JP2009118331A - Electric machine filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric machine filter using an MEMS technology for preventing a connection section from being asymmetrically distorted in a vibration mode, and for obtaining satisfactory filter characteristics. <P>SOLUTION: Symmetrical external forces are added to a coupling section configuring an electric machine filter so that the spring constants of the coupling section can be changed without affecting the vibration mode of the coupling section, and a coupling coefficient between resonance modes is adjusted, and a frequency band is changed. This electric machine filter includes a control part for applying an electrostatic force to the coupling section so that a stress can be applied to the structure, and that the spring constants can be changed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electromechanical filter, and more particularly, to an electromechanical filter manufactured using MEMS (Micro Electro Mechanical Systems) technology.

  Currently, in a situation where the market of mobile phones is growing in the world, a filter of a wireless communication system that is mainly used is a surface acoustic wave (SAW) filter that uses surface acoustic waves. Although such a filter arrange | positions an electrode on the surface of a piezoelectric material and brings about a surface acoustic wave, since a piezoelectric material is difficult to make monolithic with an integrated circuit, size reduction becomes a subject. In addition, an electronic element that becomes a bottleneck when a next-generation mobile phone of the future will have higher performance and a smaller size is a high-frequency filter portion that is externally attached to the integrated circuit.

  Therefore, in recent years, MEMS technology using an electromechanical element that realizes ultra-miniaturization has been developed, and in particular, an electromechanical resonator using a silicon process as a manufacturing method and a vibrator constituting a plurality of resonators. Realization of monolithic electromechanical filters connected via a coupling portion is expected.

FIG. 8 shows an example of an electromechanical filter (non-patent document 1) using a conventional beam resonator. The filter includes beam-type vibrators 101 and 103 and a coupling beam 109. When a driving voltage is applied to the input electrode 105, a driving force is generated between the electrode 105 and the vibrator 101, and the vibrator 103 is excited. As the mechanical vibration mode of this filter, the vibrators 101 and 103 and the coupling beam 109 both have a vertical bending vibration mode. 8A and 8B show two mechanical vibration modes of the filter system, FIG. 8A shows a vibration mode in which the resonators 101 and 103 resonate at the same phase, and FIG. 8B shows a resonance. It is a perspective view which shows the vibration mode which the container 101,103 reversed the phase. Here, the coupling beam 109 in FIG. 8A couples the resonator in the fundamental mode of the flexural vibration mode, and FIG. 8B is configured by the secondary mode of the flexural vibration. The electric signal of the filter is detected as an output voltage from the output electrode 107 via the load resistor _RL as shown in FIG.

As in the electromechanical filter of FIG. 8, the filter system in which two resonators are coupled includes two mechanical vibration modes, and each vibration mode vibrates at a close resonance frequency. The frequency band BW of the filter is expressed by Equation 4 described later _, and is determined by the relationship between the resonance frequency f _o, of the vibrators 101 and 103, the spring constant K _couple of the coupling portion, the spring constant K _rc of the resonator, and the filter constant C _12. I know it will be.

  Patent Document 1 discloses a method for adjusting the frequency characteristics of an electromechanical filter based on the above configuration. As shown in a top view in FIG. 9, resonators 127 and 128 in which an input electrode 120 and an output electrode 121 are added to vibrators 122 and 123 are vibrationally coupled by a coupling unit 124 to form a filter. When an electric signal is passed through the input electrode 120, the vibrator 122 resonates in the elastic wave vibration mode, and the vibrator 123 is also excited by the vibration coupling of the coupling portion 124. Further, by providing a control electrode 125 in the coupling unit 124 and changing the voltage applied by the variable voltage supply unit 126, the vibration of the coupling unit 124 changes, and the coupling coefficient of the filter can be adjusted. Similarly, it is possible to adjust the center frequency of the filter by installing control electrodes on the vibrators 122 and 123 and changing the vibration modes of the resonators 127 and 128. Thus, the characteristic of the electromechanical filter is adjusted by using the external driving force that is electro-mechanically converted by arranging the control electrode 125 in the vibration region of the resonator and the coupling portion 124.

  FIG. 10 shows a cross-sectional view A-A ′ of the coupling portion 124 of FIG. 9. FIG. 10A shows a case where the vibrators 122 and 123 and the coupling portion 124 resonate in an elastic wave mode that vibrates in parallel with the substrate. FIG. 10B shows a state in which a voltage is applied to the control electrode 125. The vibration distortion of the coupling portion generated at this time is because a constant electrostatic force is generated on the control electrode side. Control asymmetrically.

Frank D Bannon, John R. Clark, Clark T.-C. Nguyen, `` High-Q HF Microelectromechanical Filters '' IEEE Journal of Solid-State Circuits, Vol. 35, No. 4, April 2000. JP 2004-112378 A

As described above, in the frequency characteristic changing method of the electromechanical filter according to Patent Document 1, since the control electrode is installed only on one side of the coupling portion, an asymmetric driving force is applied to the mechanical vibration, and the filter characteristic is improved. There was a problem of causing distortion.
The present invention has been made in view of the above circumstances, and prevents the coupling portion from being asymmetrically distorted in the vibration mode, and can adjust the frequency band or the center frequency without distortion, and has good filter characteristics. An object is to provide an electromechanical filter.

  In order to achieve the above object, in the present invention, by applying a symmetrical external force to the coupling portion constituting the electromechanical filter, the spring constant of the coupling portion is changed without affecting the vibration mode of the coupling portion. The coupling coefficient between the resonance modes is adjusted. The present invention is characterized by including a control unit that applies an electrostatic force symmetrical to the vibration direction of the coupling unit. For example, by arranging control electrodes symmetrically with respect to the vibration direction on both sides of the coupling portion so that the vibration mode of the coupling portion is not asymmetrically distorted in the arrangement of the control electrode, an external force is applied to the control electrode. It is possible to realize an electromechanical filter capable of adjusting the filter characteristics such as adjusting the spring constant of the coupling portion depending on the coupling coefficient and adjusting the frequency band.

  In the present invention, by applying a symmetrical external force to the vibrator constituting the electromechanical filter, the spring constant of the vibrator changes without affecting the vibration mode of the vibrator, and the center frequency of the filter is adjusted. It becomes possible to do. The present invention is characterized by including a control unit that applies an electrostatic force that is symmetrical with respect to the vibration direction of the vibrator. Mainly in the arrangement of the control electrodes, the control electrodes are installed symmetrically with respect to the vibration direction on both sides of the vibrators constituting the resonator so that the vibrators are not asymmetrically distorted according to the vibration mode of the vibrator. By applying an external force to the control electrode, an electromechanical filter capable of adjusting the filter characteristics can be realized. In particular, an electromechanical filter that adjusts the center frequency of the filter can be realized by independently controlling the vibration of one or both of the vibrators.

  According to the electromechanical filter of the present invention, the spring constant can be changed without asymmetrically distorting the vibration of each element coupled through the coupling portion, and the frequency characteristic can be adjusted with high accuracy. Become.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing the concept of the electromechanical filter according to Embodiment 1 of the present invention.
FIG. 1B is characterized by comprising a control unit for applying an electrostatic force to the coupling unit so as to be symmetric in a plane perpendicular to the vibration direction of the coupling unit. Here, the connecting portion 12 is shown as a doubly supported beam. The coupling portion 12 is formed on the same plane as the two vibrators, and sandwiches the coupling portion with a pair of control electrodes 10 and 11 disposed symmetrically with respect to the vibrator and the coupling surface. Is formed. The control unit C includes a pair of control electrodes 10 and 11 and a variable voltage supply element 13 that adjusts the voltage applied to the control electrodes 10 and 11, and is symmetric with respect to the coupling unit 12 in the vibration direction. It is comprised so that a static force may be applied. Here, FIG. 1A shows an initial value of a vibration mode in which the electromechanical filter resonates in parallel with the element substrate when the control unit is not provided. These vibrations include, for example, an elastic wave mode described in Patent Document 1 and a longitudinal vibration mode of a beam type structure.

1A is a cross-sectional view of the initial vibration direction in which the electromechanical filter resonates, and FIG. 1B is a cross-sectional view of the vibration after the control electrodes 10 and 11 are added. Here, the diagonal lines indicate the distortion of the structure due to the electrostatic force, and the change in the position of the coupling portion 12 that is distorted by the vibration is indicated by the dotted line. In this electromechanical filter, the coupling portion is formed on the same plane as two transducers, and the coupling is performed by a pair of control electrodes 10 and 11 arranged symmetrically with respect to the transducer and the coupling surface. It is formed so as to sandwich the portion 12. Then, by applying a DC voltage to the control electrodes 10 and 11 from the same variable voltage supply element 13, the beam is stressed in a direction symmetric and perpendicular to the vibration direction, and the initial value beam is distorted. Arise. Due to this distortion, the spring constant k _couple in the vibration direction increases, and the frequency band of the filter can be modulated. Conversely, when the spring constant of the coupling portion increases, the vibration amplitude x decreases. Here, of the vibrators 14 and 15 constituting the filter, the vibrator 14 can resonate with a signal input from the input electrode 18, and the vibration connected to the vibrator 14 via the coupling portion 12. And an output electrode 19 as a detection electrode disposed at a predetermined interval, and outputs as an electric signal by detecting a change in capacitance between the vibrator 15 and the output electrode 19. Configured to do.
The control unit controls the variable voltage supply element 13 so as to increase the spring constant of the coupling unit 12 by applying a DC voltage to the control electrodes 10 and 11.

  As shown in a top view in FIG. 2, this electromechanical filter is obtained by oscillating and coupling resonators A1 and A2 in which an input electrode 18 and an output electrode 19 are added to vibrators 14 and 15 by a coupling portion 12. Constitute. When an electric signal is passed through the input electrode 18, the vibrator 14 resonates in the elastic wave vibration mode, and the vibrator 15 is also excited by the vibration coupling of the coupling portion 12. Further, the coupling portion 12 is provided with the control electrodes 10 and 11, and the vibration applied to the coupling portion 12 is changed by changing the voltage applied by the variable voltage supply portion 13, and the coupling coefficient of the filter can be adjusted. . Similarly, it is possible to adjust the center frequency of the filter by installing control electrodes on the vibrators 14 and 15 and changing the vibration modes of the resonators A1 and A2. As described above, the characteristic of the electromechanical filter can be adjusted by using the external driving force that is electro-mechanically converted by arranging the control unit including the control electrode in the vibration region of the resonator and the coupling unit 12. Reference numeral 16 denotes a post that supports the vibrator.

Next, the principle of adjusting the frequency band of this electromechanical filter will be described.
First, a filter system in which two resonators are coupled includes two mechanical vibration modes, and each vibration mode vibrates at a close resonance frequency. The center frequency of the filter is determined by the resonance frequency of the vibrators 14 and 15, and the band of the filter is determined as shown below.
First, the Young's modulus of the material is expressed by the following formula (1).

  Moreover, when the electrostatic force according to the hook law is expressed by a spring constant, it is expressed by the following equation (2).

  Furthermore, the spring constant k is expressed by the following expression (3) from the expressions (1) and (2). Here, the amplitude x corresponds to the elongation amount ΔL of the length of the coupling portion.

  From the above formulas (2) and (3), giving an electrostatic force actually changes the spring constant of the structure by changing the Young's modulus of the material.

  The value obtained by adding a variable Young's modulus to the Young's modulus of the material that is originally present in order to vibrate the joint in a state where the electrostatic force is applied to the joint and the joint is distorted by electrostatic force as in the present invention. That is, the spring constant for specifying the frequency is determined from the sum of Young's moduli.

  Since the frequency band of the filter represented by the following equation (4) is determined by the spring constants of the coupling portion and the resonator, the variable spring constant changes the filter characteristics.

  In the present embodiment, since the resonator resonates in the elastic wave mode, an electrostatic force perpendicular to the vibration direction of the coupling portion is given to the coupling portion that vibrates in the longitudinal vibration mode, so that the spring constant increases and vibration occurs. The amplitude of becomes smaller and the frequency band is expanded.

  In practice, the electromechanical filter includes two resonators formed with a gap on the input electrode and the detection electrode formed on the substrate via an insulating layer (not shown), A control electrode is arranged at a coupling portion of these resonators so as to be symmetric with respect to the axis of the coupling portion, and a DC voltage is applied to the control electrode to thereby set a spring constant of the coupling portion. It is configured to change uniformly. By changing the magnitude of the DC voltage, the spring constant changes to a desired value.

  Note that one of the vibrators is capable of resonating with an input signal, and includes a detection electrode disposed at a predetermined interval from the other of the vibrators connected to one of the vibrators via a coupling portion. By detecting a change in electrostatic capacitance between the other of the vibrators and the detection electrode, it is configured to output as an electric signal, thereby constituting an electromechanical filter.

(Embodiment 2)
Next, a second embodiment will be described. The second embodiment is different from the first embodiment in that the vibration mode of the resonator is elastic wave vibration, but the vibration mode of the coupling portion is different. FIG. 3 (a) shows that the electromechanical filter resonates in the flexural vibration mode. Sectional drawing of the coupling | bond part 22 to represent is represented. FIG. 3B shows a cross-sectional view when the control electrodes 21 and 22 are added to the filter, and the amplitude of the flexural vibration is amplified symmetrically. FIG. 4 is a diagram showing the electromechanical filter of the present embodiment. Here, FIG. 3A shows the vibration direction of the coupling portion, and when the resonator resonates in the elastic wave vibration mode and the coupling portion vibrates in the flexural vibration mode, as shown in FIG. A control unit that applies an electrostatic force parallel to the vibration direction of the coupling part and symmetrical to the axis of the coupling part to the coupling part is provided. The part is shown as 22. The coupling portion is formed on the same plane as the two vibrators 14 and 15, and is a pair of control electrodes 20 and 21 arranged symmetrically with respect to the formation surface of the vibrators 14 and 15 and the coupling portion 22. It is formed so as to sandwich the coupling portion 22. FIG. 3A shows a state in which the resonator vibrates in the elastic wave vibration mode and the coupling portion 22 resonates in the flexural vibration mode when the control unit is not provided.
Here, a control unit including a pair of control electrodes 20 and 21 and a variable voltage supply element 24 for applying an electrostatic force symmetrical to the vibration surface of the vibrator is provided.

  That is, in this filter, the coupling portion 22 is formed on the same plane as the two vibrators 14 and 15, and a pair of symmetrically arranged planes on which the vibrators 14 and 15 and the coupling portion 22 are formed. Control electrodes 20 and 21 are formed to sandwich the coupling portion 22. When a DC voltage is applied to the control electrodes 20 and 21 from the same variable voltage supply element 24, stress is applied to the coupling portion in parallel with the vibration direction, and the structure is distorted. This distortion is indicated by a dotted line. As a result, the Young's modulus of the joint portion is determined by the sum of the Young's modulus increased by the external stress with respect to the Young's modulus of the initial value, and the spring constant is increased from the above equation (3). Increasing the spring constant broadens the frequency band of the filter from the above equation (4).

In the first and second embodiments, a pair of electrodes are arranged symmetrically with respect to the vibration axis of the coupling portion, and the same voltage is applied to both electrodes. However, the applied voltage is adjusted when the positions of the electrodes are slightly shifted. By doing so, an electrostatic force symmetrical to the vibration axis of the coupling portion can be applied.
That is, it is desirable that the pair of control electrodes be formed so as to be symmetric with respect to the axis at the stationary position of the coupling portion. However, due to space constraints, the control electrode and the coupling portion axis are When the distance, that is, the gap between the control electrode and the coupling portion at the stationary position is not equal, the voltage applied to each control electrode is differentiated and the electrostatic force perpendicular to the vibration direction of the coupling portion is adjusted to be equal. Thus, it is possible to achieve the same effect as that provided at the symmetrical position.

(Embodiment 3)
Next, a third embodiment will be described.
In the first and second embodiments, the example in which the electrostatic force is applied to the coupling portion has been described. However, in this embodiment, the electrostatic force symmetrical to the vibration axis is applied to the vibrators 14 and 15. It is characterized by that. FIG. 5A shows a top view of a state in which the vibrators 14 and 15 of the electromechanical filter resonate in the elastic wave vibration mode. FIG. 5B shows a top view when the vibrator control electrodes 30 and 31 are added to the vibrator 14, and an electrostatic force is applied in a direction perpendicular to the vibration direction of the elastic wave vibration mode to suppress the amplitude symmetrically. It will be. FIG. 6 is a diagram showing the electromechanical filter of the present embodiment. Here, FIG. 5A shows the initial vibration direction of the vibrator. When the resonator resonates in the elastic wave vibration mode and the coupling portion vibrates in the longitudinal vibration mode, as shown in FIG. 5B. In addition, since a control unit to be applied to the vibrator is provided, stress is generated perpendicular to the vibration direction, and the structure can be distorted (shaded). FIG. 5A illustrates a state in which the resonator vibrates in the elastic wave vibration mode and the vibrators 14 and 15 resonate in the elastic vibration mode when the control unit is not provided.

  Here, a control unit including a pair of control electrodes 30 and 31 for applying an electrostatic force symmetrical to the vibration surface of the vibrator 14 and the variable voltage supply element 13 is provided. On the other hand, for the vibrator 15 connected to the vibrator 14 via the coupling portion 12, like the vibrator 14, a pair of control electrodes 32 and 33 for applying an electrostatic force symmetrical to the vibration surface of the vibrator 15, and A control unit including the variable voltage supply element 13 is provided.

That is, in this filter, the coupling portion 12 is formed on the same plane as the two vibrators 14 and 15, and a pair of control electrodes 30 and 31 and control electrodes arranged symmetrically with respect to the vibrators 14 and 15. 32 and 33 are formed so as to sandwich the vibrators 14 and 15, respectively. Then, by applying a DC voltage from the same variable voltage supply element 13 to the control electrodes 30, 31 and the control electrodes 32, 33, an electrostatic force perpendicular to the vibration direction is applied, and the vibration amplitude is reduced.
As a result, a force perpendicular to the vibration direction of the vibrator is applied, the spring constant is increased, the vibration amplitude is reduced, and the frequency band is increased from the above equations (1) to (4).

  In the third embodiment, a pair of symmetrical control electrodes is provided for each of the two vibrators 14 and 15, and the same electrostatic force is applied to each other. However, only one vibrator is applied. An electrostatic force may be applied, or different electrostatic forces may be applied. Thereby, the center frequency can be changed.

  Moreover, you may make it provide the electrostatic force which becomes symmetrical with respect to a vibration direction not only to the vibrator | oscillators 14 and 15 but to a connection part. Further, these electrostatic forces may be applied collectively by the vibrator and the coupling portion, or may be controlled independently.

(Embodiment 4)
FIG. 7 is a schematic perspective view showing an electromechanical filter according to Embodiment 4 of the present invention.
FIG. 7 shows an electromechanical filter in which two electromechanical resonators are connected by a coupling portion 54, and includes vibrators 50 and 52, an input electrode 60, an output electrode 61, and control electrodes 62, 63, 64 and 65. When a voltage is applied to the control electrodes 62 and 63, the vibrations of the vibrators 50 and 52 are distorted. As a result, the spring constant of the vibrator can be varied to adjust the center frequency, f _o of the filter system. Further, when a voltage is applied to the control electrodes 64 and 65, the spring constant and k _couple of the coupling portion 54 are changed, and the frequency band and BW of the filter system can be adjusted (see equations (1) to (4)). ).
At this time, when a voltage is applied to the control electrodes 62 and 63, the vibration of the vibrators 50 and 52 is distorted. On the other hand, when a voltage is applied to the control electrodes 64 and 65, the spring constant k _couple of the coupling portion 54 changes. These control voltages are adjusted so that the vibrator and the coupling portion vibrate symmetrically.

In this electromechanical filter, the vibrator 50 can resonate with an input signal, and is arranged at a predetermined interval from the vibrator 52 connected to the vibrator 50 via the coupling portion 54. An output electrode 61 is provided as a detection electrode, and is configured to output an electrical signal by detecting a change in electrostatic capacitance between the vibrator 52 and the output electrode 61.
As an example, the vibration mode of the electromechanical filter shown here has a configuration in which the vibrator is in an elastic wave vibration mode and the coupling portion is in a longitudinal vibration mode.

  The electromechanical filter according to the present invention can control the frequency characteristics without affecting the mechanical vibration of the vibrator, and can be applied to a miniaturized, high-performance electromechanical resonator and filter.

Sectional drawing which shows the coupling | bond part of the electromechanical filter in Embodiment 1 of this invention 1 is an overall schematic diagram showing an electromechanical filter according to Embodiment 1 of the present invention. Sectional drawing which shows the coupling | bond part of the electromechanical filter in Embodiment 2 of this invention. Overall schematic diagram showing an electromechanical filter according to Embodiment 2 of the present invention Sectional drawing which shows the coupling | bond part of the electromechanical filter in Embodiment 3 of this invention. Overall schematic diagram showing an electromechanical filter according to Embodiment 3 of the present invention Overall schematic perspective view showing an electromechanical filter according to Embodiment 4 of the present invention. The perspective view which shows the electromechanical filter of a nonpatent literature 1. Top view showing electromechanical filter of Patent Document 1 Sectional drawing which shows the vibration direction of the electromechanical filter of patent document 1

Explanation of symbols

12, 22, 32 Coupling unit 14, 15, 50, 52 Vibrator 51, 53 Support unit 54 Coupling unit 60 Input electrode 61 Output electrode 62, 63, 64, 65 Control electrode

Claims (10)

An electromechanical filter in which vibrators constituting at least two resonators are connected via a coupling portion,
An electromechanical filter including a control unit that applies a symmetrical electrostatic force with respect to a vibration direction of the coupling unit. The electromechanical filter according to claim 1,
The control unit is an electromechanical filter that applies an electrostatic force perpendicular to the vibration direction to the coupling unit. The electromechanical filter according to claim 1,
The control unit is an electromechanical filter that applies an electrostatic force parallel to the vibration direction to the coupling unit. The electromechanical filter according to any one of claims 1 to 3,
The coupling portion is formed on the same plane as the two vibrators,
The control unit includes an electromechanical filter formed by a pair of control electrodes arranged symmetrically with respect to the coupling unit so as to sandwich the coupling unit, and a variable voltage supply element that applies a voltage to the control electrode. . The electromechanical filter according to claim 4,
One of the vibrators can resonate with an input signal, and a detection electrode disposed at a predetermined interval from the other of the vibrators connected to one of the vibrators via a coupling portion. And detecting a change in electrostatic capacitance between the other of the vibrator and the detection electrode, and configured to output as an electric signal.
The electromechanical filter configured to control the control unit with a variable voltage supply element so as to uniformly change a spring constant of the coupling unit by applying a DC voltage to the control electrode. An electromechanical filter in which vibrators constituting at least two resonators are connected via a coupling portion,
An electromechanical filter provided with a control unit that applies a symmetrical electrostatic force with respect to the vibration direction of the vibrator. The electromechanical filter according to claim 6,
An electromechanical filter including a control unit that applies a force perpendicular to the vibration direction to the vibrator. The electromechanical filter according to claim 6 or 7,
The coupling portion is formed on the same plane as the two vibrators,
An electromechanical filter formed such that the vibrator is sandwiched between a pair of control electrodes arranged symmetrically with respect to the formation surface of the vibrator and the coupling portion. The electromechanical filter according to claim 6 or 7,
The coupling portion is disposed at an end portion of the two vibrators arranged so as to be parallel to each other so as to be substantially orthogonal to the vibrator, and the pair of vibrators disposed at both ends thereof. An electromechanical filter formed so as to be sandwiched between control electrodes. An electromechanical filter according to claim 9,
One of the vibrators can resonate with an input signal, and a detection electrode disposed at a predetermined interval from the other of the vibrators connected to one of the vibrators via a coupling portion. And detecting a change in electrostatic capacitance between the other of the vibrator and the detection electrode, and configured to output as an electric signal.
The electromechanical filter configured to control the control unit with a variable voltage supply element so as to uniformly change at least one spring constant of the vibrator by applying a DC voltage to the control electrode.

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