JP3825736B2 - Thin film piezoelectric resonator and high frequency filter - Google Patents

Description

例えば、５ＧＨｚ無線ＬＡＮ（Local Area Network）向けの帯域通過フィルタを構成するには、圧電体として弾性定数が大きいＡｌＮ（窒化アルミニウム）を選択すると有利である。これは、直列抵抗を減らすため共振器における上下電極の間隔を１５０〜２００ｎｍ程度としても、ＡｌＮの弾性定数が大きいことから共振周波数を５ＧＨｚ程度にまで上げることができるためである。
【０００５】
しかしながら、ＡｌＮの結合定数はおよそ６％であり、式（１）によればΔｆ〜１２０ＭＨｚとなる。よってＡｌＮを圧電体として用いる薄膜圧電共振器を複数組み合わせて帯域通過フィルタを構成すると、その通過帯域幅は約１７０ＭＨｚとなる。図１７は、従来の薄膜圧電共振器の共振周波数特性を示す図である。図示されるように、通過帯域半値幅付近における通過帯域幅は約１７０ＭＨｚであることがわかる。
【０００６】
ところで、近年の通信システムにおいては、日本向けの仕様と欧州向けの仕様とで要求される通信帯域が異なる場合が有る。例えば無線ＬＡＮシステムにおいては、日本向けの仕様では帯域通過フィルタの通過帯域として約１００ＭＨｚ（５．１５〜５．２５ＧＨｚ）確保できれば良いため、ＡｌＮを圧電体として用いる薄膜圧電共振器を組み合わせることで充分に仕様を満たすことができる。しかしながら欧州向けの仕様では帯域通過フィルタの通過帯域として約２００ＭＨｚ（５．１５〜５．３５ＧＨｚ）を要求される。よって従来の薄膜圧電共振器を用いた帯域フィルタには、少なくとも欧州向けの仕様に応えることができないという不具合がある。
【０００７】
このような不具合を解決するために通過帯域を拡大する方法としては、第１に、インダクタンスを接続してΔｆを広げるという手法がある。第２に、直列に接続される薄膜圧電共振器の共振周波数と、並列に接続される薄膜圧電共振器の反共振周波数とをわずかにずらすという手法がある。
【０００８】
しかしながらいずれの手法にも、帯域内の挿入損失を増やすといった弊害がある。また薄膜圧電共振器を用いた高周波フィルタの帯域幅の最大値は、薄膜圧電体材料の物性値によってほぼ決定付けられるため、これらの手法により如何に帯域幅を広げたとしても高々２００ＭＨｚ程度が限度である。よって構内用の無線ＬＡＮシステムの帯域だけでなく、４．９ＧＨｚ帯や５．８ＧＨｚ帯を使用する公衆サービスなどを含めた無線ＬＡＮにも対応するためには複数のフィルタを回路を並列に接続する必要が生じ、挿入損失がさらに増加するという悪循環に陥る。
【０００９】
なお、ＦＢＡＲを用いたフィルタに関わる技術を開示した公知文献として、下記の特許文献１がある。この文献に記載の発明は、例えばＣＤＭＡ（Code Division Multiple Access）を利用する無線通信装置に用いられる送受切換器において、１ワットを超える電力レベルによって送受切換器の信頼性又はフィルタ特性の長期安定性が損なわれることのない、十分に急峻なフィルタ特性を備える送受切換器を提供することを目的とする。また、当該文献に記載される発明のもう１つの目的は、セラミック・フィルタ又はＳＡＷフィルタをベースにした現行の送受切換器よりかなり小型であって、製造コストを低く保つことができるように個別同調を必要としない送受切換器を提供することも目的とする。
【００１０】
【特許文献１】
特開２００１−０２４４７６号公報（段落番号［００１２］）
【００１１】
【発明が解決しようとする課題】
以上述べたように従来の薄膜圧電共振器を用いた高周波フィルタには、その帯域幅の最大値が薄膜圧電体材料の物性値によってほぼ決定付けられるため、広帯域化が困難であるという不具合がある。
本発明は上記事情によりなされたもので、その目的は、通過帯域の広帯域化を図った高周波フィルタおよび薄膜圧電共振器を提供することにある。
【００１２】
【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関わる薄膜圧電共振器は、一方の面とこの面と対向する他方の面とを有する薄膜圧電体と、入力信号が印加され前記一方の面に取り付けられる第１の極板と、前記他方の面に前記第１の極板と対向して取り付けられ高周波的に接地される第２の極板と、前記一方の面に取り付けられ高周波的に接地される第３の極板と、前記他方の面に前記第３の極板と対向して取り付けられ共振信号を出力する第４の極板とを具備することを特徴とする。
このような構成であるから、第４の極板から入力信号と逆相の共振出力を取り出すことが可能となる。
【００１３】
また本発明に関わる高周波フィルタは、並列接続され互いに中心周波数の異なる第１および第２のフィルタに高周波信号を分配し並列合成して濾波出力を得る高周波フィルタであって、前記第１のフィルタは、前記高周波信号の分配路中に直列接続される第１の共振器と、この第１の共振器に並列接続される第２の共振器とを備え、前記第２のフィルタは、例えば上記逆相出力を得る手段を有する薄膜圧電共振器からなる第３の共振器と、この第３の共振器に並列接続される第４の共振器とを備えることを特徴とする。
【００１４】
このような手段を講じたことにより、第２のフィルタからは入力される高周波信号と逆相の共振出力を得ることができる。ここで、例えば第１の極板と第２の極板との厚みを変えることで、第１および第２のフィルタの中心周波数を異ならせることができ、その差に相当する通過帯域を有する高周波フィルタを実現することが可能となる。これにより、薄膜圧電体の材料によって決められる薄膜圧電共振器フィルタの最大帯域幅以上の帯域幅を実現することができる。
【００１５】
【発明の実施の形態】
以下、図面を参照して本発明の実施の形態を詳細に説明する。
【００１６】
（第１の実施形態）
図１は本発明に係わる高周波フィルタの第１の実施形態を示す回路図である。図１において、高周波の入力信号ＲＦ_ｉｎは２分岐され、並列接続される第１のフィルタおよび第２のフィルタに分配されたのち合成され、濾波出力ＲＦ_ｏｕｔが得られる。
【００１７】
第１のフィルタは薄膜圧電共振器１０１，１０２とからなる。薄膜圧電共振器１０１は高周波信号の分配路に直列に接続され、薄膜圧電共振器１０２は薄膜圧電共振器１０１に並列に接続される。第２のフィルタは薄膜圧電共振器１０３，１０４とからなる。薄膜圧電共振器１０３は高周波信号の分配路に直列に接続され、薄膜圧電共振器１０４は薄膜圧電共振器１０３に並列に接続される。ここで、薄膜圧電共振器１０３は入力された信号の位相を反転させる機能を持ち、従って第１および第２のフィルタの共振出力は互いに反転した状態で合成される。
【００１８】
図２は、図１に示される各フィルタの周波数スペクトルを示す図である。本実施形態においては各フィルタに異なる中心周波数を持たせる。図２（ａ）に示されるように第１のフィルタの中心周波数をｆ１とする。図２（ｂ）に示されるように第２のフィルタの中心周波数をｆ２とする。各フィルタの通過帯域を合成すると、図２（ｃ）に示される広帯域化された特性が得られる。これは、帯域が重なり合う部分を互いに逆相で合成することにより、当該部分がインピーダンス的に和合成されるためである。
【００１９】
図３は、図１に示される薄膜圧電共振器１０１，１０２，１０４の一構成例を模式的に示す断面図である。図３において、向かい合う極板３０２により薄膜圧電体３０１を挟み込み、この構造を支持層３０４および基板３０３で支える。さらに、薄膜圧電体３０１および極板３０２と基板３０３の間に空気層３０５を設ける。なお空気層３０５に代えて、真空層を設けても良い。
【００２０】
図３の構成の薄膜圧電共振器の動作原理を以下に説明する。極板３０２に印加される電圧により薄膜圧電体３０１が振動する。その振動を対向の極板が波として検値し、出力電圧に変換することにより共振出力が得られる。
【００２１】
薄膜圧電体３０１の振動による共振周波数、反共振周波数は、薄膜圧電体３０１の厚みｔ、極板３０２の厚みｈ、および薄膜圧電体の材料により決定される。薄膜圧電体材料としては、例えば窒化アルミニウム（ＡｌＮ）、チタン酸バリウム（ＢａＴｉＯ₃：ＢＴＯ）、およびチタン酸バリウムストロンチウム（Ｂａ_xＳｒ_1-xＴｉＯ₃：ＢＳＴＯ）などの物質がある。極板３０２はアルミニウム、金、および銅などの金属電極を使用できる。基板３０３には、例えばＳｉなどの半導体プロセスが使用できる材料を使用する。支持層３０４は例えば基板がＳｉである場合はＳｉ０₂などの材料を使用する。空気層３０５は例えば選択性エッチングなどの手法を用いて形成される。
【００２２】
図４は、図１に示される薄膜圧電共振器１０１，１０２，１０４の等価回路を示す回路図である。Ｃ_０（４０１）がＬ_１（４０２）、およびＣ_１（４０３）に並列接続されている構造をとる。Ｃ_０（４０１）は、極板面積、薄膜圧電体の厚み、および誘電率などの金属／圧電体（誘電体）／金属構造の物理形状に起因するキャパシタンスである。Ｌ_１（４０２）、Ｃ_１（４０３）は、主に薄膜圧電体の分極率など、圧電体としての物性に起因するインダクタンスとキャパシタンスである。
【００２３】
図４の等価回路における合成インピーダンスは次式（２）で表される。
【数２】

また、式（２）から導かれる共振周波数ｆ_ｒ（インピーダンス零の周波数）および反共振周波数ｆ_ａ（インピーダンス無限大の周波数）は次式（３）、（４）で表される。
【数３】

【数４】

このように、共振周波数ｆ_ｒおよび反共振周波数ｆ_ａは、Ｃ_０（４０１）、Ｌ_１（４０２）およびＣ_１（４０３）により決定される。
【００２４】
図５は図３の等価回路におけるインピーダンス特性|Ｚ|を表す図である。図５に示されるように共振周波数ｆ_ｒにおいてインピーダンスはゼロとなり、周波数の増加につれインピーダンスは単調に増加し、反共振周波数ｆ_ａにおいて無限大となる。
【００２５】
図６は、薄膜圧電共振器を用いて構成される高周波フィルタの一構成例を示す回路図である。入力側に直列に接続される薄膜圧電共振器６０１に対して薄膜圧電共振器６０２を並列に接続することにより、フィルタ特性を実現できる。
【００２６】
図７は、薄膜圧電共振器を用いて構成されるフィルタの他の構成例を示す回路図である。図示されるように、薄膜圧電共振器６０１を出力側に直列に接続するようにしてもフィルタ特性を実現できる。なお薄膜圧電共振器６０１，６０２は図１の薄膜圧電共振器１０１，１０２，１０４に相当し、いずれも図３に示される構成を有する。また図６、図７に示される接続形態は、いわゆるラダー構成と称される。
【００２７】
この種の高周波フィルタは、一つの薄膜圧電共振器に一つ以上のキャパシタンス、または一つ以上のインダクタンスをラダー状接続しても実現できる。あるいは、これらの素子を任意の組み合わせで適宜接続しても実現できる。
【００２８】
図６、図７に示される高周波フィルタの通過周波数帯域は、次のようにして得られる。まず、直列接続される薄膜圧電共振器６０１の共振周波数ｆ_ｒを決定する。さらに、並列接続される薄膜圧電共振器６０２の共振周波数を、薄膜圧電共振器６０１の反共振周波数ｆ_ａに合わせて設計することで、通過周波数帯域ＢＷを次式（５）に示されるように決定できる。
【数５】

このときの中心周波数ｆ_{ｃｅｎｔｅｒ}は、次式（６）に示される。
【数６】

図８は、本実施形態に係わる高周波フィルタのインピーダンス特性|Ｚ|を示す図である。図８において、点線は図６、図７の高周波フィルタの直列接続薄膜圧電共振器６０１のインピーダンス特性を、破線は並列接続薄膜圧電共振器６０２のインピーダンス特性を、実線は合成インピーダンス特性をそれぞれ示す。
【００２９】
通過周波数帯域ＢＷは、薄膜圧電共振器６０２の共振周波数を適当な値にすることで設定できる。薄膜圧電共振器の共振周波数は、先に述べたように薄膜圧電体の材料、厚さ、および金属極板の厚さを変化させることにより適切な値に設定することができる。
【００３０】
図９は、図１に示される位相を反転させる手段を有する薄膜圧電共振器１０３の一構成例を示す図である。この薄膜圧電共振器１０３は、薄膜圧電体９０７を、それぞれ対向して設けられる２対の極板９０１〜９０４で挟み込んだ構成となっている。このうち極板９０１と９０２、および極板９０３と９０４が互いに向かい合う。極板９０１と９０３、および極板９０２と９０４が、それぞれ薄膜圧電体９０７の同一面に取り付けられる。さらに、極板９０２と９０３とは接地され、極板９０１が入力ポート、極板９０４が出力ポートとなる。
【００３１】
図９において、極板９０２と９０４とが取り付けられる面を基準面９０５とする。基準面９０５に入射される入力波は、基準面９０６において検波され出力される。入射波は薄膜圧電体９０７への入力電圧が圧電効果により波に変換されることにより生成される。
【００３２】
高周波出力信号ＲＦ_ｏｕｔの波形は、対向面に設置される極板の電位により決まる。極板９０２を接地電位として極板９０１に正の電圧Ｖが印加されると、極板９０４も電圧Ｖを出力する。ここで極板９０４の電位基準となる対向極板９０３が接地されているので、極板９０４にはＶの符号が反転して現れることになる。従って、例えば正弦波を入力すると、位相の反転した正弦波が得られる。
【００３３】
図１０は、図９に示される薄膜圧電共振器１０３の一構成例を模式的に示す図である。図１０（ａ）が上面図を、図１０（ｂ）が断面図を示す。図１０において、対向する金属極板１００２および金属極板１００３により薄膜圧電体１００１が挟持される。金属極板１００２は入力または出力の信号線となり、金属極板１００３はいずれも接地線に接続される。
【００３４】
図１１は本実施形態に係わる高周波フィルタの別の構成を示す回路図である。この高周波フィルタは、図１に示される高周波フィルタを並列に多段接続した構成を有する。図１１の構成において、図１の構成に対応する部分をここではサブフィルタと称する。図１１の点線囲み部分が一つのサブフィルタに対応する。各サブフィルタを構成する第１および第２のフィルタの中心周波数を、低域から高域へと順にｆ１、ｆ２、ｆ３、ｆ４、…、ｆｎとする。
【００３５】
上記構成においては、中心周波数がｆ１、ｆ３、ｆ５、…となる第１のフィルタの出力特性は、入力信号ＲＦ_ｉｎと同相になる。中心周波数がｆ２、ｆ４、ｆ６、…となる第２のフィルタの出力特性は、入力信号ＲＦ_ｉｎと逆相になる。これにより出力信号ＲＦ_ｏｕｔに得られる通過帯域の周波数スペクトルは、図１２に示されるようになる。
【００３６】
図１２は、図１１に示される高周波フィルタの周波数スペクトルを示す図である。このように、隣り合う帯域を受け持つフィルタの入出力特性を、同相→逆相→同相→逆相→…というように順次配列することにより、帯域が重なり合う部分がインピーダンス的に和合成され、一つの拡大された通過帯域を形成することが可能になる。
【００３７】
なお、フィルタの開始段および最終段での同相、逆相の区別は無い。要するに、隣り合う帯域で位相が互いに逆転する関係が保たれていれば、図１２に示されるような帯域の拡大を実現することができる。また、装置への実装過程においても、中心周波数の配列の順序や同相信号、逆相信号の配列の順序も、図示と厳密に対応させる必要はない。
【００３８】
図１３は、図１１の構成により得られる周波数スペクトルの別の例を示す図である。中心周波数が異なり、かつ出力が同じ位相となる一対の薄膜圧電共振器フィルタでは、帯域が重なりあう部分で信号を減衰させることができる。そこで、図１１の構成において、各サブフィルタの第１および第２のフィルタの周波数配置を順にｆ１、ｆ２、（ｆ４）、（ｆ３）、ｆ５、ｆ６、（ｆ８）、（ｆ７）、ｆ９、…というように配列することにより、隣り合う帯域での出力が、同相→逆相→逆相→同相→同相→逆相→逆相→…となるように配列される。これにより図１３に示されるように、帯域が重なりあう部分の周波数成分を持つ信号を除去することが可能となる。
【００３９】
図１３においては、帯域が重なり合う部分を点線で示し、通過帯域を実線で示す。このような通過帯域特性により、例えば高周波領域で周波数分割多重された信号を分離するための用途を実現できる。なお、フィルタの開始段および最終段で同相、逆相の区別は無い。あるいは中心周波数の順番通り、また同相および逆相の関係を図示のとおり配列してフィルタを配置する必要は無い。
【００４０】
以上述べたように本実施形態では、それぞれ対向する２対の極板で薄膜圧電体を挟み込み、薄膜圧電共振器１０３を形成する。この薄膜圧電共振器１０３各対の極板のうち薄膜圧電体１０３の異なる面に取り付けられる極板を接地することにより、入力信号に対して位相の反転した共振出力を得る。そして、薄膜圧電共振器１０１，１０２をラダー状接続して中心周波数ｆ１の第１のフィルタを形成し、薄膜圧電共振器１０３，１０４をラダー状接続してｆ１と異なる中心周波数ｆ２の第２のフィルタを形成する。これらのフィルタを並列接続してフィルタを形成するようにしている。
【００４１】
すなわち、図１に示される位相を反転させる手段を持つ薄膜圧電共振器１０３を形成し、この薄膜圧電共振器１０３を用いて入力信号の位相を反転させるフィルタ（第２のフィルタ）を構成する。そして、このフィルタを、中心周波数の異なる別のフィルタ（第１のフィルタ）と並列に接続することにより、各フィルタの通過帯域が重なり合う部分を滑らかに接続して中心周波数の差に相当する通過帯域を得る。
【００４２】
このように、薄膜圧電共振器を用いることでギガヘルツ帯などの超高周波領域においても充分に動作可能な高周波フィルタを実現することができる。しかも位相を反転させる手段を持つ薄膜圧電共振器により通過帯域の異なる複数のフィルタの帯域を滑らかに接続することができるようになり、これらのフィルタを複数接続することで通過帯域を自由に拡大することができる。また接続されるフィルタの中心周波数を適切に設定することで、複数の通過帯域を有するバンドパスフィルタを構成することもできる。
【００４３】
（第２の実施形態）
図１４は、本発明に係わる高周波フィルタの第２の実施形態を示す回路図である。これは、一枚の薄膜圧電体を３対の極板で挟み込んだ構成となっている。そして、薄膜圧電体における、入力信号ＲＦ_ｉｎが入力される極板が取り付けられる面と同じ面に、極板１１０１を取り付け、この面の対向面に、極板１１０２を取り付ける。入力信号ＲＦｉｎが入力される極板に対向する極板と、極板１１０１に対向する極板と、極板１１０２に対向する極板とを、それぞれ接地する。
【００４４】
このような構成によれば、入力信号ＲＦ_ｉｎと同相の共振出力（ＲＦ_ｏｕｔ１）が極板１１０１から出力される。また、入力信号ＲＦ_ｉｎと逆相の共振出力（ＲＦ_ｏｕｔ２）が極板１１０２から出力される。そして、同相出力ＲＦ_ｏｕｔ１と逆相出力ＲＦ_ｏｕｔ２とが合成されて、濾波出力ＲＦ_ｏｕｔが得られる。
本実施形態では、一枚の薄膜圧電体で異なる共振周波数の二つ以上の出力を得るための方法としては、極板の厚みを変化させる手法が有る。
【００４５】
図１４の構成は、図６で示されるフィルタ構造を並列接続したものに相当し、図１の高周波フィルタと同様の機能を実現できる。しかも本実施形態によれば、薄膜圧電体の面積を小さくすることができるとともに、薄膜圧電共振器の数を減らせることから、図１の構成に比べサイズをより小さくした高周波フィルタを実現することができる。
【００４６】
図１５は、この実施形態に係わる高周波フィルタの別の構成を示す回路図である。この構成は、図１４で示される広帯域薄膜圧電共振器フィルタを、多段並列に組み合わせたものである。この構成においても、各サブフィルタの中心周波数を適切に設定することにより、図１２または図１３と同様の通過帯域特性を実現することができる。しかも本実施形態においては一つ一つのサブフィルタのサイズを小さくできることから、全体でのサイズを更に縮小することが可能になる。
【００４７】
図１６は、本発明に係わる高周波フィルタの実施形態における別の構成例を示す回路図である。図１６の構成は、同相出力の高周波フィルタを２つ直列接続したものと、同相出力と逆相出力の高周波フィルタを直列接続したものとを並列に接続した構造を有する。ここでは、直列接続される高周波フィルタの中心周波数を互いに同じに設定する。
【００４８】
一般に、同じ中心周波数を持つ複数のバンドパスフィルタを直列に接続すると、単独での特性に比べて通過帯域のスカート特性の向上を促すことができる。従って図１６の構成によれば、広帯域化とともにスカート特性を向上させた高周波フィルタを実現することが可能になる。
【００４９】
【発明の効果】
以上詳しく述べたように本発明によれば、通過帯域の広帯域を図った高周波フィルタおよびこの高周波フィルタを実現する薄膜圧電共振器を実現することができる。
【図面の簡単な説明】
【図１】 本発明に係わる高周波フィルタの第１の実施形態を示す回路図。
【図２】 図１に示される第１および第２のフィルタの周波数スペクトルおよび合成スペクトルを示す図。
【図３】 図１に示される薄膜圧電共振器１０１，１０２，１０４の一構成例を模式的に示す断面図。
【図４】 図１に示される薄膜圧電共振器１０１，１０２，１０４の等価回路を示す回路図。
【図５】 図３の等価回路におけるインピーダンス特性|Ｚ|を示す図。
【図６】 薄膜圧電共振器を用いて構成される高周波フィルタの一構成例を示す回路図。
【図７】 薄膜圧電共振器を用いて構成されるフィルタの他の構成例を示す回路図。
【図８】 図６または図７に示される高周波フィルタのインピーダンス特性|Ｚ|を示す図。
【図９】 図１に示される位相を反転させる手段を有する薄膜圧電共振器１０３の一構成例を示す図。
【図１０】 図９に示される薄膜圧電共振器１０３の一構成例を示す模式図。
【図１１】 本発明の第１の実施形態に係わる高周波フィルタの別の構成を示す回路図。
【図１２】 図１１に示される高周波フィルタの周波数スペクトルを示す図。
【図１３】 図１１の構成により得られる周波数スペクトルの別の例を示す図。
【図１４】 本発明に係わる高周波フィルタの第２の実施形態を示す回路図。
【図１５】 本発明の第２の実施形態に係わる高周波フィルタの別の構成を示す回路図。
【図１６】 本発明に係わる高周波フィルタの実施形態における別の構成例を示す回路図。
【図１７】 従来の薄膜圧電共振器の共振周波数特性を示す図。
【符号の説明】
１０１，１０２…薄膜圧電共振器
１０３，１０４…薄膜圧電共振器
３０１…薄膜圧電体
３０２…極板
３０３…基板
３０４…支持層
３０５…空気層
４０１…物理形状に起因するキャパシタンスＣ０
４０２…圧電体の物性に起因するインダクタンスＬ１
４０３…圧電体の物性に起因するキャパシタンスＣ１
６０１，６０２…薄膜圧電共振器
９０１〜９０４…極板
９０５…基準面
９０６…基準面
９０７…薄膜圧電体
１００１…薄膜圧電体
１００２，１００３…金属極板
１１０１，１１０２…極板[0001]
BACKGROUND OF THE INVENTION
The present invention is applied to a high frequency band such as a microwave band, and particularly relates to an RF (Radio Frequency) filter using a thin film piezoelectric resonator (FBAR) and a thin film piezoelectric resonator realizing the high frequency filter. .
[0002]
[Prior art]
For example, a surface acoustic wave (SAW) filter is known as a small filter element suitably used in a mobile radio communication apparatus. In particular, in recent years, attention has been focused on a thin film piezoelectric resonator capable of handling a gigahertz band signal and an RF filter (hereinafter referred to as a high frequency filter) using the thin film piezoelectric resonator.
[0003]
In order to construct a bandpass filter circuit using a thin film piezoelectric resonator, the resonance frequency of the thin film piezoelectric resonator connected in series and the anti-resonance frequency of the thin film piezoelectric resonator connected in parallel are almost the same. Generally, a method for designing a resonator is generally used. It is derived from the theory of the filter circuit that the bandwidth of the filter configured in this way takes a value of about 1.4 times the interval (referred to as Δf) between the resonance frequency and the antiresonance frequency of the resonator. Δf is proportional to an electromechanical coupling constant is a piezoelectric material-specific material constant for a resonator (k t ^_2), satisfies the relationship represented by the following formula (1). Here, fr is a resonance frequency.
[0004]
[Expression 1]

For example, in order to construct a bandpass filter for 5 GHz wireless LAN (Local Area Network), it is advantageous to select AlN (aluminum nitride) having a large elastic constant as the piezoelectric body. This is because the resonance frequency can be increased to about 5 GHz because the elastic constant of AlN is large even if the distance between the upper and lower electrodes in the resonator is about 150 to 200 nm in order to reduce the series resistance.
[0005]
However, the coupling constant of AlN is approximately 6%, which is Δf to 120 MHz according to the equation (1). Therefore, when a band pass filter is configured by combining a plurality of thin film piezoelectric resonators using AlN as a piezoelectric body, the pass band width is about 170 MHz. FIG. 17 is a diagram showing resonance frequency characteristics of a conventional thin film piezoelectric resonator. As shown in the figure, it can be seen that the pass band width in the vicinity of the half band width of the pass band is about 170 MHz.
[0006]
By the way, in recent communication systems, there are cases where the required communication band differs between the specifications for Japan and the specifications for Europe. For example, in a wireless LAN system, it is sufficient to secure about 100 MHz (5.15 to 5.25 GHz) as a pass band of a band pass filter in the specification for Japan. Therefore, it is sufficient to combine a thin film piezoelectric resonator using AlN as a piezoelectric body. Can meet the specifications. However, in the specification for Europe, about 200 MHz (5.15 to 5.35 GHz) is required as the pass band of the band pass filter. Therefore, the conventional bandpass filter using the thin film piezoelectric resonator has a problem that it cannot meet at least the specification for Europe.
[0007]
As a method of expanding the pass band in order to solve such a problem, first, there is a method of expanding Δf by connecting an inductance. Second, there is a technique of slightly shifting the resonance frequency of the thin film piezoelectric resonators connected in series and the anti-resonance frequency of the thin film piezoelectric resonators connected in parallel.
[0008]
However, both methods have a harmful effect of increasing the in-band insertion loss. The maximum bandwidth of a high-frequency filter using a thin-film piezoelectric resonator is almost determined by the physical property values of the thin-film piezoelectric material. Therefore, no matter how wide the bandwidth is increased by these methods, the maximum is about 200 MHz. It is. Therefore, in order to support not only the wireless LAN system band for the premises but also the wireless LAN including public services using the 4.9 GHz band and the 5.8 GHz band, a plurality of filters are connected in parallel. This creates a vicious circle where the need arises and the insertion loss further increases.
[0009]
As a publicly known document disclosing a technique related to a filter using FBAR, there is the following Patent Document 1. The invention described in this document is, for example, a duplexer used in a radio communication apparatus using CDMA (Code Division Multiple Access), and the reliability of the duplexer or the long-term stability of the filter characteristics depending on the power level exceeding 1 watt. An object of the present invention is to provide a transmission / reception switching device having a sufficiently steep filter characteristic that does not impair the performance. Another object of the invention described in this document is to be individually tuned so that it is much smaller than current duplexers based on ceramic filters or SAW filters and can keep manufacturing costs low. Another object of the present invention is to provide a transmission / reception switching device that does not need to be used.
[0010]
[Patent Document 1]
JP 2001-024476 A (paragraph number [0012])
[0011]
[Problems to be solved by the invention]
As described above, the conventional high frequency filter using a thin film piezoelectric resonator has a problem that it is difficult to increase the bandwidth because the maximum bandwidth is almost determined by the physical property value of the thin film piezoelectric material. .
The present invention has been made under the circumstances described above, and an object of the present invention is to provide a high-frequency filter and a thin-film piezoelectric resonator having a wide pass band.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a thin film piezoelectric resonator according to the present invention includes a thin film piezoelectric body having one surface and the other surface opposite to the first surface, and a first thin film piezoelectric body attached to the one surface to which an input signal is applied. A first electrode plate, a second electrode plate mounted on the other surface opposite to the first electrode plate and grounded at a high frequency, and a second electrode plate mounted on the one surface and grounded at a high frequency. And a fourth electrode plate that is attached to the other surface opposite to the third electrode plate and outputs a resonance signal.
With such a configuration, it is possible to extract a resonance output having a phase opposite to that of the input signal from the fourth electrode plate.
[0013]
A high-frequency filter according to the present invention is a high-frequency filter that distributes high-frequency signals to first and second filters that are connected in parallel and have different center frequencies, and obtains a filtered output by parallel synthesis. A first resonator connected in series in the high-frequency signal distribution path, and a second resonator connected in parallel to the first resonator. A third resonator comprising a thin film piezoelectric resonator having means for obtaining a phase output, and a fourth resonator connected in parallel to the third resonator are provided.
[0014]
By taking such means, a resonance output having a phase opposite to that of the input high-frequency signal can be obtained from the second filter. Here, for example, by changing the thicknesses of the first electrode plate and the second electrode plate, the center frequencies of the first and second filters can be made different, and a high frequency signal having a pass band corresponding to the difference therebetween. A filter can be realized. Thereby, the bandwidth more than the maximum bandwidth of the thin film piezoelectric resonator filter determined by the material of the thin film piezoelectric body can be realized.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
(First embodiment)
FIG. 1 is a circuit diagram showing a first embodiment of a high-frequency filter according to the present invention. In FIG. 1, a high-frequency input signal RF _in is branched into two, distributed to a first filter and a second filter connected in parallel, and then combined to obtain a filtered output RF _out .
[0017]
The first filter includes thin film piezoelectric resonators 101 and 102. The thin film piezoelectric resonator 101 is connected in series to a high-frequency signal distribution path, and the thin film piezoelectric resonator 102 is connected to the thin film piezoelectric resonator 101 in parallel. The second filter includes thin film piezoelectric resonators 103 and 104. The thin film piezoelectric resonator 103 is connected in series to a high-frequency signal distribution path, and the thin film piezoelectric resonator 104 is connected to the thin film piezoelectric resonator 103 in parallel. Here, the thin film piezoelectric resonator 103 has a function of inverting the phase of the input signal. Therefore, the resonance outputs of the first and second filters are synthesized in a mutually inverted state.
[0018]
FIG. 2 is a diagram showing the frequency spectrum of each filter shown in FIG. In this embodiment, each filter has a different center frequency. As shown in FIG. 2A, the center frequency of the first filter is f1. As shown in FIG. 2B, the center frequency of the second filter is set to f2. When the passbands of the filters are combined, the broadband characteristics shown in FIG. 2C are obtained. This is because by synthesizing the portions where the bands overlap with each other in opposite phases, the portions are summed in terms of impedance.
[0019]
FIG. 3 is a cross-sectional view schematically showing a configuration example of the thin film piezoelectric resonators 101, 102, and 104 shown in FIG. In FIG. 3, the thin film piezoelectric body 301 is sandwiched between opposing electrode plates 302, and this structure is supported by a support layer 304 and a substrate 303. Further, an air layer 305 is provided between the thin film piezoelectric body 301 and the electrode plate 302 and the substrate 303. Note that a vacuum layer may be provided instead of the air layer 305.
[0020]
The operation principle of the thin film piezoelectric resonator having the configuration shown in FIG. 3 will be described below. The thin film piezoelectric body 301 vibrates due to the voltage applied to the electrode plate 302. The vibration is detected as a wave by the opposing electrode plate and converted into an output voltage to obtain a resonance output.
[0021]
The resonance frequency and antiresonance frequency due to vibration of the thin film piezoelectric body 301 are determined by the thickness t of the thin film piezoelectric body 301, the thickness h of the electrode plate 302, and the material of the thin film piezoelectric body. Examples of the thin film piezoelectric material include substances such as aluminum nitride (AlN), barium titanate (BaTiO ₃ : BTO), and barium strontium titanate (Ba _x Sr _1-x TiO ₃ : BSTO). The electrode plate 302 can use metal electrodes such as aluminum, gold, and copper. For the substrate 303, a material that can be used for a semiconductor process, such as Si, is used. For example, when the substrate is Si, the support layer 304 is made of a material such as SiO ₂ . The air layer 305 is formed using a technique such as selective etching, for example.
[0022]
FIG. 4 is a circuit diagram showing an equivalent circuit of the thin film piezoelectric resonators 101, 102, 104 shown in FIG. It has a structure in which C ₀ (401) is connected in parallel to L ₁ (402) and C ₁ (403). C ₀ (401) is the capacitance resulting from the physical shape of the metal / piezoelectric (dielectric) / metal structure, such as the electrode plate area, the thickness of the thin film piezoelectric, and the dielectric constant. L ₁ (402) and C ₁ (403) are inductance and capacitance mainly resulting from the physical properties of the piezoelectric body, such as the polarizability of the thin film piezoelectric body.
[0023]
The combined impedance in the equivalent circuit of FIG. 4 is expressed by the following equation (2).
[Expression 2]

The resonance frequency f _r (frequency with zero impedance) and anti-resonance frequency f _a (frequency with infinite impedance) derived from the equation (2) are expressed by the following equations (3) and (4).
[Equation 3]

[Expression 4]

Thus, the resonance frequency _fr and the anti-resonance frequency f _a are determined by C ₀ (401), L ₁ (402) and C ₁ (403).
[0024]
FIG. 5 is a diagram illustrating the impedance characteristic | Z | in the equivalent circuit of FIG. Impedance at the resonance frequency f _r as shown in FIG. 5 is zero, the impedance increases monotonically as the increasing frequency becomes infinite at the antiresonant frequency f _a.
[0025]
FIG. 6 is a circuit diagram showing a configuration example of a high-frequency filter configured using a thin film piezoelectric resonator. Filter characteristics can be realized by connecting the thin film piezoelectric resonator 602 in parallel to the thin film piezoelectric resonator 601 connected in series on the input side.
[0026]
FIG. 7 is a circuit diagram showing another configuration example of a filter configured using a thin film piezoelectric resonator. As shown in the figure, the filter characteristics can also be realized by connecting the thin film piezoelectric resonator 601 in series to the output side. The thin film piezoelectric resonators 601 and 602 correspond to the thin film piezoelectric resonators 101, 102, and 104 in FIG. 1, and all have the configuration shown in FIG. The connection form shown in FIGS. 6 and 7 is called a so-called ladder configuration.
[0027]
This type of high frequency filter can also be realized by connecting one or more capacitances or one or more inductances to one thin film piezoelectric resonator in a ladder shape. Alternatively, it can be realized by appropriately connecting these elements in any combination.
[0028]
The pass frequency band of the high frequency filter shown in FIGS. 6 and 7 is obtained as follows. First, to determine the resonance frequency f _r of the thin-film piezoelectric resonator 601 connected in series. Further, the resonance frequency of the FBAR 602 are connected in parallel, by designing in accordance with the anti-resonance frequency f _a of the thin-film piezoelectric resonator 601, as shown the frequency passband BW in equation (5) Can be determined.
[Equation 5]

The center frequency f _{center at} this time is represented by the following equation (6).
[Formula 6]

FIG. 8 is a diagram showing the impedance characteristic | Z | of the high-frequency filter according to the present embodiment. In FIG. 8, the dotted line indicates the impedance characteristic of the serial connection thin film piezoelectric resonator 601 of the high frequency filter of FIGS. 6 and 7, the broken line indicates the impedance characteristic of the parallel connection thin film piezoelectric resonator 602, and the solid line indicates the combined impedance characteristic.
[0029]
The pass frequency band BW can be set by setting the resonance frequency of the thin film piezoelectric resonator 602 to an appropriate value. As described above, the resonance frequency of the thin film piezoelectric resonator can be set to an appropriate value by changing the material, thickness, and thickness of the metal electrode plate of the thin film piezoelectric body.
[0030]
FIG. 9 is a diagram showing a configuration example of the thin film piezoelectric resonator 103 having means for inverting the phase shown in FIG. The thin film piezoelectric resonator 103 has a structure in which a thin film piezoelectric body 907 is sandwiched between two pairs of electrode plates 901 to 904 provided to face each other. Of these, the electrode plates 901 and 902 and the electrode plates 903 and 904 face each other. The electrode plates 901 and 903 and the electrode plates 902 and 904 are attached to the same surface of the thin film piezoelectric body 907, respectively. Further, the electrode plates 902 and 903 are grounded, the electrode plate 901 is an input port, and the electrode plate 904 is an output port.
[0031]
In FIG. 9, a surface to which the electrode plates 902 and 904 are attached is a reference surface 905. An input wave incident on the reference plane 905 is detected and output at the reference plane 906. The incident wave is generated by converting the input voltage to the thin film piezoelectric body 907 into a wave by the piezoelectric effect.
[0032]
The waveform of the RF output signal RF _out is determined by the potential of the electrode plate installed on the opposing surface. When a positive voltage V is applied to the electrode plate 901 with the electrode plate 902 as the ground potential, the electrode plate 904 also outputs the voltage V. Here, since the counter electrode plate 903 serving as the potential reference of the electrode plate 904 is grounded, the sign of V appears on the electrode plate 904 in an inverted manner. Therefore, for example, when a sine wave is input, a sine wave having an inverted phase is obtained.
[0033]
FIG. 10 is a diagram schematically showing a configuration example of the thin film piezoelectric resonator 103 shown in FIG. FIG. 10A shows a top view and FIG. 10B shows a cross-sectional view. In FIG. 10, the thin film piezoelectric body 1001 is sandwiched between the opposing metal electrode plate 1002 and metal electrode plate 1003. The metal electrode plate 1002 serves as an input or output signal line, and both of the metal electrode plates 1003 are connected to a ground line.
[0034]
FIG. 11 is a circuit diagram showing another configuration of the high-frequency filter according to this embodiment. This high frequency filter has a configuration in which the high frequency filters shown in FIG. 1 are connected in multiple stages in parallel. In the configuration of FIG. 11, a portion corresponding to the configuration of FIG. 1 is referred to as a sub-filter here. A portion surrounded by a dotted line in FIG. 11 corresponds to one subfilter. The center frequencies of the first and second filters constituting each sub-filter are assumed to be f1, f2, f3, f4,..., Fn in order from low to high.
[0035]
In the above configuration, the output characteristics of the first filter having the center frequencies of f1, f3, f5,... Are _in phase with the input signal RF _in . The output characteristics of the second filter whose center frequencies are f2, f4, f6,... Have a phase opposite to that of the input signal RF _in . As a result, the frequency spectrum of the pass band obtained in the output signal RF _out is as shown in FIG.
[0036]
FIG. 12 is a diagram showing a frequency spectrum of the high frequency filter shown in FIG. In this way, by sequentially arranging the input / output characteristics of the filters that handle adjacent bands in the order of in-phase → reverse phase → in-phase → reverse phase →... An expanded passband can be formed.
[0037]
There is no distinction between in-phase and anti-phase at the start stage and the final stage of the filter. In short, if the relationship in which the phases are reversed in adjacent bands is maintained, the band expansion as shown in FIG. 12 can be realized. Also, in the mounting process in the apparatus, the order of arrangement of the center frequencies and the order of arrangement of the in-phase signal and the anti-phase signal need not correspond exactly to those shown in the drawing.
[0038]
FIG. 13 is a diagram showing another example of the frequency spectrum obtained by the configuration of FIG. In a pair of thin film piezoelectric resonator filters having different center frequencies and the same phase, the signal can be attenuated at the portion where the bands overlap. Therefore, in the configuration of FIG. 11, the frequency arrangement of the first and second filters of each sub-filter is sequentially changed to f1, f2, (f4), (f3), f5, f6, (f8), (f7), f9, By arranging in this manner, outputs in adjacent bands are arranged in the order of in-phase → reverse phase → reverse phase → in-phase → in-phase → reverse phase → reverse phase →. As a result, as shown in FIG. 13, it is possible to remove a signal having a frequency component of a portion where the bands overlap.
[0039]
In FIG. 13, a portion where the bands overlap is indicated by a dotted line, and a pass band is indicated by a solid line. With such passband characteristics, for example, it is possible to realize an application for separating a frequency-division multiplexed signal in a high frequency region. There is no distinction between in-phase and anti-phase in the start stage and the final stage of the filter. Alternatively, it is not necessary to arrange the filters in the order of the center frequencies and by arranging the in-phase and anti-phase relationships as illustrated.
[0040]
As described above, in the present embodiment, the thin film piezoelectric resonator 103 is formed by sandwiching the thin film piezoelectric body between two pairs of electrode plates facing each other. By grounding the electrode plates attached to different surfaces of the thin film piezoelectric body 103 among the electrode plates of each pair of the thin film piezoelectric resonators 103, a resonance output whose phase is inverted with respect to the input signal is obtained. The thin film piezoelectric resonators 101 and 102 are connected in a ladder shape to form a first filter having a center frequency f1, and the thin film piezoelectric resonators 103 and 104 are connected in a ladder shape to form a second filter having a center frequency f2 different from f1. Form a filter. These filters are connected in parallel to form a filter.
[0041]
That is, the thin film piezoelectric resonator 103 having the means for inverting the phase shown in FIG. 1 is formed, and a filter (second filter) for inverting the phase of the input signal is configured using the thin film piezoelectric resonator 103. Then, by connecting this filter in parallel with another filter (first filter) having a different center frequency, a portion where the pass bands of the filters overlap is smoothly connected, and a pass band corresponding to the difference in center frequency is obtained. Get.
[0042]
As described above, a high-frequency filter that can operate sufficiently even in an ultra-high frequency region such as a gigahertz band can be realized by using a thin film piezoelectric resonator. In addition, a thin film piezoelectric resonator having a means for inverting the phase makes it possible to smoothly connect the bands of a plurality of filters having different pass bands, and the pass band can be freely expanded by connecting a plurality of these filters. be able to. A bandpass filter having a plurality of passbands can be configured by appropriately setting the center frequency of the connected filter.
[0043]
(Second Embodiment)
FIG. 14 is a circuit diagram showing a second embodiment of the high-frequency filter according to the present invention. In this configuration, one thin film piezoelectric body is sandwiched between three pairs of electrode plates. Then, the electrode plate 1101 is attached to the same surface as the surface to which the electrode plate to which the input signal RF _in is input is attached, and the electrode plate 1102 is attached to the opposite surface of this surface. The electrode plate facing the electrode plate to which the input signal RFin is input, the electrode plate facing the electrode plate 1101, and the electrode plate facing the electrode plate 1102 are grounded.
[0044]
According to such a configuration, a resonance output (RF _out1 ) _in phase with the input signal RF _in is output from the electrode plate 1101. In addition, a resonance output (RF _out2 ) having a phase opposite to that of the input signal RF _in is output from the electrode plate 1102. Then, the in-phase output RF _out1 and the anti-phase output RF _out2 are combined to obtain the filtered output RF _out .
In the present embodiment, as a method for obtaining two or more outputs having different resonance frequencies with one thin film piezoelectric body, there is a method of changing the thickness of the electrode plate.
[0045]
The configuration of FIG. 14 corresponds to the filter structure shown in FIG. 6 connected in parallel, and the same function as the high-frequency filter of FIG. 1 can be realized. Moreover, according to the present embodiment, the area of the thin film piezoelectric body can be reduced and the number of thin film piezoelectric resonators can be reduced, so that a high frequency filter having a smaller size than the configuration of FIG. 1 can be realized. Can do.
[0046]
FIG. 15 is a circuit diagram showing another configuration of the high-frequency filter according to this embodiment. In this configuration, the broadband thin film piezoelectric resonator filters shown in FIG. 14 are combined in parallel in multiple stages. Also in this configuration, the passband characteristics similar to those in FIG. 12 or FIG. 13 can be realized by appropriately setting the center frequency of each sub-filter. In addition, since the size of each sub-filter can be reduced in this embodiment, the overall size can be further reduced.
[0047]
FIG. 16 is a circuit diagram showing another configuration example in the embodiment of the high-frequency filter according to the present invention. The configuration of FIG. 16 has a structure in which two high-frequency filters with in-phase output are connected in series and one in which an in-phase output and a high-frequency filter with opposite-phase output are connected in series are connected in parallel. Here, the center frequencies of the high-frequency filters connected in series are set to be the same.
[0048]
In general, when a plurality of bandpass filters having the same center frequency are connected in series, it is possible to promote an improvement in the skirt characteristic of the passband as compared with a single characteristic. Therefore, according to the configuration of FIG. 16, it is possible to realize a high-frequency filter having a wide band and an improved skirt characteristic.
[0049]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to realize a high-frequency filter having a wide pass band and a thin-film piezoelectric resonator that realizes the high-frequency filter.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of a high-frequency filter according to the present invention.
FIG. 2 is a diagram showing a frequency spectrum and a combined spectrum of the first and second filters shown in FIG.
3 is a cross-sectional view schematically showing a configuration example of the thin film piezoelectric resonators 101, 102, and 104 shown in FIG.
4 is a circuit diagram showing an equivalent circuit of the thin film piezoelectric resonators 101, 102, 104 shown in FIG.
5 is a diagram showing an impedance characteristic | Z | in the equivalent circuit of FIG. 3;
FIG. 6 is a circuit diagram showing a configuration example of a high-frequency filter configured using a thin film piezoelectric resonator.
FIG. 7 is a circuit diagram showing another configuration example of a filter configured using a thin film piezoelectric resonator.
FIG. 8 is a diagram showing an impedance characteristic | Z | of the high frequency filter shown in FIG. 6 or FIG. 7;
9 is a diagram showing a configuration example of a thin film piezoelectric resonator 103 having means for inverting the phase shown in FIG.
10 is a schematic diagram showing a configuration example of the thin film piezoelectric resonator 103 shown in FIG.
FIG. 11 is a circuit diagram showing another configuration of the high-frequency filter according to the first embodiment of the present invention.
12 is a diagram showing a frequency spectrum of the high frequency filter shown in FIG.
13 is a diagram showing another example of a frequency spectrum obtained by the configuration of FIG.
FIG. 14 is a circuit diagram showing a second embodiment of a high-frequency filter according to the present invention.
FIG. 15 is a circuit diagram showing another configuration of the high-frequency filter according to the second embodiment of the present invention.
FIG. 16 is a circuit diagram showing another configuration example in the embodiment of the high-frequency filter according to the present invention.
FIG. 17 is a diagram showing resonance frequency characteristics of a conventional thin film piezoelectric resonator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101,102 ... Thin film piezoelectric resonator 103,104 ... Thin film piezoelectric resonator 301 ... Thin film piezoelectric body 302 ... Electrode plate 303 ... Substrate 304 ... Support layer 305 ... Air layer 401 ... Capacitance C0 resulting from a physical shape
402: Inductance L1 due to the physical properties of the piezoelectric body
403: Capacitance C1 resulting from the physical properties of the piezoelectric body
601, 602 ... Thin film piezoelectric resonators 901-904 ... Electrode plate 905 ... Reference surface 906 ... Reference surface 907 ... Thin film piezoelectric member 1001 ... Thin film piezoelectric member 1002, 1003 ... Metal electrode plate 1101, 1102 ... Electrode plate

Claims (7)

A thin film piezoelectric body having one surface and the other surface facing the surface;
A first electrode plate to which an input signal is applied and attached to the one surface;
A second electrode plate mounted on the other surface opposite to the first electrode plate and grounded at a high frequency;
A third electrode plate attached to the one surface and grounded at a high frequency;
A fourth electrode plate attached to the other surface opposite to the third electrode plate and outputting a first resonance signal;
A fifth electrode plate attached to the other surface and grounded at a high frequency;
A thin-film piezoelectric resonator comprising: a sixth electrode plate that is attached to the one surface opposite to the fifth electrode plate and outputs a second resonance signal. A high-frequency filter that distributes high-frequency signals to first and second filters that are connected in parallel and have different center frequencies to obtain a filtered output by parallel synthesis,
The first filter is:
A first resonator connected in series in the high-frequency signal distribution path;
A second resonator connected in parallel to the first resonator,
The second filter is:
A third resonator connected in series in the high-frequency signal distribution path and having phase inversion means for inverting the phase of the high-frequency signal propagating through the distribution path;
A fourth resonator connected in parallel to the third resonator ,
The first resonator includes:
A thin film piezoelectric body having one surface and the other surface facing the surface;
A first electrode plate to which the high-frequency signal is applied and attached to the one surface;
A second electrode plate mounted on the other surface opposite to the first electrode plate and grounded at a high frequency;
A third electrode plate attached to the one surface and grounded at a high frequency;
A fourth electrode plate attached to the other surface opposite to the third electrode plate and outputting a first resonance signal having a phase opposite to the high-frequency signal;
A fifth electrode plate attached to the other surface and grounded at a high frequency;
A high-frequency filter comprising: a sixth electrode plate that is attached to the one surface so as to face the fifth electrode plate and outputs a second resonance signal in phase with the high-frequency signal .   A high-frequency filter comprising the high-frequency filter according to claim 2 connected in multiple stages in parallel. The third resonator includes:
A thin film piezoelectric body having one surface and the other surface facing the surface;
A first electrode plate to which the distributed high frequency signal is applied and attached to the one surface;
A second electrode plate mounted on the other surface opposite to the first electrode plate and grounded at a high frequency;
A third electrode plate attached to the one surface and grounded at a high frequency;
4. The high frequency filter according to claim 2, further comprising a fourth electrode plate that is attached to the other surface so as to face the third electrode plate and outputs a resonance signal. 5. A first resonator to which a high-frequency signal is applied and which outputs a first resonance signal having a phase opposite to the high-frequency signal and a second resonance signal having the same phase as the high-frequency signal;
A second resonator connected in parallel to the path of the first resonance signal;
A third resonator connected in parallel to the path of the second resonance signal,
The first resonator includes:
A thin film piezoelectric body having one surface and the other surface facing the surface;
A first electrode plate to which the high-frequency signal is applied and attached to the one surface;
A second electrode plate mounted on the other surface opposite to the first electrode plate and grounded at a high frequency;
A third electrode plate attached to the one surface and grounded at a high frequency;
A fourth electrode plate attached to the other surface opposite to the third electrode plate and outputting the first resonance signal;
A fifth electrode plate attached to the other surface and grounded at a high frequency;
A high-frequency filter comprising: a sixth electrode plate that is attached to the one surface so as to face the fifth electrode plate and outputs the second resonance signal .   A high frequency filter comprising the high frequency filter according to claim 5 connected in multiple stages in parallel. 6. The high frequency filter according to claim 5, wherein a thickness of at least one of the first to sixth electrode plates is different from a thickness of another electrode plate .

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