JP2004328076A - Mems type resonator and manufacturing method thereof, and filter - Google Patents

Mems type resonator and manufacturing method thereof, and filter Download PDF

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JP2004328076A
JP2004328076A JP2003116148A JP2003116148A JP2004328076A JP 2004328076 A JP2004328076 A JP 2004328076A JP 2003116148 A JP2003116148 A JP 2003116148A JP 2003116148 A JP2003116148 A JP 2003116148A JP 2004328076 A JP2004328076 A JP 2004328076A
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electrode
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output
electrodes
mems resonator
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JP4341288B2 (en
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Koji Nanbada
康治 難波田
Takashi Kinoshita
隆 木下
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Sony Corp
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Sony Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To improve the S/N of an output signal in an MEMS resonator and a filter equipped with the MEMS type resonator. <P>SOLUTION: The MEMS resonator is configured to include: a first electrode 14 for receiving a high frequency signal; a second electrode 15 for outputting the high frequency signal; and a third electrode 17 acting as a diaphragm located by sandwiching a space 16 between the first and second electrodes 14 and 15, on the same plane of a substrate 12. Further, a fourth electrode 32 for supplying the ground potential is provided between the first electrode 14 and the second electrode 15. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【0001】
【発明の属する技術分野】
本発明は、MEMS型共振器及びその製造方法、並びにMEMS型共振器を有するフィルタに関する。
【0002】
【従来の技術】
近年、マイクロマシン(MEMS:Micro Electro Mechanical Systems、超小型電気的・機械的複合体)素子、及びMEMS素子を組み込んだ小型機器が、注目されている。MEMS素子の基本的な特徴は、機械的構造として構成されている駆動体が素子の一部に組み込まれていることであって、駆動体の駆動は、電極間のクローン力などを応用して電気的に行われる。
【0003】
半導体プロセスによるマイクロマニシング技術を用いて形成された微小振動素子は、デバイスの占有面積が小さいこと、高いQ値を実現できること、他の半導体デバイスとの集積が可能なこと、という特長により、無線通信デバイスの中でも中間周波数(IF)フィルタ、高周波(RF)フィルタとしての利用がミシガン大学を始めとする研究機関から提案されている(非特許文献1参照)。
【0004】
図16は、非特許文献1に記載された高周波フィルタを構成する振動素子、即ちMEMS型の振動素子の概略を示す。この振動素子1は、半導体基板2上に絶縁膜3を介して例えば多結晶シリコンによる入力側配線層4と出力電極5が形成され、この出力電極5に対向して空隙6を挟んで例えば多結晶シリコンによる振動可能なビーム、所謂ビーム型の振動電極7が形成されて成る。振動電極7は、両端のアンカー部(支持部)8〔8A,8B〕にて支持されるように、出力電極5をブリッジ状に跨いで入力側配線層4に接続される。振動電極7は入力電極となる。入力側配線層4の端部には、例えば金(Au)膜9が形成される。この振動素子1では、入力側配線層4の金(Au)膜9より入力端子t1 、出力電極5より出力端子t2 が導出される。
【0005】
この振動素子1は、振動電極7と接地間にDCバイアス電圧V1 が印加された状態で、入力端子t1 を通じて振動電極7に高周波信号S1 が供給される。即ち、入力端子t1 からDCバイアス電圧V1 と高周波信号S1 が重畳された入力信号が供給される。目的周波数の高周波信号S1 が入力されると、長さLで決まる固有振動数を有する振動電極7が、出力電極5と振動電極7間に生じる静電力で振動する。この振動によって、出力電極5と振動電極7との間の容量の時間変化とDCバイアス電圧に応じた高周波信号が出力電極5(したがって、出力端子t2 )から出力される。高周波フィルタでは振動電極7の固有振動数(共振周波数)に対応した信号が出力される。
【0006】
【非特許文献1】
C.T.−Nguyen,″Micromechanical components for miniaturized low−power communications(invited plenary),″proceedings,1999 IEEE MTT−S International Microwave Symposium RF MEMS Workshop,June,18,1999,pp.48−77.
【0007】
【発明が解決しようとする課題】
ところで、これまでに提案され、検証された微小振動子の共振周波数は、最高でも200MHzを超えず、従来の表面弾性波(SAW)あるいは薄膜弾性波(FBAR)によるGHz領域のフィルタに対して、微小振動子の特性である高いQ値をGHz帯周波数領域で提供することができていない。
【0008】
現在のところ、一般的に高い周波数領域では出力信号としての共振ピークが小さくなる傾向があり、良好なフィルタ特性を得るためには、共振ピークのSN比を向上する必要がある。ミシガン大学の文献に係るディスク型の振動子によれば、出力信号のノイズ成分は、入力電極なる振動電極7と出力電極5間に構成される寄生容量C0 を直接透過する信号によっている。一方においてディスク型の振動子で、十分な出力信号を得るには、30Vを超えるDCバイアス電圧が必要であるために、実用的な振動電極構造としては両持ち梁を用いたビーム型の構造であることが望ましい。
【0009】
しかし、上述の図16の振動子1の場合、振動電極7と出力電極5間の空隙6が小さく、両電極7及び5の対向面積も所要の大きさを持っているので、入力電極となる振動電極7と出力電極5間の寄生容量C0 が大きくなる。このため、寄生容量C0 のインピーダンスZ0 と、共振系(抵抗Rx,インダクタンスLx,容量Cx)のインピーダンスZxとの比Z0 /Zxが小さくなり、出力信号のSN比が小さくなる。振動電極7と出力電極5間の空隙を小さくして出力信号を大きく取ろうとすれば、寄生容量C0 も大きくなるという、ジレンマを抱える。
【0010】
本発明は、上述の点に鑑み、出力信号のSN比を向上させたMEMS型共振器及びその製造方法を提供するものである。
また、本発明は、出力信号のSN比を向上させたMEMS型共振器を有するフィルタを提供するものである。
【0011】
【課題を解決するための手段】
本発明に係るMEMS型共振器は、基板の同一平面上に高周波信号を入力する第1の電極と、高周波信号を出力する第2の電極と、第1及び第2の電極に対して空間を挟んで配置された振動板となる第3の電極とを有して成る。
より好ましくは、基板上の第1の電極と第2の電極との間に、接地電位が供給される第4の電極を配置して成る。
【0012】
本発明のMEMS型共振器においては、基板の同一平面上に第1の電極すなわち入力電極と第2の電極即ち出力電極とが形成され、これら入出力電極に対向して第3の電極すなわち振動電極が形成されるので、入出力電極間の対向面積が小さくなり且つ入出力電極間の間隔が従来に比して大きくとることができる。従って、入出力電極間の寄生容量が低減し、入力電極から出力電極への寄生容量を介した信号の透過が抑制される。
基板上の上記入力電極と上記出力電極との間に、接地電位が供給される第4の電極すなわち接地電極を配置するときは、入出力電極間の寄生容量が限りなく小さくなる。寄生容量を通して入出力電極間に流れんとする信号は、接地電極に流れることになる。従って、入力電極から出力電極への寄生容量を介した信号の透過がさらに抑制される。
【0013】
本発明に係るフィルタは、基板の同一平面上に高周波信号を入力する第1の電極と、高周波信号を出力する第2の電極と、第1及び第2の電極に対して空間を挟んで配置された振動板となる第3の電極とからなるMEMS型共振器を有して成る。
より好ましくは、MEMS型共振器における基板上の第1の電極と第2の電極との間に、接地電位が供給される第4の電極を配置して成る。
【0014】
本発明のフィルタにおいては、基板の同一平面上に第1の電極すなわち入力電極と第2の電極即ち出力電極とが形成され、これら入出力電極に対向して第3の電極すなわち振動電極が形成されたMEMS型共振器を有して構成されるので、上記のようにMEMS型共振器における入出力電極間の寄生容量が低減し、入力電極から出力電極への寄生容量を介した信号の透過が抑制される。
MEMS型共振器における基板上の入力電極と上記出力電極との間に、接地電位が供給される第4の電極すなわち接地電極を配置するときは、上記のようにMEMS型共振器における入出力で間の寄生容量が限りなく小さくなり、入力電極から出力電極への寄生容量を介した信号の透過がさらに抑制される。
【0015】
本発明に係るMEMS型共振器の製造方法は、基板上に互いに所定間隔を置いて入力となる第1の電極と、出力となる第2の電極と、第1及び第2の電極の両側に位置する導電層とを選択的に形成する工程と、第1、第2の電極及び導電層を含む全面上に犠牲層を形成し、この犠牲層を平坦化する工程と、導電層に一部接続されるように犠牲層上に振動板となる第3の電極を形成する工程と、犠牲層を選択的に除去する工程とを有する。
【0016】
本発明のMEMS型共振器の製造方法においては、基板上に第1の電極すなわち入力電極、第2の電極すなわち出力電極及び配線層を形成し、犠牲層を形成した後、犠牲層を平坦化する工程を有するので、第3の電極すなわち振動電極と入出力電極間の間隔(いわゆる空間)を精度よく制御できる。また振動電極が平坦に形成され、各振動モードに適した振動板として形成される。そして、上記一連の工程により、精度よく且つ容易に入出力電極間の寄生容量を低減した目的のMEMS型共振器の製造が可能になる。
【0017】
本発明に係るMEMS型共振器の製造方法は、基板上に入力となる第1の電極と、出力となる第2の電極と、接地される第4の電極と、第1、第2及び第4の電極の両側に位置する導電層とを選択的に形成する工程と、第1、第2、第4の電極及び導電層を含む全面上に犠牲層を形成し、この犠牲層を平坦化する工程と、導電層に一部接続されるように犠牲層上に振動板となる第3の電極を形成する工程と、犠牲層を選択的に除去する工程とを有する
【0018】
本発明のMEMS型共振器の製造方法においては、基板上に第1の電極すなわち入力電極、第2の電極すなわち出力電極、第4の電極即ち接地電極及び配線層を形成し、犠牲層を形成した後、犠牲層を平坦化する工程を有するので、第3の電極すなわち振動電極と入出力電極間の間隔(いわゆる空間)を精度よく制御できる。また振動電極が平坦に形成され、各振動モードに適した振動板として形成される。そして、上記一連の工程により、精度よく且つ容易に入出力電極間の寄生容量を限りなく小さくした目的のMEMS型共振器の製造が可能になる。
【0019】
【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説明する。
【0020】
MEMS型の振動子によるRF共振器は、図10に示すような等価回路に置き換えることができる。即ち、入力端子t1 と出力端子t2 間に、共振系を構成する抵抗RxとインダクタンスLxと容量Cxの直列回路と、入出力電極間の空隙による寄生容量C0 が並列に挿入される。振動系のインピーダンスをZx、寄生容量C0 のインピーダンスをZ0 とすると、出力信号のSN比は、Z0 /Zxに相当する。Z0 /Zxの値が大きいほど共振系の信号は、寄生容量C0 を等価する信号に比べて大きく、1に近づくにつれ共振系を等価する信号と寄生容量C0 を透過する信号は同程度となる。また、Z0 /Zx∝1/C0 が成り立つ。従って、入力電極と出力電極間の容量C0 の低減は、SN比を向上させるために最も重要なポイントの一つである。
【0021】
図1及び図2は、本発明に係るMEMS型共振器の一実施の形態を示す。本実施の形態に係るMEMS型共振器11は、基板12の同一平面上、即ち基板12の少なくとも絶縁性を有する表面上に、互いに所要の間隔を置いて配置された高周波信号13を入力する第1の電極(以下、入力電極という)14と、高周波信号を出力する第2の電極(以下、出力電極という)15と、これら入力電極14及び出力電極15に対して空間16を挟んで配置された振動板となる第3電極(以下、振動電極という)17とを有して成る。振動電極17は、入出力電極14、15をブリッジ状に跨ぎ、入出力電極14、15の外側に配置した配線層18に接続されるように、両端を支持部(いわゆるアンカー部)19〔19A,19B〕で一体に支持される。
【0022】
基板12は、例えばシリコン(Si)やガリウム砒素(GaAs)などの半導体基板上に絶縁膜を形成した基板、石英基板やガラス基板のような絶縁性基板等が用いられる。本例では、シリコン基板21上にシリコン酸化膜22及びシリコン窒化膜23を積層した基板12が用いられる。入力電極14、出力電極15及び配線層18は、同じ導電材料で形成し、例えば多結晶シリコン膜、アルミニウム(Al)などの金属膜にて形成することができる。振動電極17は、例えば多結晶シリコン膜、アルミニウム(Al)などの金属膜にて形成することができる。
【0023】
入力電極14には入力端子t1 が導出され、入力端子t1 を通じて入力電極14に高周波信号S2 が入力されるようになす。振動電極15には出力端子t2 が導出され、出力端子t2 から目的周波数の高周波信号が出力されるようになす。振動電極17には所要のDCバイアス電圧V2 が印加されるようになす。
【0024】
本実施の形態に係るMEMS型共振器11の動作は次の通りである。
振動電極17には所要のDCバイアス電圧V2 が印加さる。入力端子t1 を通じて高周波信号S2 が入力電極14に入力される。目的周波数の高周波信号が入力されると、振動電極17と入力電極14間に生じる静電力で図3に示すように、2次の振動モード25で振動電極17が共振する。この振動電極17の共振で出力電極15から出力端子t2 を通じて目的周波数の高周波信号が出力される。他の周波数の信号が入力されたときは振動電極17が共振せず、出力端子t2 からは信号が出力されない。
【0025】
本実施の形態に係るMEMS型共振器11によれば、前述の図16のMEMS型の振動子1に比べて、入出力電極14及び15の対向面積が小さく且つ入出力電極14及び15間の間隔を大きくすることができので、入出力電極14及び15間の寄生容量C0 は小さくなる。一方、大きな出力信号を得るために振動電極17と入出力電極14、15との空間16を小さくすることができる。この空間16を小さくすることは寄生容量C0 に影響を与えない。このため、本実施の形態のMEMS型共振器11は、図16の従来のものに比べて出力信号のSN比を向上させることができる。
【0026】
上例では1つの入力電極14と1つの出力電極15を配置して2次振動モードのMEMS型共振器を構成したが、その他、図示せざるも2つの入力電極と、両入力電極間に1つの出力電極を配置して3次振動モードにする等、入力電極及び出力電極の数、配置を変更して多次振動モードのMEMS型共振器を構成することもできる。
【0027】
図12〜図13は、上述のMEMS型共振器11の製造方法の一例を示す。
先ず、図12Aに示すように、基板12上に電極となるべき導電膜41を形成する。本例ではシリコン基板21上に絶縁膜であるシリコン酸化膜22及びシリコン窒化膜23を積層した基板12を用いる。導電膜41としては、後の犠牲層とエッチング比がとれる材料で形成する必要があり、本例では多結晶シリコン膜で形成する。
【0028】
次に、図12Bに示すように、導電膜41をパターニングして入力電極14、出力電極15及び外側の配線層18を形成する。
次に、図12Cに示すように、入力電極14、出力電極15及び配線層18を含む全面に犠牲層42を形成する。犠牲層42は、下地の絶縁膜(本例ではシリコン窒化(SiN)膜)及び多結晶シリコンによる各電極14、14、32及び配線層18とエッチング比がとれる材料、本例ではシリコン酸化(SiO )膜で形成する。
【0029】
次に、図12Dに示すように、例えば化学機械研磨(CMP)法などにより犠牲層42を平坦化する。
次に、図13Eに示すように、両外側の配線層18上の犠牲層42に選択エッチングによりコンタクト孔43を形成する。
【0030】
次に、図13Fに示すように、コンタクト孔43内を含む犠牲層42上に振動電極となる導電膜44、本例では犠牲層42とエッチング比が多結晶シリコン膜を形成する。その後、この導電膜44をパターニングして外側の両配線層18に接続された多結晶シリコン膜からなる振動電極17を形成する。振動電極17と配線層18間の部分が振動電極17を両持ち梁構造として支持する支持部(アンカー)19〔19A,19B〕となる。
【0031】
次に、図13Gに示すように、犠牲層42をエッチング除去する。犠牲層42のエッチング除去は、本例ではシリコン酸化膜であるので、フッ酸溶液によりウェットエッチングで行う。かくして目的のMEMS型共振器31を得る。
【0032】
なお、電極14、15及び配線層18を金属の例えばアルミニウム(Al)膜で形成し、犠牲層42を非晶質シリコン層で形成するときは、犠牲層42をXeF2 ガスによるドライエッチングで除去することができる。また、下地絶縁膜をシリコン酸化(SiO )膜とし、電極14、15及び配線層18を多結晶シリコン膜またはアルミニウム(Al)膜とし、犠牲層42をフォトレジスト膜としたときには、犠牲層42を酸素O プラズマによるドライエッチングで除去することができる。
【0033】
本実施の形態の製造方法によれば、基板12上に入力電極14、出力電極15及び配線層18を同じ導電膜41で形成し、犠牲層42を形成した後、犠牲層42を平坦化する工程を有するので、振動電極17と入出力電極14、15との間に間隔(空間16)を精度良く制御できる。また振動電極17を平坦に形成することができ、各振動モードに適した振動板として形成することができる。そして、上記一連の工程により、精度よく且つ容易に入出力電極間の寄生容量C0 が低減し、SN比が向上した目的のMEMS型共振器11を製造することができる。
【0034】
図4及び図5は、更にSN比を向上させ本発明に係るMEMS型共振器の他の実施の形態を示す。本実施の形態に係るMEMS型共振器31は、基板12の同一平面上、即ち基板12の少なくとも絶縁性を有する表面上に、相互に所要の間隔を置いて配置された高周波信号13を入力する第1電極である入力電極14と、高周波信号を出力する第2の電極である出力電極15と、入出力電極14及び15の間に配置された接地電位を供給する第4の電極(以下、接地電極という)32と、これら入力電極14、出力電極15及び接地電極32に対して空間16を挟んで配置された振動板となる第3電極の振動電極17とを有して成る。振動電極17は、入出力電極14、15及び接地電極32をブリッジ状に跨ぎ、入出力電極14、15、接地電極32の外側に配置した配線層18に接続されるように、両端を支持部(いわゆるアンカー部)19〔19A,19B〕で一体に支持される。ここで、振動電極17と入出力電極14,15との間のギャップX1と、入出力電極14,15と接地電極32との間のギャップX2は、X2>X1とすることができる。
【0035】
入力電極14、出力電極15、接地電極32及び配線層18は、同じ導電材料で形成し、例えば多結晶シリコン膜、アルミニウム(Al)などの金属膜にて形成することができる。振動電極17は、例えば多結晶シリコン膜、アルミニウム(Al)などの金属膜にて形成することができる。入力電極14には入力端子t1 が導出され、入力端子t1 を通じて入力電極14に高周波信号S2 が入力されるようになす。振動電極15には出力端子t2 が導出され、出力端子t2 から目的周波数の高周波信号が出力されるようになす。接地電極32には接地(GND)電位が印加されるようになす。振動電極17には所要のDCバイアス電圧V2 が印加されるようになす。
【0036】
その他の構成は、前述の図1及び図2と同様であるので、対応する部分には同一符号を付して重複説明を省略する。
【0037】
本実施の形態に係るMEMS型共振器31の動作は、図1及び図2の場合と同様である。即ち、振動電極17には所要のDCバイアス電圧V2 が印加さる。入力端子t1 を通じて高周波信号S2 が入力電極14に入力される。目的周波数の高周波信号が入力されると、振動電極17と入力電極14間に生じる静電力で図6に示すように、2次の振動モード25で振動電極17が共振する。この振動電極17の共振で出力電極15から出力端子t2 を通じて目的周波数の高周波信号が出力される。他の周波数の信号が入力されたときは振動電極17が共振せず、出力端子t2 からは信号が出力されない。
【0038】
本実施の形態に係るMEMS型共振器31によれば、入力電極14と出力電極15との間に接地電極32を配置することにより、図11の等価回路に示すように、入力電極14及び出力電極15間の寄生容量C0 が限りなく小さくなる。即ち、この等価回路では、図1でのMEMS型共振器11に元々有った寄生容量C0 が、接地電極32との間の容量C01と容量C02に分配された形になる。これにより、元々の寄生容量C0 を透過する信号が接地電極32側に流れ、出力電極15側に流れない。従って、入力された高周波信号の漏れがなくなり、出力信号のSN比が向上する。信号の一部は接地側に流れるので、信号レベルは落ちるも、信号レベルは出力側の負荷抵抗R0 等により電気的に補償するようになせばよい。従って、図1及び図2のMEMS型共振器11に比べてさらに寄生容量C0 を低減し、さらにSN比を向上させることができる。
【0039】
図14〜図15は、上述のMEMS型共振器31の製造方法の一例を示す。
先ず、図14Aに示すように、基板12上に電極となるべき導電膜41を形成する。本例ではシリコン基板21上に絶縁膜であるシリコン酸化膜22及びシリコン窒化膜23を積層した基板12を用いる。導電膜41としては、後の犠牲層とエッチング比がとれる材料で形成する必要があり、本例では多結晶シリコン膜で形成する。
【0040】
次に、図14Bに示すように、導電膜41をパターニングして入力電極14、出力電極15、両電極14及び15間の接地電極32、外側の配線層18を形成する。
次に、図14Cに示すように、入力電極14、出力電極15、接地電極32及び配線層18を含む全面に犠牲層42を形成する。犠牲層42は、下地の絶縁膜(本例ではシリコン窒化(SiN)膜)及び多結晶シリコンによる各電極14、14、32及び配線層18とエッチング比がとれる材料、本例ではシリコン酸化(SiO )膜で形成する。
【0041】
次に、図14Dに示すように、例えば化学機械研磨(CMP)法などにより犠牲層42を平坦化する。
【0042】
次に、図15Eに示すように、両外側の配線層18上の犠牲層42に選択エッチングによりコンタクト孔43を形成する。
【0043】
次に、図15Fに示すように、コンタクト孔43内を含む犠牲層42上に振動電極となる導電膜44、本例では犠牲層42とエッチング比が多結晶シリコン膜を形成する。その後、この導電膜44をパターニングして外側の両配線層18に接続された多結晶シリコン膜からなる振動電極17を形成する。振動電極17と配線層18間の部分が振動電極17を両持ち梁構造として支持する支持部(アンカー)19〔19A,19B〕となる。
【0044】
次に、図15Gに示すように、犠牲層42をエッチング除去する。犠牲層42のエッチング除去は、本例ではシリコン酸化膜であるので、フッ酸溶液によりウェットエッチングで行う。かくして目的のMEMS型共振器31を得る。
【0045】
なお、電極14、15、32及び配線層18となる導電膜41、犠牲層42、下地絶縁膜23の材料の組み合わせ、さらに犠牲層42のエッチャント等は、前述と同様のものを選択することができる。
【0046】
本実施の形態の製造方法によれば、基板12上に入力電極14、出力電極15、接地電極32及び配線層18を同じ導電膜41で形成し、犠牲層42を形成した後、犠牲層42を平坦化する工程を有するので、振動電極17と入出力電極14、15との間に間隔(空間16)を精度良く制御できる。また振動電極17を平坦に形成することができ、各振動モードに適した振動板として形成することができる。そして、上記一連の工程により、精度よく且つ容易に入出力電極間の寄生容量C0 が低減し、SN比が向上した目的のMEMS型共振器31を製造することができる。
【0047】
図7及び図8は、本発明に係るMEMS型共振器の他の実施の形態を示す。本実施の形態に係るMEMS型共振器35は、基板12の同一平面上、即ち基板12の少なくとも絶縁性を有する表面上に、相互に所要の間隔を置いて配置された高周波信号13を入力する2つの入力電極14〔14A,14B〕と、高周波信号を出力する1つの出力電極15と、入力電極14Aと出力電極15間、入力電極14Bと出力電極15間に、それぞれ配置した接地電極32〔32A,32B〕と、これら入力電極14〔14A,14B〕、出力電極15及び接地電極32〔32A,32B〕に対して空間16を挟んで配置された振動電極17とを有して成る。本例では中央に出力電極15が配置され、これの両側に接地電極32〔32A,3B〕、入力電極14〔14A,14B〕が配置される。振動電極17は、入出力電極14〔14A,14B〕、15及び接地電極32〔32A,32B〕をブリッジ状に跨ぎ、入出力電極14、15、接地電極32の外側に配置した導電層18に接続されるように、両端を支持部(いわゆるアンカー部)19〔19A,19B〕で一体に支持される。ここで、接地電極32A,32Bは、後述するように振動電極17の振動の節となる部分に近接して配置される。
【0048】
入力電極14〔14A,14B〕には入力端子t1 が導出され、入力端子t1 を通じて入力電極14〔14A,14B〕に高周波信号S2 が入力されるようになす。振動電極15には出力端子t2 が導出され、出力端子t2 から目的周波数の高周波信号が出力されるようになす。接地電極32〔32A,32B〕には接地(GND)電位が印加されるようになす。振動電極17には所要のDCバイアス電圧V2 が印加されるようになす。なお、2つの入力電極14A及び14Bは1つの入力電極パッドから分岐して形成され、2つの接地電極32A及び32Bは1つの接地電極パッドから分岐して形成される。
る。
【0049】
基板12、入力電極14〔14A,14B〕、出力電極15、接地電極32〔32A,32B〕及び導電層18〔18A,18B〕等、その他の構成は図4及び図5と同様であるので、対応する部分に同一符号を付して重複説明を省略する。
なお、上例では中央を出力電極15とし、これを挟んで2つの入力電極14A,14Bを配置し、入出力電極間に接地電極32を配置した構成であるが、中央を入力電極14とし、これを挟んで2つの出力電極15を配置し、入出力で間に接地電極32を配置した構成とすることもできる。
【0050】
本実施の形態に係るMEMS型共振器35の動作は、図4及び図5の場合と同様である。即ち、振動電極17には所要のDCバイアス電圧V2 が印加さる。入力端子t1 を通じて高周波信号S2 が入力電極14〔14A,14B〕に入力される。目的周波数の高周波信号が入力されると、振動電極17と入力電極14〔14A,14B〕間に生じる静電力で振動電極17が共振する。この場合、図9に示すように、3次の振動モード26で振動電極17が共振する。この振動電極17の共振で出力電極15から出力端子t2 を通じて目的周波数の高周波信号が出力される。他の周波数の信号が入力されたときは振動電極17が共振せず、出力端子t2 からは信号が出力されない。
【0051】
本実施の形態に係るMEMS型共振器35によれば、入力電極14〔14A,14B〕と出力電極15との間に夫々接地電極32〔32A,32B〕を配置することにより、入力電極14及び出力電極15間の寄生容量C0 を図4及び図5と同様に低減することができる。従って、MEMS型共振器11に比べてさらにSN比を向上させることができる。
【0052】
本実施の形態に係るMEMS型共振器35の製造方法は、図14Aから図15Gで示した前述のMEMS型共振器31の製造方法と同様にして製造することができる。
【0053】
図1及び図2のMEMS型共振器11において、入力電極14及び出力電極15のいずれか一方の電極を中心に配し、他方の電極を一方の電極を中心としてリング状に配置し、振動電極17を両電極14、15上に対向して配置するようにした構成とすることもできる。電極の形状は、円形、四角形状、その他の形状等、適宜選択できる。
図4及び図5のMEMS型共振器31、あるいは図7及び図8のMEMS型共振器31において、入力電極14及び出力電極15のいずれか一方の電極を中心に配し、他方の電極及び接地電極32を一方の電極を中心としてリング状に配置し、振動電極17を電極14、15及び32上に対向して配置するようにした構成とすることもできる。電極の形状は、円形、四角形状、その他の形状等、適宜選択できる。
【0054】
上述の実施の形態では、2次振動モード及び3次振動モードのMEMS型共振器に適用したが、4次振動モード以上の多次振動モードのMEMS型共振器にも適用可能である。
【0055】
本発明は、上述の実施の形態に係るMEMS型共振器11あるいはMEMS型共振器31を有して高周波フィルタ、中間周波フィルタ等のフィルタを構成する。
MEMS型共振器11を有してフィルタを構成することにより、入出力電極間の寄生容量C0 を従来よりも低減することができ、出力信号のSN比を向上することができる。
MEMS型共振器31を有してフィルタを構成することにより、入出力電極14及び15間に接地電極32が配置されるので、寄生容量C0 を限りなく小さくなり、さらに出力信号のSN比を向上することができる。
【0056】
【発明の効果】
本発明に係るMEMS型共振器によれば、基板の同一平面上に高周波信号を入力する第1の電極と高周波信号を出力する第2の電極を配置し、これら第1、第2の電極に対向して振動板となる第3の電極を配置した構成とすることにより、第1及び第2の電極間、つまり入出力電極極間の寄生容量が低減し、出力信号のSN比を向上することができる。
本発明に係るMEMS型共振器によれば、さらに上記第1の電極と第2の電極との間に接地電位が供給される第4の電極を配置することにより、第1及び第2の電極間、つまり入出力電極極間の寄生容量が限りなく小さくなり、より出力信号のSN比を向上することができる。
【0057】
本発明に係るフィルタによれば、上記MEMS型共振器を有することにより、出力信号のSN比を向上することができる。
本発明に係るフィルタによれば、さらに上記第1の電極と第2の電極との間に接地電位の第3の電極を配置するようにしたMEMS型共振器を有することにより、さらに出力信号のSN比を向上することができる。
【0058】
本発明に係るMEMS型共振器の製造方法によれば、入出力電極となる第1、第2の電極と振動板となる第3ので間の間隔を精度よく制御することができると共に、第3の電極を振動に適した平坦に形成することができる。そして入出力電極間の寄生容量を低減、あるいは限りなく小さくしたMEMS型共振器を、精度良く且つ容易に製造することができる。
【図面の簡単な説明】
【図1】本発明に係るMEMS型共振器の一実施の形態を示す構成図である。
【図2】本発明に係るMEMS型共振器の一実施の形態を示す平面図である。
【図3】本発明に係るMEMS型共振器の一実施の形態の振動モードを示す説明図である。
【図4】本発明に係るMEMS型共振器の他の実施の形態を示す構成図である。
【図5】本発明に係るMEMS型共振器の他の実施の形態を示す平面図である。
【図6】本発明に係るMEMS型共振器の他の実施の形態の振動モードを示す説明図である。
【図7】本発明に係るMEMS型共振器の更に他の実施の形態を示す構成図である。
【図8】本発明に係るMEMS型共振器の更に他の実施の形態を示す平面図である。
【図9】本発明に係るMEMS型共振器の更に他の実施の形態の振動モードを示す説明図である。
【図10】MEMS型共振器の等価回路図である。
【図11】図4の実施の形態に係るMEMS型共振器の等価回路図である。
【図12】A〜D 本発明に係るMEMS型共振器の製造方法の実施の形態の一例を示す製造工程図(その1)である。
【図13】E〜G 本発明に係るMEMS型共振器の製造方法の実施の形態の一例を示す製造工程図(その2)である。
【図14】A〜D 本発明に係るMEMS型共振器の製造方法の実施の形態の他の一例を示す製造工程図(その1)である。
【図15】E〜G 本発明に係るMEMS型共振器の製造方法の実施の形態の他の例を示す製造工程図(その2)である。
【図16】従来のMEMS型の振動子の例を示す構成図である。
【符号の説明】
11、31、35・・MEMS型共振器、12・・基板、14、14A、14B・・入力電極、15・・出力電極、16・・空間、17・・振動電極、18・・配線層、19〔19A,19B〕・・支持部、21・・シリコン基板、22・・シリコン酸化膜、23・・シリコン窒化膜、32、32A、32B・・接地電極、41・・導電膜、42・・犠牲層、43・・コンタクト孔、44・・導電膜
[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a MEMS resonator, a method for manufacturing the same, and a filter having the MEMS resonator.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a micromachine (MEMS: Micro Electro Mechanical Systems) element and a small device incorporating a MEMS element have attracted attention. A basic feature of the MEMS element is that a driving body configured as a mechanical structure is incorporated in a part of the element, and the driving of the driving body is performed by applying a cloning force between electrodes and the like. It is done electrically.
[0003]
Micro-vibration elements formed using micro-machining technology based on semiconductor processes are characterized by their small footprint, high Q value, and the ability to integrate with other semiconductor devices. Among communication devices, use as intermediate frequency (IF) filters and high frequency (RF) filters has been proposed by research institutions such as the University of Michigan (see Non-Patent Document 1).
[0004]
FIG. 16 schematically shows a vibrating element constituting a high-frequency filter described in Non-Patent Document 1, that is, a MEMS-type vibrating element. In the vibration element 1, an input-side wiring layer 4 and an output electrode 5 made of, for example, polycrystalline silicon are formed on a semiconductor substrate 2 with an insulating film 3 interposed therebetween. A vibrating beam made of crystalline silicon, a so-called beam type vibrating electrode 7 is formed. The vibration electrode 7 is connected to the input-side wiring layer 4 across the output electrode 5 in a bridge-like manner so as to be supported by anchor portions (support portions) 8 [8A, 8B] at both ends. The vibration electrode 7 becomes an input electrode. For example, a gold (Au) film 9 is formed at an end of the input side wiring layer 4. In this vibration element 1, an input terminal t 1 is derived from the gold (Au) film 9 of the input side wiring layer 4, and an output terminal t 2 is derived from the output electrode 5.
[0005]
In the vibration element 1, a high-frequency signal S1 is supplied to the vibration electrode 7 through the input terminal t1 in a state where the DC bias voltage V1 is applied between the vibration electrode 7 and the ground. That is, an input signal in which the DC bias voltage V1 and the high frequency signal S1 are superimposed is supplied from the input terminal t1. When the high frequency signal S1 of the target frequency is input, the vibrating electrode 7 having a natural frequency determined by the length L vibrates with an electrostatic force generated between the output electrode 5 and the vibrating electrode 7. Due to this vibration, a high-frequency signal corresponding to the time change of the capacitance between the output electrode 5 and the vibration electrode 7 and the DC bias voltage is output from the output electrode 5 (therefore, the output terminal t2). The high frequency filter outputs a signal corresponding to the natural frequency (resonance frequency) of the vibration electrode 7.
[0006]
[Non-patent document 1]
C. T. -Nguyen, "Micromechanical components for minimized low-power communications (invited plenary)," proceedings, 1999 IEEE MTT-Sep, International Microwave Society, Microelectronics. 48-77.
[0007]
[Problems to be solved by the invention]
By the way, the resonance frequency of the micro-vibrator proposed and verified so far does not exceed 200 MHz at the maximum, and is compared with a conventional filter in a GHz region by a surface acoustic wave (SAW) or a thin film elastic wave (FBAR). A high Q value, which is a characteristic of a micro-vibrator, cannot be provided in a GHz band frequency region.
[0008]
At present, the resonance peak as an output signal generally tends to be small in a high frequency region, and it is necessary to improve the SN ratio of the resonance peak in order to obtain good filter characteristics. According to the disk-type vibrator disclosed in the University of Michigan document, the noise component of the output signal depends on the signal directly passing through the parasitic capacitance C0 formed between the vibrating electrode 7 serving as the input electrode and the output electrode 5. On the other hand, in order to obtain a sufficient output signal with a disk-type vibrator, a DC bias voltage exceeding 30 V is required. Therefore, a practical vibrating electrode structure is a beam-type structure using a doubly supported beam. Desirably.
[0009]
However, in the case of the vibrator 1 of FIG. 16 described above, the gap 6 between the vibrating electrode 7 and the output electrode 5 is small, and the facing area between the electrodes 7 and 5 also has a required size, so that it becomes an input electrode. The parasitic capacitance C0 between the vibration electrode 7 and the output electrode 5 increases. For this reason, the ratio Z0 / Zx between the impedance Z0 of the parasitic capacitance C0 and the impedance Zx of the resonance system (resistance Rx, inductance Lx, capacitance Cx) decreases, and the SN ratio of the output signal decreases. If an attempt is made to increase the output signal by reducing the gap between the vibrating electrode 7 and the output electrode 5, there is a dilemma that the parasitic capacitance C0 also increases.
[0010]
The present invention has been made in view of the above circumstances, and provides a MEMS resonator having an improved SN ratio of an output signal and a method of manufacturing the same.
Another object of the present invention is to provide a filter having a MEMS resonator having an improved SN ratio of an output signal.
[0011]
[Means for Solving the Problems]
The MEMS resonator according to the present invention provides a space between the first electrode for inputting a high-frequency signal, the second electrode for outputting a high-frequency signal, and the first and second electrodes on the same plane of the substrate. And a third electrode serving as a diaphragm interposed therebetween.
More preferably, a fourth electrode to which a ground potential is supplied is arranged between the first electrode and the second electrode on the substrate.
[0012]
In the MEMS resonator of the present invention, a first electrode, ie, an input electrode, and a second electrode, ie, an output electrode, are formed on the same plane of a substrate, and a third electrode, ie, a vibrator is opposed to these input / output electrodes. Since the electrodes are formed, the facing area between the input and output electrodes can be reduced, and the distance between the input and output electrodes can be increased as compared with the related art. Therefore, the parasitic capacitance between the input and output electrodes is reduced, and transmission of a signal from the input electrode to the output electrode via the parasitic capacitance is suppressed.
When a fourth electrode to which a ground potential is supplied, that is, a ground electrode, is arranged between the input electrode and the output electrode on the substrate, the parasitic capacitance between the input and output electrodes becomes extremely small. A signal flowing between the input and output electrodes through the parasitic capacitance will flow to the ground electrode. Therefore, transmission of a signal from the input electrode to the output electrode via the parasitic capacitance is further suppressed.
[0013]
A filter according to the present invention has a first electrode for inputting a high-frequency signal, a second electrode for outputting a high-frequency signal, and a space between the first and second electrodes on the same plane of the substrate. And a third electrode serving as a vibrating plate.
More preferably, a fourth electrode to which a ground potential is supplied is arranged between the first electrode and the second electrode on the substrate in the MEMS type resonator.
[0014]
In the filter of the present invention, a first electrode, ie, an input electrode, and a second electrode, ie, an output electrode, are formed on the same plane of a substrate, and a third electrode, ie, a vibrating electrode is formed facing these input / output electrodes. As described above, the parasitic capacitance between the input and output electrodes in the MEMS resonator is reduced, and the transmission of signals from the input electrode to the output electrode via the parasitic capacitance is reduced. Is suppressed.
When the fourth electrode to which the ground potential is supplied, that is, the ground electrode is arranged between the input electrode on the substrate and the output electrode in the MEMS resonator, as described above, the input / output of the MEMS resonator is The parasitic capacitance between the electrodes becomes extremely small, and transmission of a signal from the input electrode to the output electrode via the parasitic capacitance is further suppressed.
[0015]
The method of manufacturing a MEMS resonator according to the present invention includes a first electrode serving as an input, a second electrode serving as an output, and both sides of the first and second electrodes at predetermined intervals on a substrate. Selectively forming a conductive layer located thereon; forming a sacrificial layer over the entire surface including the first and second electrodes and the conductive layer; planarizing the sacrificial layer; The method includes a step of forming a third electrode serving as a diaphragm on the sacrificial layer so as to be connected, and a step of selectively removing the sacrificial layer.
[0016]
In the method of manufacturing a MEMS resonator according to the present invention, a first electrode, that is, an input electrode, a second electrode, that is, an output electrode, and a wiring layer are formed on a substrate, and after forming a sacrifice layer, the sacrifice layer is planarized. Therefore, the distance (so-called space) between the third electrode, that is, the vibration electrode and the input / output electrode can be controlled with high accuracy. Further, the vibration electrode is formed flat, and is formed as a vibration plate suitable for each vibration mode. Then, through the above-described series of steps, it is possible to accurately and easily manufacture a target MEMS resonator in which the parasitic capacitance between the input and output electrodes is reduced.
[0017]
According to the method of manufacturing a MEMS resonator according to the present invention, a first electrode serving as an input, a second electrode serving as an output, a fourth electrode grounded, a first electrode, a second electrode, and a second electrode are provided on a substrate. A step of selectively forming conductive layers located on both sides of the fourth electrode, and forming a sacrificial layer on the entire surface including the first, second, and fourth electrodes and the conductive layer, and flattening the sacrificial layer. And forming a third electrode serving as a diaphragm on the sacrificial layer so as to be partially connected to the conductive layer, and selectively removing the sacrificial layer.
[0018]
In the method of manufacturing a MEMS resonator of the present invention, a first electrode, ie, an input electrode, a second electrode, ie, an output electrode, a fourth electrode, ie, a ground electrode, and a wiring layer are formed on a substrate, and a sacrificial layer is formed. After that, the step of flattening the sacrificial layer is provided, so that the distance (so-called space) between the third electrode, that is, the vibration electrode and the input / output electrode can be accurately controlled. Further, the vibration electrode is formed flat, and is formed as a vibration plate suitable for each vibration mode. Then, through the above-described series of steps, it is possible to accurately and easily manufacture a target MEMS resonator in which the parasitic capacitance between the input and output electrodes is reduced as much as possible.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0020]
An RF resonator using a MEMS type vibrator can be replaced with an equivalent circuit as shown in FIG. That is, between the input terminal t1 and the output terminal t2, a series circuit of the resistor Rx, the inductance Lx, and the capacitor Cx constituting the resonance system and the parasitic capacitance C0 due to the gap between the input and output electrodes are inserted in parallel. Assuming that the impedance of the vibration system is Zx and the impedance of the parasitic capacitance C0 is Z0, the SN ratio of the output signal is equivalent to Z0 / Zx. As the value of Z0 / Zx is larger, the signal of the resonance system is larger than the signal equivalent to the parasitic capacitance C0, and as the value approaches 1, the signal equivalent to the resonance system and the signal transmitted through the parasitic capacitance C0 become approximately the same. Also, Z0 / Zx∝1 / C0 holds. Therefore, reduction of the capacitance C0 between the input electrode and the output electrode is one of the most important points for improving the SN ratio.
[0021]
1 and 2 show one embodiment of a MEMS resonator according to the present invention. The MEMS resonator 11 according to the present embodiment is configured to input a high-frequency signal 13 arranged at a required interval from each other on the same plane of the substrate 12, that is, on at least the insulating surface of the substrate 12. One electrode (hereinafter, referred to as an input electrode) 14, a second electrode (hereinafter, referred to as an output electrode) 15 for outputting a high-frequency signal, and a space 16 are arranged between the input electrode 14 and the output electrode 15. And a third electrode (hereinafter referred to as a vibration electrode) 17 serving as a vibrating plate. The vibrating electrode 17 straddles the input / output electrodes 14 and 15 in a bridge shape, and has both ends supporting portions (so-called anchor portions) 19 [19A] so as to be connected to the wiring layer 18 disposed outside the input / output electrodes 14 and 15. , 19B].
[0022]
As the substrate 12, for example, a substrate in which an insulating film is formed on a semiconductor substrate such as silicon (Si) or gallium arsenide (GaAs), or an insulating substrate such as a quartz substrate or a glass substrate is used. In this example, a substrate 12 in which a silicon oxide film 22 and a silicon nitride film 23 are stacked on a silicon substrate 21 is used. The input electrode 14, the output electrode 15, and the wiring layer 18 are formed of the same conductive material, and can be formed of, for example, a polycrystalline silicon film or a metal film such as aluminum (Al). The vibration electrode 17 can be formed of, for example, a polycrystalline silicon film or a metal film such as aluminum (Al).
[0023]
An input terminal t1 is derived from the input electrode 14, and a high-frequency signal S2 is input to the input electrode 14 through the input terminal t1. An output terminal t2 is led to the vibration electrode 15, and a high-frequency signal of a target frequency is output from the output terminal t2. A required DC bias voltage V2 is applied to the vibration electrode 17.
[0024]
The operation of the MEMS resonator 11 according to the present embodiment is as follows.
A required DC bias voltage V2 is applied to the vibration electrode 17. The high-frequency signal S2 is input to the input electrode 14 through the input terminal t1. When a high-frequency signal of a target frequency is input, the vibrating electrode 17 resonates in a secondary vibration mode 25 as shown in FIG. 3 by electrostatic force generated between the vibrating electrode 17 and the input electrode 14. Due to the resonance of the vibration electrode 17, a high-frequency signal of a target frequency is output from the output electrode 15 through the output terminal t2. When a signal of another frequency is input, the vibration electrode 17 does not resonate, and no signal is output from the output terminal t2.
[0025]
According to the MEMS resonator 11 according to the present embodiment, the facing area of the input / output electrodes 14 and 15 is smaller than that of the MEMS resonator 1 of FIG. Since the distance can be increased, the parasitic capacitance C0 between the input / output electrodes 14 and 15 decreases. On the other hand, the space 16 between the vibration electrode 17 and the input / output electrodes 14 and 15 can be reduced to obtain a large output signal. Reducing the space 16 does not affect the parasitic capacitance C0. Therefore, the MEMS resonator 11 of the present embodiment can improve the SN ratio of the output signal as compared with the conventional one shown in FIG.
[0026]
In the above example, one input electrode 14 and one output electrode 15 are arranged to form a secondary vibration mode MEMS resonator, but in addition, two input electrodes (not shown) and one between the two input electrodes are provided. For example, the number and arrangement of the input electrodes and the output electrodes may be changed to arrange a MEMS type resonator in a multi-order vibration mode by arranging one output electrode for a third-order vibration mode.
[0027]
12 and 13 show an example of a method for manufacturing the MEMS resonator 11 described above.
First, as shown in FIG. 12A, a conductive film 41 to be an electrode is formed on the substrate 12. In this example, a substrate 12 in which a silicon oxide film 22 and a silicon nitride film 23 as insulating films are stacked on a silicon substrate 21 is used. The conductive film 41 needs to be formed of a material having an etching ratio with the later sacrificial layer. In this example, the conductive film 41 is formed of a polycrystalline silicon film.
[0028]
Next, as shown in FIG. 12B, the conductive film 41 is patterned to form the input electrode 14, the output electrode 15, and the outer wiring layer 18.
Next, as shown in FIG. 12C, a sacrificial layer 42 is formed on the entire surface including the input electrode 14, the output electrode 15, and the wiring layer 18. The sacrifice layer 42 is made of a material having an etching ratio with the electrodes 14, 14, 32 and the wiring layer 18 of a base insulating film (in this example, a silicon nitride (SiN) film) and polycrystalline silicon, in this example, silicon oxide (SiO 2). 2 ) Formed with a film.
[0029]
Next, as shown in FIG. 12D, the sacrificial layer 42 is flattened by, for example, a chemical mechanical polishing (CMP) method.
Next, as shown in FIG. 13E, a contact hole 43 is formed in the sacrificial layer 42 on both outer wiring layers 18 by selective etching.
[0030]
Next, as shown in FIG. 13F, a polycrystalline silicon film is formed on the sacrificial layer 42 including the inside of the contact hole 43 so as to serve as a vibrating electrode, in this example, the etching ratio with the sacrificial layer 42. Thereafter, the conductive film 44 is patterned to form the vibrating electrode 17 made of a polycrystalline silicon film connected to both outer wiring layers 18. A portion between the vibration electrode 17 and the wiring layer 18 becomes a support portion (anchor) 19 [19A, 19B] for supporting the vibration electrode 17 as a doubly supported structure.
[0031]
Next, as shown in FIG. 13G, the sacrificial layer 42 is removed by etching. Since the sacrifice layer 42 is removed by etching in this embodiment, the sacrifice layer 42 is formed by wet etching using a hydrofluoric acid solution. Thus, the desired MEMS resonator 31 is obtained.
[0032]
When the electrodes 14, 15 and the wiring layer 18 are formed of a metal such as an aluminum (Al) film, and the sacrifice layer 42 is formed of an amorphous silicon layer, the sacrifice layer 42 is removed by dry etching using XeF2 gas. be able to. Further, the underlying insulating film is made of silicon oxide (SiO 2). 2 ) When the electrodes 14, 15 and the wiring layer 18 are polycrystalline silicon films or aluminum (Al) films, and the sacrificial layer 42 is a photoresist film, the sacrificial layer 42 is 2 It can be removed by dry etching using plasma.
[0033]
According to the manufacturing method of the present embodiment, the input electrode 14, the output electrode 15, and the wiring layer 18 are formed of the same conductive film 41 on the substrate 12, and after the sacrifice layer 42 is formed, the sacrifice layer 42 is planarized. Since the process is included, the space (space 16) between the vibration electrode 17 and the input / output electrodes 14 and 15 can be accurately controlled. Further, the vibration electrode 17 can be formed flat, and can be formed as a vibration plate suitable for each vibration mode. Through the above-described series of steps, the objective MEMS resonator 11 in which the parasitic capacitance C0 between the input and output electrodes is reduced accurately and easily and the SN ratio is improved can be manufactured.
[0034]
4 and 5 show another embodiment of the MEMS resonator according to the present invention in which the SN ratio is further improved. The MEMS resonator 31 according to the present embodiment inputs the high-frequency signals 13 arranged at a predetermined interval from each other on the same plane of the substrate 12, that is, on at least the insulating surface of the substrate 12. An input electrode 14 serving as a first electrode, an output electrode 15 serving as a second electrode for outputting a high-frequency signal, and a fourth electrode (hereinafter, referred to as an electrode) disposed between the input / output electrodes 14 and 15 for supplying a ground potential. And a third vibrating electrode 17 serving as a vibrating plate arranged with the space 16 interposed between the input electrode 14, the output electrode 15, and the ground electrode 32. The vibrating electrode 17 straddles the input / output electrodes 14 and 15 and the ground electrode 32 in a bridge-like manner, and has both ends supporting portions so as to be connected to the wiring layer 18 disposed outside the input / output electrodes 14 and 15 and the ground electrode 32. (So-called anchor portions) 19 [19A, 19B] are integrally supported. Here, the gap X1 between the vibration electrode 17 and the input / output electrodes 14, 15 and the gap X2 between the input / output electrodes 14, 15 and the ground electrode 32 can satisfy X2> X1.
[0035]
The input electrode 14, the output electrode 15, the ground electrode 32, and the wiring layer 18 are formed of the same conductive material, and can be formed of, for example, a polycrystalline silicon film or a metal film such as aluminum (Al). The vibration electrode 17 can be formed of, for example, a polycrystalline silicon film or a metal film such as aluminum (Al). An input terminal t1 is derived from the input electrode 14, and a high-frequency signal S2 is input to the input electrode 14 through the input terminal t1. An output terminal t2 is led to the vibration electrode 15, and a high-frequency signal of a target frequency is output from the output terminal t2. The ground (GND) potential is applied to the ground electrode 32. A required DC bias voltage V2 is applied to the vibration electrode 17.
[0036]
Other configurations are the same as those in FIG. 1 and FIG. 2 described above.
[0037]
The operation of the MEMS resonator 31 according to the present embodiment is the same as in the case of FIGS. That is, the required DC bias voltage V2 is applied to the vibration electrode 17. The high-frequency signal S2 is input to the input electrode 14 through the input terminal t1. When a high-frequency signal having a target frequency is input, the vibrating electrode 17 resonates in a secondary vibration mode 25 as shown in FIG. 6 by electrostatic force generated between the vibrating electrode 17 and the input electrode 14. Due to the resonance of the vibration electrode 17, a high-frequency signal of a target frequency is output from the output electrode 15 through the output terminal t2. When a signal of another frequency is input, the vibration electrode 17 does not resonate, and no signal is output from the output terminal t2.
[0038]
According to the MEMS resonator 31 according to the present embodiment, by arranging the ground electrode 32 between the input electrode 14 and the output electrode 15, as shown in the equivalent circuit of FIG. The parasitic capacitance C0 between the electrodes 15 becomes extremely small. That is, in this equivalent circuit, the parasitic capacitance C0 originally in the MEMS resonator 11 in FIG. 1 is distributed to the capacitance C01 and the capacitance C02 between the ground electrode 32. As a result, the signal transmitted through the original parasitic capacitance C0 flows to the ground electrode 32 side and does not flow to the output electrode 15 side. Accordingly, leakage of the input high-frequency signal is eliminated, and the S / N ratio of the output signal is improved. Since a part of the signal flows to the ground side, the signal level drops, but the signal level may be electrically compensated by the load resistor R0 on the output side. Therefore, the parasitic capacitance C0 can be further reduced and the SN ratio can be further improved as compared with the MEMS resonator 11 shown in FIGS.
[0039]
14 and 15 show an example of a method for manufacturing the above-described MEMS resonator 31.
First, as shown in FIG. 14A, a conductive film 41 to be an electrode is formed on the substrate 12. In this example, a substrate 12 in which a silicon oxide film 22 and a silicon nitride film 23 as insulating films are stacked on a silicon substrate 21 is used. The conductive film 41 needs to be formed of a material having an etching ratio with the later sacrificial layer. In this example, the conductive film 41 is formed of a polycrystalline silicon film.
[0040]
Next, as shown in FIG. 14B, the conductive film 41 is patterned to form the input electrode 14, the output electrode 15, the ground electrode 32 between the electrodes 14 and 15, and the outer wiring layer 18.
Next, as shown in FIG. 14C, a sacrifice layer 42 is formed on the entire surface including the input electrode 14, the output electrode 15, the ground electrode 32, and the wiring layer 18. The sacrifice layer 42 is made of a material having an etching ratio with the electrodes 14, 14, 32 and the wiring layer 18 of a base insulating film (in this example, a silicon nitride (SiN) film) and polycrystalline silicon, in this example, silicon oxide (SiO 2). 2 ) Formed with a film.
[0041]
Next, as shown in FIG. 14D, the sacrificial layer 42 is flattened by, for example, a chemical mechanical polishing (CMP) method.
[0042]
Next, as shown in FIG. 15E, a contact hole 43 is formed in the sacrificial layer 42 on both outer wiring layers 18 by selective etching.
[0043]
Next, as shown in FIG. 15F, a polycrystalline silicon film is formed on the sacrificial layer 42 including the inside of the contact hole 43 so as to have a conductive film 44 serving as a vibrating electrode, in this example, an etching ratio with the sacrificial layer 42. Thereafter, the conductive film 44 is patterned to form the vibrating electrode 17 made of a polycrystalline silicon film connected to both outer wiring layers 18. A portion between the vibration electrode 17 and the wiring layer 18 becomes a support portion (anchor) 19 [19A, 19B] for supporting the vibration electrode 17 as a doubly supported structure.
[0044]
Next, as shown in FIG. 15G, the sacrificial layer 42 is removed by etching. Since the sacrifice layer 42 is removed by etching in this embodiment, the sacrifice layer 42 is formed by wet etching using a hydrofluoric acid solution. Thus, the desired MEMS resonator 31 is obtained.
[0045]
It should be noted that a combination of the materials of the conductive films 41, the sacrifice layer 42, and the underlying insulating film 23, which are the electrodes 14, 15, and 32, and the wiring layer 18, as well as the etchant of the sacrifice layer 42, may be the same as those described above. it can.
[0046]
According to the manufacturing method of the present embodiment, the input electrode 14, the output electrode 15, the ground electrode 32, and the wiring layer 18 are formed of the same conductive film 41 on the substrate 12, and the sacrificial layer 42 is formed. Is flattened, so that the space (space 16) between the vibration electrode 17 and the input / output electrodes 14 and 15 can be accurately controlled. Further, the vibration electrode 17 can be formed flat, and can be formed as a vibration plate suitable for each vibration mode. Through the above-described series of steps, the objective MEMS resonator 31 in which the parasitic capacitance C0 between the input and output electrodes is reduced accurately and easily and the SN ratio is improved can be manufactured.
[0047]
7 and 8 show another embodiment of the MEMS resonator according to the present invention. The MEMS resonator 35 according to the present embodiment inputs the high-frequency signals 13 arranged at a required interval from each other on the same plane of the substrate 12, that is, on at least the insulating surface of the substrate 12. Two input electrodes 14 [14A, 14B], one output electrode 15 for outputting a high-frequency signal, a ground electrode 32 disposed between the input electrode 14A and the output electrode 15, and between the input electrode 14B and the output electrode 15, respectively. 32A, 32B], and a vibrating electrode 17 arranged with the space 16 interposed between the input electrode 14 [14A, 14B], the output electrode 15, and the ground electrode 32 [32A, 32B]. In this example, the output electrode 15 is arranged at the center, and the ground electrode 32 [32A, 3B] and the input electrode 14 [14A, 14B] are arranged on both sides of the output electrode 15. The vibrating electrode 17 extends over the input / output electrodes 14 [14A, 14B] and 15 and the ground electrode 32 [32A and 32B] in a bridge shape, and is formed on the conductive layer 18 disposed outside the input / output electrodes 14 and 15 and the ground electrode 32. Both ends are integrally supported by support portions (so-called anchor portions) 19 [19A, 19B] so as to be connected. Here, the ground electrodes 32A and 32B are arranged close to a portion of the vibration electrode 17 that serves as a node of vibration, as described later.
[0048]
An input terminal t1 is derived from the input electrode 14 [14A, 14B], and a high-frequency signal S2 is input to the input electrode 14 [14A, 14B] through the input terminal t1. An output terminal t2 is led to the vibration electrode 15, and a high-frequency signal of a target frequency is output from the output terminal t2. A ground (GND) potential is applied to the ground electrode 32 [32A, 32B]. A required DC bias voltage V2 is applied to the vibration electrode 17. The two input electrodes 14A and 14B are formed by branching from one input electrode pad, and the two ground electrodes 32A and 32B are formed by branching from one ground electrode pad.
You.
[0049]
Other configurations such as the substrate 12, the input electrode 14 [14A, 14B], the output electrode 15, the ground electrode 32 [32A, 32B], and the conductive layer 18 [18A, 18B] are the same as those in FIGS. Corresponding parts have the same reference characters allotted, and description thereof will not be repeated.
In the above example, the output electrode 15 is located at the center, two input electrodes 14A and 14B are interposed therebetween, and the ground electrode 32 is arranged between the input and output electrodes. It is also possible to adopt a configuration in which two output electrodes 15 are arranged with this interposed therebetween, and a ground electrode 32 is arranged between the input and output.
[0050]
The operation of the MEMS resonator 35 according to the present embodiment is the same as in the case of FIGS. That is, the required DC bias voltage V2 is applied to the vibration electrode 17. The high frequency signal S2 is input to the input electrode 14 [14A, 14B] through the input terminal t1. When a high-frequency signal of the target frequency is input, the vibrating electrode 17 resonates with an electrostatic force generated between the vibrating electrode 17 and the input electrode 14 [14A, 14B]. In this case, as shown in FIG. 9, the vibration electrode 17 resonates in the third vibration mode 26. Due to the resonance of the vibration electrode 17, a high-frequency signal of a target frequency is output from the output electrode 15 through the output terminal t2. When a signal of another frequency is input, the vibration electrode 17 does not resonate, and no signal is output from the output terminal t2.
[0051]
According to the MEMS resonator 35 according to the present embodiment, by arranging the ground electrodes 32 [32A, 32B] between the input electrode 14 [14A, 14B] and the output electrode 15, respectively, The parasitic capacitance C0 between the output electrodes 15 can be reduced as in FIGS. Therefore, the SN ratio can be further improved as compared with the MEMS resonator 11.
[0052]
The method of manufacturing the MEMS resonator 35 according to the present embodiment can be manufactured in the same manner as the above-described method of manufacturing the MEMS resonator 31 shown in FIGS. 14A to 15G.
[0053]
In the MEMS resonator 11 shown in FIGS. 1 and 2, one of the input electrode 14 and the output electrode 15 is arranged at the center, and the other electrode is arranged in a ring around the one electrode. 17 may be arranged on both electrodes 14 and 15 so as to face each other. The shape of the electrode can be appropriately selected from a circle, a square, and other shapes.
In the MEMS resonator 31 shown in FIGS. 4 and 5, or the MEMS resonator 31 shown in FIGS. 7 and 8, one of the input electrode 14 and the output electrode 15 is arranged at the center, and the other electrode and the ground are connected. The electrode 32 may be arranged in a ring shape around one electrode, and the vibrating electrode 17 may be arranged on the electrodes 14, 15 and 32 so as to face each other. The shape of the electrode can be appropriately selected from a circle, a square, and other shapes.
[0054]
In the above-described embodiment, the present invention is applied to the MEMS resonators in the secondary vibration mode and the tertiary vibration mode, but can also be applied to the MEMS resonators in the multi-order vibration mode equal to or higher than the fourth vibration mode.
[0055]
The present invention includes the MEMS resonator 11 or the MEMS resonator 31 according to the above-described embodiment to configure a filter such as a high-frequency filter and an intermediate-frequency filter.
By configuring the filter with the MEMS resonator 11, the parasitic capacitance C0 between the input and output electrodes can be reduced as compared with the conventional case, and the SN ratio of the output signal can be improved.
Since the ground electrode 32 is arranged between the input / output electrodes 14 and 15 by forming a filter having the MEMS type resonator 31, the parasitic capacitance C0 is reduced as much as possible, and the SN ratio of the output signal is further improved. can do.
[0056]
【The invention's effect】
According to the MEMS resonator according to the present invention, the first electrode for inputting a high-frequency signal and the second electrode for outputting a high-frequency signal are arranged on the same plane of the substrate, and the first and second electrodes are provided on the first and second electrodes. With the configuration in which the third electrode that is the diaphragm is opposed to the first electrode, the parasitic capacitance between the first and second electrodes, that is, between the input and output electrode electrodes is reduced, and the SN ratio of the output signal is improved. be able to.
According to the MEMS resonator according to the present invention, furthermore, the fourth electrode to which the ground potential is supplied is arranged between the first electrode and the second electrode, so that the first and second electrodes are provided. The parasitic capacitance between the electrodes, that is, between the input and output electrode poles is reduced as much as possible, and the S / N ratio of the output signal can be further improved.
[0057]
According to the filter according to the present invention, by including the MEMS resonator, the SN ratio of the output signal can be improved.
According to the filter of the present invention, the MEMS-type resonator in which the third electrode having the ground potential is arranged between the first electrode and the second electrode further increases the output signal. The S / N ratio can be improved.
[0058]
According to the method of manufacturing the MEMS resonator according to the present invention, the distance between the first and second electrodes serving as input / output electrodes and the third electrode serving as the diaphragm can be accurately controlled, and the third electrode can be controlled. Can be formed flat so as to be suitable for vibration. In addition, a MEMS resonator having reduced or infinitely small parasitic capacitance between input and output electrodes can be manufactured accurately and easily.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing one embodiment of a MEMS resonator according to the present invention.
FIG. 2 is a plan view showing one embodiment of a MEMS resonator according to the present invention.
FIG. 3 is an explanatory diagram showing a vibration mode of the MEMS resonator according to one embodiment of the present invention.
FIG. 4 is a configuration diagram showing another embodiment of the MEMS resonator according to the present invention.
FIG. 5 is a plan view showing another embodiment of the MEMS resonator according to the present invention.
FIG. 6 is an explanatory diagram showing a vibration mode of another embodiment of the MEMS resonator according to the present invention.
FIG. 7 is a configuration diagram showing still another embodiment of the MEMS resonator according to the present invention.
FIG. 8 is a plan view showing still another embodiment of the MEMS resonator according to the present invention.
FIG. 9 is an explanatory diagram showing a vibration mode of still another embodiment of the MEMS resonator according to the present invention.
FIG. 10 is an equivalent circuit diagram of the MEMS resonator.
FIG. 11 is an equivalent circuit diagram of the MEMS resonator according to the embodiment of FIG.
12A to 12D are manufacturing process diagrams (part 1) illustrating an example of an embodiment of a method for manufacturing a MEMS resonator according to the present invention.
13A to 13G are manufacturing process diagrams (part 2) illustrating an example of an embodiment of a method for manufacturing a MEMS resonator according to the present invention.
14A to 14D are manufacturing process diagrams (part 1) illustrating another example of the embodiment of the method of manufacturing the MEMS resonator according to the present invention.
FIGS. 15A to 15G are manufacturing process diagrams (part 2) illustrating another example of the embodiment of the method for manufacturing the MEMS resonator according to the present invention.
FIG. 16 is a configuration diagram showing an example of a conventional MEMS type vibrator.
[Explanation of symbols]
11, 31, 35 MEMS resonator, 12 substrate, 14 A, 14 B input electrode, 15 output electrode, 16 space, 17 vibration electrode, 18 wiring layer, 19 [19A, 19B] · · · support portion, 21 · · · silicon substrate, 22 · · · silicon oxide film, 23 · · · silicon nitride film, 32, 32A, 32B · · · ground electrode, 41 · · · conductive film, 42 · · · Sacrifice layer, 43 contact hole, 44 conductive film

Claims (6)

基板の同一平面上に高周波信号を入力する第1の電極と、高周波信号を出力する第2の電極と、前記第1及び第2の電極に対して空間を挟んで配置された振動板となる第3の電極とを有して成る
ことを特徴とするMEMS共振器。
A first electrode for inputting a high-frequency signal, a second electrode for outputting a high-frequency signal, and a diaphragm arranged with a space between the first and second electrodes are provided on the same plane of the substrate. A MEMS resonator comprising: a third electrode.
前記基板上の前記第1の電極と第2の電極との間に、接地電位が供給される第4の電極が配置されて成る
ことを特徴とする請求項1記載のMEMS共振器。
2. The MEMS resonator according to claim 1, wherein a fourth electrode to which a ground potential is supplied is arranged between the first electrode and the second electrode on the substrate.
基板の同一平面上に高周波信号を入力する第1の電極と、高周波信号を出力する第2の電極と、前記第1及び第2の電極に対して空間を挟んで配置された振動板となる第3の電極とからなるMEMS型共振器を有して成る
ことを特徴とするフィルタ。
A first electrode for inputting a high-frequency signal, a second electrode for outputting a high-frequency signal, and a diaphragm arranged with a space between the first and second electrodes are provided on the same plane of the substrate. A filter comprising a MEMS resonator including a third electrode.
前記MEMS型共振器における前記基板上の前記第1の電極と第2の電極との間に、接地電位が供給される第4の電極が配置されて成る
ことを特徴とする請求項3記載のフィルタ。
4. The MEMS resonator according to claim 3, wherein a fourth electrode to which a ground potential is supplied is disposed between the first electrode and the second electrode on the substrate. filter.
基板上に互いに所定間隔を置いて高周波信号を入力する第1の電極と、高周波信号を出力する第2の電極と、前記第1及び第2の電極の両側に位置する導電層とを選択的に形成する工程と、
前記第1、第2の電極及び導電層を含む全面上に犠牲層を形成し、該犠牲層を平坦化する工程と、
前記導電層に一部接続されるように前記犠牲層上に振動板となる第3の電極を形成する工程と、
前記犠牲層を選択的に除去する工程とを有する
ことを特徴とするMEMS型共振器の製造方法。
A first electrode for inputting a high-frequency signal at a predetermined interval on a substrate, a second electrode for outputting a high-frequency signal, and conductive layers located on both sides of the first and second electrodes are selectively provided. Forming a
Forming a sacrificial layer on the entire surface including the first and second electrodes and the conductive layer, and flattening the sacrificial layer;
Forming a third electrode serving as a diaphragm on the sacrificial layer so as to be partially connected to the conductive layer;
Selectively removing the sacrificial layer. A method for manufacturing a MEMS resonator.
基板上に高周波信号を入力する第1の電極と、高周波信号を出力する第2の電極と、接地電位が供給される第4の電極と、前記第1、第2及び第4の電極の両側に位置する導電層とを選択的に形成する工程と、
前記第1、第2、第4の電極及び導電層を含む全面上に犠牲層を形成し、該犠牲層を平坦化する工程と、
前記導電層に一部接続されるように前記犠牲層上に振動板となる第3の電極を形成する工程と、
前記犠牲層を選択的に除去する工程とを有する
ことを特徴とするMEMS型共振器の製造方法。
A first electrode for inputting a high-frequency signal on a substrate, a second electrode for outputting a high-frequency signal, a fourth electrode to which a ground potential is supplied, and both sides of the first, second and fourth electrodes Selectively forming a conductive layer located at
Forming a sacrificial layer on the entire surface including the first, second, and fourth electrodes and the conductive layer, and planarizing the sacrificial layer;
Forming a third electrode serving as a diaphragm on the sacrificial layer so as to be partially connected to the conductive layer;
Selectively removing the sacrificial layer. A method for manufacturing a MEMS resonator.
JP2003116148A 2003-04-21 2003-04-21 MEMS resonator, method of manufacturing the same, and filter Expired - Fee Related JP4341288B2 (en)

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