KR100829166B1 - Mems acceleration sensor - Google Patents

Abstract

An MEMS(Micro Electro Mechanical System) acceleration sensor is provided to measure an acceleration by amplifying a temperature difference between a reference temperature with acceleration and a measured temperature without the acceleration. An MEMS acceleration sensor includes a substrate(111), a heating material(120), a thermal-electric pair(130), a cavity(112), and a nano structure(141). The heating material is arranged on the substrate and emits heat by an applied current. The thermal-electric pair is arranged to be adjacent to the heating material on the substrate and measures a temperature of a fluid. The cavity is arranged on the substrate and passes the fluid under the thermal-electric pair and the heating material. The nano structure is arranged on the heating material and includes an upper surface and plural pores. The pores are engraved on the upper surface and arranged on the overall upper surface, so that contact areas between the nano structure and the fluid are increased.

Description

MEMS acceleration sensor {MEMS acceleration sensor}

1 is a plan view of an example of a conventional acceleration sensor.

2 is a cross-sectional view of the acceleration sensor of FIG.

3 is a perspective view of a MEMS acceleration sensor in accordance with an embodiment of the present invention.

4 is a cross-sectional view taken along line IV-IV of the MEMS acceleration sensor of FIG. 3.

5 is a micrograph of the nanostructure of the MEMS acceleration sensor of FIG. 3.

FIG. 6 is a photomicrograph at 20,000 times magnification of the nanostructure of FIG. 5. FIG.

FIG. 7 is a micrograph at 100,000 times magnification of the nanostructure of FIG. 5. FIG.

<Description of the symbols for the main parts of the drawings>

100 MEMS acceleration sensor 111 substrate

112: cavity 114: insulator thin film

120: heating element 123: heat generating vertex

130: thermocouple 131: first conductive wire

132: second conductive line 133: thermocouple junction

140: aluminum thin film 141: nanostructure

142: top surface of the aluminum thin film 143: pores

The present invention relates to a micro electro-mechanical system (MEMS) acceleration sensor, and more particularly, to an MEMS acceleration sensor capable of sensitively detecting a small amount of acceleration by improving heat transfer performance from a heating element to a fluid.

Currently, acceleration sensors are typically used for airbags and suspension devices of automobiles, position control devices for aviation and military vehicles, motion input devices and shock detection devices for electronic products such as computers and mobile phones. Such an acceleration sensor may be generally classified into a servo type, piezoelectric type, piezoresistive type, capacitive type, and convection type according to an operation method. Among the conventional acceleration sensors, a convective acceleration sensor filed by the present applicant (Korean application) No. 10-2005-0049721 is shown in FIGS. 1 and 2.

1 is a schematic plan view of an example of a conventional acceleration sensor, and FIG. 2 is a schematic cross-sectional view of the acceleration sensor of FIG. 1.

1 and 2, the acceleration sensor 10 is for measuring acceleration using a tropical flow of a fluid, and includes a container 11, a heating element 20, and a thermocouple 30. .

The container 11 contains a fluid 1, that is, either gas or liquid.

The heat generating body 20 is disposed in the container 11 and has a heat generating vertex 23 at a central portion thereof. The heating element 20 is electrically connected to the heating element electrodes 26 and 27 at both ends thereof. When current is supplied through the heating element electrodes 26 and 27, Joule heat is applied to the heating element 20. Is generated.

The thermocouple 30 includes a first conductive line 31 and a second conductive line 32 made of different metals, and a thermocouple junction point 33. The thermocouple junction 33 is provided at a position where one end of the first conductive line 31 and the second conductive line 32 are electrically connected to each other, and is in contact with the heat generating vertex 23. The temperature of the fluid may be measured by measuring the voltage between the thermocouple electrodes 36 and 37 connected to the other end of the first conductive line 31 and the second conductive line 32.

In such a conventional convective acceleration sensor, in the upper spaces (x> 0, z> 0) of the heating element (20), a tropical flow phenomenon of the fluid occurs due to Joule heat of the heating element (20). The fluid is in a high temperature state, and the fluid in the upper space (x <0, z> 0) of the thermocouple 30 is relatively low temperature compared to the fluid in the upper space (x> 0, z> 0) of the heating element 20. Becomes According to the direction of acceleration, the temperature of the fluid in the upper space (x> 0, z> 0) of the heating element 20 or the fluid in the upper space (x <0, z> 0) of the thermocouple 30 is the thermocouple 30. By detecting by, the magnitude and direction of the acceleration can be measured using the difference between the reference temperature in the absence of acceleration and the measured temperature in the presence of acceleration.

However, the surface of the heat generating vertex 23 portion of the conventional acceleration sensor is made of a smooth plane, so that heat transfer from the heat generating vertex portion 23 to the fluid in the upper space (x> 0, z> 0) is effectively performed. As a result, the fluid in the upper spaces x> 0 and z> 0 of the heat generating vertex 23 may not be heated to a sufficient temperature. Therefore, when a small acceleration acts, the difference between the reference temperature in the absence of acceleration and the measurement temperature in the presence of acceleration is extremely small, and thus has a range within the resolution of the thermocouple. There is a problem that becomes impossible.

The present invention has been made in order to solve the above problems, by adding a fine convex portion on the upper side of the heating element that generates heat to transfer the heat to the fluid side located in the upper side, heat transfer performance from the heating element to the fluid It is an object of the present invention to provide an MEMS acceleration sensor whose structure is improved to improve the efficiency of the sensor.

MEMS acceleration sensor of the present invention to achieve the above object, for measuring the acceleration using a tropical flow of the fluid, the substrate; A heating element disposed on the substrate and generating heat by an applied current; A thermocouple disposed adjacent to the heating element on the substrate and configured to measure a temperature of the fluid; A cavity provided in the substrate and capable of passing a fluid through a lower portion of the thermocouple and the heating element; And a nano structure having an upper surface and a plurality of pores formed to be recessed from the upper surface so as to be in contact with the fluid and having a plurality of pores arranged over the entire upper surface, and formed on an upper side of the heating element. It features.

In the MEMS acceleration sensor according to the present invention, preferably, the pores have a diameter of 50 nm or more and 500 nm or less.

In the MEMS acceleration sensor according to the present invention, Preferably, the nanostructure, the heating element and the thermocouple are electrically insulated by an insulator thin film formed between each.

In the MEMS acceleration sensor according to the present invention, preferably, the nanostructure is formed by forming a thin film of a metal material on the upper side of the heating element and anodizing the thin film of the metal material.

In the MEMS acceleration sensor according to the present invention, Preferably, the thin film of the metal material is an aluminum thin film.

Hereinafter, preferred embodiments of the MEMS acceleration sensor according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a perspective view of a MEMS acceleration sensor according to an embodiment of the present invention, FIG. 4 is a cross-sectional view taken along line IV-IV of the MEMS acceleration sensor of FIG. 3, and FIGS. 5 to 7 are nanostructures of the MEMS acceleration sensor of FIG. 3. Magnified micrographs.

3 to 7, the MEMS acceleration sensor 100 according to the present embodiment is for measuring acceleration using a tropical flow of a fluid, and includes a substrate 111, a heating element 120, and a thermocouple ( 130 and a nanostructure 141.

The substrate 111 serves as a frame of the MEMS acceleration sensor 100, and includes a substrate main body 111a made of a semiconductor material such as silicon and silicon nitride or the like deposited on the upper surface of the substrate main body 111a. It consists of the compound thin film 111b. The silicon compound thin film 111b deposited on the upper surface of the substrate main body 111a serves to support the heating element 120, the thermocouple 130, and the nanostructure 141 which will be described later. The silicon compound thin film 111b is deposited on the upper surface of the substrate body 111a through chemical vapor deposition, and a planar shape is formed through photolithography and reactive ion etching.

The substrate 111 is provided with a cavity 112 for passing the fluid flowing by the tropical flow to the lower portion of the heating element 120 and the thermocouple 130 to be described later, the cavity 112 is a concave groove It is formed in the center of the substrate 111 in the form. The cavity 112 is formed through an isotropic etching method using photolithography and non-fluorinated non-gas.

The heat generator 120 is provided on the substrate 111. The heating element 120 is made of a conductive material such as nickel, chromium, and generates heat by its own resistance when a current is supplied. In the present embodiment, the heating element 120 is a "a" shaped conductive thin film, the heat generating vertex 123 is located at the vertex portion of the "a" shaped heating element 120. Two heating element electrodes 126 and 127 for supplying current are electrically connected to both ends of the heating element 120. The heating element electrodes 126 and 127 are current supply devices for supplying current. Is connected to). The heating element electrodes 126 and 127 are formed of a thin film of a metal material having a low resistance, such as gold (Au), in order to minimize heat generation and electrical noise thereof. The heating element 120 and the heating element electrodes 126 and 127 are deposited by electron beam deposition or sputtering, and a planar shape is formed through photolithography, a lift-off method or wet etching using an etching solution. do.

The thermocouple 130 is used to measure the temperature of the fluid flowing on the upper side of the substrate 111. The thermocouple 130 obtains a first conductive line 131, a second conductive line 132, and a thermocouple junction 133. Compared. The first conductive line 131 and the second conductive line 132 are made of different kinds of metals from among metal materials such as nickel and chromium. For example, when the first conductive line 131 is made of nickel, The two conductive lines 132 are made of a metal other than nickel, such as chromium. In the present exemplary embodiment, the first conductive line 131 and the second conductive line 132 are bonded to each other in an “a” shape and electrically connected to each other, and a thermocouple junction 133 is positioned at a vertex portion thereof. Thermocouple electrodes 136 and 137 are provided at ends of the first conductive line 131 and the second conductive line 132. The thermocouple electrodes 136 and 137 are connected to a voltage measuring device (not shown) for measuring the voltage between the electrodes 136 and 137. The first conductive line 131, the second conductive line 132, and the thermocouple electrodes 136 and 137 are deposited by electron beam deposition or sputtering, and wet etching using a photolithography, a lift-off method, or an etching solution. Through the planar shape is formed.

In the present embodiment, the heat generating vertex 123 and the thermocouple junction 133 are spaced apart from each other along the x-axis direction in space and used to measure the acceleration in the x-axis direction.

The nanostructure 141 is to improve the heat transfer performance from the heating element 120 to the fluid, and is formed on the upper side of the heating element 120, in particular, on the upper portion of the heat generating vertex 123. The nanostructure 141 is formed by anodizing a thin film of a metal material deposited on an upper portion of the heat generating vertex 123. In the present embodiment, the thin film of the metal material, has a good thermal conductivity to transfer the heat transferred from the heating element 120 to the fluid side well, aluminum that can be easily oxidized when anodizing (anodizing) treatment The thin film 140 is used. Anodizing electrodes 146 and 147 are provided at both ends of the aluminum thin film 140, and the aluminum thin film 140 and the anodizing electrodes 146 and 147 are electrically connected to each other. The aluminum thin film 140 and the anodizing electrodes 146 and 147 are deposited by electron beam deposition or sputtering, and are planarly formed through photolithography, a lift-off method or wet etching using an etching solution. Is formed.

The nanostructure 141 includes an upper surface 142 and a plurality of pores 143 formed to be recessed from the upper surface 142 and arranged over the entire upper surface 142. In the present embodiment, the pores 143 are formed to have a diameter of 50 nm or more and 500 nm or less. When the diameter of the pores 143 is less than 50 nm, the diameter thereof is too small so that the flow of fluid in the pores 143 is less likely to occur, and when the diameter of the pores 143 is more than 500 nm, anodizing treatment is performed. The pores 143 are stuck together, making it difficult to form the nanostructured pores 143 themselves.

To form the nanostructure 141, first, an aluminum thin film 140 is formed to overlap a portion of the heating element 120 at an upper portion of the heating vertex 123. After depositing the photoresist on the aluminum thin film 140, the photoresist deposited on the upper portion of the portion where the nanostructure 141 is to be formed so that the portion where the nanostructure 141 is to be formed and the anodizing solution may contact. Patterning is done using photolithography. After the photoresist is immersed in the anodizing solution to the portion of the aluminum thin film 140 patterned, and then supplied with electricity through the anodizing electrode 146, 147, nano to the portion of the aluminum thin film 140 patterned photoresist The structure 141 is formed.

The thermocouple 130, the heating element 120, and the nanostructure 141 are electrically insulated from each other by an insulator thin film 114, such as silicon oxide, formed therebetween. The insulator thin film 114 is deposited through chemical vapor deposition, and has a planar shape through photolithography and reactive ion etching.

Hereinafter, the operating principle of the MEMS acceleration sensor 100 of the present embodiment configured as described above will be described schematically with reference to FIGS. 3 to 7.

When a current is applied to the heating element 120 from the current supply device, Joule heat is generated around the heating element 120 to increase the temperature of the fluid in the upper space (x> 0, z> 0) of the heating element 120. . On the other hand, the fluid in the upper space (x <0, z> 0) of the thermocouple 130 is not heated by the heating element 120, so that the upper space (x> 0, z> 0) of the heating element 120 It is relatively cold compared to the fluid.

In this temperature distribution state, for example, when the acceleration in the "+ x" axial direction acts on the MEMS acceleration sensor 100, the fluid in the space above the heat generating vertex 123 and the thermocouple junction 133 in terms of relative motion is " Acceleration in the "-x" axis direction opposite to the + x "axis direction is acted upon. By the flow of the fluid in the "-x" axial direction, the thermocouple junction 133 detects the temperature of the fluid in the upper space (x> 0, z> 0) of the heating element 120 having a relatively high temperature. . As described above, if the difference between the measured temperature detected in the state of acceleration and the reference temperature in the state of no acceleration is obtained, and the sign and the magnitude are used, the direction and magnitude of the acceleration can be measured.

On the other hand, the aluminum thin film 140 is anodized, so that a plurality of pores 143 are formed in the aluminum thin film 140. Fluid flows into the pores 143 as the fluid flows by Joule heat generated by the heating element 120, and the fluid inside the pores 143 is also drawn out. Through this process, the area where the heat is generated and the fluid in contact with each other is widened, and the heat transfer from the heating element 120 to the fluid is actively performed. Even when the same current as that applied to the conventional acceleration sensor is applied to the heating element electrodes 126 and 127, the fluid in the heating element upper space (x> 0, z> 0) is heated to a higher temperature and there is no acceleration The difference from the reference temperature becomes larger. As a result, in the MEMS acceleration sensor 100 of the present embodiment measuring acceleration by the difference between the reference temperature and the measurement temperature, the nanostructure 141 serves as a kind of amplifier.

By using the MEMS acceleration sensor according to the present embodiment configured as described above, the heat transfer performance from the heating element to the fluid is improved by the nanostructure having a fine concavo-convex shape, so that there is no reference temperature and acceleration in the state without acceleration. The difference in temperature can be further amplified. Therefore, in the case of very small acceleration, the difference between the reference temperature and the measurement temperature is very small in the MEMS acceleration sensor without the nanostructure, and thus the acceleration may not be measured due to the range within the resolution of the thermocouple. In the MEMS acceleration sensor having a nanostructure, the difference between the reference temperature and the measured temperature is amplified even when the same amount of current is applied as in the prior art, and thus the acceleration can be measured, and the acceleration can be more accurately measured.

Although preferred embodiments and modifications have been described above, the MEMS acceleration sensor according to the present invention is not limited to the above-described examples, and various modifications and combinations thereof may be made within the scope without departing from the technical spirit of the present invention. MEMS acceleration sensors of the type can be embodied.

MEMS acceleration sensor according to the present invention, even if the current amount to the same amount of current applied to the heating element electrode in the conventional acceleration sensor, the heat transfer performance from the heating element to the fluid is improved to measure the state of the reference temperature and acceleration state without acceleration Since the temperature difference is amplified, a small amount of acceleration can be sufficiently measured using a thermocouple having a constant resolution, and the acceleration can be measured more accurately than a conventional acceleration sensor.

Claims (5)

For measuring acceleration using a tropical flow of fluid, Board; A heating element disposed on the substrate and generating heat by an applied current; A thermocouple disposed adjacent to the heating element on the substrate and configured to measure a temperature of the fluid; A cavity provided in the substrate and capable of passing a fluid through a lower portion of the thermocouple and the heating element; And And a nano structure formed on an upper side of the heating element so as to have an area in contact with the fluid, the upper surface and the plurality of pores formed to be recessed from the upper surface and arranged over the entire upper surface thereof. MEMS acceleration sensor. The method of claim 1, The pore has a diameter of 50 nm or more and 500 nm or less. The method of claim 1, The nanostructure, the heating element and the thermocouple are each electrically insulated by an insulator thin film formed between each of the MEMS acceleration sensor. The method of claim 1, The nanostructures, MEMS acceleration sensor, characterized in that formed by forming a thin film of a metal material on the upper side of the heating element and anodizing the thin film of the metal material. The method of claim 4, wherein MEMS acceleration sensor, characterized in that the thin film of the metal material is an aluminum thin film.

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