MEMS temperature sensor

Abstract

To provide an MEMS temperature sensor for enabling temperature correction to an MEMS resonator or the like with high accuracy.SOLUTION: An MEMS temperature sensor is an MEMS temperature sensor including a substrate, a recessed part provided on the substrate, and a first electrode and a second electrode supported in midair in the recessed part and arranged oppositely to each other to detect capacity between the first electrode and the second electrode. The first electrode is further provided with a stress film having a thermal expansion coefficient different from the first electrode. The stress film is an embedded film embedded in an asymmetric area with respect to a center line in a longer direction of the first electrode when viewed from the top face of the first electrode, or a thin film provided on the top face of the first electrode.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a MEMS temperature sensor, and more particularly to a MEMS temperature sensor formed on a MEMS chip.

Background Art

[0002] In a silicon MEMS resonator, there has been a problem that the resonance frequency is affected by the ambient temperature and a high-precision resonance frequency cannot be obtained. In contrast, a temperature sensor is disposed on a control IC provided in the same package as the MEMS resonator, the temperature inside the package is measured by this temperature sensor, and temperature correction of the MEMS resonator is performed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0004] However, the temperature inside the package measured by the temperature sensor on the control IC may be different from the temperature of the MEMS resonator, and there has been a problem that temperature correction cannot be performed with high precision for the MEMS resonator.

[0005] Therefore, an object of the present invention is to provide a MEMS temperature sensor capable of performing temperature correction with high precision for a MEMS resonator or the like.

[0006] The present disclosure is a substrate, a recess provided in the substrate, a first electrode and a second electrode that are supported hollowly in the recess and are arranged opposite to each other, and a MEMS temperature sensor that detects a capacitance between the first electrode and the second electrode, wherein the first electrode further includes a stress film having a coefficient of thermal expansion different from that of the first electrode.

[0007] In addition, the present disclosure relates to the above-described MEMS temperature sensor and a MEMS device formed on the same substrate, and is also a device in which the MEMS device is corrected based on the detection result of the MEMS temperature sensor.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0009] <Embodiment 1> FIG. 1 is a top view of an MEMS temperature sensor according to Embodiment 1 of the present invention, which is denoted by 100 as a whole, and FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1.

[0010] As shown in FIGS. 1 and 2, the MEMS temperature sensor 100 includes a substrate 10 made of, for example, silicon, and a recess 20 provided inside the substrate 10.

[0011] Inside the recess 20, there are included a first electrode 30 fixed to the substrate 10 on the side surface of the recess 20, and two second electrodes 40a, 40b arranged parallel to each other with the first electrode 30 interposed therebetween. The first electrode 30 and the second electrodes 40a, 40b are held hollow inside the recess 20 and form comb teeth electrodes arranged opposite to each other.

[0012] Between the first electrode 30 and the substrate 10, and between the second electrodes 40a, 40b and the substrate 10, isolation joints (IJ) 35, 45 made of silicon oxide are respectively provided. Thereby, between the first electrode 30 and the substrate 10, and between the second electrodes 40a, 40b and the substrate 10, they are electrically insulated.

[0013] The first electrode 30, the second electrodes 40a, 40b are electrically connected to pad electrodes 60, 60a, 60b respectively through wiring layers 50, 50a, 50b made of, for example, aluminum.

[0014] Furthermore, a stress film 38 is formed along the longitudinal direction on the first electrode 30. The stress film 38 is formed by providing a hole or a through hole in the first electrode 30 and thermally oxidizing the inside and filling it with silicon oxide. When viewed in the top view of FIG. 1, the stress film 38 is formed in a region biased in the direction of the second electrode 40a with respect to the central axis A - A in the longitudinal direction of the first electrode 30.

[0015] In the MEMS temperature sensor 100, the thermal expansion coefficients of the stress film 38 made of silicon oxide and the first electrode 30 made of silicon are different. For this reason, as shown in FIG. 3, depending on the ambient temperature, the distance between the first electrode 30 and the second electrodes 40a and 40b changes. In FIG. 3, the tip of the first electrode 30 is displaced in the direction of the second electrode 40a (Y - axis direction). Thereby, by measuring the change in the capacitance C1 and / or the capacitance C2, the temperature change around the MEMS temperature sensor 100 can be detected.

[0016] In the MEMS temperature sensor 100, a voltage is applied between the pad electrode 60 and the pad electrode 60a and / or the pad electrode 60b, and the capacitance C1 and / or the capacitance C2 at this time is measured to detect the temperature.

[0017] Note that the temperature can be detected by using only one of the capacitances C1 and C2, but the measurement accuracy is improved when both are used.

[0018] Also, here, the stress film 38 embedded in the first electrode 30 is used. However, for example, an oxide film may be formed in a region of the surface of the first electrode 30 that is offset with respect to the central axis A-A as the stress film.

[0019] FIG. 4 is a layout diagram of a resonator 1000 in which the MEMS temperature sensor 100 according to Embodiment 1 and the MEMS resonator 300 are fabricated on the same substrate. By forming the MEMS resonator 300 and the MEMS temperature sensor 100 adjacent to each other on the same substrate, the ambient temperature of the MEMS resonator 300 can be accurately measured by the MEMS temperature sensor 100, and temperature correction of the MEMS resonator 300 can be performed with higher accuracy using the measurement result of the MEMS temperature sensor 100.

[0020] The temperature correction of the resonance frequency of the MEMS resonator 300 is performed by correcting the electrical signal obtained from the MEMS resonator 300 based on the temperature detected by the MEMS temperature sensor 100 by a separately provided control IC (not shown).

[0021] <Embodiment 2> FIG. 5 is a top view of the MEMS temperature sensor according to Embodiment 2 of the present invention, which is represented by 200 as a whole, and FIG. 6 is a cross-sectional view when FIG. 5 is viewed in the VI-VI direction. In FIGS. 5 and 6, the same reference numerals as those in FIGS. 1 and 2 indicate the same or corresponding portions.

[0022] As shown in FIGS. 5 and 6, the MEMS temperature sensor 200 includes a substrate 10 made of, for example, silicon, and a recess 20 provided inside the substrate 10.

[0023] The recess 20 includes a first electrode 130 fixed to the substrate 10 on the side surface of the recess 20, and two second electrodes 140 arranged parallel to each other with the first electrode 130 interposed therebetween. The second electrodes 140 are held hollow within the recess 20 and form opposed comb electrodes.

[0024] Insulation joints (IJ) 135 and 145 made of silicon oxide are provided between the first electrode 130 and the substrate 10, and between the second electrode 140 and the substrate 10, respectively. Thereby, the first electrode 130 and the substrate 10, and the second electrode 140 and the substrate 10 are electrically insulated from each other.

[0025] The first electrode 130 and the second electrode 140 are electrically connected to the pad electrodes 160 via a wiring layer 150 made of, for example, aluminum, respectively.

[0026] In the MEMS temperature sensor 200, a stress film 138 is provided on the upper surface of the first electrode. The stress film 138 is formed by thermally oxidizing the surface of the silicon substrate 10 to form a silicon oxide film over the entire surface, and then etching away the unnecessary portions of the silicon oxide film.

[0027] In the MEMS temperature sensor 200, the distances between the first electrode 130 and the two second electrodes 140 are equal, and the capacitances between the first electrode 130 and the second electrodes 140 are both C3.

[0028] In the MEMS temperature sensor 200, the thermal expansion coefficients of the stress film 138 made of silicon oxide and the first electrode 130 made of silicon are different. Therefore, as shown in FIG. 7, depending on the ambient temperature, the tip of the first electrode 130 is displaced in the vertical direction (Z-axis direction). As a result, the opposed area between the first electrode 130 and the second electrodes 140 changes, that is, the capacitance C3 changes. By measuring the change in the capacitance C3, the temperature change around the MEMS temperature sensor 200 can be detected.

[0029] In the MEMS temperature sensor 200, a voltage is applied between the two pad electrodes 160, and the capacitance C3 at this time is measured to detect the temperature.

[0030] Note that the temperature can be detected using only one of the two capacitances C3, but the measurement accuracy is improved when the sum of the two capacitances C3 is used.

[0031] FIG. 8 is a layout diagram of a resonator 2000 in which a MEMS temperature sensor 200 according to Embodiment 2 and a MEMS resonator 300 are fabricated on the same substrate. By forming the MEMS resonator 300 and the MEMS temperature sensor 200 adjacent to each other on the same substrate, the ambient temperature around the MEMS resonator 300 can be accurately measured by the MEMS temperature sensor 200. Therefore, temperature correction of the MEMS resonator 300 can be performed with higher accuracy using the measurement result of the MEMS temperature sensor 200.

[0032] Temperature correction of the resonance frequency of the MEMS resonator 300 is performed by a separately provided control IC (not shown) by correcting an electrical signal obtained from the MEMS resonator 300 based on the temperature obtained by the MEMS temperature sensor 200.

[0033] In Embodiments 1 and 2, examples in which the MEMS temperature sensors 100 and 200 are used for temperature correction of the MEMS resonator 300 are shown, but this is just an example. For example, by using an acceleration sensor, a pressure sensor, etc. instead of the MEMS resonator 300, it is also possible to perform temperature correction of these sensors.

[0034] <Appendix> This disclosure relates to a substrate, a recess provided in the substrate, a first electrode and a second electrode that are supported hollowly in the recess and are arranged opposite to each other, and a MEMS temperature sensor that detects the capacitance between the first electrode and the second electrode, wherein the first electrode is a MEMS temperature sensor further including a stress film having a coefficient of thermal expansion different from that of the first electrode. By utilizing the difference in the coefficients of thermal expansion between the first electrode and the stress film and detecting the capacitance between the first electrode and the second electrode, it becomes possible to measure the ambient temperature.

[0035] In the present disclosure, the stress film is an embedded film embedded in an area asymmetric with respect to the longitudinal center line of the first electrode when viewed from the upper surface of the first electrode. By using such a structure, it becomes possible to displace the first electrode in the horizontal direction.

[0036] In the present disclosure, the tip of the first electrode is displaced in the horizontal direction depending on the environmental temperature. As a result, the capacitance between the first electrode and the second electrode changes depending on the environmental temperature.

[0037] In the present disclosure, the stress film is a thin film provided on the upper surface of the first electrode. By using such a structure, it is possible to displace the first electrode in the vertical direction.

[0038] In the present disclosure, the tip of the first electrode is displaced in the vertical direction depending on the environmental temperature. As a result, the capacitance between the first electrode and the second electrode changes depending on the environmental temperature.

[0039] In the present disclosure, the first electrode and the second electrode are made of silicon, and the stress film is made of silicon oxide. By using such materials, the stress film can be easily fabricated.

[0040] The present disclosure includes the above-described MEMS temperature sensor and an MEMS device, which are formed on the same substrate, and is a device in which the MEMS device is corrected based on the detection result of the MEMS temperature sensor. By fabricating the MEMS device and the MEMS sensor on the same substrate, the environmental temperature of the MEMS device can be accurately measured, and accurate temperature correction of the measured value of the MEMS device becomes possible.

[0041] In the present disclosure, the MEMS device is an acceleration sensor, a pressure sensor, or a resonator. Accurate temperature correction of these MEMS devices becomes possible.

Industrial Applicability

[0042] The MEMS temperature sensor of the present invention can be applied to temperature correction of MEMS devices such as acceleration sensors, pressure sensors, and resonators.

Description of Reference Numerals

[0043] 10 Substrate 20 Concave portion 30, 130 First electrode 35, 45, 135, 145 Isolation joint (IJ) 38, 138 Stress film 40a, 40b, 140 Second electrode 50, 50a, 50b, 150 Wiring layer 60, 60a, 60b, 160 Pad electrode 100, 200 MEMS temperature sensor 300 MEMS resonator 1000, 2000 Resonator

Claims

1. A substrate; A recess provided in the substrate; a first electrode and a second electrode that are supported in the hollow of the recess and disposed opposite each other; 1. A MEMS temperature sensor that detects a capacitance between a first electrode and a second electrode, The MEMS temperature sensor, wherein the first electrode further comprises a stress film having a different thermal expansion coefficient than the first electrode.

2. The MEMS temperature sensor according to claim 1 , wherein the stress film is a buried film buried in an area asymmetric with respect to a center line of the first electrode in a longitudinal direction when viewed from above the first electrode.

3. The MEMS temperature sensor according to claim 2 , wherein the tip of the first electrode is displaced in a horizontal direction depending on the ambient temperature.

4. The MEMS temperature sensor according to claim 1 , wherein the stress film is a thin film provided on an upper surface of the first electrode.

5. The MEMS temperature sensor according to claim 4 , wherein the tip of the first electrode is displaced in the vertical direction depending on the ambient temperature.

6. 6. The MEMS temperature sensor according to claim 1, wherein the first electrode and the second electrode are made of silicon, and the stress film is made of silicon oxide.

7. A MEMS temperature sensor according to any one of claims 1 to 5, A MEMS device is formed on the same substrate; An apparatus in which a MEMS device is corrected based on the detection results of a MEMS temperature sensor.

8. The apparatus of claim 7 , wherein the MEMS device is an acceleration sensor, a pressure sensor, or a resonator.

Images