A self-sensing MEMS thermal expansion flow gyroscope

Abstract

The application discloses an independent sensitive MEMS thermal expansion flow gyroscope, which comprises a sensitive layer and a cover plate; the upper surface of the sensitive layer is provided with two heaters and two pairs of thermistors, and a rectangular groove is etched at the center position of the lower surface of the sensitive layer; the four thermistors are symmetrically distributed in pairs and are respectively distributed on the two sides of the two heaters; the thermistors on the two sides of one heater form an independent sensitive unit, and there are two independent sensitive units for sensing the angular velocity of the Z axis; the cover plate is engraved with a cavity and is tightly connected with the sensitive layer to form a sealed working space. The application inherits the advantages of the MEMS thermal expansion flow gyroscope, has a compact structure, a small volume, a light weight, and is easy to be intelligentized and integrated. The independent sensitive unit is adopted, so that the gyroscope has high sensitivity. The sensitive element of the application does not have a cantilever beam structure, has good impact resistance, a simple structure, extremely low cost, high reliability and other characteristics.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of detecting angular velocity attitude parameters of a moving body by utilizing Coriolis force deflection of a thermal flow sensitive body, and particularly relates to an independent sensitive MEMS thermal expansion flow gyroscope, belonging to the field of inertial measurement. BACKGROUND

[0002] Since the end of last century, micro inertial sensors based on thermal expansion principle using micro electro mechanical system (MEMS) technology have been developed for about 20 years, and have the advantages of simple structure, low cost, strong impact resistance, large measurement range, low power consumption, etc., and are extremely promising in medium or low precision measurement scenarios. Micro inertial sensors are mainly divided into two categories: one is an accelerometer for measuring linear velocity and linear acceleration; the other is a gyroscope for measuring angular velocity and angular acceleration.

[0003] A traditional micro gyroscope (micro mechanical gyroscope) is based on the Coriolis effect, uses a high-frequency vibrating solid mass as a movable sensitive element, and is a microelectronic and micro mechanical combined miniaturized rate gyroscope. The solid mass of this gyroscope needs to be suspended by a mechanical elastic body to realize its vibration. This gyroscope has poor impact resistance and is easily damaged under high-speed impact. At the same time, the structure of this gyroscope is complex, the cost is high, and fatigue damage and vibration noise will occur during long-term operation. The micro inertial sensor based on thermal expansion principle uses gas instead of the traditional solid mass, and obtains the angular velocity of the outside world by sensing the temperature change of the temperature field due to the angular velocity through a temperature sensor. Because there is no solid mass, vibration and sensitive structure of the traditional inertial sensor, the micro inertial sensor based on thermal expansion principle has very high impact resistance, has a high measurement range under the condition of ensuring a certain precision, and is widely used in the fields of aerospace, navigation, electronic equipment, etc.

[0004] The working principle of a micro thermal expansion flow gyroscope is to use the temperature change of a temperature field to realize the measurement of angular velocity. When the heater is heated under the action of a driving current, the heater heats the surrounding gas to produce thermal expansion flow to form a temperature field, and the thermal expansion flow uniformly flows to the thermal resistors on both sides. In the absence of angular velocity input, the temperature of the temperature field is symmetrically distributed along the heater, at which time the temperatures sensed by the thermal resistors are the same, and the output voltage of the detection circuit is zero. When there is an angular velocity signal input in the Z direction, a Y direction Coriolis acceleration is generated on the X direction moving gas. This acceleration causes the temperature of the temperature field to shift in the Y direction, thereby causing the thermal resistors at the symmetric positions in the Y direction to change differently, and a voltage proportional to the input angular velocity is output through the Wheatstone bridge, and the angular velocity value is obtained.

[0005] In the Chinese patent application: a "cross" type push-pull flow micromechanical three-axis thin film gyroscope (patent application number CN202010584698.1), the heater of the micro push-pull type mechanical three-axis thin film gyroscope alternately expands and flows, and the thermistor connected to the same Wheatstone bridge is continuously affected by the thermal expansion flow generated by the heater, so the cooling effect of the thermistor is poor, thereby weakening the sensitive effect of the thermistor to temperature change, reducing the resistance value change range of the thermistor, and the sensitivity of the sensor is low. In the existing solution, although the sensitivity can be improved by increasing the power of the heater, although the sensitivity can be improved by reducing the thickness of the sensitive layer to improve heat dissipation, but the sensitivity of the gyroscope is not substantially improved due to the limitation of the stability of the gyroscope structure, so solving the above problems becomes a technical problem that technicians in the field urgently need to solve. SUMMARY

[0006] The purpose of the present application is to provide an independent sensitive MEMS thermal expansion flow gyroscope to solve the technical problems existing in the prior art.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] The present application provides an independent sensitive MEMS thermal expansion flow gyroscope, comprising a sensitive layer and a cover plate, wherein,

[0009] The upper surface of the sensitive layer has two heaters and two pairs of thermistors, and a rectangular groove is etched at the center position of the lower surface of the sensitive layer;

[0010] The length and width directions of the sensitive layer are defined as X and Y directions respectively, and the height direction of the sensitive layer is Z direction; the heaters are distributed on both sides of the groove and are symmetric to the center of the groove and perpendicular to the X axis; the thermistors are placed perpendicular to the X direction, and the four thermistors are symmetrically distributed, respectively distributed on both sides of the two heaters, and the thermistors on both sides of a heater form an independent sensitive unit, there are two independent sensitive units for detecting the angular velocity of Z axis;

[0011] The two ends of the heater are covered with symmetrical electrodes along the Y direction to form an alternating heating heat source;

[0012] The two ends of the thermistor of the sensitive unit are provided with symmetrical electrodes along the X direction;

[0013] The energization mode of the two heaters is periodic push-pull energization, that is, one working cycle of the heater includes pulse voltage excitation time and power-off interval time;

[0014] The heaters are driven by two square wave signals of the same frequency, the phase difference is 90 degrees, and the pulse duty cycle is 50%;

[0015] The power supply mode of the independent sensitive unit is constant current;

[0016] The cover plate is engraved with a cavity, and is closely connected with the sensitive layer to form a sealed working space; the depth of the groove on the lower surface of the sensitive layer and the cavity of the upper cover is the total cavity height z, 800 μm≤z≤1500 μm.

[0017] As a further technical solution, the height of the rectangular groove is 1 / 2 to 3 / 4 of the height of the entire sensitive layer.

[0018] As a further technical solution, the depth of the groove etched on the cover plate is 500 μm to 1000 μm.

[0019] As a further technical solution, the outer edge of the rectangular groove is larger than the outer contour of the upper surface heater and the thermistor.

[0020] As a further technical solution, the height of the heater and the thermistor on the upper surface of the sensitive layer is 20 nm to 40 nm.

[0021] As a further technical solution, the heater and the thermistor are both composed of a metal layer composed of a chromium layer (adhesion layer), a platinum layer (resistance layer) and a gold layer.

[0022] By adopting the above technical solution, the present application has the following beneficial effects:

[0023] 1. This independent detection type MEMS thermal expansion flow gyroscope inherits the advantages of MEMS thermal expansion flow gyroscopes, and has a compact structure, small size, light weight, and is easy to be intelligentized and integrated.

[0024] 2. This thermal expansion flow gyroscope adopts an independent sensitive unit. The thermistors on both sides of a heater form an independent sensitive unit. This independent sensitive feature is that one sensitive unit only senses the temperature change of one heater. When the heaters are heated alternately, the sensitive unit is not affected by other heaters, so that the sensitive unit has better cooling effect, and can sense a larger temperature difference when the sensitive temperature changes, thereby improving the sensitivity of the gyroscope.

[0025] 3. The sensitive element of the independent sensitive type MEMS thermal expansion flow gyroscope has no cantilever beam structure, and has the advantages of good impact resistance, simple structure, extremely low cost, high reliability and the like.

[0026] 4. It has the advantages of high impact resistance, simple structure, low cost, high reliability, high sensitivity and the like.

[0027] 5. Good consistency, easy to introduce a microcomputer embedded system (single-chip microcomputer) for temperature compensation and non-linearity compensation, and can realize batch production. BRIEF DESCRIPTION OF DRAWINGS

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 A three-dimensional structural diagram of a gyroscope provided in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the three-dimensional structure of the cover plate provided in an embodiment of the present invention;

[0031] Figure 3 A top view of the sensitive layer provided in an embodiment of the present invention;

[0032] Figure 4 for Figure 3 Sectional view along axis AA;

[0033] Figure 5 This is the specific structure of the thermal expansion flow gyroscope thermistor in the embodiment of the present invention;

[0034] Figure 6 The specific structure of the heater in the embodiment of the present invention;

[0035] Figure 7 A schematic diagram illustrating the working principle of an embodiment of the present invention;

[0036] Figure 8 The fabrication process flow diagram of the independently detectable MEMS thermal expansion flow gyroscope provided in this embodiment of the invention.

[0037] Icons: 1-Sensitive layer, 2-Thermistor, 3-Heater, 4-Thermistor, 5-Rectangular groove, 6-Thermistor, 7-Heater, 8-Thermistor, 9-Cover plate, 10-Cavity, 11-Thermistor wire, 12-Thermistor wire, 13-Heating resistance wire. Implementation

[0038] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application.

[0040] In combination Figures 1-6 As shown in the drawings, the embodiment provides an independent sensitive MEMS thermal expansion flow gyroscope, which comprises a sensitive layer 1 and a cover plate 9, wherein,

[0041] The upper surface of the sensitive layer is provided with two heaters and two pairs of thermistors, and the lower surface of the sensitive layer is etched with a rectangular groove 5. The rectangular groove 5 is arranged to make the main body thickness of the sensitive layer very thin, i.e. a silicon thin film structure, which is beneficial to the thermal diffusion of the working thermal flow in the sealed cavity.

[0042] The length and width directions of the sensitive layer are defined as X and Y directions respectively, and the height direction of the sensitive layer is defined as Z direction. The placement directions of the heaters and the thermistors are parallel or perpendicular to the X or Y direction. The thermistors on both sides of a heater form a sensitive unit, and two independent sensitive units are formed in total.

[0043] The heater 3 (H1) and the heater 7 (H2) are placed in the Y-axis direction and perpendicular to the X-axis, and are symmetrically arranged with the center of the groove.

[0044] The thermistors on both sides of the heater 3, i.e. the thermistor 2 (TD a1 ) and the thermistor 4 (TD a2 ), are symmetrically placed along the heater 3 and are perpendicular to the X-axis and parallel to the Y-axis.

[0045] The thermistors on both sides of the heater 7, i.e. the thermistor 6 (TD b2 ) and the thermistor 8 (TD b1 ), are symmetrically placed along the heater 7 and are perpendicular to the X-axis and parallel to the Y-axis. The heater is composed of a plurality of heating resistance wires 13 connected in series, and the thermistor is composed of a plurality of thermistor wires 11 / 12 connected in series.

[0046] The cover plate 9 is etched with a cavity 10, which is in airtight connection with the upper surface of the sensitive layer 1.

[0047] In combination Figure 7As shown, in this embodiment, as a further technical solution, the two heaters are driven by two square wave signals of the same frequency, with a phase difference of 90 degrees and a pulse duty cycle of 50%. The heater generates Joule heat, releases heat to the surrounding gas, and performs heat diffusion to form a thermal expansion flow. The square wave acting on the heater alternately heats and cools each pair of heaters, forming a push-pull thermal expansion flow between each pair of heaters. The square wave driving the heater works in two stages. In the first stage, heater 3 is powered to heat and generate a thermal expansion flow, and heater 7 is not powered and is at ambient temperature. In the second stage, heater 7 is powered to heat and generate a thermal expansion flow, and heater 3 is not powered and is at ambient temperature. When there is no angular velocity input in the Z-axis, in the first stage, the thermal expansion flow generated by heater 3 diffuses uniformly, and thermistor 2 and thermistor 4 sense the same temperature. In the second stage, the thermal expansion flow generated by heater 7 diffuses uniformly, and thermistor 6 and thermistor 8 sense the same temperature. When there is angular velocity input in the Z-axis, due to the principle of Coriolis force, in the first stage, the thermal expansion flow generated by heater 3 will be deflected in the YOX plane. The temperature of the thermistor to which the thermal flow is deflected is higher than that of the thermistor on the other side of the heater. Therefore, thermistor 2 and thermistor 4 sense a temperature difference proportional to the angular velocity. At this time, the independent sensing unit composed of thermistor 2 and thermistor 4 works, and the independent sensing unit composed of thermistor 6 and thermistor 8 cools. In the second stage, the thermal expansion flow generated by heater 7 will be deflected in the YOX plane. The temperature of the thermistor to which the thermal flow is deflected is higher than that of the thermistor on the other side of the heater. Therefore, thermistor 6 and thermistor 8 sense a temperature difference proportional to the angular velocity. At this time, the independent sensing unit composed of thermistor 6 and thermistor 8 works, and the independent sensing unit composed of thermistor 2 and thermistor 4 cools. The two pairs of thermistors 2 and 4, thermistors 6 and 8 are connected to form two equal arms of a Wheatstone bridge. Heating will change the resistance of the hot wire. The change in resistance is converted into a voltage V proportional to the angular velocity of the Z-axis by the Wheatstone bridge, thereby sensing the angular velocity in the Z-axis. z Output, thereby sensing the angular velocity in the Z-axis. The sensing unit of this working mode works independently, and the temperature difference sensed in the first stage and the second stage does not affect each other, which has better cooling effect and thus improves the sensitivity.

[0048] The cover plate and the sensing layer isolate the intermediate groove and the cavity gas medium from the outside, forming a sealed working space; the depth of the intermediate heating cavity and the groove in the upper cover is the total cavity height z, 800 μm≤z≤1500 μm.

[0049] In this embodiment, as a further technical solution, the height of the rectangular groove 5 is 2 / 3 to 3 / 4 of the height of the entire sensing layer 1, so that the total cavity height is in the order of hundreds of microns.

[0050] In the embodiment, as a further technical solution, the height of the heater and the thermistor on the upper surface of the sensitive layer is 20-40 microns, and the total cavity height is in the order of hundreds of microns, which can effectively inhibit the natural convection of gas flow in the cavity, thereby improving the sensor performance.

[0051] In the embodiment, as a further technical solution, the energization mode of the two heaters is a periodic push-pull energization, that is, one working cycle of the heater includes a pulse voltage excitation time and a power-off interval time; and the energization mode of the thermistor is constant current.

[0052] In the embodiment, as a further technical solution, the length of the thermistor and the heater is consistent, and is 1 / 7-1 / 6 of the width of the entire sensitive layer, which can improve the sensitivity of the sensor.

[0053] In combination with Figure 8 As shown in the figure, the specific process flow of the disclosed independent sensitive MEMS thermal expansion flow gyroscope is as follows:

[0054] Step (a): thermally oxidizing a 200-micron-thick silicon dioxide film on an N-type (100) 300-micron single crystal silicon wafer;

[0055] Steps (b), (c), and (d): forming a thermistor structure pattern on the silicon dioxide film by photolithography;

[0056] Steps (e) and (f): etching away a portion of the silicon dioxide by a wet etching process;

[0057] Step (g): etching and processing a 400-micron-deep groove by a silicon etching process, so that the thermistor and the heater are suspended and fixed on the sensitive layer through the silicon dioxide film, and the fabrication of the sensitive layer is completed;

[0058] Steps (h) and (i): sputtering a metal layer composed of a chromium layer (adhesion layer), a platinum layer (resistor layer), and a gold layer on the photoresist and the silicon dioxide in sequence by a magnetron sputtering process;

[0059] Step (j): stripping away the metal layer outside the thermistor structure pattern by an ultrasonic stripping process to form the thermistor structure; bonding the cover plate and the sensitive layer by a bonding process, leading out the metal pins by wire bonding, so that the upper surface of the sensitive layer is in a sealed cavity, and the fabrication of the sensitive element is completed.

[0060] In summary, the application inherits the advantages of the MEMS thermal expansion flow gyroscope, and has compact structure, small volume, light weight, easy intelligentization and integration. The thermistor of the gyroscope adopts an independent sensitive structure, the cooling effect of the thermistor is better, a higher temperature difference can be sensed, and the sensitivity is higher. The independent sensitive MEMS thermal expansion flow gyroscope has no cantilever beam structure, and has good impact resistance. The consistency is good, the subsequent sensor conditioning circuit can be easily introduced, temperature compensation and non-linearity compensation can be performed, and batch production can be realized. The gyroscope has the advantages of compact structure, moderate sensitivity, extremely low cost, high reliability and the like.

[0061] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A self-sensing MEMS thermal expansion flow gyro, characterized by, It comprises a sensitive layer and a cover plate, wherein, two heaters and two pairs of thermistors are arranged on the upper surface of the sensitive layer, and a rectangular groove is etched at the center of the lower surface of the sensitive layer; the length and width directions of the sensitive layer are defined as X and Y directions respectively, and the height direction of the sensitive layer is defined as Z direction; the heaters are distributed on both sides of the groove and symmetric to the center of the groove and perpendicular to the X axis; the thermistors are arranged perpendicular to the X direction, and four thermistors are symmetrically distributed on both sides of two heaters, and the thermistors on both sides of one heater form an independent sensitive unit without cantilever beam structure, and there are two independent sensitive units for detecting the angular velocity of the Z axis; the two ends of the heater are covered with symmetric electrodes along the Y direction to form a heat source with alternating heating; the two ends of the thermistors of the sensitive unit are provided with symmetric electrodes along the X direction; the energization mode of the two heaters is periodic push-pull energization, that is, one working cycle of the heater includes pulse voltage excitation time and power-off interval time; the heaters are driven by two square wave signals with the same frequency, the phase difference is 90 degrees, and the pulse duty cycle is 50%; the energization mode of the independent sensitive unit is constant current; the cover plate is etched with a cavity and is closely connected with the sensitive layer to form a sealed working space; the depth of the groove on the lower surface of the sensitive layer and the cavity on the upper cover is the total cavity height z, and 800 μm≤z≤1500 μm.

2. The self-sensing MEMS thermal expansion flow gyroscope of claim 1, wherein, The height of the rectangular groove is 1 / 2 to 3 / 4 of the height of the entire sensitive layer.

3. The self-sensing MEMS thermal expansion flow gyroscope of claim 1, wherein, The depth of the groove etched on the cover plate is 500 μm to 1000 μm.

4. The self-sensing MEMS thermal expansion flow gyroscope of claim 1, wherein, The outer edge of the rectangular groove is larger than the outer contour of the upper surface heater and thermistor.

5. The self-sensing MEMS thermal bulge flow gyroscope of claim 1, wherein, The height of the heater and thermistor on the upper surface of the sensitive layer is 20 nm to 40 nm.

6. The self-sensing MEMS thermal bulge flow gyroscope of claim 1, wherein, The heater and thermistor are both composed of a metal layer composed of a chromium layer, a platinum layer and a gold layer.

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