JP5057148B2 - Piezoelectric vibration device - Google Patents

Piezoelectric vibration device Download PDF

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JP5057148B2
JP5057148B2 JP2007269154A JP2007269154A JP5057148B2 JP 5057148 B2 JP5057148 B2 JP 5057148B2 JP 2007269154 A JP2007269154 A JP 2007269154A JP 2007269154 A JP2007269154 A JP 2007269154A JP 5057148 B2 JP5057148 B2 JP 5057148B2
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film
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piezoelectric vibration
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JP2009100196A (en
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健一 上坂
始 神藤
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Murata Manufacturing Co Ltd
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Description

本発明は圧電振動装置に関し、詳しくは、バルク波の輪郭振動モードを利用する圧電振動装置に関する。   The present invention relates to a piezoelectric vibration device, and more particularly to a piezoelectric vibration device using a contour vibration mode of a bulk wave.

バルク波を利用する圧電振動装置には、バルク波の中の厚み振動モードを利用するタイプや、バルク波の中の拡がり振動モード、長さ振動モード又は幅振動モードなどの輪郭振動モードを利用するタイプがある。   Piezoelectric vibration devices that use bulk waves use types that use thickness vibration modes in bulk waves, and contour vibration modes such as spreading vibration mode, length vibration mode, and width vibration mode in bulk waves. There are types.

後者の輪郭振動モードを利用する圧電振動装置において、図５の断面図に示すように、電極５，７間に圧電膜６が挟まれてなり、空隙３を介して基板２から浮いている圧電振動部９の上下に、温度補償膜４，８を備えることが提案されている。例えば、温度補償膜４，８として、ＳｉＯ２膜が１層ずつ形成される（例えば、特許文献１参照）。
ＷＯ２００７／０８８６９６号公報 In the piezoelectric vibration device using the latter contour vibration mode, as shown in the cross-sectional view of FIG. 5, the piezoelectric film 6 is sandwiched between the electrodes 5 and 7, and the piezoelectric floating from the substrate 2 through the gap 3. It has been proposed to provide temperature compensation films 4 and 8 above and below the vibration part 9. For example, SiO 2 films are formed one by one as the temperature compensation films 4 and 8 (see, for example, Patent Document 1).
WO2007 / 086696

このように温度補償膜を備える圧電振動装置は、例えば図６に示すように、ヒステリシス現象が起きる。図６は、厚さ１．６μｍのＡｌＮ膜の圧電膜を含む圧電振動部の上に、厚さ３．３μｍのＳｉＯ２膜の温度補償膜を形成し、圧電振動部の下に厚さ１．７μｍのＳｉＯ２膜の温度補償膜を形成した圧電振動装置について、振動数とインピーダンスの関係を示すグラフである。実線は、周波数の高い方から低い方へスイープしたときのインピーダンス特性を示す。破線は、周波数の低い方から高い方へスイープしたときのインピーダンス特性を示す。破線と実線が重なっていない部分があり、測定時の周波数のスイープ方向によってインピーダンス波形が異なるというヒステリシス現象が起きることが分かる。 In the piezoelectric vibration device including the temperature compensation film as described above, a hysteresis phenomenon occurs as shown in FIG. 6, for example. In FIG. 6, a temperature compensation film of an SiO 2 film having a thickness of 3.3 μm is formed on a piezoelectric vibration portion including a piezoelectric film of an AlN film having a thickness of 1.6 μm, and a thickness of 1 is formed below the piezoelectric vibration portion. a piezoelectric vibration device forming the temperature compensating film of SiO 2 film .7Myuemu, is a graph showing the relationship between frequency and impedance. The solid line shows the impedance characteristic when sweeping from the higher frequency to the lower frequency. A broken line shows an impedance characteristic when sweeping from a lower frequency to a higher frequency. It can be seen that there is a portion where the broken line and the solid line do not overlap, and a hysteresis phenomenon occurs in which the impedance waveform varies depending on the frequency sweep direction at the time of measurement.

このタイプの圧電振動装置で小型化し、かつヒステリシス現象を抑制しようとすると、圧電膜のＡｌＮ膜より音速の小さいＳｉＯ２膜を厚くすることが望ましい。しかし、温度補償膜であるＳｉＯ２膜を厚くすると、温度特性が劣化してしまう。 In order to reduce the size and suppress the hysteresis phenomenon with this type of piezoelectric vibration device, it is desirable to thicken the SiO 2 film having a lower sound speed than the AlN film of the piezoelectric film. However, if the SiO 2 film, which is a temperature compensation film, is thickened, the temperature characteristics deteriorate.

本発明は、かかる実情に鑑み、温度特性を維持しつつ、小型化とヒステリシス現象の抑制との実現が可能である、圧電振動装置を提供しようとするものである。   In view of such circumstances, the present invention intends to provide a piezoelectric vibration device capable of realizing miniaturization and suppression of hysteresis phenomenon while maintaining temperature characteristics.

本発明は、上記課題を解決するために、以下のように構成した圧電振動装置を提供する。   In order to solve the above problems, the present invention provides a piezoelectric vibration device configured as follows.

圧電振動装置は、（ａ）基板と、（ｂ）圧電膜と前記圧電膜の両主面にそれぞれ配置された第１及び第２の電極とを含み、前記圧電膜の膜厚方向から透視したときに前記第１及び第２の電極が前記圧電膜を介して重なり合う圧電振動部が前記基板から浮いた状態で、前記圧電振動部以外の支持部が前記基板に支持された、圧電薄膜部とを備え、前記圧電振動部の輪郭振動を利用するタイプの圧電振動装置である。圧電振動装置は、（ｃ）少なくとも前記圧電振動部上に、温度補償膜及び補強膜をさらに備える。前記補強膜は、前記圧電膜の音速より小さい音速を有し、かつ、温度特性の符号が前記温度補償膜の温度特性の符号と異なる。   The piezoelectric vibration device includes (a) a substrate, and (b) a piezoelectric film and first and second electrodes respectively disposed on both main surfaces of the piezoelectric film, and is seen through from the film thickness direction of the piezoelectric film. A piezoelectric thin film portion in which a support portion other than the piezoelectric vibration portion is supported by the substrate in a state where the piezoelectric vibration portion in which the first and second electrodes overlap with each other via the piezoelectric film floats from the substrate; And a piezoelectric vibration device of the type that utilizes contour vibration of the piezoelectric vibration part. The piezoelectric vibration device further includes (c) a temperature compensation film and a reinforcing film on at least the piezoelectric vibration part. The reinforcing film has a sound velocity lower than the sound velocity of the piezoelectric film, and the sign of the temperature characteristic is different from the sign of the temperature characteristic of the temperature compensation film.

上記構成によれば、圧電振動部の上に、圧電膜の音速より小さい音速を有する補強膜を形成すると、圧電振動部上に形成された補強膜も圧電振動部と連動して面方向に振動するため、素子の縦波音速を小さくすることができ、振動子の小型化が可能となる。   According to the above configuration, when a reinforcing film having a sound velocity lower than that of the piezoelectric film is formed on the piezoelectric vibrating portion, the reinforcing film formed on the piezoelectric vibrating portion also vibrates in the plane direction in conjunction with the piezoelectric vibrating portion. Therefore, the longitudinal wave sound velocity of the element can be reduced, and the vibrator can be miniaturized.

圧電振動部上に温度補償膜及び補強膜が形成されると、膜厚が厚くなり、振動変位が小さくなるため、ヒステリシス現象が抑制される。   When the temperature compensation film and the reinforcing film are formed on the piezoelectric vibration part, the film thickness is increased and the vibration displacement is reduced, so that the hysteresis phenomenon is suppressed.

補強膜の温度特性の符号が温度補償膜の温度特性の符号と異なるので、温度特性を維持することができる。   Since the sign of the temperature characteristic of the reinforcing film is different from the sign of the temperature characteristic of the temperature compensation film, the temperature characteristic can be maintained.

好ましくは、前記温度補償膜及び前記補強膜の少なくとも一方が等方体である。   Preferably, at least one of the temperature compensation film and the reinforcing film is isotropic.

この場合、等方振動が励起されるため、共振特性が劣化しない。   In this case, since the isotropic vibration is excited, the resonance characteristics do not deteriorate.

好ましくは、前記補強膜がＴａ２Ｏ５である。 Preferably, the reinforcing film is Ta 2 O 5 .

この場合、音速が特に小さいＴａ２Ｏ５を補強膜に用いるため、より小型化が可能である。 In this case, since Ta 2 O 5 having a particularly low sound velocity is used for the reinforcing film, the size can be further reduced.

本発明によれば、温度特性を維持しつつ、小型化とヒステリシス現象の抑制との実現が可能である。   According to the present invention, it is possible to reduce the size and suppress the hysteresis phenomenon while maintaining the temperature characteristics.

以下、本発明の実施の形態について、図１〜図４を参照しながら説明する。   Hereinafter, embodiments of the present invention will be described with reference to FIGS.

＜実施例＞ 図１は、本発明の圧電振動装置１０の断面図である。図２は、圧電振動装置１０の膜構成を模式的に示す分解斜視図である。   <Example> FIG. 1: is sectional drawing of the piezoelectric vibration apparatus 10 of this invention. FIG. 2 is an exploded perspective view schematically showing the film configuration of the piezoelectric vibration device 10.

図１及び図２に示すように、本発明の圧電振動装置１０は圧電共振子であり、基板１２上に、支持膜１４、下部電極１５、圧電膜１６、上部電極１７、補強膜１８、温度補償膜１９が積層され、各膜１４〜１９の矩形の本体部１４ａ〜１９ａが順に積層されている。電極１５，１７の本体部１５ａ，１７ａの間に圧電膜１６の本体部１６ａが挟まれている圧電振動部２０は、その上に、補強膜１８及び温度補償膜１９の本体部１８ａ，１９ａが配置され、その下に、支持膜１４の本体部１４ａが配置されている。   As shown in FIGS. 1 and 2, the piezoelectric vibration device 10 of the present invention is a piezoelectric resonator, on a substrate 12, a support film 14, a lower electrode 15, a piezoelectric film 16, an upper electrode 17, a reinforcing film 18, a temperature. The compensation film 19 is laminated, and the rectangular main body portions 14a to 19a of the films 14 to 19 are laminated in order. The piezoelectric vibrating portion 20 in which the main body portion 16a of the piezoelectric film 16 is sandwiched between the main body portions 15a and 17a of the electrodes 15 and 17 has the main body portions 18a and 19a of the reinforcing film 18 and the temperature compensation film 19 thereon. The main body portion 14a of the support film 14 is disposed below the main body portion 14a.

支持膜１４、圧電膜１６、補強膜１８、温度補償膜１９には、膜厚方向に貫通する貫通溝１４ｘ，１６ｘ，１８ｘ，１９ｘが形成され、貫通溝１４ｘ，１６ｘ，１８ｘ，１９ｘで囲まれた内側に、本体部１４ａ，１６ａ，１８ａ，１９ａが形成されている。   The support film 14, the piezoelectric film 16, the reinforcing film 18, and the temperature compensation film 19 are formed with through grooves 14x, 16x, 18x, and 19x penetrating in the film thickness direction and surrounded by the through grooves 14x, 16x, 18x, and 19x. On the inner side, main body portions 14a, 16a, 18a, 19a are formed.

下部電極１５及び上部電極１７は、矩形の本体部１５ａ，１７ａと、パッド１５ｂ，１７ｂとの間が、接続部１５ｓ，１７ｓを介して接続されている。図１に示すように、パッド１５ｂ，１７ｂ上には、何も積層されておらず、外部と電気的に接続できるようになっている。   The lower electrode 15 and the upper electrode 17 are connected between the rectangular main body portions 15a and 17a and the pads 15b and 17b via connection portions 15s and 17s. As shown in FIG. 1, nothing is stacked on the pads 15b and 17b so that they can be electrically connected to the outside.

図１に示すように、圧電振動部２０は、基板１２から空隙１３を介して浮いた状態である。圧電振動部２０は、基板１２に支持された支持部２２との間が接続部２４を介して接続されている。   As shown in FIG. 1, the piezoelectric vibrating portion 20 is in a state of floating from the substrate 12 through the gap 13. The piezoelectric vibration part 20 is connected to the support part 22 supported by the substrate 12 via a connection part 24.

圧電膜１６は、酸化亜鉛（ＺｎＯ）、窒化アルミニウム（ＡｌＮ）、チタン酸ジルコン酸鉛（ＰＺＴ）、ニオブ酸リチウム（ＬｉＮｂＯ３）、タンタル酸リチウム（ＬｉＴａＯ３）、水晶などの圧電膜を用いることができる。実施例ではＡｌＮを用いている。 As the piezoelectric film 16, a piezoelectric film such as zinc oxide (ZnO), aluminum nitride (AlN), lead zirconate titanate (PZT), lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), or quartz is used. Can do. In the embodiment, AlN is used.

電極１５，１７は、圧電膜１６に電圧を印加する役割を持ち、Ａｌ、Ｃｕ、Ａｕ、Ｐｔ、Ｍｏ、Ｗ、Ｎｉ、エリンバー、インバーなど導電性を持つ材料、あるいはこれらの積層体を使用する。下部電極１５と支持膜１４の間や、電極１５，１７と圧電膜１６の間には、密着性を高めるために、Ｔｉ、Ｃｒなどの材料を用いて密着層を形成してもよい。また、電極１５，１７は、圧電振動部２０からの引き出し電極（接続部１５ｓ，１７ｓ及びパッド１５ｂ，１７ｂ）に、配線抵抗を下げるための厚付け配線を別途形成してもよい。   The electrodes 15 and 17 have a role of applying a voltage to the piezoelectric film 16 and use a conductive material such as Al, Cu, Au, Pt, Mo, W, Ni, Erin bar, Invar, or a laminate thereof. . In order to improve the adhesion between the lower electrode 15 and the support film 14 or between the electrodes 15 and 17 and the piezoelectric film 16, an adhesion layer may be formed using a material such as Ti or Cr. For the electrodes 15 and 17, thick wiring for reducing wiring resistance may be separately formed on the lead electrodes (connection portions 15 s and 17 s and pads 15 b and 17 b) from the piezoelectric vibrating portion 20.

圧電振動部２０の上下に付加した膜１４，１８，１９は、共振周波数の温度補償、パッシペーション、共振周波数の調整などの役割を持つ。温度補償として、縦波音速の温度係数の符号が圧電膜１６と逆の膜を形成するが、ＳｉＯ２が用いられることが多い。パッシペーションとしての機能を果たすため、なるべく電極１５，１７及び圧電膜１６の表面及び側壁まで覆うように形成する。 The films 14, 18, and 19 added to the top and bottom of the piezoelectric vibration unit 20 have roles such as temperature compensation of the resonance frequency, passivation, and adjustment of the resonance frequency. As temperature compensation, a film having a sign of the temperature coefficient of longitudinal wave sound velocity opposite to that of the piezoelectric film 16 is formed, but SiO 2 is often used. In order to fulfill the function as a passivation, the electrodes 15 and 17 and the piezoelectric film 16 are formed so as to cover the surfaces and side walls as much as possible.

共振周波数の調整では、圧電振動部２０の上に形成した膜をミリングやエッチングで薄くする手法が知られている。材料は、主に、ＳｉＯ２、ＳｉＮ、Ｔａ２Ｏ５などの誘電体膜を用いることができるが、Ａｌ、Ｃｕ、エリンバー、インバーのような導電性材料、ＺｎＯ、ＡｌＮ、チタン酸ジルコン酸鉛（ＰＺＴ）、ニオブ酸リチウム（ＬｉＮｂＯ３）、タンタル酸リチウム（ＬｉＴａＯ３）のような圧電材料、Ｓｉのような半導体材料であってもよく、これらの中から所望の材料を選択する。 For adjusting the resonance frequency, a method is known in which a film formed on the piezoelectric vibrating portion 20 is thinned by milling or etching. The material can mainly be a dielectric film such as SiO 2 , SiN, Ta 2 O 5, etc., but conductive materials such as Al, Cu, Elinvar, Invar, ZnO, AlN, lead zirconate titanate A piezoelectric material such as (PZT), lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), or a semiconductor material such as Si may be used, and a desired material is selected from these materials.

また、圧電振動部２０の上の膜１８，１９は、横方向の振動のみが励起されないことがないよう、等方体であることが望ましい。等方体は特定の結晶構造をもたず、一般的に形成温度が低い。圧電振動部２０の上の膜１８，１９は、圧電振動部２０と連動して振動するため、圧電振動部２０と十分な密着強度を有することが望ましく、テープ剥離試験で剥がれないことが望ましい。できればセロハンテープの接着力のＪＩＳ規格（Ｚ １５２２）に記載の強度以上の密着強度を有することが好ましい。   The films 18 and 19 on the piezoelectric vibration unit 20 are preferably isotropic so that only lateral vibrations are not excited. Isotropic bodies do not have a specific crystal structure and generally have a low formation temperature. Since the films 18 and 19 on the piezoelectric vibration part 20 vibrate in conjunction with the piezoelectric vibration part 20, it is desirable that the films 18 and 19 have sufficient adhesion strength with the piezoelectric vibration part 20 and are not peeled off by the tape peeling test. If possible, the adhesive strength of the cellophane tape is preferably higher than the strength described in JIS standard (Z 1522).

実施例では、圧電振動部２０の上側に、ＳｉＯ２の温度補償膜１９と、Ｔａ２Ｏ５の補強膜１８を形成し、下側にＳｉＯ２の支持膜１４を形成している。ＳｉＯ２は縦波音速の温度特性の符号がＡｌＮと反対であること、Ｔａ２Ｏ５は、次の表１に示すように音速がＡｌＮの半分以下で、縦波音速の温度特性の符号がＳｉＯ２の逆であることから、温度特性の調整と素子の小型化が可能となる。これらの薄膜は、例えばＰＶＤ法もしくはＣＶＤ法によって成膜する。

Figure 0005057148
圧電振動部２０を含む基板１２から浮いている部分が基板１２に接触しないよう、薄膜の応力調整をすることが望ましい。例えば、圧電膜１６の膜応力が圧縮応力のとき、圧電振動部２０の上下に付加する膜１４，１８，１９の少なくともひとつの膜応力を、逆の引張応力にすることで、圧電振動部２０の反りが抑制できる。 In the embodiment, the temperature compensation film 19 of SiO 2 and the reinforcing film 18 of Ta 2 O 5 are formed on the upper side of the piezoelectric vibrating portion 20, and the support film 14 of SiO 2 is formed on the lower side. The sign of the temperature characteristic of longitudinal wave sound velocity is opposite to that of AlN for SiO 2, and the sign of the temperature characteristic of longitudinal wave sound speed is Ta 2 O 5 , as shown in Table 1 below. Since it is the reverse of SiO 2 , temperature characteristics can be adjusted and the element can be downsized. These thin films are formed by, for example, the PVD method or the CVD method.
Figure 0005057148
 It is desirable to adjust the stress of the thin film so that the portion floating from the substrate 12 including the piezoelectric vibrating portion 20 does not contact the substrate 12. For example, when the film stress of the piezoelectric film 16 is a compressive stress, the piezoelectric vibration part 20 is formed by changing at least one film stress of the films 14, 18, 19 added to the top and bottom of the piezoelectric vibration part 20 to a reverse tensile stress. Can be suppressed.

膜１４〜１９のパターニングは、ドライエッチング、ウェットエッチング、あるいはリフトオフ法により行う。その中でも、リフトオフ法はパターニング精度がよく、振動子の寸法ばらつきを小さくできるので好ましい。また、圧電振動部２０の上下の膜１４，１８，１９の形成では、構成膜間の位置ずれをなくすため、同じマスクパターンを用いて一括形成することが望ましい。   Patterning of the films 14 to 19 is performed by dry etching, wet etching, or a lift-off method. Among them, the lift-off method is preferable because the patterning accuracy is high and the dimensional variation of the vibrator can be reduced. In forming the upper and lower films 14, 18, 19 of the piezoelectric vibrating portion 20, it is desirable to form them collectively using the same mask pattern in order to eliminate positional deviation between the constituent films.

空隙１３は、基板１２上に犠牲層を配置し、その上に支持膜１４等を積層した後に、犠牲層を除去することによって形成する。   The gap 13 is formed by disposing a sacrificial layer on the substrate 12, laminating the support film 14 and the like thereon, and then removing the sacrificial layer.

基板１２は、Ｓｉのような半導体基板、もしくはガラスのような絶縁体基板を用いる。あるいは表面に酸化膜や窒化膜が形成された基板でもよい。   As the substrate 12, a semiconductor substrate such as Si or an insulator substrate such as glass is used. Alternatively, a substrate having an oxide film or nitride film formed on the surface may be used.

本発明の圧電振動装置１０は、圧電膜１６より縦波音速が小さく、縦波音速の温度係数の符号が温度補償膜１９と逆の補強膜１８を形成することによって、温度特性を維持しつつ、素子の小型化とヒステリシス現象の抑制の実現が可能となる。以下、詳しく説明する。   The piezoelectric vibration device 10 according to the present invention has a longitudinal wave sound velocity smaller than that of the piezoelectric film 16 and maintains a temperature characteristic by forming a reinforcing film 18 whose temperature coefficient sign is opposite to that of the temperature compensation film 19. Therefore, it is possible to realize downsizing of the element and suppression of the hysteresis phenomenon. This will be described in detail below.

薄膜による輪郭振動を用いた従来例の圧電振動装置は、図６に示したように、測定時の周波数のスイープ方向によってインピーダンス波形が異なるというヒステリシス現象が起きる。   As shown in FIG. 6, the conventional piezoelectric vibration device using the contour vibration by the thin film has a hysteresis phenomenon that the impedance waveform varies depending on the frequency sweep direction at the time of measurement.

ヒステリシス現象は、圧電膜が強く振動すると振動変位が大きくなり、変位と応力の関係が比例ではなくなり非線形領域に入り、この非線形領域ではスイープ方向によってインピーダンス波形が変わるために起きると推測される。ヒステリシス現象を抑制するには、振動変位を小さくすることが望ましい。   The hysteresis phenomenon is presumed to occur because the vibration displacement increases when the piezoelectric film vibrates strongly, and the relationship between the displacement and the stress becomes non-proportional and enters the non-linear region. In this non-linear region, the impedance waveform changes depending on the sweep direction. In order to suppress the hysteresis phenomenon, it is desirable to reduce the vibration displacement.

圧電振動部に付加する膜の膜厚が厚いほど、振動変位が小さくなるので、ヒステリシス現象は、圧電振動部に付加する膜の膜厚が厚いほど、抑制できる。   As the thickness of the film added to the piezoelectric vibrating portion increases, the vibration displacement decreases. Therefore, the hysteresis phenomenon can be suppressed as the thickness of the film added to the piezoelectric vibrating portion increases.

また、一般に、長さ振動モード、幅振動モード、拡がり振動モードなど、主としてＸＹ方向の輪郭振動を用いた振動子は、共振周波数が幅、長さなどの平面寸法によって決定される。振動モードの様子を、図４に示す。図４は、上下の電極で挟まれた領域（圧電振動部）の圧電膜を、電極側から見た平面図である。   In general, in a vibrator using contour vibration mainly in the XY directions such as the length vibration mode, the width vibration mode, and the spread vibration mode, the resonance frequency is determined by the planar dimensions such as the width and the length. The state of the vibration mode is shown in FIG. FIG. 4 is a plan view of a piezoelectric film in a region (piezoelectric vibration portion) sandwiched between upper and lower electrodes as viewed from the electrode side.

式（１）に長さ方向に一様な長さモード振動子の共振周波数ｆｒの理論式を示す。   Equation (1) shows a theoretical formula of the resonance frequency fr of the length mode vibrator which is uniform in the length direction.

ｆｒ＝２Ｌ／Ｖｐ ・・・（１）
ここで、Ｌ：振動子長さ、Ｖｐ：素子の縦波音速
この式（１）から、共振周波数（ｆｒ）を一定に保ちながら振動子を小型化する、つまり、振動子長さ（Ｌ）を小さくするには、素子の縦波音速（Ｖｐ）を小さくすればよいことが分かる。素子の縦波音速を小さくするには、縦波音遠の小さい圧電材料を用いることが考えられる。しかし、圧電膜の材料を変えるには、形成方法の条件出しにかなりの手間がかかり、容易ではない。 fr = 2L / Vp (1)
Here, L: vibrator length, Vp: longitudinal wave sound velocity of the element From this equation (1), the vibrator is downsized while keeping the resonance frequency (fr) constant, that is, the vibrator length (L). It can be seen that the longitudinal wave sound velocity (Vp) of the element should be reduced in order to reduce the. In order to reduce the longitudinal wave sound velocity of the element, it is conceivable to use a piezoelectric material having a small longitudinal wave sound distance. However, changing the material of the piezoelectric film is not easy because it takes a lot of work to determine the conditions for the formation method.

そこで、圧電膜の材料を変えずに、共振子上に圧電膜より縦波音速の小さい材料を形成すると、圧電振動部上に形成された材料も圧電振動部と連動して面方向に振動するため、素子の音速が、圧電膜の縦波音速より小さくなり、共振子上に形成された膜の縦波音速より大きくなる。よって、素子の縦波音速を小さくすることができ、振動子の小型化が可能となる。   Therefore, if a material having a lower longitudinal acoustic velocity than the piezoelectric film is formed on the resonator without changing the material of the piezoelectric film, the material formed on the piezoelectric vibrating part also vibrates in the plane direction in conjunction with the piezoelectric vibrating part. Therefore, the sound speed of the element is smaller than the longitudinal wave sound speed of the piezoelectric film, and is larger than the longitudinal wave sound speed of the film formed on the resonator. Therefore, the longitudinal wave sound velocity of the element can be reduced, and the vibrator can be miniaturized.

同時に、共振子上に形成された膜で膜厚が厚くなるため、ヒステリシス現象が抑制される。   At the same time, the thickness of the film formed on the resonator is increased, so that the hysteresis phenomenon is suppressed.

以上より、従来構造に対して素子を小型化し、かつヒステリシス現象を抑制しようとすると、圧電膜１６のＡｌＮより縦波音速の小さい温度補償膜１９のＳｉＯ２を厚くするのが望ましい。しかし、温度補償膜１９のＳｉＯ２を厚くすると、温度特性が劣化してしまう。 From the above, in order to reduce the size of the element and suppress the hysteresis phenomenon compared to the conventional structure, it is desirable to increase the thickness of SiO 2 of the temperature compensation film 19 having a longitudinal wave sound velocity smaller than that of AlN of the piezoelectric film 16. However, when the thickness of SiO 2 of the temperature compensation film 19, the temperature characteristic is deteriorated.

そこで、ＳｉＯ２とは逆の温度係数の符号を持つＴａ２Ｏ５の補強膜１８を新たに形成すると、温度特性を維持しつつ、ヒステリシス現象の抑制が可能となる。また、新たに形成した補強膜１８の音速を、圧電膜１６の音速より小さくすることで、素子の小型化も可能となる。 Therefore, by newly forming a Ta 2 O 5 reinforcing film 18 having a temperature coefficient opposite to that of SiO 2 , the hysteresis phenomenon can be suppressed while maintaining the temperature characteristics. Further, by making the sound velocity of the newly formed reinforcing film 18 smaller than the sound velocity of the piezoelectric film 16, the element can be miniaturized.

圧電膜、温度補償膜、補強膜が上記のＡｌＮ，ＳｉＯ２，Ｔａ２Ｏ５の組み合わせ以外でも、同様の効果が得られる。例えば、圧電膜、温度補償膜、補強膜の他の組み合わせとして、ＡｌＮ，ＳｉＯ２，ＺｎＯや、ＺｎＯ，ＳｉＯ２，Ｔａ２Ｏ５が挙げられる。 The piezoelectric film, the temperature compensation film, even in the reinforcement layer other than the above combinations of AlN, SiO2, Ta 2 O 5 , the same effect can be obtained. For example, AlN, SiO 2 , ZnO, ZnO, SiO 2 , Ta 2 O 5 can be cited as other combinations of the piezoelectric film, the temperature compensation film, and the reinforcing film.

＜作製例＞ 次に、作製例について説明する。   <Production Example> Next, a production example will be described.

図１及び図２に示した実施例の作製例の膜構成は、基板：Ｓｉ、支持膜：ＳｉＯ２（膜厚３．０μｍ）、下部電極及び上部電極：Ｐｔ（各膜厚０．１μｍ）、圧電膜：ＡｌＮ（膜厚１．６μｍ）、補強膜：Ｔａ２Ｏ５（膜厚２．０μｍ）、温度補償膜：ＳｉＯ２（膜厚３．７μｍ）である。 The film structure of the manufacturing example of the embodiment shown in FIGS. 1 and 2 is as follows: substrate: Si, support film: SiO 2 (film thickness: 3.0 μm), lower electrode and upper electrode: Pt (each film thickness: 0.1 μm) Piezoelectric film: AlN (film thickness 1.6 μm), reinforcing film: Ta 2 O 5 (film thickness 2.0 μm), temperature compensation film: SiO 2 (film thickness 3.7 μm).

図５に示した従来構造の比較例の膜構成は、基板：Ｓｉ、支持膜：ＳｉＯ２（膜厚１．７μｍ）、下部電極及び上部電極：Ｐｔ（各膜厚０．１μｍ）、圧電膜：ＡｌＮ（膜厚１．６μｍ）、温度補償膜：ＳｉＯ２（膜厚３．３μｍ）である。 The film structure of the comparative example of the conventional structure shown in FIG. 5 is as follows: substrate: Si, support film: SiO 2 (film thickness 1.7 μm), lower electrode and upper electrode: Pt (each film thickness 0.1 μm), piezoelectric film : AlN (film thickness 1.6 μm), temperature compensation film: SiO 2 (film thickness 3.3 μm).

実施例は、ＳｉＯ２（支持膜、温度補償膜）の合計膜厚が比較例の５．０μｍから６．７μｍになり、１．７μｍ厚くなっている。また、実施例は、Ｔａ２Ｏ５が比較例の０μｍから２．０μｍになり、２．０μｍ厚くなっている。 In the example, the total film thickness of SiO 2 (support film, temperature compensation film) is increased from 5.0 μm of the comparative example to 6.7 μm, and is increased to 1.7 μm. In the example, Ta 2 O 5 is changed from 0 μm to 2.0 μm, which is 2.0 μm thick.

上記の２種類の構造について、ＦＥＭにて長さモードの共振周波数が約１３ＭＨｚになるように振動子の面積を計算した。結果を、次の表２に示す。

Figure 0005057148
また、図３にインピーダンス特性のグラフを示す。実線は実施例、破線は比較例を示す。実施例は、インピーダンス特性が比較例よりも若干劣化するものの、実用上は問題がない特性といえる。 For the above two types of structures, the area of the vibrator was calculated by FEM so that the resonance frequency of the length mode was about 13 MHz. The results are shown in Table 2 below.
Figure 0005057148
 FIG. 3 shows a graph of impedance characteristics. A solid line indicates an example, and a broken line indicates a comparative example. Although the impedance characteristic is slightly deteriorated compared with the comparative example, it can be said that the example has no problem in practical use.

実施例は、補強膜のＴａ２Ｏ５の音速が圧電膜のＡｌＮの半分以下であるため、圧電振動部の面積比で従来構造の比較例の約７２％に小型化が可能である。 In the example, since the sound velocity of the reinforcing film Ta 2 O 5 is less than half that of AlN of the piezoelectric film, the area ratio of the piezoelectric vibrating portion can be reduced to about 72% of the comparative example of the conventional structure.

実施例は、圧電振動部に付加される膜の厚さの合計が比較例よりも大きいため、ヒステリシス現象の抑制効果が高まる。   In the example, since the total thickness of the films added to the piezoelectric vibrating portion is larger than that in the comparative example, the effect of suppressing the hysteresis phenomenon is enhanced.

実施例は、縦波音速の温度係数の符号がＳｉＯ２とは逆のＴａ２Ｏ５を新たに形成することにより、ＳｉＯ２の膜厚が増えたことによる温度特性の悪化を補うことができる。 Examples can be the sign of the temperature coefficient of the longitudinal wave acoustic velocity by newly formed opposite Ta 2 O 5 and SiO 2, compensate for the deterioration of the temperature characteristic due to the film thickness of SiO 2 is increased .

＜まとめ＞ 以上に説明した圧電振動装置１０は、圧電膜１６より縦波音速が小さく、縦波音速の温度係数の符号が温度補償膜１９と逆の補強膜１８を形成することによって、温度特性を維持しつつ、素子の小型化とヒステリシス現象の抑制の実現が可能となる。   <Summary> In the piezoelectric vibration device 10 described above, the longitudinal wave sound velocity is smaller than that of the piezoelectric film 16, and the temperature characteristic is obtained by forming the reinforcing film 18 whose sign of the temperature coefficient of the longitudinal wave sound velocity is opposite to that of the temperature compensation film 19. While maintaining the above, it is possible to reduce the size of the element and suppress the hysteresis phenomenon.

なお、本発明は、上記実施の形態に限定されるものではなく、種々変更を加えて実施することが可能である。   The present invention is not limited to the above embodiment, and can be implemented with various modifications.

圧電振動装置の断面図である。（実施例）It is sectional drawing of a piezoelectric vibration apparatus. (Example) 圧電振動装置の膜構成を示す分解斜視図である。（実施例）It is a disassembled perspective view which shows the film | membrane structure of a piezoelectric vibration apparatus. (Example) インピーダンス特性を示すグラフである。（実施例、比較例）It is a graph which shows an impedance characteristic. (Examples and comparative examples) 面方向の振動モードの様子を示す平面図である。It is a top view which shows the mode of the vibration mode of a surface direction. 圧電振動装置の断面図である。（従来例）It is sectional drawing of a piezoelectric vibration apparatus. (Conventional example) インピーダンス特性を示すグラフである。（従来例）It is a graph which shows an impedance characteristic. (Conventional example)

符号の説明Explanation of symbols

１０ 圧電振動装置
１２ 基板
１３ 空隙
１４ 支持膜
１５ 下部電極
１６ 圧電膜
１７ 上部電極
１８ 補強膜
１９ 温度補償膜
２０ 圧電振動部 DESCRIPTION OF SYMBOLS 10 Piezoelectric vibration apparatus 12 Board | substrate 13 Cavity 14 Support film 15 Lower electrode 16 Piezoelectric film 17 Upper electrode 18 Reinforcement film 19 Temperature compensation film 20 Piezoelectric vibration part

Claims (3)

基板と、
圧電膜と前記圧電膜の両主面にそれぞれ配置された第１及び第２の電極とを含み、前記圧電膜の膜厚方向から透視したときに前記第１及び第２の電極が前記圧電膜を介して重なり合う圧電振動部が前記基板から浮いた状態で、前記圧電振動部以外の支持部が前記基板に支持された、圧電薄膜部と、
を備え、
前記圧電振動部の輪郭振動を利用する、圧電振動装置であって、
少なくとも前記圧電振動部上に、温度補償膜及び補強膜をさらに備え、
前記補強膜は、前記圧電膜の音速より小さい音速を有し、かつ、温度特性の符号が前記温度補償膜の温度特性の符号と異なることを特徴とする、圧電振動装置。 A substrate,
A piezoelectric film and first and second electrodes respectively disposed on both principal surfaces of the piezoelectric film, wherein the first and second electrodes are seen through the piezoelectric film in a film thickness direction. A piezoelectric thin film part in which a support part other than the piezoelectric vibration part is supported by the substrate in a state where the piezoelectric vibration part overlapping with the substrate floats from the substrate,
With
A piezoelectric vibration device that utilizes contour vibration of the piezoelectric vibration unit,
A temperature compensation film and a reinforcing film are further provided on at least the piezoelectric vibration part,
The piezoelectric vibration device, wherein the reinforcing film has a sound velocity lower than that of the piezoelectric film, and a sign of a temperature characteristic is different from a sign of a temperature characteristic of the temperature compensation film. 前記温度補償膜及び前記補強膜の少なくとも一方が等方体であることを特徴とする、請求項１に記載の圧電振動装置。   The piezoelectric vibration device according to claim 1, wherein at least one of the temperature compensation film and the reinforcing film is an isotropic body. 前記補強膜がＴａ２Ｏ５であることを特徴とする、請求項１又は２に記載の圧電振動装置。 The piezoelectric vibration device according to claim 1, wherein the reinforcing film is Ta 2 O 5 .
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