JP2008078984A - Saw device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a SAW device and an electronic apparatus capable of acquiring a high Q value. <P>SOLUTION: The SAW device 10, which is a resonator type, includes: a interdigital transducer (IDT) 20; and reflectors 30, wherein the transducer 20 and the reflectors 30 are placed on a piezoelectric board 12, and the reflectors 30 are arranged at positions where they sandwiches the transducer 20. The piezoelectric board 12 is provided with a quartz plate 14 having an Euler angle (0°, 113-135°, ±(40-49°)). The SAW device 10 sets the ratio η(η=electrode line-width L/inter-electrode pitch P) of the electrode line-width L to inter-electrode pitch P of the interdigital electrode 20 at 0.14 to below 0.22 so as to acquire a high Q value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave (SAW) device and an electronic apparatus.

In the resonator type SAW device, interdigital transducers (IDTs) and reflectors are provided on a quartz plate. In the 1-port SAW device, when an electric signal is supplied to one comb portion constituting the IDT, the SAW is excited on the quartz plate and a standing wave is generated between the reflectors. When the standing wave arrives, the other comb portion constituting the IDT is converted into an electric signal having a frequency corresponding to the frequency of the standing wave and is output. In such a SAW device, the width of the electrode fingers constituting the comb portion (electrode line width) varies, resulting in variations in frequency. For this reason, in the invention disclosed in Patent Document 1, by setting the ratio of the electrode line width and the inter-electrode pitch in the SAW device using the in-plane rotating ST cut quartz plate to 0.5 or more and 0.65 or less, The variation of the resonance frequency with respect to the variation in IDT is reduced.
JP 2003-258601 A

  The above-described SAW device reduces the variation of the resonance frequency, but does not consider the Q value at all. This Q value represents the degree of energy loss, and the higher the value, the smaller the energy loss. For this reason, when the SAW device is a SAW resonator, and this is incorporated in an oscillation circuit, if the Q value is low, there is a possibility that oscillation will not occur because energy loss is large. Further, if the energy loss is large, the power consumed by the oscillation circuit becomes large.

  Since the Q value depends on the oscillation circuit, the value required depends on the oscillation circuit. However, if the Q value is 8000 or more, oscillation is sufficiently possible regardless of the configuration of the oscillation circuit.

  An object of this invention is to provide the SAW device and electronic device which obtain high Q value.

  A SAW device according to the present invention is a resonator-type SAW device in which a piezoelectric plate is provided with a comb electrode and a reflector disposed at a position sandwiching the comb electrode. The piezoelectric plate has an Euler angle of (0 °, 113 ° to 135 °, ± (40 ° to 49 °)), and the ratio η (η = electrode line width L / interelectrode) between the electrode line width L of the interdigital electrode and the pitch P between the electrodes. The pitch P) is 0.14 or more and less than 0.22. As a result, the SAW device can increase the Q value, thereby reducing energy loss and reducing power consumption. If this SAW device is incorporated in an oscillation circuit, it can oscillate reliably regardless of the configuration of the oscillation circuit, and the power consumption of the oscillation circuit can be reduced. Further, since the SAW device uses the Euler angle quartz plate described above, the frequency temperature characteristics can be improved.

  The SAW device according to the present invention is characterized in that a piezoelectric plate provided with interdigital electrodes and reflectors is mounted on a package. Thereby, the SAW device can hold the piezoelectric plate and the like in a stable state, and can be easily mounted on an electronic device.

The electronic apparatus according to the present invention is characterized by mounting the SAW device having the above-described characteristics. As a result, the electronic device can use a signal that is reliably output from the SAW device, and thus can operate stably without causing any malfunction. In addition, power consumption of the electronic device can be reduced.

  The best embodiments of the SAW device and the electronic apparatus according to the present invention will be described below. FIG. 1 is a schematic plan view of a SAW device. In the resonator-type SAW device 10 according to this embodiment, an IDT 20 and a reflector 30 arranged at a position sandwiching the IDT 20 are provided on the piezoelectric plate 12. The piezoelectric plate 12 is an in-plane rotated ST-cut quartz plate 14 whose Euler angles are represented by (0 °, 113 ° to 135 °, ± (40 ° to 49 °)). FIG. 2 is an explanatory view of an in-plane rotated ST-cut quartz plate. The in-plane rotation ST-cut quartz plate 14 rotates the quartz Z plate 18 whose Euler angles are represented by (0 °, 0 °, 0 °) around the X axis by θ = 113 ° to 135 °. The SAW propagation direction is rotated from the X axis by ψ = ± (40 ° to 49 °) in the plane of the quartz plate 16. This in-plane rotated ST-cut quartz plate 14 has a small frequency change with respect to a temperature change, and has a very good frequency-temperature characteristic.

  As shown in FIG. 1, the IDT 20 has a pair of comb portions 22 (22a, 22b) in which the base ends of a plurality of electrode fingers 24 are connected by a bus bar 26, and the electrode fingers 24a constituting one comb portion 22a The electrode fingers 24b constituting the other comb portion 22b are alternately arranged. Further, the reflector 30 is formed by connecting both ends of a plurality of conductor strips 32, and is disposed on both sides of the IDT 20 in the direction in which the SAW propagates. As the electrode material of the IDT 20 and the reflector 30, aluminum, aluminum alloy, gold, silver, tungsten, tantalum, copper, or the like is used.

  In such a SAW device 10, the electrode finger 24 of the IDT 20 is adjusted in order to increase the Q value. FIG. 3 is a schematic cross-sectional view of the SAW device. In addition, the center part of FIG. 3 has shown the cross section of the part which provided IDT20, and the both ends have shown the cross section of the part which provided the reflector 30. FIG. The width (electrode line width) of the electrode fingers 24 of the IDT 20 is L, the inter-electrode pitch of the electrode fingers 24 of the IDT 20 is P, and the height of the electrode fingers 24 of the IDT 20 is H. The width of the conductor strip 32 of the reflector 30 is Lr, and the pitch between the electrodes of the conductor strip 32 of the reflector 30 is Pr.

  FIG. 4 is a graph showing the relationship between the Q value and η. Here, η is a ratio between the electrode line width L of the IDT 20 and the interelectrode pitch P, and η = electrode line width L / interelectrode pitch P. FIG. 4 shows the results of preparing a plurality of SAW devices 10 manufactured by changing the ratio η between the electrode line width L and the interelectrode pitch P of the IDT 20 and measuring the Q value of each SAW device 10. Each SAW device 10 for testing uses an in-plane rotating ST-cut quartz plate 14 whose Euler angles are represented by (0 °, 127 °, 45 °), and H / λ = 0.04 (λ: SAW wavelength), the number of IDT 20 pairs is 180, and the number of reflection gratings (conductor strips) of the reflector 30 is 500.

  As can be seen from FIG. 4, the Q value increases as η decreases, reaches a maximum value when η is 0.166, and decreases as η further decreases. The Q value when η is 0.166 is 8410-8236. The Q value is 8000 or more when η is in the range from 0.14 to 0.22. From these results, the SAW device 10 according to the present embodiment adjusts the IDT 20 so that the ratio η between the electrode line width L and the inter-electrode pitch P is 0.14 or more and less than 0.22.

If the SAW device 10 satisfies 0.14 ≦ η <0.22, the SAW device 10 may have any configuration such as a SAW resonance piece or a SAW filter, and the number of ports is not limited. That is, the SAW device 10 may have one port or a plurality of ports. The SAW device 10 may be a filter or the like in which three IDTs 20 are arranged and acoustically coupled to the SAW.
It should be noted that the ratio ηr between the width Lr of the conductor strip 32 of the reflector 30 and the interelectrode pitch Pr may be approximately the same as η of the IDT 20.

  As described above, since the resonator type SAW device 10 satisfies the relationship of 0.14 ≦ η <0.22, the ratio η between the electrode line width L of the IDT 20 and the pitch P between the electrodes satisfies the Q value. Can be set to a high value of 8000 or more. Thereby, energy loss can be reduced. If this SAW device 10 is incorporated in an oscillation circuit, power consumption can be reduced. Further, the oscillation circuit can oscillate reliably regardless of the circuit configuration. That is, the oscillation circuit including the SAW device 10 can operate stably because of the high Q value.

  Further, since the SAW device 10 uses the in-plane rotation ST-cut quartz plate 14, the frequency temperature characteristics can be improved. That is, the SAW device 10 according to the present embodiment has better frequency temperature characteristics than the SAW device using the ST cut quartz plate.

  Note that the SAW device may have a configuration in which the above-described SAW device 10, that is, the piezoelectric plate 12 including the IDT 20 and the reflector 30 (hereinafter referred to as “piezoelectric plate 12”) is mounted on a package. FIG. 5 is a schematic cross-sectional view of a SAW device in which a piezoelectric plate or the like is accommodated in a package. The SAW device 40 has a package 42 that accommodates the piezoelectric plate 12 and the like. The package 42 includes a package base 44 and a lid 56. The package base 44 has a recessed portion 46 opened upward, and a pad electrode 48 is provided on the bottom surface of the recessed portion 46. An external terminal 50 is provided on the back surface of the package base 44, and the external terminal 50 and the pad electrode 48 are electrically connected. The piezoelectric plate 12 or the like is fixed to the bottom surface of the recessed portion 46 using an adhesive 52 or the like. At this time, the IDT 20 and the reflector 30 (not shown in FIG. 5) face upward, and the wire 54 is joined to the bus bar 26 and the like of the IDT 20 and the pad electrode 48 to conduct them one-to-one. . The lid 56 is fixed to the upper side of the package base 44 and seals the inside of the recessed portion 46. With the SAW device 40 having such a configuration, the piezoelectric plate 12 and the like can be held in a stable state regardless of the state of the external environment, and can be easily mounted on an electronic device.

  The SAW device 40 may be mounted with an IC (integrated circuit) chip. This IC chip includes an oscillation circuit and needs only to be electrically connected to the IDT 20. As a result, the SAW device 40 can supply an electric signal from the IC chip to the IDT 20 and can input a signal output from the IDT 20, so that it becomes a SAW oscillator. The IC chip may include a voltage control circuit in addition to the oscillation circuit. As a result, the SAW device 40 can change the resonance frequency according to the control voltage input to the voltage control circuit, and thus becomes a voltage-controlled SAW oscillator (VCSO). Further, the IC chip can include a temperature compensation circuit and the like in addition to the above-described circuit.

  The SAW devices 10 and 40 described above can be mounted on various electronic devices. As an example of the electronic apparatus, a receiver illustrated in FIG. 6 can be given. The receiver 60 includes a receiving antenna 62, a low noise amplifier (LNA) 64, a mixer 66, a local oscillator 68, an intermediate frequency (IF) amplifier 70, and a detector 72. Specifically, the receiving antenna 62 is connected to the input of the mixer 66 via the LNA 64. A local oscillator 68 is also connected to the input of the mixer 66. The local oscillator 68 includes SAW devices 10 and 40 and an oscillation circuit connected to the SAW devices 10 and 40. As a result, the local oscillator 68 can reliably output the frequency signal to the mixer 66. An IF amplifier 70 and a detector 72 are connected in series to the output of the mixer 66.

  Then, the signal transmitted from the other transmitter is input to the LNA 64 through the receiving antenna 62, amplified by the LNA 64, and then input to the mixer 66. The mixer 66 receives the frequency signal from the local oscillator 68, down-converts the signal input from the LNA 64, and outputs the signal. The down-converted signal is amplified by the IF amplifier 70 and then input to the detector 72 to be detected. With such a configuration, the receiver 60 can receive a signal transmitted from the transmitter. Since the receiver 60 includes the SAW devices 10 and 40 in the local oscillator 68, the power consumption can be reduced.

It is a schematic plan view of a SAW device. It is explanatory drawing of an in-plane rotation ST cut quartz plate. It is a schematic sectional drawing of a SAW device. It is a graph which shows the relationship between Q value and (eta). It is a schematic sectional drawing of the SAW device which accommodated the piezoelectric plate etc. in the package. It is a block diagram of a receiver.

Explanation of symbols

10, 40 ......... SAW device, 12 ...... Piezoelectric plate, 14 ... In-plane rotating ST-cut quartz plate, 20 ...... IDT, 24 ...... Electrode finger, 30 ...... Reflector, 42 ... ...... Package, 44 ......... Package base, 56 ......... Lid, 60 ......... Receiver, 68 ...... Local oscillator.

Claims (3)

A resonator-type SAW device in which a comb-shaped electrode and a reflector disposed at a position sandwiching the comb-shaped electrode are provided on a piezoelectric plate,
The piezoelectric plate is a quartz plate having Euler angles (0 °, 113 ° to 135 °, ± (40 ° to 49 °)),
The ratio η between the electrode line width of the interdigital electrode and the pitch between the electrodes was set to 0.14 or more and less than 0.22.
A SAW device characterized by that.   The SAW device according to claim 1, wherein the piezoelectric plate including the interdigital electrode and the reflector is mounted on a package.   An electronic apparatus comprising the SAW device according to claim 1.

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