CN113124844A - Four-bridge cross-flow type micromechanical z-axis film gyroscope and processing method thereof - Google Patents

Abstract

The application discloses a four-bridge cross-flow type micromechanical z-axis film gyroscope and a processing method thereof, wherein the z-axis film gyroscope comprises a sensitive layer and a cover plate, and four heaters, eight thermistors, eight balance resistors and four isolation resistors which are in a square structure are arranged on the upper surface of the sensitive layer; the electrifying mode of the heater is periodic square wave drive; the cover plate is etched with a groove and is hermetically connected with the upper surface of the sensitive layer. The invention inherits the advantages of no solid sensitive mass block, vibration and impact resistance and the like of the micro heat flow gyroscope. The output of the gyroscope is output after the unbalanced voltages of the four electric bridges are averaged, so that the error is small and the precision is highest; the half-bridge is adopted, the resistance value of the balance resistor is hundreds of times of that of the thermistor, impedance matching is facilitated when the voltage signal is further amplified, interference is prevented, and anti-interference performance is high.

Description

Four-bridge cross-flow type micromechanical z-axis film gyroscope and processing method thereof

Technical Field

The invention belongs to the technical field of detecting angular velocity attitude parameters of a moving body by utilizing a Coriolis force deflection heat flow sensitive body, in particular relates to a four-bridge cross-flow type micro-mechanical z-axis film gyroscope and a processing method thereof, and belongs to the field of inertia measurement.

Background

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 gyroscope and the accelerometer are core inertial sensors for measuring and controlling the motion attitude of the carrier, and the gyroscope is a sensor sensitive to angular velocity, angular acceleration and other angular parameters. The traditional micro gyroscope (micromechanical gyroscope) is a micro rate gyroscope based on the principle of the Coriolis effect existing when a high-frequency vibrating mass is driven to rotate by a base, and micro-electronics and a micro machine are combined. The solid mass block in the gyro sensitive element needs to be suspended and vibrated through a mechanical elastic body, is easy to damage under slightly high acceleration impact, and simultaneously needs vacuum packaging for reducing damping, has complex process and can generate fatigue damage and vibration noise when working for a long time. The micro fluid inertia device is a novel device for measuring input acceleration and angular velocity by detecting flow field offset of fluid in a closed cavity, and can resist high overload because a movable part and a suspension system in a traditional micro gyroscope are not arranged; the sensitive mass of the gas sensor is gas, and the mass is almost zero, so the response time is short and the service life is long; due to the simple structure, the application requirement of low cost can be met. The micro fluid gyroscope is an angular velocity sensor which utilizes the deflection of an air flow sensitive body in a closed cavity under the action of Goldson force and senses the deflection quantity caused by angular velocity by a thermistor (hot wire). At present, the market has higher and higher requirements on the capability of the micro inertial gyroscope to adapt to severe and harsh environments, and compared with the traditional micro mechanical vibration gyroscope, the micro fluid gyroscope has higher market competitiveness and very wide application prospect due to the advantages of extremely high vibration resistance and impact resistance, low cost and the like.

The micro fluid gyroscopes based on MEMS technology can be broadly classified into four types, namely micro fluidic gyroscopes, ECF (electro-coupled fluid) fluid gyroscopes, micro thermal convection gyroscopes and micro thermal flow gyroscopes. The Chinese patent is a miniature four-channel circulating flow type three-axis silicon jet gyro (patent application number: 201510385582.4), which belongs to the miniature jet gyro, the piezoelectric sheet in the sensitive element of the miniature jet gyro increases the processing difficulty and the cost, and the volume of the miniature jet gyro is difficult to further reduce on the premise of keeping the flow rate. ECF fluid gyroscopes are relatively large (40mm x 60mm x 7mm) and are difficult to commercialize in large volumes and at low cost because of the high kilovoltage required to form the liquid jet. The miniature thermal convection gyro cannot work without a gravity field, and the sensitivity is low. The above-described microfluidic gyros have their own inherent disadvantages that make them difficult to be the low-cost choice for commercial microfluidic gyros. The micro heat flow gyro (also called thermal expansion gyro) is a new micro fluid gyro which is proposed in recent years, a voltage-free electric sheet is arranged in a sensitive element, high voltage is not needed, the micro fluid gyro can be used in a gravity-free environment, the sensitivity of the micro fluid gyro is moderate, the micro fluid gyro is between the micro fluid gyro and the micro heat convection gyro, and meanwhile, the micro fluid gyro has the advantages of simple structure and processing technology, extremely low cost, high reliability and excellent vibration and impact resistance, so that the micro fluid gyro can compete with a capacitive micro mechanical vibration gyro in the micro gyroscope market with low precision and low price.

The sensitive working principle of the micro heat flow gyroscope is that a heater is electrified to generate heat, gas around the heater is heated to form gas thermal diffusion, an air flow sensitive body moving along a certain direction is generated, and when an angular velocity is input, the air flow sensitive body deflects under the action of a Coriolis force to change a bridge arm resistor (generally composed of a thermistor) of a Wheatstone bridge, so that bridge unbalanced voltage in direct proportion to the input angular velocity is output. In chinese patents 201410140298.6 and 201210130318.2, the main components in the sensor sensing element, i.e., the heater and the thermistor, are both in a suspended cantilever beam structure, and first, since the heater and the thermistor are both suspended above the cavity, after the cavity releasing structure is etched, the heater and the thermistor may be deformed or even broken by stress, the yield is low, and the warp deformation may generate an asymmetric gas flow field under the condition of no angular velocity input, thereby causing an angular velocity detection error. Secondly, the extraction circuit and the sensitive element chip of the sensor are separated, the extraction circuit needs to be manufactured additionally, and the extraction circuit and the sensitive element are not integrated on one chip, so that the integration level is not high, and the sensor is large in size. Thirdly, if the resistors in the four-arm bridge in the discrete device are not in the same temperature field, the temperature coefficients of the resistors are different, which easily causes temperature drift and affects the accuracy of the sensor, thereby limiting the application field of the sensor. Therefore, how to overcome the above problems becomes a technical problem that needs to be solved urgently by those skilled in the art.

Disclosure of Invention

The invention aims to provide a four-bridge cross-flow type micromechanical z-axis film gyroscope 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 a four-bridge cross-flow type micromechanical z-axis film gyroscope, which comprises a sensitive layer and a cover plate, wherein,

the upper surface of the sensitive layer is provided with four heaters, eight thermistors, eight balance resistors and four isolation resistors which are in a square structure;

defining the length and width directions of the thin film gyroscope as X and Y directions respectively, and defining the height direction of the sensitive layer as Z direction; the arrangement directions of the heater, the thermistor and the balance resistor are parallel or vertical to the X or Y direction; the four heaters, the eight thermistors and the eight balance resistors form a cross network and are symmetrically arranged along two vertical coordinate axes of X, Y; the heater, the two thermistors and the two balance resistors form a measuring unit, and the measuring unit is formed by the heater, the two thermistors and the two balance resistors;

two of the four heaters are arranged in the X-axis direction and are vertical to the X-axis; the other two are arranged in the Y-axis direction and are vertical to the Y-axis;

one isolating resistor is arranged between each pair of thermistors and each pair of balance resistors;

the four heaters are powered on periodically, namely one working period of the heaters comprises pulse voltage excitation time and power-off interval time;

and the cover plate is etched with a groove and is hermetically connected with the upper surface of the sensitive layer.

As a further technical scheme, the distance from the upper surface of the sensitive layer to the top of the groove on the cover plate is the height of the gas medium working cavity, and the height is 200-1000 μm.

As a further technical scheme, the height of the heater and the thermistor on the upper surface of the sensitive layer is 15-20 μm.

As a further technical scheme, the width of the measuring unit is 1/6-1/5 of the width of the whole sensitive layer.

As a further technical scheme, the heater is composed of a TaN material resistance wire with high temperature coefficient.

As a further technical scheme, the thermistor is formed by heavily doped n-type GaAs material resistance wires.

As a further technical scheme, the isolation resistor is composed of Si with the height of 25-30 μm₃N₄A resistive line of material.

A method for processing a four-bridge cross-flow type micromechanical z-axis film gyroscope comprises the following specific process flows:

the method comprises the following steps: preparation of doping Density of 10 on GaAs wafer¹⁸cm^-3N of (A) to (B)⁺The GaAs epitaxial layer is etched to form an upper surface thermistor and a balance resistor;

step two: sputtering a TaN layer as an upper surface heater;

step three: sputtering Ti/Au/Ti respectively to form

Thick pads and sensitive resistance lines;

step four: deposited by chemical vapor deposition

Thick Si₃N₄Preparing an isolation resistor;

step five: the upper cover plate and the sensitive layer are bonded through a bonding process, so that the working environment of the gas medium is sealed;

step six: and packaging the processed structure to form the four-bridge cross-flow type micro-mechanical z-axis film gyroscope.

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

1. the gyro sensing element has no cantilever beam structure, simple process, high yield, and low cost.

2. The gas is used as sensitive mass, and the high impact resistance and the long service life are achieved.

3. The non-pressure electric pump structure has the advantages of smaller gyro structure volume, simple structure and low implementation difficulty.

4. The gyroscope has four half-equal-arm bridges, wherein two thermistors with the same resistance value are used as working resistors, the other two resistors with the same resistance value form one half-equal-arm bridge, two bridge arms are used as the working arms and participate in the deflection of sensitive hot air flow, the sensitivity is twice of that of a single working arm, and the sensitivity of the gyroscope is greatly improved.

5. The heater and the thermistor are realized on one chip, and the same structure ensures that the resistance discrete degree of the resistance wire is small, and temperature drift caused by different temperature coefficients can not be caused in one temperature field.

6. The output of the gyroscope is output after the unbalanced voltages of the four bridges are averaged, the error is small, and the precision is higher

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 a sensitive layer provided by an embodiment of the present 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 structural diagram of a heater according to an embodiment of the present invention;

FIG. 7 is a schematic structural diagram of a thermistor according to an embodiment of the present invention;

FIG. 8 is a flow chart of a manufacturing process of a four-bridge cross-flow micromechanical z-axis thin-film gyroscope according to an embodiment of the present invention;

icon: 1-sensitive layer, 2-cover plate, 3-groove, 4-heater, 5-heater, 6-heater, 7-heater, 8-thermistor, 9-thermistor, 10-thermistor, 11-thermistor, 12-thermistor, 13-thermistor, 14-thermistor, 15-thermistor, 16-balanced resistor, 17-balanced resistor, 18-balanced resistor, 19-balanced resistor, 20-balanced resistor, 21-balanced resistor, 22-balanced resistor, 23-balanced resistor, 24-isolation resistor, 25-isolation resistor, 26-isolation resistor, 27-isolation resistor, 28-TaN material resistor block, 29-Si-groove, 3-heater, 5-heater, 6-heater, 7-heater, 8-thermistor, 9-balanced resistor, 21-thermistor, 22-balanced resistor, 23-balanced resistor, 24-isolation resistor, 25-isolation resistor, 26-isolation resistor₃N₄The resistor comprises a material resistor block, a 30-TaN material resistor block and a 31-heavily doped n-type GaAs material resistor block.

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.

As shown in fig. 1 to 5, the present embodiment provides a four-bridge cross-flow type micromechanical z-axis thin-film gyroscope, which includes a sensitive layer 1 and a cover plate 2, wherein,

the upper surface of the sensitive layer 1 is provided with four heaters, eight thermistors, eight balance resistors and four isolation resistors which are in a square structure;

defining the length and width directions of the gyroscope to be X and Y directions respectively, and defining the height direction of the sensitive layer 1 to be Z direction; the arrangement directions of the heater and the thermistor are parallel or vertical to the X or Y direction; for detecting the angular velocity of the Z-axis; the heater, the two thermistors and the two balance resistors form a measuring unit, and the measuring unit is formed by four measuring units;

one isolating resistor is arranged between each pair of thermistors and each pair of balance resistors; namely: an isolation resistor 24 is arranged between the thermistor 8 and 9 and the balance resistor 16 and 17; an isolation resistor 25 is arranged between the thermistor 10 and the thermistor 11 and between the balance resistor 18 and the balance resistor 19; an isolation resistor 26 is arranged between the thermistor 12 and the thermistor 13 and between the balance resistor 20 and the balance resistor 21; an isolation resistor 27 is provided between the thermistors 14 and 15 and the balance resistors 22 and 23.

The electrifying mode of the thermistor is constant current;

and the cover plate 2 is etched with a groove 3 and is hermetically connected with the upper surface of the sensitive layer 1.

In the embodiment, as a further technical scheme, four resistance-type heaters 4, 5, 6 and 7 are arranged in a square shape and driven by square waves, the resistors are electrified to generate joule heat, the joule heat is released to surrounding gas to carry out heat diffusion, oscillation heat flows are formed on two sides of the heaters, and cross-shaped heat flows are formed on the outer sides of the four heaters. The working principle of a four-bridge cross-flow type micromechanical z-axis film gyroscope is illustrated by taking one working unit as an example. If an angular velocity Ω Z is input in the Z-axis direction, the heat flow generated by the heater 4 is deflected in the XOY plane due to Coriolis force (Coriolis force) principle, and the thermistor 8 whose heat flow is deflected is higher in temperature than the thermistor 9 parallel thereto, so that a temperature difference proportional to the input angular velocity Ω Z is generated between the two parallel thermistors 8 and 9. Wherein the thermistor 8 and 9 participate in the deflection of the sensitive airflow, while the balancing resistor 16 and 17 do not participate in the deflection of the airflow, thus forming a half-equal-arm wheatstone bridge. The temperature difference which is in direct proportion to the input angular velocity omega Z is generated between the thermistor 8 and the thermistor 9, and is converted into unbalanced voltage delta Vout which is in direct proportion to the input angular velocity through the change of the resistance value of a half-equal arm Wheatstone bridge arm, and the unbalanced voltage delta Vout is output, so that the angular velocity on the Z axis is sensed. The resistance value of the balance resistor is 100 times higher than that of the thermistor, so that the sensitivity of the unbalanced voltage of the bridge and the impedance matching during voltage amplification are greatly improved.

In this embodiment, as a further technical solution, the distance from the upper surface of the sensitive layer 1 to the top of the groove on the cover plate 2 is the height of the gas medium working cavity, and the height is 200 μm to 1000 μm.

In this embodiment, as a further technical solution, the height of the heater and the thermistor on the upper surface of the sensitive layer 1 is 15 μm to 20 μm.

As a further technical scheme, the isolation resistor is composed of Si with the height of 25-30 μm₃N₄A resistive line of material.

In this embodiment, as a further technical solution, the lengths of the heater and the thermistor are the same, and are 1/6 to 1/5 of the width of the whole sensitive layer.

In this embodiment, as a further technical solution, the distance between the heater and the thermistor for detecting the angular velocity in the Z-axis direction is 1/4 to 1/3 of the length of the heater.

In this embodiment, as a further technical solution, the heaters are made of resistive wires of TaN material with high temperature coefficient, as shown in fig. 6-7. The thermistors are all composed of n-type heavily doped GaAs material resistance wires. Wherein the heater comprises 2 symmetrical TaN resistive blocks 28, 30 and 1 Si₃N₄A resistive block of material 29. The TaN material resistor block 28 is composed of 4 series-connected resistors, and each resistor is embodied in the form of 3 parallel TaN material resistor lines with high temperature coefficients. By designing the TaN material resistance wire in this way, the heater can generate more heat, thereby being beneficial to improving the sensitivity of gyro detection. The n-type heavily doped GaAs material resistance block 31 is composed of 5 n-type heavily doped GaAs material resistance lines which are connected in series. By designing the GaAs material resistance wire in such a way, the thermistor can obtain larger voltage signal output, thereby being beneficial to improving the sensitivity of gyro detection.

Referring to fig. 8, the four-bridge cross-flow micromechanical z-axis thin-film gyroscope disclosed by the present invention can be prepared by using GaAs-MMIC technology, and the specific process flow is as follows:

step (a): preparation of doping Density of 10 on GaAs wafer¹⁸cm^-3And etching the n + GaAs epitaxial layer to form the thermistor and the balance resistor.

Step (b): a TaN (tantalum nitride) layer is sputtered as a heater (heating resistor).

Step (c): respectively sputtering Ti/Au/Ti, photoetching and etching to form

Thick pads and connecting wires.

Step (d): prepared by adopting a Plasma Enhanced Chemical Vapor Deposition (PECVD) technology

Thick Si₃N₄As an isolation resistor.

A step (e): and the upper cover plate is bonded with the sensitive layer through a bonding process, so that the working environment of the gas medium is sealed.

Step (f): and packaging the processed structure to form the four-bridge cross-flow type micro-mechanical z-axis film gyroscope.

In conclusion, the invention inherits the advantages of no solid sensitive mass block, vibration resistance, impact resistance and the like of the micro heat flow gyroscope, the gyroscope sensitive element has no cantilever beam structure, the process is simple, the yield of the sensitive element is high, and the cost is low because the sensitive element can be produced in batch. The gyroscope has four half-equal-arm bridges, wherein two thermistors with the same resistance value are used as working resistors, the other two resistors with the same resistance value form one half-equal-arm bridge, two bridge arms are used as the working arms and participate in the deflection of sensitive hot air flow, the sensitivity is twice of that of a single working arm, and the sensitivity of the gyroscope is greatly improved. The output of the gyroscope is output after the unbalanced voltages of the four electric bridges are averaged, so that the error is small and the precision is high. The resistance value of the balance resistor is hundreds times of that of the thermistor, which is beneficial to impedance matching when the voltage signal is further amplified, interference is prevented, and the anti-interference performance is strong. The process adopted by the invention is compatible with the integrated circuit process, the driving circuit and the extraction circuit are easily manufactured on the same chip, and the potential of high integration level is realized. Because the sensitive mass of the sensor does not contain a solid mass block, compared with micro inertial sensors with other working principles, the sensor has the advantages of large impact resistance, simple structure, extremely low cost and high reliability.

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 (9)

1. A four-bridge cross-flow type micromechanical z-axis film gyroscope is characterized by comprising a sensitive layer and a cover plate, wherein,

the upper surface of the sensitive layer is provided with four heaters, eight thermistors, eight balance resistors and four isolation resistors which are in a square structure;

defining the length and width directions of the thin film gyroscope as X and Y directions respectively, and defining the height direction of the sensitive layer as Z direction; the arrangement directions of the heater, the thermistor and the balance resistor are parallel or vertical to the X or Y direction; the four heaters, the eight thermistors and the eight balance resistors form a cross network and are symmetrically arranged along two vertical coordinate axes of X, Y; the heater, the two thermistors and the two balance resistors form a measuring unit, and the measuring unit is formed by four measuring units;

one isolating resistor is arranged between each pair of thermistors and each pair of balance resistors;

the heater is powered on periodically, namely one working period of the heater comprises pulse voltage excitation time and power-off interval time;

and the cover plate is etched with a groove and is hermetically connected with the upper surface of the sensitive layer.

2. The four-bridge cross-flow micromachined z-axis membrane gyroscope of claim 1, wherein each of the heaters is driven by a square wave signal.

3. The four-bridge cross-flow micromechanical z-axis membrane gyroscope of claim 1, wherein the distance from the upper surface of the sensitive layer to the top of the groove on the cover plate is the height of the gas medium working cavity, and the height is 200 μm to 1000 μm.

4. The four-bridge cross-flow micromachined z-axis membrane gyroscope of claim 1, wherein the heater and thermistor height at the upper surface of the sensitive layer is 15 μ ι η to 20 μ ι η.

5. The four-bridge cross-flow micromachined z-axis membrane gyroscope of claim 1, wherein the heater and the thermistor are of uniform length, each 1/6 through 1/5 of the entire width of the sensing layer.

6. The four-bridge cross-flow micromachined z-axis thin film gyroscope of claim 1, wherein the heaters are each comprised of a resistive line of TaN material having a high temperature coefficient.

7. The four-bridge cross-flow micromachined z-axis membrane gyroscope of claim 1, wherein the thermistors are each comprised of n-type heavily doped GaAs material resistance wire.

8. The four-bridge cross-flow micromechanical z-axis membrane gyroscope of claim 1, wherein the isolation resistors do not participate in the deflection of the sensitive gas flow and are made of 1 Si₃N₄A resistive line of material.

9. A method for processing the four-bridge cross-flow type micromechanical z-axis thin-film gyroscope according to any one of claims 1-8, characterized in that the specific process flow is as follows:

the method comprises the following steps: preparation of doping Density of 10 on GaAs wafer¹⁸cm^-3N of (A) to (B)⁺The GaAs epitaxial layer is etched to form an upper surface thermistor and a balance resistor;

step two: sputtering a TaN layer as an upper surface heater;

step three: sputtering Ti/Au/Ti respectively to form

Thick pads and sensitive resistance lines;

step four: deposited by chemical vapor deposition

Thick Si₃N₄Preparing an isolation resistor;

step five: the upper cover plate and the sensitive layer are bonded through a bonding process, so that the working environment of the gas medium is sealed;

step six: and packaging the processed structure to form the four-bridge cross-flow type micro-mechanical z-axis film gyroscope.

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