JP2019198936A - MEMS element - Google Patents

Abstract

To provide a MEMS element having high sensitivity.SOLUTION: This MEMS element has a slit 5 which is formed in a part of a vibration film 3 fixed to a handle substrate 1, and comprises a vibration area having a free end. The vibration area has the free end, and therefore, greatly vibrates compared to vibration of the vibration film 3 fixed to the handle substrate 1. Transistors D, G, S are provided in the vibration areas, whereby detection result can be obtained from fluctuation in an output signal due to Piezo effect in association with vibration of the film which constitutes the transistors D, G, S.SELECTED DRAWING: Figure 1

Description

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

  As a MEMS (Micro Electro Mechanical Systems) element using a semiconductor process, a movable electrode, a sacrificial layer, and a fixed electrode are formed on a semiconductor substrate, and then a part of the sacrificial layer is removed, so that A capacitive MEMS element in which an air gap (hollow) structure is formed between the movable electrode and the movable electrode is known.

  For example, in a capacitive MEMS element, a fixed electrode having a plurality of through-holes and a movable electrode that vibrates in response to sound pressure or the like are arranged opposite to each other, and displacement of the movable electrode due to vibration changes in capacitance between the electrodes. Is detected. This type of MEMS element is described in Patent Document 1, for example.

  The operation of the conventional MEMS device is schematically shown in FIG. A movable electrode film 23 (corresponding to a vibration film) including a conductive movable electrode and a fixed electrode film 24 including a conductive fixed electrode are arranged on a handle substrate 21 via an insulating film 22 via a spacer 25, and sound is transmitted. When the movable electrode film 23 vibrates due to pressure or the like, the distance between the fixed electrode film 24 changes, and a capacitor formed between the fixed electrode of the fixed electrode film 24 and the movable electrode of the movable electrode film 23. The capacitance value of changes. By extracting this capacitance value from an electrode (not shown), it is possible to obtain an output signal corresponding to the sound pressure received by the movable electrode film 23.

JP 2011-55087 A

  By the way, in this type of MEMS element, as shown in FIG. 5, the movable electrode film 23 is sandwiched and fixed by the spacer 25 and the insulating film 22, and even when it receives a large sound pressure or the like, There was a limit to the amount of displacement. Therefore, in a general MEMS element, the change in capacitance value caused by the displacement of the variable electrode film 23 is about several percent or less, the sensor sensitivity is very low, and high sensitivity is desired. In view of such a situation, an object of the present invention is to provide a highly sensitive MEMS element.

  In order to achieve the above object, an invention according to claim 1 of the present application is a MEMS device including a handle substrate having a back chamber and a vibration film fixed on the handle substrate, wherein a part of the vibration film is formed as a transistor. The transistor forming region is defined by a slit disposed so as to surround a part of the vibration film, and includes a vibration region that can vibrate larger than vibration of the vibration film fixed on the handle substrate, At least a part of the transistor is disposed on the vibration region, and the output current of the transistor that varies with the vibration in the vibration region is output as a detection signal.

  The invention according to claim 2 of the present application is the MEMS element according to claim 1, wherein the transistor has a current flowing between the first region and the second region that are separated from each other. A structure controlled by a voltage applied to a third region disposed between the two regions, wherein at least one of the first region and the second region is disposed in the vibration region, When the voltage between the first region and the second region and the voltage applied to the third region are set to predetermined values, the first region and the second region that vary with vibration of the vibration region The current flowing between and is output as the detection signal.

  The invention according to claim 3 of the present application is the MEMS element according to claim 1 or 2, wherein at least a part of the vibration film is a film made of a semiconductor, and the transistor is formed in the film made of the semiconductor. It is characterized by.

  According to a fourth aspect of the present invention, in the MEMS element according to any one of the first to third aspects, a conductive counter electrode film is disposed on the conductive vibration film via a spacer so as to face the counter electrode film. A predetermined potential can be applied between the vibrating membranes.

  The MEMS element of the present invention includes a vibration region that can vibrate larger than the vibration film fixed to the handle substrate, and a transistor is arranged in this vibration region. Therefore, the film constituting the transistor is distorted with the vibration in the vibration region, and the output current of the transistor varies due to the piezoelectric effect. By adopting a configuration in which the output current in the non-saturated region of this transistor is output as a detection signal, the change in the detection signal increases with respect to the change in the magnitude of vibration, and a highly sensitive MEMS element can be obtained. .

  The vibration film of the MEMS element of the present invention is composed of a film made of a semiconductor constituting a transistor, and the film itself constituting the transistor vibrates, whereby a highly sensitive MEMS element can be obtained.

  In the MEMS element of the present invention, a plurality of transistor formation regions can be disposed on the vibration film, and the output currents of the respective transistors can be added together to form a detection signal.

  Furthermore, in the present invention, the counter electrode film is disposed so as to face the vibration film, and the vibration film can be vibrated with a predetermined voltage applied between the vibration film and the counter electrode film, so that the vibration film is not distorted. It is possible to operate the MEMS element in a state where the vibration film can vibrate greatly or to obtain a highly sensitive MEMS element.

It is explanatory drawing of the MEMS element of the 1st Example of this invention. It is a figure explaining arrangement | positioning of the slit of the 1st Example of this invention. It is a figure explaining the transistor formation area of the 1st example of the present invention. It is explanatory drawing of the MEMS element of the 2nd Example of this invention. It is a figure explaining operation | movement of a general MEMS element.

  The MEMS element of the present invention includes a vibration region in which a slit is formed in a part of a vibration film fixed on a handle substrate and includes a free end. By providing this free end, the vibration region vibrates greatly as compared with the vibration film fixed to the handle substrate. The present invention has a configuration in which a transistor is provided in this vibration region, and a detection result is obtained from fluctuations in an output signal due to a piezo effect caused by vibration of a film forming the transistor. Hereinafter, the present invention will be described in detail with reference to examples.

  An embodiment of the present invention will be described by taking a microphone as an example of a MEMS element. The microphone of the present invention comprises a single crystal silicon film having a thickness of about 2 μm on a handle substrate 1 made of silicon having a crystal orientation (100) plane of 420 μm and a thermal oxide film 2 having a thickness of about 1 μm. The vibration film 3 is laminated. An SOI substrate in which a single crystal semiconductor layer is formed on a silicon substrate via an insulating film can also be used, and the single crystal silicon film may be used as the vibration film 3. A part of the handle substrate 1 is removed to form a back chamber 4. A part of the vibration film 3 is a P-type region 6 for forming a transistor.

  A slit 5 is formed in the vibration film 3. For example, the slit 5 is arranged as shown in FIG. 2 shows an example in which the slit 5 is formed in the vibration film 3a which is a part of the vibration film 3 shown in FIG. As shown in FIG. 1, the vibration film 3 is fixed to the handle substrate 1 via the thermal oxide film 2. On the other hand, when the slit 5 is formed as shown in FIG. 2, the region surrounded by the slit 5 (partitioned region) becomes a movable piece having a free end and vibrates more greatly than the region fixed to the handle substrate 1. The vibration region 3b that can be formed is formed.

  FIG. 3 is an enlarged cross-sectional view of a part of the transistor formation region surrounded by the slit 5. As shown in FIG. 2, two transistors are formed in a transistor formation region including two vibration regions 3b surrounded by two slits 5 and a vibration film 3 between the two vibration regions 3b. The example shown in FIG. 3 shows a case where two MOS transistors are formed.

  The MOS transistor shown in FIG. 3 can be formed by a normal manufacturing method. Specifically, a single crystal silicon film to be the vibration film 3 is formed on a silicon substrate to be the handle substrate 1, and ions are implanted into a part of the single crystal silicon film to form a P-type region 6, and P-type A gate oxide film 7 and a gate electrode 8 are formed on the region 6. N-type source region 9 and drain region 10 may be formed by implanting impurity ions at both ends of gate electrode 8. In FIG. 3, description of electrodes connected to the source region 9 and the drain region 10 and extraction electrodes such as the gate electrode 8 is omitted.

  According to the normal manufacturing method of the MEMS element, after forming the MOS type transistor described above, a part of the back surface side of the handle substrate 1 is removed to form the back chamber 4 to obtain the MEMS element shown in FIG. Can be formed.

  In the MEMS element having such a structure, when sound pressure or the like is applied to the vibration film 3, the vibration film 3 is deformed. At that time, in the MEMS element of the present embodiment, the vibration region 3b defined by the slit 5 can vibrate more greatly than the vibration of the vibration film 3 having a free end and fixed to the handle substrate 1. . Therefore, when a large sound pressure or the like is applied, the vibration region 3b vibrates greatly.

  A MOS transistor is formed in the vibration region 3b. In the example shown in FIG. 3, the source region 9 side vibrates greatly. In other words, when a desired voltage is applied between the source and drain and the gate electrode so that the MOS transistor is in an operating state, and a predetermined current flows between the source and drain, the vibration region 3b vibrates greatly. The source region 9, the channel region between the source region 9 and the drain region 10, and further the drain region are compressed or expanded, and the current flowing between the source and the drain changes due to the piezoelectric effect. By using this current value as a detection signal, it is possible to detect a change in sound pressure or the like that the vibration region receives.

  In the example shown in FIG. 3, the two vibration regions 3b are arranged so as to be symmetric, and two MOS transistors are arranged so as to be symmetric at the center of the two vibration regions 3b. As a result, the current value changes twice and is output.

  Next, a second embodiment will be described. The MEMS element according to the first embodiment described above vibrates in accordance with the magnitude of the vibration region when sound pressure or the like is applied. On the other hand, it is also possible to arrange a conductive counter electrode film and control its vibration.

  FIG. 4 is an explanatory diagram of the MEMS element according to the second embodiment of the present invention. A counter electrode film 12 is disposed on the MEMS element described in the first embodiment via a spacer 11. The counter electrode film 12 corresponds to a fixed electrode film of a capacitive transducer, and a through hole 13 is formed so as not to fluctuate due to sound pressure or the like.

  The vibration film 3 and the counter electrode film 12 are each made of a conductive material, and a predetermined voltage is applied to the conductive vibration film 3 (P-type region 6) and the conductive counter electrode film 12. . By applying this voltage, it is possible to control the displacement of the vibrating membrane 3, particularly the vibrating region 3b. For example, the vibration region 3b is not distorted in a state where there is no vibration. The transistor can be configured so that the change in the source-drain current increases.

  Although the MEMS element of the present invention has been described above, it is needless to say that the present invention is not limited to the above embodiments. For example, in the above embodiment, an example in which two MOS transistors are formed on the vibration film 3 has been described. However, if the arrangement is made so that output signals obtained from a plurality of transistors are added, the number of transistors is appropriately determined. Selectable. Further, not only a MOS transistor but also a bipolar transistor can be selected as appropriate. Furthermore, the present invention is not limited to the case where the vibration film 3 is formed of only a semiconductor film, and a laminated structure of an insulating film and a semiconductor film can be appropriately selected.

1: Handle substrate, 2: Thermal oxide film, 3: Vibration film, 3b: Vibration area, 4: Back chamber, 5: Slit, 6: P-type area, 7: Gate oxide film, 8: Gate electrode, 9: Source Region: 10: drain region, 11: spacer, 12: counter electrode film, 13: through-hole, 21: handle substrate, 22: insulating film, 23: movable electrode film, 24: fixed electrode film, 25: spacer

Claims (4)

In a MEMS device including a handle substrate having a back chamber and a vibration film fixed on the handle substrate,
A part of the vibration film becomes a transistor formation region,
The transistor formation region is partitioned by a slit disposed so as to surround a part of the vibration film, and includes a vibration region that can vibrate larger than vibration of the vibration film fixed on the handle substrate,
Arranging at least a part of the transistor on the vibration region;
An MEMS element that outputs an output current of the transistor, which fluctuates with vibration in the vibration region, as a detection signal. The MEMS device according to claim 1, wherein
In the transistor, a current flowing between a first region and a second region which are separated from each other is controlled by a voltage applied to a third region disposed between the first region and the second region. Structure
Arranging at least one of the first region and the second region in the vibration region;
When the voltage between the first region and the second region and the voltage applied to the third region are set to predetermined values, the first region and the second region that vary with vibration of the vibration region A MEMS element that outputs a current flowing between the region and the region as the detection signal.   3. The MEMS element according to claim 1, wherein at least a part of the vibration film is a film made of a semiconductor, and the transistor is formed on the film made of the semiconductor.   4. The MEMS element according to claim 1, wherein a conductive counter electrode film is disposed on the conductive vibration film via a spacer, and a predetermined potential is applied between the counter electrode film and the vibration film. A MEMS element characterized in that application is possible.

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