CN102052989B - Capacitive pressure sensor with high Q value and large relative change - Google Patents

Abstract

The invention discloses a capacitive pressure sensor for wireless passive measurement. The capacitor is composed of elastic vibrating diaphragms fixed around the periphery. By adjusting the ratio of the radius of the circular electrode to the vibrating diaphragm, setting insulating bumps and other means, the The vibrating diaphragm is in a state of large strain, and the ratio of the maximum capacitance to the initial capacitance is as large as possible, so that the capacitance can achieve the purpose of large relative change and high Q value. After the capacitive pressure sensor with high Q value and large relative capacitance variation of the present invention is connected with a surface acoustic wave transmitter, high-precision wireless passive measurement of pressure can be realized, and the sensor can be used in the field of automobile tire pressure monitoring.

Description

Capacitive pressure sensor with high Q value and large relative change

Technical field:

The invention belongs to the technical field of pressure monitoring, and in particular relates to a pressure sensor suitable for passive wireless sensing, especially a capacitive pressure sensor with variable pole distance.

technical background:

Sensors that work in a passive wireless manner are suitable for harsh working environments, such as high temperature, heavy pollution, strong interference, etc., as well as various physical, chemical or biological conditions that are not suitable for wiring and battery-provided energy on rotating and moving objects Quantity measurement. There are mainly two types of sensors working in a passive wireless manner in the prior art: LC resonance type and SAW (surface acoustic wave) type. The former generally adopts a capacitive sensor, takes the resonant frequency as the measurement quantity, and realizes energy and information transmission by inductive coupling, and adapts to a shorter working distance.

The latter utilizes the characteristics of SAW components (including resonators and delay lines) such as small size, light weight, high operating frequency, and low insertion loss. The SAW component itself can be used as a sensing element, or the SAW component can be used as a transmission channel and a traditional impedance sensor. Together to achieve passive wireless sensing. The combination of SAW components and traditional impedance sensors can enable traditional impedance sensors to work in a passive wireless manner to achieve long-distance data transmission, and can expand the application field of SAW sensors.

The passive wireless sensor based on SAW components has two requirements for the impedance load sensor: one is a high quality factor, and the other is that its value, such as capacitance, has a large relative change.

Chinese patent document CN1127354A discloses a capacitive pressure or differential pressure sensor, comprising a substrate made of ceramic material, on one side thereof an electrode and a glass layer made of raw glass material; a membrane made of ceramic material The diaphragm is bonded and pressure sealed to the substrate by the raw glass frit acting as a spacer layer which holds the diaphragm and the substrate at a distance to form a cavity. This invention patent is used to solve the short circuit problem of the capacitive pressure sensor.

Chinese patent document CN1334451A discloses a ceramic pressure sensor and a differential pressure sensor, the base and the diaphragm are made of the same ceramic material, air holes are arranged on the base, and the corresponding surfaces of the base and the diaphragm are respectively provided with surface-covered inorganic materials for insulation The electrodes of the first layer, the periphery of the base and the diaphragm are all provided with a circle of bosses with inorganic materials, and the middle of the corresponding surfaces of the bosses is sealed with a sealing glass layer. The insulating layer covering the electrodes plays the role of preventing short circuit and overload.

The above-mentioned patent documents cover the electrode with an insulating material layer to solve the problem of electrode short circuit, but it also produces the problem that the deformation of the vibrating membrane is reduced under the action of external pressure, that is, the existence of the insulating layer increases the thickness of the vibrating membrane, Reduce the deformation under the same external force.

In addition, none of the above patent documents pay attention to the relative variation of capacitance and the Q value.

Invention content:

The purpose of the present invention is not only to provide a ceramic capacitive pressure sensor with small creep, fast response, good temperature stability, corrosion resistance, anti-interference, anti-overload, and high precision, but also to provide a high Q value and Ceramic capacitive pressure sensor with large relative capacitance change.

The ceramic capacitive pressure sensor provided by the invention comprises a circular elastic vibrating diaphragm, a sealing ring, bumps of insulating material, a circular metal film electrode, lead-out wires of the inner metal film of the electrode and an outer metal film electrode.

In the present invention, the capacitor is composed of elastic vibrating diaphragms fixed around the periphery, and the vibrating diaphragm is placed in a state of large strain (the ratio of the minimum distance to the initial distance is less than 0.99), the ratio of the maximum capacitance to the initial capacitance is as large as possible, so that the capacitance can achieve a large relative change.

The concrete technical scheme adopted for realizing the object of the present invention is:

A capacitive pressure sensor, comprising two circular elastic vibrating diaphragms, a ring made of sealing material, two circular metal film electrodes, lead-out wires of the inner metal film of the electrodes and an outer metal film electrode, the two circular elastic vibration The outer edge of the diaphragm is bonded together by a ring made of the sealing material to form an elastic film with a cavity inside and a fixed support around the periphery. The two circular metal film electrodes are respectively arranged on two circular elastic diaphragms On the inner side of the chip, the inner metal film lead wire of the electrode is buried in the middle of the ring made of sealing material, and is used to connect the circular metal film electrode and the outer metal film electrode. One end of the outer metal film electrode is set on the sealing material. On the ring made of connecting material, it is connected with the lead-out line of the metal film in the electrode, and the other end is exposed as the lead-out line of the whole sensor. It is characterized in that the radius of the metal film circular electrode is smaller than the radius of the circular elastic vibrating diaphragm , so that the sensor can work in a large strain state. In addition, the capacitive pressure sensor also includes a plurality of insulating material bumps, which are evenly arranged on one of the two circular elastic diaphragms and/or the circular metal film On the electrode, it is used to prevent short circuit of the electrode and play the role of overload protection.

As a further improvement of the present invention, the material of the circular elastic vibrating diaphragm is alumina ceramics.

As a further improvement of the present invention, the sealing material is low temperature glass.

The bumps made of the insulating material play the role of preventing electrode short circuit and overload protection. Due to the discrete distribution of several points, its influence on the strain of the vibrating membrane is negligible compared with that of the insulating layer, which overcomes the influence of the insulating layer covering the electrodes on the deformation of the vibrating membrane in the aforementioned patent.

The capacitive electrodes and inner and outer leads of the ceramic capacitive pressure sensor are made by thick film technology, such as screen printing technology and metal film calendering technology (such as rolled copper foil with a thickness of 12 microns); the inner and outer leads are soldered without solder , such as ultrasonic metal welding. The wide and thick film and solid flux-free bonding plane not only ensure that the capacitor can have a high quality factor Q, but also provide convenience for subsequent processes such as screen printing sealing layer.

The above technical solution can obtain short-circuit and overload protection measures that have little influence on the strain of the vibrating membrane, and at the same time obtain a higher quality factor and a larger relative capacitance change, and meet the requirements of a passive wireless sensor system based on SAW components.

Description of drawings

Figure 1 is a schematic diagram of the force of the double vibrating membrane structure;

Fig. 2 is the relationship between the maximum capacitance and the initial capacitance of the capacitive pressure sensor;

Fig. 3 is a side view of the present invention; Fig. 4 is a top view of Fig. 3;

The same reference numerals in Figs. 3 and 4 represent the same parts of the sensor. The names of the parts corresponding to the labels are:

1 circular elastic diaphragm

2 circular elastic diaphragm or base

3,4 Rings made of sealing material

5, 6 circular metal film electrodes

7, 8 electrode inner metal film lead wire

9, 10 outer metal film electrode

11 bumps of insulating material

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

The capacitive pressure sensor of the present invention comprises a circular elastic vibrating diaphragm 1, a circular elastic vibrating diaphragm or base 2, rings 3 and 4 made of sealing materials, circular metal film electrodes 5 and 6, metal film leads in the electrodes Lines 7 and 8, outer metal film electrodes 9 and 10, and a plurality of insulating material bumps 11

The circular elastic vibrating diaphragm 1, the circular elastic vibrating diaphragm or the base 2 adopts a bonding process so that its edges are bonded to the sealing rings 3, 4 to form an elastic film fixed around the periphery, as a detection Deformable parts under pressure. Diaphragm materials include, but are not limited to, alumina ceramics.

The circular rings 3 and 4 made of the sealing material are located between the circular elastic vibrating membranes 1 and 2 and are used to fix the edges of the vibrating membranes 1 and 2 . Sealing materials include but are not limited to cryogenic glass.

The circular metal film electrode 5 is arranged inside the circular elastic vibrating diaphragm 1, and the circular metal film electrode 6 is arranged on the inner side of the circular elastic vibrating diaphragm or the base 2, and is used as an electrode of a capacitor, wherein the metal film circular The radius of the shaped electrode is smaller than the radius of the circular elastic vibrating diaphragm.

The lead-out wires 7 and 8 of the inner metal film of the electrodes are buried in the middle of the rings 3 and 4 made of sealing materials before sintering during manufacture, and are used to connect the circular metal film electrodes 5 and 6 and the outer metal film electrodes 9 and 10 . Metal film lead-out wires 7 and 8 in the electrode are made of thick metal film.

One end of the outer metal film electrodes 9 and 10 is arranged in the middle of the rings 3 and 4 made of sealing material to connect with the lead wires 7 and 8 of the inner metal film of the electrodes, and the other end is exposed as the lead wire of the whole sensor.

The plurality of bumps 11 of insulating material are arranged on one of the two circular elastic vibrating diaphragms or the supporting circular metal film electrode. The bumps (Figs. 3 and 4) made of the insulating material play the role of preventing electrode short circuit and overload protection. Due to the discrete distribution of several points, its influence on the strain of the vibrating membrane is negligible compared with that of the insulating layer, which overcomes the influence of the insulating layer covering the electrodes on the deformation of the vibrating membrane.

When the external pressure changes, the circular elastic vibrating diaphragm 1 and the circular elastic vibrating diaphragm or base 2 are deformed, and since both ends are fixed on the rings 3 and 4 made of sealing materials, the middle part is deformed At a maximum, the deformation decreases away from the center of the diaphragm and decreases to zero at the fixed edges. The circular elastic vibrating diaphragm 1 and the circular elastic vibrating diaphragm or the substrate 2 are in a working state with a large deformation, so that a relatively large relative change in capacitance can be obtained, thereby expanding the measuring range of the sensor. The provided bumps 11 of insulating material can prevent excessive deformation of the vibrating membranes 1 and 2 or short circuit of the electrodes due to contact. With the deformation of 1 and 2, the distance between the circular metal film electrodes 5 and 6 attached to 1 and 2 also changes, so the capacitance between them also changes accordingly. The inner metal film leads 7, 8 lead out to the outer metal film electrodes 9, 10, and are connected to the external surface acoustic wave sensor for measurement.

Wherein, the reason why the radius of the circular electrode needs to be smaller than the radius of the vibrating membrane is that the thin-plate-type elastic vibrating membrane supported around the periphery has the largest deflection _d0 at the center point under the action of external force, and the farther away from the center, the smaller the deflection, as shown in the formula (1) shown.

$\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where a is the radius of the vibrating membrane, and r is the distance from the investigation point to the center of the vibrating membrane.

Due to the additivity of capacitance, the total capacitance after applying pressure is the integral of the capacitance of each deflection element:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="ma"\; filenames="DEST\_PATH\_110118150705.png"\; state="\{\{state\}\}">ma</figure-callout></span>}}\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; d</span>}}\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; dr</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&pi;\&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; ma</span>}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; d</span>}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="t\; g\; dr"\; filenames="DEST\_PATH\_110118150705.png"\; state="\{\{state\}\}">t</figure-callout></span><figure-callout\; id="2"\; label="t\; g\; dr"\; filenames="DEST\_PATH\_110118150705.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}}{}^{}{\mathrm{<span\; class="notranslate">\; dr</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

$<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&pi;\&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; ma</span>}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; dr</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&pi;\&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}\frac{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; tanh</span>}<span\; class="notranslate">\; (</span>\sqrt{\mathrm{<span\; class="notranslate">\; k</span>}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="m"\; filenames="DEST\_PATH\_110118150705.png"\; state="\{\{state\}\}">m</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; tanh</span>}<span\; class="notranslate">\; (</span>\sqrt{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}$

Among them, t _g is the thickness of the dielectric cavity, and m is the ratio of the radius of the capacitive electrode to the radius of the vibrating membrane.

In addition, the formula for calculating the initial capacitance is:

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="C"\; filenames="101117144241.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; ma</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

From the above two formulas, the relationship between the initial capacitance and the capacitance corresponding to the maximum range can be obtained. For example, when the ratio of the minimum spacing to the initial spacing is k=0.98, the influence of different values of m on the ratio of the two capacitances is shown in Figure 2. It can be seen from the figure that the smaller m is, the larger the two ratios are. When m=0.37, the maximum capacitance is about 10 times of the initial capacitance. The reason is that when the electrode radius r is small, each point on the electrode has a large deflection, which corresponds to a large change in the pole distance of the capacitance as a whole, so that the capacitance value has a large relative change (about 10 ).

Claims (3)

1. A capacitive pressure sensor, comprising two circular elastic vibrating diaphragms (1, 2), annulus (3, 4) made of sealing material, two circular metal film electrodes (5, 6), and electrodes Metal film lead wires (7, 8) and outer metal film electrodes (9, 10), the outer edges of the two circular elastic vibrating diaphragms (1, 2) pass through the rings (3, 4) made of the sealing material ) are bonded together to form an elastic film with a cavity inside and a fixed support around the periphery. The two circular metal film electrodes (5, 6) are respectively attached to two circular elastic vibrating diaphragms (1, 2) to face each other. On the inner side of the electrode, one end of the metal film lead wire (7, 8) in the electrode is buried in the ring (3, 4) made of sealing material, and the other end is contacted and connected with the circular metal film electrode (5, 6) , one end of the outer metal film electrode (9, 10) is arranged on the ring (3, 4) made of the sealing material, connected with the lead wire (7, 8) of the inner metal film of the electrode, and the other end is exposed as the whole The lead-out line of the sensor is characterized in that: The radius of the metal film circular electrodes (5, 6) is smaller than the radius of the circular elastic vibrating diaphragm (1, 2), so that the sensor can work in a large strain state; the capacitive pressure sensor also has multiple a bump (11) of insulating material, which is evenly arranged on one of the two circular elastic vibrating diaphragms (1, 2) and/or on the circular metal film electrode (5, 6), for preventing short circuit of electrodes and starting The role of overload protection. 2. A capacitive pressure sensor according to claim 1, characterized in that the material of the circular elastic vibrating diaphragm (1, 2) is alumina ceramics. 3. A capacitive pressure sensor according to claim 1 or 2, characterized in that the sealing material is low temperature glass.

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