JP5045063B2 - Surface acoustic wave resonator - Google Patents

Surface acoustic wave resonator

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JP5045063B2
JP5045063B2 JP2006295149A JP2006295149A JP5045063B2 JP 5045063 B2 JP5045063 B2 JP 5045063B2 JP 2006295149 A JP2006295149 A JP 2006295149A JP 2006295149 A JP2006295149 A JP 2006295149A JP 5045063 B2 JP5045063 B2 JP 5045063B2
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acoustic wave
surface acoustic
wave resonator
region
bus bar
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JP2008113273A (en
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朝尚 田崎
和紀 西村
関　　俊一
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Panasonic Corp
Panasonic Holdings Corp
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Panasonic Corp
Matsushita Electric Industrial Co Ltd
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本発明は、主として移動体通信機器にて使用される弾性表面波共振子に関するものである。   The present invention relates to a surface acoustic wave resonator mainly used in mobile communication equipment.

一般にこの種の弾性表面波共振子としては、図４に示すように、回転ＹカットＸ伝播ＬｉＴａＯ3からなる圧電基板１の上面に形成されたバスバー２と電極指３とからなる櫛型電極４により形成されており、櫛型電極４内にエネルギーを閉じ込める為、バスバー２に切欠き５を所定の間隔で配置したグレーティング領域６を形成し、電極指３が交差する領域７とグレーティング領域６での表面波の伝播速度を異ならせ、導波路状態を形成していた。 Generally, as this type of surface acoustic wave resonator, as shown in FIG. 4, a comb-shaped electrode 4 comprising a bus bar 2 and electrode fingers 3 formed on the upper surface of a piezoelectric substrate 1 made of rotated Y-cut X-propagating LiTaO 3. In order to confine energy in the comb-shaped electrode 4, a grating region 6 in which notches 5 are arranged at a predetermined interval is formed in the bus bar 2, and the region 7 and the grating region 6 where the electrode fingers 3 intersect are formed. The propagation speed of the surface wave was varied to form a waveguide state.

なお、この出願の発明に関する先行技術文献情報としては、例えば、特許文献１が知られている。
特開平１１−２９８２８６号公報 As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.
Japanese Patent Laid-Open No. 11-298286

しかしながら、グレーティング領域６を形成するにあたり切欠き５を複数配置したことで、その部分に圧電基板１の表面が露出した自由表面が形成されてしまい、回転ＹカットＸ伝播ＬｉＴａＯ3からなる圧電基板１を用いた弾性表面波共振子においてはこの自由表面からＳＳＢＷ（Ｓｕｒｆａｃｅ Ｓｋｉｍｍｉｎｇ Ｂｕｌｋ Ｗａｖｅ）が放射されてエネルギー損失が生じてしまうという問題を有していた。 However, when the plurality of notches 5 are arranged in forming the grating region 6, a free surface where the surface of the piezoelectric substrate 1 is exposed is formed in that portion, and the piezoelectric substrate 1 made of rotated Y-cut X-propagating LiTaO 3 is formed. In the surface acoustic wave resonator using the SSBW, there is a problem in that SSBW (Surface Skiing Bulk Wave) is radiated from the free surface to cause energy loss.

本発明は、上記従来の課題を解決するもので、弾性表面波共振子におけるエネルギーの閉じ込み効率を向上させることを目的とするものである。   An object of the present invention is to solve the above-described conventional problems, and to improve energy confinement efficiency in a surface acoustic wave resonator.

上記目的を達成するために本発明は、回転ＹカットＸ伝播ＬｉＴａＯ3からなる圧電基板上と、この圧電基板上に形成された櫛型電極を有し、櫛型電極は一対のバスバーと、それぞれのバスバーから対向するバスバー側に交互に延出された複数の電極指とから構成され、バスバーは伝播方向にその厚みが厚い領域と薄い領域が周期性を持って形成されたグレーティング領域を設けた構成とした。 In order to achieve the above object, the present invention has a piezoelectric substrate made of rotated Y-cut X-propagating LiTaO 3 and a comb-shaped electrode formed on the piezoelectric substrate. The comb-shaped electrode includes a pair of bus bars, The bus bar is provided with a grating region in which a thick region and a thin region are formed with periodicity in the propagation direction. The configuration.

本発明の弾性表面波共振子によれば、弾性表面波共振子におけるエネルギーの閉じ込み効率を向上させることが出来るのである。   According to the surface acoustic wave resonator of the present invention, the energy confinement efficiency in the surface acoustic wave resonator can be improved.

以下、本発明の一実施の形態について図を用いて説明する。   Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

図１は弾性表面波共振子の上面図であり、回転ＹカットＸ伝播ＬｉＴａＯ3からなる圧電基板８上に形成された櫛型電極９が配置された構成で、この櫛型電極９は、一対のバスバー１０ａ，１０ｂと、一方のバスバー１０ａ（１０ｂ）から対向する他方のバスバー１０ｂ（１０ａ）に向けて交互に延出された複数の電極指１１とから構成されている。 FIG. 1 is a top view of a surface acoustic wave resonator in which a comb-shaped electrode 9 formed on a piezoelectric substrate 8 made of rotated Y-cut X-propagating LiTaO 3 is disposed. Bus bars 10a, 10b and a plurality of electrode fingers 11 alternately extended from one bus bar 10a (10b) toward the other bus bar 10b (10a) facing each other.

そして、この弾性表面波共振子においては、バスバー１０ａ，１０ｂにその厚みが厚い領域１２と薄い領域１３が伝播方向に対して周期性を持つよう交互に並べたグレーティング領域１４を形成することにより、弾性表面波共振子のエネルギー閉じ込み効率を向上させている。   In this surface acoustic wave resonator, by forming the grating regions 14 in which the thick regions 12 and the thin regions 13 are alternately arranged in the bus bars 10a and 10b so as to have periodicity in the propagation direction, The energy confinement efficiency of the surface acoustic wave resonator is improved.

すなわち、グレーティング領域１４がバスバー１０ａ（１０ｂ）の厚みが厚い領域１２と薄い領域１３が伝播方向に対して周期性を持つよう交互に並べた構造としたことで、この電極厚みの差を形成することにより図４に示す従来の切欠き５を設ける構造と同様の効果、つまりバスバー１０ａ（１０ｂ）内における伝播速度を遅くできエネルギーの閉じ込み作用が得られるのである。   In other words, the grating region 14 has a structure in which the regions 12 and the thin regions 13 where the bus bar 10a (10b) is thick are alternately arranged so as to have periodicity in the propagation direction, thereby forming this difference in electrode thickness. As a result, the same effect as the structure in which the conventional notch 5 shown in FIG. 4 is provided, that is, the propagation speed in the bus bar 10a (10b) can be reduced, and the energy confining action can be obtained.

さらに、このバスバー１０ａ，１０ｂ内にＳＳＢＷの発生原因となる自由表面を形成する切欠きが形成されていないのでＳＳＢＷの放射が抑制されて、ＳＳＢＷの放射に伴うエネルギー損失を抑制、すなわちエネルギーの閉じ込み効果が向上できるのである。   Further, since the notches forming the free surface that causes SSBW are not formed in the bus bars 10a and 10b, the radiation of the SSBW is suppressed, and the energy loss accompanying the radiation of the SSBW is suppressed, that is, the energy is closed. The effect of embedding can be improved.

また、回転ＹカットＸ伝播ＬｉＴａＯ3からなる圧電基板８で構成した弾性表面波共振子においては、電極指１１が交差する領域１５の伝播速度よりグレーティング領域の伝播速度を遅くすることで、導波路状態を形成しエネルギーの閉じ込み作用を得るものであり、この一実施形態においてはバスバー１０ａ，１０ｂにおける周期を電極指１１の周期より大きくすることで閉じ込み効果をさらに良くしている。 Further, in the surface acoustic wave resonator formed of the piezoelectric substrate 8 made of rotated Y-cut X-propagating LiTaO 3 , the propagation speed of the grating region is made slower than the propagation speed of the region 15 where the electrode fingers 11 intersect, so that the waveguide In this embodiment, the confinement effect is further improved by making the period of the bus bars 10a and 10b larger than the period of the electrode fingers 11.

すなわち、グレーティング領域１４の周期を電極指１１が交差する領域１５の周期より大きくすることで、弾性表面波共振子の周波数特性における共振周波数と反共振周波数との間にグレーティング領域１４の反射特性における中心周波数を設定することができ、弾性表面波共振子にとって必要となる周波数の弾性表面波をグレーティング領域１４において効率よく閉じ込めることが出来るからである。   That is, by making the period of the grating region 14 larger than the period of the region 15 where the electrode fingers 11 intersect, the reflection characteristic of the grating region 14 is between the resonance frequency and the antiresonance frequency in the frequency characteristic of the surface acoustic wave resonator. This is because the center frequency can be set and the surface acoustic wave having the frequency required for the surface acoustic wave resonator can be efficiently confined in the grating region 14.

また、このような弾性表面波共振子において電極指１１やバスバー１０ａ，１０ｂなどの電極はフォトリソで形成することが多く、上述したグレーティング領域を形成する場合、バスバー１０ａ，１０ｂを図２に示されるよう下層電極膜１６と上層電極膜１７の２層構成とし、下層電極膜１６に抜きパターン１８を形成して段差構造とし、この下層電極膜１６および抜きパターン１８を上層電極膜１７で覆う構造とすることで周期性の精度が向上できるのである。   Further, in such a surface acoustic wave resonator, electrodes such as the electrode fingers 11 and the bus bars 10a and 10b are often formed by photolithography, and the bus bars 10a and 10b are shown in FIG. The lower electrode film 16 and the upper electrode film 17 have a two-layer structure, the lower electrode film 16 is formed with a blank pattern 18 to form a stepped structure, and the lower electrode film 16 and the blank pattern 18 are covered with the upper electrode film 17. By doing so, the accuracy of periodicity can be improved.

すなわち、抜きパターン１８のパターンニングが必要となる下層電極膜１６の形成が平坦度の良い圧電基板８上に形成されるため寸法精度がよくなり、パターンニングがなく寸法精度の影響を受けにくい上層電極膜１７を下層電極膜１６上に形成する為、トータルの寸法精度が高くなるからである。   That is, since the formation of the lower electrode film 16 that requires patterning of the punched pattern 18 is formed on the piezoelectric substrate 8 with good flatness, the dimensional accuracy is improved, and there is no patterning and the upper layer is not easily affected by the dimensional accuracy This is because since the electrode film 17 is formed on the lower electrode film 16, the total dimensional accuracy is increased.

また、この一実施の形態における弾性表面波共振子は、グレーティング領域１４をバスバー１０ａ，１０ｂ内に設けた構造を挙げて説明したが、図３に示すようにバスバー１０ａ，１０ｂの電極指１１側端辺部分にグレーティング領域１９を設けても同様の作用効果が得られるものである。   The surface acoustic wave resonator according to this embodiment has been described with reference to the structure in which the grating region 14 is provided in the bus bars 10a and 10b, but as shown in FIG. 3, the electrode fingers 11 side of the bus bars 10a and 10b. Even if the grating region 19 is provided at the end portion, the same effect can be obtained.

なお、この図３に示した弾性表面波共振子では電極指１１の先端からグレーティング領域１９までの距離が、先に述べた図１に示すグレーティング領域１４をバスバー１０ａ，１０ｂ内に設けたものより小さく設定することができ、この部分からのＳＳＢＷの放射を抑制でき、さらにエネルギーの閉じ込み効果を高めることが出来るのである。   In the surface acoustic wave resonator shown in FIG. 3, the distance from the tip of the electrode finger 11 to the grating region 19 is greater than that in which the grating region 14 shown in FIG. 1 is provided in the bus bars 10a and 10b. It can be set small, SSBW radiation from this portion can be suppressed, and the energy confinement effect can be further enhanced.

また、上述した実施形態においては圧電基板上に単一の弾性表面波共振子を配置した構造を例に挙げて説明したが、本発明はこの実施の形態に限定されるものでなく、複数の弾性表面波共振子を適宜組み合わせた形態にでも適応できるものである。   In the above-described embodiment, a structure in which a single surface acoustic wave resonator is disposed on a piezoelectric substrate has been described as an example. However, the present invention is not limited to this embodiment, and a plurality of The present invention can also be applied to a form in which surface acoustic wave resonators are appropriately combined.

本発明に係る弾性表面波共振子は、エネルギーの閉じ込み効率を向上できるという作用を有し、主として移動体通信機器に用いられる弾性表面波フィルタに使用される弾性表面波共振子において有用となるものである。   The surface acoustic wave resonator according to the present invention has an effect that energy confinement efficiency can be improved, and is useful in a surface acoustic wave resonator mainly used for a surface acoustic wave filter used in a mobile communication device. Is.

本発明の一実施の形態における弾性表面波共振子の模式図1 is a schematic diagram of a surface acoustic wave resonator according to an embodiment of the present invention. 図１におけるＸ−Ｘ線断面図XX sectional view in FIG. 他の実施の形態における弾性表面波共振子の模式図Schematic diagram of a surface acoustic wave resonator according to another embodiment 従来の弾性表面波共振子の模式図Schematic diagram of a conventional surface acoustic wave resonator

符号の説明Explanation of symbols

８ 圧電基板
９ 櫛型電極
１０ａ，１０ｂ バスバー
１１ 電極指
１２ 厚い領域
１３ 薄い領域
１４ グレーティング領域
１６ 下層電極膜
１７ 上層電極膜 8 Piezoelectric substrate 9 Comb electrodes 10a, 10b Bus bar 11 Electrode finger 12 Thick region 13 Thin region 14 Grating region 16 Lower electrode film 17 Upper electrode film

Claims (3)

ＬｉＴａＯ 3 からなる圧電基板と、この圧電基板上に形成された櫛型電極を有し、前記櫛型電極は一対のバスバーと、前記それぞれのバスバーから対向するバスバー側に交互に延出された複数の電極指とから構成され、前記バスバーは前記伝播方向にその厚みが厚い領域と薄い領域が周期性を持って形成されたグレーティング領域を有し、前記バスバーにおける前記グレーティングの周期を前記電極指の周期より大きくしたことを特徴とする弾性表面波共振子。 A piezoelectric substrate made of LiTaO 3, has a comb electrode formed on the piezoelectric substrate, a plurality the comb electrode which extends alternately to the bus bar side facing the pair of bus bars, from said each of the bus bars The bus bar has a grating region in which a thick region and a thin region are formed with periodicity in the propagation direction, and the period of the grating in the bus bar is defined by the electrode finger. A surface acoustic wave resonator having a larger period. 回転ＹカットＸ伝播ＬｉＴａＯRotating Y-cut X-propagating LiTaO 3Three からなる圧電基板と、この圧電基板上に形成された櫛型電極を有し、前記櫛型電極は一対のバスバーと、前記それぞれのバスバーから対向するバスバー側に交互に延出された複数の電極指とから構成され、前記バスバーは前記伝播方向にその厚みが厚い領域と薄い領域が周期性を持って形成されたグレーティング領域を有し、前記バスバーにおける前記グレーティングの周期を前記電極指の周期より大きくしたことを特徴とする弾性表面波共振子。A comb-shaped electrode formed on the piezoelectric substrate, and the comb-shaped electrode has a pair of bus bars and a plurality of electrodes alternately extended from the respective bus bars to the opposite bus bar side. The bus bar has a grating region in which a thick region and a thin region are formed with periodicity in the propagation direction, and the period of the grating in the bus bar is greater than the period of the electrode finger. A surface acoustic wave resonator characterized by being enlarged. 前記グレーティング領域の反射特性の中心周波数を、前記弾性表面波共振子の共振周波数と反共振周波数との間に設けた請求項１または請求項２に記載の弾性表面波共振子。 The surface acoustic wave resonator according to claim 1 , wherein a center frequency of reflection characteristics of the grating region is provided between a resonance frequency and an anti-resonance frequency of the surface acoustic wave resonator.
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