CN113670994A - MEMS humidity sensor based on phase detection principle and preparation method thereof - Google Patents
MEMS humidity sensor based on phase detection principle and preparation method thereof Download PDFInfo
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Abstract
本发明提供基于相位检测原理的MEMS湿度传感器及制备方法，包括：CPW传输线，设置在衬底上，该CPW传输线包括CPW信号线以及CPW信号线两侧的CPW地线，在CPW信号线中间部位的下方衬底设置凹槽；MEMS梁，位于凹槽的底面和靠近CPW地线的两个侧面上；MEMS薄膜，位于凹槽上方，与CPW信号线的底面接触，且MEMS薄膜表面设置通孔；感湿层，位于MEMS梁和MEMS薄膜之间并填满凹槽的内部空间。利用凹槽内感湿层的吸水性来感测外部环境的湿度，感湿层的介电常数会随着湿度发生变化，引起MEMS梁与CPW信号线之间的电容改变，使CPW传输线上RF信号的相位发生变化，测量RF信号的相位便可获取环境湿度。
The invention provides a MEMS humidity sensor based on a phase detection principle and a preparation method, including: a CPW transmission line, which is arranged on a substrate, and the CPW transmission line includes a CPW signal line and a CPW ground line on both sides of the CPW signal line, in the middle part of the CPW signal line The bottom substrate is provided with a groove; the MEMS beam is located on the bottom surface of the groove and on the two sides close to the CPW ground line; the MEMS film is located above the groove, in contact with the bottom surface of the CPW signal line, and the surface of the MEMS film is provided with through holes ; a moisture-sensing layer that is located between the MEMS beam and the MEMS film and fills the inner space of the groove. The moisture absorption of the moisture-sensing layer in the groove is used to sense the humidity of the external environment. The dielectric constant of the moisture-sensing layer will change with the humidity, causing the capacitance between the MEMS beam and the CPW signal line to change, making the RF on the CPW transmission line change. The phase of the signal changes, and the ambient humidity can be obtained by measuring the phase of the RF signal.
Description
Technical Field
The invention relates to the technical field of radio frequency micro-electro-mechanical systems (RF MEMS), in particular to an MEMS humidity sensor based on a phase detection principle and a preparation method thereof.
Background
Humidity, generally referred to as the water vapor content of the air, is used to reflect the dryness of the atmosphere. Air humidity is directly related to daily work, life and production of people, so that the air humidity monitoring and controlling device is more and more important. However, among the conventional environmental parameters, humidity is one of the most difficult parameters to accurately measure. The traditional hygrometers are increasingly unable to meet the actual requirements at the present stage, so that research on novel humidity sensors is necessary. Humidity sensors have been widely used in many fields including national defense aviation, meteorological detection, industrial control, agricultural production, medical equipment, etc., and in recent years, miniaturization is an important direction for the development of humidity sensors, and existing miniature humidity sensors mainly include capacitive type, resistive type, piezoresistive type, etc. At present, a MEMS humidity sensor with high performance, simple structure, high sensitivity, and low cost is urgently needed. With the human step into the information age, the MEMS sensor has also been rapidly developed as a device for capturing information, and has a significant position in the development of modern highly information-oriented society science and technology, and as the RF MEMS technology and the moisture-sensitive material are deeply studied, the MEMS humidity sensor based on the phase detection principle satisfying the above characteristics becomes possible.
Disclosure of Invention
In order to solve the above problems, the present invention provides a MEMS humidity sensor based on the phase detection principle and a method for manufacturing the same, in which a groove is formed on a substrate, and the moisture absorption of a moisture-sensitive layer in the groove is used to sense the humidity of the external environment, and the dielectric constant of the moisture-sensitive layer changes with the humidity of the external environment, which causes the capacitance between the MEMS beam and the CPW signal line to change, and further causes the phase of the RF signal on the CPW transmission line to change, so that the environmental humidity can be obtained by measuring the phase of the RF signal.
In order to achieve the above purpose, the invention adopts a technical scheme that:
a MEMS humidity sensor based on the principle of phase detection, 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, the CPW signal line and the CPW ground lines are parallel to each other, a groove is arranged on the substrate and is positioned below the middle of the CPW signal line; the MEMS beam is positioned on the bottom surface of the groove and two side surfaces close to the CPW ground wire, is in an inverted arch bridge shape and is connected with the CPW ground wire; the MEMS film is positioned above the groove, is in contact with the bottom surface of the CPW signal line, has two ends arranged on the CPW ground line, and is provided with through holes at the parts positioned at the two sides of the CPW signal line; and the humidity sensing layer is positioned between the MEMS beam and the MEMS film and fills the inner space of the groove.
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.
Further, the through holes on the MEMS film are composed of a plurality of dense small holes, so that the humidity sensing layer can be sufficiently contacted with the external air.
Further, a layer of buffer medium layer is arranged on the surfaces of the substrate and the groove.
A method for manufacturing the MEMS humidity sensor based on the phase 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, sequentially carrying out photoetching, evaporation and stripping on the buffer medium layer to obtain the MEMS beam and the CPW ground wire; s30 depositing and photoetching a humidity sensing layer, and reserving the humidity sensing layer in the groove; s40, forming a MEMS film on the moisture-sensing layer by adopting a Plasma Enhanced Chemical Vapor Deposition (PECVD) process, and forming through holes at the parts of the MEMS film, which are positioned at the two sides of the CPW signal line; s50, evaporating the titanium, gold and titanium seed layers in sequence, and carrying out photoetching, electroplating, photoresist removal and reverse etching to form the CPW signal line.
Furthermore, the MEMS beam, the CPW ground line, and the CPW signal 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 beam, the CPW ground line, and the CPW signal line is 0.5-5 μm.
Furthermore, the humidity sensing layer is made of polyimide, graphene oxide and the like.
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 humidity sensor based on the phase detection principle and the preparation method thereof are combined with the RF MEMS technology, and have the advantages of simple structure, good consistency and easy measurement.
(2) According to the MEMS humidity sensor based on the phase detection principle and the preparation method thereof, the humidity value of the external environment is solved by acquiring the change of the phase value of the device by utilizing the water absorption of the humidity sensing layer, and the device has high sensitivity.
(3) According to the MEMS humidity sensor based on the phase detection principle and the preparation method thereof, the MEMS beam is arranged in the groove on the substrate, so that the device is easy to package.
(4) According to the MEMS humidity sensor based on the phase detection principle and the preparation method thereof, the preparation process of the MEMS humidity sensor is compatible with the Si-based process; due to the small volume, the chip area is saved, the integration level is improved, and the price is relatively low under the condition of batch production; meanwhile, a fully passive structure is adopted, and zero direct-current power consumption is achieved.
Drawings
FIG. 1 is a top view of a MEMS humidity sensor based on the principle of phase detection according to an embodiment of the present invention;
FIG. 2 is a cross-sectional view A-A of a MEMS humidity sensor based on the phase detection principle according to an embodiment of the present invention;
FIG. 3 is a cross-sectional view illustrating a cross-sectional view of a MEMS humidity sensor based on the phase detection principle according to an embodiment of the present invention;
FIG. 4 is a flow chart of a method for manufacturing a MEMS humidity sensor based on the principle of phase detection according to an embodiment of the present invention;
FIGS. 5-9 are flow charts illustrating a process for manufacturing a MEMS humidity sensor based on the phase detection principle according to an embodiment of the present invention;
the parts in the figure are numbered as follows:
the MEMS substrate comprises a 1CPW signal line, a 12 CPW ground line, a 13 substrate, a 131 groove, a 132 buffer medium layer, a 2 MEMS film, a 3 MEMS beam, a 4 moisture-sensing layer and a 5 through hole.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be appreciated by those of ordinary skill in the art that numerous technical details are set forth in order to provide a better understanding of the present application in various embodiments of the present invention. However, the technical solution claimed in the present application can be implemented without these technical details and various changes and modifications based on the following embodiments. The following embodiments are divided for convenience of description, and should not constitute any limitation to the specific implementation manner of the present invention, and the embodiments may be mutually incorporated and referred to without contradiction.
Example 1
The present embodiment provides a MEMS humidity sensor based on a phase detection principle, as shown in fig. 1 to 3, including: the CPW transmission line, the substrate 13, the groove 131, the buffer dielectric layer 132, the MEMS film 2, the MEMS beam 3, the moisture-sensing layer 4 and the through hole 5.
Specifically, the CPW transmission line is horizontally disposed on the substrate 13, and includes a CPW signal line 1 located in the middle of the substrate 13 and two CPW ground lines 12 located on two sides of the CPW signal line 1, and the CPW signal line 1 and the CPW ground lines 12 may be disposed in parallel with each other.
The groove 131 is located on the substrate 13 right below the CPW signal line 1, the groove 131 is, for example, a U-shaped groove, and a central axis of the groove 131 is parallel to the CPW signal line 1; the surface of the substrate 13 and the groove 131 is provided with a buffer medium layer 132.
The MEMS beam 3 is disposed on the bottom surface of the groove 131 and two side surfaces close to the CPW ground lines 12 and is in an inverted arch bridge shape, and the MEMS beam 3 is connected to both of the CPW ground lines 12.
The MEMS film 2 is located right above the groove 131 and directly contacts with the back surface of the CPW signal line 1, two ends of the MEMS film 2 are placed on the CPW ground line 12, and a through hole 5 is provided in a portion of the MEMS film 2 located on both sides of the CPW signal line 1, and the through hole 5 is composed of a plurality of dense small holes, for example.
The moisture sensing layer 4 is located between the MEMS beam 2 and the MEMS film 3 and fills the inner space of the groove 131, the moisture sensing layer 4 is made of, for example, polyimide, graphene oxide, or the like, the moisture sensing layer 4 has water absorption property, the dielectric constant of the moisture sensing layer 4 changes with the humidity of the external environment, and the moisture sensing layer 4 is communicated with the external environment through the through hole 5.
When the MEMS humidity sensor based on the phase detection principle works, the plate capacitor formed by the MEMS beam and the CPW signal line takes the moisture sensing layer as a dielectric layer, and the moisture sensing layer has water absorption, so that the dielectric constant of the moisture sensing layer can change along with the humidity of the external environment, the capacitance between the MEMS beam and the CPW signal line is changed, the phase value of the RF signal on the CPW transmission line is changed, and the environment humidity can be obtained by measuring the phase of the RF signal.
Example 2
The invention also provides a preparation method of the MEMS humidity sensor based on the phase detection principle, which comprises the following steps as shown in FIGS. 4-9:
s10 preparing a substrate, which may be a common semiconductor substrate, for example, a silicon substrate, using high-resistance silicon, having a resistivity of more than 1k Ω · cm. The higher the resistance of the silicon substrate is, the lower the loss of transmitted RF signals is when CPW is manufactured on silicon, the better the RF performance is, and if the capacitance changes due to the external humidity changes, the more obvious the phase change of the RF signals is.
Etching a groove 131 on a substrate, and growing a buffer dielectric layer 132 on the substrate by thermal oxidation, as shown in fig. 5, wherein the depth of the groove is, for example, 1-10 μm;
s20 is sequentially subjected to photoetching, evaporation and stripping on the buffer medium layer to obtain an MEMS beam 3 and a CPW ground wire 12, as shown in FIG. 6, wherein the thicknesses of the MEMS beam and the CPW ground wire are 0.5-5 μm;
s30, depositing and photoetching the humidity sensing layer 4, and reserving the humidity sensing layer 4 inside the groove, as shown in FIG. 7;
s40, forming a MEMS film 2 on the moisture-sensing layer 4 by using, for example, a Plasma Enhanced Chemical Vapor Deposition (PECVD) process, and forming through holes 5 at portions of the MEMS film 2 located at both sides of the CPW signal line, as shown in fig. 8;
s50, evaporating the titanium, gold and titanium seed layers in sequence, and carrying out photoetching, electroplating, photoresist removal and reverse etching to form the CPW signal line 1, as shown in FIG. 9, wherein the thickness of the CPW signal line is 0.5-5 μm.
Compared with the prior art, the technical scheme of the invention has the following advantages:
(1) the MEMS humidity sensor based on the phase detection principle and the preparation method thereof are combined with the RF MEMS technology, and have the advantages of simple structure, good consistency and easy measurement.
(2) According to the MEMS humidity sensor based on the phase detection principle and the preparation method thereof, the humidity value of the external environment is solved by acquiring the change of the phase value of the device by utilizing the water absorption of the humidity sensing layer, and the device has high sensitivity.
(3) According to the MEMS humidity sensor based on the phase detection principle and the preparation method thereof, the MEMS beam is arranged in the groove on the substrate, so that the device is easy to package.
(4) According to the MEMS humidity sensor based on the phase detection principle and the preparation method thereof, the preparation process of the MEMS humidity sensor is compatible with the Si-based process; due to the small volume, the chip area is saved, the integration level is improved, and the price is relatively low under the condition of batch production; meanwhile, a fully passive structure is adopted, and zero direct-current power consumption is achieved.
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.
Claims (10)
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