阅读说明：本技术 基于频率检测原理的mems压力传感器及制备方法 (MEMS pressure sensor based on frequency detection principle and preparation method ) 是由 侯鸿道 兰之康 董振兴 于 2021-08-30 设计创作，主要内容包括：基于频率检测原理的MEMS压力传感器,采用平面螺旋电感,且在该电感的一侧设置MEMS可变平行板电容,构成LC谐振电路；MEMS电容并联到CPW信号线和地线之间,其上极板为CPW信号线,且该上极板直接置于MEMS薄膜上,该MEMS薄膜正下方的衬底上设置凹槽,MEMS电容的下极板位于凹槽的底面和靠近地线的两个侧面上,且与地线相连；MEMS薄膜两端置于地线上,与凹槽形成密闭腔体。利用密闭腔体感测外部压强,当密闭腔体内外压差发生变化时,MEMS薄膜发生挠曲,引起MEMS电容的上极板和下极板之间的电容发生变化,使得CPW传输线上RF信号的谐振频率产生偏移,通过测量谐振频率值便可表征检测压力的大小。(The MEMS pressure sensor based on the frequency detection principle adopts a planar spiral inductor, and an MEMS variable parallel plate capacitor is arranged on one side of the inductor to form an LC resonance circuit; the MEMS capacitor is connected between the CPW signal line and the ground wire in parallel, the upper polar plate of the MEMS capacitor is the CPW signal line and is directly arranged on the MEMS film, a groove is arranged on the substrate right below the MEMS film, and the lower polar plate of the MEMS capacitor is positioned on the bottom surface of the groove and two side surfaces close to the ground wire and is connected with the ground wire; two ends of the MEMS film are arranged on the ground line, and a closed cavity is formed by the MEMS film and the groove. The closed cavity is used for sensing external pressure, when the pressure difference between the inside and the outside of the closed cavity is changed, the MEMS film is bent, the capacitance between the upper polar plate and the lower polar plate of the MEMS capacitor is changed, the resonance frequency of an RF signal on the CPW transmission line is deviated, and the detection pressure can be represented by measuring the resonance frequency value.)

1. A MEMS pressure sensor based on the principle of detecting frequency changes, comprising:

a substrate;

the CPW transmission line is arranged on the substrate and comprises a CPW signal line and CPW ground lines positioned on two sides of the CPW signal line, and the CPW signal line and the CPW ground lines are parallel to each other;

the planar spiral inductor comprises a lower layer channel and a coil and is positioned between the two CPW ground wires;

the MEMS variable parallel plate capacitor is arranged on one side of the planar spiral inductor and connected between the CPW signal line and the CPW ground wire in parallel, the MEMS variable parallel plate capacitor comprises an upper polar plate and a lower polar plate, a groove is arranged on the substrate right below the upper polar plate, the lower polar plate is arranged on the bottom surface of the groove and two side surfaces close to the CPW ground wire, and the lower polar plate is connected with the CPW ground wire; and

and the MEMS film is arranged at the top of the groove and is in direct contact with the bottom surface of the upper polar plate, two ends of the MEMS film are respectively arranged on the two CPW ground lines, and the MEMS film and the groove form a closed cavity.

2. The MEMS pressure sensor based on the principle of detecting frequency changes according to claim 1, wherein the coil of the planar spiral inductor is elevated above the substrate, and the lower channel is located on the substrate; the external joint of the coil is connected with the CPW signal wire, and the internal joint of the coil is connected with the lower-layer channel; the other end of the lower layer channel is connected with the CPW signal wire; an insulating medium layer covers the lower-layer channel below the coil; a buffer medium layer is arranged on the upper surface of the substrate.

3. The MEMS pressure sensor according to claim 2, wherein the groove is a U-shaped groove, the central axis of the groove is parallel to the CPW signal line, and the CPW signal line is located right above the groove.

4. The MEMS pressure sensor based on the principle of detecting frequency variation according to claim 3, wherein the sealed cavity formed by the MEMS membrane and the groove is a completely sealed space, i.e. the air inside the sealed cavity is not communicated with the outside air.

5. The MEMS pressure sensor based on the principle of detecting frequency variation according to claim 1, wherein the depth of the groove is 1-10 μm, and the thickness of the MEMS film, the CPW ground line and the CPW signal line is 0.5-5 μm.

6. Method for preparing a MEMS pressure sensor based on the principle of detecting frequency variations according to any of claims 1 to 5, characterized in that it comprises the following steps:

preparing a substrate, etching a groove on the substrate, and growing a buffer medium layer on the substrate in a thermal oxidation mode;

photoetching, evaporating and stripping are sequentially carried out on the buffer dielectric layer to obtain a lower channel of the planar spiral inductor and a lower polar plate of the MEMS variable parallel plate capacitor, and a CPW signal line and a CPW ground line are preliminarily obtained;

depositing and photoetching a sacrificial layer, and reserving the sacrificial layer in the groove;

forming an MEMS film on the sacrificial layer, reserving release holes at the parts of the MEMS film, which are positioned at the two sides of the CPW signal line, for releasing the sacrificial layer in the subsequent step, and then forming an insulating medium layer between the lower channel and the coil;

evaporating the titanium, gold and titanium seed layers in sequence, and carrying out photoetching, electroplating, photoresist removal and reverse etching to completely form the CPW signal line, the CPW ground wire, the planar spiral inductor and the MEMS variable parallel plate capacitor;

and releasing the sacrificial layer and filling release holes in the MEMS film.

7. The method for manufacturing a MEMS pressure sensor based on the principle of detecting frequency variation according to claim 6, wherein the materials of the MEMS variable parallel plate capacitor, the planar spiral inductor, the CPW signal line and the CPW ground line are gold.

8. The method for manufacturing a MEMS pressure sensor based on the principle of detecting frequency variation according to claim 6, wherein the substrate is made of high-resistivity silicon, and the resistivity thereof is greater than 1k Ω -cm.

9. The method of claim 8, wherein the depth of the groove is 1-10 μm, and the thickness of the MEMS film, the CPW ground line and the CPW signal line is 0.5-5 μm.

10. The method for manufacturing a MEMS pressure sensor based on the principle of detecting frequency variation according to claim 9, wherein the MEMS thin film is silicon nitride with a thickness of 0.5-3 μm.

Technical Field

The invention relates to the technical field of radio frequency micro-electro-mechanical systems (RF MEMS), in particular to an MEMS pressure sensor based on a frequency detection principle and a preparation method thereof.

Background

The pressure sensor can sense pressure signals and convert the pressure signals into output electric signals which are easy to measure according to a certain rule. The sensor is widely applied to the fields of automotive electronics, automatic control, aerospace, biomedical treatment, environmental monitoring and the like, and is one of the commonly used sensors in the industry. With the development of the MEMS technology, the pressure sensor prepared by the MEMS micromachining process has the advantages of miniaturization, low power consumption, batch production and the like; according to different pressure test types, the pressure sensor can be divided into a gauge pressure type, a differential pressure type and an absolute pressure type, and according to different pressure test principles, the pressure sensor can be mainly divided into a piezoresistive type, a capacitance type, a resonance type, a piezoelectric type and other principles. The piezoresistive pressure sensor is based on the piezoresistive effect principle of semiconductor materials (such as polysilicon and the like), has a simple structure, is greatly influenced by temperature, and needs a special temperature drift inhibition design; the capacitance type pressure sensor is based on the principle that capacitance variation is caused by capacitance distance or area variation, has high sensitivity but poor linearity and is easy to be interfered; the piezoelectric pressure sensor is based on the piezoelectric effect principle of materials (such as PZT, AlN and the like), has higher response speed, but the piezoelectric material is complex to prepare, and part of the piezoelectric material is difficult to be compatible with a standard process; the resonant pressure sensor is based on the principle that the resonant frequency of the structure changes along with the pressure, has high sensitivity, but has low resolution because the pressure changes little to the frequency deviation. With the increasing requirements for pressure measurement in consumer electronics, engineering applications, etc., there is an urgent need for a high-performance MEMS pressure sensor having the characteristics of simple and flexible structure, high accuracy, high sensitivity, high resolution, low cost, etc. Today, RF MEMS technology is being intensively studied to make possible MEMS pressure sensors based on the RF frequency detection principle and satisfying the above characteristics.

Disclosure of Invention

In order to solve the problems, the invention provides an MEMS pressure sensor based on a frequency detection principle and a preparation method thereof, an LC resonance circuit is formed by adopting a planar spiral inductor and an MEMS variable parallel plate capacitor, the pressure of the external environment is sensed by utilizing a closed cavity formed by a groove on a substrate and an MEMS film, when the pressure difference between the inside and the outside of the closed cavity is changed, the pressure is deflected by the acting force generated on the MEMS film, the capacitance between an upper plate and a lower plate of the MEMS variable parallel plate capacitor is changed, and further the resonance frequency of an RF signal on a CPW transmission line is shifted along with the capacitance, so that the environmental pressure can be obtained by measuring the value of the resonance frequency.

In order to achieve the above purpose, the invention adopts a technical scheme that:

a MEMS pressure sensor based on frequency detection principles, comprising: the CPW transmission line is arranged on the substrate and comprises a CPW signal line positioned in the middle of the substrate and CPW ground lines positioned on two sides of the CPW signal line, and the CPW signal line and the CPW ground lines are parallel to each other; the planar spiral inductor comprises a lower layer channel and a coil and is positioned between the two CPW ground wires; the MEMS variable parallel plate capacitor is arranged on one side of the planar spiral inductor and is connected between the CPW signal line and the CPW ground wire in parallel, the MEMS variable parallel plate capacitor is divided into an upper polar plate and a lower polar plate, a groove is arranged on the substrate right below the upper polar plate, the lower polar plate is arranged on the bottom surface of the groove and two side surfaces close to the CPW ground wire and is in an inverted arch bridge shape, and the lower polar plate is connected with the CPW ground wire; the MEMS film is arranged at the top of the groove and is in contact with the bottom surface of the upper polar plate, the MEMS film and the upper polar plate are in an integral relation, two ends of the MEMS film are respectively arranged on the two CPW ground lines, and the MEMS film and the groove form a closed cavity.

Further, the coil of the planar spiral inductor is overhead above the substrate, and the lower channel is located on the substrate; the external joint of the coil is connected with the CPW signal wire, and the internal joint of the coil is connected with the lower-layer channel; the other end of the lower layer channel is connected with the CPW signal wire; and an insulating medium layer covers the lower-layer channel below the coil.

Further, the recess is U type groove, the axis of recess with the CPW signal line is parallel, the CPW signal line is located directly over the recess.

Furthermore, a sealed cavity formed by the MEMS film and the groove is a completely sealed space, namely, the air in the sealed cavity does not circulate with the outside air.

Further, the MEMS film and the CPW signal line are integrated, that is, the upper plate above the groove can move upward or downward together with the MEMS film along with the change of the internal and external pressure difference of the sealed cavity.

Furthermore, a buffer medium layer is arranged on the upper surface of the substrate.

A method for preparing the MEMS pressure sensor based on the frequency detection principle as described above, comprising the steps of: s10, preparing a Si substrate, etching a groove on the substrate, and growing a buffer medium layer on the substrate in a thermal oxidation mode; s20 is sequentially subjected to photoetching, evaporation and stripping on the buffer medium layer to obtain a lower channel of the planar spiral inductor and a lower polar plate of the MEMS variable parallel plate capacitor, and a CPW signal line and a CPW ground line are preliminarily obtained; s30, depositing and photoetching a PSG sacrificial layer, and reserving the PSG sacrificial layer in the groove; s40, forming a MEMS film on the PSG sacrificial layer by adopting a Plasma Enhanced Chemical Vapor Deposition (PECVD) process, reserving release holes at the parts of the MEMS film, which are positioned at the two sides of the CPW signal line, for releasing the PSG sacrificial layer in the subsequent steps, and then forming an insulating medium layer between the lower channel and the coil; s50, evaporating the titanium, gold and titanium seed layers in sequence, and performing photoetching, electroplating, photoresist removal and reverse etching to completely form the CPW signal line, the CPW ground wire, the planar spiral inductor and the MEMS variable parallel plate capacitor; s60 releases the PSG sacrificial layer and fills the release holes in the MEMS membrane with a silicon nitride material.

Further, the MEMS variable parallel plate capacitor, the planar spiral inductor, the CPW signal line and the CPW ground line are made of gold.

Furthermore, the substrate is made of high-resistance silicon, and the resistivity of the substrate is larger than 1k omega cm.

Further, the depth of the groove is 1-10 μm, and the thickness of the MEMS film, the CPW ground line and the CPW signal line is 0.5-5 μm.

Furthermore, the MEMS film adopts silicon nitride, and the thickness of the MEMS film is 0.5-3 μm.

Compared with the prior art, the technical scheme of the invention has the following advantages:

(1) the MEMS pressure sensor based on the frequency detection principle and the preparation method thereof are combined with the RF MEMS technology, and have simple structure and easy measurement.

(2) According to the MEMS pressure sensor based on the frequency detection principle and the preparation method thereof, the external pressure value is solved by acquiring the change of the resonant frequency of the device, and the device has high sensitivity.

(3) According to the MEMS pressure sensor based on the frequency detection principle and the preparation method thereof, the change of the inductance and the capacitance can be realized by adjusting the number of turns of the coil of the planar spiral inductor and the distance between the upper polar plate and the lower polar plate of the MEMS variable parallel plate capacitor, so that the frequency range and the signal amplitude of the resonant frequency can be regulated and controlled, and the performance of the device can be improved.

(4) According to the MEMS pressure sensor based on the frequency detection principle and the preparation method thereof, the preparation process of the MEMS pressure sensor is compatible with the Si-based process; due to the small volume, the chip area is greatly reduced, the integration level is improved, and the price is relatively low under the condition of batch production; meanwhile, the device is formed by a fully passive structure and has zero direct-current power consumption.

Drawings

The technical solution and the advantages of the present invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings.

FIG. 1 is a top view of a MEMS pressure sensor based on the principle of detecting frequency variations according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view A-A of a MEMS pressure sensor based on the principle of detecting frequency variations according to an embodiment of the present invention;

FIG. 3 is a cross-sectional view B-B of a MEMS pressure sensor based on the principle of detecting frequency variations according to an embodiment of the present invention;

FIG. 4 is an equivalent circuit diagram of a MEMS pressure sensor based on the principle of detecting frequency variations according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of detecting the resonant frequency of the MEMS pressure sensor based on the principle of detecting frequency variation according to an embodiment of the present invention;

FIG. 6 is a flow chart of a method for manufacturing a MEMS pressure sensor based on the principle of detecting frequency variations according to an embodiment of the present invention;

FIGS. 7-12 are flow charts illustrating a process for manufacturing a MEMS pressure sensor based on the principle of detecting frequency variations according to an embodiment of the present invention;

the parts in the figure are numbered as follows:

the capacitive touch panel comprises a 1CPW signal line, a 12 CPW ground line, a 13 substrate, a 131 groove, a 132 buffer dielectric layer, a 2 MEMS film, a 3 MEMS variable parallel plate capacitor, a 31 upper polar plate, a 32 lower polar plate, a 4-plane spiral inductor, a 41 coil, a 42 lower channel and a 43 insulating dielectric layer.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. 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.

The present embodiment provides a MEMS pressure sensor based on the principle of detecting frequency variation, as shown in fig. 1 to 3, a buffer dielectric layer 132, a CPW transmission line, a planar spiral inductor 4, a MEMS variable parallel plate capacitor 3, a MEMS thin film 2, a groove 131, and an insulating dielectric layer 43 are disposed on a substrate 13.

The CPW transmission line includes a CPW signal line 1 located in the middle of a substrate 13 and two CPW ground lines 12 located at both sides of the CPW signal line 1, and the CPW signal line 1 and the CPW ground lines 12 are arranged in parallel.

The planar spiral inductor 4 is between the two CPW ground lines 12, and includes two parts, namely a coil 41 and a lower channel 42; the coil 41 is positioned above the substrate 13 and the lower channel 42 is positioned above the substrate 13; the external terminal of the coil 41 is connected to the CPW signal line 1 and the internal terminal thereof is connected to the lower channel 42; the other end of the lower channel 42 is connected with the CPW signal line 1; the lower channel 42 is covered with an insulating medium layer 43 to prevent an electrical short circuit between the coil 41 and the lower channel 42; the lower channel 42 is a port of the planar spiral inductor 4 and is used as the input or output of a signal, and the external terminal of the coil 41 connected to the CPW signal line 1 is used as the other port of the planar spiral inductor and is used as the output or input of a signal.

As shown in fig. 3, the lower channel 42 is a conductive layer, and is prepared from the same material and process as the lower plate 32 of the MEMS variable parallel plate capacitor, the bottom metal layer of the CPW signal line and the bottom metal layer of the CPW ground line.

The MEMS variable parallel plate capacitor 3 is arranged on one side of the planar spiral inductor 4 and connected in parallel between the CPW signal line 1 and the CPW ground line 12, the MEMS variable parallel plate capacitor 3 is divided into an upper electrode plate 31 and a lower electrode plate 32, the substrate 13 right below the upper electrode plate 31 is provided with the groove 131, the lower electrode plate 32 is arranged on the bottom surface of the groove 131 and two side surfaces close to the CPW ground line 12 and is in an inverted arch bridge shape, and the lower electrode plate 32 is connected with the CPW ground line 12.

The MEMS film 2 is located on the top of the groove 131 and directly contacts the bottom of the upper plate 31, two ends of the MEMS film 2 are respectively disposed on the two CPW ground lines 12, the MEMS film 2 and the groove 131 form a sealed cavity, and the sealed cavity is a completely sealed space, that is, the air inside the sealed cavity does not circulate with the outside air.

The groove 131 is a U-shaped groove, and the central axis of the groove is parallel to the CPW signal line 1, the MEMS film 2, and the MEMS variable parallel plate capacitor 3.

The MEMS film 2 is mechanically coupled to the upper plate 31, that is, the upper plate 31 above the groove 131 is directly connected to the MEMS film 2, and can move up or down with the MEMS film 2 along with the change of the internal and external pressure difference of the sealed cavity.

A layer of buffer medium layer 132 is disposed on the upper surface of the substrate 13, and the buffer medium layer 132 is used for realizing electrical isolation between the substrate 13 and the lower plate 32 of the MEMS variable parallel plate capacitor 3.

As shown in fig. 4, the MEMS pressure sensor based on the principle of detecting frequency variation of the present invention can be equivalent to a two-port RF network, the CPW transmission line is used as the input and output ports of the RF signal, the inductance of the planar spiral inductor 4 is L, and the capacitance of the MEMS variable parallel plate capacitor is C; when the MEMS thin film micro-electromechanical system works, because the pressure in the closed cavity does not change along with the change of the environmental pressure, when the external environmental pressure (or the pressure F) changes, the pressure difference inside and outside the closed cavity changes, the MEMS thin film 2 deforms upwards or downwards, and the CPW signal line 1 above the groove 131 deforms correspondingly along with the MEMS thin film 2; when transmitting an RF signal on the CPW transmission line, the planar spiral inductor 4 and the MEMS variable parallel-plate capacitor 3 form an RF resonant circuit, and the RF signal is affected by the distance between the upper plate 31 and the lower plate 32 of the MEMS variable parallel-plate capacitor 3 (i.e., the capacitance C), resulting in a resonant frequency (C:)f1、f2、f3…) As shown in fig. 5. Therefore, when the external ambient pressure changes, the resonant frequency of the RF signal of the structure may be shifted, and as shown in fig. 5, the magnitude of the ambient pressure at this time can be obtained by measuring the magnitude of the resonant frequency of the RF signal on the CPW transmission line.

The invention also provides a preparation method of the MEMS pressure sensor based on the detection frequency change principle, which comprises the following steps as shown in FIGS. 6-12:

s10 a Si substrate is prepared, and the substrate is made of, for example, high-resistance silicon and has a resistivity of more than 1k Ω · cm.

Etching a groove on the substrate, wherein the depth of the groove is 1-10 μm for example; then growing a layer of buffer medium layer 132 on the substrate by a thermal oxidation mode; the buffer dielectric layer is, for example, a silicon dioxide layer with a thickness of 0.1-0.5 μm, as shown in FIG. 7;

s20 spin-coating a layer of photoresist on the buffer dielectric layer 132, removing the photoresist in the region of the metal layer to be subsequently evaporated by photolithography, then evaporating a metal layer, where a part of the metal layer is on the buffer dielectric layer 132 and another part of the metal layer is on the photoresist, and finally removing the remaining photoresist and the metal layer on the photoresist by lift-off process, thereby completely forming the lower channel of the planar spiral inductor and the lower plate 32 of the MEMS variable parallel plate capacitor, and initially forming the CPW signal line and the CPW ground line, i.e. the bottom metal layer of the CPW signal line and the CPW ground line, as shown in fig. 8;

s30 depositing and photoetching a sacrificial layer, such as PSG in this embodiment, but it will be understood by those skilled in the art that other applicable materials may be used as the sacrificial layer, and the PSG sacrificial layer inside the groove is remained, as shown in fig. 9;

s40 forming a MEMS film on the sacrificial layer, wherein the preparation process is, for example, Plasma Enhanced Chemical Vapor Deposition (PECVD) process, and release holes are left in the portions of the MEMS film located at both sides of the CPW signal line for releasing the PSG sacrificial layer in the subsequent step, and then forming an insulating dielectric layer between the lower channel and the coil, as shown in fig. 10;

s50 evaporating the titanium, gold and titanium seed layers in sequence, and performing photoetching, electroplating, photoresist removal and reverse etching to completely form the CPW signal line, the CPW ground wire, the planar spiral inductor and the MEMS variable parallel plate capacitor, as shown in FIG. 11; wherein, the thickness of the MEMS film, the CPW ground wire and the CPW signal wire is 0.5-5 μm, for example.

S60 releases the PSG sacrificial layer and fills the release holes in the MEMS membrane with silicon nitride material, as shown in fig. 12.

The above description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above embodiment, but equivalent modifications or changes made by those skilled in the art according to the present disclosure should be included in the scope of the present invention as set forth in the appended claims.