A sensitivity-enhanced pressure sensor based on weakly coupled resonators

Abstract

The present invention provides a sensitivity-enhanced pressure sensor based on weakly coupled resonators, which includes a weakly coupled resonator and a heat conduction body. The weakly coupled resonator is connected to the heat conduction body. The heat conduction body is arranged in a curved and coiled manner. Each main resonator of the weakly coupled resonator is composed of different materials, and each of the main resonators and its attached heat conduction body are composed of the same material. This pressure sensor organically combines a Pirani vacuum gauge and a weakly coupled resonator. The stress sensed by the weakly coupled resonator comes from the thermal stress generated by the heat conduction body, providing a stiffness perturbation for the weakly coupled resonator to realize the measurement of vacuum pressure, expand the measurement lower limit and improve the comprehensive performance. Moreover, without sacrificing the test range of the Pirani vacuum gauge, it can realize the measurement of medium and low vacuum pressure by the same sensitive core body, and the measurement range can be extended to near atmospheric pressure.

Description

Technical Field

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

[0002] Thermal conduction vacuum gauges are a type of sensors widely used for monitoring vacuum pressure. The most classic one is the Pirani vacuum gauge, whose basic principle is that the heat dissipation / thermal conduction speed of a powered metal wire (usually made of metals such as nickel or platinum) is different under different air pressure environments, so the electric current for maintaining the constant temperature of the metal wire is different. Existing Pirani vacuum gauges can sense pressures from atmospheric pressure (10 5 Pa) to 10 -2 Pa. However, it is difficult to guarantee the sensitivity and accuracy in the medium vacuum pressure range (<100 Pa, >10 -2 Pa), and it is also difficult to further lower the measurement lower limit. Existing published patents such as CN201310070529 and CN202311533623 combine the Pirani with sensitive cores based on other principles such as piezoresistance and single resonators to improve the comprehensive effect of pressure measurement. However, they can only optimize the low vacuum measurement indicators and cannot improve the performance of the sensor in the medium vacuum pressure range, resulting in low detection accuracy and sensitivity in the medium vacuum pressure range. In addition, the traditional method of optimizing the structural parameters of the Pirani also has very limited expansion of the lower limit of the measurement range.

[0003] Weakly coupled resonant sensors are a type of new resonant sensors that use weakly coupled resonators to improve the sensitivity of the sensor to changes in stiffness, and are expected to improve the measurement lower limit and resolution of the sensor. A weakly coupled resonator is a multi-degree-of-freedom resonator formed by coupling multiple single-body resonators with similar fundamental frequencies through a connection structure. When the coupling stiffness of the connection structure is much lower than (usually not greater than 0.1 times) the stiffness of the single-body resonator, this 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 extensive research has also been carried out on the measurement of pressure. However, existing research shows that it is difficult to further expand the lower limit of vacuum sensors based on membrane strain and weakly coupled resonators, such as the solutions based on pressure-sensitive membranes and weakly coupled resonators described in Chinese patents CN201910893549, CN202210759226, and CN202410056171. The main reason is that further reducing the measurement lower limit in this solution must rely on thinner and larger pressure-sensitive membranes and resonators with smaller cross-sectional areas, which have extremely strict requirements on the manufacturing process error and are difficult to achieve. Summary of the Invention

[0004] To solve the problems of the above-mentioned existing technologies, an embodiment of the present invention provides a sensitivity-enhanced pressure sensor based on a weakly coupled resonator, which organically combines a Pirani vacuum gauge and a weakly coupled resonator. The stress source sensed by the weakly coupled resonator is no longer membrane strain but thermal stress generated by unbalanced heat conduction, providing a stiffness perturbation to the weakly coupled resonator, realizing the measurement of vacuum pressure, and improving the comprehensive performance of medium vacuum pressure measurement.

[0005] The object of the present invention can be achieved by 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, the weakly coupled resonator is connected to the heat conduction body, the heat conduction body is bent and spirally arranged, and each main resonator of the weakly coupled resonator is composed of different materials, and each of the main resonators and its attached heat conduction body are composed of the same material.

[0006] Preferably, the material is single-layer or multi-layer, and the thermal expansion coefficients between the multi-layers are different.

[0007] Preferably, the multi-layer material sequentially 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-crystalline silicon, the insulating layer is glass or silicon, and the substrate layer is one of silicon, glass, and ceramic.

[0008] Preferably, multiple main resonators are connected by 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 vibrating beam, a fixed electrode, and an anchor point. Both 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 vibrating beams are installed on the main resonator, and the vibrating beams vibrate in phase or anti-phase. Fixed electrodes are arranged above and below the vibrating beams, and the fixed electrodes are fixed on the substrate layer.

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

[0011] As can be seen from the above solution, the embodiment of the present invention provides a sensitivity-enhanced pressure sensor based on a weakly coupled resonator, which organically combines a Pirani vacuum gauge and a weakly coupled resonator. The stress source sensed by the weakly coupled resonator is no longer membrane strain but thermal stress generated by the heat conduction of the Pirani vacuum gauge. A layer of metal or other material with a large difference in thermal conductivity from single-crystalline silicon is covered on the surface of the weakly coupled resonator and the heat conduction body. At this time, when a voltage is applied to the resonator and the heat conduction body, the self-temperature of the heat conduction body will change with the measured pressure due to its heat conduction ability, and at the same time, this temperature will change the self-thermal stress of the resonator, thereby providing a stiffness perturbation for the weakly coupled resonator. Under the action of the weakly coupled resonator, this stress will be highly sensitively sensed, so as to realize the measurement of vacuum pressure, expand the measurement lower limit and improve the comprehensive performance. In addition, when the vacuum pressure is large, the resonator will no longer vibrate. At this time, it is similar to a traditional MEMS heat conduction vacuum gauge and only senses pressure through heat conduction, thereby expanding the measurement upper limit to near atmospheric pressure. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0013] Figure 2 FIG. shows a schematic diagram of 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 FIG. shows a longitudinal sectional view of a first main resonator, a second main resonator and a heat conduction body according to an embodiment of the present invention.

[0015] In the figure, 1 is the first main resonator; 1-1 is the first anchor point; 1-2 is the first vibrating beam; 1-3 is the first fixed electrode; 1-4 is the first heat conduction body; 1-5 is the second anchor point; 2 is the coupling structure; 3 is the second main resonator, 3-1 is the third anchor point; 3-2 is the second vibrating beam; 3-3 is the second fixed electrode; 3-4 is the second heat conduction body; 3-5 is the fourth anchor point. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0017] Embodiment

[0018] As Figures 1 to 3As shown in the figure, a sensitivity-enhanced pressure sensor based on a weakly coupled resonator in this embodiment includes a weakly coupled resonator, where 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 resonators that make up the weakly coupled resonator can be main resonators of any structure and any normally operating resonance modes, such as torsional pendulum resonators and bulk acoustic wave resonators, etc., and their specific resonance modes such as torsional pendulum modes. The degree of freedom of the weakly coupled resonator can also be greater than 2. In this 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 made of multi-layer (not less than two layers) materials or single-layer materials. Their geometric parameters are the same, but the number of material layers or material properties are different.

[0019] As Figure 3 As shown in the figure, the first main resonator 1, the second main resonator 3, and the heat conduction main body successively 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 and is single-crystalline silicon with medium resistivity or low resistivity. The lower substrate layer 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, etc., the insulating layer can be glass or silicon. The upper side is a metal layer, and the metal layer includes nickel and platinum, but is not limited to nickel and platinum, and is used to adjust the heat conduction characteristics of the main body of the sensitive structure. The purpose of the different number of material layers or material properties of the first main resonator 1 and its attached heat conduction main body 1-5 and the second main resonator 3 and its attached heat conduction main body 3-5 is to ensure different stiffness perturbation amounts of the resonator induced by different measured pressures.

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

[0021] The first main resonator 1 is fixed on the substrate through the first anchor 1-1, and the first 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 vibration signals. The first main resonator 1 has two vibration beams 1-2 arranged in parallel. In the resonant state, they can vibrate in phase or out of phase, which is collectively referred to as the tensile mode of the first resonator 1. One end of the first heat conduction body 1-4 is connected to the end of the first main resonator 1, and the other end is fixed on the substrate through the second anchor 1-5. The first heat conduction body 1-4 is also composed of a multi-layer material composite, and the material composition is the same as that of the first main resonator 1. The bent and coiled first heat conduction body 1-4 can amplify the heat conduction effect of this body, and the number, length and cross-sectional area of the bent and folded parts can be optimized to achieve the best effect. On the one hand, the temperature of the vibration beam 1-2 and the first heat conduction body 1-4 themselves will change with the measured pressure due to the heat conduction effect. On the other hand, the thermal expansion coefficients of the multi-layer composite materials of the first main resonator 1 are different from each other, resulting in a large influence of temperature on its 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 measured pressure, that is, the influence of the measured pressure is converted into the stiffness perturbation 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 third anchor 3-1. The second fixed electrode 3-3 is also fixed on the substrate, which is used to provide an electrostatic driving force for the second main resonator 3 or pick up vibration signals. The two vibration beams 3-2 can operate in the in-phase vibration or out-of-phase vibration mode. One end of the second heat conduction body 3-4 is connected to the end of the second main resonator 3, and the other end is fixed on the substrate through the fourth anchor 3-5. The second heat conduction body 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 first heat conduction body 1-4. Thus, the axial stress of the second main resonator 3 will also change with the change of the measured pressure, but the change rate (i.e., sensitivity) is different from that of the first resonator 1. In addition, if the second main resonator 3 has no second heat conduction body 3-5 and the second main resonator 3 itself does not have heat conduction properties, 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 the equivalent stiffness of the coupling structure 2 is much smaller (but not zero) than that of 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 first anchor point 1-1 and the second anchor point 1-5, and the voltage or current applied to the second main resonator 3 should be between the third anchor point 3-1 and the fourth anchor point 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 second anchor point 1-5 and the fourth anchor point 3-5.

[0024] As Figure 2 shown, the first main resonator 1 and the second main resonator 3 preferably operate in an anti-phase stretching mode (the vibrating beam 1-2 and the vibrating beam 3-2 vibrate in opposite directions), and the weakly coupled resonator composed of the two also preferably operates in an anti-phase mode (the vibrating beams at the same position of the two main resonators vibrate in opposite directions). To increase the temperature sensitivity of the weakly coupled resonator, the weakly coupled resonator is mainly made of silicon material, and the method of covering with a multi-layer composite material is used to increase the degree of thermal expansion mismatch. When measuring low pressure, the weakly coupled resonator operates in a resonant state, and the directly sensitive pressure to be measured is provided by the heat conduction body connected thereto. The temperatures T1 and T2 of the heat conduction body have a monotonic functional relationship with the pressure. On the one hand, the thermal conductivities of both the metal and silicon materials are relatively high, so the temperatures T1 and T2 will be quickly conducted to the weakly coupled resonator, and the output of the weakly coupled resonator will change through the way of thermal stress. On the other hand, the heat conduction body itself will also deform due to heat, and the deformation amount will stretch or compress the weakly coupled resonator, resulting in changes in the axial stresses σ1 and σ2, and further changing the output of the weakly coupled resonator. In this way, the sensitivity of the traditional Pirani heat conduction method is increased (increased sensitivity).

[0025] In this embodiment, the heat conduction body is combined with the weakly coupled resonator, and the thermal stress generated by the heat conduction body that changes with the pressure is used to provide a stress or stiffness perturbation 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 perturbation, so as to realize high-sensitivity measurement under medium vacuum pressure and the expansion of the measurement lower limit.

[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 influence of common-mode interference and further increase the sensitivity. When measuring a relatively high air pressure, the weakly coupled resonator stops vibrating, and the sensor operates in the same state as a traditional Pirani vacuum sensor. The weakly coupled resonator and the heat conduction body are sensitive to the pressure to be measured together. In this way, the sensor can measure the vacuum pressure in a wide range, and has higher resolution, sensitivity and accuracy than the traditional Pirani structure when measuring low pressure.

[0027] This sensitivity-enhanced pressure sensor integrates the sensing principle at the structural level, rather than the function 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 in the pressure range. And it 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 the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A sensitivity-enhanced pressure sensor based on weakly coupled resonators, comprising a weakly coupled resonator and a heat conduction body, characterized in that, The weakly coupled resonator is connected to the heat conduction body, the heat conduction body is bent and coiled, each main resonator of the weakly coupled resonator is composed of different materials, and each of the main resonators and its attached heat conduction body are composed of the same material; The material is multi-layered, and the coefficients of thermal expansion between the multi-layers are different; The multi-layer material sequentially 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-crystalline silicon, the insulating layer is glass or silicon, and the substrate layer is one of silicon, glass, and ceramic; Multiple main resonators are connected by 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; The main resonator includes a vibrating beam, a fixed electrode, and an anchor point. Both ends of the weakly coupled resonator are fixed on the substrate layer through the anchor points. One end of the main resonator is connected to the anchor point through the heat conduction body. Two parallelly arranged vibrating beams are installed on the main resonator. The vibrating beams vibrate in phase or out of phase. Fixed electrodes are arranged above and below the vibrating beams, and the fixed electrodes are fixed on the substrate layer.

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