JP5350715B2 - MEMS vibrator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an MEMS (Micro Electro Mechanical System) vibrator which is easy to process, can reduce power consumption, and more easily adjusts its resonance frequency than the conventional one. <P>SOLUTION: The MEMS vibrator is provided with: an oscillating body 721 which is fixed on a board 111 or at a plurality of points and has one or more groups of comb-like projections on the surface; one or more electrostatic electrodes 161, 162, 163 and 164 which form a comb-like capacitor between themselves and the group of comb-like projections of the oscillating body 721 and have the group of comb-like projections formed on the surface; a drive electrode 141; and a detection electrode 151. The oscillating body 721 comprises a vibration part 722 for oscillating by the drive voltage from the drive electrode 141 and one or more vibration restriction parts 723 joined to the vibration part 722. A DC voltage is applied to a comb-like capacitor to change a frequency of vibration of the vibration part 722. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a MEMS vibrator.

The MEMS vibrator is a vibration element that can be used for a reference frequency oscillation source or the like in a communication circuit, which is created using a MEMS (Micro Electro Mechanical System) technique.
A conventional MEMS vibrator includes a vibrating body held at a position slightly lifted from a substrate by one or more holding means, a driving electrode arranged with a slight gap in the vibration direction of the vibrating body, and a driving electrode. A detection electrode disposed at a position facing the vibration member with a slight gap, and applying a driving AC voltage biased with a DC voltage to the driving electrode from a driving circuit connected to the driving electrode. The vibration body is vibrated by and the vibration is detected as an electric signal by the detection electrode. When the drive AC voltage has a certain frequency, the vibrating body vibrates strongly, and the signal detected by the detection electrode is also a strong and stable signal. The specific frequency is called a resonance frequency.

FIG. 4 is a perspective view showing a basic configuration of a conventional MEMS vibrator. In the figure, the vibrating body 621 is held at a position slightly lifted from the substrate 611 by the fixing portions 631 and 632. A drive electrode 641 is disposed with a gap d1 from the vibrating body 621 in the x-axis direction, and a detection electrode 651 is disposed with a gap d2 from the vibrating body 621 at a position facing the driving electrode 641 with the vibrating body 621 interposed therebetween. It is fixed to. The vibrator 621 vibrates in the x-axis direction by using the alternating voltage biased by the direct current voltage Vp as a drive voltage and applying the drive voltage to the gap d1 from a drive circuit (not shown) connected to the drive electrode 641. The vibration is detected as an electric signal by a detection circuit (not shown) connected to the detection electrode 651. When the frequency of the AC component of the drive voltage is f, the vibrating body 621 vibrates strongly, and the signal detected by the detection electrode 651 is also a strong and stable signal. In that case, the frequency f is called a resonance frequency.
In the conventional MEMS vibrator having the configuration shown in FIG. 4, it is known that the resonance frequency f can be finely adjusted by changing the DC voltage Vp or the gap d1 (Patent Document 1).
US Pat. No. 6,987,432.

As described above, the conventional MEMS vibrator can finely adjust the resonance frequency f by changing the DC voltage Vp. By the adjustment, it was possible to correct a deviation from the target value of the resonance frequency caused by a dimensional error during device fabrication. When the DC voltage Vp is increased, the amount of change in the resonance frequency also increases. Therefore, even in the conventional MEMS vibrator, the variable range of the resonance frequency can be widened by making the DC voltage Vp variable over a wide range.
However, if the DC voltage Vp is excessively increased, the vibrating body sticks to the driving electrode and short-circuits due to the electrostatic force acting between the vibrating body and the driving electrode. In general, when the DC voltage Vp is increased, power consumption in the drive circuit is increased. Therefore, it is desirable that the DC voltage Vp is low.
However, if the variable range of the DC voltage Vp is limited to a low range, the variable range of the resonance frequency is narrowed. If the variable range of the resonance frequency is narrow, the allowable range of dimensional error during device fabrication is narrow, and high processing accuracy is required to obtain a desired resonance frequency by adjustment. When the variable range of the DC voltage Vp is limited to a low range, the resonance frequency is difficult to adjust unless the processing accuracy is high.
Therefore, it has been difficult for the conventional MEMS vibrator to achieve at the same time the ease of processing at the time of fabrication, low power consumption, and easy adjustment of the resonance frequency. Therefore, there has been a demand for a MEMS vibrator that can be easily processed, can reduce power consumption, and can easily adjust the resonance frequency.

The present invention has been made in order to solve the above-described problems, and includes a vibrating body fixed on one or more points on a substrate and having comb-like protrusions formed on a surface thereof, and the comb of the vibrating body. An electrostatic electrode having a comb-like protrusion formed on a surface thereof, a drive electrode, and a detection electrode that constitute a comb-shaped capacitor with the tooth-like protrusion, and the vibrating body includes the drive A vibrating part that vibrates by a driving voltage from the electrode, one or a plurality of vibration limiting parts that are coupled to the vibrating part, and a fixing part that fixes an end of the vibrating part. An input unit for applying a voltage; and the vibration limiting unit is coupled to the vibration unit at a node of vibration by the vibration unit, and the comb-shaped protrusion includes the fixing unit and the vibration limiting unit. a MEMS vibrator you being formed between the.

  According to the MEMS vibrator according to the present invention, processing is easy, power consumption can be reduced, and the resonance frequency can be easily adjusted as compared with the related art.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a plan view showing a structure of a MEMS vibrator according to an embodiment of the present invention. In FIG. 1, the vibrating body 721 includes a vibration portion 722 (shaded portion) held by fixing portions 131 and 132 connected to the substrate 111 and a vibration limiting portion held by a fixing portion 733 connected to the substrate 111. 723, and a vibration portion 722 and a vibration limiting portion 723 are combined at a node 781. A drive electrode 141 is disposed in the x-axis direction with a gap from the vibration portion 722, and a detection electrode 151 is disposed at a position facing the drive electrode 141 across the vibration portion 722 with a gap from the vibration portion 722. It is fixed. An alternating voltage biased with the direct current voltage Vp is used as a driving voltage, and the driving voltage is applied to a gap between the vibrating unit 722 and the driving electrode 141 from a driving circuit (not shown) connected to the driving electrode 141, thereby vibrating the unit 722. Vibrates in the x-axis direction. The vibration is vibration with the node 781 as a vibration node. The vibration is detected as an electric signal by a detection circuit (not shown) connected to the detection electrode 151. The vibration unit 722 vibrates strongly when the frequency of the AC component of the drive voltage is the resonance frequency f.

  Comb teeth 171 and 172 are formed on both side surfaces of the vibrating portion 722 perpendicular to the substrate in the vicinity of the connection portion with the fixed portion 131, and on both side surfaces perpendicular to the substrate in the vicinity of the connection portion with the fixed portion 132. The comb teeth 173 and 174 are formed. FIG. 2 is an enlarged plan view of a connecting portion between the vibrating portion 722 and the fixed portion 131. An electrostatic electrode 161 having a comb tooth 175 at a position facing the comb tooth 171 and an electrostatic electrode 162 having a comb tooth 176 at a position facing the comb tooth 172 are respectively arranged and fixed to the substrate 111. Yes. An electrostatic electrode 163 having a comb tooth 177 at a position facing the comb tooth 173 is formed near the comb tooth 174 in the vicinity of the connection portion between the vibrating portion 722 and the fixed portion 132, which is opposite to the side shown in FIG. Electrostatic electrodes 164 having comb teeth 178 at the opposing positions are respectively arranged and fixed to the substrate 111. The protrusions constituting the comb teeth 171 are arranged alternately with the protrusions constituting the comb teeth 175 with a gap therebetween. Similarly, in the other comb tooth pairs, the respective protrusions constituting the comb teeth are alternately arranged with a gap therebetween. The gaps between the comb teeth 171 and the comb teeth 175 and the gaps between the comb teeth 172 and the comb teeth 176 are more negative in the y-axis direction from the protrusions constituting the comb teeth 171 and 172. It is narrower than the one in the positive direction. On the other hand, the gaps between the comb teeth 173 and the comb teeth 177 and the gaps between the comb teeth 174 and the comb teeth 178 are more positive in the y-axis direction from the protrusions constituting the comb teeth 173 and 174. It is narrower than the negative direction in the y-axis direction. With the above structure, the comb-tooth pairs facing each other constitute a comb-shaped capacitor.

  When a DC voltage Vq is applied to each comb-shaped capacitor from a voltage supply circuit (not shown), an electrostatic force in the y-axis direction is generated between the capacitors. At this time, according to the structure of FIGS. 1 and 2, the range of the vibrating portion 722 from the fixed portion 131 to the node 781 closer to the fixed portion 131 is pulled in the negative direction in the y-axis direction, The range up to the node 781 is pulled in the positive direction in the y-axis direction. Further, the node 781 closer to the fixed portion 131 is pulled in the negative direction in the y-axis direction, and the node 781 closer to the fixed portion 132 is pulled in the positive direction in the y-axis direction. A tensile stress in the y-axis direction acts on the range from one node 781 to the other node 781.

  When a tensile stress in the y-axis direction acts on the range from one node 781 to the other node 781 of the vibration unit 722, the resonance frequency f increases. That is, the resonance frequency f can be increased by applying Vq. FIG. 3 is a graph showing how the resonance frequency f changes due to changes in Vp and Vq. The resonance frequency f decreases as Vp increases, and the resonance frequency f increases as Vq increases. And. It is assumed that the variable range of the resonance frequency f when Vq is not applied is a range from a to b. The resonance frequency f is increased by applying Vq. When the maximum value is c, the variable range of the resonance frequency f can be expanded from a to c by changing the applied Vq. It is also possible to configure each comb-type capacitor so that the compressive stress in the y-axis direction acts on the range from one node 781 to the other node 781 of the vibration unit 722. If each comb-shaped capacitor is configured as described above, the resonance frequency f can be lowered by increasing the applied Vq. Also in this case, the variable range of the resonance frequency f is expanded as compared with the case where Vq is not applied.

  Hereinafter, the resonance frequency f when the DC voltage Vp is constant and the DC voltage Vq is not applied to each comb-shaped capacitor is defined and used as the reference resonance frequency f0. According to the conventional structure in which the vibration body cannot be configured so that the desired position on the vibration body becomes a node of vibration (hereinafter referred to as the conventional structure), if the length of the vibration body in the y-axis direction is different, other dimensions Even if the materials are of the same structure, the reference resonance frequency f0 is different. However, according to the structure according to the present embodiment, even if the length of the vibrating portion 722 in the y-axis direction is different, the length from one node 781 to the other node 781 is equal, and other dimensions and materials are equal. In the case of the structure, the reference resonance frequency f0 is equal. For this reason, it is possible to lengthen the vibration part 722 in the y-axis direction while keeping the reference resonance frequency f0 constant. When the vibration part 722 becomes longer in the y-axis direction, the number of protrusions constituting the comb teeth of each comb-shaped capacitor can be increased, and the capacitance of each comb-shaped capacitor can be increased. Therefore, compared to the conventional structure, the electrostatic force when the DC voltage Vq is applied to each comb-shaped capacitor can be increased, and the vibration portion 722 acts in the range from one node 781 to the other node 781. The magnitude of stress to be applied can be increased. Thereby, the amount of change in the resonance frequency f from the reference resonance frequency f0 can be increased. That is, according to the structure according to the present embodiment, the variable range of the resonance frequency f can be expanded as compared with the conventional structure.

  If the variable range of the resonance frequency f is expanded, the allowable range of dimensional errors at the time of device fabrication is also increased. The comb-tooth structure looks a little complicated, but if the gap between the protrusions alternately arranged from the comb teeth facing each other is taken to be the same size as the gap between the vibration part 722 and the detection electrode 141 or the drive electrode 151, it is obtained. There is no change in processing accuracy. Therefore, according to the structure according to the present embodiment, the structure can be easily processed by the extent that the allowable range of the dimensional error is expanded as compared with the conventional structure.

  In general, a comb-type capacitor can have a larger capacitance than a normal parallel plate capacitor of the same size, and a larger electrostatic force can be obtained by applying a low DC voltage Vq. When the electrostatic force between the comb-shaped capacitors is increased, the DC component Vp of the drive voltage can be lowered while maintaining the variable range of the resonance frequency f, and the power consumption in the drive circuit can be reduced. Even in the voltage supply circuit that applies the DC voltage Vq, power is consumed, but by increasing the comb-shaped protrusions, Vq can be lowered while maintaining the electrostatic force, thereby reducing the power consumption in the voltage supply circuit. Can be suppressed. As a result, even if the power consumption by the drive circuit and the power consumption by the voltage supply circuit of each comb-shaped capacitor are combined, the power consumption in the conventional drive circuit can be reduced. Therefore, according to the MEMS vibrator according to the present embodiment, the power consumption can be reduced as compared with the related art.

  Further, by increasing the number of protrusions constituting the comb teeth of each comb-shaped capacitor, the power consumption is reduced and the resonance frequency f can be easily adjusted while maintaining the ease of processing at the time of manufacture as compared with the conventional case. And become possible.

  As described above, according to the MEMS vibrator according to the present embodiment, the power consumption can be reduced while the processing at the time of manufacture is easy, and the resonance frequency can be easily adjusted as compared with the conventional case.

It is a top view which shows the structure of the MEMS vibrator | oscillator by embodiment of this invention. FIG. 2 is an enlarged plan view of a connection part between a vibration part 722 and a fixing part 131 in FIG. 1. It is a graph which shows a mode that the resonant frequency f changes by the change of Vp and Vq. It is a perspective view which shows the basic composition of the conventional MEMS vibrator.

Explanation of symbols

111, 611 Substrate 121, 621, 721 Vibrating body 722 Vibrating part 723 Vibration restricting part 131, 132, 631, 632, 733 Fixed part 141, 641 Drive electrode 151, 651 Detection electrode 161, 162, 163, 164 Electrostatic electrode 171 , 172, 173, 174, 175, 176, 177, 178 Comb teeth 781 Node d1, d2 Gap Vp DC voltage in drive voltage Vq DC voltage applied between comb teeth f Resonance frequency f0 Reference resonance frequency

Claims (3)

A surface constituting a comb-shaped capacitor between a vibrating body fixed at one or a plurality of points on a substrate and having comb-like protrusions formed on the surface, and the comb-like protrusions of the vibrating body. An electrostatic electrode having a comb-like projection formed on the electrode, a drive electrode, and a detection electrode, and the vibrating body is coupled to the vibrating portion and vibrates in response to a driving voltage from the driving electrode. A plurality of vibration limiting portions, and a fixing portion that fixes an end portion of the vibration portion,
An input unit for applying a DC voltage to the electrostatic electrode;
The vibration limiting unit is coupled to the vibration unit at a vibration node by the vibration unit ,
The comb-like projections, MEMS resonator you being formed between said fixed portion and the vibrating limiting unit.   The MEMS vibrator according to claim 1, wherein a tensile stress is generated in a major axis direction of the vibrating body by applying a DC voltage to the comb-shaped capacitor, and the frequency of the vibrating body is increased by the tensile stress.   The MEMS vibrator according to claim 1, wherein a compressive stress is generated in a major axis direction of the vibrating body by applying a DC voltage to the comb-shaped capacitor, and the frequency of the vibrating body is reduced by the compressive stress.

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