JP2017135456A - MEMS element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow for compaction without decreasing the sensitivity or mechanical strength.SOLUTION: A MEMS element has a fixed electrode 8 fixed to the support layer 7 of a substrate 1, a displaceable movable electrode 6 placed substantially in parallel with the fixed electrode 8, and a spring layer 3 fixed to the support layer 7 of the substrate 1 at a position above or below the movable electrode 6. The movable electrode 6 is mechanically supported for the spring layer 3 via a pin-like support 5 and connected electrically, and one turn or more of spiral slits 12 are formed around the spring layer 3 of the pin-like support 5. Since no stress is applied from the substrate 1 or support member to the movable electrode 6, the whole movable electrode can displace in the horizontal direction and vertical direction, and thereby the sensitivity is improved.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, MEMS (Micro Electro Mechanical System) elements have been used for microphones, sensors, actuators, electronic circuits, mechanical component parts, etc. For example, in the market of portable devices, the microphone of the MEMS element is replaced with an electret condenser microphone. In recent years, there has been an increasing demand for higher sensitivity in addition to downsizing.

  In such a microphone, the movable electrode and the fixed electrode formed on the semiconductor substrate form a parallel plate capacitor, and the capacitance displacement caused by the vibration of the movable electrode due to sound pressure is converted into a voltage change. The sound is converted into an electric signal.

  FIG. 8 shows an example (cross-sectional view) of a conventional MEMS microphone. In this microphone, a movable electrode (diaphragm) 66 is formed on a semiconductor substrate 61 via an insulating film 62, and a support layer (sacrificial). A fixed electrode 68 is provided via 67 (consisting of part of the layer). The fixed electrode 68 and the movable electrode 66 are arranged so as to be parallel to each other, and a large number of sound holes 71 are formed in the fixed electrode 68 with an insulating film 69 provided thereon.

JP, 2014-233059, A

By the way, the sensitivity of the microphone is improved by increasing the rate of change in capacitance caused by the displacement of the movable electrode 66 that receives the sound pressure. However, a general MEMS microphone as shown in FIG. Since the periphery of the electrode 66 is fixed by the substrate 61, the support layer 67, etc., the capacitance is changed only by the curvature in the movable electrode 66.
On the other hand, in the movable electrode 66, the smaller the tensile stress applied thereto, the easier it is to bend and the sensitivity is improved, but conversely, if it turns to compressive stress, the movable electrode 66 bends and does not operate as a microphone. For this reason, it is important to set the tensile stress as small as possible in the film forming process of the movable electrode 66 and the subsequent annealing process, and the material used for the movable electrode 66 is also limited.

  In the conventional microphone, since the periphery of the movable electrode 66 is fixed as described above, the capacitance does not change due to the entire displacement of the movable electrode 66, and the smaller the diameter of the movable electrode 66, the more There is a problem that the sensitivity is lowered because the displacement is reduced. Therefore, it is difficult to reduce the size while maintaining the sensitivity.

  In the microphone disclosed in Patent Document 1, a slit is provided on the outer periphery of the movable electrode to facilitate displacement. On the other hand, in order to alleviate the stress concentration around the slit, it is necessary to increase the thickness of the movable electrode, which hinders displacement of the movable electrode. Therefore, there is a demand for a method that does not hinder the displacement of the movable electrode while reducing the stress concentration.

  Further, if the microphone is miniaturized under the condition that the periphery of the movable electrode 66 is fixed, the resonance frequency is shifted to the high sound region side, and the sensitivity in the middle and low sound region is lowered. There is a method of increasing the resistance component of the air vibration, so-called acoustic resistance, in order to prevent the lowering of the sensitivity in the mid-low range. For example, by providing a shield in the gap between the movable electrode 66 and the fixed electrode 68, the acoustic resistance is increased. However, since the shielding object reduces the effective area of the capacitor that can contribute to the change in capacitance, there is a disadvantage in that the sensitivity of the entire sound range is lowered while the sensitivity of the mid-low range is prevented.

Furthermore, by reducing the thickness of the movable electrode 66 or reducing the number of support portions (62, 67) for fixing, the movable electrode 66 can be easily displaced and the sensitivity can be improved, but the mechanical strength is increased. There arises a problem that the movable electrode 66 is liable to be destroyed due to the decrease. From the above, it has been difficult to reduce the size of a conventional microphone as a MEMS element because it involves either a decrease in sensitivity or a decrease in mechanical strength.
Such a decrease in sensitivity and a decrease in mechanical strength are not only limited to the above-described microphone, but are also a problem to be solved for other MEMS elements that convert displacement and vibration into an electric quantity.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a MEMS device that can be miniaturized without a decrease in sensitivity or a decrease in mechanical strength.

In order to achieve the above object, a MEMS device according to the invention of claim 1 includes a fixed electrode fixed to a support layer of a substrate, a displaceable movable electrode disposed substantially parallel to the fixed electrode, and the movable element. A spring layer fixed to the support layer of the substrate at a position above or below the electrode, and mechanically supporting the movable electrode with respect to the spring layer via a support and electrically connecting It is characterized by becoming.
According to a second aspect of the present invention, a plurality of the support bodies are arranged in the form of dots or lines in plan view, and the spring layer has at least one spiral slit around the dot or line support bodies. Is formed.
According to a third aspect of the present invention, the support body is annularly arranged around the spring layer in a plan view, and one or more spiral slits are formed in the spring layer along the outer periphery of the annular support body. It is characterized by that.

According to the above configuration, for example, the support is provided at the center of the spiral slit formed in the spring layer, and the movable electrode is attached to the spring layer via the support, so that the movable electrode is interposed via the spiral spring. To be supported above or below the spring layer. The movable electrode is electrically connected to the spring layer and to the circuit portion through a support (which may be a contact).
As a result, stress from the substrate or support layer applied to the movable electrode is eliminated, and the entire movable electrode can be displaced not only in the horizontal direction but also in the vertical direction. For example, in a microphone, due to sensitive displacement and vibration with respect to sound pressure. Good sensitivity can be obtained.

  According to the present invention, since the movable electrode can be displaced in the horizontal direction and the vertical direction (omnidirectional direction), the displacement in the movable electrode, the vibration, the displacement of the entire movable electrode, and the vibration can be obtained. As the accuracy of the rate of change in capacitance with respect to is ensured and the sensitivity is improved, it is possible to reduce the size without lowering the sensitivity or lowering the mechanical strength.

Further, by providing the spiral slit, the slit absorbs the horizontal stress applied from the support layer to the spring layer, and the movable electrode can keep the flat plate while being displaced in the horizontal direction. For this reason, the range of stress control in the film forming process is widened, and it becomes possible to use a material having high mechanical strength or a composite material that could not be used as a movable electrode in the past.
Furthermore, by selecting the material of the spring layer, the number of spiral slits, the slit shape, the slit width, the number of windings, and the mass of the movable electrode, it is possible to design a wide resonance frequency band, which is There is an effect that it is possible to suppress a decrease in sensitivity in the low frequency range.

It is sectional drawing which shows the structure of the microphone which is a MEMS element of 1st Example of this invention. It is a top view of the state which showed the structure of the microphone of 1st Example and excluded the fixed electrode part. It is the top view which looked at the spiral slit of the spring layer of 1st Example from the cavity side. FIG. 4 is a cross-sectional view taken along the line AA of FIG. 3, showing a spiral slit portion of the first embodiment. It is a top view which shows the modification of the spiral slit of 1st Example. The structure of the microphone apparatus of 2nd Example is shown, A figure (A) is a top view of the state except a fixed electrode part, A figure (B) is an enlarged view of 100 part of a figure (A). It is a top view of the state which showed the structure of the microphone of 3rd Example and remove | excluded the fixed electrode part. It is sectional drawing which shows the structure of the microphone of a prior art example.

  1 to 4 show a configuration of a microphone that is a MEMS element according to the first embodiment. As shown in FIG. 1, the microphone includes a semiconductor substrate 1 having a cavity 30 in the center, and the substrate 1. The insulating film 2 formed on the insulating film 2, the spring layer formed on the insulating film 2 and having an opening in the center (the hatched portion indicating the cross section is omitted), and around the central opening 3 a of the spring layer 3 at a predetermined interval A pin-shaped support 5 that is disposed (connected to the hole of the spring layer) and also serves as an electrical connection (contact), and a movable electrode 6 to which the pin-shaped support 5 is attached are provided. The movable electrode 6 is an electrode made of a film (diaphragm) that can be displaced by the action of pressure.

Further, a fixed electrode 8 provided in parallel with the movable electrode 6 via a support layer (sacrificial layer) 7 above the spring layer 3 and an insulating film 9 for holding the fixed electrode 8 are provided. The fixed electrode 8 is held by the insulating layer 9 and supported by the support layer 7, thereby forming a gap 10 with the movable electrode 6. The fixed electrode 8 and the insulating film 9 are provided with a plurality of sound holes 11.
In the embodiment, as shown in FIGS. 2 to 4, a circular shape centering on the pin-like support body (support body provided in a dotted shape in plan view) 5 around the central opening 3 a of the spring layer 3. A plurality of spiral slits 12 are provided.

The spring layer 3, the pin-like support 5 and the movable electrode 6 are made of a conductive material for taking out sound pressure as an electric signal, and a part of the outer periphery of the spring layer 3 is connected to an external electrode (not shown). In addition, in the spring layer 3 and the pin-shaped support body 5, it is good also considering a part formed with an electroconductive material as a part. Also in the fixed electrode 8, a part of the fixed electrode 8 made of a conductive material is drawn out to the outer periphery and connected to an external electrode (not shown).
In addition to the polysilicon film to which impurities are added, the spring layer 3 uses a refractory metal such as titanium or tungsten or a silicide compound obtained by reacting a polysilicon film and a metal film, and has a conductive surface. Therefore, for example, a laminated film in which a refractory metal is deposited on an insulating film such as a nitride film may be used.
The movable electrode 6 has only to be electrically connected to the electrode portion forming the flat capacitor and the pin-like support 5 (all or part). In addition to the polysilicon film doped with impurities, titanium or tungsten It is possible to use a high melting point metal such as a material having an insulating film such as a nitride film stacked on a conductive material.

  As shown in FIGS. 3 and 4, the spiral slit 12 provided around the central opening of the spring layer 3 constitutes a spiral spring portion, and the movable electrode 6 is placed at the center of the spiral slit 12. By arranging the pin-like support 5 to be supported, the movable electrode 6 is supported by a plurality of spiral springs. The spiral slit 12 may be formed by at least one or more spirals, and can thereby be displaced in the horizontal direction and the vertical direction.

  According to the configuration of the microphone, air vibration due to sound pressure is transmitted to the movable electrode 6 through the sound hole 11 formed in the fixed electrode 8 and the insulating film 9, and the movable electrode 6 is a spiral slit 12 of the spring layer 3. The movable electrode 6 is displaced and vibrated while being parallel to the fixed electrode 8 by being supported by the spiral spring portion formed by the above-described electrostatic force between the movable electrode 6 and the fixed electrode 8 generated by the displacement and vibration. The change in capacitance is converted into an electrical signal. In this case, the displacement / vibration of the movable electrode 6 includes not only the vibration in the electrode but also the horizontal and vertical vibrations of the entire electrode, thereby converting the sound pressure into an electrical signal with good sensitivity. It will be possible.

  In addition, since the movable electrode 6 is supported by the spring portion of the spiral slit 12 of the spring layer 3, stress generated from the support member (around the movable electrode 6) such as the substrate 1 and the support layer 7 is relieved. The That is, when the movable electrode 6 is directly fixed to the support layer or the like, when the movable electrode 6 is subjected to compressive stress, the movable electrode 6 is displaced outward, and when the movable electrode 6 is subjected to tensile stress, the movable electrode 6 is displaced inward. In the example, since these stresses are absorbed by the spiral slit 12 and the movable electrode 6 can be displaced in the vertical direction and the horizontal direction, the movable electrode 6 and the fixed electrode can be subjected to either sound pressure or stress. 8 is maintained in parallel, and high sensitivity is maintained.

  Further, the opening 3a provided in the central portion of the spring layer 3 is not essential, but in the embodiment, the stress can be relieved also by forming the opening 3a. That is, the outer periphery of the spring layer 3 is fixed and supported by the insulating film 2 and the support layer 7, and a compressive stress or a tensile stress is applied from these support members, but by providing an opening 3a in the central portion, the spring layer By subtracting 3, there is an advantage that the stress applied to the movable electrode 6 is relaxed.

  FIG. 5 shows a modified example of the spiral of the first embodiment. As shown in the spiral slit 13 of FIG. 5, the spiral is provided so as to gradually expand from the center, and between the slits of the spring layer 3. It may be a spiral slit with a thick line width.

  FIG. 6 shows the configuration of the microphone according to the second embodiment. This second embodiment is provided with four spiral slits that are arcuate as a whole. As shown in FIGS. 6A and 6B, the movable electrode 6 and the spring layer 3 are mechanically and electrically disposed at a position around the opening 3 a of the spring layer 3 on the lower side of the outer peripheral portion of the movable electrode 6. An arc-shaped support piece (a support provided linearly in a plan view) 15 is provided for connection to the electrode, and one or more turns are wound around the arc-shaped support piece 15 around the support piece 15. A spiral slit 16 is formed. Other configurations are the same as those in FIG.

In the microphones of the first and second embodiments, as shown in FIG. 1, the air introduced into the microphone by the sound pressure passes through the plurality of sound holes 11 of the fixed electrode 8 and the insulating film 9 and moves to the movable electrode 6. From the outside, it passes between the spiral slits 12 and 16 or the supports (pieces) 5 and 15 and goes out to the cavity 30.
However, in the case of the second embodiment, only four spiral slits 16 (and support pieces 15) are provided, and the number of gaps between the support pieces is smaller than that of the first embodiment. Therefore, the acoustic resistance is increased, and the sensitivity in the mid-low range can be increased.

  Also in the second embodiment, the movable electrode 6 supported by the support piece 15 can be displaced and vibrated in the horizontal direction and the vertical direction by the spiral slit 16 of the spring layer 3. Regardless of the stress, the entire surface can be displaced and vibrated with respect to the sound pressure while maintaining the parallelism with the fixed electrode 8.

  FIG. 7 shows the configuration of the microphone according to the third embodiment. In the third embodiment, one spiral slit is provided as a whole. As shown in FIG. 7, on the lower side of the outer peripheral portion of the movable electrode 6, one piece for mechanically and electrically connecting the movable electrode 6 and the spring layer 3 along the periphery of the opening 3 a of the spring layer 3. An annular support body (support body provided in an annular shape in plan view) 17 is provided, and a spiral slit 18 having an outer periphery wound one or more times is formed outside the annular support body 17. Other configurations are the same as those in FIG.

  According to the configuration of the third embodiment, there is no gap between the supports as in the first and second embodiments, and the air introduced by the sound pressure escapes only from the spiral slit 18 to the cavity 30, so that The resistance becomes larger than those in the first and second embodiments, and the sensitivity in the mid-low range can be increased. Also in the third embodiment, since the movable electrode 6 can be displaced in the horizontal and vertical directions by the spiral slit 18 and the annular support 5 provided in the spring layer 3, the movable electrode 6 is subjected to stress. Regardless, the entire surface can be displaced and vibrated with respect to the sound pressure while maintaining parallelism with the fixed electrode 8.

  Not only the configuration of each of the embodiments described above, it is possible to arrange the spring layer 3 in combination with spiral slits having different shapes. For example, by providing a plurality of spiral slits having different shapes, it is possible to prevent the movable electrode 6 from resonating with a specific frequency external vibration that shakes the entire microphone, and being destroyed due to a large shake. In addition, you may arrange | position the slit from which a shape differs, for example in combination of the magnitude | size of the spiral of a slit, the width | variety of a slit, and a different winding number.

  In the above embodiment, the movable electrode 6 is disposed on the upper side (upper layer) of the spring layer 3. However, the movable electrode 6 may be disposed on the lower side (lower layer) of the spring layer 3.

1, 61 ... Semiconductor substrate, 2, 9, 62, 69 ... Insulating film,
3 ... spring layer, 5 ... pin-shaped support,
6, 66 ... movable electrode, 7, 67 ... support layer (sacrificial layer),
8, 68 ... fixed electrode, 10 ... gap,
11, 71 ... sound holes, 12, 13, 16, 18 ... spiral slits,
15 ... arc-shaped support piece, 17 ... annular support,
30 ... cavity.

Claims (3)

A fixed electrode fixed to the support layer of the substrate;
A displaceable movable electrode disposed substantially parallel to the fixed electrode;
A spring layer fixed to the support layer of the substrate at a position above or below the movable electrode,
A MEMS element, wherein the movable electrode is mechanically supported and electrically connected to the spring layer via a support.   A plurality of the support bodies are arranged in the form of dots or lines in a plan view, and at least one or more spiral slits are formed in the spring layer around the dot or line supports. The MEMS device according to claim 1.   The said support body is cyclically | annularly arrange | positioned around the said spring layer in planar view, The spiral slit of 1 volume or more was formed in the said spring layer along the outer periphery of the said cyclic | annular support body. 1. The MEMS device according to 1.

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