JP2017120974A - MEMS element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a MEMS element suitable for improving the sensitivity.SOLUTION: The movable electrode of a MEMS element is fixed to a back plate including a fixed electrode 5 by means of a coupling part 11. The movable electrode thus fixed includes a first movable region 3a vibrating by receiving the external pressure at both ends of the coupling part, and a second movable region 3b placed at a position away from the coupling part 11. The second movable region 3b is placed oppositely to the fixed electrode 5, and detects the magnitude of the external pressure received by the first movable region 3a as a capacitance change.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a MEMS element, and more particularly to a capacitive MEMS element used as a microphone, various sensors, switches, and the like.

  Conventionally, in a micro electro mechanical systems (MEMS) device using a semiconductor process, a fixed electrode, a sacrificial layer, and a movable electrode are formed on a semiconductor substrate, and then a part of the sacrificial layer is removed to be fixed via a spacer. An air gap (hollow) structure is formed between the fixed electrode and the movable electrode.

  For example, in a condenser microphone that is a capacitive MEMS element, a fixed electrode having a plurality of through-holes that allow sound pressure, which is one of external pressures, to pass through and a movable electrode that vibrates in response to sound pressure are arranged to face each other. The displacement of the movable electrode that receives pressure and vibrates is detected as a change in capacitance between the electrodes.

  By the way, in order to improve the S / N ratio of the condenser microphone, it is necessary to increase the displacement of the movable electrode due to the sound pressure. Therefore, a method for reducing the spring property of the movable electrode has been proposed. In addition, it is known that noise generated in an air gap formed by a movable electrode and a fixed electrode may be reduced (Patent Document 1, paragraph numbers 0003 to 0004).

  A cross-sectional view of a general MEMS device of this type is shown in FIG. As shown in FIG. 6A, a movable electrode film 3 is formed on a substrate 1 via a thermal oxide film 2. A fixed electrode film 5 and a nitride film 6 are formed on the movable electrode film 3 via a spacer 4, and a through hole 7 is formed in a back plate made of the fixed electrode film 5 and the nitride film 6. In addition, an air gap 9 is formed between the movable electrode film 3 and the fixed electrode film 5, and wiring portions 10 connected to the fixed electrode film 3 and the fixed electrode film 5 are formed.

  In the MEMS element shown in FIG. 6A, when the movable electrode film 3 is fixed over the entire circumference by the thermal oxide film 2 and the spacer 4, the spring property of the movable electrode film 3 is increased and the movable range is narrowed. End up. Therefore, as schematically shown in FIG. 6B, a slit 8 is formed by cutting out a part of the outer periphery of the movable electrode film 3, and the end of the movable electrode film 3 between the slits 8 is formed as shown in FIG. As shown in FIG. 4B, the movable electrode film 3 is fixed by the thermal oxide film 2 and the spacer 4 so that the spring property of the movable electrode film 3 is reduced. As a result, the displacement of the movable electrode film 3 can be increased, and the sensitivity can be improved. FIG. 6B is a plan view showing a state in which the movable electrode film 3 is exposed. The wiring portion 10 described in FIG. 6A and the drawing electrode for connecting to the wiring portion 10 are not shown. doing.

  By the way, although the movable electrode film 3 shown in FIG. 6 has a wider movable range as compared with the structure without the slit 8, the movable electrode film 3 is sandwiched between the thermal oxide film 2 and the spacer 4. Therefore, the displacement range is limited, and there is a limit to improving the sensitivity.

  On the other hand, reducing the noise generated in the air gap can be solved by increasing the dimension (interval of the air gap) between the movable electrode film 3 and the fixed electrode film 5. However, increasing the dimension between the movable electrode film 3 and the fixed electrode film 5 causes a decrease in the detected capacitance value (signal), and is not effective for improving the S / N ratio.

  Furthermore, it is necessary to reduce the noise generated when the sound pressure passes through the through hole 7. Reducing the noise generated in the through hole 7 can be solved by increasing the through hole 7. However, increasing the size of the through hole 7 also causes a decrease in the detected capacitance value (signal), and is not effective for improving the S / N ratio.

JP 2012-175509 A

  In the conventional MEMS element, the method of weakening the spring property of the movable electrode film while the end of the movable electrode film is fixed has limited the displacement width and cannot further improve the sensitivity. Further, in the method of adjusting the distance between the movable electrode film 3 and the fixed electrode film 5 and the size of the through-hole, if the distance is increased or the through-hole is enlarged, the signal decreases simultaneously with the noise reduction, and conversely the distance is narrowed. However, when the through hole is made small, noise increases simultaneously with an increase in signal, and it is difficult to obtain desired characteristics. An object of the present invention is to solve such problems and provide a MEMS element suitable for improving sensitivity.

  In order to achieve the above object, an invention according to claim 1 of the present application is a MEMS device in which a back plate including a fixed electrode and a movable electrode are arranged opposite to each other on a substrate provided with a back chamber. The first movable region fixed to the back plate including the fixed electrode and displaced by receiving an external force disposed on one side of the connecting portion, and the first movable region disposed on the other side of the connecting portion. A second movable region that is displaced according to the displacement generated in the region, and the second movable region is disposed opposite to the fixed electrode, and between the second movable region and the fixed electrode. The external pressure received by the first movable region is detected from a change in capacity.

  The invention according to claim 2 of the present application is the MEMS element according to claim 1, wherein an opening is provided in a part of the fixed electrode, and the first movable region is exposed in the opening. .

  The invention according to claim 3 of the present application is the MEMS element according to claim 1 or 2, wherein the connecting portion constitutes a partition that separates the first movable region and the second movable region. And

  In the MEMS element of the present invention, a back plate including a fixed electrode and a movable electrode are fixed by a connecting portion, and a first movable region that receives external pressure on one of the movable electrodes is sandwiched between the connecting portions, and a fixed electrode on the other side. The second movable area for detecting the change in capacitance between the second movable area and the end of the second movable area is a free end, so that there is no restriction on the displacement of the second movable area, and the sensitivity It is possible to improve.

  The first movable region and the second movable region constituting the movable electrode of the MEMS element of the present invention are configured to be displaced in opposite directions with the connecting portion as a fulcrum. In other words, it will move like a lever. With this configuration, it is possible to detect a large capacitance change by disposing the fixed electrode and the movable electrode apart from the connecting portion by a predetermined dimension, and it is possible to improve the sensitivity of the MEMS element. It is said.

  In addition, the MEMS element of the present invention has a configuration in which a wide opening is provided, so that noise due to the through hole formed in the back plate shown in the conventional example is eliminated, and the sensitivity of the MEMS element can be improved. It is said.

  Furthermore, the MEMS element of the present invention is suitable because the low-frequency sensitivity can be adjusted only by adjusting the size of the through-hole formed in the movable electrode by forming the partition with a continuous structure of the connecting portion. .

It is a figure explaining the MEMS element of this invention. It is a figure explaining the MEMS element of this invention. It is a figure explaining the MEMS element of this invention. It is a figure explaining the MEMS element of this invention. It is a figure explaining the MEMS element of this invention. It is a figure explaining this kind of conventional MEMS element.

  The MEMS element according to the present invention is configured to fix the movable electrode and the back plate including the fixed electrode by the connecting portion. The movable electrode is disposed on the other side of the first movable region that receives the external pressure disposed on one side of the connecting portion and the connecting portion that is displaced according to the magnitude of the external pressure received on the first movable region. The second movable region is included. The first movable region that receives the external pressure is preferably exposed to increase the area that receives the external pressure. Since the second movable region is disposed to face the fixed electrode and is displaced according to the external pressure received by the first movable region, the magnitude of the external pressure can be detected from this displacement. Examples of the present invention will be described below by taking a condenser microphone as an example of the MEMS element.

  A first embodiment of the present invention will be described in accordance with its manufacturing process. First, a thermal oxide film 2 having a thickness of about 1 μm is formed on a silicon substrate 1 having a crystal orientation (100) plane of 420 μm, and a thickness of 0 is formed on the thermal oxide film 2 by a CVD (Chemical Vapor Deposition) method. A 4 μm conductive polysilicon film is laminated. Next, patterning is performed by a normal photolithography method to form a movable electrode film 3 (corresponding to a movable electrode). Here, in the present invention, the movable electrode film 3 has a shape as shown in FIG. That is, a shape is formed in which a plurality of slits are formed from the outer periphery toward the center of the circular movable electrode film 3. The slit does not reach the center, and a part of the movable electrode separated in a fan shape is integrated in a circular center. A through hole 12 is formed at the center.

  Thereafter, a sacrificial layer 4a made of a USG (Undoped Silicate Glass) film having a thickness of about 2.0 to 4.0 μm is laminated on the movable electrode film 3 and patterned by a normal photolithography method to form a connection portion formation region. The sacrificial layer 4a is removed by etching, and the movable electrode film 3 is exposed. The connection portion formation scheduled region has a ring shape surrounding the central portion where there is no slit. The connection portion 11 is formed by filling the etching-removed region where the connection portion is to be formed with the sacrificial layer 4a and a material that can be selectively etched, flattening, and etching back (FIG. 1). The film constituting the connecting portion 11 may be either an insulating material or a conductive material, but has sufficient adhesion to the movable electrode film 3 and a film constituting the back plate described later, specifically, a nitride film. Further, since it is necessary to withstand the deformation of the movable electrode film 3, it is preferable to use a metal film. Needless to say, when the metal film is used, the movable electrode film 3 and the fixed electrode film 5 are not electrically connected.

  A conductive polysilicon film having a thickness of about 0.1 to 1.0 μm is formed on the sacrificial layer 4a. Next, patterning is performed by a normal photolithography method, and a fixed electrode film 5 (corresponding to a fixed electrode) is formed in a stacked manner (FIG. 2). The fixed electrode film 5 is not formed so as to face the entire surface of the previously formed movable electrode film 3, but is formed so as to face the separated outer peripheral region as shown in FIG. Preferably formed.

  After the nitride film 6 is deposited on the entire surface, it is patterned by a normal photolithography method so as to cover the previously formed connecting portion 11 and to expose the movable electrode film 3 disposed inside the connecting portion 11. The opening 13 is formed (FIG. 3).

  After forming the wiring part 10 to which the movable electrode film 3 and the fixed electrode film 5 are connected, a part of the silicon substrate 1 and the thermal oxide film 2 is removed from the back side of the silicon substrate 1 to form a back chamber 14 ( FIG. 4). Here, the size of the back chamber 14 is set such that the movable electrode film 3 excluding the extraction electrode is exposed, and a part of the sacrificial layer 4a is exposed on the back chamber 14 side.

  Thereafter, a part of the sacrificial layer 4a exposed to the opening 13 and the back chamber 14 side is removed, and the spacer 4 and the air gap 9 are formed. As shown in FIG. 5, the MEMS element formed in this way is in a state in which the movable electrode films 3 a and 3 b are fixed to the back plate including the fixed electrode film 5 and the nitride film 6 via the connecting portion 11. Here, the movable electrode film 3a closer to the opening 13 than the connecting portion 11 corresponds to the first movable region, and the movable electrode film 3b closer to the fixed electrode film 5 than the connecting portion 11 corresponds to the second movable region. The movable electrode film 3b and the fixed electrode film 5 in the second movable region are arranged to face each other, and a capacitance value is detected between the two electrode films.

  Next, the operation of the MEMS element shown in FIG. 5 will be described. The external pressure displaces the movable electrode film 3 a serving as the first movable region through the opening 13. A part of the external pressure passes from the through hole 12 to the back chamber 14 side, and prevents the movable electrode film 3a from being damaged by the excessive external pressure. Since the movable electrode film 3a is not used for detecting the capacitance value, the size of the opening 13 can be set to a sufficiently large shape so that noise does not occur when sound pressure passes.

  The size of the through hole 12 is adjusted to a size with which a desired low frequency sensitivity can be obtained. In this embodiment, since the connecting portion is formed in a ring shape, pressure does not leak from the opening 13 through the connecting portion 11, so that the sensitivity can be adjusted only by adjusting the size of the through hole 12. is there. Although sensitivity adjustment is complicated, there is no problem even if the connecting portion 11 is not ring-shaped and separated into a plurality of parts.

  The displacement generated in the movable electrode film 3a in the first movable region operates like a “lever” with the connecting portion 11 as a fulcrum, and is transmitted as a reverse movement to the movable electrode film 3b in the second movable region. That is, when the movable electrode film 3a is displaced downward, the movable electrode film 3b is displaced upward, and when the movable electrode film 3a is displaced upward, the movable electrode film 3b is displaced downward.

  The change in capacitance value is detected by the magnitude of displacement of the movable electrode film 3b facing the fixed electrode film 5. As shown in FIG. 5, the displacement of the movable electrode film 3b disposed at a position away from the connecting portion 11 serving as a fulcrum is larger than the displacement of the movable electrode film 3a that vibrates by receiving external pressure, and the capacitance It can be seen that the change in the value also increases and the sensitivity is improved.

  As described above, the MEMS element of this embodiment can amplify the displacement of the movable electrode film 3a serving as the first movable region and transmit the amplified displacement to the movable electrode film 3b serving as the second movable region. Can be formed.

  As mentioned above, although the Example of this invention was described, it cannot be overemphasized that this invention is not limited to these. For example, the shapes of the movable electrode film 3 and the fixed electrode film 5 are not limited to a circular shape or a ring shape, and may be a rectangular shape such as a rectangle. In addition, there is no problem even if the slit formed in the movable electrode 3 described in the first embodiment extends to the center and the movable electrode is separated into a plurality of shapes.

1: silicon substrate, 2: thermal oxide film, 3: movable electrode film, 4: spacer, 4a: sacrificial layer, 5: fixed electrode film, 6: nitride film, 7: through-hole, 8: slit, 9: air gap 10: Wiring part, 11: Connection part, 12: Through hole, 13: Opening part, 14: Back chamber

Claims (3)

In a MEMS element in which a back plate including a fixed electrode and a movable electrode are arranged opposite to each other on a substrate having a back chamber,
The movable electrode is fixed to a back plate including the fixed electrode by a connecting portion, and is displaced by receiving an external force disposed on one side of the connecting portion and on the other side of the connecting portion. A second movable region that is displaced in accordance with a displacement generated in the first movable region that is disposed,
The second movable region is disposed opposite to the fixed electrode, and detects the magnitude of the external pressure received by the first movable region from a capacitance change between the second movable region and the fixed electrode. A MEMS element characterized in that: The MEMS device according to claim 1, wherein
An opening is provided in a part of the fixed electrode,
The MEMS element, wherein the first movable region is exposed in the opening. The MEMS element according to claim 1 or 2,
The MEMS element according to claim 1, wherein the connecting portion constitutes a partition that separates the first movable region and the second movable region.

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