JP4846509B2 - Piezoelectric resonator and method for manufacturing the same - Google Patents

Description

  The present invention relates to a piezoelectric resonator using a piezoelectric thin film and a method for manufacturing the piezoelectric resonator, which are used in wireless communication devices typified by mobile phones and wireless LANs.

  Components built in portable communication devices and the like are required to be smaller and lighter while maintaining high performance. For example, a filter or duplexer for selecting a high frequency signal used in a mobile phone is required to be small and have a small insertion loss. As one of filters satisfying this requirement, a filter using a piezoelectric resonator using a piezoelectric thin film is known. See, for example, US Pat.

FIG. 8A is a top view schematically showing the structure of a conventional piezoelectric resonator. FIG. 8B is a YY sectional view of the conventional piezoelectric resonator shown in FIG. 8A.
This conventional piezoelectric resonator has a structure in which a lower electrode 702 is formed on a substrate 705, a piezoelectric layer 701 is formed on the lower electrode 702, and an upper electrode 703 is formed on the piezoelectric layer 701. is there. Among these, a region where the lower electrode 702, the piezoelectric layer 701, and the upper electrode 703 overlap in the vertical projection direction functions as the vibration unit 704. The substrate 705 is formed with a cavity 706 for ensuring vibration at the vibration unit 704, and the vibration unit 704 is placed on the substrate 705 so as to cover the cavity 706. Accordingly, a part of the lower electrode 702 and / or the piezoelectric layer 701 that does not belong to the vibrating portion 704 serves as a supporting portion that supports the piezoelectric resonator on the substrate 705. In the actual product, wiring electrodes 708 for connecting the lower electrode 702 and the upper electrode 703 to the input / output electrode 707 are provided.

This conventional piezoelectric resonator is manufactured by the following procedure.
First, the lower electrode 702, the piezoelectric layer 701, and the upper electrode 703 are sequentially formed on the substrate 705 by vapor deposition or sputtering. Next, the upper electrode 703 to the lower electrode 702 are patterned into a desired shape by using a photolithography technique. When the material is the same as that of the lower electrode 702 and the upper electrode 703, the input / output electrode 707 and the wiring electrode 708 are formed at the same time when the lower electrode 702 and the upper electrode 703 are patterned. Finally, the cavity 706 is formed by dry etching or the like from the back surface of the substrate 705.

The piezoelectric resonator having the above structure operates as a resonator by mechanically distorting the piezoelectric layer 701 by applying an electric field between the lower electrode 702 and the upper electrode 703 and electrically extracting the distortion. Although there are many vibration modes by the piezoelectric layer 701, thickness longitudinal vibration having a high resonance frequency is used for wireless communication devices typified by mobile phones and wireless LANs.
JP 2002-374144 A

  As is well known, in the piezoelectric resonator, when the vibration part is in a free vibration state floating in space, the Q value representing the resonance sharpness and the difference Δf between the resonance frequency and the antiresonance frequency are the best. Become. However, it is impossible to manufacture a vibration part having a structure that physically floats in space, and a support part must be present.

  In the conventional piezoelectric resonator described above, since a part of the lower electrode 702 is in contact with the substrate 705 that is the support portion, the vibration of the vibration portion 704 leaks to the substrate 705 and has a problem that the frequency characteristics deteriorate. It was. Further, even if the lower electrode 702 has a structure in which a part of the lower electrode 702 is not in contact with the substrate 705, the wiring electrode 708 is in contact with the substrate 705. Had.

  Therefore, an object of the present invention is to provide a piezoelectric resonator capable of obtaining good frequency characteristics by suppressing the vibration of the vibrating portion from leaking from the support portion, and a method for manufacturing the piezoelectric resonator.

  The present invention is directed to a piezoelectric resonator that vibrates at a predetermined frequency. In order to achieve the above object, a piezoelectric resonator according to the present invention includes a piezoelectric layer made of a piezoelectric thin film, an upper electrode formed on one main surface of the piezoelectric layer, and the other main surface of the piezoelectric layer. A lower electrode formed on the substrate; a support portion provided between the piezoelectric layer and the substrate; and the support portion is provided at a position where neither the lower electrode nor the upper electrode overlaps with the vertical projection direction. It is characterized by that.

The support portion may be composed of a plurality of support columns. In addition, a region where the lower electrode, the piezoelectric layer, and the upper electrode overlap in the vertical projection direction is a vibration part, and the support part is provided in a shape and position that is non-rotational symmetric with respect to the vibration center point of the vibration part . It is preferable to provide a shape and a position that are non-axisymmetric with respect to a straight line passing through the vibration center point of the vibration part . Furthermore, it is preferable that the support portion is provided at a position where the maximum linear distance with the lower electrode is larger than the maximum linear distance between the outer peripheral end of the upper electrode and the outer peripheral end of the lower electrode. This support part is formed of a conductive material.

  The piezoelectric resonator having the above structure includes a step of forming a piezoelectric layer on a first substrate, a step of forming a lower electrode on one main surface of the piezoelectric layer, and a piezoelectric layer excluding a region where the lower electrode is formed. On the other hand, a step of forming a first support portion layer on the main surface, a step of forming a second support portion layer on the second substrate, a first support portion layer and a second support portion layer And a step of separating the first substrate after the bonding step and transferring the piezoelectric layer on which the lower electrode is formed from the first substrate to the second substrate; The upper electrode is formed on the other main surface of the piezoelectric layer that does not overlap with any of the two support portion layers in the vertical projection direction.

  Typically, the bonding step is performed by eutectic crystal bonding of the first support portion layer and the second support portion layer. In this case, it is desirable that the first support part layer and the second support part layer are multilayer films containing at least gold tin (AuSn) or gold silicon (AuSi).

  In addition, although the piezoelectric resonator of the present invention described above functions alone, it may be configured as a piezoelectric filter including a plurality of piezoelectric resonators, a duplexer, and a communication device.

  According to the present invention, since the vibration part and the support part are not in contact with each other, the Q value and Δf of the piezoelectric resonator are improved as compared with the related art. Therefore, it is possible to realize a filter or duplexer having a low loss, a wide band and a steep passband characteristic, and a high-quality communication device with low power consumption and low noise.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Structure of piezoelectric resonator)
FIG. 1A is a top view schematically showing the structure of a piezoelectric resonator according to an embodiment of the present invention. 1B is an XX cross-sectional view of the piezoelectric resonator shown in FIG. 1A. The piezoelectric resonator according to this embodiment has the following structure.

  An upper electrode 103 is formed on one main surface of the piezoelectric layer 101 and a lower electrode 102 is formed on the other main surface. The vibration unit 104 is a region where the lower electrode 102, the piezoelectric layer 101, and the upper electrode 103 overlap in the vertical projection direction. In addition, wiring electrodes 108 for connecting the lower electrode 102 and the upper electrode 103 to the input / output electrode 107 are provided on one main surface and the other main surface of the piezoelectric layer 101, respectively. The vibrating unit 104 is mounted (bonded) on the substrate 105 via the support unit 109. A space between the substrate 105 and the lower electrode 102 becomes a cavity 106.

  The piezoelectric layer 101 includes aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), or potassium niobate (KNbO3). A piezoelectric material such as) is used. For the lower electrode 102, the upper electrode 103, the input / output electrode 107, and the wiring electrode 108, molybdenum (Mo), aluminum (Al), tungsten (W), platinum (Pt), gold (Au), silver (Ag), A conductive material such as titanium (Ti) or copper (Cu), or a laminated metal or alloy thereof is used. From the viewpoint of the manufacturing process, it is preferable to select the same material as that of the lower electrode 102 and the upper electrode 103 as the material used for the input / output electrode 107 and the wiring electrode 108.

  For the substrate 105, a material such as silicon (Si), gallium arsenide (GaAs), glass, or sapphire is used. Since the support unit 109 uses a characteristic piezoelectric resonator manufacturing method described later, a conductor such as an alloy of titanium, gold, tin (Sn), chromium (Cr), gold tin (AuSn), or gold silicon (AuSi) is used. Material is used. These conductive materials may be used in a single structure or in a multilayer structure. Note that the support portion 109 can be formed of a conductive bump.

  A feature of the piezoelectric resonator of the present invention is that the supporting portion 109 is located at the position of the piezoelectric layer 101 excluding the region where the vibrating portion 104 is formed and the region where the input / output electrode 107 and the wiring electrode 108 are formed. Is to be formed. That is, the support portion 109 is provided at a position that does not overlap any electrode in the vertical projection direction.

  If this feature is satisfied, as illustrated in FIGS. 2A to 2C, the relationship between the number of support pillars constituting the support portion 109, the cross-sectional shape of the support portion 109, and the positions and sizes of the upper electrode 103 and the lower electrode 102. Etc. can be designed freely.

  Here, in order to suppress unnecessary vibration that leaks from the piezoelectric resonator to the substrate 105, a straight line that does not become rotationally symmetric at the vibration center point of the vibration unit 104 and / or passes through the vibration center point of the vibration unit 104 is used. It is preferable to form the support portion 109 in a shape and position that are not symmetrical. Further, as shown in FIG. 1B, the maximum linear distance α between the outer peripheral end of the lower electrode 102 and the support portion 109 is made larger than the maximum linear distance β between the outer peripheral end of the upper electrode 103 and the outer peripheral end of the lower electrode 102. It is preferable. In this way, the capacitive component generated between the lower electrode 102 and the upper electrode 103 and the support portion 109 can be suppressed as much as possible.

(Method for manufacturing piezoelectric resonator)
3A and 3B are diagrams schematically showing a procedure of a method for manufacturing a piezoelectric resonator according to the present embodiment. In this manufacturing method, the piezoelectric resonator shown in FIGS. 1A and 1B is manufactured by using a bonding method.

  First, a film-forming substrate 111 made of silicon, glass, sapphire, or the like is prepared, and an insulating film (not shown) such as a thermal oxide film or a nitride film is formed on the film-forming substrate 111. A piezoelectric layer 101 is formed thereon (FIG. 3A, step a). Next, an electrode film 112 to be the lower electrode 102 is formed on the piezoelectric layer 101 (FIG. 3A, step b). The piezoelectric layer 101 and the electrode film 112 need to be adjusted to thicknesses for obtaining a desired resonance frequency in consideration of the thickness of the insulating film. For example, when a resonance frequency of several GHz is generated using the longitudinal vibration of the piezoelectric layer 101, the thickness of the piezoelectric layer 101 is about 1 μm.

  Thereafter, the electrode film 112 is patterned by photolithography or lift-off processing to form a support layer 119a that is a base for the lower electrode 102 and the support 109 (FIG. 3A, step c). Further, a support layer 119b to be a part of the support 109 is formed on the support layer 119a by using electron beam evaporation or sputtering (FIG. 3A, step d). If the material is the same, the support layer 119a and the support layer 119b may be integrally formed. Thereby, the preparation of the film-forming substrate 111 is completed.

  Next, a substrate 105 that supports the vibration unit 104 is prepared, an insulating film (not shown) such as a thermal oxide film or a nitride film is formed on the substrate 105, and an electron beam evaporation or sputtering method is formed thereon. Etc. are used to form the conductor layer 119 (FIG. 3A, step e). Next, the conductor layer 119 is patterned by photolithography or lift-off processing to form a support layer 119c that becomes a part of the support 109 (FIG. 3A, step f). In this embodiment, the support 109 is patterned in the order of Ti / Au / AuSn so that the AuSn alloy layer is in contact with the substrate 105 facing the film-forming substrate 111 using electron beam evaporation. Note that the pattern of the support layer 119c formed on the substrate 105 does not need to be completely matched with the pattern of the support layer 119b formed on the deposition substrate 111, and the alignment accuracy of both substrates is taken into consideration. It is preferable to provide a margin.

  Next, the support layer 119b of the film-forming substrate 111 and the support layer 119c of the substrate 105 are faced to each other, and gold and tin are bonded together by eutectic crystal (FIG. 3B, step g). At this time, pressure may be applied to both substrates. Further, a strong metal bond can be obtained by heating the bonded substrates to bring AuSn in contact with each other into a molten state and lowering the temperature. Thereby, the piezoelectric resonator excellent in joining reliability can be obtained. For example, it is possible to easily join by melting gold tin once at 375 ° C. and 0.3 MPa and solidifying again.

  In this embodiment, an AuSn alloy is used for the support portion 109, but the present invention is not limited to this. For example, when two substrates are bonded together by the support portion 109 being in a semi-molten state or a molten state, the melting point (solidus temperature) is higher than the solder reflow temperature when the piezoelectric resonator is mounted on the motherboard. And higher than the melting point of the electrode material of the piezoelectric resonator. In addition, the support portion 109 may be bonded by diffusion bonding by mutual diffusion of metals below the melting temperature, or may be bonded at room temperature by activating the connection surface by plasma treatment or the like. By bonding at room temperature, the residual thermal stress in the vibration part can be eliminated, and thus a piezoelectric resonator having a high manufacturing yield and a small change with time such as frequency fluctuation can be obtained.

  Next, the film-forming substrate 111 is removed from the formed product obtained by bonding the two substrates (FIG. 3B, step h). For example, the deposition substrate 111 can be removed by dry etching. Through the steps g and h, the formed material originally on the film-forming substrate 111 is transferred to the substrate 105. Next, an electrode film 113 to be the upper electrode 103 is formed on the piezoelectric layer 101 from which the film formation substrate 111 has been removed (FIG. 3B, step i). Then, the electrode film 113 is patterned to form the upper electrode 103 (FIG. 3B, step j). Finally, input / output electrodes and wiring electrodes are formed to complete the piezoelectric resonator shown in FIGS. 1A and 1B.

  In the above manufacturing method, the example in which the electrode film 113 to be the upper electrode 103 is formed last is shown. However, before the piezoelectric layer 101 is formed on the film formation substrate 111, the film formation substrate 111 is formed. An electrode film 113 may be formed thereon. In this case, the upper electrode 103 is formed by patterning the electrode film 113 after removing the film formation substrate 111 in the step h.

  As described above, according to the piezoelectric resonator according to the embodiment of the present invention, since the support portion 109 is separated from the vibrating portion 104, the Q value and Δf can be improved. In particular, by arranging the support portion 109 in a non-rotationally symmetric or non-linearly symmetric arrangement, an unnecessary mode in the horizontal direction is hardly generated, and an effect of reducing unnecessary spurious can be obtained.

(Example of configuration using piezoelectric resonator)
FIG. 4 is a diagram showing an example of a piezoelectric filter circuit using the piezoelectric resonator of the present invention. FIG. 5 is a top view schematically showing a portion surrounded by a dotted line in FIG. The piezoelectric filter circuit shown in FIGS. 4 and 5 includes a series piezoelectric resonator 302 inserted in series between an input / output terminal 301 and a parallel piezoelectric resonator 303 inserted in parallel with a bypass piezoelectric resonator 304 connected in a lattice shape. The parallel piezoelectric resonator 303 is grounded via the inductor 305.

  By substantially matching the resonance frequency of the series piezoelectric resonator 302 and the anti-resonance frequency of the parallel piezoelectric resonator 303, a bandpass characteristic having poles on the low band side and the high band side of the pass band can be realized. Further, by setting the resonance frequency of the bypass piezoelectric resonator 304 to be lower than the resonance frequency of the parallel piezoelectric resonator 303, it is possible to ensure a large attenuation in the stop band without deteriorating the insertion loss in the pass band. It becomes possible.

  Since the resonance frequency of the piezoelectric thin film resonator is inversely proportional to the film thickness, the resonance of each piezoelectric resonator is formed by forming a frequency adjustment layer with an insulating layer such as oxide or nitride after the upper electrode 103 is formed. The frequency can be set to a desired value. By using this frequency adjustment process, it is possible to realize a piezoelectric filter circuit having the above band-pass characteristics and a low-loss and wide-band filter characteristics.

  Further, since the resonator characteristics (Q value, Δf) of the bypass piezoelectric resonator 304 do not greatly affect the filter characteristics, the vibrating portion 104 of the bypass piezoelectric resonator 304 is positioned so as to overlap the support portion 109 in the vertical projection direction. May be arranged. In this case, the wiring member can be reduced by using a part of the support portion 109 as the wiring.

  FIG. 6 is a diagram showing an example of a duplexer using the piezoelectric resonator of the present invention. The duplexer shown in FIG. 6 has a configuration in which two piezoelectric filter circuits shown in FIG. 5 are connected in series. In this duplexer, one input / output terminal 301a is used as a transmission terminal, the other input / output terminal 301b is used as a reception terminal, and the mutually connected input / output terminal 301c is used as an antenna terminal. A phase shift inductor 306 is connected to the input / output terminal 301c as a phase shift circuit.

  In this duplexer, the impedance and phase are adjusted by the phase-shifting inductor 306, the transmission path impedance viewed from the input / output terminal 301c is open in the reception band, and the reception path impedance viewed from the input / output terminal 301c is the transmission band. Is designed to be open. According to this configuration, the isolation between the transmission path and the reception path can be increased.

  FIG. 7 is a diagram illustrating an example of the communication device 420 using the duplexer illustrated in FIG. In the communication device 420 illustrated in FIG. 7, the signal input from the transmission terminal 421 passes through the baseband unit 423, is amplified by the power amplifier (PA) 424, is filtered by the duplexer 425, and is transmitted as a radio wave from the antenna 428. The A signal received by the antenna 428 is filtered by the duplexer 425, amplified by the low noise amplifier (LNA) 427, passed through the baseband unit 423, and transmitted to the reception terminal 422. According to this configuration, it is possible to realize a communication device with low power consumption and low noise.

  The piezoelectric resonator of the present invention can be used for wireless communication devices such as mobile phones and wireless LANs, and in particular, when it is desired to obtain good frequency characteristics by suppressing the vibration of the vibration part from leaking from the support part. Etc. are useful.

The figure which showed typically the structure of the piezoelectric resonator which concerns on one Embodiment of this invention. The figure which showed typically the structure of the piezoelectric resonator which concerns on one Embodiment of this invention. The figure which showed typically the structure of the other piezoelectric resonator which concerns on one Embodiment of this invention. The figure which showed typically the structure of the other piezoelectric resonator which concerns on one Embodiment of this invention. The figure which showed typically the structure of the other piezoelectric resonator which concerns on one Embodiment of this invention. The figure which showed schematically the procedure of the manufacturing method of the piezoelectric resonator of FIG. 1B. The figure which showed schematically the procedure of the manufacturing method of the piezoelectric resonator of FIG. 1B. The figure which shows the example of the piezoelectric filter circuit using the piezoelectric resonator of this invention The figure which showed the structure of the piezoelectric filter circuit of FIG. 4 typically The figure which shows the example of the duplexer using the piezoelectric resonator of this invention The figure which shows the example of the communication apparatus using the piezoelectric resonator of this invention A diagram schematically showing the structure of a conventional piezoelectric resonator A diagram schematically showing the structure of a conventional piezoelectric resonator

Explanation of symbols

101, 701 Piezoelectric layer 102, 103, 702, 703 Electrode 104, 704 Vibrating part 105, 705 Substrate 106, 706 Cavity 107, 707 Input / output electrode 108, 708 Wiring electrode 109 Support part 111 Deposition substrate 112, 113 Electrode Film 119 Conductor layers 119a to 119c Support layer 302 to 304 Piezoelectric resonators 305 and 306 Inductor 420 Communication device 423 Baseband unit 424 Power amplifier (PA)
425 Duplexer 427 Low noise amplifier (LNA)
428 antenna

Claims (9)

A piezoelectric resonator that vibrates at a predetermined frequency,
A piezoelectric layer composed of a piezoelectric thin film;
An upper electrode formed on one main surface of the piezoelectric layer;
A lower electrode formed on the other main surface of the piezoelectric layer;
A substrate,
A support portion provided between the piezoelectric layer and the substrate;
The support portion is provided at a position where neither the lower electrode nor the upper electrode overlaps in the vertical projection direction,
A region where the lower electrode, the piezoelectric layer, and the upper electrode overlap in the vertical projection direction is a vibrating portion,
The support part is provided in a shape and position that is non-rotationally symmetric with respect to the vibration center point of the vibration part, or in a shape and position that is non-symmetrical with respect to a straight line passing through the vibration center point of the vibration part. A piezoelectric resonator, characterized in that   The piezoelectric resonator according to claim 1, wherein the support portion is configured by a plurality of support columns.   The support part is provided at a position where a maximum linear distance to the lower electrode is larger than a maximum linear distance between an outer peripheral end of the upper electrode and an outer peripheral end of the lower electrode. 2. The piezoelectric resonator according to 1.   The piezoelectric resonator according to claim 1, wherein the support portion is made of a conductive material. A method for manufacturing a piezoelectric resonator according to claim 1,
Forming a piezoelectric layer on the first substrate;
Forming a lower electrode on one main surface of the piezoelectric layer;
Forming a first support layer on one main surface of the piezoelectric layer excluding the region where the lower electrode is formed;
Forming a second support layer on the second substrate;
Bonding the first support layer and the second support layer;
Separating the first substrate after the bonding step, and transferring the piezoelectric layer on which the lower electrode is formed from the first substrate to the second substrate;
And a step of forming an upper electrode on the other main surface of the piezoelectric layer that does not overlap with any of the first and second support layer in the vertical projection direction.   The manufacturing method according to claim 5, wherein the bonding step is performed by eutectic crystal bonding between the first support part layer and the second support part layer.   6. The manufacturing method according to claim 5, wherein the first support part layer and the second support part layer are multilayer films containing at least gold tin (AuSn) or gold silicon (AuSi).   A piezoelectric filter comprising a plurality of piezoelectric resonators, comprising at least one piezoelectric resonator according to claim 1.   A duplexer including a transmission filter and a reception filter, wherein the piezoelectric filter according to claim 8 is provided in at least one of the transmission filter and the reception filter.

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