CN108489577B

CN108489577B - Micro-mass sensor

Info

Publication number: CN108489577B
Application number: CN201810253647.3A
Authority: CN
Inventors: 李凯; 彭志辉
Original assignee: Wenzhou University
Current assignee: Wenzhou University
Priority date: 2018-03-26
Filing date: 2018-03-26
Publication date: 2020-02-07
Anticipated expiration: 2038-03-26
Also published as: CN108489577A

Abstract

A micro mass sensor. The variable capacitance vibration device comprises a substrate, a fixed electrode and an adsorption layer, wherein the fixed electrode and the adsorption layer are arranged on the substrate, a vibration structure is further arranged on the substrate and comprises a metal movable plate, a supporting beam and anchor points of the beam, the metal movable plate is connected with the supporting beam and fixed on the substrate through the anchor points, and the metal movable plate is simultaneously used as a movable electrode and forms a variable capacitance with the fixed electrode. The invention works by utilizing the principle that the vibration frequency of a vibration structure is changed after a micro-mass substance is adsorbed on the vibration structure. The movable plate and the support beam form a vibration structure, so that the influence of the position of a micro-mass substance on the vibration structure on a measurement result can be effectively inhibited; the metal movable plate is used as the moving electrode, so that the area is large, the electrostatic driving force on the moving electrode is favorably improved, the capacitance value between the moving electrode and the fixed electrode is favorably improved, and the anti-interference performance of the sensor is favorably improved.

Description

Micro-mass sensor

Technical Field

The invention relates to the field of sensors, in particular to a micro-mass sensor which is formed by a circular plate and a supporting beam to form a vibration structure and is based on vibration frequency measurement and electrostatic driving.

Background

The micro-quality detection technology has important application significance in the fields of environmental monitoring, biomedicine and the like. The vibration frequency of the vibrating body is very sensitive to mass changes, so that detection of micro-masses can be achieved on the basis thereof. Through the search of domestic and foreign documents, the vibration structure of the existing electrostatic driving micro-mass sensor based on vibration frequency measurement is mainly a beam structure, and also has a plate structure respectively. The domestic and foreign documents show that, because the whole beam structure or plate structure deforms during working, if micro-mass substances are adsorbed on the structures sporadically in a particle form or are unevenly distributed on the structures, the random positions of the micro-mass substances can obviously influence the vibration frequency and further influence the measurement accuracy of the micro-mass. In addition, the beam structure has a small electrostatic driving force due to the limited electrode area which can be arranged, the generated amplitude is weak, which is not favorable for detection and is easily interfered by external mechanical loads, and when vibration information is extracted in a capacitance detection mode, the capacitance value between electrodes is small due to the small electrode area, which is easily interfered by stray capacitance and the like; the plate structure also has the disadvantage of weak amplitude due to high rigidity.

Disclosure of Invention

In order to solve the problems in the background art, the invention provides a micro mass sensor based on vibration frequency measurement and electrostatic driving, which is insensitive to the distribution position of micro-substances on a vibration structure and has high sensitivity and high anti-interference performance.

The technical scheme adopted by the invention for solving the technical problems is as follows: a micro mass sensor, comprising: the vibration structure comprises a metal movable plate, a supporting beam and anchor points of the beam, wherein the metal movable plate is connected with the supporting beam and is fixed on the substrate through the anchor points.

The metal movable plate is simultaneously used as a movable electrode and forms a variable capacitor with the fixed electrode.

The adsorption layer is located on the upper surface of the metal movable plate.

The fixed electrode is covered with a first insulating layer, and a second insulating layer is arranged between the metal movable plate and the adsorption layer.

The metal movable plate is a rigid circular plate.

The supporting beam, the anchor points and the rigid circular plate form an integrated combined structure and are made of metal materials.

When the sensor is in a working state, the metal movable plate only moves in a translation mode, and only the supporting beam deforms.

The supporting beam is a variable-section beam, and the sectional area of the fixed support position of the supporting beam is the largest.

The vibrating structure is driven by electrostatic force.

Any one of the movable electrode and the fixed electrode is grounded and is simultaneously connected to the driving circuit and the detection circuit. When the other electrode is used for detecting the micro-mass, a driving voltage is firstly applied to enable the circular plate-beam structure to vibrate, and then the electrode is connected to a capacitance detection circuit.

The invention has the beneficial effects that: the vibration structure adopts a plate-beam structure, the metal movable plate is simultaneously used as a moving electrode and only does translational motion when in work, is insensitive to the position of the measured micro-mass substance on the vibration structure and continuously keeps high sensitivity to the micro-mass, has larger electrostatic driving power, can generate stronger vibration and is beneficial to inhibiting the interference of external mechanical load, and the electrodes have larger capacitance value and are beneficial to detecting vibration signals and inhibiting the interference of stray capacitance.

Description of the drawings:

fig. 1 is a cross-sectional view of an embodiment of the present invention (in order to clearly reflect the structure of the device, the ratio of the dimensions in the height direction in the drawing is greatly different from the actual situation, the same applies below).

Fig. 2 is a cross-sectional view of the inventive structure in the direction a-a of fig. 1.

Figure 3 is a rigid circular plate-variable cross section beam structure.

Detailed Description

The embodiments of the invention will be further described with reference to the accompanying drawings in which:

in an embodiment of the present invention, a micro mass sensor includes: the vibration structure comprises a substrate 1, a fixed electrode 2 and an adsorption layer 8, wherein the fixed electrode 2 and the adsorption layer 8 are arranged on the substrate 1, a first insulation layer 3 covers the fixed electrode, a vibration structure is further arranged on the substrate 1 and comprises a metal movable plate 6, a supporting beam 5 and an anchor point 4 of the beam, the metal movable plate 6 is connected with the supporting beam 5, and the metal movable plate is fixed on the substrate 1 through the anchor point 4.

The metal movable plate 6 is a rigid circular plate, and the support beams are uniformly distributed on the edge of the metal movable plate 6. Since the maximum bending stress of the plate-beam structure occurs at the clamped end of the beam, the beam is a variable cross-section beam and the sectional area of the clamped end is large. The adsorption layer 8 is positioned on the upper surface of the metal movable plate 6, and because the adsorption layer of some substances is made of metal, the insulating layer 7 is laid between the adsorption layer 8 and the metal movable plate 6, the adsorption layer technology is widely used in sensors in the fields of biology, chemistry and the like, and the specific materials used in the invention need to be different according to the different substances with the measured micro-mass.

The vibration structure of the micro-mass sensor is composed of a metal movable plate 6 and a supporting beam 5 (the insulating layer 7 and the adsorption layer 8 have very little influence on the vibration of the plate-beam structure due to small thickness), the rigidity of the plate-beam structure can be adjusted in a large range by changing the number and the size of the supporting beams, and therefore the vibration frequency of the structure can be adjusted in a large range, so that the structure can be applied to the detection of micro-masses with different orders of magnitude, and the requirements of different fields are met.

The metal movable plate 6, the support beam 5 and the anchor points 4 are made of metal materials, the metal movable plate 6 is used as a movable electrode, the fixed electrode 2 is positioned on an insulating substrate, an insulating layer covers the fixed electrode to prevent the fixed electrode from short circuit, and the metal movable plate 6 and the fixed electrode 2 form a variable capacitor.

The measured micro-mass substance is adsorbed on the rigid circular plate without deformation, and all the supporting beams are uniformly distributed on the edge of the circular plate, and finite element simulation calculation shows that the adsorption position of the micro-mass substance has very little influence on the vibration frequency of the rigid circular plate-beam structure.

Because the movable electrode is arranged on the plate and only does translational motion compared with the fixed electrode, compared with the condition that the movable electrode is arranged on the beam, the plate-beam structure has larger electrode area and can generate larger electrostatic force, and in addition, the existence of the supporting beam also enables the rigidity of the plate-beam structure to be lower than that of the common plate structure, so that the amplitude of the plate-beam structure driven by the electrostatic force is larger, thereby not only reducing the interference of external mechanical load on vibration, but also being capable of maintaining stronger vibration for a longer time after the driving voltage is removed. In addition, the larger electrode area also enables the capacitance between the movable electrode and the fixed electrode to be larger, thereby further ensuring that the capacitance change caused by vibration can be measured in a longer time after the driving voltage is removed, and being beneficial to inhibiting the interference of stray capacitance to measurement.

One of the moving and fixed electrodes is grounded and connected to the driving circuit and the detecting circuit simultaneously. When the other electrode is used for detecting the micro-mass, firstly, a driving voltage is applied to enable the circular plate-beam structure to vibrate, then the electrode is connected to a capacitance detection circuit, at the moment, the vibration structure still continues to move due to inertia until the amplitude is attenuated to zero, and finally, a vibration frequency value can be obtained by detecting the capacitance change between the movable electrode and the fixed electrode and processing the capacitance change through a filtering circuit, a shaping circuit and a counting circuit. After the substances with different masses are adsorbed on the metal movable plate, different changes of the mass of the vibrating body are caused, and further different changes of the vibration frequency are caused, so that the mass of the adsorbed substances can be obtained according to the vibration frequency.

With conventional micro-processing equipment, the processing technology of the embodiment can have various schemes, and the following is one of the main steps: firstly, a fixed electrode 2 is processed on a substrate 1 by adopting a sputtering process, then an insulating layer 3 is processed on the fixed electrode by adopting the sputtering process again, then a metal movable plate 6, a beam 5 and anchor points 4 thereof are processed by adopting an electroforming and sacrificial layer process, an insulating layer 7 is processed by adopting the sputtering process, and an adsorption layer 8 is processed on the insulating layer by adopting the sputtering process.

The skilled person should understand that: although the invention has been described in terms of the above specific embodiments, the inventive concept is not limited thereto and any modification applying the inventive concept is intended to be included within the scope of the patent claims.

Claims

1. A micro mass sensor, comprising: substrate (1), locate deciding electrode (2), adsorbed layer (8) on substrate (1), its characterized in that: the sensor is characterized in that the substrate (1) is also provided with a vibration structure, the vibration structure comprises a metal movable plate (6), a supporting beam (5) and an anchor point (4) of the beam, the metal movable plate (6) is connected with the supporting beam (5) and is fixed on the substrate (1) through the anchor point (4), the metal movable plate (6) is simultaneously used as a movable electrode and forms a variable capacitor with the fixed electrode (2), the metal movable plate (6) is a rigid circular plate, when the sensor is in a working state, the metal movable plate (6) only makes translational motion because the rigidity is far larger than that of the supporting beam (5), only the supporting beam (5) deforms, any one of the fixed electrode and the movable electrode is grounded and simultaneously connected to the driving circuit and the detection circuit, and the other electrode firstly applies driving voltage to enable the vibration structure to vibrate through electrostatic force when detecting the micro-mass and then is connected to the, the supporting beam (5) and the anchor point (4) thereof and the rigid circular plate form an integrated combined structure which is also made of metal materials.

2. The micro mass sensor of claim 1, wherein: the adsorption layer (8) is positioned on the upper surface of the metal movable plate (6).

3. The micro mass sensor of claim 1, wherein: the fixed electrode (2) is covered with a first insulating layer (3), and a second insulating layer (7) is arranged between the metal movable plate (6) and the adsorption layer (8).

4. The micro mass sensor of claim 1, wherein: the supporting beam (5) is a variable cross-section beam, and the cross section area of the fixed support position of the supporting beam is the largest.