阅读说明：本技术 一种谐振式压力传感器及其制备方法 (Resonant pressure sensor and preparation method thereof ) 是由 王淞立 方续东 蒋庄德 李�杰 高博楠 方子艳 孙昊 赵立波 田边 吴晨 邓武彬 于 2021-06-17 设计创作，主要内容包括：本发明公开了一种谐振式压力传感器及其制备方法,压力传感器包括碳化硅谐振器,碳化硅谐振器与压力敏感膜通过锚点相连,碳化硅谐振器包括支撑梁,支撑梁通过柔性梁与外部框架连接,支撑梁与固定电极连接并固定在锚点处,质量块结构通过谐振梁与支撑梁连接,耦合梁通过三角梁与质量块结构连接,耦合梁与可动电极连接,质量块结构与另一可动电极连接,固定电极与可动电极均为梳齿电极,并构成两对梳齿电极对,耦合梁上设置有拾振电阻,并连接有金属电极引线,通过三角梁的设计增大了耦合梁应力集中区域,配合拾振电阻的布置,提升了压力传感器的检测精度,基于第三代半导体材料碳化硅的优良特性,同时获得了高温环境下工作的长期稳定性。(The invention discloses a resonant pressure sensor and a preparation method thereof, the pressure sensor comprises a silicon carbide resonator, the silicon carbide resonator is connected with a pressure sensitive film through an anchor point, the silicon carbide resonator comprises a supporting beam, the supporting beam is connected with an external frame through a flexible beam, the supporting beam is connected with a fixed electrode and fixed at the anchor point, a mass block structure is connected with the supporting beam through a resonant beam, a coupling beam is connected with a mass block structure through a triangular beam, the coupling beam is connected with a movable electrode, the mass block structure is connected with another movable electrode, the fixed electrode and the movable electrode are both comb-tooth electrodes and form two pairs of comb-tooth electrodes, a vibration pickup resistor is arranged on the coupling beam and connected with a metal electrode lead, the stress concentration area of the coupling beam is increased through the design of the triangular beam, and the detection precision of the pressure sensor is improved by matching with the arrangement of the vibration pickup resistor, based on the excellent characteristics of the third generation semiconductor material silicon carbide, the long-term stability of the high-temperature environment is obtained.)

1. A resonant pressure sensor is characterized by comprising a resonator (1), wherein the resonator (1) is connected with a pressure sensitive film (13) through an anchor point (2); the resonator (1) comprises a supporting beam (3), the supporting beam (3) is connected with an external frame, two ends of the supporting beam (3) are respectively connected with a first fixed electrode (71) and a second fixed electrode (72), the supporting beam (3) is connected with a mass block structure (8) through a resonance beam (5), one side of the mass block structure (8) is connected with one side of a coupling beam (10) through a triangular beam (9), the coupling beam (10) is connected with a vibration pickup beam (17), vibration pickup resistors (11) are arranged on the vibration pickup beam (17), the other side of the coupling beam (10) is connected with a first movable electrode (61), and the other side of the mass block structure (8) is connected with a second movable electrode (62).

2. A resonant pressure sensor according to claim 1, characterized in that the triangular beam (9) is connected to the mass structure (8) by a connecting beam (16).

3. A resonant pressure transducer according to claim 1, characterized in that the pick-up beam (17) is located on an inner side wall of the coupling beam (10), which side wall is connected to one end of the triangular beam (9).

4. The resonant pressure sensor according to claim 1, wherein the first fixed electrode (71), the second fixed electrode (72), the first movable electrode (61), and the second movable electrode (62) are comb-teeth electrodes, the first fixed electrode (71) and the first movable electrode (61) form one pair of comb-teeth electrodes, and the second fixed electrode (72) and the second movable electrode (62) form the other pair of comb-teeth electrodes.

5. A resonant pressure sensor according to claim 1, characterized in that the supporting beam (3) is connected to the outer frame by a number of flexible beams (4).

6. A resonant pressure sensor according to claim 1, characterized in that the resonator (1) is provided at its upper end with a sealing cover plate (15).

7. A method of manufacturing a resonant pressure sensor according to claim 1, comprising the steps of:

step 1: taking a wafer as a substrate as a pressure sensitive film substrate layer (131);

step 2: respectively forming a silicon dioxide insulating layer (132) on the upper surface and the lower surface of the pressure sensitive film substrate layer (131);

and step 3: patterning the silicon dioxide insulating layer (132), and etching on the pressure-sensitive film substrate layer (131) to form anchor points (2);

and 4, step 4: forming a silicon dioxide insulating layer on the surface of the product obtained in the step 3;

and 5: in a resonatorForming silicon dioxide layers on the upper surface and the lower surface of the sheet (111); and dry etching to form SiO₂A mask layer (121);

step 6: SiO on the upper part of the resonator plate (111)₂Forming a coupling beam thinning area in an area covered by the mask layer (121);

and 7: carrying out vacuum bonding on the structure obtained in the step 6 and the structure obtained in the step 4;

and 8: polishing the thinned structure obtained in the step (7);

and step 9: lightly doping boron ions in the structure obtained in the step 8 to form a lightly doped region (112), and after diffusion annealing of the lightly doped region (112), forming a vibration pickup resistor (11);

step 10: carrying out boron ion heavy doping on the structure obtained in the step 9 to form an ohmic contact region (113);

step 11: a Ti/Al layer is made on the whole upper surface of the structure obtained in the step 10, and a metal electrode lead (12) and a bonding pad are formed by electrode patterning;

step 12: etching the structure obtained in the step 11 to form a support beam (3), a resonance beam (5), a first movable electrode (61), a second movable electrode (62), a first fixed electrode (71), a second fixed electrode (72), a mass block structure (8), a triangular beam (9), a coupling beam (10) and a vibration pickup beam (17) of the resonator (1);

step 13: etching a cavity at the lower part of the structure formed in the step 12 to form a pressure sensitive film (13);

step 14: and packaging the structure of the step 13.

8. The method according to claim 7, wherein in the step 1, the wafer is a silicon carbide wafer; in the step 5, the resonator plate is a silicon carbide resonator plate.

Technical Field

The invention belongs to the technical field of MEMS, and particularly relates to a resonant pressure sensor and a preparation method thereof.

Background

The pressure sensor is a device for converting non-electricity into an electric signal, has wide application in production measurement, is commonly used in various production automation control fields, and plays an important role in improving the precision, safety and quality of equipment. The pressure sensor is widely applied to the fields of novel fighters, aerospace aircrafts, cruise missiles, aircraft carriers, aerospace ground test systems, unmanned aerial vehicle monitoring and other heavy projects.

Common pressure sensors include resonant pressure sensors, capacitive pressure sensors, and the like. The capacitive pressure sensor has the main advantages of low input energy, quick dynamic response and good environmental adaptability. But the pressure detection range is limited, the nonlinearity is obvious, and the method is difficult to be applied to large-range pressure detection. Compared with a capacitive pressure sensor, the resonant pressure sensor has the advantages of high measurement sensitivity, good linearity and simpler processing. For a resonant pressure sensor, common excitation methods include electrostatic excitation, thermal excitation, and electromagnetic excitation, and meanwhile, detection methods include piezoresistive detection, capacitive detection, and the like. Thermal excitation typically contacts the resonator, damaging the resonator surface and reducing detection accuracy. Electromagnetic excitation requires an external magnetic field, and miniaturization of the sensor is difficult to realize. Compared with thermal excitation and electromagnetic excitation, the electrostatic excitation sensor has the advantages of small volume, high detection precision, long service life and the like, and is commonly used in the design of comb-tooth type pressure sensors. In the detection mode, the capacitance detection is easily interfered by the environment, and is a detection mode with weaker anti-interference capability, and the piezoresistive detection has high precision and strong anti-interference capability, and meanwhile, the piezoresistive detection has good output capability and higher signal-to-noise ratio. Meanwhile, common pressure sensors all adopt silicon as a sensitive film structure, so that the temperature drift is large, the stability is insufficient, and the pressure sensors are difficult to use under the high-temperature condition.

The resonant pressure sensor based on electrostatic excitation and piezoresistive detection needs a high quality factor, and meanwhile, in order to obtain high detection precision, the design and arrangement requirements of the coupling beam and the vibration pickup resistor are relatively high.

Disclosure of Invention

In order to solve the problems, the invention provides a high-temperature-resistant silicon carbide resonant pressure sensor and a preparation method thereof, which improve the sensitivity and detection precision of the resonant pressure sensor.

In order to achieve the above object, a resonant pressure sensor includes a resonator connected to a pressure sensitive membrane via an anchor point; the resonator comprises a supporting beam, the supporting beam is connected with an external frame, two ends of the supporting beam are respectively connected with a first fixed electrode and a second fixed electrode, the supporting beam is connected with a mass block structure through a resonance beam, one side of the mass block structure is connected with one side of a coupling beam through a triangular beam, the coupling beam is connected with a vibration pickup beam, vibration pickup resistors are arranged on the vibration pickup beam, the other side of the coupling beam is connected with a first movable electrode, and the other side of the mass block structure is connected with a second movable electrode.

Furthermore, the triangular beam is connected with the mass block structure through the connecting beam.

Further, the vibration pickup beam is positioned on the inner side wall of the coupling beam, and the side wall is connected with one end of the triangular beam.

Furthermore, the first fixed electrode, the second fixed electrode, the first movable electrode and the second movable electrode are all comb-tooth electrodes, the first fixed electrode and the first movable electrode form one pair of comb-tooth electrode pairs, and the second fixed electrode and the second movable electrode form the other pair of comb-tooth electrode pairs.

Further, the support beam is connected to the outer frame by a plurality of flexible beams.

Furthermore, a sealing cover plate is arranged at the upper end of the resonator.

The preparation method of the resonant pressure sensor comprises the following steps:

step 1: taking a wafer as a substrate as a pressure sensitive film substrate layer;

step 2: respectively forming a silicon dioxide insulating layer on the upper surface and the lower surface of the pressure sensitive film substrate layer;

and step 3: patterning the silicon dioxide insulating layer, and etching the pressure sensitive film substrate layer to form anchor points;

and 4, step 4: forming a silicon dioxide insulating layer on the surface of the product obtained in the step 3;

and 5: forming silicon dioxide layers on the upper surface and the lower surface of the resonator plate; and dry etching is carried out to form a SiO2 mask layer;

step 6: forming a coupling beam thinning area in an area covered by the SiO2 mask layer on the upper part of the resonator;

and 7: carrying out vacuum bonding on the structure obtained in the step 6 and the structure obtained in the step 4;

and 8: polishing the thinned structure obtained in the step (7);

and step 9: lightly doping boron ions in the structure obtained in the step 8 to form a lightly doped region, and forming a vibration pickup resistor after diffusion annealing of the lightly doped region;

step 10: carrying out boron ion heavy doping on the structure obtained in the step 9 to form an ohmic contact region;

step 11: making a Ti/Al layer on the whole upper surface of the structure obtained in the step 10, and patterning the electrode to form a metal electrode lead and a bonding pad;

step 12: etching the structure obtained in the step 11 to form a supporting beam, a resonance beam, a first movable electrode, a second movable electrode, a first fixed electrode, a second fixed electrode, a mass block structure, a triangular beam, a coupling beam and a vibration pickup beam of the resonator;

step 13: etching a cavity at the lower part of the structure formed in the step 12 to form a pressure sensitive film;

step 14: and packaging the structure of the step 13.

Further, in the step 1, the wafer is a silicon carbide wafer; in the step 5, the resonator plate is a silicon carbide resonator plate.

Compared with the prior art, the invention at least has the following beneficial technical effects:

1) the resonant pressure sensor is characterized in that a triangular beam is arranged between a coupling beam and a connecting beam, wherein the connecting part of the triangular beam and the connecting beam is the bottom edge of a triangle formed by the triangular beam, compared with the direct connection of the coupling beam and the connecting beam, the existence of the triangular beam promotes the increase of the connecting width of the connecting part, effectively increases the fixed constraint condition of the end part of the coupling beam, is beneficial to concentrating stress on a vibration pickup resistor, simultaneously, the interface of the triangular beam and the coupling beam is closer to the vibration pickup resistor, changes the original stress distribution, increases the stress concentration effect of the vibration pickup resistor of the coupling beam, and effectively improves the piezoresistive effect of the sensor and enhances the output of detection signals by matching with the arrangement of the vibration pickup resistor, thereby achieving the purposes of improving the quality factor, the sensitivity and the detection precision of the sensor.

2) The design of the supporting beam and the flexible beam plays a role in enhancing rigidity, and the quality factor of the sensor is in direct proportion to the rigidity of the resonator, so that the quality factor of the sensor is improved, and the sensitivity and the detection precision of the pressure sensor are further improved.

The preparation method of the pressure sensor provided by the invention adopts a mature process, is simple in manufacturing method, high in reliability and easy for batch production.

Furthermore, the silicon carbide film is adopted to replace the silicon film as the pressure bearing film, so that the temperature drift of the resonant sensor is reduced, the working temperature of the pressure sensor is improved, and the stability of the sensor is enhanced.

Drawings

Fig. 1 is an overall schematic diagram of a high-temperature-resistant silicon carbide resonant pressure sensor;

FIG. 2 is a longitudinal section of FIG. 1;

FIG. 3 is a top view of FIG. 1;

FIG. 4 is an enlarged view of a portion of the coupling beam and the triangular beam;

FIG. 5 is a schematic view of a process flow for preparing the present invention.

In the drawings: 1. resonator 111, resonator piece 2, anchor point 3, support beam 4, flexible beam 5, resonant beam 61, first movable electrode 62, second movable electrode 71, first fixed electrode 72, second fixed electrode 8, mass block structure 9, triangular beam 10, coupling beam 11, vibration pickup resistor 112, lightly doped region 113, ohmic contact region 114, thinning region 12, metal electrode lead wire 121, SiO₂Mask layer 13, pressure sensitive film 131, pressure sensitive film substrate layer 132, silicon dioxide insulating layer 14, glass pressure guide plate 15, sealing cover 16, connecting beam 17 and vibration pickup beam.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.

Referring to fig. 1, 2 and 3, a resonant pressure sensor includes a sealing cover 15, a resonator 1, an anchor point 2 and a glass pressure guide plate 14, which are sequentially disposed from top to bottom. The resonator 1 includes a pressure-sensitive membrane 13, a support beam 3, a flexible beam 4, a first fixed electrode 71, a second fixed electrode 72, a mass structure 8, four resonance beams 5, two coupling beams 10, two triangular beams 9, a connection beam 16, a connection beam 17, a first movable electrode 61, and a second movable electrode 62.

Referring to fig. 1 and 3, a resonator 1 is connected with a pressure sensitive membrane 13 through an anchor point 2, a support beam 3 arranged on the resonator 1 is connected with an external frame through a flexible beam 4, two ends of the support beam 3 are connected with fixed electrodes 7 and fixed on the anchor point 2, a mass block structure 8 is connected with the support beam 3 through four resonant beams 5, two sides of two coupling beams 10 are respectively connected with the small ends of triangular beams 9, the large ends of the two triangular beams 9 are connected to one side of the same connecting beam, and the other side of a connecting beam 16 is connected with the mass block structure 8; the other side of the coupling beam 10 is connected to the first movable electrode 61. The two triangular beams 9 and the connecting beam 16 are of an integral structure, and the connecting beam 16 is H-shaped; the mass block structure 8 is connected to the second movable electrode 62, the first fixed electrode 71, the second fixed electrode 72, the first movable electrode 61, and the second movable electrode 62 are all comb-teeth electrodes, the first fixed electrode 71 and the first movable electrode 61 form one pair of comb-teeth electrode pairs, and the second fixed electrode 72 and the second movable electrode 62 form the other pair of comb-teeth electrode pairs.

Referring to fig. 4, each coupling beam 10 includes four side walls connected end to end in sequence, a vibration pickup beam 17 is disposed in the middle of the inner side of the side wall connected to the triangular beam 9, a vibration pickup resistor 11 is disposed on the vibration pickup beam 17, the vibration pickup resistor 11 is connected to a metal electrode lead 12, and the metal electrode lead 12 is connected to an external output pad in sequence through the triangular beam 9, the connecting beam 16, the resonance beam 5, the support beam 3, and the flexible beam 4 to provide an output signal.

When in work, the movable electrode 6 in the two pairs of comb teeth electrodes and the fixed electrode 7 generate reciprocating motion under the action of alternating current, the vibration pickup resistor 11 generates periodic signal output to introduce pressure into the glass pressure guide plate 14, the pressure sensitive film 13 senses pressure and generates deformation, the anchor point 2 drives the frame beam 3 of the resonator 1 to generate displacement, meanwhile, the flexible beams 4 can effectively increase the rigidity and reduce the out-of-plane displacement of the resonator 1, the displacement generated by the frame beams 3 can change the rigidity of the four resonant beams 5 and the mass block structure 8, meanwhile, the resonance beam 5 is strained and deformed to generate resonance frequency change, the triangular beam 9 concentrates strain on the vibration pickup resistor 11 on the vibration pickup beam 17, so as to increase the output signal and improve the signal-to-noise ratio, and finally sense the magnitude of the loaded pressure by detecting the change of the output signal frequency of the Wheatstone half bridge consisting of the vibration pickup resistor 11 on the vibration pickup beam 17.

Referring to fig. 5, a method for manufacturing a high temperature resistant silicon carbide resonant pressure sensor specifically includes the following steps:

step 1, taking a (100) crystal orientation silicon carbide wafer as a substrate, cleaning and preparing the wafer to form a pressure sensitive film substrate layer 131;

step 2, adopting double-sided dry-wet-dry field oxidation to form a silicon dioxide insulating layer

Performing double-sided thermal oxidation on the pressure sensitive film substrate layer 131 by adopting a dry-wet-dry field oxidation process, and respectively forming a layer of compact silicon dioxide insulating layer 132 on the upper surface and the lower surface of the pressure sensitive film substrate layer 131;

step 3, etching silicon dioxide and silicon carbide to form anchor point structures

After gluing and developing, etching the silicon dioxide insulating layer 132 on the upper surface of the pressure sensitive film substrate layer 131 to form a mask layer, and forming anchor points 2 on the silicon carbide pressure sensitive film substrate layer 131 by adopting dry etching;

step 4, carrying out secondary thermal oxidation on the product obtained in the step 3, and forming a silicon dioxide insulating layer on the surface of the product;

step 5, etching SiO₂Formation of SiO₂Mask layer

Another piece (100) of crystal orientation silicon carbide wafer is taken as a resonator piece 111, and a silicon dioxide layer is formed on the upper surface and the lower surface of the resonator piece 111 by adopting a dry-wet-dry field oxidation method; and dry etching is used to form SiO on the upper surface of the resonator plate 111₂A mask layer 121;

step 6: dry etching of resonator plate 111

Forming a coupling beam 10 thinning region 114 on the surface of the resonator piece 111 by adopting a deep reactive ion etching process;

and 7: vacuum bonding

Carrying out vacuum bonding on the structure obtained in the step 6 and the structure obtained in the step 4, wherein the bonding pressure is 40kN, and the vacuum degree is 10^{- 5}mbar；

And 8: adopting a chemical mechanical polishing process, thinning the structure obtained in the step 7, and polishing;

and step 9: lightly doped

Depositing a layer of SiO on the structure obtained in step 8₂Layer, and patterning to form SiO₂Masking a layer, and then lightly doping with boron ions to form a lightly doped region 112; after diffusion annealing, the lightly doped region 112 forms a vibration pickup resistor 11 with uniformly distributed impurity concentration;

step 10: heavy doping

Depositing a layer of SiO on the structure obtained in the step 9₂Layer, and patterning to form SiO₂A mask layer is adopted, boron ions are adopted for heavy doping, a low-resistance ohmic contact region 113 is formed, and after diffusion annealing, an ohmic contact region with uniformly distributed impurity concentration is formed;

step 11: electrode patterning

Manufacturing a Ti/Al layer on the whole surface of the upper end face of the structure obtained in the step 10, and patterning the electrode to form a metal electrode lead 12 and a bonding pad;

step 12: deep reactive ion etching

Carrying out deep reactive ion etching to etch the silicon carbide layer and the silicon dioxide layer to form a supporting beam 3, a flexible beam 4, a resonant beam 5, a first movable electrode 61, a second movable electrode 62, a first fixed electrode 71, a second fixed electrode 72, a mass block structure 8, a triangular beam 9, a coupling beam 10 and a vibration pickup beam 17 of the resonator 1;

step 13: dry etching

Dry etching is adopted at the lower part of the structure formed in the step 12 to form a pressure sensitive film 13;

step 14: seal for a motor vehicle

And (4) carrying out vacuum anodic bonding on the structure in the step (13), the sealing cover (15) and the stress glass pressure guide plate (14) to finish integral packaging.

The invention provides a resonant pressure sensor, which has the main technical indexes that:

pressure range: 0kPa to 300 kPa;

working temperature: -20 ℃ to 800 ℃;

and (3) measuring precision: 0.02% FS

Response time: less than or equal to 100ms

The above description is only one embodiment of the present invention, and not all or only one embodiment, and any equivalent changes to the technical solutions of the present invention, which are made by those skilled in the art through reading the present specification, are covered by the claims of the present invention.