Sensitization type pressure sensor based on weak coupling resonator

Abstract

The invention provides a weakly coupled resonator-based sensitization pressure sensor, which comprises a weakly coupled resonator and a heat conduction main body, the weakly coupled resonator is connected with the heat conduction main body, the heat conduction main body is arranged in a bending and circling manner, each main resonator of the weakly coupled resonator is made of different materials, and each main resonator is made of different materials. Each main resonator and the affiliated heat conduction main body are made of the same material, the pressure sensor organically combines the Pirani vacuum gauge and the weak coupling resonator, the sensitive stress of the weak coupling resonator comes from the thermal stress generated by the heat conduction main body, rigidity disturbance is provided for the weak coupling resonator, the measurement of vacuum pressure is realized, and the measurement precision is improved. According to the Pirani vacuum gauge, the measurement lower limit is expanded, the comprehensive performance is improved, on the premise that the test range of the Pirani vacuum gauge is not sacrificed, the same sensitive core can measure medium and low vacuum pressure, and the measuring range can be expanded to be close to the atmospheric pressure.

Description

Technical Field

[0001] The invention belongs to the technical field of MEMS vacuum pressure sensors, and in particular relates to a sensitivity-enhanced pressure sensor based on a weakly coupled resonator. Background Art

[0002] Thermal conductivity vacuum gauges are a type of sensor widely used to monitor vacuum pressure. The most classic one is the Pirani vacuum gauge, whose basic principle is that the heat dissipation / heat conduction speed of the energized metal wire (usually made of metal nickel or platinum, etc.) is different under different air pressure environments, so the current required to maintain the constant temperature of the metal wire is different. The existing Pirani vacuum gauge can sense atmospheric pressure (10 5 Pa) to 10 -2 Pa pressure, however, in the medium vacuum pressure range (<100Pa,>10 -2 It is difficult to ensure the sensitivity and accuracy below 0.04 Pa, and it is also difficult to further reduce the lower limit of measurement. Existing public patents such as CN201310070529 and CN202311533623 combine Pirani with sensitive cores based on other principles, such as piezoresistance and single resonator, to improve the comprehensive effect of pressure measurement. However, it can only optimize the low vacuum measurement index and cannot improve the performance of the sensor in the medium vacuum pressure section, resulting in low detection accuracy and sensitivity in the medium vacuum pressure range. In addition, the traditional method of optimizing the Pirani structural parameters is also very limited in expanding the lower limit of the range.

[0003] Weakly coupled resonant sensors are a new type of resonant sensors that use weakly coupled resonators to improve the sensitivity of the sensor to changes in stiffness, which is expected to improve the lower limit and resolution of the sensor. A weakly coupled resonator is a multi-degree-of-freedom resonator formed by coupling multiple monomer resonators with similar fundamental frequencies through a connecting structure. When the coupling stiffness of the connecting structure is much lower than (usually not more than 0.1 times) the stiffness of the monomer resonator, the resonator is called a weakly coupled resonator. It has been widely used in the measurement of physical quantities such as acceleration and electric field, and the measurement of pressure has also been widely carried out. However, existing studies have shown that the lower limit of vacuum sensors based on membrane strain and weakly coupled resonators is difficult to further expand, such as the scheme based on pressure-sensitive membranes and weakly coupled resonators described in Chinese patents CN201910893549, CN202210759226, and CN202410056171. The main reason is that in this scheme, further reducing the lower limit of measurement must rely on thinner and larger pressure-sensitive membranes and resonators with smaller cross-sectional areas, which places extremely stringent requirements on the error of the manufacturing process and is difficult to achieve. Summary of the invention

[0004] In order to solve the problems of the above-mentioned prior art, an embodiment of the present invention provides a sensitivity-enhanced pressure sensor based on a weakly coupled resonator, which organically combines the Pirani vacuum gauge and the weakly coupled resonator. The stress source to which the weakly coupled resonator is sensitive is no longer the membrane strain but the thermal stress generated by the imbalance of thermal conduction, which provides stiffness disturbance for the weakly coupled resonator, realizes the measurement of vacuum pressure, and improves the comprehensive performance of medium vacuum pressure measurement.

[0005] The objective of the present invention can be achieved through the following technical solutions: a sensitivity-enhanced pressure sensor based on a weakly coupled resonator, comprising a weakly coupled resonator and a heat conduction body, wherein the weakly coupled resonator is connected to the heat conduction body, the heat conduction body is bent and spiraled, each main resonator of the weakly coupled resonator is composed of different materials, and each main resonator and its attached heat conduction body are composed of the same material.

[0006] Preferably, the material is a single layer or multiple layers, and the thermal expansion coefficients of the multiple layers are different.

[0007] Preferably, the multilayer material comprises a metal layer, a silicon layer, an insulating layer and a substrate layer from top to bottom, the metal layer comprises nickel and platinum, the silicon layer comprises single crystal silicon, the insulating layer is glass or silicon, and the substrate layer is one of silicon, glass and ceramic.

[0008] Preferably, the plurality of main resonators are connected via a coupling structure, the coupling structure is a single-layer material, and the single-layer material is a low-resistivity material or a high-resistivity material.

[0009] Preferably, the main resonator includes a vibration beam, a fixed electrode and an anchor point, both ends of the weakly coupled resonator are fixed to the substrate layer through the anchor point, one end of the main resonator is connected to the anchor point through the heat conduction body, two parallel vibration beams are installed on the main resonator, the vibration beams vibrate in the same phase or in opposite phases, the fixed electrodes are arranged above and below the vibration beam, and the fixed electrodes are fixed to the substrate layer.

[0010] The beneficial effects brought by the present invention are as follows:

[0011] It can be seen from the above scheme that the embodiment of the present invention provides a sensitive pressure sensor based on a weakly coupled resonator, which organically combines the Pirani vacuum gauge and the weakly coupled resonator. The source of stress that the weakly coupled resonator is sensitive to is no longer the membrane strain but the thermal stress generated by the thermal conduction of the Pirani vacuum gauge. Cover the surface of the weakly coupled resonator and the thermal conduction body with a layer of metal or other materials that are very different from the thermal conductivity of single crystal silicon. At this time, when a voltage is applied to the resonator and the thermal conduction body, the temperature of the thermal conduction body itself will change with the pressure to be measured due to the thermal conduction capacity. At the same time, this temperature will change the thermal stress of the resonator itself, thereby providing stiffness disturbance for the weakly coupled resonator. Under the action of the weakly coupled resonator, this stress will be highly sensitively sensed, thereby realizing the measurement of vacuum pressure, expanding the lower limit of measurement and improving the overall performance. In addition, when the vacuum pressure is large, the resonator will no longer vibrate. At this time, it is similar to the traditional MEMS thermal conduction vacuum gauge, and is only sensitive to pressure through thermal conduction, thereby expanding the upper limit of measurement to near atmospheric pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A schematic structural diagram showing a sensitivity-enhanced pressure sensor based on a weakly coupled resonator according to an embodiment of the present invention;

[0013] Figure 2 A schematic diagram showing the working state of a sensitivity-enhanced pressure sensor based on a weakly coupled resonator according to an embodiment of the present invention;

[0014] Figure 3 A longitudinal cross-sectional view showing a first main resonator, a second main resonator and a heat conducting body according to an embodiment of the present invention.

[0015] In the figure, 1 is the first main resonator; 1-1 is anchor point one; 1-2 is vibration beam one; 1-3 is fixed electrode one; 1-4 is heat conduction body one; 1-5 is anchor point two; 2 is coupling structure; 3 is the second main resonator, 3-1 is anchor point three; 3-2 is vibration beam two; 3-3 is fixed electrode two; 3-4 is heat conduction body two; 3-5 is anchor point four. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] Example

[0018] like Figures 1 to 3As shown, a sensitivity-enhanced pressure sensor based on a weakly coupled resonator in this embodiment includes a weakly coupled resonator, and the weakly coupled resonator is a two-degree-of-freedom weakly coupled resonator, and the weakly coupled resonator is composed of a first main resonator 1, a second main resonator 3 and a coupling structure 2. The main resonator constituting the weakly coupled resonator can be a main resonator of any structure and any resonant mode that can work normally, such as a wiggling resonator and a bulk acoustic wave resonator and their unique wiggling modes and other resonant modes. The degree of freedom of the weakly coupled resonator can also be greater than 2, in which case only the two outermost main resonators are designed to have an obvious heat conduction effect, or only one main resonator has a heat conduction effect. The first main resonator 1 and the second main resonator 3 are resonators of multi-layer (not less than two layers) material composites or single-layer materials, and the two have the same geometric parameters, but different material layers or material properties.

[0019] like Figure 3 As shown, the first main resonator 1, the second main resonator 3 and the heat conduction body include a metal layer, a silicon layer, an insulating layer and a substrate layer from top to bottom. The middle silicon layer is the main material of the above structure, which is single crystal silicon with medium resistivity or low resistivity. The substrate layer on the lower side can be silicon or glass. If the substrate layer is silicon, an insulating layer such as silicon dioxide should be added between the substrate layer and the silicon layer. If the substrate layer is glass or ceramic, the insulating layer can be glass or silicon. The upper side is a metal layer, which includes nickel and platinum, but is not limited to nickel and platinum, and is used to adjust the thermal conductivity characteristics of the sensitive structure body. The purpose of the different number of material layers or material characteristics of the first main resonator 1 and the attached heat conduction body 1-5 and the second main resonator 3 and the attached heat conduction body 2 3-5 is to ensure that the resonator stiffness disturbance induced by different pressures to be measured is different.

[0020] like Figure 1 As shown, the heat conduction body in this embodiment includes a heat conduction body 1-4 and a heat conduction body 2 3-4, the heat conduction body 1-4 is connected to the first main resonator 1, the heat conduction body 2 3-4 is connected to the second main resonator 3, the anchor points include an anchor point 1-1, an anchor point 2 1-5, an anchor point 3-1 and an anchor point 4 3-5, the anchor point 1-1 and the anchor point 2 1-5 are connected to the first main resonator 1, the anchor point 3-1 and the anchor point 4 3-5 are connected to the second main resonator 3.

[0021] The first main resonator 1 is fixed on the substrate through an anchor point 1-1, and a fixed electrode 1-3 is also fixed on the substrate, which is used to provide an electrostatic driving force for the first main resonator 1 or pick up a vibration signal. The first main resonator 1 has two parallel arranged vibration beams 1-2, which can vibrate in phase or in antiphase in the resonant state, collectively referred to as the tensile mode of the first resonator 1. One end of the heat conduction body 1-4 is connected to the end of the first main resonator 1, and the other end is fixed to the substrate through an anchor point 2 1-5. The heat conduction body 1-4 is also composed of a composite of multiple layers of materials, and the material composition is the same as that of the first main resonator 1. The curved and coiled heat conduction body 1-4 can amplify the heat conduction effect of this body, and the number, length and cross-sectional area of ​​the bending folds can be optimized to achieve the best effect. On the one hand, the temperature of the vibration beam 1-2 and the heat conduction body 1-4 will change with the pressure to be measured due to the heat conduction effect. On the other hand, the thermal expansion coefficients of the multilayer composite materials of the first main resonator 1 are different from each other, which leads to a large influence of temperature on the equivalent stiffness, that is, high sensitivity to temperature. Therefore, the axial stress of the first main resonator 1 will change with the change of the pressure to be measured, that is, the influence of the pressure to be measured is converted into the stiffness disturbance of the first main resonator 1 through heat conduction.

[0022] The second main resonator 3 is similar to the first main resonator 1, and is also fixed on the substrate through the anchor point three 3-1. The fixed electrode two 3-3 is also fixed on the substrate to provide an electrostatic driving force for the second main resonator 3 or to pick up a vibration signal. The two vibration beams two 3-2 can work in the same phase vibration or anti-phase vibration mode. One end of the heat conduction body two 3-4 is connected to the end of the second main resonator 3, and the other end is fixed on the substrate through the anchor point four 3-5. The heat conduction body two 3-4 is also composed of a multi-layer material composite, and the material composition is the same as that of the second main resonator 3, but the number of material layers or material properties of the two are different from those of the first main resonator 1 and the heat conduction body one 1-4. In this way, the axial stress of the second main resonator 3 will also change with the change of the pressure to be measured, but the rate of change (i.e., sensitivity) is different from that of the first resonator 1. In addition, if the second main resonator 3 does not have a heat conduction body two 3-5, and the second main resonator 3 itself does not have a heat conduction property, the above purpose can also be achieved.

[0023] The coupling structure 2 is a single-layer material, which can be the same as or different from the substrate layer material, and can be a low-resistivity material or a high-resistivity material. It couples the first main resonator 1 and the second main resonator 3, and satisfies that the equivalent stiffness of the coupling structure 2 is much smaller than (but not zero) the first main resonator 1 and the second main resonator 3. When the coupling structure 2 is a high-resistivity material, the voltage or current applied to the first main resonator 1 should be between the anchor point 1-1 and the anchor point 2 1-5, and the voltage or current applied to the second main resonator 3 should be between the anchor point 3 3-1 and the anchor point 4 3-5. When the coupling structure 2 is a low-resistivity material, the voltage or current applied to the first main resonator 1 and the second main resonator 3 should be between the anchor point 2 1-5 and the anchor point 4 3-5.

[0024] like Figure 2 As shown, the first main resonator 1 and the second main resonator 3 themselves preferably work in the anti-phase tensile mode (vibration beam 1-2 and vibration beam 2 3-2 vibrate in opposite directions), and the weak coupling resonator composed of the two preferably works in the anti-phase mode (vibration beams at the same position of the two main resonators vibrate in opposite directions). In order to increase the sensitivity of the weak coupling resonator to temperature, the weak coupling resonator is mainly made of silicon material, and the degree of thermal expansion mismatch is increased by covering with a multi-layer composite material. When measuring low air pressure, the weakly coupled resonator works in a resonant state, and the heat conduction body connected to it is directly sensitive to the pressure to be measured. The temperatures T1 and T2 of the heat conduction body are monotonically related to the pressure. On the one hand, the thermal conductivity of metal and silicon materials is relatively high, so the temperatures T1 and T2 will be quickly transmitted to the weakly coupled resonator, causing the output of the weakly coupled resonator to change through thermal stress. On the other hand, the heat conduction body itself will also be deformed due to heat, and the deformation will stretch or compress the weakly coupled resonator, thereby causing the axial stresses σ1 and σ2 to change, and further change the output of the weakly coupled resonator, thereby achieving sensitization (increasing sensitivity) of the traditional Pirani heat conduction method.

[0025] This embodiment combines a heat conduction body with a weakly coupled resonator, and uses the heat conduction body to generate thermal stress that changes with pressure, providing a stress or stiffness disturbance source for the weakly coupled resonator, inducing a change in the equivalent stiffness of the resonator. The weakly coupled resonator further amplifies the influence of the stress or stiffness disturbance, thereby achieving high-sensitivity measurement under medium vacuum pressure and expanding the lower limit of measurement.

[0026] The temperature characteristics of the first main resonator 1 and the second main resonator 3 are inconsistent, that is, T1≠T2 and σ1≠σ2 in the weakly coupled resonator system. This design can effectively reduce the impact of common-mode interference and further increase sensitivity. When measuring higher air pressure, the weakly coupled resonator no longer vibrates, and the sensor works in the same state as the traditional Pirani vacuum sensor. The weakly coupled resonator and the heat conduction body are sensitive to the pressure to be measured. In this way, the sensor can measure a wide range of vacuum pressures, and has higher resolution, sensitivity and accuracy than the traditional Pirani structure when measuring low pressure.

[0027] This enhanced-sensitivity pressure sensor integrates the sensitive principle at the structural level rather than the functional stacking in the traditional solution, which can improve the sensitivity of the sensor under medium vacuum pressure, thereby improving key indicators such as resolution and accuracy within the pressure range, and can achieve high sensitivity and high accuracy measurement of medium and low vacuum pressures with the same sensitive core without sacrificing the test range of the traditional Pirani vacuum gauge.

[0028] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A sensitivity-enhanced pressure sensor based on a weakly coupled resonator, comprising a weakly coupled resonator and a heat conduction body, characterized in that: The weakly coupled resonator is connected to the heat conducting body, the heat conducting body is bent and spiraled, each main resonator of the weakly coupled resonator is composed of different materials, and each main resonator and its attached heat conducting body are composed of the same material.

2. The sensitivity-enhanced pressure sensor based on weakly coupled resonator according to claim 1, characterized in that: The material is a single layer or multiple layers, and the thermal expansion coefficients of the multiple layers are different.

3. The sensitivity-enhanced pressure sensor based on weakly coupled resonator according to claim 2 is characterized in that: The multilayer material includes a metal layer, a silicon layer, an insulating layer and a substrate layer from top to bottom, the metal layer includes nickel and platinum, the silicon layer includes single crystal silicon, the insulating layer is glass or silicon, and the substrate layer is one of silicon, glass and ceramic.

4. The sensitivity-enhanced pressure sensor based on weakly coupled resonator according to claim 1, characterized in that: The plurality of main resonators are connected via a coupling structure, the coupling structure is a single-layer material, and the single-layer material is a low-resistivity material or a high-resistivity material.

5. The sensitivity-enhanced pressure sensor based on weakly coupled resonator according to claim 3 is characterized in that: The main resonator includes a vibration beam, a fixed electrode and an anchor point, the two ends of the weakly coupled resonator are fixed on the substrate layer through the anchor point, one end of the main resonator is connected to the anchor point through the heat conduction body, two parallel vibration beams are installed on the main resonator, the vibration beams vibrate in the same phase or in opposite phases, the fixed electrodes are arranged above and below the vibration beam, and the fixed electrodes are fixed on the substrate layer.

Images