MEMS APPARATUS FOR MEASURING ACCELERATION IN THREE AXES

TECHNICAL FIELD

The present invention relates to a triple-axis micro electro-mechanical system (MEMS) acceleration sensor, and more particularly, to a triple-axis MEMS acceleration sensor operates based on the degree of cooling of a heating element cooled by thermal convection of a gas or liquid depends on the direction and magnitude of acceleration.

BACKGROUND ART Acceleration sensors are mainly used in air bags and suspension devices of automobiles, location control devices of moving bodies for aeronautic and military purposes, and motion input devices and impact detection devices of electronic products such as computers or mobile phones.

Conventional acceleration sensors are classified into servo sensors, piezo- electrical sensors, piezoresistive sensors, and capacitance-type sensors according to the operating method. In the conventional acceleration sensors, after a moving body having a constant mass m is accelerated to a constant acceleration a by applying a force (F=ma) to the moving body, in this accelerated state, an acceleration is obtained by measuring a control signal, a piezoelectric pressure, a piezoelectric resistance, or a capacitance, which varies according to the displacement of the moving body. Also, in the conventional acceleration sensors, in order to increase a measuring precision of the acceleration, a structure must be included to precisely measure the displacement of the moving body that varies with the acceleration. However, the realization of such moving body requires a complicated manufacturing process, and reduces the durability of the acceleration sensors.

Thermal convection type acceleration sensors using a fluid have been disclosed in U.S. Patent Nos. 2,440,189, 2,455,394, 5,581 ,034, and 6,182,509, and Japanese Patent Publication Nos. 7-260820 and 2000-193677.

With regard to the conventional convection type acceleration sensors, double- axis acceleration sensors that can measure accelerations with respect to two axes that cross each other in a plane are widely used. Also, in the case of conventional convection type triple-axis acceleration sensors that can measure acceleration with respect to the directions of three axes crossing each other in a space, in order to i

measure the acceleration at least three substrates must be stacked. Therefore, the acceleration sensors have large sizes and the manufacturing process is complicated, thereby decreasing yield and increasing manufacturing costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a triple-axis MEMS acceleration sensor according to an embodiment of the present invention;

FIG. 2 is a plan view of a first substrate of the triple-axis MEMS acceleration sensor of FIG. 1 , according to an embodiment of the present invention; FIG. 3 is a plan view of a second substrate of the triple-axis MEMS acceleration sensor of FIG. 1 , according to an embodiment of the present invention

FIG. 4 is a cross-sectional view taken along line IV-IV of the first substrate of FIG. 2, according to an embodiment of the present invention;

FIG. 5 is a cross-sectional view taken along line V-V of the second substrate of FIG. 3, according to an embodiment of the present invention;

FIG. 6 is a circuit diagram for supplying current to the triple-axis MEMS acceleration sensor of FIG. 1 , according to an embodiment of the present invention; and

FIG. 7 is a circuit diagram for measuring a voltage of the triple-axis MEMS acceleration sensor of FIG. 1 , according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL PROBLEM

The present invention provides a triple-axis MEMS acceleration sensor that can be simply manufactured in a small size using a MEMS process or a semiconductor fine processing technique by using a structure in which two substrates are disposed parallel to each other, thereby increasing productivity and reducing manufacturing costs.

ADVANTAGEOUS EFFECTS

A three axis MEMS acceleration sensor according to the present invention can measure accelerations along three axes that spatially cross each other via a structure in which two substrates are disposed parallel to each other. Thus, the size of the sensor can be reduced using a MEMS process or a semiconductor fine processing technique, thereby increasing yield and reducing manufacturing costs.

Also, the three axis MEMS acceleration sensor according to the present invention includes a function of correcting a pressure change of a fluid. Thus, acceleration in a space can be precisely measured without additionally measuring the pressure of the fluid using an external device.

BEST MODE

According to an aspect of the present invention, there is provided a triple-axis MEMS acceleration sensor that measures accelerations in the directions of a first axis, a second axis, and a third axis that spatially cross each other by using convection of a fluid, the triple-axis MEMS acceleration sensor comprising: a first substrate having a first heating point, a second heating point, a third heating point, and a fourth heating point that generate heat in response to an applied current; a first thermocouple, a second thermocouple, a third thermocouple, and a fourth thermocouple, which have thermocouple junction points that respectively contact the first through fourth heating points to measure temperatures at each of the first through fourth heating points; a first cavity that allows the fluid to pass under the first through fourth heating points; a second substrate that is parallel to the first substrate, has a fifth heating point that generates heat in response to an applied current, has a fifth thermocouple having a thermocouple junction point that contacts the fifth heating point to measure a temperature at the fifth heating point, and has a second cavity that allows the fluid to pass under the fifth heating point, wherein the first heating point and the second heating point are separated from each other in a direction of the first axis, the third heating point and the fourth heating point are separated from each other in a direction of the second axis that crosses the first axis, the fifth heating point and the first heating point are separated from each other in a direction of the third axis that crosses the first substrate and the second substrate, and an acceleration in the direction of the first axis is measured using a temperature difference between the first heating point and the second heating point, an acceleration in the direction of the second axis is measured using a temperature difference between the third heating point and the fourth heating point, and an acceleration in the direction of the third axis is measured using a temperature difference between the fifth heating point and the first heating point.

An angle formed by the direction of the first axis and the direction of the second axis may be a right angle, an angle formed by the direction of the third axis and the

direction of the first axis may be a right angle, and an angle formed by the direction of the third axis and the direction of the second axis may be a right angle.

The first heating point, the second heating point, the third heating point, and the fourth heating point respectively may be located on apexes of a conductive thin film having a rectangular band shape, and may be electrically connected to each other, and four electrodes respectively may be formed between the adjacent heating points to apply a current to the heating points.

In order to correct the effect of pressure variation of the fluid on the temperatures of each of the heating points, the pressure of the fluid may be measured using a sum of temperatures of two heating points separated from each other in a direction of one axis of the first, second, and third axes.

The second substrate may further comprise a sixth heating point that is separated from the fifth heating point in a direction of the first axis and generates heat in response to a current applied thereto, and a sixth thermocouple having a thermocouple junction point that contacts the sixth heating point to measure the temperature of the sixth heating point, wherein the fluid pressure is measured using a sum of temperatures of the fifth heating point and the sixth heating point.

MODE OF THE INVENTION A triple-axis MEMS acceleration sensor according to the present invention will now be described more fully with reference to the accompanying drawings in which exemplary embodiments of the invention are shown.

FIG. 1 is a perspective view of a triple-axis MEMS acceleration sensor 100 according to an embodiment of the present invention. FIG. 2 is a plan view of a first substrate of the triple-axis MEMS acceleration sensor 100 of FIG. 1 , and FIG. 3 is a plan view of a second substrate of the triple-axis MEMS acceleration sensor 100 of FIG. 1 , according to an embodiment of the present invention. FIG. 4 is a cross-sectional view taken along line IV-IV of the first substrate of FIG. 2, and FIG. 5 is a cross- sectional view taken along line V-V of the second substrate of FIG. 3, according to an embodiment of the present invention. FIG. 6 is a circuit diagram for supplying current to the triple-axis MEMS acceleration sensor 100 of FIG. 1 , and FIG. 7 is a circuit diagram for measuring a voltage of the triple-axis MEMS acceleration sensor 100 of FIG. 1 , according to an embodiment of the present invention.

Referring to FIGS. 1 through 7, the triple-axis MEMS acceleration sensor 100 measures acceleration along first, second, and third axes A1 , A2, and A3 that spatially cross by using thermal convection of a fluid, and includes a first substrate 20 and a second substrate 120. The first substrate 20 is to measure accelerations in the directions of the first and second axes A1 and A2 that cross each other on a plane, and includes a first substrate main body 21 , a first heating element 70, a first heating point 71 , a second heating point 72, a third heating point 73, and a fourth heating point 74, a first thermocouple 30, a second thermocouple 40, a third thermocouple 50, and a fourth thermocouple 60. The first substrate main body 21 includes an intermediate board 21 a formed of a semiconductor material such as silicon and silicon compound thin films 21b and 21c formed of silicon nitride deposited on upper and lower surfaces of the intermediate board 21a. The silicon compound thin film 21 b deposited on the upper surface of the intermediate board 21a supports the first heating element 70, the first thermocouple 30, the second thermocouple 40, the third thermocouple 50, and the fourth thermocouple 60, and the silicon compound thin film 21c deposited on the lower surface of the intermediate board 21a protects the intermediate board 21a. A first cavity 22 is formed in the first substrate main body 21 to allow a fluid to pass therethrough due to thermal convection. The first cavity 22 passes through the first substrate main body 21 at the center of the first substrate main body 21.

The silicon compound thin films 21b and 21c are deposited on the upper and lower surfaces of the intermediate board 21a using a chemical vapor deposition (CVD) method, and are formed in a planar shape through photolithography and reactive ion etching. The first cavity 22 is formed by photolithography and anisotropic etching using a tetramethyl-ammonium-hydroxide solution.

The first heating element 70 is formed on the first substrate main body 21. The first heating element 70 is formed of a conductive material such as Ni or Cr to generate heat due to self resistance in response to an applied current. In the present embodiment, the first heating element 70 is a conductive thin film having a rectangular band shape. The first heating point 71 , the second heating point 72, the third heating point 72, and the fourth heating point 74 are respectively located at apexes of the first heating element 70 having a rectangular band shape. Four electrodes 75, 76, 77, and 78 for supplying a current to the first heating element 70 are formed on the first

substrate 20, and the four electrodes 75, 76, 77, and 78 are respectively disposed between the adjacent heating points (71 ₎ 73),(73,72),(72,74), and (74,71 ). An end of each of the electrodes 75, 76, 77, and 78 is electrically connected to one of sides of the first heating element 70, and the other end of each of the electrodes 75, 76, 77, and 78 is connected to a current supply apparatus 201 that can supply current to the first heating element 70 through the electrodes 75, 76, 77, and 78. The electrodes 75, 76,

77, and 78 are formed in a thin film using a metal having low resistivity such as Au in order to minimize heat generation and electrical noise in the electrodes 75, 76, 77, and

78. The first heating element 70 and the electrodes 75, 76, 77, and 78 are deposited using an electron beam deposition method or a sputtering method, and formed in a planar shape by photolithography, a lift-off method, or wet etching using an etching solution.

When a current is supplied to the first hearting element 70 from the current supply apparatus 201 through the electrodes 75, 76, 77, and 78, Joule heat is generated from the first heating element 70. Thus, the first through fourth heating points 71 , 72, 73, and 74 which respectively correspond to the apexes of the first heating element 70 have a temperature higher than a temperature of the perimeter fluid.

As depicted in FIG. 6, when a current is applied to the first heating element 70 from the current supply apparatus 201 through the electrodes 75 and 76, the current returns to the current supply apparatus 201 through the electrodes 77 and 78. At this point, a magnitude of the current supplied from the current supply apparatus 201 is i, and a current having a magnitude of i/4 flows in the first heating element 70 according to the Kirchhoff s Law.

The first heating point 71 and the second heating point 72 are separated from each other in the direction of the first axis A1 , and are used for measuring the acceleration in the direction of the first axis A1. Also, the third heating point 73 and the fourth heating point 74 are separated from each other in direction of the second axis A2 and are used for measuring the acceleration in the direction of the second axis A2. The first axis A1 and the second axis A2 cross each other at a point on a plane formed by the first substrate 20 without overlapping each other. In the present embodiment, an angle that is formed by the first axis A1 and the second axis A2 is a right angle, and the distances from the center point 23 where an imaginary line that connects the first heating point 71 and the second heating point 72 meets an imaginary line that connects

the third heating point 73 and the fourth heating point 74 to each of the heating point 71 , 72, 73, and 74 are equal to each other. Accordingly, the first heating point 71 and the second heating point 72, and the third heating point 73 and the fourth heating point 74 respectively are point symmetrical with respect to the center point 23. The first through fourth thermocouples 30, 40, 50, and 60 are to measure temperatures at the first through fourth heating points 71 , 72, 73, and 74, and respectively include first conductive lines 31 , 41 , 51 , and 61 , second conductive lines 32, 42, 52, and 62, and thermocouple junction points 33, 43, 53, and 63. The first conductive lines 31 , 41 , 51 , and 61 and the second conductive lines 32, 42, 52, and 62 respectively are formed in thin films and formed of metals such as Ni or Cr. The first conductive lines 31 , 41 , 51 , and 61 and the second conductive lines 32, 42, 52, and 62 are formed of different materials from each other, for example, if the first conductive lines 31 , 41 , 51 , and 61 are formed of Ni, the second conductive lines 32, 42, 52, and 62 are formed of a metal different from Ni, for example, Cr. The thermocouple junction points 33, 43, 53, and 63 are formed by electrical connecting ends of the first conductive lines 31 , 41 , 51 , and 61 and the second conductive lines 32, 42, 52, and 62. The thermocouple junction points 33, 43, 53, and 63 respectively contact the first through fourth heating points 71 , 72, 73, and 74 with an insulating thin film 24 formed of silicon oxide therebetween. Electrode pads (36, 37), (46, 47), (56, 57), and (66, 67) are respectively formed on both ends of the first through fourth thermocouples 30, 40, 50, and 60. An amplifier 211 is connected to the electrode pad 37 of the first thermocouple 30 and the electrode pad 47 of the second thermocouple 40, and a voltage amplified by the amplifier 211 is measured by a voltage measuring apparatus (not shown). Also, an amplifier 212 is connected to the electrode pad 56 of the third thermocouple 50 and the electrode pad 66 of the fourth thermocouple 60, and a voltage amplified by the amplifier 212 is measured by a voltage measuring apparatus (not shown).

The insulating thin film 24 is deposited using a chemical vapor deposition (CVD) method, and is formed in a planar shape using photolithography and reactive ion etching. The first conductive lines 31 , 41 , 51 , and 61 , the second conductive lines 32, 42, 52, and 62, and the electrode pads (36, 37), (46, 47), (56, 57), and (66, 67) are deposited using an electron beam deposition method or a sputtering method, and are formed in a planar shape using photolithography and a lift-off method or a wet etching using an etchant.

The second substrate 120 is disposed parallel to the first substrate 20 in order to measure the acceleration in the direction of the third axis A3 that crosses the plane formed by the first substrate 20, and includes a second substrate main body 121 , second heating elements 170a and 170b, a fifth heating point 171 , a sixth heating point 172, a fifth thermocouple 130, and a sixth thermocouple 140. In the present embodiment, the second substrate 120 is disposed under the first substrate 20.

The second substrate main body 121 includes an intermediate board 121a formed of a semiconductor material such as silicon and a silicon compound thin film 121b formed of silicon nitride deposited on an upper surface of the intermediate board 121a. The silicon compound thin film 121 b is a structure that supports the second heating elements 170a and 170b, the fifth thermocouple 130, and the sixth thermocouple 140. A second cavity 122 is formed in the center of the second substrate main body 121 to allow a fluid to pass therethrough due to thermal convection. The silicon compound thin film 121b is deposited on an upper surface of the intermediate board 121a, and is formed in a planar shape using photolithography and reactive ion etching. The second cavity 122 is formed by photolithography and isotropic etching using xenon difluoride XeF2 gas.

The second heating elements 170a and 170b are formed on the second substrate main body 121. The second heating elements 170a and 170b, like the first heating element 70, are formed of a conductive material such as Ni or Cr, and thus, generate heat in response to an applied current. In the present embodiment, the second heating elements 170a and 170b are conductive thin films having a "π " shape, and a pair of the second heating elements 170a and 170b are disposed such that apexes of the "π " shape face each other. The fifth heating point 171 and the sixth heating point 172 respectively are positioned on the apexes of the "π " shaped second heating elements 170a and 170b. The fifth and sixth heating points 171 and 172 respectively are located vertically below the first heating point 71 and the second heating point 72, respectively. Four electrodes 175, 176, 177, and 178 for supplying a current to the second heating elements 170a and 170b are formed on the second substrate 120. One end of each of the electrodes 175, 176, 177, and 178 is electrically connected to the second heating elements 170a and 170b, and other end of each of the electrodes 175, 176, 177, and 178 are connected to a current supply apparatus 202 that

can supply current to the second heating elements 170a and 170b through the electrodes 175, 176, 177, and 178. The electrodes 175, 176, 177, and 178 are formed ih a thin film using a metal having low resistivity such as Au to minimize heat generation and electrical noise of the electrodes 175, 176, 177, and 178. The second heating elements 170a and 170b and the electrodes 175, 176, 177, and 178 are deposited using an electron beam method or a sputtering method, and is formed in a planar shape through photolithography and a lift-off method or wet etching using an etchant. As depicted in FIG. 6, a current is supplied to the pair of second heating elements 170a and 170b from the current supply apparatus 202 through the electrodes 175 and 176, and the current returns to the current supply apparatus 202 from the pair of second heating elements 170a and 170b through the electrodes 177 and 178. At this point, the magnitude of the current supplied from the current supply apparatus 202 connected to the second substrate 120 is i/2, and a current having a magnitude of i/4 flows in the second heating elements 170a and 170b according to the Kirchhoff's Law like in the first heating element 70. The same amount of current is supplied to each of the heating elements 70, 170a, and 170b so that the same amount of heat is generated at each heating points 71 , 72, 73, 74, 171 , and 172.

The fifth heating point 171 and the first heating point 71 are separated in a direction of the third axis A3, and are used to measure the acceleration in the direction of the third axis A3. The sixth heating point 172 and the fifth heating point 171 can be separated in the direction of the first axis A1 or the second axis A2. In the present embodiment, the sixth heating point 172 and the fifth heating point 171 are separated in the direction of the first axis A1. The third axis A3 intersects a plane formed by the first substrate 20 and a plane formed by the second substrate 120. In the present embodiment, an angle formed between the first axis A1 and the third axis A3 is a right angle, and an angle formed between the second axis A2 and the third axis A3 is also a right angle.

The second substrate 120 includes the fifth and sixth thermocouples 130 and 140 for measuring temperatures at the fifth and sixth heating points 171 and 172. The fifth and sixth thermocouples 130 and 140 are formed of the same material and structure as the first through fourth thermocouples 30, 40, 50, and 60 formed in the first substrate 20. A thermocouple junction point 133 of the fifth thermocouple 130 contacts the fifth heating point 171 with an insulating thin film 124 formed of silicon oxide therebetween,

and a thermocouple junction point 143 of the sixth thermocouple 140 contacts the sixth heating point 172 with the insulating thin film 124 formed of silicon oxide therebetween. Electrode pads (136, 137) and (146, 147) respectively are formed on both ends of the fifth and sixth thermocouples 130 and 140. An amplifier 213 is connected to the electrode pad 137 of the fifth thermocouple 130 and the electrode pad 37 of the first thermocouple 30, and a voltage amplified by the amplifier 213 is measured by a voltage measuring apparatus (not shown).

The insulating thin film 124 is deposited by a CVD method and is formed in a planar shape using photolithography and reactive ion etching. First conductive lines 131 and 141 , second conductive lines 132 and 142, and the electrode pads (136, 137) and (146, 147) are deposited using an electron beam deposition method or a sputtering method, and are formed in a planar shape using photolithography and a lift-off method or wet etching using an etchant.

In order to correct the effect of pressure variation of the fluid on the temperatures of the first through sixth heating points 71 , 72, 73, 74, 171 , and 172, the pressure of the fluid is measured using a sum of temperatures of two heating points separated from each other on one axis of the first through third axes A1 , A2, and A3. That is, the pressure of the fluid can be measured using one of the sum of temperatures of the first heating point 71 and the second heating point 72 separated in the direction of the first axis A1 , a sum of temperatures of the third heating point 73 and the fourth heating point 74 separated in the direction of the second axis A2, a sum of temperatures of the fifth heating point 171 and the first heating point 71 separated in the direction of the third axis A3, or a sum of temperatures of the fifth heating point 171 and the sixth heating point 172 separated in a direction of the first axis A1. In the present embodiment, the pressure of the fluid is measured using the sum of temperatures of the fifth heating point 171 and the sixth heating point 172. An amplifier 214 is connected to the electrode pad 137 of the fifth thermocouple 130 that contacts the fifth heating point 171 and to the electrode pad 146 of the sixth thermocouple 140 that contacts the sixth heating point 172, and a voltage amplified by the amplifier 214 is measured by a voltage measuring apparatus (not shown).

An operation principle of a triple-axis MEMS acceleration sensor 100 having the above configuration according to the present embodiment will now be briefly described with reference to FIGS. 1 through 7. As an example, a principle of measuring the

acceleration in the direction of the first axis of first through third axes that spatially cross each other will be described.

When a current is applied to the first heating element 70 from the current supply apparatus 201 , Joule's heat is generated around the first heating element 70, and thus, the temperature of a fluid around the first heating element 70 increases. The first heating element 70 can be divided into an inner side and an outer side due to a rectangular band shape of the first heating element 70, and the temperature of the fluid present in the inner side of the first heating element 70 is higher than that of the fluid present in the outer side of the first heating element 70 due to the Joule's heat of the first heating element 70.

Accordingly, in the triple-axis MEMS acceleration sensor 100, if acceleration is acted in a direction of the first axis A1 , the first heating point 71 and the second heating point 72 have different degrees of cooling due to the moving of fluid in the direction of the first axis A1. For example, the triple-axis MEMS acceleration sensor 100 is accelerated in a "+A1 " direction, which is a direction of the first axis A1 , in view of a relative movement, an acceleration in an "-A1" direction, which is another direction of the first axis A1 , acts on the fluid present around the first and second heating points 71 and 72. Due to the flow of the fluid in the "-A1 " direction, the second heating point 72 is cooled by the fluid which is present in the inner side of the first heating element 70 and has a temperature higher than an average temperature of the entire fluid, and the first heating point 71 is cooled by the fluid which is present in the outer side of the first heating element 70 and has a temperature lower than an average temperature of the entire fluid. Thus, the second heating point 72 has a temperature higher than that of the first heating point 71. On the contrary, the triple-axis MEMS acceleration sensor 100 is accelerated in the "-A1 " direction of the first axis A1 , the first heating point 71 has a temperature higher than that of the second heating point 72.

As described above, the first and second heating points 71 and 72 have different degrees of cooling due to the convection of the fluid having different temperatures, and the temperature difference is outputted as a voltage difference between a voltage outputted from the first thermocouple 30 that contacts the first heating point 71 and a voltage outputted from the second thermocouple 40 that contacts the second heating point 72. The first and second thermocouples 30 and 40 are connected in a differential type, and thus, a voltage V1 amplified by the amplifier 211 is a value proportional to the

acceleration in the direction of the first axis A1. In this manner, the direction (a positive or negative direction) and the magnitude of the acceleration acted in the first axis direction can be obtained.

As the same principle as above, an output voltage difference which is caused between the third thermocouple 50 and the fourth thermocouple 60 due to the temperature difference between the third heating point 73 and the fourth heating point 74 is amplified by the amplifier 212, and a voltage V2 amplified by the amplifier 212 is a value proportional to the acceleration in the direction of the second axis A2. An output voltage difference which is caused between the fifth thermocouple 130 and the first thermocouple 30 due to the temperature difference between the fifth heating point 171 and the first heating point 71 is amplified by the amplifier 213, and a voltage V3 amplified by the amplifier 213 is a value proportional to the acceleration in the direction of the third axis A3.

The degree of cooling of the heating points is different according to the variation of the pressure of the fluid that moves. In general, when the pressure of the fluid increases, the degree of cooling of the heating point increases since the convection is well developed, and when the pressure of the fluid decreases, the degree of cooling of the heating point by convection of the fluid is reduced. Thus, when the pressure of the fluid varies, a principle of precisely measuring the magnitude of the acceleration by measuring another variable from the temperature of the heating point is as follows.

When the triple-axis MEMS acceleration sensor 100 is accelerated in the "+A1" direction or the "-A1" direction, the fifth heating point 171 and the sixth heating point 172 undergo opposite cooling effects from each other. Therefore, the sum of temperatures of the fifth heating point 171 and the sixth heating point 172 is constant regardless of the direction of the accelerations. However, the sum of the temperatures of the fifth heating point 171 and the sixth heating point 172 depends on the pressure of the total fluid. That is, if the fluid has a high pressure, the sum of the temperatures of the fifth heating point 171 and the sixth heating point 172 is low, and if the fluid has a low pressure, the sum of the temperatures of the fifth heating point 171 and the sixth heating point 172 is high. The electrode pad 137 of the fifth thermocouple 130 and the electrode pad 146 of the sixth thermocouple 140 are connected to the amplifier 214 in a thermopile type so that the outputs can be added. Thus, a voltage Vp amplified by the amplifier 214 is given by a function of the pressure. Accordingly, the pressure of the

fluid can be obtained from the sum of the temperatures of the fifth heating point 171 and the sixth heating point 172, and using the pressure of the fluid, the temperature difference between the first heating point 71 and the second heating point 72 can be corrected to the temperature difference under a specific standard pressure. Thus, even in the case that the pressure of the fluid varies, the magnitude of the acceleration in the direction of the first axis A1 can be correctly obtained.

In the acceleration sensors, the principle of obtaining acceleration by measuring temperatures and thus correcting pressure variation is well known in the art as disclosed in the PCT international patent application PCT/KR2005/002509, and thus, a detailed description thereof will be omitted.

When the triple-axis MEMS acceleration sensor having the configuration as described above is used, an acceleration in the directions of the first, second, and third axes that spatially cross each other can be measured based on the structure in which two substrate are disposed parallel to each other. Therefore, the size of the acceleration sensor can be reduced using a MEMS process or a semiconductor fine processing technique, the manufacturing process of the acceleration sensor is simple, thereby increasing yield and reducing manufacturing costs.

Also, in the triple-axis MEMS acceleration sensor having the configuration as described above, the pressure of a fluid is measured regardless of the acceleration. Thus, since the effect of the pressure change of the fluid can be corrected, accelerations in the directions of the first, second, and third axes that spatially cross each other can be correctly measured.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, the triple-axis MEMS acceleration sensor according to the present invention is not limited to the examples, and it will be understood by one of ordinary skill in the art that various triple-axis MEMS acceleration sensors may be made therein without departing from the spirit and scope of the present invention. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims.