[0022] (2) High versatility: The same SMR structure can be adapted to different sensitive materials to detect a variety of gases.

[0023] (3) High sensitivity: the frequency change can reach the kHz level.

[0024] (4) High stability: high Q value and low noise.

[0025] (5) The present invention is small in size, consumes little power, is easy to integrate, and can be integrated with CMOS circuits.

[0026] (6) The present invention has a unified structure, the detection function is easy to adjust quickly, it can be mass-produced, and it is compatible with MEMS process. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the SMR gas sensor structure of the present invention.

[0028] Figure 2 This is a schematic diagram of the frequency response of the sensor of the present invention. Detailed Implementation

[0029] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0030] Example 1:

[0031] like Figure 1 and Figure 2 As shown, a general-purpose SMR gas sensor structure includes an SMR resonant structure 2 disposed on a substrate 1, and a sensitive layer 3 disposed on the SMR resonant structure 2. The structure of the SMR resonant structure 2 remains unchanged, while the material of the sensitive layer 3 can be selected and replaced with a corresponding sensitive material according to the requirements of the gas to be detected.

[0032] The SMR resonant structure 2 comprises, from bottom to top, a substrate 1, an acoustic reflective layer 2-1, a lower electrode 2-2, a piezoelectric layer 2-3, and an upper electrode 2-4 stacked sequentially, with the sensitive layer 3 deposited on the surface of the upper electrode 2-4.

[0033] The substrate can be made of Si, glass, AlN / Si, SOI, or SiC, and is not limited to these materials.

[0034] Depending on the process requirements, adhesion layers may be provided between the functional layers. Specifically, adhesion layers made of different materials are used between the substrate 1, acoustic reflection layer 2-1, lower electrode 2-2, piezoelectric layer 2-3, upper electrode 2-4, and sensitive layer 4 for bonding. The material of the adhesion layer is determined by the material of the functional layer to be adhered to. These adhesion layer materials include Ti, Cr, and Ta. Some materials used to form semiconductor devices cannot adhere well to other materials used; for example, a Pd layer cannot adhere well to a Mo layer, requiring an additional 5-10 nm Ti layer as an adhesion layer.

[0035] The acoustic reflective layer is made of alternating layers of high acoustic impedance material and low acoustic impedance material. The combination of high acoustic impedance material and low acoustic impedance material can be selected from the following combinations: W / SiO2, Mo / SiO2, W / AlN, and is not limited to these materials.

[0036] The piezoelectric layer can be made of AlN, ScAlN, ZnO, or other materials, and is not limited to these materials.

[0037] The materials for the lower and upper electrodes can be Mo, Pt, Al, Au, or W, and are not limited to these materials.

[0038] This invention can detect industrial or environmental gases such as H2, VOC, NH3, NO2, CO, and air humidity by selecting different sensitive layers.

[0039] A basic SMR gas sensor structure based on the present invention comprises, from bottom to top, the following stacked structures and the materials used for the response structure:

[0040] -Substrate: Made of Si material.

[0041] - Bottom electrode: Made of Mo material.

[0042] - Acoustic reflective layer: It adopts a multi-layer structure of alternating W / SiO2, with a total of 5 layers stacked.

[0043] - Piezoelectric layer: Made of AlN material, the piezoelectric layer has a thickness of 500nm.

[0044] - Upper electrode: Made of Mo material.

[0045] - Sensitive layer: Pd, Ag, Ni and other materials can be used to directly deposit on the surface of the upper electrode, and the thickness of the sensitive layer is 80-200nm.

[0046] - Packaging: This sensor adopts a top-opening design, which allows the sensitive layer to be directly exposed to the gas to be detected, thereby improving the sensitivity and accuracy of detection.

[0047] The working principle of this device is as follows:

[0048] The gas to be detected is adsorbed onto the sensitive layer → changes in the mass, elastic modulus, and stress of the sensitive layer → changes in the SMR resonance frequency, thereby detecting the presence of the gas to be detected.

[0049] Example 2:

[0050] This invention allows for easy replacement and adjustment of the material of the sensitive layer 3 based on the type of gas to be detected, while maintaining the platform structure. Depending on the gas being detected, the sensitive layer can be made of metals, metal oxides, or composite metals. Specific examples of metals, metal oxides, composite metals, and non-metallic materials include Pd, Pt, Au, Ag, Ni, Cu; ZnO, SnO2, WO3, Al2O3, TiO2, In2O3; MOFs, COFs, carbon nanotubes (CNTs), and graphene (rGo).

[0051] The sensitive layer can also be made of graphene, MoS2, MOF, polymer, composite material, nanostructure, etc., where the nanostructure can be in the form of nanoparticles, nanowires, nanoporous membranes, etc.

[0052] The SMR structure of this invention remains unchanged; different gases can be detected simply by changing the material of the sensitive layer. The table below shows the data of the sensitive layer when detecting different gases on this platform:

[0053] <![CDATA[H2]]> Pd, PdAg, PdNi 20–200nm High sensitivity and fast response VOC MOF, polymer 50–200nm High selectivity <![CDATA[NH3]]> <![CDATA[WO3、MoS2]]> 20–200nm Low temperature response <![CDATA[NO2]]> <![CDATA[SnO2、In2O3]]> 20–150nm High sensitivity Ambient humidity Polyimide, PVA 50–500nm Good reversibility

[0054] The present invention has the following advantages:

[0055] (1) Sensor platform structure: The same SMR structure can be adapted to different sensitive materials of different sensitive layers.

[0056] (2) High versatility: The same SMR structure can be adapted to different sensitive materials to detect a variety of gases.

[0057] Example 3:

[0058] The manufacturing process of this invention is as follows:

[0059] 1. Substrate cleaning (cleaning, thermal oxidation, CMP if necessary);

[0060] 2. Multi-layer sputtering of acoustic reflective layer;

[0061] 3. Lower electrode deposition and patterning (sputtering Mo / Pt / Al, photolithography + dry etching or wet etching, stress control, roughness control).

[0062] 4. Piezoelectric layer deposition (AlN / AlScN, reactive sputtering, controlling c-axis orientation, stress, and thickness) sputtering and annealing;

[0063] 5. Top electrode deposition and patterning (sputtering Mo / Pt / Al / Au, photolithography + etching);

[0064] 6. Sensitive layer deposition (sputtering, ALD, spin coating, drop coating, etc.);

[0065] 7. Packaging;

[0066] 8. Circuit integration.

[0067] Example 4:

[0068] Performance testing of the hydrogen detection sensor produced by this invention:

[0069] - Frequency: 0.52—3GHz;

[0070] -Q value: 800-2000;

[0071] - Hydrogen sensitivity: 10-200kHz / ppm;

[0072] - Response time: <7s

[0073] - Temperature drift: <5ppm / ℃ (compensation can be added).

[0074] The present invention has the following advantages:

[0075] (1) Low operating temperature and low power consumption;

[0076] (2) High sensitivity: the frequency change can reach the kHz level.

[0077] (3) High stability: high Q value and low noise.

[0078] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0079] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A general-purpose SMR gas sensor structure, comprising an SMR resonant structure disposed on a substrate, characterized in that: A sensitive layer is provided on the SMR resonant structure.

2. The general-purpose SMR gas sensor structure according to claim 1, characterized in that: The SMR resonant structure comprises, from bottom to top, a substrate, an acoustic reflective layer, a lower electrode, a piezoelectric layer, and an upper electrode stacked sequentially, with the sensitive layer deposited on the surface of the upper electrode.

3. The general-purpose SMR gas sensor structure according to claim 1 or 2, characterized in that: The material of the sensitive layer is changed or adjusted according to the type of gas to be detected.

4. The general-purpose SMR gas sensor structure according to claim 1 or 2, characterized in that: The sensitive layer can be made of metal, metal oxide, composite metal, or non-metallic materials.

5. The general-purpose SMR gas sensor structure according to claim 4, characterized in that: The metals, metal oxides, composite metals, and non-metallic materials include Pd, Pt, Au, Ag, Ni, Cu; ZnO, SnO2, WO3, Al2O3, TiO2, In2O3; MOFs, COFs, carbon nanotubes (CNTs), and graphene (rGo).

6. The general-purpose SMR gas sensor structure according to claim 2, characterized in that: The substrate material includes Si, glass, AlN / Si, SOI, and SiC; The acoustic reflective layer is constructed by alternating layers of high acoustic impedance material and low acoustic impedance material, and the combination of high acoustic impedance material and low acoustic impedance material includes W / SiO2, Mo / SiO2, Ru / SiO2, Pt / SiO2, W / AlN, and Ta / SiN. The piezoelectric layer is made of AlN, ScAlN, or ZnO. The materials of the lower electrode and the upper electrode include Mo, Pt, Al, Au, and W; An adhesion layer is also provided between each functional layer according to process requirements, and the material of the adhesion layer includes Ti, Cr, and Ta.

7. The general-purpose SMR gas sensor structure according to claim 2, characterized in that: The gases being detected include H2, VOC, NH3, NO2, CO, and air humidity.

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