JPH1188100A - Surface acoustic wave device - Google Patents
Surface acoustic wave deviceInfo
- Publication number
- JPH1188100A JPH1188100A JP25436197A JP25436197A JPH1188100A JP H1188100 A JPH1188100 A JP H1188100A JP 25436197 A JP25436197 A JP 25436197A JP 25436197 A JP25436197 A JP 25436197A JP H1188100 A JPH1188100 A JP H1188100A
- Authority
- JP
- Japan
- Prior art keywords
- idt
- acoustic wave
- surface acoustic
- lithium niobate
- saw
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、圧電基板にニオブ
酸リチウムを用いた弾性表面波デバイスに関し、特にリ
ーキーＳＡＷ共振子の容量比を従来のものより改善した
弾性表面波デバイスに関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device using lithium niobate for a piezoelectric substrate, and more particularly to a surface acoustic wave device having a leaky SAW resonator with a capacitance ratio improved from that of the prior art.
【０００２】[0002]
【従来の技術】近年、弾性表面波デバイスの小型化、低
損失化、低価格等はめざましいものがあり、各種通信機
器等の普及に大きく貢献している。特に、移動体通信機
の普及は急速であり、その要請に応じるべくアナログ方
式から通信チャネルの増大、各種サービスに適したディ
ジタル方式へと推移している。上記のように通信方式の
ディジタル化に伴い、通信帯域が広帯域化し、通信機器
のＲＦ段、ＩＦ段で用いられるフィルタはより広帯域な
通過域のものが要求されている。また、ミキサ段に用い
るＶＣＯ（電圧制御発振器）には発振周波数の可変範囲
が従来よりも広帯域なものが要求されている。2. Description of the Related Art In recent years, there have been remarkable reductions in size, loss, and cost of surface acoustic wave devices, which have greatly contributed to the spread of various communication devices. In particular, the spread of mobile communication devices has been rapid, and in response to the demand, there has been a shift from an analog system to an increase in communication channels and a digital system suitable for various services. As described above, with the digitization of the communication system, the communication band is widened, and a filter used in the RF stage and the IF stage of the communication device is required to have a broader pass band. In addition, a VCO (voltage controlled oscillator) used for the mixer stage is required to have a variable oscillation frequency range wider than before.
【０００３】通信機器の中で、最も普及している携帯電
話等のＲＦ段にはラダー型弾性表面波フィルタ（以下、
ラダー型ＳＡＷフィルタと称す）が用いられる場合が多
い。周知のように、ラダー型ＳＡＷフィルタは、図６に
示すごとく複数のＳＡＷ共振子を梯子型に配列して構成
する共振子型ＳＡＷフィルタである。図６は入力及び出
力に並列共振子（並列腕にあるＳＡＷ共振子）Ｓｐを配
した構成である。また、入力及び出力に直列共振子（直
列腕にあるＳＡＷ共振子）Ｓｓを配した構成もあり、両
タイプともフィルタ特性は同じであるが、入出力インピ
ーダンス特性は互いに異なる。ラダー型ＳＡＷフィルタ
のそれぞれの直列ＳＡＷ共振子Ｓｓ及び並列ＳＡＷ共振
子Ｓｐとも、１つの圧電基板上に互いに間挿し合う複数
本の電極指を有する一対のくし形電極（ＩＤＴ）により
構成され、各ＳＡＷ共振子間にリード電極を配してラダ
ー型ＳＡＷフィルタを構成する。また、各ＳＡＷ共振子
は、設計により、図７（ａ）に平面図を示すようにＩＤ
Ｔ電極の両側に反射器を配置する場合と、同（ｂ）に示
すように反射器を配さない場合とがある。[0003] Among communication devices, a ladder type surface acoustic wave filter (hereinafter, referred to as an RF stage) is most commonly used for an RF stage of a mobile phone or the like.
A ladder-type SAW filter is often used. As is well known, a ladder type SAW filter is a resonator type SAW filter configured by arranging a plurality of SAW resonators in a ladder type as shown in FIG. FIG. 6 shows a configuration in which a parallel resonator (SAW resonator in a parallel arm) Sp is arranged at the input and output. There is also a configuration in which a series resonator (SAW resonator in a series arm) Ss is provided at the input and the output. Both types have the same filter characteristics but different input / output impedance characteristics. Each of the series SAW resonators Ss and the parallel SAW resonators Sp of the ladder-type SAW filter is constituted by a pair of comb-shaped electrodes (IDT) having a plurality of electrode fingers interposed on one piezoelectric substrate. A ladder-type SAW filter is configured by disposing lead electrodes between SAW resonators. Further, each SAW resonator has an ID as shown in a plan view in FIG.
There are cases where reflectors are arranged on both sides of the T electrode and cases where no reflectors are arranged as shown in FIG.
【０００４】１つの並列ＳＡＷ共振子Ｓｐと１つの直列
ＳＡＷ共振子Ｓｓとで構成されるラダー型ＳＡＷフィル
タ１区間の周波数−インピーダンス特性を図８（ａ）に
示す。並列ＳＡＷ共振子Ｓｐの***振周波数ｆａｐと直
列ＳＡＷ共振子Ｓｓの共振周波数ｆｒｓを概ね一致させ
ることにより図８（ｂ）に示すように、通過域の両側に
並列ＳＡＷ共振子Ｓｐの共振周波数ｆｒｐと直列ＳＡＷ
共振子Ｓｓの***振周波数ｆａｓとからなる減衰極を有
するフィルタ特性が得られる。FIG. 8A shows a frequency-impedance characteristic of one section of a ladder-type SAW filter composed of one parallel SAW resonator Sp and one series SAW resonator Ss. By making the anti-resonance frequency fap of the parallel SAW resonator Sp substantially equal to the resonance frequency frs of the series SAW resonator Ss, as shown in FIG. 8B, the resonance frequency frp of the parallel SAW resonator Sp on both sides of the pass band. And series SAW
A filter characteristic having an attenuation pole composed of the anti-resonance frequency fas of the resonator Ss is obtained.
【０００５】図９（ａ）は単体のＳＡＷ共振子の電気的
等価回路であり、図９（ｂ）はその周波数−インピーダ
ンス特性である。ラダー型ＳＡＷフィルタにおいて、通
過帯域を広帯域化するには、図９（ｂ）に示す共振周波
数ｆｒと***振周波数ｆａとの差周波数の大きいＳＡＷ
共振子が必要となる。一般的に共振周波数ｆｒと***振
周波数ｆａの間には ｆａ2＝ｆｒ2（１＋１／γ） （１） の関係がある。ここでγはＳＡＷ共振子の容量比で、図
９（ａ）に示す電気的等価回路の静電容量Ｃ0とモーシ
ョナルキャパシタンスＣ1との比（Ｃ0／Ｃ1）で表され
る。周知のように、ＳＡＷ共振子の容量比γは圧電材料
種類と切断方位とでほぼ決まる。そして、式１より、容
量比γが小さいほど共振周波数ｆｒと***振周波数ｆａ
との差周波数の大きなＳＡＷ共振子が得られることにな
る。従って、容量比γの小さなＳＡＷ共振子を用いるこ
とにより、ラダー型ＳＡＷフィルタの通過帯域幅を広く
することができる。FIG. 9A shows an electrical equivalent circuit of a single SAW resonator, and FIG. 9B shows a frequency-impedance characteristic thereof. In order to widen the pass band in the ladder type SAW filter, a SAW having a large difference frequency between the resonance frequency fr and the anti-resonance frequency fa shown in FIG.
A resonator is required. Generally, there is a relationship of fa 2 = fr 2 (1 + 1 / γ) (1) between the resonance frequency fr and the anti-resonance frequency fa. Here, γ is the capacitance ratio of the SAW resonator, and is represented by the ratio (C 0 / C 1 ) between the capacitance C 0 and the motional capacitance C 1 of the electric equivalent circuit shown in FIG. As is well known, the capacitance ratio γ of the SAW resonator is substantially determined by the type of piezoelectric material and the cutting direction. From equation (1), as the capacitance ratio γ decreases, the resonance frequency fr and the anti-resonance frequency fa decrease.
Thus, a SAW resonator having a large difference frequency from the above can be obtained. Therefore, by using a SAW resonator having a small capacitance ratio γ, the pass band width of the ladder-type SAW filter can be widened.
【０００６】また、周知のように、容量比γは電気機械
結合係数ｋの自乗ｋ2に逆比例するので、容量比γの小
さなＳＡＷ共振子を実現するには、電気機械結合係数ｋ
2の大きな圧電基板が必要となる。「J.Appl.Phys.,Vol.
43,No.3,pp.856-862(March1972)」（文献１と称す）に
報告されたように、圧電基板に４１度回転ＹカットＸ伝
搬ニオブ酸リチウムを用いたＳＡＷデバイスは、大きな
電気機械結合係数ｋ2が得られることで知られている。
ここで、θ度回転Ｙカット基板とは周知のようにＹカッ
ト板をＸ軸の周りにθ度回転したものである。また、特
開平９−１２１１３６には４１度回転ＹカットＸ伝搬ニ
オブ酸リチウムを圧電基板として用い、ＩＤＴの周期λ
と電極膜厚Ｈとの比、即ち基準化膜厚Ｈ／λを、０．０
２５≦Ｈ／λ≦０．０７５の範囲に選ぶことにより、ス
プリアスのない広帯域のラダー型ＳＡＷフィルタが実現
できると述べられている。Further, as is well known, since the capacitance ratio γ is inversely proportional to the square k 2 of the electromechanical coupling coefficient k, to realize a SAW resonator having a small capacitance ratio γ, the electromechanical coupling coefficient k
2 large piezoelectric substrates are required. `` J. Appl. Phys., Vol.
43, No. 3, pp. 856-862 (March1972) ”(referred to as Reference 1), a SAW device using a 41-degree rotated Y-cut X-propagating lithium niobate for a piezoelectric substrate has a large electric power. It is known that a mechanical coupling coefficient k 2 can be obtained.
Here, the θ-degree rotated Y-cut substrate is obtained by rotating the Y-cut plate around the X-axis by θ degrees as is well known. Japanese Patent Application Laid-Open No. Hei 9-121136 discloses that a 41-degree rotated Y-cut X-propagating lithium niobate is used as a piezoelectric substrate, and the IDT period λ
And the thickness of the electrode H, that is, the normalized thickness H / λ is 0.0
It is stated that by selecting the range of 25 ≦ H / λ ≦ 0.075, a wide band ladder type SAW filter having no spurious can be realized.
【０００７】図１０（ａ）〜（ｃ）は、本願発明者らの
実験により得られた４１度回転ＹカットＸ伝搬ニオブ酸
リチウムを圧電基板に用いたＳＡＷ共振子の周波数−イ
ンピーダンス特性例である。横軸に周波数、縦軸にイン
ピーダンスＺの絶対値（Ω）をとっている。図１０
（ａ）は、ニオブ酸リチウム上に配設したＩＤＴの基準
化膜厚Ｈ／λを０．０６とした場合であり、同（ｂ）は
基準化膜厚Ｈ／λを０．０８、同（ｃ）は基準化膜厚Ｈ
／λを０．１０とした場合の周波数−インピーダンス特
性である。この試作例では基準化膜厚Ｈ／λ以外のパラ
メータは全て同一としている。 特開平９−１２１１３
６記述されているように、基準化膜厚Ｈ／λが０．０７
５より大きな場合である図１０（ｂ）、同（ｃ）の周波
数−インピーダンス特性には、共振周波数と***振周波
数の間に周期的な小さなスプリアスが共振特性に重畳し
ている。一方、基準化膜厚が０．０２５≦Ｈ／λ≦０．
０７５の範囲にある図１０（ａ）の周波数−インピーダ
ンス特性には前記のようなスプリアスは重畳していない
ことがわかる。FIGS. 10A to 10C show frequency-impedance characteristics of a SAW resonator using a 41-degree rotated Y-cut X-propagating lithium niobate as a piezoelectric substrate, obtained by an experiment conducted by the present inventors. is there. The horizontal axis represents the frequency, and the vertical axis represents the absolute value (Ω) of the impedance Z. FIG.
(A) shows the case where the normalized thickness H / λ of the IDT disposed on lithium niobate is set to 0.06, and (b) shows the case where the normalized thickness H / λ is set to 0.08 and the same. (C) is the normalized film thickness H
It is a frequency-impedance characteristic when / λ is set to 0.10. In this prototype, all parameters other than the standardized film thickness H / λ are the same. JP-A-9-12113
6 As described, the normalized film thickness H / λ is 0.07
In the frequency-impedance characteristics shown in FIGS. 10B and 10C, which are larger than 5, small periodic spurious components are superimposed on the resonance characteristics between the resonance frequency and the antiresonance frequency. On the other hand, when the normalized film thickness is 0.025 ≦ H / λ ≦ 0.
It can be seen that the above-mentioned spurious is not superimposed on the frequency-impedance characteristic of FIG. 10A in the range of 075.
【０００８】特開平９−１２１１３６には、ニオブ酸リ
チウム基板上に配設したＩＤＴの対向する電極指に交差
幅重み付けを施すことにより、通過帯域内にスプリアス
が発生せず、平坦で広帯域なラダー型ＳＡＷフィルタが
得られることが記述されている。また、ＩＤＴ電極指の
ライン幅をＬｍ、スペース幅をＬｇとした場合、ライン
幅とスペース幅の関係を０．２≦Ｌｍ／（Ｌｍ＋Ｌｇ）
≦０．５となるように構成することにより、通過帯域内
が平坦で広帯域なラダー型ＳＡＷフィルタが得られるこ
とも記されている。Japanese Patent Application Laid-Open No. Hei 9-121136 discloses a flat broadband ladder that does not generate spurious components in a pass band by weighting an intersection of electrodes facing an IDT disposed on a lithium niobate substrate. It is described that a type SAW filter is obtained. When the line width of the IDT electrode finger is Lm and the space width is Lg, the relationship between the line width and the space width is 0.2 ≦ Lm / (Lm + Lg).
It is also described that a ladder type SAW filter having a flat passband and a wide band can be obtained by configuring so as to satisfy ≦ 0.5.
【０００９】本明細書ではＬｍ／（Ｌｍ＋Ｌｇ）をライ
ン占有率ｔと称し、特に断りのない場合、反射器のライ
ン占有率とＩＤＴのライン占有率ｔは概ね同一とする。
ライン占有率ｔに関する前記内容を確認すべく、ＩＤＴ
の電極指に図１１に示す交差幅重み付けを施したＳＡＷ
共振子を試作した。ライン占有率ｔは０．３、０．４、
０．５、０．６、０．７の５種類と、基準化膜厚Ｈ／λ
は０．０６、０．０８、０．１０の３種類で、合計１５
種類である。図１２は各ＳＡＷ共振子の容量比γを詳細
に実測した結果を図に示したものであり、この図より明
らかなように、ＳＡＷ共振子の容量比γの最小値はいず
れの場合も約４．６４であることがわかる。In this specification, Lm / (Lm + Lg) is referred to as a line occupancy t. Unless otherwise specified, the line occupancy of the reflector and the line occupancy t of the IDT are substantially the same.
To confirm the contents regarding the line occupancy t, the IDT
SAW in which the electrode fingers of FIG.
A resonator was prototyped. The line occupancy t is 0.3, 0.4,
Five types of 0.5, 0.6 and 0.7, and a standardized film thickness H / λ
Are three types of 0.06, 0.08, and 0.10.
Kind. FIG. 12 shows the result of the detailed measurement of the capacitance ratio γ of each SAW resonator. As is clear from FIG. 12, the minimum value of the capacitance ratio γ of the SAW resonator is approximately equal in each case. It turns out that it is 4.64.
【００１０】[0010]
【発明が解決しようとする課題】しかしながら、上記の
実験結果から明らかなように、４１度回転ＹカットＸ伝
搬ニオブ酸リチウムを圧電基板に用いたＳＡＷ共振子の
容量比は、種々のパラメータを変えてもその最小値は約
４．６４であり、これより小さな容量比を得ることはで
きないという問題があった。本発明は上記課題を解決す
るためになされたものであって、容量比の小さなＳＡＷ
デバイスを提供することを目的とする。However, as is apparent from the above experimental results, the capacitance ratio of a SAW resonator using a 41-degree rotated Y-cut X-propagating lithium niobate as a piezoelectric substrate varies with various parameters. However, the minimum value is about 4.64, and there is a problem that a smaller capacity ratio cannot be obtained. The present invention has been made in order to solve the above-mentioned problems, and has a small capacity ratio SAW.
The purpose is to provide a device.
【００１１】[0011]
【課題を解決するための手段】上記目的を達成するため
に本発明に係る弾性表面波デバイスの請求項１記載の発
明は、回転Ｙカットニオブ酸リチウム基板上に少なくと
も１つのＩＤＴを配置した弾性表面波デバイスにおい
て、前記圧電基板の切断角度θがθ≦４０度であると共
に前記ＩＤＴの対向する電極指に交差幅重み付けを施
し、前記ＩＤＴの基準化膜厚Ｈ／λを０．０５３＜Ｈ／
λ＜０．１０２の範囲内に設定したことを特徴とする弾
性表面波デバイスである。請求項２記載の発明は、回転
Ｙカットニオブ酸リチウム基板上に少なくとも１つのＩ
ＤＴを配置した弾性表面波デバイスにおいて、前記圧電
基板の切断角度θがθ≦４０度であると共に前記ＩＤＴ
の対向する電極指の交差幅が同一であり、前記ＩＤＴの
基準化膜厚Ｈ／λを０．０５３＜Ｈ／λ≦０．０７５の
範囲内に設定したことを特徴とする弾性表面波デバイス
である。請求項３記載の発明は、前記ＩＤＴの対向する
電極指のライン幅をＬｍ、スペース幅をＬｇとしたと
き、Ｌｍ／（Ｌｍ＋Ｌｇ）＜０．６２の関係を満たすこ
とを特徴とする請求項１および２記載の弾性表面波デバ
イスである。請求項４記載の発明は、前記ＩＤＴの両側
に反射器を配置したことを特徴とする請求項１乃至３記
載の弾性表面波デバイスである。請求項５記載の発明
は、回転Ｙカットニオブ酸リチウム基板上に複数の一端
子対弾性表面波共振子を形成し、該一端子対弾性表面波
共振子を梯子型に接続した弾性表面波フィルタにおい
て、前記複数の一端子対弾性表面波共振子の少なくとも
１つが請求項１乃至４に記載の弾性表面波デバイスであ
ることを特徴とする弾性表面波フィルタである。According to a first aspect of the present invention, there is provided a surface acoustic wave device according to the present invention, wherein at least one IDT is disposed on a rotating Y-cut lithium niobate substrate. In the surface acoustic wave device, the cutting angle θ of the piezoelectric substrate is θ ≦ 40 degrees, and the electrode width of the IDT is set to 0.053 <H. /
A surface acoustic wave device characterized in that λ is set within a range of 0.102. According to the second aspect of the present invention, at least one I
In the surface acoustic wave device in which the DT is disposed, the cutting angle θ of the piezoelectric substrate is θ ≦ 40 degrees and the IDT
Wherein the intersection width of the opposing electrode fingers is the same, and the standardized film thickness H / λ of the IDT is set in the range of 0.053 <H / λ ≦ 0.075. It is. The invention according to claim 3 is characterized in that, when the line width of the electrode finger facing the IDT is Lm and the space width is Lg, the relationship of Lm / (Lm + Lg) <0.62 is satisfied. And 2 are surface acoustic wave devices. According to a fourth aspect of the present invention, there is provided the surface acoustic wave device according to any one of the first to third aspects, wherein reflectors are arranged on both sides of the IDT. According to a fifth aspect of the present invention, there is provided a surface acoustic wave filter in which a plurality of one-port pair surface acoustic wave resonators are formed on a rotating Y-cut lithium niobate substrate, and the one-port pair surface acoustic wave resonators are connected in a ladder form. 5. A surface acoustic wave filter according to claim 1, wherein at least one of the plurality of one-port surface acoustic wave resonators is the surface acoustic wave device according to any one of claims 1 to 4.
【００１２】[0012]
【発明の実施の形態】以下本発明を図面に示した実施の
形態に基づいて詳細に説明する。本願発明者らは、前記
文献１に記載されているように、θ度回転Ｙカットニオ
ブ酸リチウム基板上を伝搬する漏洩弾性表面波（以下、
リーキーＳＡＷと称す）の伝搬速度（位相速度）が圧電
基板の切断角度の増加につれて大きく変化することに着
目した。しかも、基板表面をメタライズした場合のリー
キーＳＡＷの伝搬速度と、基板表面が電気的に開放され
ている場合のリーキーＳＡＷの伝搬速度とが、基板の切
断角度により異なる。基板表面をメタライズした場合の
リーキーＳＡＷの伝搬速度をＶｍ、基板表面が電気的に
開放されている場合のリーキーＳＡＷの伝搬速度をＶｆ
とすると、電気機械結合係数ｋ2はｋ2＝２（Ｖｆ−Ｖ
ｍ）／Ｖｆと表される。従って、伝搬速ＶｆとＶｍとの
差を大きくすれば、電気機械結合係数ｋ2を大きくする
ことが可能となる。DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. As described in the above-mentioned Document 1, the inventors of the present invention have developed a leaky surface acoustic wave (hereinafter, referred to as a “propagation”) propagating on a θ-degree rotated Y-cut lithium niobate substrate.
It is noted that the propagation speed (phase speed) of the leaky SAW greatly changes as the cutting angle of the piezoelectric substrate increases. In addition, the propagation speed of the leaky SAW when the substrate surface is metallized and the propagation speed of the leaky SAW when the substrate surface is electrically open differ depending on the cutting angle of the substrate. The propagation speed of the leaky SAW when the substrate surface is metallized is Vm, and the propagation speed of the leaky SAW when the substrate surface is electrically open is Vf.
Then, the electromechanical coupling coefficient k 2 is k 2 = 2 (Vf−V
m) / Vf. Therefore, by increasing the difference between the propagation speed Vf and Vm, it becomes possible to increase the electromechanical coupling coefficient k 2.
【００１３】文献１に記載されているように、伝搬速度
ＶｆとＶｍとの差は、ニオブ酸リチウム基板の切断角度
をこれまで最良値と云われていた４１度より小さくする
ほど、大きくなることが分かる。即ち、θ度回転Ｙカッ
トニオブ酸リチウム基板は基板の切断角度θを４１度よ
り小さくするつれ、電気機械結合係数ｋ2が大きくなる
ことが予想される。前記したように、容量比γは電気機
械結合係数ｋの自乗ｋ2に逆比例するので、電気機械結
合係数ｋ2を大きくすると容量比γを小さくすることが
できるはずである。即ち、ニオブ酸リチウム基板の切断
角度θを４１度より小さくすれば、容量比γが小さくな
ることが予見される。しかしながら、文献１によれば、
ニオブ酸リチウム基板の表面をメタライズした場合は、
切断角度を約６０度より小さくするとリーキーＳＡＷの
伝搬損失が増大することが示されている。また、ニオブ
酸リチウム基板の表面を電気的に開放した場合は、角度
θが３６度近傍より小さい領域ではリーキーＳＡＷの伝
搬損失が増大することが示されている。As described in Document 1, the difference between the propagation velocities Vf and Vm becomes larger as the cutting angle of the lithium niobate substrate is made smaller than 41 degrees which has been said to be the best value. I understand. That is, it is expected that the electromechanical coupling coefficient k 2 will increase as the cutting angle θ of the substrate becomes smaller than 41 degrees in the θ-degree rotated Y-cut lithium niobate substrate. As described above, since the capacitance ratio γ is inversely proportional to the square k 2 of the electromechanical coupling coefficient k, the capacitance ratio γ should be able to be reduced by increasing the electromechanical coupling coefficient k 2 . That is, if the cutting angle θ of the lithium niobate substrate is smaller than 41 degrees, the capacity ratio γ is expected to be small. However, according to Document 1,
If the surface of the lithium niobate substrate is metallized,
It is shown that when the cutting angle is smaller than about 60 degrees, the propagation loss of leaky SAW increases. Further, it is shown that when the surface of the lithium niobate substrate is electrically opened, the propagation loss of leaky SAW increases in a region where the angle θ is smaller than around 36 degrees.
【００１４】従って、切断角度が４１度より小さなＳＡ
Ｗ共振子を製作した場合、共振特性の劣化、特に共振抵
抗Ｒ１が増大することが予想される。そこで、本願発明
者らは、４１度より回転角の小さなθ度回転Ｙカットニ
オブ酸リチウム基板を用い、基準化膜厚Ｈ／λとライン
占有率ｔとをパラメータにして、種々のＳＡＷ共振子を
試作し、圧電基板に配置したＩＤＴの基準化膜厚Ｈ／λ
とライン占有率ｔによる電気的定数、共振特性への影響
を調べた。ここで、ＩＤＴ電極の材料はアルミニウム合
金を用いた。Therefore, SA having a cutting angle smaller than 41 degrees
When a W resonator is manufactured, it is expected that the resonance characteristics deteriorate, and in particular, the resonance resistance R1 increases. Therefore, the inventors of the present application used a θ-degree rotated Y-cut lithium niobate substrate having a rotation angle smaller than 41 degrees, and set various SAW resonators using the normalized film thickness H / λ and the line occupancy t as parameters. Was prototyped, and the normalized thickness H / λ of the IDT arranged on the piezoelectric substrate was
And the influence of the line occupancy t on the electrical constant and resonance characteristics. Here, the material of the IDT electrode was an aluminum alloy.
【００１５】図１はニオブ酸リチウム基板の切断角度を
θ＝３５度、ＩＤＴのライン占有率をｔ＝０．４とし、
ＩＤＴの対向する電極指に交差幅重み付けを施したＳＡ
Ｗ共振子において、基準化膜厚Ｈ／λを変化させた時、
基準化膜厚Ｈ／λと容量比γとの関係をプロットした図
である。この図から明らかなように、基準化膜厚Ｈ／λ
を０．０５３から０．１０２の範囲に選べば、４１度回
転ＹカットＸ伝搬ニオブ酸リチウム基板を用いたＳＡＷ
共振子の容量比γよりも容量比γを小さくできることが
わかる。また、図２はニオブ酸リチウム基板の切断角度
をθ＝３５度、基準化膜厚Ｈ／λを０．０８とし、ＩＤ
Ｔの対向する電極指に交差幅重み付けを施したＳＡＷ共
振子において、ＩＤＴのライン占有率ｔを変化させた
時、ライン占有率ｔと容量比γの関係をプロットした図
である。この図よりライン占有率ｔを０．６２より小さ
く設定すれば、４１度回転ＹカットＸ伝搬ニオブ酸リチ
ウム基板を用いたＳＡＷ共振子の容量比γよりも容量比
γを小さくできることがわかる。FIG. 1 shows that the cutting angle of the lithium niobate substrate is θ = 35 degrees, the line occupancy of the IDT is t = 0.4,
SA in which the cross width is weighted to the opposing electrode fingers of the IDT
When the normalized film thickness H / λ is changed in the W resonator,
FIG. 9 is a diagram in which a relationship between a normalized film thickness H / λ and a capacitance ratio γ is plotted. As is clear from this figure, the normalized film thickness H / λ
Is selected in the range of 0.053 to 0.102, the SAW using the 41-degree rotated Y-cut X-propagating lithium niobate substrate
It can be seen that the capacitance ratio γ can be made smaller than the capacitance ratio γ of the resonator. FIG. 2 shows that the cutting angle of the lithium niobate substrate is θ = 35 degrees, the standardized film thickness H / λ is 0.08,
FIG. 13 is a diagram plotting the relationship between the line occupancy t and the capacitance ratio γ when the line occupancy t of the IDT is changed in the SAW resonator in which the electrode fingers opposed to T are weighted with the cross width. From this figure, it is understood that when the line occupancy t is set to be smaller than 0.62, the capacitance ratio γ can be made smaller than the capacitance ratio γ of the SAW resonator using the 41-degree rotated Y-cut X-propagation lithium niobate substrate.
【００１６】図３は基準化膜厚Ｈ／λを０．０８、ＩＤ
Ｔのライン占有率ｔを０．４とし、ＩＤＴの対向する電
極指に交差幅重み付けを施したＳＡＷ共振子において、
ニオブ酸リチウム基板の切断角度θを変化させた時、切
断角度θと容量比γとの関係をプロットした図である。
この図より切断角度θを４１度より小さく選べば、４１
度回転ＹカットＸ伝搬ニオブ酸リチウム基板を用いたＳ
ＡＷ共振子の容量比γよりも容量比γを小さくできるこ
とがわかる。図４は基準化膜厚Ｈ／λを０．０８、ＩＤ
Ｔのライン占有率ｔを０．４とし、ＩＤＴの対向する電
極指に交差幅重み付けを施したＳＡＷ共振子において、
ニオブ酸リチウム基板の切断角度θを変化させた時、切
断角度θと共振抵抗Ｒ１と関係をプロットした図であ
る。切断角度を小さくした場合に、実験開始前に懸念し
ていた共振抵抗Ｒ１の増大は見られず、むしろ切断角度
θを４１度より小さくするほど共振抵抗が小さくなると
いう結果が得られた。この実験結果は、文献１に示され
たニオブ酸リチウム基板の切断角度とリーキーＳＡＷの
伝搬損失との関係と一致しない結果となったが、ＩＤＴ
電極膜厚による質量負荷効果の影響を受けて、リーキー
ＳＡＷの伝搬損失が小さくなっているものと推察され
る。FIG. 3 shows the normalized film thickness H / λ of 0.08, ID
In a SAW resonator in which the line occupation ratio t of T is 0.4 and the electrode fingers facing each other of the IDT are weighted by the cross width,
FIG. 6 is a diagram plotting the relationship between the cutting angle θ and the capacity ratio γ when the cutting angle θ of the lithium niobate substrate is changed.
If the cutting angle θ is selected to be smaller than 41 degrees as shown in FIG.
Degree rotation Y-cut X-propagation lithium niobate substrate
It can be seen that the capacitance ratio γ can be made smaller than the capacitance ratio γ of the AW resonator. FIG. 4 shows the normalized film thickness H / λ of 0.08 and ID.
In a SAW resonator in which the line occupation ratio t of T is 0.4 and the electrode fingers facing each other of the IDT are weighted by the cross width,
FIG. 9 is a diagram plotting the relationship between the cutting angle θ and the resonance resistance R1 when the cutting angle θ of the lithium niobate substrate is changed. When the cutting angle was reduced, the resonance resistance R1, which was a concern before the start of the experiment, did not increase, but rather, as the cutting angle θ was smaller than 41 degrees, the resonance resistance was reduced. Although the experimental results did not agree with the relationship between the cutting angle of the lithium niobate substrate and the propagation loss of leaky SAW shown in Document 1, the IDT
It is assumed that the propagation loss of leaky SAW is reduced due to the effect of the mass load effect due to the electrode film thickness.
【００１７】図５は従来の４１度回転ＹカットＸ伝搬ニ
オブ酸リチウム基板を用いたＳＡＷ共振子（破線）と、
本発明の一実施例である３５度回転ＹカットＸ伝搬ニオ
ブ酸リチウム基板を用いたＳＡＷ共振子（実線）とのイ
ンピーダンス特性の比較である。いずれの共振子におい
ても、ＩＤＴ電極形状、電極対数、交差幅重み付け、基
準化膜厚及びライン占有率は同一としている。この図か
らも明らかなように、共振特性を劣化させることなしに
容量比を増大することができた。即ち、共振周波数と反
共振周波数との差を広くすることが可能となった。FIG. 5 shows a conventional SAW resonator (dashed line) using a 41-degree rotated Y-cut X-propagating lithium niobate substrate,
4 is a comparison of impedance characteristics with a SAW resonator (solid line) using a 35-degree rotated Y-cut X-propagating lithium niobate substrate according to one embodiment of the present invention. In each resonator, the IDT electrode shape, the number of electrode pairs, the intersection width weighting, the standardized film thickness, and the line occupancy are the same. As is clear from this figure, the capacitance ratio could be increased without deteriorating the resonance characteristics. That is, it is possible to widen the difference between the resonance frequency and the anti-resonance frequency.
【００１８】以上の説明ではＩＤＴの対向する電極指に
交差幅重み付けを施したＳＡＷ共振子の例を挙げたが、
ＩＤＴの対向する各電極指の交差幅が全て同じ場合は、
基準化膜厚Ｈ／λを０．０７５より大きくとすると共振
周波数と***振周波数の間に周期的な小さなスプリアス
が発生するので、基準化膜厚は０．０５３＜Ｈ／λ≦
０．０７５の範囲に選ぶとよいことを実験により確認し
ている。以上の結果を要約すると、θ度回転Ｙカットニ
オブ酸リチウム基板の切断角度θを４１度より小さく
し、ＩＤＴの対向する電極指に交差幅重み付けを施した
ＳＡＷ共振子において、基準化膜厚Ｈ／λを０．０５３
＜Ｈ／λ＜０．１０２の範囲に選び、ＩＤＴの対向する
各電極指の交差幅が全て同一の場合は、基準化膜厚Ｈ／
λを０．０５３＜Ｈ／λ≦０．０７５の範囲に選べば、
共振特性を劣化させることなく容量比γを小さくするこ
とができ、ＩＤＴのライン占有率ｔをｔ＜０．６２とす
ることにより共振特性を劣化させることなく、更に容量
比γを小さくすることが可能である。In the above description, an example of the SAW resonator in which the electrode fingers facing each other of the IDT are weighted by the intersection width has been described.
If the intersection width of each electrode finger facing the IDT is the same,
When the standardized film thickness H / λ is set to be larger than 0.075, a periodic small spurious is generated between the resonance frequency and the antiresonance frequency. Therefore, the standardized film thickness is 0.053 <H / λ ≦
It has been confirmed by experiments that it is preferable to select a value within the range of 0.075. To summarize the above results, in the SAW resonator in which the cutting angle θ of the θ-degree rotated Y-cut lithium niobate substrate is smaller than 41 degrees and the width of the electrode finger facing the IDT is weighted by the cross width, the standardized film thickness H / Λ is 0.053
<H / λ <0.102, and when the intersection width of each electrode finger facing the IDT is the same, the standardized film thickness H /
If λ is selected in the range of 0.053 <H / λ ≦ 0.075,
The capacitance ratio γ can be reduced without deteriorating the resonance characteristics. By setting the line occupancy t of the IDT to t <0.62, the capacitance ratio γ can be further reduced without deteriorating the resonance characteristics. It is possible.
【００１９】以上の説明ではリーキーＳＡＷ共振子を例
に挙げ、該共振子をラダー型ＳＡＷフィルタに適用すれ
ば、通過帯域内の挿入損失を増大することなく、通過帯
域幅を拡大したフィルタ特性を実現することができるこ
とを述べた。本発明はこれに限ることなく、例えばＳＡ
Ｗ共振子を格子型に接続したラチス型ＳＡＷフィルタ
や、複数の表面波振動を反射器間に閉じ込めた、所謂多
重モードＳＡＷフィルタにも適用できることは云うまで
もない。また、本発明になるＳＡＷ共振子をＶＣＯ（電
圧制御発振器）に適用すれば周波数可変幅の広いＶＣＯ
を実現することが可能である。In the above description, a leaky SAW resonator is taken as an example, and if the resonator is applied to a ladder type SAW filter, the filter characteristics in which the pass band width is expanded without increasing the insertion loss in the pass band can be obtained. Said that can be realized. The present invention is not limited to this.
It is needless to say that the present invention can be applied to a lattice type SAW filter in which W resonators are connected in a lattice type, and a so-called multi-mode SAW filter in which a plurality of surface wave vibrations are confined between reflectors. Further, when the SAW resonator according to the present invention is applied to a VCO (voltage controlled oscillator), a VCO having a wide frequency variable width can be obtained.
Can be realized.
【００２０】[0020]
【発明の効果】本発明は、以上説明したように構成した
ので、リーキーＳＡＷ共振子の容量比を従来のＳＡＷ共
振子の容量比より小さくすることが可能となり、広帯域
のラダー型ＳＡＷフィルタを実現する上で、優れた効果
を表す。一方、本発明になるＳＡＷ共振子をＶＣＯに適
用すれば、周波数可変幅の広い発振器を実現することが
可能であり、ディジタル通信の高速化には著しい効果を
奏する。According to the present invention, as described above, the capacitance ratio of a leaky SAW resonator can be made smaller than that of a conventional SAW resonator, and a wideband ladder-type SAW filter is realized. In doing so, it shows an excellent effect. On the other hand, if the SAW resonator according to the present invention is applied to a VCO, it is possible to realize an oscillator having a wide frequency variable width, and this has a remarkable effect on speeding up digital communication.
【図１】本発明に係る基準化膜厚Ｈ／λと容量比γとの
関係を示す図である。FIG. 1 is a diagram showing a relationship between a normalized film thickness H / λ and a capacitance ratio γ according to the present invention.
【図２】本発明に係るライン占有率ｔと容量比γとの関
係を示す図である。FIG. 2 is a diagram showing a relationship between a line occupation ratio t and a capacitance ratio γ according to the present invention.
【図３】本発明に係るニオブ酸リチウム基板の切断角度
θと容量比γとの関係を示す図である。FIG. 3 is a diagram showing a relationship between a cutting angle θ and a capacity ratio γ of the lithium niobate substrate according to the present invention.
【図４】本発明に係るニオブ酸リチウム基板の切断角度
θと等価抵抗Ｒ１との関係を示す図である。FIG. 4 is a diagram showing a relationship between a cutting angle θ of a lithium niobate substrate according to the present invention and an equivalent resistance R1.
【図５】本発明に係るリーキーＳＡＷ共振子のインピー
ダンス特性（実線）と従来のリーキーＳＡＷ共振子（破
線）のインピーダンス特性との比較を示す図である。FIG. 5 is a diagram showing a comparison between the impedance characteristic of a leaky SAW resonator according to the present invention (solid line) and the impedance characteristic of a conventional leaky SAW resonator (dashed line).
【図６】従来のラダー型ＳＡＷフィルタの回路構成を示
す図である。FIG. 6 is a diagram illustrating a circuit configuration of a conventional ladder-type SAW filter.
【図７】（ａ）は反射器の付いた１端子対ＳＡＷ共振子
の平面図、（ｂ）は反射器のない１端子対ＳＡＷ共振子
の平面図である。7A is a plan view of a one-port SAW resonator with a reflector, and FIG. 7B is a plan view of a one-port SAW resonator without a reflector.
【図８】（ａ）は従来のラダー型フィルタ１区間の周波
数−インピーダンス特性、（ｂ）はそのフィルタ特性を
示す図である。8A is a diagram showing a frequency-impedance characteristic of one section of a conventional ladder filter, and FIG. 8B is a diagram showing the filter characteristic.
【図９】（ａ）は１端子対ＳＡＷ共振子の電気的等価回
路、（ｂ）はそのインピーダンス特性を示す図である。9A is an electrical equivalent circuit diagram of a one-port SAW resonator, and FIG. 9B is a diagram illustrating impedance characteristics thereof.
【図１０】（ａ）〜（ｃ）は基準化膜厚Ｈ／λを０．０
６〜０．１０まで変化させた時のインピーダンス特性で
ある。FIGS. 10A to 10C show a case where the normalized film thickness H / λ is set to 0.0.
It is an impedance characteristic when changing from 6 to 0.10.
【図１１】ＩＤＴの交差幅に重み付けを施した１端子対
ＳＡＷ共振子の平面図である。FIG. 11 is a plan view of a one-port SAW resonator in which an intersection width of an IDT is weighted.
【図１２】従来のリーキーＳＡＷ共振子のライン占有率
ｔをパラメータにした場合の基準化膜厚Ｈ／λと容量比
γとの関係を示す図である。FIG. 12 is a diagram showing a relationship between a standardized film thickness H / λ and a capacitance ratio γ when a line occupancy t of a conventional leaky SAW resonator is used as a parameter.
γ・・共振子の容量比 λ・・ＩＤＴの周期（波長） Ｈ・・ＩＤＴの電極膜厚 Ｈ／λ・・ＩＤＴの基準化膜厚 θ・・ニオブ酸リチウムＹ板のＸ軸回りの回転角度 Ｒ１・・ＳＡＷ共振子の電気的等価抵抗 Ｚ・・ ＳＡＷ共振子のインピーダンス γ ·· Resonator capacitance ratio λ ·· IDT period (wavelength) H ··· IDT electrode film thickness H / λ ··· IDT standardized film thickness θ ·· Rotation of lithium niobate Y plate around X axis Angle R1 ··· Equivalent electrical resistance of SAW resonator Z ··· Impedance of SAW resonator
Claims (5)
少なくとも１つのＩＤＴを配置した弾性表面波デバイス
において、前記圧電基板の切断角度θがθ≦４０度であ
ると共に前記ＩＤＴの対向する電極指に交差幅重み付け
を施し、前記ＩＤＴの基準化膜厚Ｈ／λを０．０５３＜
Ｈ／λ＜０．１０２の範囲内に設定したことを特徴とす
る弾性表面波デバイス。（但しλはＩＤＴの周期）1. A surface acoustic wave device in which at least one IDT is disposed on a rotating Y-cut lithium niobate substrate, wherein a cutting angle θ of the piezoelectric substrate is θ ≦ 40 degrees, and an electrode finger facing the IDT is provided. The intersection width is weighted, and the normalized thickness H / λ of the IDT is set to 0.053 <
A surface acoustic wave device wherein H / λ is set within the range of 0.102. (However, λ is the period of IDT)
少なくとも１つのＩＤＴを配置した弾性表面波デバイス
において、前記圧電基板の切断角度θがθ≦４０度であ
ると共に前記ＩＤＴの対向する電極指の交差幅が同一で
あり、前記ＩＤＴの基準化膜厚Ｈ／λを０．０５３＜Ｈ
／λ≦０．０７５の範囲内に設定したことを特徴とする
弾性表面波デバイス。（但しλはＩＤＴの周期）2. A surface acoustic wave device in which at least one IDT is arranged on a rotating Y-cut lithium niobate substrate, wherein the cutting angle θ of the piezoelectric substrate is θ ≦ 40 degrees and the IDT of the opposing electrode fingers of the IDT is The intersection width is the same, and the standardized film thickness H / λ of the IDT is 0.053 <H
A surface acoustic wave device characterized by being set within the range of /λ≦0.075. (However, λ is the period of IDT)
をＬｍ、スペース幅をＬｇとしたとき、Ｌｍ／（Ｌｍ＋
Ｌｇ）＜０．６２の関係を満たすことを特徴とする請求
項１および２記載の弾性表面波デバイス。3. When the line width of the electrode finger facing the IDT is Lm and the space width is Lg, Lm / (Lm +
3. The surface acoustic wave device according to claim 1, wherein a relationship of Lg) <0.62 is satisfied.
とを特徴とする請求項１乃至３記載の弾性表面波デバイ
ス。4. The surface acoustic wave device according to claim 1, wherein reflectors are arranged on both sides of the IDT.
複数の一端子対弾性表面波共振子を形成し、該一端子対
弾性表面波共振子を梯子型に接続した弾性表面波フィル
タにおいて、前記複数の一端子対弾性表面波共振子の少
なくとも１つが請求項１乃至４に記載の弾性表面波デバ
イスであることを特徴とする弾性表面波フィルタ。5. A surface acoustic wave filter in which a plurality of one-port pair surface acoustic wave resonators are formed on a rotating Y-cut lithium niobate substrate, and the one-port pair surface acoustic wave resonators are connected in a ladder form. A surface acoustic wave filter characterized in that at least one of the plurality of one-port surface acoustic wave resonators is the surface acoustic wave device according to any one of claims 1 to 4.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25436197A JPH1188100A (en) | 1997-09-03 | 1997-09-03 | Surface acoustic wave device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25436197A JPH1188100A (en) | 1997-09-03 | 1997-09-03 | Surface acoustic wave device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH1188100A true JPH1188100A (en) | 1999-03-30 |
Family
ID=17263929
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP25436197A Pending JPH1188100A (en) | 1997-09-03 | 1997-09-03 | Surface acoustic wave device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH1188100A (en) |
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|---|---|---|---|---|
| JP2006319679A (en) * | 2005-05-12 | 2006-11-24 | Shin Etsu Chem Co Ltd | Compound piezoelectric substrate |
| JP2007221416A (en) * | 2006-02-16 | 2007-08-30 | Matsushita Electric Ind Co Ltd | Electronic component and electronic apparatus using the same |
| JP2008078981A (en) * | 2006-09-21 | 2008-04-03 | Matsushita Electric Ind Co Ltd | Surface acoustic wave resonator, surface acoustic wave filter and antenna duplexer using the same |
| JP2008099339A (en) * | 2008-01-11 | 2008-04-24 | Epson Toyocom Corp | Surface acoustic wave device and module device or oscillation circuit using the same |
| JP2008148184A (en) * | 2006-12-13 | 2008-06-26 | Matsushita Electric Ind Co Ltd | Surface acoustic wave resonator |
| JP2011139513A (en) * | 2006-11-08 | 2011-07-14 | Panasonic Corp | Surface acoustic wave resonator |
| US8035460B2 (en) | 2006-02-16 | 2011-10-11 | Panasonic Corporation | Surface acoustic wave device, surface acoustic wave filter and antenna duplexer using the same, and electronic equipment using the same |
| CN103314529A (en) * | 2011-01-24 | 2013-09-18 | 埃普科斯股份有限公司 | Surface acoustic wave filter |
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1997
- 1997-09-03 JP JP25436197A patent/JPH1188100A/en active Pending
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006319679A (en) * | 2005-05-12 | 2006-11-24 | Shin Etsu Chem Co Ltd | Compound piezoelectric substrate |
| JP4657002B2 (en) * | 2005-05-12 | 2011-03-23 | 信越化学工業株式会社 | Composite piezoelectric substrate |
| JP2007221416A (en) * | 2006-02-16 | 2007-08-30 | Matsushita Electric Ind Co Ltd | Electronic component and electronic apparatus using the same |
| US8035460B2 (en) | 2006-02-16 | 2011-10-11 | Panasonic Corporation | Surface acoustic wave device, surface acoustic wave filter and antenna duplexer using the same, and electronic equipment using the same |
| JP2008078981A (en) * | 2006-09-21 | 2008-04-03 | Matsushita Electric Ind Co Ltd | Surface acoustic wave resonator, surface acoustic wave filter and antenna duplexer using the same |
| JP4544227B2 (en) * | 2006-09-21 | 2010-09-15 | パナソニック株式会社 | Elastic wave resonator, elastic wave filter and antenna duplexer using the same |
| JP2011160488A (en) * | 2006-11-08 | 2011-08-18 | Panasonic Corp | Surface acoustic wave resonator |
| US8084915B2 (en) | 2006-11-08 | 2011-12-27 | Panasonic Corporation | Surface acoustic wave resonator having comb electrodes with different overlapping lengths |
| JP2011139513A (en) * | 2006-11-08 | 2011-07-14 | Panasonic Corp | Surface acoustic wave resonator |
| JP2008148184A (en) * | 2006-12-13 | 2008-06-26 | Matsushita Electric Ind Co Ltd | Surface acoustic wave resonator |
| JP4582150B2 (en) * | 2008-01-11 | 2010-11-17 | エプソントヨコム株式会社 | Surface acoustic wave device and module device or oscillation circuit using the same |
| JP2008099339A (en) * | 2008-01-11 | 2008-04-24 | Epson Toyocom Corp | Surface acoustic wave device and module device or oscillation circuit using the same |
| CN103314529A (en) * | 2011-01-24 | 2013-09-18 | 埃普科斯股份有限公司 | Surface acoustic wave filter |
| JP2014504827A (en) * | 2011-01-24 | 2014-02-24 | エプコス アクチエンゲゼルシャフト | Surface acoustic wave filter |
| US9391589B2 (en) | 2011-01-24 | 2016-07-12 | Epcos Ag | Surface acoustic wave filter on a lithium niobate substrate |
| US11146229B2 (en) | 2018-08-10 | 2021-10-12 | Murata Manufacturing Co., Ltd. | Filter and multiplexer |
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