JP2005311568A - Filter device and transceiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter device for developing a filtering function equivalent to that of a band-pass filter, without mutual mechanical connecting the beam electrodes of two minute resonators. <P>SOLUTION: A plurality of minute resonators 15, 16, 17, 18 are electrically interconnected in a lattice form among two input terminals for balanced input and two output terminals for balanced output, by respectively connecting the minute resonator 15 (16), each having a beam structure in series between the input terminal 11 (12) and the output terminal 13 (14) and by respectively connecting the minute resonator 17 (18), each having a beam structure in series in between the input terminal 11 (12) and the output terminal 14 (13). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a filter device configured using a microresonator and a transceiver including the filter device.

  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 micro-electro-mechanical system (MEMS) element or the like as a resonator is known.

  A resonator using a microelectromechanical system element (hereinafter also referred to as a microresonator) is formed on a semiconductor chip 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. Therefore, use as a frequency filter (RF filter, IF filter) has been proposed among wireless communication devices.

  In a microresonator, a beam electrode and an input / output electrode are arranged to face each other through a minute gap, and a signal of a certain frequency is input, whereby electrostatic attraction and electrostatic force are generated between the beam electrode and the input electrode. The beam electrode is resonated by generating repulsive force alternately, and a minute gap change between the beam electrode and the output electrode is extracted as an electric signal. At that time, a signal in a frequency band corresponding to the resonance frequency of the beam electrode is output from the output electrode of the microresonator.

  As a filter device (frequency filter) using such a microresonator, one described in Non-Patent Document 1 below is known. In the filter device described in Non-Patent Document 1, a signal in a certain frequency band is selectively passed by mechanically connecting (connecting) beam electrodes of two microresonators with rod-shaped elastic pieces. This realizes a function as a so-called band pass filter.

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

  However, when the beam electrodes of the two microresonators are mechanically connected as described above, the filter structure is complicated and high processing accuracy is required for the manufacturing process. Therefore, the reliability as the filter device is reduced and the cost is increased.

  The present invention has been made in order to solve the above-mentioned problems, and its object is to provide a filter function equivalent to that of a band-pass filter without mechanically connecting the beam electrodes of two microresonators. It is to realize a filter device that exhibits.

  A filter device according to the present invention has a configuration in which a plurality of microresonators having a beam structure are electrically connected in a lattice shape between two input terminals for balanced input and two output terminals for balanced output. It has become. The transceiver according to the present invention includes the filter device having the above-described configuration.

  In the filter device according to the present invention and a transceiver including the same, by electrically connecting a plurality of microresonators having a beam structure in a lattice shape between two input terminals and two output terminals, A filter function equivalent to a band pass filter can be realized.

  According to the present invention, a plurality of microresonators having a beam structure are electrically connected in a lattice shape between two input terminals and two output terminals, thereby providing a filter function equivalent to a bandpass filter. A filter device can be realized. In this filter device, since the microresonators are electrically connected to each other, the filter structure is simplified and the filter structure is simplified as compared with the case where the beam electrodes of two microresonators are mechanically connected to each other. The device can be manufactured easily. Therefore, the filter device can be reduced in size, cost, and reliability.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. Note that in the embodiment of the present invention, a resonator having a beam structure formed using a microelement such as a MEMS element which is one of micromachines is described as a microresonator.

  FIG. 1 shows a configuration example of a microresonator used in the present invention, in which (A) is a plan view of the microresonator and (B) is a side sectional view of the microresonator. 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 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, whereby the microresonator shown in FIG. 1 is obtained.

  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 the opposing distance between the beam electrode 5 and the output electrode 4 changes accordingly. Therefore, a signal in a frequency band corresponding to the resonance frequency of the beam electrode 5 is output from the output electrode 4.

  FIG. 4 is a schematic view showing the configuration of the filter device according to the embodiment of the present invention. In FIG. 4, a plurality of microresonators 15, 16, 17, and 18 are electrically latticed between two input terminals 11 and 12 for balanced input and two output terminals 13 and 14 for balanced output. Connected to the mold. Each of the microresonators 15, 16, 17, and 18 has a beam structure similar to that of the microresonator (see FIG. 1) obtained by the above manufacturing process. However, in order to lower the impedance, it is also possible to configure each microresonator 15, 16, 17, 18 using a plurality of microresonator groups connected in parallel to each other. Frequency signals with opposite phases are input to the input terminals 11 and 12, and frequency signals with opposite phases are output from the output terminals 13 and 14.

  Among the plurality of microresonators 15, 16, 17, and 18, the microresonator 15 is connected in series between one input terminal 11 and one output terminal 13 corresponding thereto, and the microresonator 16. Are connected in series between the other input terminal 12 and the other output terminal 14 corresponding thereto. The microresonator 17 is connected in series between the one input terminal 11 and the other output terminal 14, and the microresonator 18 includes the other input terminal 12 and the one output terminal 13. Are connected in series.

  FIG. 5 is a detailed view showing the configuration of the filter device according to the embodiment of the present invention. In FIG. 5, the microresonator 15 has an input electrode 151, an output electrode 152, and a beam electrode 153. Similarly, the microresonator 16 includes an input electrode 161, an output electrode 162, and a beam electrode 163, the microresonator 17 includes an input electrode 171, an output electrode 172, and a beam electrode 173, and the microresonator 18 includes An input electrode 181, an output electrode 182, and a beam electrode 183 are included. Among these, the input electrodes 151, 161, 171, 181 correspond to the input electrode 3 of the microresonator shown in FIG. 1, and the output electrodes 152, 162, 172, 182 are the output electrodes of the microresonator shown in FIG. Corresponding to 4. The beam electrodes 153, 163, 173, and 183 correspond to the beam electrode 5 of the microresonator shown in FIG.

  The input electrode 151 of the microresonator 15 is electrically connected to the input terminal 11 via the wiring line L11, and the input electrode 161 of the microresonator 16 is electrically connected to the input terminal 12 via the wiring line L12. Yes. The input electrode 171 of the microresonator 17 is electrically connected to the input terminal 11 via the wiring lines L13 and L11, and the input electrode 181 of the microresonator 18 is connected to the input terminal 12 via the wiring lines L14 and L12. Electrically connected.

  On the other hand, the output electrode 152 of the microresonator 15 is electrically connected to the output terminal 13 via the wiring line L15, and the output electrode 162 of the microresonator 16 is electrically connected to the output terminal 14 via the wiring line L16. Has been. The output electrode 172 of the microresonator 17 is electrically connected to the input terminal 14 via the wiring lines L17 and L16, and the output electrode 182 of the microresonator 18 is connected to the input terminal 13 via the wiring lines L18 and L15. Electrically connected. In addition, at the intersection of the wiring lines L17 and L18, the wiring layer of one wiring line L18 has a two-layer structure, and the wiring lines L17 and L18 are connected to each other by electrically connecting the layers through the contact hole portion 19. Crossed non-conducting.

  Further, the resonance frequencies of the microresonators 15 and 16 are set substantially equal, and the resonance frequencies of the microresonators 17 and 18 are also set approximately equal. However, the resonance frequency of the microresonators 15 and 16 and the resonance frequency of the microresonators 17 and 18 are set to different frequencies. For example, when the resonance frequency of the microresonators 15 and 16 is “F1” and the resonance frequency of the microresonators 17 and 18 is “F2”, the relationship of F1> F2 (for example, F1 = 100 MHz, F2 = 98 MHz) is established. Is set.

  Here, the resonance frequency of the microresonator depends on the natural frequency of the beam electrode, and this natural frequency depends on the length and mass of the beam electrode. Therefore, in setting the resonance frequency of the microresonator, for example, the lengths of the beam electrodes 153 and 163 of the microresonators 15 and 16 are longer than the lengths of the beam electrodes 173 and 183 of the microresonators 17 and 18. By designing the pattern dimensions of the beam electrodes 153, 163, 173, and 183 so as to shorten the resonance frequency, the resonance frequency can be set in the relationship of F1> F2.

  When operating the filter device having the above-described configuration, a DC voltage is applied to the beam electrodes 153, 163, 173, and 183 of the two input terminals 11 and 12 or the plurality of microresonators 15, 16, 17, and 18, respectively. In this state, frequency signals (RF signal, IF signal, etc.) having opposite phases to each other are input to the two input terminals 11 and 12. Then, the frequency signal input from the input terminal 11 is applied to the input electrodes 151 and 171 of the microresonators 15 and 17, and the frequency signal input from the input terminal 12 is input to the input electrodes of the microresonators 16 and 18. 161, 181. Thereby, in each of the microresonators 15, 16, 17, and 18, the corresponding beam electrodes 153, 163, 173, and 183 resonate according to their own natural frequencies, and a frequency signal corresponding to this resonance frequency is generated. , Are taken out from the corresponding output electrodes 152, 162, 172, 182. At this time, the frequency signals extracted from the output electrodes 152 and 182 of the microresonators 15 and 18 are output from the output terminal 13, and the frequency signals extracted from the output electrodes 162 and 172 of the microresonators 16 and 17 are output terminals. 14 is output.

  Thus, the frequency band of the frequency signal output from the two output terminals 13 and 14 corresponds to the resonance frequency F1 of the two microresonators 15 and 16 and the resonance frequency F2 of the two microresonators 17 and 18. Will be. That is, the characteristics of the filter device according to the present embodiment are expressed as shown in FIG. 6 with the S parameter (S21) indicating transmission characteristics on the vertical axis and the frequency on the horizontal axis. In this filter characteristic, only the signal in a certain frequency band can be selectively extracted from the output terminals 13 and 14 with the signal transmission band between the resonance frequencies F1 and F2 described above. Accordingly, the filter device (frequency filter) can be configured by electrically connecting the plurality of microresonators 15, 16, 17, and 18 in a lattice shape, thereby allowing the filter device to function as a bandpass filter. . Further, by considering each microresonator 15, 16, 17, 18 as an impedance element, each microresonator 15, 16, 17, 18 can be regarded as one component of an electric circuit. Therefore, it is possible to perform circuit design using an electric circuit simulation technique.

  Each of the microresonators 15, 16, 17, and 18 constituting the filter device has a parasitic capacitance between the input electrode and the output electrode (space), but is balanced in the lattice-type electrical connection form described above. In the case of the input, the parasitic capacitances interposed in the microresonators 15, 16, 17, and 18 are canceled with each other. Therefore, it is possible to suppress a decrease in the resonance peak due to the presence of parasitic capacitance and improve the SN ratio of the output signal. In addition, since the circuit configuration is symmetric when viewed from the input side of the frequency signal, the symmetry as the filter characteristic is also good. In addition, since many of the circuits of ICs (for example, ICs for IF applications) to which the filter device is connected are balanced circuits, a balun (balanced-unbalanced conversion circuit) is used when connecting the filter device to this IC. It becomes unnecessary.

  Further, the plurality of microresonators 15, 16, 17, and 18 electrically connected in a lattice shape as described above are, for example, one filter unit Fu as shown in FIG. 7, and the filter unit Fu is input. By providing two stages (or three or more stages) in series between the terminals 11 and 12 and the output terminals 13 and 14, it is possible to improve filter characteristics (transmission characteristics).

  By the way, when the parasitic capacitance is canceled as described above, a merit such as an improvement in the S / N ratio can be obtained. However, as the influence of the parasitic capacitance (reduction in the resonance peak) decreases, the degree of suppression of the signal cutoff band increases accordingly. . Therefore, for example, when an interference wave exists in the vicinity of the signal transmission band (F1-F2 band), the interference wave cannot be removed by the filter device.

  In such a case, the parasitic capacitance of the microresonator having a relatively high resonance frequency among the plurality of microresonators 15, 16, 17, and 18 constituting the filter device is changed to a microresonance having a relatively low resonance frequency. It is desirable to make it larger than the parasitic capacitance of the vessel. For example, when the resonance frequency F1 of the microresonators 15 and 16 is 100 MHz and the resonance frequency of the microresonators 17 and 18 is 98 MHz as described above, the parasitic capacitance of the microresonators 15 and 16 is changed to the microresonator 17. , 18 is larger than the parasitic capacitance.

  Specifically, as shown in FIG. 8A, a capacitor C1 is added to each of the two microresonators 15 and 16 having a relatively high resonance frequency. In the case where a multi-stage filter unit is provided, as shown in FIG. 8B, a capacitor C1 is added to each of the two microresonators 15 and 16 in each filter unit. Taking the microresonator 15 as an example, the capacitor C1 is provided with an extension portion 152A extending toward the input electrode 151 on the output electrode 152 as shown in FIG. 9A, for example, and the extension portion 152A. Thus, it can be added by partially narrowing the interval between the input electrode 151 and the output electrode 152. Further, as shown in FIG. 9B, a pair of conductor layers (metal layers) 20A and 20B constituting a capacitor are formed on the wiring pattern of the filter device connected to the microresonator 15, and the pair of conductor layers. The capacitor C1 can also be added by electrically connecting one conductor layer 20A of 20A and 20B to the input electrode 151 and electrically connecting the other conductor layer 20B to the output electrode 152. 9C, a chip capacitor 21 is mounted on the wiring pattern of the filter device connected to the microresonator 15, and each electrode terminal of the chip capacitor 21 is connected to the input electrode 151 and the output electrode 152, respectively. The capacitor C1 can also be added by electrical connection.

  Among these, in the configuration shown in FIG. 9A, the extension portion 152A is a capacitance addition portion, and in the configuration shown in FIG. 9B, the pair of conductor layers 20A and 20B is a capacitance addition portion, and FIG. In the configuration shown, the chip capacitor 21 serves as a capacitance adding unit. 9A and 9B, the plurality of microresonators 15, 16, 17, 18 and 18 are formed on a semiconductor chip on which a plurality of microresonators 15, 16, 17, 18 are formed. The capacitance adding portion (152A, 20A, 20B) is integrally formed. In the configuration shown in FIG. 9C, the capacitance is added on the semiconductor chip on which the plurality of microresonators 15, 16, 17, 18 are formed. The part (21) is mounted. In particular, in the case where the capacitance adding portion (152A, 20A, 20B) is formed integrally with the plurality of microresonators 15, 16, 17, 18 in the manufacturing process of the microresonator, the filter device is manufactured. A capacity addition part can be formed. Therefore, it is not necessary to provide a separate process for forming the capacitance adding portion. Further, in the case shown in FIG. 9A, the capacity addition portion (152A) can be formed only by partial change of the electrode shape, and in the case shown in FIG. 9B, a slight empty space is used. Since the capacity addition portions (20A, 20B) can be formed, the layout is not forced to change.

  When the capacitance C1 is added to each of the two microresonators 15 and 16 in this way, the balance with the parasitic capacitances of the other two microresonators 17 and 18 is lost, so the filter capacity depends on the size of the capacitance C1. The degree of suppression changes. FIG. 10 shows the change of the filter characteristics depending on the size of the additional capacitance. Here, the size of the additional capacitance C1 is divided into four stages of “large”, “medium”, “small”, and “none”, corresponding to them. The filter characteristics are shown. As can be seen from FIG. 10, the degree of suppression increases as the additional capacity C1 decreases, and the degree of suppression decreases as the additional capacity C1 increases. Therefore, even when an interference wave exists in the vicinity of the signal transmission band (F1-F2 band), the interference wave can be removed by adding a capacitor C1 having an appropriate size to the microresonators 15 and 16. .

  Incidentally, since the capacitor C1 needs to be added to a microresonator having a relatively high resonance frequency, for example, when the resonance frequency of the microresonators 15 and 16 is lower than the resonance frequency of the microresonators 17 and 18, The capacitor C1 is added to the microresonators 17 and 18.

  The present invention is not limited to a filter device using a microresonator, but communicates using electromagnetic waves such as a mobile phone, a wireless LAN device, a TV tuner, and a radio tuner configured using the filter device. It can also be provided as a transceiver.

It is a figure which shows the structural example 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 filter apparatus which concerns on embodiment of this invention. It is detail drawing which shows the structure of the filter apparatus which concerns on embodiment of this invention. It is a figure which shows the characteristic of the filter apparatus which concerns on embodiment of this invention. It is the schematic which shows the other structural example of the filter apparatus which concerns on embodiment of this invention. It is the schematic which shows the structural example of the filter apparatus which concerns on other embodiment of this invention. It is a figure which shows the specific structural example of a capacity | capacitance addition part. It is a figure which shows the change of the filter characteristic by the magnitude | size of additional capacity | capacitance.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11, 12 ... Input terminal, 13, 14 ... Output terminal, 15, 16, 17, 18 ... Micro resonator, 151, 161, 171, 181 ... Input electrode, 152, 162, 172, 182 ... Output electrode, 153 163, 173, 183 ... Beam electrodes

Claims (8)

A filter device comprising a plurality of microresonators having a beam structure electrically connected in a lattice form between two input terminals for balanced input and two output terminals for balanced output. The two input terminals include a first input terminal and a second input terminal,
The two output terminals include a first output terminal and a second output terminal,
The plurality of microresonators are connected in series between the first input terminal and the first output terminal and between the second input terminal and the second output terminal, respectively. A second resonator connected in series between the first microresonator, the first input terminal and the second output terminal, and the second input terminal and the first output terminal. The filter device according to claim 1, further comprising: a microresonator. The filter device according to claim 1, wherein a resonance frequency of the first microresonator is different from a resonance frequency of the second microresonator. Of the first microresonator and the second microresonator, the parasitic capacitance of one microresonator having a relatively high resonance frequency is made larger than the parasitic capacitance of the other microresonator. The filter device according to claim 3. The filter device according to claim 4, wherein a capacitor is added to the one microresonator. The filter device according to claim 5, wherein a capacitance adding portion is formed integrally with the plurality of microresonators on a semiconductor chip on which the plurality of microresonators are formed. The filter device according to claim 5, wherein a capacitor addition unit is mounted on a semiconductor chip on which the plurality of microresonators are formed. A filter device comprising a plurality of microresonators having a beam structure electrically connected in a lattice shape between two input terminals for balanced input and two output terminals for balanced output, Transmitter / receiver.

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