1. A single heat source full-bridge type 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 a heater and four thermistors;

defining the length and width directions of the rectangular thin film gyroscope as an X direction and a Y direction respectively, and defining the height direction of the sensitive layer as a Z direction; the arrangement directions of the heater and the thermistor are both vertical to the X direction; the four thermistors are arranged oppositely in pairs and used for detecting the angular speed of the Z axis;

the heater is vertically arranged at the center of the upper surface of the sensitive layer, and the four thermistors are symmetrically arranged in the left direction and the right direction of the heater along the Y direction;

the heater is powered on in a periodic square wave mode, 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 single heat source full-bridge z-axis thin film gyroscope of claim 1, wherein the heater is driven by a square wave signal at a frequency of 18Hz with a 50% duty cycle pulse and a heater heating power of 70 mW.

3. The single heat source full-bridge z-axis thin film gyroscope of claim 1, wherein the distance from the upper surface of the sensing layer to the top of the recess in the cover plate is the height of the gas medium working cavity, and the height is 200 μm to 1000 μm.

4. The single heat source full-bridge z-axis thin film gyroscope of claim 1, wherein the height of the heater above the sensing layer is 15 μm to 20 μm.

5. The single heat source full-bridge z-axis thin film gyroscope of claim 1, wherein the height of the thermistor on the upper surface of the sensing layer is 95 μm to 100 μm.

6. The single heat source full bridge z-axis thin film gyroscope of claim 1, wherein the heater is spaced from the thermistor by 1/3 to 1/2 of heater length.

7. The single heat source full-bridge z-axis thin film gyroscope of claim 1, wherein the heater is comprised of a resistive line of TaN material having a high temperature coefficient.

8. The single heat source full-bridge z-axis thin film gyroscope of claim 1, wherein the thermistors are each comprised of resistive wire of n-type heavily doped GaAs material.

9. A method of fabricating a single heat source full-bridge z-axis thin film gyroscope according to any of claims 1-8, wherein 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 formThick pads and sensitive resistance lines;

step four: deposited by chemical vapor depositionThick 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 single heat source full-bridge type z-axis film gyroscope.

Background

The Micro inertial sensor manufactured by using the 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-precision 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 the micro fluid inertia device does not have a movable part and a suspension system in the traditional micro gyroscope; 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 the 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 the advantages of extremely high vibration resistance and impact resistance, low cost and the like, has market competitiveness and has very wide application prospect.

At present, micro fluid gyroscopes based on MEMS technology can be roughly divided into four categories: micro-fluidic gyroscopes, ECF (electro-coupled fluid) fluidic gyroscopes, micro-thermal convective gyroscopes and micro-thermal fluidic 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, and the piezoelectric sheet in the sensitive element increases the processing difficulty and cost, and the volume of the miniature four-channel circulating flow type three-axis silicon 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 commercial micro-gyros of choice. The micro heat flow gyro (also called thermal expansion gyro) is a new micro fluid gyro which is proposed in recent years, a sensing element has no piezoelectric plate, high voltage is not needed, the micro heat flow gyro can be used in a gravity-free environment, the sensitivity of the micro heat flow gyro is moderate, the micro heat flow gyro is between the micro heat flow gyro and the micro heat convection gyro, and meanwhile, the micro heat flow 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 heat flow gyro can compete with a capacitive micro mechanical vibration gyro in the micro gyro 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 suspended over the cavity, and 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 warping deformation may generate an asymmetric gas flow field without 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 single heat source full-bridge type z-axis thin film gyroscope and a processing method thereof, and aims 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 single heat source full-bridge type z-axis thin film gyroscope, which comprises a sensitive layer and a cover plate, wherein,

the upper surface of the sensitive layer is provided with a resistance heater (hereinafter referred to as heater) and a thermal resistor;

defining the length and width directions of the rectangular thin film gyroscope as an X direction and a Y direction respectively, and defining the height direction of the sensitive layer as a Z direction; the arrangement directions of the heater and the thermistor are both vertical to the X direction; the four thermistors are arranged oppositely in pairs and used for detecting the angular speed of the Z axis;

the heater is vertically arranged at the center of the upper surface of the sensitive layer, and the four thermistors are symmetrically arranged in the left direction and the right direction of the heater along the Y direction;

the heater is powered on in a periodic square wave mode, namely one working period of the heater comprises pulse voltage excitation time and power-off interval time;

as a further technical scheme, a groove is etched in the cover plate and is connected with the upper surface of the sensitive layer in a sealing mode.

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 1 is 15-20 μm.

As a further technical scheme, the distance between the heater and the thermistor is 1/3-1/2 of the length of the heater.

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

A method for processing a single-heat-source full-bridge type 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 formThick pads and sensitive resistance lines;

step four: deposited by chemical vapor depositionThick 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 single heat source full-bridge type z-axis thin 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 gyro sensitive element takes gas as sensitive mass, and has the advantages of large impact resistance, simple structure, extremely low cost and high reliability.

3. 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.

4. The four thermistors form an equal-arm bridge, the four bridge arms as working arms all participate in the deflection of the sensitive hot air flow, the sensitivity is four times that of a single working arm, and the sensitivity of the gyroscope is greatly improved.

5. The extraction circuit is an equal-arm bridge, and the nonlinearity of the relationship between the resistance change of bridge arms of the equal-arm bridge and the output unbalanced voltage of the bridge is minimum, so that the nonlinearity of the gyroscope is greatly reduced.

7. The process adopted by the invention is compatible with the integrated circuit process, and has the potential of high integration level.

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 three-dimensional structure 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 a single heat source full-bridge z-axis thin film gyroscope according to an embodiment 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 process for fabricating a single heat source full-bridge z-axis thin film gyroscope according to an embodiment of the present invention;

icon: 1-sensitive layer, 2-cover plate, 3-rectangular groove, 4-heater, 5-thermistor, 6-thermistor, 7-thermistor, 8-thermistor, 9-TaN material resistor block, 10-TaN material resistor block, 11-Si₃N₄A material resistance block and a 12-n type heavily doped GaAs material resistance block.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and obviously, 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 those shown in the drawings, and are only for convenience of description and simplification of description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed in a specific orientation, and be operated, 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 meaning of the above terms in the present invention can be understood according to specific situations by those of ordinary skill in the art.

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 intended for purposes of illustration and explanation only and are not intended to limit the scope of the invention.

As shown in fig. 1 to 4, the present embodiment provides a single heat source micro-mechanical 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 a heater and four thermistors;

defining the length and width directions of the rectangular thin film gyroscope as an X direction and a Y direction respectively, and defining the height direction of the sensitive layer as a Z direction; the arrangement directions of the heater and the thermistor are parallel or vertical to the X or Y direction; the four thermistors are arranged oppositely in pairs and used for detecting the angular speed of the Z axis;

the heater 4 is arranged at the center of the upper surface of the sensitive layer in a way of being vertical to the X axis, and the thermistor 5, the thermistor 6, the thermistor 7 and the thermistor 8 are symmetrically arranged in the left direction and the right direction of the heater;

the two heaters are electrified in a periodic square wave mode, namely one working period of the heaters comprises pulse voltage excitation time and power-off interval time;

the electrifying mode of the thermistor is constant current;

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

As shown in fig. 5, in this embodiment, as a further technical solution, the resistance-type heater 4 is driven by a square wave, and the resistance is energized to generate joule heat, which releases heat to the surrounding air to perform heat diffusion, so as to form two oscillating heat flows on two sides of the heater 4. Four thermistors with the same resistance R1 (thermistor 8), R2 (thermistor 7), R3 (thermistor 6) and R4 (thermistor 5) form an equiarm Wheatstone bridge, and all serve as working arms to participate in the deflection of sensitive airflow to form a full bridge. When there is an angular velocity input Ω Z in the Z-axis direction, the heat flow from the heater 4 will be deflected in the XOY plane due to Coriolis force principle, and the thermistor 5 and the thermistor 8, which deflect the heat flow, are hotter than the thermistor 6 and the thermistor 7, which are parallel to it, so that the two relatively parallel R1 and R2 (thermistor 8 and thermistor 7), R3 and R4 (thermistor 6 and thermistor 5) generate a temperature difference proportional to the input angular velocity Ω Z. The changes of two adjacent bridge arm resistors R1 and R2 (thermistor 8 and thermistor 7) and R3 and R4 (thermistor 6 and thermistor 5) are increased and decreased, the resistance changes are equal in size and opposite in sign, and the change of each bridge arm resistor and the output of the bridge unbalanced voltage delta Vout meet the formula (1).

This full bridge voltage output is four times that of a single thermistor participating in a sensible heat flow deflection bridge, according to equation (1). The temperature difference generated by the input angular velocity is converted into a voltage unbalance voltage delta Vout which is in direct proportion to the angular velocity omega Z through the change of the resistance value of the bridge arm of the Wheatstone bridge and is output by VZ, so that the angular velocity on the Z axis is sensed.

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.

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 1/3 to 1/2 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 material resistance blocks 9, 10 and 1 Si₃N₄A resistive block of material 11. The TaN material resistance block is composed of 4 series-connected resistors, and each resistor is specifically realized in the form of 3 parallel TaN material resistance 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 thermistor is an n-type heavily doped GaAs material resistor block 12. Wherein the n-type heavily doped GaAs material resistance block 12 consists of 5 n-type heavily doped GaAs material resistance lines connected in series. By designing the GaAs material in this wayThe material resistance wire and the thermistor can obtain larger voltage signal output, thereby being beneficial to improving the sensitivity of gyro detection.

Referring to fig. 8, the single heat source full-bridge z-axis thin film gyroscope disclosed by the invention can be prepared by using a GaAs-MMIC technique, 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 formThick pads and sensitive resistance lines.

Step (d): prepared by adopting a Plasma Enhanced Chemical Vapor Deposition (PECVD) technologyThick Si₃N₄As an isolation resistor block.

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 single heat source full-bridge type 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. Four thermistors form an equal-arm bridge, four bridge arms as working arms all participate in the deflection of sensitive hot air flow, the sensitivity is four times that of a single working arm, and the sensitivity of the gyroscope is greatly improved. The extraction circuit is an equal-arm bridge, and the nonlinearity of the relationship between the resistance change of bridge arms of the equal-arm bridge and the output unbalanced voltage of the bridge is minimum, so that the nonlinearity of the gyroscope is greatly reduced. 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.