CN114002458A - Omnibearing moving heat source type single-shaft micro mechanical accelerometer and processing method thereof - Google Patents

Abstract

The application discloses an omnibearing moving heat source type uniaxial micro-mechanical accelerometer and a processing method thereof, wherein the accelerometer comprises a sensitive layer, a substrate layer and a cover plate, the sensitive layer comprises a middle heating cavity and a middle detection cavity, and an omnibearing vibrator heater and a pair of thermistors are arranged on the upper surface of the sensitive layer; the omnidirectional moving heat source swinging heater is suspended at the central position of the sensitive layer through eight completely symmetrical semicircular supporting beams; the electrifying modes of the heater and the thermistor are constant current; the cover plate is etched with a groove and is hermetically connected with the upper surface of the sensitive layer. The invention can realize the measurement of single-axis acceleration, can sense the input acceleration on the X axis, and has large measurement range and strong shock resistance. The invention inherits the advantages of MEMS sensor, has the characteristics of small volume, light weight, low cost and the like, and accords with the development direction of the sensor towards microminiature, comprehensive and intelligent. Meanwhile, the device has the advantages of simple structure and processing technology, large range, high reliability and the like.

Description

Omnibearing moving heat source type single-shaft micro mechanical accelerometer and processing method thereof

Technical Field

The invention relates to the technical field of detecting acceleration attitude parameters of a motion carrier by utilizing the swinging of an omnidirectional moving heat source pendulum under the action of linear acceleration, in particular to an omnidirectional moving heat source pendulum type single-axis micro-mechanical accelerometer and a processing method thereof, and belongs to the field of inertia measurement.

Background

Due to the application requirements of the carrier attitude measurement in various fields of civil vehicles, railway construction, industrial production, bridge construction, seismic research, geodetic surveying, geological exploration, marine investigation, satellite communication, robot engineering and the like, in recent years, the organic combination between the sensor technology and the emerging scientific technology enables the attitude sensor to develop towards microminiature, comprehensive and intelligent. The Micro inertial sensor manufactured by using Micro-Electro-Mechanical-System (MEMS) technology has the advantages of mass production, low cost, small volume, low power consumption and the like, and is an ideal product of the future medium and low precision Micro inertial sensors. The accelerometer is a core inertial sensor for measuring and controlling the motion attitude of the carrier.

The most common among accelerometers is the pendulum acceleration sensor. The pendulum tilt sensor commonly used at present has three types, namely a liquid pendulum type sensor, a solid pendulum type sensor and a heat flow type sensor. The solid pendulum type tilt angle sensor has the advantages of complex structure, high cost, large motion amplitude of the solid pendulum and difficulty in bearing high overload or impact. The main problems of the liquid pendulum tilt angle sensor are that the number of structural components is large, the response time is long, and the performance changes greatly along with the temperature. The heat flow type accelerometer has the characteristics of small sensitive mass, simple structure, high overload bearing capacity, short response time, good temperature performance, low cost and the like, and can be applied to severe environments. At present, the requirement of the market on the capability of the micro accelerometer to adapt to the harsh environment is higher and higher, so that in the micro acceleration sensor, the micro mechanical system (MEMS) heat flow acceleration is unique in the MEMS sensor by the ultra-high impact resistance and ultra-low manufacturing cost, and is not comparable to other MEMS sensors.

The working principle of the micro-mechanical (MEMS) heat flow accelerometer is as follows: the resistance heater is arranged in the closed cavity, the parallel detection thermistors are symmetrically distributed around the resistance heater, the resistance heater is electrified and heated to form a heat source to emit heat flow to the periphery, and the temperature fields are symmetrically distributed, so that the influence on the thermistors is consistent. When the external wired acceleration is input, the flowing direction of hot air flow is the same as the acceleration direction, and the hot air flow changes towards the input acceleration direction, so that the temperature field of the air flow is asymmetrically distributed, the temperature changes of two adjacent detection thermistors in the same direction are opposite, and the two detection thermistors generate temperature difference. The acceleration can be detected by detecting the temperature difference through the Wheatstone bridge. Chinese patent: in a micro-mechanical heat flow accelerometer in a silicon bridge type thermal convection acceleration sensor (patent application No. 02116842.3), a heater generates heat flow, the heat flow moves under the action of the acceleration of an input line to generate an asymmetric temperature field, and the asymmetric distribution of the temperature field is detected by arranging symmetrical thermistors. Because the velocity of hot air flow is very small, the gradient of asymmetric temperature field caused by deflection of air flow is very small, so that the unbalanced voltage output by the Wheatstone bridge formed by the thermistor is small, and the sensitivity of the sensor is low. In the conventional solution, although the sensitivity can be improved by increasing the heater power, the sensitivity is not substantially changed or improved due to the limitation of power consumption, and the bottleneck of practical use is difficult to break through.

Disclosure of Invention

The invention aims to provide an omnidirectional dynamic heat source pendulum type single-axis micromechanical accelerometer to solve the technical problems in the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides an omnidirectional dynamic heat source pendulum type single-axis micromechanical accelerometer, which mainly comprises a sensitive layer, a substrate layer and a cover plate, wherein,

the sensing layer comprises a middle heating cavity and a detection cavity, and the upper surface of the sensing layer is provided with an omnidirectional movable heat source swinging heater and a pair of thermistors;

defining the directions of the accelerometer, which are vertical to the thermistor and parallel to the thermistor, as X and Y directions respectively, and defining the height direction of the detection cavity as Z direction; the omnidirectional moving heat source swinging heater is suspended at the center of the sensitive layer through eight completely symmetrical semicircular supporting beams; the thermistors are symmetrically arranged on the left side and the right side of the heater in parallel to the Y direction and are used for detecting the acceleration of an X axis;

the omnidirectional dynamic heat source swing heater adopts a wind-fire wheel type sensitive structure, the center of the omnidirectional dynamic heat source swing heater contains a central wheel hub with a circular mass block, and the omnidirectional dynamic heat source swing heater is suspended at the central position of a sensitive layer through eight completely symmetrical semicircular supporting beams; a circular middle heating cavity is arranged below the heating cavity;

two ends of the omnidirectional moving heat source pendulum heater are covered with symmetrical electrodes along the Y direction to form a moving resistance type heat source;

the electrifying modes of the heater and the thermistor are constant current;

the cover plate and the basal layer isolate the gas media of the intermediate heating cavity and the intermediate detection cavity from the outside to form a sealed working system; the heights of the middle heating cavity and the middle detection cavity and the depth of the groove in the upper sealing layer are the total cavity height z, the z is more than or equal to 300 microns and less than or equal to 1000 microns, the total cavity height in the embodiment is hundreds of microns, and the natural convection motion of gas flow in the cavity can be effectively inhibited.

As a further technical scheme, the space for flowing the gas is increased in order to increase the depth of the groove of the cover plate, and the depth of the groove of the cover plate is 2/3 of the height of the cover plate.

As a further technical scheme, in order to form the thin film resistor which has small resistance value change along with temperature and is more stable and reliable, the heights of the heater and the thermistor on the upper surface of the sensitive layer are 100nm to 1000 nm.

As a further technical scheme, in order to increase the stability and the shock resistance of the sensor, the two thermistors have the same length, and are 1/6-1/5 of the width of the whole sensitive layer.

As a further technical solution, the heater and the thermistor are formed of a metal layer composed of a chromium adhesion layer and a platinum layer.

A method for processing an omnidirectional heat source type single-axis micromechanical accelerometer comprises the following specific process flows:

the method comprises the following steps: thermally oxidizing a 0.5 μm thick silicon dioxide film on an N-type (100) single crystal silicon wafer;

step two: photoetching the silicon dioxide film to form structural patterns of an omnidirectional dynamic heat source pendulum heater and a thermistor;

step three: sputtering a metal layer consisting of a chromium adhesion layer and a platinum layer on the photoresist and the silicon dioxide in sequence by a magnetron sputtering process;

step four: stripping off the metal layer outside the all-directional movable heat source pendulum heater and the thermistor structure pattern by adopting an ultrasonic stripping process to form an all-directional movable heat source pendulum heater and a thermistor structure;

step five: etching off a part of silicon dioxide by adopting photoetching and wet etching processes;

step six: a groove with the depth of 300 mu m is formed by corrosion processing by adopting a silicon etching process, so that the omnidirectional moving heat source pendulum heater and the thermistor are suspended and fixed on the sensitive layer through a silicon dioxide film to finish the processing of the sensitive layer;

step seven: and bonding the cover plate and the sensitive layer by a bonding process to enable the upper surface of the sensitive layer to be positioned in the closed cavity to complete the processing of the sensitive element.

By adopting the technical scheme, the invention has the following beneficial effects:

1. the omnidirectional heat source type single-shaft micro mechanical accelerometer inherits the advantages of an MEMS heat flow accelerometer, and has the advantages of simple structure, small volume, light weight, low cost and potential of batch production.

2. The sensitive structure of the accelerometer is a middle omnidirectional movable heat source pendulum, the omnidirectional movable heat source pendulum can swing up and down along a Z axis vertical to the plane of a sensitive layer, and the omnidirectional movable heat source pendulum has the freedom degree of inertia force on any azimuth angle on the plane of the sensitive layer XOY. The X-axis acceleration can be measured, the sensitivity is high, and the response speed is high.

3. The omnibearing dynamic heat source pendulum type resistance heater is suspended in the center of the sensitive layer through eight completely symmetrical semicircular supporting beams, can sense the input acceleration on an X axis, and has the advantages of large measurement range and strong impact resistance.

4. The omnibearing movable heat source pendulum adopts a wind-fire wheel type sensitive structure, and can realize the manufacture of a relatively long elastic element and a relatively large mass block in a small area, thereby obtaining high inertia force sensitivity.

5. The accelerometer sensor has simple processing technology, low cost and high reliability, and makes it possible to compete with the solid pendulum type micro mechanical accelerometer in the micro accelerometer market with medium, low precision and low price. Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic three-dimensional structure diagram of a sensitive layer provided in an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a cover plate according to an embodiment of the present invention;

FIG. 3 is a top view of an accelerometer according to an embodiment of the invention;

FIG. 4 is a sectional view taken along line A-A of FIG. 3;

FIG. 5 is a schematic diagram of the operation of the present invention;

FIG. 6 is a schematic diagram of an output circuit provided by an embodiment of the invention;

fig. 7 is a flow chart of a manufacturing process of the omnidirectional dynamic heat source pendulum type single-axis micro mechanical accelerometer according to the embodiment of the present invention;

icon: 1-sensitive layer, 2-substrate layer, 3-middle detection cavity, 4-middle heating cavity, 5-cover plate, 6-groove, 7-omnidirectional movable heat source pendulum heater, 8-thermistor, 9-thermistor and 10-electrode.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

Referring to fig. 1-5, the present embodiment provides an omnidirectional moving heat source type uniaxial micro-mechanical accelerometer, which comprises a sensitive layer 1, a substrate layer 2 and a cover plate 5, wherein,

defining the directions of the accelerometer, which are vertical to the thermistor and parallel to the thermistor, as X and Y directions respectively, and the height direction of the detection cavity as Z direction;

an omnidirectional moving heat source swinging heater 7 is arranged in the center of the upper surface of the sensitive layer 1, the heater 7 is an omnidirectional moving heat source swinging heater and is suspended in the center of the sensitive layer 1 through eight completely symmetrical semicircular supporting beams, and the heater 7 can swing along the z axis vertical to the sensitive layer and also can swing along any azimuth angle in an XOY plane where the sensitive layer 1 is located;

the thermistor 8 and the thermistor 9 are symmetrically arranged on the left side and the right side of the heater in parallel to the Y direction and used for detecting the acceleration of the X axis;

two ends of the omnidirectional moving heat source pendulum heater are covered with symmetrical electrodes 10 along the Y direction to form a moving resistance type heat source;

the heater 7 and the thermistor are powered on in a constant current mode;

and a groove 6 is etched on the cover plate 5 and is hermetically connected with the upper surface of the sensitive layer 1. In the embodiment, as a further technical scheme, a constant current is swung to the omnidirectional dynamic heat source, the resistance heater is electrified to generate joule heat, the joule heat is released to the surrounding gas to carry out heat diffusion, heat flow is formed around the joule heat, and a temperature field generated by the heat flow is symmetrically distributed between two thermistors in the same direction. If linear acceleration is input in the X-axis direction, the omnidirectional dynamic heat source pendulum moves along the same direction with the acceleration due to the acceleration action, so that the gas is asymmetrically distributed, and two opposite thermistors T in the same direction_x1And T_x2The temperature changes are opposite, the temperature of the thermistor with the omnibearing movable heat source swing deflection is higher than that of the thermistor parallel to the thermistor, and the two symmetrical thermistors T_x1And T_x2A temperature difference is generated. As shown in fig. 6, the thermistor 8 and the thermistor 9 are connected to form two arms of an schrader bridge, and a temperature difference caused by an input linear velocity is converted into a change in resistance of the arms by a thermal resistance effect, thereby causing a bridge unbalanced voltage V proportional to an input acceleration_X. The linear acceleration of the X axis can be calculated according to the output voltage, so that the acceleration in the X direction is sensed.

In this embodiment, as a further technical solution, the cover plate 5 and the substrate layer 2 isolate the gas media of the intermediate heating chamber 4 and the intermediate detection chamber 3 from the outside, so as to form a sealed working system; the height of the middle heating cavity 4 and the middle detection cavity 3 and the depth of the groove 6 in the upper sealing layer are the total cavity height z, and z is more than or equal to 300 mu m and less than or equal to 1000 mu m.

In this embodiment, as a further technical solution, the depth of the groove 6 is 2/3 of the height of the cover plate 5.

In this embodiment, as a further technical solution, the height of the heater and the thermistor on the upper surface of the sensitive layer is 100nm to 1000 nm.

In this embodiment, as a further technical solution, the length of the thermistor 8 is identical to that of the thermistor 9, and both are 1/6 to 1/5 of the width of the whole sensitive layer.

Referring to fig. 7, the specific process flow of the omnidirectional moving heat source type uniaxial micro-mechanical accelerometer disclosed by the invention is as follows:

step (a): a0.5 μm thick silicon dioxide film was thermally oxidized on an N-type (100) single crystal silicon wafer.

Step (b): and photoetching the silicon dioxide film to form structural patterns of the omnidirectional movable heat source pendulum heater and the thermistor.

Step (c): and sputtering a metal layer consisting of a chromium adhesion layer and a platinum layer on the photoresist and the silicon dioxide in sequence by using a magnetron sputtering process.

Step (d): and stripping off the metal layers except the omnibearing movable heat source pendulum heater and the thermistor structure pattern by adopting an ultrasonic stripping process to form an omnibearing vibrator heater and a thermistor structure.

A step (e): and etching off a part of silicon dioxide by adopting photoetching and wet etching processes.

Step (f): and etching and processing the substrate to form a groove with the depth of 300 mu m by adopting a silicon etching process, so that the omnidirectional moving heat source pendulum heater and the thermistor are suspended and fixed on the sensitive layer through the silicon dioxide film to complete the processing of the sensitive layer.

Step (g): and bonding the cover plate and the sensitive layer by a bonding process to enable the upper surface of the sensitive layer to be positioned in the closed cavity to complete the processing of the sensitive element.

In summary, the invention breaks through the inherent mode of the previous research on the heat flow accelerometer, and provides the omnidirectional dynamic heat source pendulum type uniaxial micro mechanical accelerometer, so that the heater with a very high temperature gradient moves, the heater deflects under the action of the inertia force to form a large temperature gradient at the thermistor, and the output with high sensitivity is realized. The sensitive structure of the accelerometer is a middle omnidirectional movable heat source pendulum, the omnidirectional movable heat source pendulum can swing up and down along a Z axis vertical to the plane of a sensitive layer, and the omnidirectional movable heat source pendulum has the freedom degree of inertia force on any azimuth angle on the plane of the sensitive layer XOY. The X-axis acceleration can be measured, the sensitivity is high, and the response speed is high. The accelerometer has the advantages of simple structure and processing technology, extremely low cost, high reliability and excellent vibration and impact resistance. The sensitive element adopted by the invention is manufactured on a silicon chip by the processes of photoetching, corrosion and the like, has good consistency, is convenient to introduce a microcomputer embedded system (singlechip) to carry out temperature compensation and nonlinear degree compensation, not only can improve the performance of the sensor, but also can realize batch production.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (6)

1. An omnidirectional moving heat source type uniaxial micro-mechanical accelerometer is characterized by comprising a substrate layer, a sensitive layer and a cover plate, wherein,

the sensing layer comprises a middle heating cavity and a middle detection cavity, and an omnidirectional dynamic heat source swinging type resistance heater and a pair of thermistors are arranged on the upper surface of the sensing layer;

defining the directions of the accelerometer, which are vertical to the thermistor and parallel to the thermistor, as X and Y directions respectively, and defining the height direction of the detection cavity as Z direction; the omnibearing dynamic heat source pendulum type resistance heater is suspended in the center of the sensitive layer through eight completely symmetrical semicircular supporting beams; the thermistors are symmetrically arranged on the left side and the right side of the heater in parallel to the Y direction and are used for detecting the acceleration of an X axis;

the omnibearing dynamic heat source pendulum type resistance heater adopts a wind-fire wheel type sensitive structure, the center of the resistance heater contains a central wheel hub with a circular mass block, and the resistance heater is suspended at the central position of a sensitive layer through eight completely symmetrical semicircular supporting beams; the middle heating cavity is circular below the middle heating cavity; the middle detection cavity is arranged below the thermistor;

the omnidirectional moving heat source swinging heater can swing along a Z axis vertical to the sensitive layer and also can swing along any azimuth angle in an XOY plane where the sensitive layer is located;

two ends of the omnibearing movable heat source pendulum type resistance heater are covered with symmetrical electrodes along the Y direction to form a movable resistance type heat source;

the electrifying modes of the heater and the thermistor are constant current;

the cover plate and the substrate layer isolate the gas media of the intermediate heating cavity and the intermediate detection cavity from the outside to form a sealed working system; the height of the middle heating cavity and the middle detection cavity and the depth of the groove in the upper sealing layer are the total cavity height z, and z is more than or equal to 300 mu m and less than or equal to 1000 mu m.

2. The omni-directional, heat source, uniaxial, micro-mechanical accelerometer of claim 1, wherein the recess depth of said cover is 2/3 of cover height.

3. The accelerometer of claim 1, wherein the pendulum-type resistive heater and thermistor have a height of 100nm to 1000 nm.

4. The omni-directional, heat source, uniaxial, micromechanical accelerometer according to claim 1, wherein both said thermistors have a uniform length, each 1/6 to 1/5 of the entire width of the sensitive layer.

5. The accelerometer according to claim 1, wherein the resistive heaters and thermistors of the pendulum type are made of metal layers consisting of a chromium adhesion layer and a platinum layer.

6. A method for processing the omnidirectional moving heat source type uniaxial micro-mechanical accelerometer according to any one of claims 1-5, wherein the specific process flow is as follows:

the method comprises the following steps: thermally oxidizing a 0.5 μm thick silicon dioxide film on an N-type (100) single crystal silicon wafer;

step two: photoetching the silicon dioxide film to form structural patterns of an omnidirectional dynamic heat source pendulum heater and a thermistor;

step three: sputtering a metal layer consisting of a chromium adhesion layer and a platinum layer on the photoresist and the silicon dioxide in sequence by a magnetron sputtering process;

step four: stripping off the metal layer outside the all-directional movable heat source pendulum heater and the thermistor structure pattern by adopting an ultrasonic stripping process to form an all-directional movable heat source pendulum heater and a thermistor structure;

step five: etching off a part of silicon dioxide by adopting photoetching and wet etching processes;

step six: a groove with the depth of 300 mu m is formed by corrosion processing by adopting a silicon etching process, so that the omnidirectional moving heat source pendulum heater and the thermistor are suspended and fixed on the sensitive layer through a silicon dioxide film to finish the processing of the sensitive layer;

step seven: and bonding the cover plate and the sensitive layer by a bonding process to enable the upper surface of the sensitive layer to be positioned in the closed cavity to complete the processing of the sensitive element.

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