JP2005311737A - Minute resonator and transceiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of improving the resonance characteristics of a minute resonator, by suppressing the effect of parasitic capacitance in the minute resonator. <P>SOLUTION: The minute resonator is configured to include an input electrode which receives a frequency signal; a beam electrode vibrated by the frequency signal received by the input electrode; a resonance circuit section 13, including an output electrode for outputting a signal, in response to the vibration frequency of the beam electrode; and an inductor 14 connected in parallel with the resonance circuit section 13. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a microresonator configured using a MEMS element or the like and a transceiver including the microresonator.

  In recent years, with the development of IT (Information Technology), the number of devices using a network has increased dramatically. Under such circumstances, the demand for wireless network technology is increasing especially from the viewpoint of usability. RF front-end modules used in wireless communication include semiconductor chips as well as SAW (Surface Acoustic Wave) filters and dielectric filters for RF filters (high frequency filters) and IF filters (intermediate frequency filters). Large-sized parts are incorporated, and the presence of these parts is a factor that hinders downsizing and cost reduction of the RF front-end module. Therefore, attempts have been made to realize a reduction in size and cost of the RF front-end module by incorporating these filter functions into a semiconductor chip. Specifically, a technique using a MEMS (Micro-Electro-Mechanical System) element, which is one of micromachines, as a resonator is known.

  A resonator using a MEMS element (hereinafter also referred to as a microresonator) is formed on a semiconductor chip by using a semiconductor process, and has a beam structure for functioning as a resonator. A microresonator has features such as a small device occupation area, a high Q value (energy / loss ratio), and integration with other semiconductor devices. Then, utilization as a frequency filter (RF filter, IF filter) is proposed among radio | wireless communication devices (for example, refer the following nonpatent literature 1).

"IEEE Journal of Solid-state Circuits" (USA), April 2000, Vol. 35, No. 4, p. 512-526

  However, since the microresonator proposed in Non-Patent Document 1 has a very high impedance, it is easily affected by parasitic capacitance. The parasitic capacitance is interposed between the input / output electrodes of the microresonator, and causes a deterioration of the SN ratio. Therefore, if the influence of the parasitic capacitance is increased, it becomes difficult to cope with the higher frequency of the signal.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the resonance characteristics by suppressing the influence of parasitic capacitance in the microresonator.

  The microresonator according to the present invention includes an input electrode to which a frequency signal is input, a beam electrode that vibrates by the frequency signal input to the input electrode, and an output electrode that outputs a signal corresponding to the frequency of the beam electrode. And a inductor connected in parallel to the resonance circuit unit. A transceiver according to the present invention uses the microresonator having the above-described configuration.

  In the microresonator according to the present invention and a transceiver using the same, by connecting an inductor in parallel to the resonant circuit unit, it is possible to suppress the influence of parasitic capacitance interposed in the resonant circuit unit. .

  According to the present invention, by connecting the inductor in parallel to the resonance circuit unit, it is possible to improve the resonance characteristics by suppressing the influence of the parasitic capacitance interposed in the resonance circuit unit.

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

  FIG. 1 shows a configuration example of a main part of a microresonator used in the present invention, in which (A) is a plan view and (B) is a side sectional view thereof. In FIG. 1, an insulating film 2 is formed on a semiconductor substrate 1 serving as a base. The semiconductor substrate 1 is composed of, for example, a silicon substrate, and the insulating film 2 is composed of, for example, a silicon nitride film.

  An input electrode 3 and an output electrode 4 are formed on the insulating film 2. A beam electrode 5 is formed above the input electrode 3 and the output electrode 4 so as to face the two electrodes 3 and 4. Both ends of the beam electrode 5 are supported in a fixed state (both-supported beam state) by a pair of support portions 6. Further, the beam electrode 5 is formed so as to straddle the input electrode 3 and the output electrode 4 through a minute gap between each electrode surface of the input electrode 3 and the output electrode 4. Further, the input electrode 3 and the output electrode 4 are arranged at a position equidistant from the center of the beam electrode 5 in the length direction (left-right direction in FIG. 1).

  2 and 3 are flowcharts showing an example of a manufacturing process of the microresonator used in the present invention. First, in manufacturing a microresonator, as shown in FIG. 2A, an insulating film 2 is formed on a semiconductor substrate 1 such as a silicon substrate. The insulating film 2 is formed, for example, by depositing a silicon nitride film with a thickness of 1 μm. Next, as shown in FIG. 2B, a lower electrode layer 7 made of a polycrystalline silicon layer having a thickness of 0.5 μm, for example, is formed on the insulating film 2 formed earlier by vapor deposition, and then the lower electrode layer is formed. By patterning 7 using a photolithography technique, the input electrode 3, the output electrode 4 and the pair of support portions 6 are formed as shown in FIG.

  Next, as shown in FIG. 2D, a sacrificial layer 8 is formed on the insulating film 2 of the semiconductor substrate 1 so as to cover the input electrode 3, the output electrode 4, and the support portion 6. The sacrificial layer 8 is formed, for example, by depositing silicon dioxide with a thickness of 0.5 μm. Next, as shown in FIG. 2E, the surface (upper surface) of the sacrificial layer 8 is planarized by a CMP (Chemical Mechanical Polishing) method.

  Subsequently, as shown in FIG. 3A, after an opening (contact hole) 9 is formed in the sacrificial layer 8 on the pair of support parts 6, the opening 9 is formed as shown in FIG. An upper electrode layer 10 made of, for example, a polycrystalline silicon layer having a thickness of 0.5 μm is formed on the sacrificial layer 8 in a state of being embedded. Next, as shown in FIG. 3C, the beam electrode 5 is formed by patterning the upper electrode layer 10 by photolithography. Thereafter, as shown in FIG. 3D, the sacrificial layer 8 is removed using a solvent such as hydrofluoric acid to obtain a microresonator having the beam structure shown in FIG.

  In a microresonator obtained by such a manufacturing process, for example, when a frequency signal (RF signal, IF signal, etc.) is input while applying a direct-current voltage (DC) to the input electrode 3, the beam electrode 5 and the input electrode 3 The electrostatic attractive force and the electrostatic repulsive force, collectively called Coulomb force, are repeatedly generated in the opposite portion of the. Among these, when the electrostatic attractive force is generated, the beam electrode 5 is minutely displaced in the direction approaching the input electrode 3, and when the electrostatic repulsive force is generated, the beam electrode 5 is minutely displaced in the direction away from the input electrode 3. To do. By repeating this, the beam electrode 5 resonates (vibrates) according to its own natural frequency, and a signal in a frequency band corresponding to the resonance frequency (vibration frequency) is output from the output electrode 4. Incidentally, the direct current may be applied to the beam electrode 5 in some cases.

  FIG. 4 is a schematic diagram showing the configuration of the microresonator according to the embodiment of the present invention. In the figure, a resonance circuit unit 13 is connected in series between a signal input terminal 11 and an output terminal 12. The input terminal 11 is a signal terminal for inputting a frequency signal to the resonance circuit unit 13, and the output terminal 12 is a signal terminal for taking out the frequency signal output from the resonance circuit unit 13. The resonance circuit unit 13 is configured using the main part of the microresonator shown in FIG. 1, that is, the input electrode 3, the output electrode 4, the beam electrode 5, and the like.

  Between the input terminal 11 and the output terminal 12, an inductor 14 is connected in parallel to the resonance circuit unit 13. One end of the inductor 14 is electrically connected to a wiring line L11 extending from the input terminal 11 to the input electrode 3 (see FIG. 1) of the resonance circuit unit 13, and the other end of the inductor 14 is the output electrode 4 ( It is electrically connected to a wiring line L12 extending from the output terminal 12 (see FIG. 1).

  For example, as shown in FIG. 5, the inductor 14 includes a spiral wiring portion 14 </ b> A electrically connected to wiring lines L <b> 11 and L <b> 12 drawn from the input electrode 3 and the output electrode 4 of the resonance circuit portion 13. Is. The wiring line L13 connected to the innermost peripheral portion of the spiral wiring portion 14A is drawn to the outer peripheral side by a wiring layer different from the spiral wiring portion 14A using the contact holes 15A and 15B, and is wired through the wiring line L14. It is electrically connected to the line L11. Further, the wiring line L15 connected to the outermost peripheral portion of the spiral wiring portion 14A is electrically connected to the wiring line L12. With the above configuration, the resonance circuit unit 13 and the inductor 14 are formed on the same substrate (on the semiconductor substrate 1 in FIG. 1).

  FIG. 6 is an equivalent circuit diagram of the microresonator according to the embodiment of the present invention. In the figure, the resonance circuit unit 13 constitutes a series resonance circuit of R, Lx, and Cx. On the other hand, the parasitic capacitance C0 interposed between the input electrode 3 and the output electrode 4 of the resonance circuit unit 13 is connected in parallel to the resonance circuit unit 13, and the inductance L due to the inductor 14 described above is The resonance circuit unit 13 and the parasitic capacitance C0 are connected in parallel. Further, as described above, the inductance L and the parasitic capacitance C0 constitute the parallel resonance circuit 15 with respect to the resonance circuit unit 13 constituting the series resonance circuit.

  In such a case, since the resonance frequency of the resonance circuit unit 13 is determined by Lx and Cx, by setting the value of the inductance L so that the parallel resonance circuit 15 causes parallel resonance by the Lx and Cx, the resonance circuit unit 13 can resonate. When this is done, the impedance of the parallel resonant circuit 15 is maximized. Specifically, by setting the value of the inductance L under the condition “L = Cx · Lx / C0”, the impedance of the parallel resonant circuit 15 is theoretically infinite. However, in practice, since a resistance component always exists, the impedance of the parallel resonant circuit 15 does not become infinite, but becomes a very large value compared to the impedance of the resonant circuit unit 13. Therefore, the addition of the inductor 14 can suppress the influence (signal leakage) of the parasitic capacitance C0 and improve the resonance characteristics of the microresonator. Therefore, it becomes easy to cope with high frequency signals. Further, by using this microresonator, it is possible to realize a frequency filter and an oscillator having excellent characteristics.

  Further, by forming the resonant circuit unit 13 and the inductor 14 on the same substrate as described above, the resonant circuit unit 13 and the inductor 14 can be formed simultaneously in a series of semiconductor manufacturing processes. In addition, the microresonator including the resonance circuit unit 13 and the inductor 14 can be compactly manufactured as one device. Furthermore, by configuring the inductor 14 with the spiral wiring portion 14A, the inductor 14 can be manufactured simultaneously with the patterning of the wiring line in the manufacturing process of the microresonator.

  In the above embodiment, the resonance circuit unit 13 is connected in series between the signal input terminal 11 and the output terminal 12, and the inductor 14 is connected in parallel to the resonance circuit unit 13. However, the present invention is not limited to this. For example, as shown in FIG. 7, a resonance circuit unit 13 is connected in parallel between an input terminal 11 and an output terminal 12, and an inductor 14 is connected in parallel to the resonance circuit unit 13. Good.

  In this case, the input electrode 3 (see FIG. 1) of the resonance circuit unit 13 is electrically connected to the wiring line between the input electrode 11 and the output electrode 12, and the output electrode 4 of the resonance circuit unit 13 (see FIG. 1). ) Is electrically connected (grounded) to the ground (GND). In addition, one end of the inductor 14 is electrically connected to a wiring line connected to the input electrode 3 of the resonance circuit unit 13, and the other end of the inductor 14 is electrically connected to a wiring line connected to the output electrode 4 of the resonance circuit unit 13. Will be. Therefore, the equivalent circuit in this case is expressed as shown in FIG. Even in such a configuration, by setting the value of the inductance L under the same conditions as described above, the influence of the parasitic capacitance C0 can be effectively suppressed and the resonance characteristics of the microresonator can be improved.

  In addition, the present invention is not limited to a microresonator, and is provided as a transceiver that communicates using electromagnetic waves, such as a mobile phone, a wireless LAN device, a TV tuner, and a radio tuner that are configured using the microresonator. It is also possible.

It is a figure which shows the structural example of the principal part of the microresonator used for this invention. It is a flowchart (the 1) which shows an example of the manufacturing process of the microresonator used for this invention. It is a flowchart (the 2) which shows an example of the manufacturing process of the microresonator used for this invention. It is the schematic which shows the structure of the microresonator which concerns on embodiment of this invention. It is a top view which shows the inductor addition structure example of the microresonator which concerns on embodiment of this invention. It is a transmission circuit diagram of the microresonator which concerns on embodiment of this invention. It is the schematic which shows the structure of the microresonator which concerns on other embodiment of this invention. FIG. 6 is a transmission circuit diagram of a microresonator according to another embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 3 ... Input electrode, 4 ... Output electrode, 5 ... Beam electrode, 11 ... Input terminal, 12 ... Output terminal, 13 ... Resonance circuit part, 14 ... Inductor, 15 ... Parallel resonance circuit

Claims (4)

A resonant circuit unit having an input electrode to which a frequency signal is input, a beam electrode that vibrates by the frequency signal input to the input electrode, and an output electrode that outputs a signal corresponding to the frequency of the beam electrode;
An inductor connected in parallel to the resonant circuit unit. The microresonator according to claim 1, wherein the resonance circuit unit and the inductor are formed on the same substrate. The microresonator according to claim 2, wherein the inductor is configured by a spiral wiring portion electrically connected to a wiring line drawn from the resonance circuit portion. A resonant circuit unit having an input electrode to which a frequency signal is input, a beam electrode that vibrates by the frequency signal input to the input electrode, and an output electrode that outputs a signal corresponding to the frequency of the beam electrode;
A transceiver comprising: an inductor connected in parallel to the resonance circuit unit.

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