JP2019126856A - MEMS element - Google Patents

Abstract

To provide an MEMS element having high sensitivity and high mechanical strength.SOLUTION: A protrusion is disposed between a movable film and a stationary film. The protrusion displaces a first region 7a of the stationary film by vibration of the movable film. A detection element 11 is disposed between a first region and a second region 7b of a stationary electrode separated from the first region. When the protrusion pushes up the first region, stress is applied to the detection element, and an output signal outputted from the detection element is changed, thereby obtaining an output signal generated along the vibration of the movable film.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a MEMS device, and more particularly to a MEMS device that can be used as various sensors such as a transducer.

  A MEMS (Micro Electro Mechanical Systems) element formed using a semiconductor process forms a movable electrode, a sacrificial layer and a fixed electrode on a semiconductor substrate, and then removes a part of the sacrificial layer to form a spacer. An air gap (hollow) structure is formed between the fixed electrode and the movable electrode.

  For example, in a capacitive MEMS element, a fixed electrode film including a fixed electrode having a plurality of through-holes and a movable electrode film including a movable electrode that vibrates in response to sound pressure or the like are disposed to face each other, and vibration is caused. The displacement of the movable electrode is detected as a change in capacitance between the electrodes. A MEMS device of this type is described, for example, in Patent Document 1.

  The operation of the conventional MEMS device is schematically shown in FIG. A movable electrode film 23 including a conductive movable electrode and a fixed electrode film 24 including a conductive fixed electrode are interposed via a spacer 25 on a silicon substrate 21 as a support substrate via an insulating film 22 made of a thermal oxide film. Are arranged. The movable electrode film 23 is vibrated by receiving sound pressure or the like, so that the capacitance value of the capacitor formed between the fixed electrode of the fixed electrode film 24 and the movable electrode of the movable electrode film 23 changes. By taking out this capacitance value from an electrode (not shown), it becomes possible to obtain an output signal according to the sound pressure etc. which the movable electrode film 23 receives.

  In order to increase the output sensitivity in the MEMS element having such a structure, it is necessary to increase the displacement of the movable electrode due to the sound pressure or the like. Therefore, the movable electrode film 23 is generally formed of a film having a weak spring property. On the other hand, it is also known that a membrane having a weak spring property has a disadvantage that the strength is reduced.

JP 2011-55087 A

  When the movable electrode film is formed of a film having a weak spring property in order to improve sensitivity in the conventional MEMS element, there is a problem that the strength is lowered and the film cannot be used. SUMMARY OF THE INVENTION It is an object of the present invention to solve such problems and to provide a MEMS device having high sensitivity and high mechanical strength.

  In order to achieve the above object, the invention according to claim 1 relates to a substrate provided with a back chamber, and a MEMS element in which a fixed film and a movable film are disposed opposite to each other with a spacer on the substrate. A protrusion that is disposed between the movable film and the fixed film and projects from one film to the other film side, a first area of the fixed film that is displaceably disposed, and the first area A second region of the fixed film separated from the second region, and a gap between the first region and the second region, one end of which is connected to the wiring portion on the first region, and the other end And a sensing element connected to the wiring portion on the second region, and the protrusion is displaced by the vibration of the movable film, and the first region is displaced by the displacement of the protrusion. A change in the output signal from the detection element is detected.

  The invention according to claim 2 is the MEMS element according to claim 1, wherein the sensing element is such that the stress applied to the sensing element is changed by the displacement of the first region, and the output signal is changed. It is characterized by being.

  The invention according to claim 3 of the present application is characterized in that in the MEMS element according to claim 1 or 2, the detection element is an element that outputs a current signal or a voltage signal.

  The MEMS element of the present invention is configured to include a protrusion between the movable film and the first region of the fixed film, and by reducing the size of the gap between the protrusion and the film facing the protrusion, Displacement can be transmitted to the first region of the fixed membrane. Therefore, there is an advantage that a sufficient output signal can be obtained even when a strong spring film having a small displacement and a strong displacement is used.

  The MEMS element of the present invention is configured to obtain an output signal using the piezoelectric effect of the detection element, so that a large output signal can be obtained compared to the conventional output signal based on capacitance change, and the sensitivity is high. A MEMS element can be configured.

  In addition, since a current signal or a voltage signal is output from the sensing element, it is not necessary to form a capacitive element having a large area, and there is an advantage that the MEMS element can be downsized.

It is a figure explaining the manufacturing process of the MEMS element of this invention. It is a figure explaining the manufacturing process of the MEMS element of this invention. It is a figure explaining the manufacturing process of the MEMS element of this invention. It is a figure explaining the manufacturing process of the MEMS element of this invention. It is a figure explaining the manufacturing process of the MEMS element of this invention. It is a figure explaining the composition of the sensing element of the MEMS element of the present invention. It is a figure explaining the manufacturing process of the MEMS element of this invention. It is a figure explaining operation | movement of the MEMS element of this invention. It is a figure explaining the conventional MEMS element.

  In the MEMS element of the present invention, a protrusion is provided between the movable film and the fixed film, and the protrusion displaces the first region of the fixed film by the vibration of the movable film. On the other hand, the second region of the fixed membrane is not displaced due to the structure separated from the first region. A sensing element is disposed between the first region and the second region, and stress is applied to the sensing element when the protrusion displaces the first region. As a result, the output signal output from the sensing element changes, and an output signal accompanying the vibration of the movable film can be obtained. Hereinafter, the MEMS element of the present invention will be described in detail according to the manufacturing process.

  First, the MEMS element of the first embodiment of the present invention will be described according to the manufacturing process. The MEMS device of the present embodiment will be described in the case where a protrusion is formed on the movable film. Similar to a normal MEMS element, the silicon substrate 1 is thermally oxidized to form an insulating film 2 on the surface of the silicon substrate 1. A movable film 3 made of a conductive polysilicon film is laminated on the insulating film 2 (FIG. 1).

  On the movable film 3, a sacrificial layer 4 made of a USG (Undoped Silicate Glass) film is laminated. Thereafter, a recess 5 is formed in the center of the movable film 3 in order to form a protrusion described later. The recess 5 is preferably arranged at a location where the displacement of the movable film 3 is large, and in the example shown in FIG. 2, it is formed at the center of the back chamber described later. A nitride film is formed on the surface of the sacrificial layer 4 so as to fill the nitride film 6 in the recess 5. Thereafter, the nitride film on the surface of the sacrificial layer 4 is removed to expose the surface of the sacrificial layer 4, whereby the recess 5 can be selectively filled with the nitride film 6 (FIG. 2). The material filling the recess 5 is not limited to the nitride film, but a sacrificial layer 4 described later, such as a two-layer structure of a nitride film and an oxide film, or a three-layer structure of a nitride film, an oxide film, and a nitride film. If it is a material which remains without being etched at the same time when removing it, it is possible to change appropriately.

  In addition, the material filled in the recess 5 becomes a protrusion to be described later, and has a structure to push up the first fixed film, so that the first fixed film with which the protrusion abuts is not broken. You may process a front-end | tip part in the shape without a corner | angular part.

  A sacrificial layer 4 a is further formed on the exposed surface of the nitride film 6 and the surface of the sacrificial layer 4. Since the thickness of the sacrificial layer 4a formed here is a dimension between the tip of the protrusion formed of the nitride film 6 and the first fixed film, the MEMS element is adjusted to have desired characteristics ((1) Figure 3).

  A conductive polysilicon film to be a fixed film is formed on the sacrificial layer 4a. This polysilicon film includes the first fixed film 7a in the portion of the first fixed film 7a (corresponding to the first region) and the portion of the second fixed film 7b (corresponding to the second region). It isolate | separates by the gap | interval part 8 formed so that it might surround. In the fixed film, as in the case of a fixed film of a general MEMS element, through holes 9 through which sound pressure and the like pass are formed on the entire surface. Although no through hole is shown in the first fixed film 7a in FIG. 4, a through hole may be formed also in the first through hole 7a.

  Thereafter, the insulating film 10 is filled in the gaps 8 and the through holes 9 and planarized. The insulating film 10 is preferably selected from materials that can be removed at the same time when the sacrificial layers 4 and 4a described later are removed. For example, the insulating film 10 is an oxide film. After that, a resistance element corresponding to a detection element is formed between the first fixed film 7a and the second fixed film 7b.

  A plurality of resistance elements can be provided around the first fixed film 7a. FIG. 6 schematically shows an example in which a detection element in which two resistance elements 11 are connected in series is arranged at a position facing the center of the first fixed film 7a. As shown in FIG. 6, each resistance element 11 is arranged so as to cross the gap 8 between the first fixed film 7a and the second fixed film 7b. Wirings for extracting the current value or the voltage value of the resistance element 11 as an output signal are connected to both ends of the resistance element 11, respectively. When the resistance element 11 having such a structure is formed, the resistance element 11 and the wiring on the first fixed film 7a are formed of a high-resistance polysilicon film, and the wiring on the second fixed film 7b has a low resistance. It may be formed of a polysilicon film of Here, the wiring on the first fixed film 7a has a structure also serving as the polysilicon film constituting the first fixed film 7a, and no special wiring is required. On the other hand, the wiring formed on the second fixed film 7b may be formed of the wiring 12a and the wiring 12b having a multilayer wiring structure. As a result, it is possible to form a detection element in which two resistance elements are connected in series between the wiring 12 a and the wiring 12 b. There is no problem if the wiring on the first fixed film 7a is formed of another low resistance wiring metal. Further, the arrangement of the resistance element 11 can be variously changed, and is not limited to the structure shown in FIG.

  In the case of forming a multilayer wiring on the second fixed film 7b, it is necessary to form a necessary insulating structure, so the nitride film 13 is formed on the resistance element 11, and the wirings 12a and 12b are formed on the nitride film 13. Form (FIG. 5).

  Thereafter, in accordance with the usual manufacturing process of the MEMS device, the spacer 14 consisting of a part of the sacrificial layer 4, 4 a is formed. The spacer 14 is formed by removing the exposed sacrificial layer 4a and the sacrificial layer 4 after removing the insulating film 10 exposed on the surface. By removing the sacrificial layers 4 and 4a, a protrusion 15 made of the nitride film 6 protruding toward the first fixed film 7a is formed on the movable film 3. Further, a part of the silicon substrate 1 is removed from the back surface side, and a back chamber 16 is formed. (Figure 7). Electrodes and the like connected to the movable film 3, the second fixed film 7 b, and the wirings 12 a and 12 b (not shown) are formed, and the MEMS element is completed.

  Next, the operation of the MEMS element will be described. When a sound pressure or the like is applied and the movable film 3 vibrates, the tip of the projection 15 is also displaced with the vibration. When the movable film 3 is displaced upward by ΔA from the state shown in the left drawing of FIG. 8 to the state shown in the right drawing, the tip of the projection part is displaced upward by ΔA and pushes up the first fixed film 7a. . The second fixed film 7b may be slightly displaced as the first fixed film 7a is pushed up, but is basically not displaced. As a result, the resistance element 11 disposed in the gap 8 between the first fixed film 7a and the second fixed film 7b is deformed. Due to this deformation, the resistance value of the resistance element 11 changes.

  By taking out this change in resistance value from a current signal change or voltage signal change from an electrode (not shown), it is possible to obtain an output signal corresponding to the sound pressure received by the movable film 3.

  The MEMS element having such a structure can extract a signal even when the displacement of the movable film 3 is small as compared with a conventional capacitive MEMS element. Therefore, it is possible to select a strong film as the movable film 3.

Although the embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the above embodiments. For example, the protrusion has a structure that protrudes from the fixed film side to the movable film side instead of protruding from the movable film side, and the tip of the protrusion that protrudes from the fixed film side when the movable film is displaced There is no problem as a configuration that deforms the sensing element by pushing up.

  Further, the detection element is not limited to the resistance element, and any element whose output signal changes due to the piezoelectric effect when the detection element is deformed may be used.

1: silicon substrate, 2: insulating film, 3: movable film, 4: sacrificial layer, 5: recess, 6: nitride film, 7, 7a: first fixed film, 7b: second fixed film, 8 gaps , 9: through hole, 10: insulating film, 11: resistance element, 12a, 12b: wiring, 13: nitride film, 14: spacer, 15: protrusion, 16: back chamber, 21: silicon substrate, 22: insulating film , 23: movable electrode film, 24: fixed electrode film

Claims (3)

In a MEMS device in which a substrate provided with a back chamber and a fixed film and a movable film are arranged opposite to each other with a spacer interposed therebetween on the substrate,
A protrusion disposed between the movable film and the fixed film, which protrudes from one film to the other;
A first region of the fixed membrane disposed displaceably;
A second region of the fixed membrane separated from the first region;
It is disposed in a gap between the first region and the second region, one end is connected to the wiring portion on the first region, and the other end is connected to the wiring portion on the second region. And a detection element,
10. A MEMS device, comprising: a change in an output signal from the detection element caused by displacement of the protrusion due to vibration of the movable film and displacement of the first region due to displacement of the protrusion.   2. The MEMS element according to claim 1, wherein the sensing element is an element in which a stress applied to the sensing element changes due to displacement of the first region, and the output signal changes. 3. .   3. The MEMS element according to claim 1, wherein the sensing element is an element that outputs a current signal or a voltage signal. 4.

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