Triple-heat source triaxial micromechanical accelerometer

Abstract

This invention discloses a three-heat-source triaxial micromechanical accelerometer, comprising a base layer, a sensitive layer, and a cover plate. The sensitive layer is divided into three parts, respectively detecting X, Z, and Y-axis accelerations. A cavity is disposed below the center of each location, and a heater is disposed at the center of the cavity. The part of the sensitive layer that detects X and Y-axis acceleration includes two thermistors, with a rectangular central detection cavity below. The thermistor for detecting Z-axis acceleration is located in the central cavity. Both the heater and the thermistors are energized with direct current. The heater of the triaxial micromechanical accelerometer is located at the center of the detection cavity, and the sensitive layer is located above the central detection cavity. The cover plate is etched with grooves and is sealed to the surface of the sensitive layer. The sensitive element used in this invention is fabricated on a silicon wafer through photolithography, etching, and other processes, resulting in good consistency and facilitating the integration of sensor conditioning circuitry for temperature compensation and nonlinearity compensation. This not only improves sensor performance but also enables mass production.

Description

Technical Field

[0001] This invention relates to a technology that uses a thermistor to detect the acceleration and attitude parameters of a moving carrier by sensing the movement of hot gas under acceleration, and particularly to a three-heat-source triaxial micromechanical accelerometer, which belongs to the field of inertial measurement. Background Technology

[0002] MEMS accelerometer technology is developing rapidly and is entering the industrialization process. Currently, piezoresistive accelerometers and thermal convection accelerometers have been industrialized, and capacitive micromechanical accelerometers have also entered small-scale production. The future development trend of MEMS accelerometers is towards achieving high-precision accelerometer chips, moving towards miniaturization, higher integration, and higher sensitivity. As a type of MEMS inertial sensor, MEMS accelerometers have the following main advantages: they can independently acquire inertial information, making them more stable, while systems such as GPS rely on external information to function properly and cannot independently complete information measurement. MEMS accelerometers are currently mainly used in fields with moderate accuracy and low cost requirements, such as earthquake research, robotics engineering, and military sacrificial devices. The main advantage for these fields is that MEMS devices are inexpensive and easy to use.

[0003] The most commonly used type of accelerometer is the pendulum accelerometer. Currently, there are three main types of pendulum accelerometers: liquid pendulum, solid pendulum, and heat flow accelerometer. Solid pendulum sensors have complex structures and high costs; the amplitude of motion of a solid pendulum is large, making it difficult to withstand high overloads or shocks. Liquid pendulum sensors suffer from numerous internal components, long response times, and performance susceptibility to temperature variations. In contrast, heat flow accelerometers have small sensitive masses, simple structures, and offer advantages such as high overload resistance, short response times, good temperature performance, and low cost, making them suitable for harsh environments. Currently, the market demands increasingly higher levels of environmental adaptability from miniature accelerometers; therefore, micromechanical systems (MEMS) heat flow accelerometers have secured a place among MEMS sensors due to their ultra-high shock resistance and ultra-low manufacturing cost.

[0004] The working principle of a micromechanical (MEMS) heat flow accelerometer is as follows: A resistive heater is placed in a sealed cavity, and symmetrically distributed parallel thermistors are placed around it. When the heater is energized, it generates a heat source that emits heat flow to the surrounding area. Due to the symmetrical temperature field distribution, the effect on the thermistors is consistent. When there is an external acceleration input, the flow direction of the hot air is the same as the acceleration direction, shifting towards the input acceleration direction. This causes an asymmetrical temperature field distribution in the airflow, resulting in opposite temperature changes for two adjacent thermistors in the same direction, creating a temperature difference between the two thermistors. Acceleration can be detected by measuring this temperature difference using a Wheatstone bridge. The micromechanical heat flow accelerometer in the Chinese patent, "Miniature Silicon Bridge Thermal Convection Accelerometer" (patent application number 02116842.3), utilizes the heat flow generated by the heater to move under the action of input linear acceleration, creating an asymmetrical temperature field. The asymmetrical temperature field distribution is detected by setting symmetrical thermistors. Because the hot airflow velocity is very low, the asymmetric temperature field gradient caused by airflow deflection is also very small. Therefore, the unbalanced voltage output by the Wheatstone bridge composed of thermistors is small, resulting in low sensor sensitivity. While existing solutions can improve sensitivity by increasing heater power, power consumption limitations prevent a substantial change or improvement in sensitivity, making it difficult to overcome this bottleneck for practical application. Summary of the Invention

[0005] The purpose of this invention is to provide a three-heat-source triaxial micromechanical accelerometer to solve the technical problems existing in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a three-heat-source triaxial micromechanical accelerometer, comprising a base layer, a sensing layer, and a top cover, wherein...

[0008] The sensitive layer is divided into three parts, which respectively detect the acceleration of the X, Z and Y axes. A cavity is set below the center of each position, and a heater is set in the center of the cavity; the base layer and the sensitive layer are bonded together.

[0009] The rectangular accelerometer is defined with its length and width directions as X and Y, respectively, and the height direction of the sensitive layer as Z. The X and Y detection thermistors are placed perpendicular to the X and Y directions, respectively, and are used to detect the acceleration along the X and Y axes. The Z-axis detection thermistor is placed perpendicular to the X-axis and together with the X-axis detection thermistor, it detects the Z-axis acceleration.

[0010] The heater is positioned at the center of the detection chamber, forming a three-heat-source triaxial micromechanical accelerometer heater; the two thermistors of the X and Y detection sections are located in the sensitive layer and are symmetrically arranged on the left and right sides of the heater along the Y and X directions, respectively; the two thermistors of the Z detection section are located in the middle cavity and are symmetrically arranged on the left and right sides of the heater.

[0011] The X and Z heaters are covered with symmetrical electrodes along the Y direction at both ends to form a heating source; the Y heater is covered with symmetrical electrodes along the X direction at both ends to form a heating source.

[0012] Both the heater and the thermistor are energized with direct current.

[0013] The cover plate and base layer isolate the gas medium in the intermediate detection chamber from the outside world, forming a sealed sensitive system; the depth of the intermediate heating chamber and the groove in the upper cover is the total cavity height z, 300μm≤z≤1000μm.

[0014] As a further technical solution, the groove depth of the cover plate is 2 / 3 of the cover plate height.

[0015] As a further technical solution, the height of the heater and thermistor on the upper surface of the sensitive layer is 100nm to 1000nm.

[0016] As a further technical solution, the length of the thermistor is 1 / 6 to 1 / 4 of the width of the entire sensitive layer.

[0017] As a further technical solution, the length of the heater is 1 / 8 to 1 / 6 of the width of the entire sensitive layer.

[0018] As a further technical solution, the thermistor and heater are composed of a metal layer consisting of a chromium layer, a platinum layer and a gold layer.

[0019] By adopting the above technical solution, the present invention has the following beneficial effects:

[0020] 1. This three-heat-source triaxial micromechanical accelerometer inherits the advantages of MEMS heat flow accelerometers, with a compact structure, small size, light weight, and easy intelligentization and integration.

[0021] 2. The sensitive structure of this accelerometer is the thermistor on both sides of the heater inside the middle cavity. It can sense the hot airflow that changes with acceleration. The signal is then collected by the acquisition system after passing through the amplification circuit, subsequent conditioning circuit, and so on.

[0022] 3. This three-heat-source triaxial micromechanical accelerometer uses a sensitive structure with central support, resulting in low structural stress.

[0023] 4. Good consistency, easy to introduce subsequent sensor conditioning circuits for temperature compensation and nonlinearity compensation, enabling mass production.

[0024] 5. It features a compact structure, moderate sensitivity, extremely low cost, high reliability, and excellent impact resistance. Attached Figure Description

[0025] 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.

[0026] Figure 1 This is a three-dimensional structural diagram of an accelerometer provided in an embodiment of the present invention;

[0027] Figure 2 This is a three-dimensional structural diagram of the accelerometer cover plate provided in an embodiment of the present invention;

[0028] Figure 3 A top view of the sensitive layer and substrate provided in an embodiment of the present invention;

[0029] Figure 4 for Figure 3 Sectional view along axis AA;

[0030] Figure 5 The specific structure of the heating element in an embodiment of the present invention;

[0031] Figure 6 This is the specific structure of the triaxial accelerometer thermistor element in an embodiment of the present invention;

[0032] Figure 7 The working principle diagrams of the X-axis and Y-axis provided in the embodiments of the present invention;

[0033] Figure 8 A schematic diagram of the Z-axis working principle provided in an embodiment of the present invention;

[0034] Figure 9 The schematic diagram of the output circuit provided in the embodiment of the present invention;

[0035] Figure 10 A process flow diagram for fabrication of a three-heat-source triaxial micromechanical accelerometer provided in this embodiment of the invention;

[0036] Icons: 1-Base layer, 2-Sensitive layer, 3-X-axis detection cavity, 4-Thermistor, 5-Heater, 6-Thermistor, 7-Z-axis detection cavity, 8-Thermistor, 9-Heater, 10-Thermistor, 11-Y-axis detection cavity, 12-Thermistor, 13-Heater, 14-Thermistor, 15-Top cover, 16-Groove, 17-Heating resistance wire, 18-Thermistor wire. Implementation

[0037] 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.

[0038] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0039] Combination Figure 1-6 As shown, this embodiment provides a three-heat-source triaxial micromechanical accelerometer, including a base layer 1, a sensing layer 2, and a cover plate 15, wherein...

[0040] The sensitive layer 2 is divided into three parts, which respectively detect the acceleration of the X, Z and Y axes. An X-axis detection cavity 3, a Z-axis detection cavity 7 and a Y-axis detection cavity 11 are respectively set below the center of each position, and heaters 5, 9 and 13 are respectively set in the center of the cavity; the base layer 1 and the sensitive layer 2 are bonded together;

[0041] The accelerometer's length and width directions are defined as X and Y, respectively, and the height direction of the sensitive layer 2 is defined as Z. The X-axis detection part, thermistors 4 and 6, are placed perpendicular to the X-axis and are used to detect the acceleration along the X-axis. The Z-axis detection part, thermistors 8 and 10, are placed perpendicular to the X-axis and together with thermistors 4 and 6, detect the acceleration along the Z-axis. The Y-axis detection part, thermistors 12 and 14, are placed along the X-axis and are used to detect the acceleration along the Z-axis.

[0042] Heaters 5, 9, and 13 are positioned at the center of the X-axis detection cavity 3, the Z-axis detection cavity 7, and the Y-axis detection cavity 11, forming a three-heat-source triaxial micromechanical accelerometer heater. The two thermistors 4 and 6 of the X-axis detection part are located in the sensitive layer 2 and are symmetrically arranged on the left and right sides of the heater 5 along the Y direction. The two thermistors of the Z-axis detection part are located in the middle cavity 7 and are symmetrically arranged on the left and right sides of the heater 9. The two thermistors 12 and 14 of the Y-axis detection part are located in the sensitive layer 2 and are symmetrically arranged on the left and right sides of the heater 13 along the X direction.

[0043] The heaters 5 and 9 have symmetrical electrodes covering their ends along the Y direction to form a heating source; the heater 13 has symmetrical electrodes covering its ends along the X direction to form a heating source.

[0044] The heaters 5, 9, and 13, and the thermistors 4 (RT1), 6 (RT2), 8 (RT3), 10 (RT4), 12 (RT5), and 14 (RT6) are all powered by direct current. The heaters are composed of several heating resistance wires 17 connected in series, and the thermistors are composed of several thermistor wires 18 connected in series.

[0045] The cover plate 15 has a rectangular groove 16 etched on it, and is sealed to the sensitive layer 2.

[0046] Combination Figure 7 and Figure 9 As shown, in this embodiment, as a further technical solution, heaters 5, 9, and 13 are supplied with a constant voltage. The resistance heaters generate Joule heating, releasing heat to the surrounding gas and diffusing it to form a heat flow around them. The temperature field generated by this heat flow is symmetrically distributed across two thermistors with the same resistance. When there is a linear acceleration input parallel to the sensitive layer direction in the X (same in the Y direction) direction, the hot gas moves in the same direction as the acceleration. When the acceleration points along the X-axis towards the thermistor input, the hot gas moves closer to one thermistor and further away from the other. The voltage difference across the two thermistors is proportional to the magnitude of the acceleration. Therefore, acceleration in the X-axis direction can be detected. The detection circuit is as follows... Figure 9 As shown.

[0047] Combination Figure 8 and Figure 9 As shown. When no acceleration is input in the Z direction, the voltage difference between thermistors 4 (6) and 8 (10) is a fixed value. When acceleration is input in the Z direction, the voltage difference between thermistors 4 (6) and 8 (10) changes, and the voltage difference is proportional to the magnitude of the acceleration. This constitutes a three-heat-source triaxial micromechanical accelerometer. The detection circuit is as follows. Figure 9 As shown.

[0048] The cover plate 15 and the base layer 1 isolate the gas medium in the intermediate cavity from the outside world, forming a sealed working system; the height of the intermediate cavity and the depth of the groove 16 in the upper sealing layer are the total cavity height z, 300μm≤z≤1000μm.

[0049] In this embodiment, as a further technical solution, the depth of the groove 16 is 2 / 3 of the height of the cover plate 15, so that the total cavity height is on the order of hundreds of micrometers.

[0050] In this embodiment, as a further technical solution, the height of the heater and thermistor is 100nm to 1000nm, and the total cavity height is on the order of hundreds of micrometers. This can effectively suppress the natural convection motion of gas flow in the cavity, thereby improving the sensor performance.

[0051] In this embodiment, as a further technical solution, the length of the thermistor is 1 / 6 to 1 / 4 of the width of the entire sensitive layer.

[0052] In this embodiment, as a further technical solution, the heating resistance is 1 / 8 to 1 / 6 of the width of the entire sensitive layer.

[0053] Combination Figure 9 As shown in the diagram, the balancing resistors range from 5kΩ to 100kΩ (R1, R2).

[0054] Combination Figure 10 As shown, the specific process flow of the three-heat-source triaxial micromechanical accelerometer disclosed in this invention is as follows:

[0055] Step (a): Thermally oxidize a 200 μm thick silicon dioxide film on an N-type (100) 300 μm single crystal silicon wafer;

[0056] Steps (b), (c), and (d): Photolithography is used to form the thermistor structure pattern on the silicon dioxide film;

[0057] Steps (e) and (f): A portion of the silicon dioxide is etched away using a wet etching process;

[0058] Step (g): A groove with a depth of 300µm is formed by etching using a silicon etching process, so that the thermistor and heater are suspended and fixed on the sensitive layer through the silicon dioxide film, thus completing the fabrication of the sensitive layer;

[0059] Step (h)(i): Using magnetron sputtering, a metal layer consisting of a chromium layer (adhesion layer), a platinum layer (resistive layer) and a gold layer is sequentially sputtered onto photoresist and silicon dioxide;

[0060] Step (j): Use ultrasonic stripping technology to remove the metal layer outside the thermistor structure pattern to form the thermistor structure; use bonding technology to bond the cover plate and the sensitive layer, and use wire bonding to lead out the metal pins so that the upper surface of the sensitive layer is in a sealed cavity, thus completing the processing of the sensitive element.

[0061] In summary, this invention inherits the advantages of MEMS heat flow accelerometers, featuring a compact structure, small size, light weight, and ease of intelligent integration. The sensitive structure of this accelerometer consists of thermistors on both sides of the heater within the central cavity, which sense the changing heat flow with acceleration. The signal is then collected by the acquisition system after amplification and subsequent conditioning circuitry. This three-heat-source, three-axis micromechanical accelerometer employs a centrally supported sensitive structure, resulting in low structural stress. It exhibits good consistency, facilitates the integration of subsequent sensor conditioning circuitry for temperature and nonlinearity compensation, and enables mass production. It boasts a compact structure, moderate sensitivity, extremely low cost, high reliability, and excellent shock resistance.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-heat-source triaxial micromechanical accelerometer, comprising a base layer, a sensing layer, and a cover plate, wherein, The sensitive layer is divided into three parts, which respectively detect the acceleration of the X, Z and Y axes. A cavity is set below the center of each position, and a heater is set in the center of the cavity; the base layer and the sensitive layer are bonded together. The accelerometer is defined with its length and width directions as X and Y, respectively, and the height direction of the sensitive layer as Z. The thermistors of the X and Y detection sections are placed perpendicular to the X and Y directions, respectively, and are used to detect the acceleration along the X and Y axes. The thermistors of the Z-axis detection section are placed perpendicular to the X-axis and together with the thermistors of the X-axis detection section, they detect the acceleration along the Z-axis. The heater is positioned at the center of the detection chamber, forming a three-heat-source triaxial micromechanical accelerometer heater; the two thermistors of the X and Y detection sections are located in the sensitive layer and are symmetrically arranged on the left and right sides of the heater along the Y and X directions, respectively; the two thermistors of the Z detection section are located in the middle cavity and are symmetrically arranged on the left and right sides of the heater along the Y direction. The X and Z heaters are covered with symmetrical electrodes along the Y direction at both ends to form a heating source; the Y heater is covered with symmetrical electrodes along the X direction at both ends to form a heating source. Both the heater and the thermistor are energized with direct current. The cover plate and base layer isolate the gas medium in the intermediate detection chamber from the outside, forming a sealed sensitive system; the depth of the intermediate heating chamber and the groove in the upper cover is the total cavity height z, 300μm≤z≤1000μm; The groove depth of the cover plate is 2 / 3 of the height of the cover plate; The total height of the heater and thermistor in the sensitive layer is 100 nm to 1000 nm; The length of the thermistor is 1 / 6 to 1 / 4 of the width of the entire sensitive layer; The length of the heater is 1 / 8 to 1 / 6 of the width of the entire sensitive layer; The thermistor and heater are composed of metal layers consisting of chromium, platinum and gold layers.

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