JPS6147009B2 - - Google Patents
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- Publication number
- JPS6147009B2 JPS6147009B2 JP17524280A JP17524280A JPS6147009B2 JP S6147009 B2 JPS6147009 B2 JP S6147009B2 JP 17524280 A JP17524280 A JP 17524280A JP 17524280 A JP17524280 A JP 17524280A JP S6147009 B2 JPS6147009 B2 JP S6147009B2
- Authority
- JP
- Japan
- Prior art keywords
- surface wave
- electrode
- transducer
- reflector
- electrode part
- 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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- 238000010897 surface acoustic wave method Methods 0.000 claims description 22
- 239000000758 substrate Substances 0.000 claims description 13
- 230000000737 periodic effect Effects 0.000 claims description 10
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 8
- 229910052782 aluminium Inorganic materials 0.000 claims description 8
- 239000013078 crystal Substances 0.000 claims description 6
- 230000005855 radiation Effects 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 239000010453 quartz Substances 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 238000005530 etching Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000010363 phase shift Effects 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 238000001020 plasma etching Methods 0.000 description 1
- 230000007261 regionalization Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000000992 sputter etching Methods 0.000 description 1
- 230000001131 transforming effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/25—Constructional features of resonators using surface acoustic waves
Landscapes
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
Description
本発明は、小形にして、共振尖鋭度が大きく、
共振抵抗の低い表面弾性波共振器に関するもので
ある。
表面弾性波共振器(以下SAW共振器と略記す
る)は、一般に、第1図に示すように、伝搬媒質
1の表面上に、格子状に並べた多数の反射電極に
より形成された1対の表面弾性波反射器2,3を
設け、その中間部に多数の電極対により形成され
た交差指電極形トランスジユーサ4を配置し、表
面弾性波が反射器2,3の間を往復することによ
り生じる共振を、電気端子5,5′を通して電気
回路と接続するように構成した、いわゆるキヤビ
テイ形が多く用いられる。たのようなキヤビテイ
形SAW共振器では、共振器の共振尖鋭度Qなら
びに共振抵抗R1は反射器の反射係数Γの最大絶
対値|Γ|nax及びトランスジユーサの放射コン
ダクタンスGaに依在し、ほぼ
Q∝1/(1−|Γ|2 nax) (1)
R1=1−|Γ|nax/2|Γ|naxGa
(2)
の関係のあることが知られている。従つて、Qが
高く、共振抵抗R1の低い実用的なSAW共振器を
得るためには、反射係数|Γ|naxを1に近づ
け、また放射コンダクタンスGaを大きくしなけ
ればならない。そのため、実際のSAW共振器で
は反射器、トランスジユーサ共にきわめて多数の
電極が必要であり、伝搬媒質に圧電反作用による
反射の小さい水晶を用いる場合、500〜1000本程
度の反射電極を設けるのがふつうで、共振器の小
形化にとつて一つの問題となつている。これに対
して最近では反射電極数を減らすために第2図に
示すように媒質に周期的な溝6を設けて反射係数
を向上させ、小形化を図る方法が有効であること
が知られている。
反射係数Γおよび放射コンダクタンスGaはと
もに電極周期L並びに周波数の関数である。従来
のSAW共振器では第1図に示すように、トラン
スジユーサの電極周期と反射器の電極周期とを同
一の値としていたが、その場合|Γ|およびSa
は第3図に示すような周波数特性となつている。
ここで横軸は周波数、縦軸は反射係数の絶対値
|Γ|および放射コンダクタンスの規格化値G
a/GNである。ただしGNは基板材料およびトラ
ンスジユーサの電極対数で決まる基準値である。
反射係数が最となる周波数(以下反射器中心周波
数という)をR、放射コンダクタンスが最大と
なる周波数(以下トランスジユーサ中心周波数と
いう)をTとすると、第3図に示されるように
T<Rの関係となつており、周波数Rの付近
ではGaはその最大値に比べ相当量低下(Ga/G
N<1)している。SAW共振器の共振周波数は反
射器中心周波数Rにほぼ一致するため、従来の
SAW共振器ではトランスジユーサの周波数選択
特性が十分に活性されていない。そのため式(2)か
ら分るように共振抵抗の低いSAW共振器を実現
するには、反射係数|Γ|naxをできるだけ1に
近づける必要があるため反射電極数をあまり減少
できず小形化のための制約となつていた。
本発明は、トランスジユーサの放射コンダクタ
ンスの周波数特性をも有効に利用することによ
り、小形・高Qにして共振抵抗が低く、かつ容量
比の小さい表面弾性波共振器を提供することを目
的とするものである。
本発明は、トランスジユーサの電極周期と反射
器の電極周期との比を最適化することにより、第
4図aに示すように反射器中心周波数Rとトラ
ンスジユーサ中心周波数Tを一致させることを
基本原理とするものである。
以下に水晶基板およびアルミニウム電極を用い
た場合を例として具体的に説明する。
第5図は本発明による表面弾性波共振器の断面
図である。基板はSTカツト水晶であり、表面弾
性波反射器2,3は斜線を施した厚さhnRの周基
電極に加えて、プラズマエツチングなどの方法に
より設けた深さhgRの周基溝を有する金属−溝構
造とし、トランスジユーサも同様に厚さhnTの周
期電極と深さhgTの周期溝を有する構造とする。
反射器の電極周期をLR、トランスジユーサの電
極周期をLTとし、反射器中心周波数Rとトラン
スジユーサ中心周波数Tを一致させるため、比
LT/LRを次に述べる解析結果に基づいて決定す
る。
反射器中心周波数R及びトランスジユーサ中
心周波数Tは式(4)及び式(5)で与えられること
が、本発明者らにより明らかにされている〔宇
野、宮本、阿部、十文字;「グループ反射器付
SAW共振器の最適製作法」電子通信学会技術報
告US80−18(1980年6月30日)以下、参考文献
(1)という〕。
R=(1−C2R)υs/LR (4)
T{1−C2T−C1T−C1T/(0.7q2 T+0.56qT+0.43)}υs/LT (5)
ここでυsは表面波の伝搬速度、C2T及びC2T
はそれぞれ反射器及びトランスジユーサについて
金属−溝周期構造に基づく摂動効果による周波数
低下量、C1Tはトランスジユーサに関して電極部
分と非電極部分との境界における弾性的な不整合
を表わす項であり、またqTはトランスジユーサ
の電極対数をNとして
qT=πC1TN (6)
で与えられる量である。
式(4)及び(5)により反射器中心周波数Rとトラ
ンスジユーサ中心周波数Tを一致させるために
は、電極周期比LT/LRを
LT/LR=1−C2T−C1T−C1T/(0.7q〓+0.56qT+0.43)/1−C2R (7)
とすれば良いことが導かれる。C2R、C2T及びC
1Tは電極としてアルミニウムを用いた場合、それ
ぞれ
C2R4.33×10-4+4.23×10-2(hnR/LR)+7.9(hnR/LR)2+10.8(hgR/LR)2
+18.5(hnR/LR)(hgR/LR) (8)
C2T4.33×10-4+4.23×10-2(hnT/LT)+7.9(hnT/LT)2+10.8(hgT/LT)2
+18.5(hnT/LT)(hgT/LT) (9)
C1T=6.25×10-4+0.12(hnT/LT)+0.172(hgT/LT) (10)
で与えられることが実験的に確かめられた(参考
文献(1))。
ところで、電極周期LR及びLTは共周周波数に
おける表面波の波長λとほとんど一致するから、
式(8)、(9)及び(10)は次のように書き換えられる。
C2R4.33×10-4+4.23×10-2(hnR/λ)+7.9(hnR/λ)2+10.8(hgR/λ)2
+18.5(hnR/λ)(hgR/λ) (11)
C2T4.33×10-4+4.23×10-2(hnT/λ)+7.9(hnT/λ)2+10.8(hgT/λ)2
+18.5(hnT/λ)(hgT/λ) (11)′
C1T=6.25×10-4+0.12(hnT/λ)+0.172(hgT/λ) (12)
式(6)、(11)及び(12)を式(7)に代入してトランスジユ
ーサの電極対数N、反射器のアルミ電極厚さhn
R、溝の深さhgT、及びトランスジユーサのアル
ミ電極厚さhgT、溝の深さhgTを与えれば電極周
期比LT/LRが決定できる。C2R、C2T及びC1T
の値は通常10-3程度のオーダであるから、LT/
LRは1よりもわずかに小さい値となる。また、
反射器あるいはトランスジユーサに周期溝を形成
しない場合には、式(8)、(9)、(10)および式(11)、
(11′)、(12)において、hgRあるいはhgTを零とお
けば良いことは言うまでもない。
ところで、実際の共振器の製作にあたつては、
式(7)の条件に正確に合わせることは困難であり、
かつその必要はなく、第4図bに示すように周波
数RにおいてGa/GN1を満たしておれば従
来の共振器に対し十分な特性改善の効果が得られ
る。そのための条件は次下の如くにして求めるこ
とができる。
Ga/GNは参考文献(2)にて求められており、そ
れを変形すると
と表わすことができる。ここで及びpは周波数
に関する変数ηを用いて
p1−η+√2−2 (14)
=qT√2−2 (15)
で与えられることが、発明者らにより参考文献(1)
に示されている。ただし、周波数とηとは
=(1−C2T−C1T+C1Tη)υS/LT(16)
の関係がある。
式(13)〜(15)からGa/GN=1となるηは
2根求まりそれぞれη1、η2とすると近似的
に、次の結果が得られる。
η1=0 (17)
η2=−1/(0.35q2 T+0.3qT+0.2) (18)
式(16)〜(18)よりGa/GN1となる周波
数範囲は
{C2T−C1T−C1T/(0.35q2 T+0.3qT+0.2)}υs/LT(1−C2T−C1T)
×υs/LT (19)
となる。式(4)で与えられる反射器中心周波数R
が式(19)で与えられる周波数範囲内に存在する
条件から、LT/LRの範囲が決定でき、次式
(20)の如く与えられる。
1−C2T−C1T−C1T/(0.35q〓+0.3qT+0.2)/1−C2RLT/LR1−C2
T−C1T/1−C2R(20)
従つて式(20)で与えられる範囲に電極周期比
LT/LRを設定すれば反射器の中心周波数Rで
Ga/GN1が満たされ、低共振抵抗のSAW共
振器が実現できることとなる。なお式(7)で与えら
れる最適値は、当然の事ながら式(20)を満たし
ている。
次に、本発明すなわちトランスジユーサと反射
器の電極周期比LT/LRを式(20)で与えられる
範囲に設定した場合の反射器−トランスジユーサ
間隔の設計指針について説明する。そのため、キ
ヤビテイ形SAW共振器の共振条件について検討
する。第5図に示すように、各反射器の電極のう
ち、最もトランスジユーサに近い電極指の中心と
トランスジユーサの端部電極指の中心との間の長
さすなわち、反射器−トランスジユーサ間隔をι
1、ι2とすると、共振条件は
2π(N+ι1/λ+ι2/λ)−φR−φT=mπ(
21)
(m:正の整数)
で与えられる。ただしφRは反射に伴なう表面波
の位相シフト量、φTはトランスジユーサを透過
する際の位相シフト量である。φRは反射器の中
心周波数Rにおいてπ/2となることが知られ
ており、またトランスジユーサの中心周波数T
におけるφTは文献(1)において、近似的に
φT(T)(0.3+0.55qT)π (22)
で与えられることが示されている。これから周波
数R(=T)における共振条件は
ι1+ι2(5n+4/10+0.28qT)λ (23)
(n:正の整数)
となることが分る。さらに、トランスジユーサに
おける表面波の位相と電気的な結合の条件を考慮
すると、ι1、ι2は
ιi=(5ni+4/20+0.14qT)λ (24)
(ni:正の整数、i=1、2)
とすればよい。ただしn1及びn2は同時に奇数又は
同時に偶数である必要があるが必ずしも同一の値
である必要はない。
実際の共振器の設計にあたつては、数値計算例
で示すように、ιi(i=1、2)を式(24)で
与えられる値の前後で比較的広範囲に変化させて
も実用上十分な特性が得られるから、ιiは電極
形成用マスクの製作条件に合わせて、最もパター
ン形成の容易な値に選ぶことができる。
第6図は、ι1=ι2としかつn1(=n2)=3
とした場合の反射器−トランスジユーサ間隔と共
振器特性の関係を示すもので、実線は本発明によ
る場合、破線は従来の構成による場合である。た
だし横軸は間隔の規格化値ι/λ(ι=ι1=ι
2)、左縦軸は共振尖鋭度Q及び容量比γ、右縦
軸はフイギユア・オブ・メリツトMで
M=1/ω0C0R1 (25)
(ω0:共振角周波数、C0:並列容量、R1:共振
抵抗)
で定義される。また、設計条件は表1に示す値を
仮定した。この場合式(11)、(12)及び(6)より
C2R=C2T=6.91×10-3
C1T=4.51×10-3
qT=1.133
となる。従つて式(20)によりLT/LRの範囲と
して
0.9908LT/LR0.9955 (26)
が得られ、また最適値は、式(7)より
LT/LR=0.993 (27)
となる。第6図の実線は式(27)を満たす場合に
相当する。共振器特性は、参考文献(2)〔小山田、
吉川、石原;「多対IDTを用いた弾性表面波共振
器の解析とその応用」電子通信学会論文誌J 60
−A、No.9 pp.805〜812(1977)〕に基づいて、
電気端子よりみたアドミタンス特性を計算するこ
とにより算出している。ただし基板の表面波伝搬
損失として、1波長当りの減衰定数を
α〓=2×10-4 (28)
と仮定している。また第6図には、後述する方法
により行なつた145MHz帯SAW共振器の実験結
果を×印にて示す。第6図から明らかな様に、
ι/λの広い範囲にわたり、従来のSAW共振器
に比べ、大幅な特性の向上が可能である。
The present invention has a small size, high resonance sharpness,
This invention relates to a surface acoustic wave resonator with low resonance resistance. A surface acoustic wave resonator (hereinafter abbreviated as a SAW resonator) generally has a pair of reflective electrodes arranged in a grid pattern on the surface of a propagation medium 1, as shown in FIG. Surface acoustic wave reflectors 2 and 3 are provided, and an interdigital electrode type transducer 4 formed by a large number of electrode pairs is placed in the middle thereof, so that the surface acoustic waves reciprocate between the reflectors 2 and 3. A so-called cavity type is often used, in which the resonance caused by this is connected to an electric circuit through electric terminals 5, 5'. In a cavity-type SAW resonator like the one shown above, the resonance sharpness Q and resonance resistance R 1 of the resonator depend on the maximum absolute value |Γ| nax of the reflection coefficient Γ of the reflector and the radiation conductance G a of the transducer. and approximately Q∝1/(1-|Γ| 2 nax ) (1) R 1 =1-|Γ| nax /2|Γ| nax G a
(2) is known to be related. Therefore, in order to obtain a practical SAW resonator with high Q and low resonant resistance R 1 , the reflection coefficient |Γ| nax must be brought close to 1, and the radiation conductance G a must be increased. Therefore, in an actual SAW resonator, an extremely large number of electrodes are required for both the reflector and the transducer, and if a crystal with low reflection due to piezoelectric reaction is used as the propagation medium, it is recommended to provide about 500 to 1000 reflecting electrodes. This is a common problem in the miniaturization of resonators. In order to reduce the number of reflective electrodes, it has recently been known that it is effective to provide periodic grooves 6 in the medium to improve the reflection coefficient and reduce the size, as shown in Figure 2. There is. Both the reflection coefficient Γ and the radiation conductance G a are functions of the electrode period L and frequency. In the conventional SAW resonator, as shown in Fig. 1, the electrode period of the transducer and the electrode period of the reflector are set to the same value, but in that case, |Γ| and S a
has a frequency characteristic as shown in FIG.
Here, the horizontal axis is the frequency, and the vertical axis is the absolute value of the reflection coefficient |Γ| and the normalized value G of the radiation conductance.
a /G N. However, G N is a reference value determined by the substrate material and the number of electrode pairs of the transducer.
Assuming that the frequency at which the reflection coefficient is maximum (hereinafter referred to as reflector center frequency) is R , and the frequency at which radiation conductance is maximum (hereinafter referred to as transducer center frequency) is T , as shown in Figure 3.
The relationship is T < R , and near frequency R , G a decreases by a considerable amount compared to its maximum value (G a /G
N <1). Since the resonant frequency of the SAW resonator almost matches the reflector center frequency R ,
In the SAW resonator, the frequency selection characteristics of the transducer are not sufficiently activated. Therefore, as can be seen from equation (2), in order to realize a SAW resonator with low resonance resistance, it is necessary to make the reflection coefficient |Γ| This had become a constraint. An object of the present invention is to provide a surface acoustic wave resonator that is small, has a high Q, has a low resonance resistance, and has a small capacitance ratio by effectively utilizing the frequency characteristics of the radiation conductance of a transducer. It is something to do. The present invention makes it possible to match the reflector center frequency R and the transducer center frequency T by optimizing the ratio of the electrode period of the transducer and the electrode period of the reflector, as shown in FIG. 4a. The basic principle is A case in which a crystal substrate and an aluminum electrode are used will be specifically explained below as an example. FIG. 5 is a cross-sectional view of a surface acoustic wave resonator according to the present invention. The substrate is ST-cut crystal, and the surface acoustic wave reflectors 2 and 3 have a circumferential base electrode with a thickness h nR marked with diagonal lines, and a circumferential base groove with a depth h gR formed by a method such as plasma etching. Similarly, the transducer has a structure having a periodic electrode having a thickness h nT and a periodic groove having a depth h gT .
Let L R be the electrode period of the reflector and L T be the electrode period of the transducer, and in order to match the reflector center frequency R and the transducer center frequency T , the ratio L T /L R is calculated as follows. Decide based on. The present inventors have clarified that the reflector center frequency R and the transducer center frequency T are given by equations (4) and (5) [Uno, Miyamoto, Abe, Jumonji; With equipment
"Optimum Manufacturing Method for SAW Resonators" IEICE Technical Report US80-18 (June 30, 1980) References below.
(1)]. R = (1-C 2R )υ s /L R (4) T {1-C 2T -C 1T -C 1T / (0.7q 2 T +0.56q T +0.43)}υ s /L T (5 ) where υ s is the propagation velocity of the surface wave, C 2T and C 2T
is the amount of frequency reduction due to the perturbation effect based on the metal-groove periodic structure for the reflector and transducer, respectively, and C 1T is a term representing the elastic mismatch at the boundary between the electrode and non-electrode portions for the transducer. , and q T is a quantity given by q T =πC 1T N (6) where N is the number of electrode pairs of the transducer. In order to match the reflector center frequency R and the transducer center frequency T using equations (4) and (5), the electrode period ratio L T /L R is set as L T /L R =1−C 2T −C 1T −C 1T /(0.7q〓+0.56q T +0.43)/1−C 2R (7) A good result can be derived. C 2R , C 2T and C
For 1T , when aluminum is used as the electrode, C 2R 4.33×10 -4 +4.23×10 -2 (h nR /L R ) +7.9 (h nR /L R ) 2 +10.8 (h gR / L R ) 2 +18.5 (h nR /L R ) (h gR /L R ) (8) C 2T 4.33×10 -4 +4.23×10 -2 (h nT /L T )+7.9 (h nT /L T ) 2 +10.8 (h gT /L T ) 2 +18.5 (h nT /L T ) (h gT /L T ) (9) C 1T =6.25×10 -4 +0.12 (h nT /L T )+0.172 (h gT /L T ) (10) It has been experimentally confirmed that it is given by (Reference (1)). By the way, since the electrode periods L R and L T almost match the wavelength λ of the surface wave at the common frequency,
Equations (8), (9) and (10) can be rewritten as follows. C 2R 4.33×10 -4 +4.23×10 -2 (h nR /λ) +7.9 (h nR /λ) 2 +10.8 (h gR /λ) 2 +18.5 (h nR /λ) ( h gR /λ) (11) C 2T 4.33×10 -4 +4.23×10 -2 (h nT /λ) +7.9 (h nT /λ) 2 +10.8 (h gT /λ) 2 +18. 5 (h nT /λ) (h gT /λ) (11)′ C 1T = 6.25×10 -4 +0.12 (h nT /λ) + 0.172 (h gT /λ) (12) Equation (6) , (11) and (12) into equation (7), the number of electrode pairs of the transducer N, and the thickness of the aluminum electrode of the reflector h n
R , the depth of the groove h gT , the thickness h gT of the aluminum electrode of the transducer, and the depth h gT of the groove, the electrode period ratio L T /L R can be determined. C 2R , C 2T and C 1T
Since the value of is usually on the order of 10 -3 , L T /
L R has a value slightly smaller than 1. Also,
When periodic grooves are not formed on the reflector or transducer, equations (8), (9), (10) and equation (11),
It goes without saying that in (11') and (12), it is sufficient to set h gR or h gT to zero. By the way, when manufacturing an actual resonator,
It is difficult to precisely match the condition of equation (7),
However, this is not necessary; as long as G a /G N 1 is satisfied at the frequency R as shown in FIG. 4B, a sufficient characteristic improvement effect can be obtained over the conventional resonator. The conditions for this can be found as follows. G a /G N is found in reference (2), and by transforming it, It can be expressed as The inventors have shown in Reference (1) that here and p are given by p1−η+√ 2 −2 (14) =q T √ 2 −2 (15) using the frequency-related variable η.
is shown. However, the relationship between frequency and η is as follows: = (1-C 2T -C 1T +C 1T η)υ S /L T (16). From equations (13) to (15), η such that G a /G N =1 is found as two roots, and if they are set as η 1 and η 2 , respectively, the following results can be obtained approximately. η 1 =0 (17) η 2 =-1/(0.35q 2 T +0.3q T +0.2) (18) From equations (16) to (18), the frequency range where G a /G N 1 is { C 2T −C 1T −C 1T /(0.35q 2 T +0.3q T +0.2)}υ s /L T (1−C 2T −C 1T )×υ s /L T (19). Reflector center frequency R given by equation (4)
The range of L T /L R can be determined from the condition that L T /L R exists within the frequency range given by Equation (19), and is given as shown in Equation (20) below. 1-C 2T -C 1T -C 1T /(0.35q〓+0.3q T +0.2)/1-C 2R L T /L R 1-C 2
T −C 1T /1−C 2R (20) Therefore, if the electrode period ratio L T /L R is set within the range given by equation (20), G a /G N 1 will be satisfied at the center frequency R of the reflector. As a result, a SAW resonator with low resonant resistance can be realized. Note that the optimal value given by equation (7) naturally satisfies equation (20). Next, a design guideline for the reflector-transducer spacing according to the present invention, that is, when the electrode period ratio L T /L R of the transducer and reflector is set within the range given by equation (20), will be explained. Therefore, we will examine the resonance conditions of the cavity type SAW resonator. As shown in FIG. 5, among the electrodes of each reflector, the length between the center of the electrode finger closest to the transducer and the center of the end electrode finger of the transducer, that is, the length between the reflector and the transducer. The user interval is ι
1 , ι 2 , the resonance condition is 2π(N+ι 1 /λ+ι 2 /λ)−φ R −φ T = mπ(
21) (m: positive integer). Here, φ R is the amount of phase shift of the surface wave due to reflection, and φ T is the amount of phase shift when passing through the transducer. It is known that φ R is π/2 at the center frequency R of the reflector, and also at the center frequency T of the transducer.
It is shown in literature (1) that φ T in is approximately given by φ T ( T ) (0.3+0.55q T ) π (22). From this, it can be seen that the resonance condition at frequency R (= T ) is ι 1 +ι 2 (5n+4/10+0.28q T )λ (23) (n: positive integer). Furthermore, considering the phase of the surface wave in the transducer and the electrical coupling conditions, ι 1 and ι 2 are ι i = (5n i +4/20+0.14q T ) λ (24) (n i : positive Integer, i=1, 2). However, n 1 and n 2 need to be odd numbers or even numbers at the same time, but do not necessarily have to be the same value. When designing an actual resonator, it is practical to vary ι i (i=1, 2) over a relatively wide range around the value given by equation (24), as shown in the numerical calculation example. Since sufficient characteristics can be obtained, ι i can be selected to the value that facilitates pattern formation in accordance with the manufacturing conditions of the electrode forming mask. Figure 6 shows that ι 1 = ι 2 and n 1 (=n 2 ) = 3
The graph shows the relationship between the reflector-transducer spacing and the resonator characteristics in the case where the solid line is the case according to the present invention and the broken line is the case according to the conventional configuration. However, the horizontal axis is the normalized value of the interval ι / λ (ι = ι 1 = ι
2 ), the left vertical axis is the resonance sharpness Q and the capacitance ratio γ, and the right vertical axis is the figure of merit M. M=1/ω 0 C 0 R 1 (25) (ω 0 : resonance angular frequency, C 0 : parallel capacitance, R 1 : resonant resistance). Furthermore, the values shown in Table 1 were assumed for the design conditions. In this case, from equations (11), (12), and (6), C 2R = C 2T = 6.91×10 −3 C 1T = 4.51×10 −3 q T = 1.133. Therefore, from equation (20), the range of L T /L R is 0.9908L T /L R 0.9955 (26), and from equation (7), the optimal value is L T /L R =0.993 (27). Become. The solid line in FIG. 6 corresponds to the case where equation (27) is satisfied. The resonator characteristics can be found in Reference (2) [Oyamada,
Yoshikawa, Ishihara; “Analysis of surface acoustic wave resonator using multi-pair IDT and its applications” IEICE Transactions J 60
-A, No.9 pp.805-812 (1977)]
It is calculated by calculating the admittance characteristics seen from the electrical terminal. However, as the surface wave propagation loss of the substrate, the attenuation constant per wavelength is assumed to be α=2×10 -4 (28). Further, in FIG. 6, the experimental results of a 145 MHz band SAW resonator conducted by the method described later are indicated by an x mark. As is clear from Figure 6,
Over a wide range of ι/λ, it is possible to significantly improve the characteristics compared to conventional SAW resonators.
【表】【table】
【表】【table】
【表】
第7図は、ι=ι1=ι2=1.0λとした場合
の、第1表の条件下での本発明によるSAW共振
器の特性の電極周期比LT/LRに対する依存性を
示す。この図から、式(20)の範囲内では、特性
上の差異は小さく、良好な特性が得られることが
分る。
次に、本発明によるSAW共振器の製作例につ
いて説明する。第1表の設計条件により、
145MHz帯SAW共振器を製作するため、第2表
に示す電極パターンを採用した。この場合、L
T/LR=0.9926とし式(26)を満足する値に選定
した。実験ではSTカツト水晶基板に、第2表の
パターンのアルミ電極を形成しておき、CF4ガス
プラズマによる反応性スパツタエツチングを用い
て水晶基板面をエツチングし溝を形成した。アル
ミニウムは水晶に比べエツチング速度が1/20以下
であるので、アルミ電極がそのまま溝形成用のマ
スクとして利用できる。第8図に溝の深さに対す
る共振器特性の依存性の計算値を実線で示し、大
気圧中での実験結果を〇及び・でプロツトした。
第1表に示すように設計条件はhg/λ=0.017
であるが、この付近で共振器特性はほぼ飽和して
いる。hg/λ=0.017まで溝加工を施した後真空
封止した結果を×で示すが、これは第6図に示し
た実験値に対応するものである。第3表に本発明
によるSAW共振器の特性を従来のSAW共振器の
特性例と比較して示す。第3表から明らかなよう
に本発明によるSAW共振器は、従来の共振器に
比べ反射電極本数が極めて少ないにもかかわら
ず、良好な特性が得られる。
以上説明したように、本発明による表面弾性波
共振器は、従来の共振器に比べ、反射電極数を減
少することにより小形化を達成できると同時に、
Q値の向上、共振抵抗の減少並びに容量比の低下
が可能であり、VHF帯〜UHF帯における小形発
振素子あるいはフイルタ等へ適用して大きな効果
を得ることができる。[Table] Figure 7 shows the dependence of the characteristics of the SAW resonator according to the present invention on the electrode period ratio L T /L R under the conditions shown in Table 1 when ι = ι 1 = ι 2 = 1.0λ. Show your gender. This figure shows that within the range of formula (20), the difference in characteristics is small and good characteristics can be obtained. Next, an example of manufacturing a SAW resonator according to the present invention will be described. According to the design conditions in Table 1,
In order to fabricate a 145MHz band SAW resonator, the electrode patterns shown in Table 2 were adopted. In this case, L
T /L R =0.9926 and a value that satisfies equation (26) was selected. In the experiment, an aluminum electrode with the pattern shown in Table 2 was formed on an ST-cut quartz substrate, and grooves were formed by etching the surface of the quartz substrate using reactive sputter etching using CF 4 gas plasma. Since the etching speed of aluminum is less than 1/20 that of quartz, the aluminum electrode can be used as is as a mask for forming grooves. In FIG. 8, the calculated dependence of the resonator characteristics on the depth of the groove is shown as a solid line, and the experimental results at atmospheric pressure are plotted as ○ and . As shown in Table 1, the design conditions are h g /λ=0.017
However, the resonator characteristics are almost saturated around this point. The results of vacuum sealing after grooving to h g /λ=0.017 are indicated by x, which corresponds to the experimental values shown in FIG. Table 3 shows the characteristics of the SAW resonator according to the present invention in comparison with an example of the characteristics of a conventional SAW resonator. As is clear from Table 3, the SAW resonator according to the present invention has good characteristics even though the number of reflective electrodes is extremely small compared to the conventional resonator. As explained above, the surface acoustic wave resonator according to the present invention can achieve miniaturization by reducing the number of reflective electrodes compared to conventional resonators, and at the same time,
It is possible to improve the Q value, reduce the resonance resistance, and lower the capacitance ratio, and it can be applied to small oscillation elements or filters in the VHF band to UHF band to obtain great effects.
第1図はキヤビテイ形表面弾性波共振器の構成
図、第2図は周期溝形反射器の断面図、第3図は
従来の表面弾性波共振器における反射器の反射係
数の絶対値|Γ|とトランスジユーサの放射コン
ダクタンスGaの周波数特性の関係を表わす図、
第4図は本発明による|Γ|とGaの関係を表わ
す図、第5図は本発明の表面弾性波共振器の構成
の断面図、第6図は本発明による水晶基板を用い
た場合の表面弾性波共振器と従来の表面弾性波共
振器の反射器とトランスジユーサとの間隔に対す
る特性の依存性並びに実験例を示す図、第7図は
本発明による水晶基板を用いた場合の表面弾性波
共振器のトランスジユーサと反射器の電極周期比
に対する特性の依存性並びに実験結果を示す図、
第8図は本発明による水晶基板を用いた場合の表
面弾性波共振器のグルーブ深さに対する特性の依
存性を示す図である。
1……圧電基板、2,3……表面弾性波反射
器、4……表面弾性波トランスジユーサ、5,
5′……電気端子、6……溝。
Figure 1 is a block diagram of a cavity-type surface acoustic wave resonator, Figure 2 is a cross-sectional view of a periodic groove reflector, and Figure 3 is the absolute value of the reflection coefficient of the reflector in a conventional surface acoustic wave resonator |Γ A diagram showing the relationship between the frequency characteristics of | and the radiation conductance G a of the transducer,
FIG. 4 is a diagram showing the relationship between |Γ| and G a according to the present invention, FIG. 5 is a cross-sectional view of the structure of the surface acoustic wave resonator according to the present invention, and FIG. 6 is a diagram showing the case where the crystal substrate according to the present invention is used. Figure 7 shows the dependence of the characteristics of the surface acoustic wave resonator and the conventional surface acoustic wave resonator on the distance between the reflector and the transducer, as well as an experimental example. A diagram showing the dependence of characteristics on the electrode period ratio of the transducer and reflector of a surface acoustic wave resonator and experimental results,
FIG. 8 is a diagram showing the dependence of characteristics on the groove depth of a surface acoustic wave resonator using a crystal substrate according to the present invention. 1...Piezoelectric substrate, 2, 3...Surface acoustic wave reflector, 4...Surface acoustic wave transducer, 5,
5'...Electric terminal, 6...Groove.
Claims (1)
非電極部とからなる周期的構造を持つ一対の表面
波反射器を形成し、両表面波反射器の中間部分に
交差指電極による電極部と非電極部とからなる周
期的構造を持つ一個の表面波トランスジユーサを
形成し、共振波長λで決まる周期摂動に基づく表
面波反射器の周波数低下量をC2Rとし、共振波長
λで決まる周波摂動に基づく表面波トランスジユ
ーサの周波数低下量をC2Tとし、また表面波トラ
ンスジユーサの電極部と非電極部の弾性的不整合
項をC1Tとし、さらにC1T並びに表面波トランス
ジユーサの電極対数Nで決まる定数qTを qT=πC1TN とおいて、表面波トランスジユーサの電極周期L
Tと表面波反射器の電極周期LRの比LT/LRを 1−C2T−C1T−C1T/(0.35qT 2+0.3qT+0.2)/1−C2R≦LT/LR≦1
−C2T−C1T/1−C2R の範囲に設定することを特徴とする表面弾性波共
振器。 2 前記圧電基板には水晶が用いられ、前記表面
波反射器は厚さhnRのすだれ状のアルミ電極とそ
のすだれ状電極間の非電極部に形成された深さh
gR(≧0)の溝からなり、前記表面波トランスジ
ユーサは厚さhnTの交差指電極とその交差指電極
間の非電極部に形成された深さhgT(≧0)の溝
からなり、前記式におけるC2R、C2T、C1Tを次
の近似式、即ち、 C2R〓4.33×10-4+4.23(hnR/λ)+7.9(hnR/λ)2+10.8(hgR/λ)2 18.5(hnR/λ)(hgr/λ) C2T〓4.33×10-4+4.23×10-2(hnT/λ)+7.9(hnT/λ)2+10.8(hgT/λ)2 18.5(hnT/λ)(hgT/λ) C1T〓6.25×10- 4+0.12(hnT/λ)+0.172(hgT/λ) によつて算出することを特徴とする特許請求の範
囲第1項記載の表面弾性波共振器。[Claims] 1. A pair of surface wave reflectors having a periodic structure consisting of an electrode part and a non-electrode part formed by interdigital electrodes are formed on a piezoelectric substrate, and a pair of surface wave reflectors are formed on a piezoelectric substrate, and a pair of surface wave reflectors are formed on a piezoelectric substrate, and a pair of surface wave reflectors having a periodic structure consisting of an electrode part and a non-electrode part are formed by interdigitated electrodes, and a pair of surface wave reflectors are formed in the middle part of both surface wave reflectors. Forming one surface wave transducer with a periodic structure consisting of an electrode part and a non-electrode part by finger electrodes, and let C 2R be the amount of frequency reduction of the surface wave reflector based on the periodic perturbation determined by the resonance wavelength λ, Let C 2T be the frequency reduction amount of the surface wave transducer based on the frequency perturbation determined by the resonant wavelength λ, let C 1T be the elastic mismatch term between the electrode part and the non-electrode part of the surface wave transducer, and let C 1T Also, assuming that the constant q T determined by the number of electrode pairs of the surface wave transducer N is q T =πC 1T N , the electrode period L of the surface wave transducer is
The ratio L T /L R of T and the electrode period L R of the surface wave reflector is 1-C 2T -C 1T -C 1T /(0.35q T 2 +0.3q T +0.2)/1-C 2R ≦ L T /L R ≦1
A surface acoustic wave resonator characterized in that the surface acoustic wave resonator is set in the range of -C 2T -C 1T /1-C 2R . 2 A crystal is used for the piezoelectric substrate, and the surface wave reflector is formed by interdigital aluminum electrodes having a thickness h nR and a depth h formed in the non-electrode portion between the interdigital electrodes.
The surface wave transducer consists of a groove of gR (≧0) and a groove of depth h gT (≧0) formed between an interdigital electrode of thickness h nT and a non-electrode portion between the interdigital electrodes. Therefore, C 2R , C 2T , and C 1T in the above equation can be expressed as the following approximate expression: C 2R 〓4.33×10 -4 +4.23(h nR /λ)+7.9(h nR /λ) 2 +10. 8 (h gR /λ) 2 18.5 (h nR /λ) (h gr /λ) C 2T 〓4.33×10 -4 +4.23×10 -2 (h nT /λ) + 7.9 (h nT /λ ) 2 +10.8 (h gT /λ) 2 18.5 (h nT /λ) (h gT /λ) C 1T 〓6.25×10 - 4 +0.12 (h nT /λ) +0.172 (h gT /λ ) The surface acoustic wave resonator according to claim 1, wherein the surface acoustic wave resonator is calculated by:
Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP17524280A JPS5799813A (en) | 1980-12-13 | 1980-12-13 | Surface acoustic wave resonator |
GB8116284A GB2078042B (en) | 1980-06-13 | 1981-05-28 | Surface acoustic wave resonator |
US06/267,680 US4387355A (en) | 1980-06-13 | 1981-05-28 | Surface acoustic wave resonator |
FR8111388A FR2484735A1 (en) | 1980-06-13 | 1981-06-10 | SURFACE ACOUSTIC WAVE RESONATOR |
NLAANVRAGE8102818,A NL187091C (en) | 1980-06-13 | 1981-06-11 | ACOUSTIC SURFACE WAVE RESONATOR. |
DE19813123410 DE3123410A1 (en) | 1980-06-13 | 1981-06-12 | ACOUSTIC SURFACE WAVE RESONATOR |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP17524280A JPS5799813A (en) | 1980-12-13 | 1980-12-13 | Surface acoustic wave resonator |
Publications (2)
Publication Number | Publication Date |
---|---|
JPS5799813A JPS5799813A (en) | 1982-06-21 |
JPS6147009B2 true JPS6147009B2 (en) | 1986-10-17 |
Family
ID=15992740
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP17524280A Granted JPS5799813A (en) | 1980-06-13 | 1980-12-13 | Surface acoustic wave resonator |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPS5799813A (en) |
Families Citing this family (15)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS61251223A (en) * | 1985-04-27 | 1986-11-08 | Pioneer Electronic Corp | Surface acoustic wave resonator |
JPH06338756A (en) * | 1993-05-27 | 1994-12-06 | Fujitsu Ltd | Resonator type surface acoustic wave filter |
JPWO2006137464A1 (en) * | 2005-06-21 | 2009-01-22 | エプソントヨコム株式会社 | Surface acoustic wave device, module, and oscillator |
EP2403141B1 (en) | 2009-02-27 | 2018-10-24 | Seiko Epson Corporation | Surface acoustic wave resonator, surface acoustic wave oscillator, and electronic device |
JP4645923B2 (en) | 2009-02-27 | 2011-03-09 | セイコーエプソン株式会社 | Surface acoustic wave resonator and surface acoustic wave oscillator |
JP5678486B2 (en) | 2010-06-17 | 2015-03-04 | セイコーエプソン株式会社 | Surface acoustic wave resonator, surface acoustic wave oscillator and electronic device |
JP2012049818A (en) | 2010-08-26 | 2012-03-08 | Seiko Epson Corp | Surface acoustic wave resonator, surface acoustic wave oscillator, and electronic apparatus |
JP5934464B2 (en) | 2010-08-26 | 2016-06-15 | セイコーエプソン株式会社 | Surface acoustic wave resonator, surface acoustic wave oscillator, and electronic device |
JP2012049817A (en) | 2010-08-26 | 2012-03-08 | Seiko Epson Corp | Surface acoustic wave device, surface acoustic wave oscillator, and electronic apparatus |
JP2012060418A (en) * | 2010-09-09 | 2012-03-22 | Seiko Epson Corp | Surface acoustic wave device, electronic apparatus and sensor device |
JP2012060420A (en) | 2010-09-09 | 2012-03-22 | Seiko Epson Corp | Surface acoustic wave device, electronic apparatus and sensor device |
JP2012060422A (en) * | 2010-09-09 | 2012-03-22 | Seiko Epson Corp | Surface acoustic wave device, electronic apparatus and sensor device |
JP5652606B2 (en) | 2010-12-03 | 2015-01-14 | セイコーエプソン株式会社 | Surface acoustic wave resonator, surface acoustic wave oscillator, and electronic device |
JP5648908B2 (en) | 2010-12-07 | 2015-01-07 | セイコーエプソン株式会社 | Vibration device, oscillator, and electronic device |
JP2015029358A (en) * | 2014-10-29 | 2015-02-12 | セイコーエプソン株式会社 | Surface acoustic wave resonator, surface acoustic wave oscillator, and electronic device |
-
1980
- 1980-12-13 JP JP17524280A patent/JPS5799813A/en active Granted
Also Published As
Publication number | Publication date |
---|---|
JPS5799813A (en) | 1982-06-21 |
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