JP2008066801A - Electrostatic vibrator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic vibrator which can improve a Q value. <P>SOLUTION: An end part 10c connecting mechanical vibrators 10a and 10b is connected to a vibration buffer part 13 through a vibration propagation part 11. Another end part 10d connecting the mechanical vibrators 10a and 10b is connected to a vibration buffer part 14 through a vibration propagation part 12. The vibration buffer part 14 is connected to a fixed part 15, and the vibration buffer part 14 is connected to a fixed part 16. Vibrations propagated from the mechanical vibrator 10 are attenuated by the vibration buffer parts 13 and 14 to suppress vibratory displacement of the fixed parts 15 and 16. Consequently, loss of vibration energy due to supporting is suppressed and a high Q value is obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrostatic vibrator used for a reference frequency oscillator of various electronic devices.

  While there is an increasing demand for miniaturization and high precision of wireless portable devices such as mobile phones, and electronic devices such as personal computers and watches, such electronic devices have small and stable high frequency. A signal source is essential. A typical electronic component for satisfying this requirement is a crystal resonator.

  It is known that a crystal resonator has a very high resonance sharpness, that is, a Q value, which is an index of quality as an oscillation element, because of good crystal stability, and exceeds 10,000. This is the reason why crystal resonators are widely used as stable high-frequency signal sources for wireless portable devices and personal computers. However, it has also become clear that this crystal resonator cannot be fully satisfied with the recent demand for strong miniaturization.

  In other words, as is well known, high-frequency electronic components other than crystal resonators have been realized with silicon IC (Micro-Electro-Mechanical-System) technology as well as with IC and integrated formation, Almost one chip. However, since it is very difficult to physically bond a crystal single crystal and a silicon crystal, it is impossible to form a single crystal including a crystal resonator because it cannot be integrally formed or bonded. The above is the reason why the quartz resonator cannot sufficiently satisfy the recent demand for miniaturization.

  In order to solve this problem, a vibrator that has been attracting attention in recent years is an electrostatic vibrator using a silicon single crystal and MEMS technology. Hereinafter, the operation principle of the electrostatic vibrator will be described with reference to FIG. The electrostatic vibrator 70 includes a mechanical vibrator 71 that functions as a mechanical vibrator and a drive electrode portion 72. The mechanical vibrator 71 is equivalently composed of a spring 73 having a spring constant K and an internal friction coefficient μ and a weight 74 having a mass m. Further, two pairs of electrodes, an electrode 75 having an area S formed on the lower surface of the weight 74 and an electrode 77 having an area S formed on the upper surface of the substrate 76 fixed at a distance d from the electrode 75, A drive electrode portion 72 is configured.

  When the high frequency voltage V is applied from the high frequency voltage source 78 to the drive electrode portion 72, the mechanical vibrator 71 induces a minute vibration displacement 700 by the action of electrostatic force. Due to the minute vibration displacement 700, the capacitance of the drive electrode portion 72 also varies, and as a result, the excitation current 701 changes.

Here, if the high-frequency voltage V applied to the drive electrode portion 72 has two components, a DC bias component v ₀ and a high-frequency component δ, it can be written as in the following equation (1). Here, t is time and ω is angular frequency.

Further, in the high-frequency voltage V, the high-frequency component δ is a minute voltage that is sufficiently smaller than the direct-current bias component v _0. Is sufficiently smaller than the separation distance d. Therefore, the dynamic equation of motion where the magnitude of the minute displacement with the electrostatic force in the mechanical vibrator 71 as the forced vibration term is x can ignore the higher-order nonlinear term and is expressed by the following equation (2). .

Here, C ₀ is the capacitance of the drive electrode unit 72 before voltage application, and can be written as the following equation (3) using the dielectric constant ε, the separation distance d, and the electrode area S in vacuum.

  Similarly, if the excitation current 701 excited by the drive electrode unit 72 is i, i can ignore the higher-order nonlinearity similarly to the equation (2), and the following equation (4) is obtained.

Here, considering that the DC bias component v ₀ is sufficiently larger than the high frequency component δ and the magnitude x of the minute displacement is sufficiently smaller than the separation distance d of the drive electrode portion 72, this (4) The equation can be further simplified, and the following equation (5) is obtained for the excitation current i.

The (5) major feature of expression, in proportion to the magnitude of the DC bias component v _0, the effect of the displacement velocity components dx / dt of the machine vibrator 71 is to come to affect the excitation current. Substituting the displacement component x determined from the equation of motion shown in Equation (2) into Equation (5) and further considering electromagnetic considerations, the AC impedance Z (ω) in the drive electrode portion 72 is the frequency ω to be applied. As a function of the following equation (6).

Here, ω ₀ is a mechanical resonance angular frequency in the equation of motion (equation (2)), and is represented by the following equation (7).

From the equation (7), it is found that the mechanical resonance angular frequency ω ₀ is reduced by about several hundred ppm compared to the mechanical resonance angular frequency when no DC bias voltage is present when the DC bias component v ₀ is applied. . However, as compared with the first term on the right side of equation (7), the second term may be considered sufficiently small.

FIG. 8 shows an electrical equivalent circuit in a crystal unit, which is composed of four types of parameters: an equivalent series resistance R _m , an equivalent inductance L _m , an equivalent series capacitance C _m , and a parallel capacitance C _p . The AC impedance Z _q (ω) of the crystal resonator determined by this equivalent circuit is expressed by the following equation (8) as a function of the applied angular frequency ω.

FIG. 9 is a characteristic diagram in which the angular frequency dependence of the AC impedance Z _q (ω) is graphed, that is, an impedance characteristic diagram. In FIG. 9, the horizontal axis is the angular frequency ω. The left vertical axis is the absolute value of impedance and corresponds to the resistance characteristic curve 903 in the figure, and the right vertical axis is the phase and corresponds to the phase characteristic curve 904 in the figure.

  Reflecting the extremely small mechanical energy loss of the crystal unit, that is, an extremely small coefficient of friction, the resonance Q value of the mechanical oscillation of the crystal unit has a large value of several thousand to several tens of thousands. As is well known, the mechanical vibration of the crystal unit is converted into electric vibration by the piezoelectricity of the crystal, so that the electric vibration also has an extremely large Q value.

FIG. 9 is a characteristic diagram schematically showing this phenomenon. In FIG. 9, the resistance characteristic curve 903 has extreme values at two points of the series resonance point 901 and the antiresonance point 902, and changes extremely steeply in the vicinity of this angular frequency. Similarly, the phase characteristic curve 903 also changes very steeply in the vicinity of the angular frequency of the series resonance point 901 / anti-resonance point 902. The absolute value of the impedance in the series resonance point 901 is the equivalent series resistance R _m according Figure 8, angular frequency is series resonance angular frequency omega _r. The series resonance angular frequency ω _r is _expressed by the following equation (9) using the equivalent inductance L _m and the equivalent series capacitance C _m shown in FIG.

It is a well-known fact that the series resonance angular frequency ω _r is equal to the mechanical resonance angular frequency determined from the physical shape dimensions and mechanical properties of the crystal resonator. Furthermore, it is a well-known fact that the equivalent series resistance R _m corresponds to the amount of mechanical energy loss of the crystal resonator.

In the case of the electrostatic vibrator shown in FIG. 7 formed from a silicon single crystal using the MEMS technology, the silicon single crystal has an internal friction coefficient comparable to that of the crystal single crystal, and therefore the mechanical characteristics of the electrostatic vibrator. Resonance Q value of vibration becomes a very high value like quartz. As shown in FIG. 7, by applying the DC bias component v ₀ together with the high frequency component δ, this mechanical property is converted into an electrical signal according to the equations (5) and (6).

Further, the impedance Z (ω) (that is, the equation (6)) has the same mathematical form as the AC impedance Z _q (ω) (that is, the equation (8)) of the crystal resonator. Therefore, the electrical equivalent circuit of the electrostatic vibrator shown in FIG. 7 has exactly the same configuration as the electrical equivalent circuit of the crystal vibrator shown in FIG. 8, and the impedance characteristics of the electrostatic vibrator are also shown in FIG. 9 is equivalent to the impedance characteristic of the crystal unit described in item 9.

In the quartz vibrator, the excellent high Q characteristic of the quartz single crystal is converted into an electric signal by the piezoelectric effect, whereas in the electrostatic vibrator, the DC bias component applied to the drive electrode portion 72 is converted. The high Q characteristic is converted into an electric signal by the effect of v ₀ . Incidentally, when the DC bias component v ₀ is not applied and only the high-frequency component δ is applied, only the second term on the right side indicating the capacitance change component exists in the equation (5). 71 properties are not extracted. In this case, since the minute vibration displacement x is smaller than the separation distance d of the drive electrode portion 72, it is impossible to obtain an electric signal having an impedance characteristic having a high Q characteristic as shown in FIG.

Thus, an electrostatic vibrator similar to a quartz vibrator can realize impedance characteristics having high Q characteristics equivalent to those of the quartz vibrator by applying a DC bias component to the drive electrode portion 72 ( For example, refer nonpatent literature 1). Therefore, it is possible to realize a one-chip oscillator that is impossible with a crystal resonator by using this electrostatic resonator.
T. Mattila et al., “14MHz Micromechanical Oscillator”, TRANSDUCERS'01 EUROSENSORS XV, The 11th International Conference on Solid-State Sensors and Actuators, Munich, Germany, 2001

  However, the conventional electrostatic vibrator has problems as described below. FIG. 10 shows a structure of a conventional electrostatic vibrator having a mechanical vibrator and a drive electrode portion formed from a silicon single crystal by using the MEMS technology. In FIG. 10, the mechanical vibrator 1000 has a shape of a doubly-supported beam type bending vibrator. Two pairs of electrodes, that is, electrodes 1001 and 1002, are formed with a gap from the mechanical vibrator 1000. The drive electrode unit 1003 of the electrostatic vibrator is configured by the two pairs of electrodes. Further, the DC bias voltage is applied with reference to the mechanical vibrator 1000 and the electrode 1001 (or electrode 1002).

The bending vibration excited in the electrostatic vibrator having such electrode arrangement and vibrator arrangement is the vibration displacement 1004. The drive electrode unit 1003 and the mechanical vibrator 1000 are integrally formed on the substrate 1005. The mechanical vibrator 1000 is integrally formed with the substrate 1005 at two locations of two pairs of fixed portions 1006 and 1007 formed at both ends thereof. In such a double-supported beam type electrostatic vibrator, the mechanical energy loss of vibration in the fixed portions 1006 and 1007 is large, and the equivalent series resistance R _m described in FIG. I will invite you. As a result, a sufficient Q value as a vibrator could not be realized.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an electrostatic vibrator capable of improving the Q value.

  The present invention has been made to solve the above-described problems, and includes a vibrating portion formed in a ring shape, a fixed portion fixed to a base, the vibrating portion, and the fixed portion connected to the vibrating portion. And a vibration attenuating portion for attenuating vibration propagating from the electrode, and an electrode disposed on an inner side and an outer side of the ring constituting the vibrating portion with a gap therebetween. It is a vibrator.

  In addition, the electrostatic vibrator according to the present invention includes an elongated first structure connected to the vibration part, an elastic part that is elastically deformed by vibration propagated from the vibration part, the elastic part, and the fixed part The vibration damping part includes a damping part that is provided between the parts and includes an elongated second structure that forms a ring-shaped structure together with the elastic part.

  The electrostatic vibrator according to the present invention includes an elongated structure having an end connected to the vibration portion and an end connected to the fixed portion, and is elastically deformed by vibration propagating from the vibration portion. A portion is included in the vibration damping unit.

  According to the present invention, the vibration propagating from the vibration part is attenuated by the vibration attenuation part, and the vibration displacement of the fixed part is suppressed. As a result, the loss of vibration energy is suppressed, so that the Q value can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the structure of an electrostatic vibrator according to an embodiment of the present invention, and FIG. 2 shows the structure of the vibrator part in a plan view. FIG. 3 shows the dimensions of the vibrator portion. The mechanical vibrator 10 (one embodiment of the vibration part of the present invention) is formed in a ring shape including two mechanical vibrators 10a and 10b. The mechanical vibrators 10a and 10b have a width dimension of W and a length dimension of L. An end portion 10 c which is one connection portion of the mechanical vibrators 10 a and 10 b is connected to the vibration buffer portion 13 via the vibration propagation portion 11. On the other hand, the other end 10 d of the mechanical vibrators 10 a and 10 b is connected to the vibration buffer 14 via the vibration propagation part 12. The corners of the ring-shaped structure constituting the mechanical vibrator 10 are rounded, but the shape of the mechanical vibrator 10 is not limited to this.

  The vibration buffer unit 13 is connected to the fixed unit 15, and the vibration buffer unit 14 is connected to the fixed unit 16. The fixing portion 15 is fixed to the substrate 1 (base body) via the insulating layer 17. Similarly, the fixing part 16 is fixed to the substrate 1 via the insulating layer 18. Electrodes 20 and 21 are arranged inside the ring constituting the mechanical vibrator 10, and electrodes 22 and 23 are arranged outside the ring. Each electrode is disposed with a gap from the mechanical vibrator 10. The electrodes 20, 21, 22, and 23 are fixed to the substrate 1 through insulating layers 24, 25, 26, and 27, respectively. An alternating voltage having the same phase is applied to the electrodes 20 and 21, and an alternating voltage having a phase different from that of the alternating voltage by 180 degrees is applied to the electrodes 22 and 23.

  The vibration buffer unit 13 has a structure for attenuating vibration propagating from the mechanical vibrator 10 via the vibration propagation unit 11. Similarly, the vibration buffer unit 14 is connected to the mechanical vibrator 10 via the vibration propagation unit 12. This is a structure for attenuating the propagating vibration. Since the structure of the vibration buffer 14 is symmetric with respect to the vibration buffer 13, only the vibration buffer 13 will be described. The vibration buffer portion 13 connects the elastic portion 13a elastically deformed by vibration propagated from the mechanical vibrator 10, the attenuation portion 13b provided between the elastic portion 13a and the fixing portion 15, and the elastic portion 13a and the attenuation portion 13b. Connecting portions 13c and 13d. The elastic portion 13a, the damping portion 13b, and the connecting portions 13c and 13d form a ring-shaped structure of the vibration buffer portion 13. The overall length dimension of the vibration buffer parts 13 and 14 is e.

  The elastic portion 13a includes an elongated structure 130 that extends from an end portion 13e that is a connection portion with the vibration propagation portion 11 toward the connection portion 13c (in a direction substantially perpendicular to a direction of a longitudinal vibration displacement 100c described later), and an end portion And an elongated structure 131 extending from the portion 13e toward the connecting portion 13d (in a direction substantially perpendicular to the direction of the longitudinal vibration displacement 100c). The width dimension of these structures 130 and 131 is a. These structures 130 and 131 are an embodiment of the first structure of the present invention.

  The attenuation portion 13b includes an elongated structure 132 that extends from an end portion 13f that is a connection portion to the fixing portion 15 toward the connection portion 13c (in a direction substantially orthogonal to the direction of the longitudinal vibration displacement 100c), and an end portion And an elongated structure 133 extending from 13f toward the connecting portion 13d (in a direction substantially perpendicular to the direction of the longitudinal vibration displacement 100c). The widths of these structures 132 and 133 are b. These structures 132 and 133 are an embodiment of the second structure of the present invention.

  The structures 130 and 131 and the structures 132 and 133 are arranged substantially in parallel with a separation distance d. The connecting portion 13c that connects the structural body 130 and the structural body 132 is formed in an arc shape, and the width dimension thereof is c. Similarly, the connecting portion 13d connected to the structure 131 and the structure 133 is also formed in an arc shape, and its width dimension is c. The connecting portions 13c and 13d are thus formed in an arc shape, but the shape of the connecting portions 13c and 13d is not limited to this.

  The ring-shaped structure constituting the mechanical vibrator 10a has four sides 10e, 10f, 10g, and 10h (see FIG. 2). Of these sides, the electrode 20 is disposed in the vicinity of the opposing sides 10e and 10g. , 21, 22, 23 are provided. The electrodes 20 and 22 are disposed along the side 10e, and the electrodes 21 and 23 are disposed along the side 10f. In addition, vibration propagation portions 11 and 12 are connected to the remaining opposing sides 10f and 10h, respectively.

The mechanical vibrator 10a performs natural vibration that generates a bending vibration displacement 100a in which the distance between the mechanical vibrator 10a and the electrodes 20 and 22 changes, and the mechanical vibrator 10b includes the mechanical vibrator 10b and the electrodes 21, The natural vibration which produces the bending-vibration displacement 100b that the distance between 23 changes is performed. The displacement amounts of the bending vibration displacement 100a and the bending vibration displacement 100b are equal to each other and their phases are different by 180 degrees. The natural frequency F _m is approximately determined by the following equation (10).

Here, _{k f} is two mechanical oscillators 10a, a frequency constant determined by the mechanical properties of 10b. Also, the natural frequency of the bending vibration of the elastic portions 13a of the vibration damping unit 13 _{F 1,} the natural frequency of the bending vibration of the damping portion 13b When _{F 2, F 1, F 2} is the following each approximately (11) Equation (12) can be written.

  In the vibration propagation unit 11, a minute longitudinal vibration displacement 100c that is displaced in a direction substantially perpendicular to the direction of the bending vibration displacements 100a and 100b is induced by the influence of the bending vibration displacements 100a and 100b. When this longitudinal vibration displacement 100c propagates to the elastic portion 13a, a bending vibration displacement having a frequency determined by the equation (10) is generated in the elastic portion 13a. Since the bending vibration displacement 100a and the bending vibration displacement 100b have the same displacement amount and 180 degrees in phase, the vibration displacement in the same direction as the bending vibration displacements 100a and 100b at the end portions 10c and 10d of the mechanical vibrator 10 is as follows. Can be ignored. Therefore, the longitudinal vibration displacement 100c displaced in the direction shown in FIG. 2 propagates to the vibration buffering portion 13, and the longitudinal vibration displacement 100d displaced in the direction shown in FIG.

At this time, with respect to natural frequencies F ₁ bending vibration of the elastic portion 13a, by setting the dimension of the elastic portion 13a so as to satisfy the following equation (13), bending vibration is localized substantially elastic portions 13a It will be.
F _m ≧ F ₁ and W> a (13)

Furthermore, when the dimension value of the attenuation part 13b is set so as to satisfy the following expression (14) with respect to the natural frequency of the attenuation part 13b, the bending vibration displacement of the elastic part 13a is hardly propagated to the attenuation part 13b. The vibration displacement of the fixed portion 15 is suppressed to a negligible level.
F _m ≦ F ₂ and b> W (14)

  Needless to say, the expressions (11) and (12) are approximate expressions, and are influenced by other dimension values c and d. These dimension values vary depending on the frequency and specifications used. However, if the dimension value is set under the conditions shown in the equations (13) and (14), the vibration buffer 13 functions sufficiently. Further, the vibration buffer unit 13 has been described above, but the same applies to the vibration buffer unit 14.

  As described above, according to the electrostatic vibrator shown in FIGS. 1 to 3, the vibration propagating from the mechanical vibrator 10 is attenuated by the vibration buffer parts 13 and 14, and the vibration displacement of the fixed parts 15 and 16 is suppressed. Is done. As a result, loss of vibration energy due to support is suppressed, so that a high Q value can be realized.

  Next, a modification of this embodiment will be described. FIG. 4 shows the structure of the electrostatic vibrator, and FIG. 5 shows the structure of the vibrator part in a plan view. FIG. 6 shows the dimensions of the vibrator portion. In this electrostatic vibrator, the structures of the vibration buffer portion and the fixed portion are different from those of the electrostatic vibrator shown in FIGS. The vibration buffer unit 30 connected to the vibration propagation unit 11 is connected to the fixed unit 32, and the vibration buffer unit 31 connected to the vibration propagation unit 12 is connected to the fixed unit 33. The fixing part 32 is fixed to the substrate 1 via an insulating layer 34. Similarly, the fixing portion 33 is fixed to the substrate 1 via the insulating layer 35.

  The vibration buffer unit 30 has a structure for attenuating vibration propagating from the mechanical vibrator 10 through the vibration propagation unit 11. Similarly, the vibration buffer unit 31 is connected to the mechanical vibrator 10 through the vibration propagation unit 12. This is a structure for attenuating the propagating vibration. Since the structure of the vibration buffer unit 31 is symmetrical to the vibration buffer unit 30, only the structure of the vibration buffer unit 30 will be described. The vibration buffer portion 30 includes an elastic portion 30 a that is elastically deformed by vibration propagated from the mechanical vibrator 10, and connection portions 30 b and 30 c that connect the elastic portion 30 a and the fixing portion 32. The overall length dimension of the vibration buffer portions 30 and 31 is e.

  The elastic portion 30a includes an elongated structure 300 extending from the end 30d, which is a connection portion with the vibration propagation portion 11, toward the connection portion 30b, and an elongated structure 301 extending from the end 30d toward the connection portion 30c. have. The structural bodies 300 and 301 are disposed substantially parallel to the side 32a of the fixing portion 32 with a separation distance d from the fixing portion 32. The width dimension of these structures 300 and 301 is a. The structure 300 is connected to the fixed portion 32 by a connection portion 30b formed in an arc shape. The structural body 301 is also connected to the fixed portion 32 by a connecting portion 30c formed in an arc shape. The width dimensions of the connecting portions 30b and 30c are both c. Although the connection parts 30b and 30c are formed in circular arc shape, the shape of the connection parts 30b and 30c is not this limitation.

  In the electrostatic vibrator shown in FIGS. 4 to 6, the fixing parts 32 and 33 also serve as the attenuation part in the electrostatic vibrator shown in FIGS. 1 to 3. The vibration displacement of the fixing portions 32 and 33 can be suppressed to a negligible level by the combination of the conditions of the expressions (13) and (14) described above and the dimension values of c and d. Therefore, even with the electrostatic vibrator shown in FIGS. 4 to 6, a high Q value can be realized.

  As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, and includes design changes and the like without departing from the gist of the present invention. .

It is a perspective view which shows the structure of the electrostatic vibrator by one Embodiment of this invention. It is a top view which shows the structure of the vibrator | oscillator part of the electrostatic vibrator by one Embodiment of this invention. It is a top view which shows the dimension of the vibrator | oscillator part of the electrostatic vibrator by one Embodiment of this invention. It is a perspective view which shows the structure of the electrostatic vibrator by one Embodiment (modified example) of this invention. It is a top view which shows the structure of the vibrator | oscillator part of the electrostatic vibrator by one Embodiment (modified example) of this invention. It is a top view which shows the dimension of the vibrator | oscillator part of the electrostatic vibrator (modification) by one Embodiment of this invention. It is explanatory drawing for demonstrating the operating principle of an electrostatic vibrator. It is a circuit diagram which shows the electrical equivalent circuit of a crystal oscillator. It is an impedance characteristic figure of a crystal oscillator. It is a perspective view which shows the structure of the conventional electrostatic vibrator.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate 10, 10a, 10b ... Mechanical vibrator, 11, 12 ... Vibration propagation part, 13, 14, 30, 31 ... Vibration buffer part, 13a, 30a ... Elastic part , 13b ... attenuating part, 15, 16, 32, 33 ... fixed part, 20, 21, 22, 23 ... electrode, 17, 18, 24, 25, 26, 27, 34, 35 ...・ Insulation layer

Claims (3)

A vibrating portion formed in a ring shape;
A fixing part fixed to the substrate;
A vibration attenuating part connected to the vibrating part and the fixed part, for attenuating vibration propagating from the vibrating part;
An electrode disposed on the inner side and the outer side of the ring that constitutes the vibrating part, with the vibrating part and a gap therebetween, and
An electrostatic vibrator characterized by comprising: An elastic part having an elongated first structure connected to the vibration part, and elastically deforming by vibration propagating from the vibration part;
A damping part that is provided between the elastic part and the fixed part and has an elongated second structure that forms a ring-shaped structure together with the elastic part;
The electrostatic vibrator according to claim 1, wherein the vibration damping unit is included in the vibration damping unit.   The vibration attenuating portion includes an elongated structure that is connected to the vibrating portion and has an end connected to the fixed portion, and elastically deformed by vibration propagating from the vibrating portion. The electrostatic vibrator according to claim 1.

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