JP2008103913A - Surface acoustic wave filter - Google Patents
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本発明は、圧電基板の異方性と相まって弾性表面波を一方向に発生させるナチュラル単相型一方向性変換器を用いた弾性表面波フィルタに関する。 The present invention relates to a surface acoustic wave filter using a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction combined with anisotropy of a piezoelectric substrate.
通信装置の高性能化に伴い、弾性表面波フィルタの低損失化、高周波化が求められている。この要求に応えるために、従来から弾性表面波フィルタの挿入損失低下と良好な位相及び周波数特性を実現する一方向性変換器が用いられている。 As the performance of communication devices increases, the surface acoustic wave filter is required to have low loss and high frequency. In order to meet this requirement, conventionally, a unidirectional converter that achieves a reduction in insertion loss of a surface acoustic wave filter and good phase and frequency characteristics has been used.
一方向性変換器にはいくつかの種類があり、すだれ状電極構造の非対称性、質量負荷効果による内部反射を用いたもの、反射バンクを配置したもの、浮き電極による反射を用いたもの、圧電基板の異方性を利用したもの等が知られている。これらの一方向性変換器を用いた弾性表面波フィルタでは、励振波と、反射波との位相差が、前進方向では同位相になり、それと反対の方向では逆位相となることによって方向性を持たせるようにしている。 There are several types of unidirectional transducers: asymmetry of interdigital electrode structure, internal reflection due to mass load effect, reflection bank, reflection using floating electrode, piezoelectric Those utilizing the anisotropy of the substrate are known. In the surface acoustic wave filter using these unidirectional transducers, the phase difference between the excitation wave and the reflected wave is the same in the forward direction and is opposite in the opposite direction. I try to have it.
特に、特許文献1には、ランガサイト単結晶基板の異方性によって電極ピッチや電極幅がλ/4の通常の電極を用いて一方向性を持たせたナチュラル単相型一方向性変換器NSPUDT(Natural Single Phase Unidirectional Transducer:以下、一方向性変換器という。)が開示されている。
In particular,
一般に、圧電基板の単結晶に対して基板表面をどの角度に設定し、弾性表面波を基板表面のどの方向に伝搬させるかによって、例えば、弾性表面波速度(Vs)、電気機械結合係数(k2)、遅延時間温度係数(TCD)、異方性定数(γ)、パワーフロー角(PFA)などの圧電性基板の各特性が変化する。 In general, depending on which angle the substrate surface is set with respect to the single crystal of the piezoelectric substrate and in which direction the surface acoustic wave is propagated, for example, the surface acoustic wave velocity (Vs), the electromechanical coupling coefficient (k 2 ) The characteristics of the piezoelectric substrate such as the delay time temperature coefficient (TCD), the anisotropy constant (γ), and the power flow angle (PFA) change.
パワーフロー角とは、すだれ電極によって弾性表面波が励振されたときに伝搬する位相速度と群速度の方向の違いを表す角度である。異方性を有する基板では弾性表面波の伝搬する伝搬速度(音速)が不均一となるため、例えば音速の大きな方向に伝搬する弾性表面波は音速の小さい方向に伝搬する弾性表面波に引きずられて弾性表面波の位相速度伝搬方向と弾性表面波のエネルギー伝搬方向である群速度伝搬方向とが異なる現象が発生する。 The power flow angle is an angle representing the difference between the direction of the phase velocity and the group velocity that propagates when a surface acoustic wave is excited by the interdigital transducer. Since the propagation velocity (sound speed) of propagation of surface acoustic waves is non-uniform in an anisotropic substrate, for example, surface acoustic waves propagating in the direction of high sound velocity are dragged by surface acoustic waves propagating in the direction of low sound velocity. Therefore, a phenomenon occurs in which the phase velocity propagation direction of surface acoustic waves differs from the group velocity propagation direction, which is the energy propagation direction of surface acoustic waves.
ここで、ランガサイト単結晶は水晶と同じ三方晶系であり電気機械結合係数が水晶よりも大きく(タンタル酸リチウムやニオブ酸リチウムに比べると小さい)、周波数温度安定性に優れ、すだれ状電極を形成するのに適した表面加工が容易である。例えば、所定のカット角で切り出されたランガサイト単結晶の基板は、弾性表面波が伝搬するときに波が拡がらないという性質(異方性定数γ=−1)を有しており、パワーフロー角も小さく、位相速度伝搬方向と群速度伝搬方向とが同じ方向にそろえ易いことから弾性表面波フィルタの基板として注目されている。 Here, the Langasite single crystal is the same trigonal system as quartz, has an electromechanical coupling coefficient larger than that of quartz (smaller than that of lithium tantalate and lithium niobate), is excellent in frequency temperature stability, and has an interdigital electrode. Surface processing suitable for forming is easy. For example, a Langasite single crystal substrate cut out at a predetermined cut angle has a property (anisotropy constant γ = −1) that a wave does not spread when a surface acoustic wave propagates. Since the flow angle is small and the phase velocity propagation direction and the group velocity propagation direction are easily aligned in the same direction, it has been attracting attention as a substrate for a surface acoustic wave filter.
特許文献2には、例えば指定範囲の中間に近い条件において、オイラー角表示で(0°,135°,28°)で切り出されたランガサイト単結晶基板は好適な結果が得られることが示されており、γ=−1、パワーフロー角がほぼ0°付近であることも示されている。
また、携帯型通信装置の小型化に伴い、回路の小型化に寄与する弾性表面波フィルタの低損失化が望まれている。本発明者は挿入損失の低減化の実現方法として、電極指のピッチが伝搬方向と直交する方向で変化する扇型のすだれ状電極指(傾斜型すだれ状電極指)を用いて低損失フィルタを実現している。なお、傾斜型すだれ状電極指(Slanted Finger IDT:SFIT)以下、斜め電極指という。 In addition, with the miniaturization of portable communication devices, it is desired to reduce the loss of surface acoustic wave filters that contribute to circuit miniaturization. As a method for realizing a reduction in insertion loss, the present inventor uses a fan-shaped interdigital electrode finger (tilted interdigital electrode finger) in which the pitch of the electrode finger changes in a direction orthogonal to the propagation direction, Realized. In addition, the slanted interdigital electrode finger (Slanted Finger IDT: SFIT) is hereinafter referred to as an oblique electrode finger.
斜め電極指を有する弾性表面波フィルタにおいて、低損失化の手法の一つとして一方向性電極を用いることがある。 In a surface acoustic wave filter having oblique electrode fingers, a unidirectional electrode is sometimes used as one of techniques for reducing loss.
ランガサイト単結晶基板は自然一方向性を有しており、基板上に1/4λピッチのシングル電極指を形成することで、容易に一方向の弾性表面波を送信(入力)させることができる。しかし、シングル電極指では同じ方向にしか弾性表面波が進まないため、シングル電極指を用いて弾性表面波を受信(出力)することができない。そこで、受信側の電極指にはダブル電極指、もしくは反転一方向電極指にする必要があり、入力側と出力側とで電極構造指の異なる弾性表面波フィルタが必要となる。 The langasite single crystal substrate has natural unidirectionality, and by forming a single electrode finger of 1 / 4λ pitch on the substrate, it is possible to easily transmit (input) a unidirectional surface acoustic wave. . However, since a surface acoustic wave travels only in the same direction with a single electrode finger, the surface acoustic wave cannot be received (output) using the single electrode finger. Therefore, the electrode finger on the receiving side needs to be a double electrode finger or an inverted one-way electrode finger, and surface acoustic wave filters having different electrode structure fingers on the input side and the output side are required.
一般的に電極指構造が異なると弾性表面波の伝搬速度(平均音速)が変化する。この原因は、例えば、非特許文献1で示されているエネルギー蓄積効果等が考えられる。このエネルギー蓄積効果により、基板表面上に形成された電極端部からの非放射バルク波が、弾性表面波の平均速度を低下させている。しかし、この平均音速の変化量は数十程度の電極指対数では特性に変化は見られないが、電極指対数を数百程度に増やすと特性劣化が生じるという問題があった。
Generally, when the electrode finger structure is different, the propagation speed (average sound speed) of the surface acoustic wave changes. The cause of this may be, for example, the energy storage effect shown in
そこで、本発明では、電極指対数を数百対程度に増やすことを可能とする弾性表面波フィルタを提供することをその目的の一つとする。 Accordingly, an object of the present invention is to provide a surface acoustic wave filter that can increase the number of electrode finger pairs to about several hundred pairs.
以上のような目的を達成するために、本発明に係る弾性表面波フィルタは、圧電基板の異方性と相まって弾性表面波を一方向に発生させるナチュラル単相型一方向性変換器となるすだれ状の入力電極指と、発生した弾性表面波を信号として取り出す方向性反転変換器となるすだれ状の出力電極指と、を有する弾性表面波フィルタにおいて、入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指のピッチを変化させて補正することを特徴とする。 In order to achieve the above-described object, the surface acoustic wave filter according to the present invention can be a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction coupled with the anisotropy of the piezoelectric substrate. Averaged due to the difference in input and output electrode finger structures in a surface acoustic wave filter having an interdigital input electrode finger and an interdigital output electrode finger serving as a directional reversal converter that extracts the generated surface acoustic wave as a signal The difference in sound speed is corrected by changing the pitch of each electrode finger.
また、本発明に係る弾性表面波フィルタは、圧電基板の異方性と相まって弾性表面波を一方向に発生させるナチュラル単相型一方向性変換器となるすだれ状の入力電極指と、発生した弾性表面波を信号として取り出す方向性反転変換器となるすだれ状の出力電極指と、を有する弾性表面波フィルタにおいて、入力電極指は、それぞれの幅がλ/4の正電極指及び負電極指をλ/4のエッジ間隔をおいて交互に配置した斜め電極指を形成するシングル電極指であり、出力電極指は、それぞれの電極指の幅がλ/8の正電極指及び負電極指を二本づつエッジ間隔がλ/8となるように交互にすだれ状に配置した斜め電極指を形成するダブル電極指であり、入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指のピッチを変化させて補正することを特徴とする。 In addition, the surface acoustic wave filter according to the present invention is generated with interdigital input electrode fingers that are natural single-phase unidirectional transducers that generate surface acoustic waves in one direction combined with the anisotropy of the piezoelectric substrate. In a surface acoustic wave filter having interdigital output electrode fingers serving as directional inversion converters that extract surface acoustic waves as signals, the input electrode fingers are positive electrode fingers and negative electrode fingers each having a width of λ / 4. Is a single electrode finger that forms diagonal electrode fingers alternately arranged with an edge interval of λ / 4, and the output electrode fingers are positive electrode fingers and negative electrode fingers each having a width of λ / 8. Double electrode fingers that form diagonal electrode fingers alternately arranged in an interdigital pattern so that the edge interval is λ / 8, and the difference in average sound speed caused by the difference in input and output electrode finger structures Changing the pitch of the finger And correcting Te.
さらに、本発明に係る弾性表面波フィルタは、圧電基板の異方性と相まって弾性表面波を一方向に発生させるナチュラル単相型一方向性変換器となるすだれ状の入力電極指と、発生した弾性表面波を信号として取り出す方向性反転変換器となるすだれ状の出力電極指と、を有する弾性表面波フィルタにおいて、入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指のメタライズ比を変化させて補正することを特徴とする。 Furthermore, the surface acoustic wave filter according to the present invention has a comb-like input electrode finger that forms a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction coupled with the anisotropy of the piezoelectric substrate. In a surface acoustic wave filter having interdigital output electrode fingers serving as directional reversal converters that extract surface acoustic waves as signals, the difference in average sound speed caused by the difference in input and output electrode finger structures is obtained. The correction is performed by changing the metallization ratio.
さらにまた、本発明に係る弾性表面波フィルタは、圧電基板の異方性と相まって弾性表面波を一方向に発生させるナチュラル単相型一方向性変換器となるすだれ状の入力電極指と、発生した弾性表面波を信号として取り出す方向性反転変換器となるすだれ状の出力電極指と、を有する弾性表面波フィルタにおいて、入力電極指は、それぞれの幅がλ/4の正電極指及び負電極指をλ/4のエッジ間隔をおいて交互に配置した斜め電極指を形成するシングル電極指であり、出力電極指は、それぞれの電極指の幅がλ/8の正電極指及び負電極指を二本づつエッジ間隔がλ/8となるように交互にすだれ状に配置した斜め電極指を形成するダブル電極指であり、入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指のメタライズ比を変化させて補正する。 Furthermore, the surface acoustic wave filter according to the present invention includes a comb-like input electrode finger that forms a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction coupled with the anisotropy of the piezoelectric substrate, In a surface acoustic wave filter having interdigital output electrode fingers serving as directional reversal converters that extract the generated surface acoustic waves as signals, the input electrode fingers are positive electrode fingers and negative electrodes each having a width of λ / 4 A single electrode finger that forms diagonal electrode fingers in which fingers are alternately arranged with an edge interval of λ / 4, and the output electrode fingers are positive electrode fingers and negative electrode fingers each having a width of λ / 8 Are double electrode fingers that form diagonal electrode fingers alternately arranged in an interdigital pattern so that the edge interval is λ / 8, and the difference in average sound speed caused by the difference in input and output electrode finger structures. Electrode finger metallization Changing the ratio to correct.
さらにまた、本発明に係る弾性表面波フィルタは、圧電基板の異方性と相まって弾性表面波を一方向に発生させるナチュラル単相型一方向性変換器となるすだれ状の入力電極指と、発生した弾性表面波を信号として取り出す方向性反転変換器となるすだれ状の出力電極指と、を有する弾性表面波フィルタにおいて、入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指の膜厚を変化させて補正することを特徴とする。 Furthermore, the surface acoustic wave filter according to the present invention includes a comb-like input electrode finger that forms a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction coupled with the anisotropy of the piezoelectric substrate, In a surface acoustic wave filter having interdigital output electrode fingers that serve as directional inversion converters that extract the generated surface acoustic waves as signals, the difference in average sound speed caused by the difference in input and output electrode finger structures is measured for each electrode finger. The film thickness is corrected by changing the film thickness.
さらにまた、本発明に係る弾性表面波フィルタは、圧電基板の異方性と相まって弾性表面波を一方向に発生させるナチュラル単相型一方向性変換器となるすだれ状の入力電極指と、発生した弾性表面波を信号として取り出す方向性反転変換器となるすだれ状の出力電極指と、を有する弾性表面波フィルタにおいて、入力電極指は、それぞれの幅がλ/4の正電極指及び負電極指をλ/4のエッジ間隔をおいて交互に配置した斜め電極指を形成するシングル電極指であり、出力電極指は、それぞれの電極指の幅がλ/8の正電極指及び負電極指を二本づつエッジ間隔がλ/8となるように交互にすだれ状に配置した斜め電極指を形成するダブル電極指であり、入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指の膜厚を変化させて補正することを特徴とする。 Furthermore, the surface acoustic wave filter according to the present invention includes a comb-like input electrode finger that forms a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction coupled with the anisotropy of the piezoelectric substrate, In a surface acoustic wave filter having interdigital output electrode fingers serving as directional reversal converters that extract the generated surface acoustic waves as signals, the input electrode fingers are positive electrode fingers and negative electrodes each having a width of λ / 4 A single electrode finger that forms diagonal electrode fingers in which fingers are alternately arranged with an edge interval of λ / 4, and the output electrode fingers are positive electrode fingers and negative electrode fingers each having a width of λ / 8 Are double electrode fingers that form diagonal electrode fingers alternately arranged in an interdigital pattern so that the edge interval is λ / 8, and the difference in average sound speed caused by the difference in input and output electrode finger structures. Change the film thickness of the electrode fingers It is allowed and correcting it.
本発明を用いると、電極指対数を数百対程度に増やすと特性が劣化するという従来の弾性表面波フィルタの問題を解決することができ、電極指対数を増やした場合においても、特性の劣化を防止することができるという効果がある。 By using the present invention, it is possible to solve the problem of the conventional surface acoustic wave filter that the characteristics are deteriorated when the number of electrode finger pairs is increased to several hundred pairs. Even when the number of electrode finger pairs is increased, the characteristics are deteriorated. There is an effect that can be prevented.
以下、本発明の実施の形態(以下実施形態という)を、図面に従って説明する。 Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
図1には、第一の実施形態に係る弾性表面波フィルタ10の概略構成が示されている。弾性表面波フィルタ10は、ランガサイト単結晶基板18上に入力側斜め電極指11,12と、出力側斜め電極指13,14と、を有している。
FIG. 1 shows a schematic configuration of a surface
入力側斜め電極指11,12は、それぞれの電極指の幅がλ/4の正電極指及び負電極指をλ/4のエッジ間隔をおいて交互に配置したシングル電極指である。さらに、出力側斜め電極指13,14は、それぞれの電極指の幅がλ/8の正電極指及び負電極指を二本づつエッジ間隔がλ/8となるように交互にすだれ状に配置した斜め電極指を形成するダブル電極指である。なお、斜め電極指11,13は入出力となる正電極指であり、斜め電極指12,14は接地された負電極指である。
The input-side
また、図1に示すように、入力側斜め電極指11,12と出力側斜め電極指13,14とは、隣り合う電極指同士(11と12,13と14)の中心間隔が弾性表面波の伝搬方向(図中X軸方向)に直交する方向(図中Y軸方向)に変化するよう形成されており、入力信号により励振される弾性表面波は、入力信号の周波数に応じて異なる領域(ΔY1,ΔY2,・・ΔYS)を伝搬する。
Further, as shown in FIG. 1, the input side
図2には、弾性表面波の伝搬方向と平行な複数のチャンネルにより構成される横軸周波数、縦軸振幅を示す各フィルタ特性図が示されている。図の縦方向には、1−ch,i−ch,・・・,S−chまでの各フィルタ特性図が示され、横方向には、入力側斜め電極指11,12と出力側斜め電極指13,14及び各斜め電極指によって得られたサブフィルタと、サブフィルタの総和が右下のSFITに示されている。本実施形態における弾性表面波フィルタ(SFIT)の特性は、サブフィルタの総和で示される特性となり、周波数f1〜fSはフィルタ特性の通過帯域を示している。
FIG. 2 is a filter characteristic diagram showing a horizontal axis frequency and a vertical axis amplitude composed of a plurality of channels parallel to the propagation direction of the surface acoustic wave. In the vertical direction of the figure, filter characteristic diagrams of 1-ch, i-ch,..., S-ch are shown, and in the horizontal direction, the input-side
次に、斜め電極指対数の違いによるフィルタ特性の変化を図3と図4を用いて示す。図中上段のグラフはフィルタの全特性を示すために、挿入損失のスケールを大きくとり、下段のグラフは、挿入損失のスケールを拡大している。また、図中の実線は入力側斜め電極指を通過する弾性表面波の平均音速と出力側斜め電極指を通過する弾性表面波の平均音速が等しい場合を示し、破線は入力側斜め電極指を通過する弾性表面波の平均音速と出力側斜め電極指を通過する弾性表面波の平均音速が0.5%ずれた場合のフィルタ特性を示している。 Next, changes in filter characteristics due to the difference in the number of diagonal electrode finger pairs will be described with reference to FIGS. In the figure, the upper graph shows a large insertion loss scale to show all the characteristics of the filter, and the lower graph enlarges the insertion loss scale. The solid line in the figure shows the case where the average sound velocity of the surface acoustic wave passing through the input side oblique electrode finger is equal to the average sound velocity of the surface acoustic wave passing through the output side oblique electrode finger, and the broken line shows the input side oblique electrode finger. The filter characteristics when the average sound velocity of the surface acoustic wave passing through and the average sound velocity of the surface acoustic wave passing through the output-side oblique electrode finger are shifted by 0.5% are shown.
図3には、入力側斜め電極指の対数が200、出力側斜め電極指の対数が180の“少電極指対数”フィルタ特性が示されている。また、図4には、電極指対数を増やし、入力側斜め電極指の対数が900、出力側斜め電極指の対数が700の場合の“多電極指対数”フィルタ特性が示されている。図3,図4とも中心周波数は380MHzを示し、各フィルタの特性を表1に示す。なお、平均音速と中心周波数との関係は平均波長λ=平均音速(v)/中心周波数(f)によって求めることができる。 FIG. 3 shows the “small number of electrode finger pairs” filter characteristic in which the number of pairs of input side oblique electrode fingers is 200 and the number of pairs of output side oblique electrode fingers is 180. FIG. 4 shows the “multi-electrode finger pair” filter characteristics when the number of electrode finger pairs is increased, the number of input side oblique electrode fingers is 900, and the number of output side oblique electrode fingers is 700. 3 and 4, the center frequency is 380 MHz, and the characteristics of each filter are shown in Table 1. The relationship between the average sound speed and the center frequency can be obtained by the average wavelength λ = average sound speed (v) / center frequency (f).
ダイナミックレンジを90dBとすると、図3の少電極指対数では中心周波数に対して通過周波数帯域幅が±8MHzとなるが、図4の多電極指対数では、挿入損失は少し劣るものの中心周波数に対する通過周波数帯域幅が±4MHzと狭くなり、フィルタの肩特性が向上している。 When the dynamic range is 90 dB, the pass frequency bandwidth is ± 8 MHz with respect to the center frequency in the case of the few electrode finger pairs in FIG. The frequency bandwidth is as narrow as ± 4 MHz, and the shoulder characteristics of the filter are improved.
次に、平均音速のずれによる影響を考察すると、図3の少電極指対数では挿入損失における実線と破線の差がほとんど無い(0.5dB程度)状態であるが、図4の多電極指対数では、平均音速のずれにより挿入損失が実線より3.5dB低い値を示している。このずれは、パワーフロー角の補正を行っても発生することから、従来の特性低下要因とは異なっていると考えられる。 Next, considering the influence of the deviation of the average sound speed, the number of small electrode finger pairs in FIG. 3 is in a state where there is almost no difference between the solid line and the broken line in insertion loss (about 0.5 dB), but the number of multi-electrode finger pairs in FIG. Shows a value where the insertion loss is 3.5 dB lower than the solid line due to the deviation of the average sound velocity. Since this deviation occurs even when the power flow angle is corrected, it is considered that this deviation is different from the conventional characteristic deterioration factor.
そこで、本発明者は、弾性表面波の平均波長を構成する電極指間のピッチを入力側斜め電極指と出力側斜め電極指とでそれぞれ異らせ、弾性表面波の伝搬速度が0.25%〜0.75%ずれるのを補正する構造とすることで、図4に示される挿入損失の低下を防止した。これは、平均波長の微妙な音速のずれが、弾性表面波フィルタの特性に影響するためである。 Therefore, the present inventor makes the pitch between the electrode fingers constituting the average wavelength of the surface acoustic wave different between the input side oblique electrode finger and the output side oblique electrode finger, and the propagation speed of the surface acoustic wave is 0.25. By adopting a structure that corrects the deviation of 0.75% to 0.75%, the reduction in insertion loss shown in FIG. 4 is prevented. This is because a subtle difference in sound speed of the average wavelength affects the characteristics of the surface acoustic wave filter.
図5には、第二の実施形態に係る弾性表面波フィルタ10の概略構成が示されている。弾性表面波フィルタ10は、ランガサイト単結晶基板18上に入力側斜め電極指11,12と、方向性反転電極で構成される出力側斜め電極指15,16、浮き電極17と、を有している。ここで、両斜め電極指12,16は接地されている。方向性反転電極の電極幅と間隔の関係は、図5の出力側斜め電極指(15,16,17)に示しているように、左からλ/10,λ/10,λ/5,λ/10,λ/10,λ/10,λ/5,λ/10とし、かつ、弾性表面波の平均波長を構成する電極指間のピッチを入力側斜め電極指と出力側斜め電極指とでそれぞれ異らせ、弾性表面波の伝搬速度が0.25%〜0.75%ずれるのを補正する構造とした。また、一般的に弾性表面波の伝搬速度は、0.5%程度ずれている。
FIG. 5 shows a schematic configuration of the surface
以上、上述したように本実施形態を用いることにより、電極指対数を数百対程度に増やすと特性が劣化するという従来の弾性表面波フィルタの問題を解決することができ、電極対数を増やした場合においても、特性の劣化を防止することができる。また、斜め電極指のメタライズ比あるいは膜厚(高さ)をエッチング加工やレーザ加工により変化させることにより、弾性表面波の平均音速を入力側と出力側で変化させて補正することも可能である。レーザ加工を用いる場合には、電極指に用いる材質はレーザ光の吸収率が良好でレーザ光による熱伝導が大きい材質(Cr,Ni,Ta,Fr,Cu等)が良く、使用するレーザとしては短時間で大きなパワーが得られるArFマキシマレーザやYAGレーザ等が好適である。 As described above, by using this embodiment as described above, it is possible to solve the problem of the conventional surface acoustic wave filter that the characteristics deteriorate when the number of electrode finger pairs is increased to several hundred pairs, and the number of electrode pairs is increased. Even in the case, the deterioration of the characteristics can be prevented. In addition, by changing the metallization ratio or the film thickness (height) of the oblique electrode fingers by etching or laser processing, it is also possible to correct by changing the average sound velocity of the surface acoustic wave between the input side and the output side. . In the case of using laser processing, the material used for the electrode fingers is preferably a material (Cr, Ni, Ta, Fr, Cu, etc.) that has a good absorption rate of laser light and a large heat conduction by the laser light. An ArF maxima laser, a YAG laser, or the like that can obtain a large power in a short time is suitable.
なお、本実施形態においては、弾性表面波の平均波長を構成する電極指間のピッチを入力側斜め電極指と出力側斜め電極指とで平均音速が一致するようにそれぞれ異らせたが、これに限定するものではなく、入力側すだれ電極指又は出力側すだれ電極指のピッチを固定して他方のピッチを増減してそれぞれの平均音速を補正してもよいし、電極の厚みを変えることで対応してもよい。また、変化量もこの値に限定するものではなく、弾性表面波フィルタ毎に適正な値を設定してもよい。 In the present embodiment, the pitch between the electrode fingers constituting the average wavelength of the surface acoustic wave is changed so that the average sound speed is the same between the input side oblique electrode finger and the output side oblique electrode finger. However, the present invention is not limited to this, and the pitch of the input interdigital transducer or the output interdigital transducer may be fixed and the other pitch may be increased or decreased to correct the average sound velocity, or the thickness of the electrode may be changed. You may respond with. Also, the amount of change is not limited to this value, and an appropriate value may be set for each surface acoustic wave filter.
さらにまた、本実施形態では、ランガサイト基板を用いたシングル電極指、ダブル電極指、方向性反転電極指等を用いて説明したが、これに限定するものではなく、その他の基板やアポタイズ電極指等を用いても好適的に実施可能である。 Furthermore, in the present embodiment, description has been made using a single electrode finger, a double electrode finger, a direction-inverted electrode finger, etc. using a langasite substrate, but the present invention is not limited to this, and other substrates and apodized electrode fingers are used. Etc. can also be suitably implemented.
10 弾性表面波フィルタ、11,12 入力側斜め電極指、13,14,15,16 出力側斜め電極指、17 浮き電極、18 ランガサイト単結晶基板。
DESCRIPTION OF
Claims (6)
入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指のピッチを変化させて補正することを特徴とする弾性表面波フィルタ。 Interdigital input electrode fingers that form a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction combined with the anisotropy of the piezoelectric substrate, and a directional inversion transducer that extracts the generated surface acoustic wave as a signal In a surface acoustic wave filter having interdigital output electrode fingers,
A surface acoustic wave filter characterized in that a difference in average sound velocity caused by a difference in input / output electrode finger structure is corrected by changing a pitch of each electrode finger.
入力電極指は、それぞれの幅がλ/4の正電極指及び負電極指をλ/4のエッジ間隔をおいて交互に配置した斜め電極指を形成するシングル電極指であり、
出力電極指は、それぞれの電極指の幅がλ/8の正電極指及び負電極指を二本づつエッジ間隔がλ/8となるように交互にすだれ状に配置した斜め電極指を形成するダブル電極指であり、
入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指のピッチを変化させて補正することを特徴とする弾性表面波フィルタ。 Interdigital input electrode fingers that form a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction combined with the anisotropy of the piezoelectric substrate, and a directional inversion transducer that extracts the generated surface acoustic wave as a signal In a surface acoustic wave filter having interdigital output electrode fingers,
The input electrode fingers are single electrode fingers that form oblique electrode fingers in which positive electrode fingers and negative electrode fingers each having a width of λ / 4 are alternately arranged with an edge interval of λ / 4,
The output electrode fingers are formed as diagonal electrode fingers in which the positive electrode fingers and the negative electrode fingers each having a width of λ / 8 are alternately arranged in an interdigital shape so that the edge interval is λ / 8. Double electrode fingers,
A surface acoustic wave filter characterized in that a difference in average sound velocity caused by a difference in input / output electrode finger structure is corrected by changing a pitch of each electrode finger.
入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指のメタライズ比を変化させて補正することを特徴とする弾性表面波フィルタ。 Interdigital input electrode fingers that form a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction combined with the anisotropy of the piezoelectric substrate, and a directional inversion transducer that extracts the generated surface acoustic wave as a signal In a surface acoustic wave filter having interdigital output electrode fingers,
A surface acoustic wave filter characterized in that a difference in average sound speed caused by a difference in input and output electrode finger structures is corrected by changing a metallization ratio of each electrode finger.
入力電極指は、それぞれの幅がλ/4の正電極指及び負電極指をλ/4のエッジ間隔をおいて交互に配置した斜め電極指を形成するシングル電極指であり、
出力電極指は、それぞれの電極指の幅がλ/8の正電極指及び負電極指を二本づつエッジ間隔がλ/8となるように交互にすだれ状に配置した斜め電極指を形成するダブル電極指であり、
入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指のメタライズ比を変化させて補正することを特徴とする弾性表面波フィルタ。 Interdigital input finger that is a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction combined with the anisotropy of the piezoelectric substrate, and a directional inversion transducer that extracts the generated surface acoustic wave as a signal In a surface acoustic wave filter having interdigital output electrode fingers,
The input electrode fingers are single electrode fingers that form oblique electrode fingers in which positive electrode fingers and negative electrode fingers each having a width of λ / 4 are alternately arranged with an edge interval of λ / 4,
The output electrode fingers are formed as diagonal electrode fingers in which the positive electrode fingers and the negative electrode fingers each having a width of λ / 8 are alternately arranged in an interdigital shape so that the edge interval is λ / 8. Double electrode fingers,
A surface acoustic wave filter characterized in that a difference in average sound speed caused by a difference in input and output electrode finger structures is corrected by changing a metallization ratio of each electrode finger.
入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指の膜厚を変化させて補正することを特徴とする弾性表面波フィルタ。 Interdigital input electrode fingers that form a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction combined with the anisotropy of the piezoelectric substrate, and a directional inversion transducer that extracts the generated surface acoustic wave as a signal In a surface acoustic wave filter having interdigital output electrode fingers,
A surface acoustic wave filter that corrects a difference in average sound speed caused by a difference in input and output electrode finger structures by changing a film thickness of each electrode finger.
入力電極指は、それぞれの幅がλ/4の正電極指及び負電極指をλ/4のエッジ間隔をおいて交互に配置した斜め電極指を形成するシングル電極指であり、
出力電極指は、それぞれの電極指の幅がλ/8の正電極指及び負電極指を二本づつエッジ間隔がλ/8となるように交互にすだれ状に配置した斜め電極指を形成するダブル電極指であり、
入出力の電極指構造の違いにより生じる平均音速の違いをそれぞれの電極指の膜厚を変化させて補正することを特徴とする弾性表面波フィルタ。 Interdigital input electrode fingers that form a natural single-phase unidirectional transducer that generates a surface acoustic wave in one direction combined with the anisotropy of the piezoelectric substrate, and a directional inversion transducer that extracts the generated surface acoustic wave as a signal In a surface acoustic wave filter having interdigital output electrode fingers,
The input electrode fingers are single electrode fingers that form diagonal electrode fingers in which positive electrode fingers and negative electrode fingers each having a width of λ / 4 are alternately arranged with an edge interval of λ / 4,
The output electrode fingers are formed as diagonal electrode fingers in which the positive electrode fingers and the negative electrode fingers each having a width of λ / 8 are alternately arranged in an interdigital shape so that the edge interval is λ / 8. Double electrode fingers,
A surface acoustic wave filter that corrects a difference in average sound speed caused by a difference in input and output electrode finger structures by changing a film thickness of each electrode finger.
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