JP2015216190A - Piezoelectric actuator and method of manufacturing the same - Google Patents
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 abstract description 6
- 229910021421 monocrystalline silicon Inorganic materials 0.000 abstract description 6
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- 238000010030 laminating Methods 0.000 abstract 1
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- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical compound [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 description 11
- 229910052719 titanium Inorganic materials 0.000 description 6
- 238000005229 chemical vapour deposition Methods 0.000 description 4
- 229910052726 zirconium Inorganic materials 0.000 description 4
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Abstract
Description
本発明はチタン酸ジルコン酸鉛（PZT）を含む圧電アクチュエータ及びその製造方法に関する。 The present invention relates to a piezoelectric actuator containing lead zirconate titanate (PZT) and a method for manufacturing the same.
Pb、Zr、Tiの各元素を含む酸化化合物であるチタン酸ジルコン酸鉛PbZrxTi1-xO3（PZT）は図４に示す立方晶系ペロブスカイト型の結晶構造を有する。尚、図４においては、斜線球は単純立法配列のPb、黒球はZrもしくはTi、白球はOを示す。図５に示すごとく、PZTは<１００>方向あるいは<１１１>方向に歪んだ場合に分極を発生し、これにより、（１００）面配向もしくは（１１１）面配向のときに優れた圧電性を発揮する（参照：特許文献１の図５、図１０）。つまり、PZTの結晶構造には正方晶系及び菱面体晶系があり、正方晶系PZTの場合には、<１００>方向（ａ軸方向）（あるいは<００１>方向（ｃ軸方向））に最も大きな圧電変位が得られ、また、菱面体晶系PZTの場合には、<１１１>方向に最も大きな圧電変位が得られると言われている。また、圧電アクチュエータとしての重要な特性である絶縁特性（耐電圧特性）についてはチタン（Ti）リッチ（x<0.5）な正方晶系PZTの方が菱面体晶系PZTより良いとされている。PZT圧電アクチュエータはセンサとして用いたMEMS素子、発電素子、ジャイロ素子等に用いられる。 Lead zirconate titanate PbZr x Ti 1-x O 3 (PZT), which is an oxide compound containing each element of Pb, Zr, and Ti, has a cubic perovskite crystal structure shown in FIG. In FIG. 4, the slanted sphere indicates simple cubic Pb, the black sphere indicates Zr or Ti, and the white sphere indicates O. As shown in FIG. 5, PZT generates polarization when strained in the <100> direction or the <111> direction, thereby exhibiting excellent piezoelectricity in the (100) or (111) plane orientation. (Reference: FIGS. 5 and 10 of Patent Document 1). That is, the crystal structure of PZT includes tetragonal system and rhombohedral system, and in the case of tetragonal system PZT, it is in the <100> direction (a-axis direction) (or <001> direction (c-axis direction)). It is said that the largest piezoelectric displacement can be obtained, and in the case of rhombohedral PZT, the largest piezoelectric displacement can be obtained in the <111> direction. In addition, with respect to insulation characteristics (voltage resistance characteristics), which is an important characteristic for piezoelectric actuators, titanium (Ti) rich (x <0.5) tetragonal PZT is said to be better than rhombohedral PZT. PZT piezoelectric actuators are used for MEMS elements, power generation elements, gyro elements and the like used as sensors.
図６は第１の従来の圧電アクチュエータを示す断面図である。図６の圧電アクチュエータはキャパシタ構造をなしており、単結晶シリコン基板１、酸化シリコン層２、Ti密着層３、Pt下部電極層４、PZT圧電体層５及びPt上部電極層６を積層して形成されている。尚、単結晶シリコン基板１はシリコンオンインシュレータ（SOI）基板に置換し得る。また、下部電極層４は、Ir、SrRuO3等を用いてもよい。さらに、Ti密着層３は酸化シリコン層２とPt下部電極層４との密着性が悪いのでこれらの間の密着性を改善すると共に応力を緩和するものである。この密着層３はTi以外にCr、あるいはTiO2、MgO、ZrO2、IrO2等の導電性酸化物を用いてもよい。 FIG. 6 is a sectional view showing a first conventional piezoelectric actuator. The piezoelectric actuator shown in FIG. 6 has a capacitor structure, in which a single crystal silicon substrate 1, a silicon oxide layer 2, a Ti adhesion layer 3, a Pt lower electrode layer 4, a PZT piezoelectric layer 5, and a Pt upper electrode layer 6 are laminated. Is formed. The single crystal silicon substrate 1 can be replaced with a silicon on insulator (SOI) substrate. The lower electrode layer 4 may be made of Ir, SrRuO 3 or the like. Further, since the Ti adhesion layer 3 has poor adhesion between the silicon oxide layer 2 and the Pt lower electrode layer 4, the adhesion between them is improved and stress is relieved. The adhesion layer 3 may be made of Cr, or a conductive oxide such as TiO 2 , MgO, ZrO 2 , and IrO 2 in addition to Ti.
図６においては、正方晶系のPZT圧電体層５の矢印方向が結晶の<１００>方向あるいは<００１>方向に向いていると、Pt下部電極層４とPt上部電極層６との間に交流電圧を印加したときに、歪みが効率よく発生する。 In FIG. 6, when the arrow direction of the tetragonal PZT piezoelectric layer 5 is oriented in the <100> direction or the <001> direction of the crystal, the Pt lower electrode layer 4 and the Pt upper electrode layer 6 are interposed. When an AC voltage is applied, distortion occurs efficiently.
図６の圧電アクチュエータの製造方法を図７のフローチャートを参照して説明する。 A method for manufacturing the piezoelectric actuator of FIG. 6 will be described with reference to the flowchart of FIG.
始めに、熱酸化工程７０１において、単結晶シリコン基板１を熱酸化して厚さ約500nmの酸化シリコン層２を形成する。尚、熱酸化処理の代りに化学的気相成長（CVD）法を用いてもよい。 First, in the thermal oxidation step 701, the single crystal silicon substrate 1 is thermally oxidized to form a silicon oxide layer 2 having a thickness of about 500 nm. A chemical vapor deposition (CVD) method may be used instead of the thermal oxidation treatment.
次に、スパッタリング工程７０２において、酸化シリコン層２上にArガス及びO２ガスを用いたスパッタリング法によって厚さ約50nmのTiOｘ(0<x<2)密着層３を形成する。引き続いて、TiOｘ密着層３上にArガスを用いたスパッタリング法によって厚さ約150nmのPt下部電極層４を形成する。 Next, in a sputtering step 702, a TiO x (0 <x <2) adhesion layer 3 having a thickness of about 50 nm is formed on the silicon oxide layer 2 by a sputtering method using Ar gas and O 2 gas. Subsequently, a Pt lower electrode layer 4 having a thickness of about 150 nm is formed on the TiO x adhesion layer 3 by sputtering using Ar gas.
次に、スパッタリング工程７０３において、Pt下部電極層４上にスパッタリング法によって厚さ約3μmのPZT層５を形成する（参照：特許文献２）。尚、スパッタリング法の代りに、CVD法を用いてもよい。あるいは、ゾル・ゲル法を用いてもよい（参照：特許文献３）。尚、ゾル・ゲル法は、一度に圧電体層を厚く成膜することができないので、圧電体前駆体層の形成、焼成を繰返して所望の厚さの圧電体層を形成する。 Next, in the sputtering step 703, a PZT layer 5 having a thickness of about 3 μm is formed on the Pt lower electrode layer 4 by a sputtering method (see Patent Document 2). Note that a CVD method may be used instead of the sputtering method. Alternatively, a sol-gel method may be used (see Patent Document 3). In the sol-gel method, since a piezoelectric layer cannot be formed thick at a time, formation of a piezoelectric precursor layer and firing are repeated to form a piezoelectric layer having a desired thickness.
最後に、スパッタリング工程７０４において、PZT圧電体層５上にスパッタリング法によって厚さ約150nmのPt上部電極層６を形成する。 Finally, in the sputtering step 704, the Pt upper electrode layer 6 having a thickness of about 150 nm is formed on the PZT piezoelectric layer 5 by sputtering.
尚、スパッタリング工程７０２、７０４におけるスパッタリング法の代りに、電子ビーム（EB）蒸着法を用いてもよい。 Note that an electron beam (EB) vapor deposition method may be used instead of the sputtering method in the sputtering steps 702 and 704.
しかしながら、図６の圧電アクチュエータにおいては、Pt下部電極層４は（１１１）に配向した膜になり易いので、その上にPZT圧電体層５を形成しても、Pt下部電極層４の影響を受けて（１１１）に配向したPZT層となり易く、従って、アクチュエータに適した配向性を有する層を得ることは難しい。 However, in the piezoelectric actuator shown in FIG. 6, the Pt lower electrode layer 4 is likely to be a (111) -oriented film. Therefore, even if the PZT piezoelectric layer 5 is formed thereon, the influence of the Pt lower electrode layer 4 is not affected. Accordingly, it becomes easy to obtain a (111) -oriented PZT layer. Therefore, it is difficult to obtain a layer having an orientation suitable for the actuator.
図８は第２の従来の圧電アクチュエータを示す断面図である（参照：特許文献４の図１）。図８においては、圧電特性を向上させるために、図６の構成要素に対して配向制御層１１、１２を付加してある。この場合、配向制御層１１は（１００）配向の酸化物層よりなり、Pt下部電極層４は配向制御層の影響を受けて（１００）に配向した層となり、配向制御層１２はPt下部電極層４の影響を受けて（１００）あるいは（００１）配向のペロブスカイト型酸化層とよりなる。これによりスパッタリング工程等によるPZT圧電体層５の配向性が従来より（１００）に配向することが容易に、もしくは高配向に成長するようになる。また、配向制御層１２によって、PZT圧電体層５の成膜初期にZr酸化物からなる結晶性の低い層が形成されないようにする。この結果、PZTの配向性つまり圧電特性は向上する。 FIG. 8 is a sectional view showing a second conventional piezoelectric actuator (see FIG. 1 of Patent Document 4). In FIG. 8, orientation control layers 11 and 12 are added to the components shown in FIG. 6 in order to improve the piezoelectric characteristics. In this case, the orientation control layer 11 is made of a (100) oriented oxide layer, the Pt lower electrode layer 4 is a layer oriented to (100) under the influence of the orientation control layer, and the orientation control layer 12 is made of a Pt lower electrode. Under the influence of the layer 4, a perovskite oxide layer having a (100) or (001) orientation is formed. As a result, the orientation of the PZT piezoelectric layer 5 by the sputtering process or the like can be easily oriented to (100) as compared with the prior art, or can grow to a high orientation. Further, the orientation control layer 12 prevents the low crystallinity layer made of Zr oxide from being formed at the initial stage of the formation of the PZT piezoelectric layer 5. As a result, the orientation of the PZT, that is, the piezoelectric characteristics is improved.
しかしながら、図８の圧電アクチュエータの製造方法においては、図７に示す製造工程に、配向制御層１１、１２の形成工程の付加によって製造工程が複雑となるため異物が混入する可能性が高くなるだけでなく、界面数が増加するので剥離などの新たな問題が発生し易くなる。しかも、下層（単結晶シリコン基板１）から上層（配向制御層１２）への結晶性等の影響からプロセスマージンが小さくなる。 However, in the method for manufacturing the piezoelectric actuator of FIG. 8, the manufacturing process becomes complicated by adding the formation process of the orientation control layers 11 and 12 to the manufacturing process shown in FIG. In addition, since the number of interfaces increases, new problems such as peeling tend to occur. In addition, the process margin is reduced due to the influence of crystallinity and the like from the lower layer (single crystal silicon substrate 1) to the upper layer (alignment control layer 12).
図９は第３の従来の圧電アクチュエータを示す断面図である（参照：特許文献５の図１）。図９においては、耐電圧特性を向上させるために、図６の圧電体層５の代りに複数のPb過剰（Pbリッチ）PZT圧電体層５ａ、Pb欠損（Pbリーン）PZT圧電体層５ｂを交互に積層したPZT圧電体層５’を設ける。すなわち、PZT圧電体層を鉛リッチの雰囲気中で化学量論組成よりもPbが多いペロブスカイト構造を有するPZT圧電体層のみで形成すればプロセスマージンが大きくなるが、PbリッチなPZT圧電体層は、結晶粒界に導電性の良い鉛酸化物を有することが多いので、耐電圧特性が低くなる。他方、PZT圧電体層を鉛リーンの雰囲気中で化学量論組成よりもPbが僅かに少ないペロブスカイト構造を有するPZT圧電体層のみで形成すれば、ZrO2などの異相が成長し易くなるのでプロセスマージンが小さくなるが、結晶粒界に鉛酸化物を有する割合が少ないので、耐電圧特性が向上する。このため、PZT圧電体層５’においては、PbリッチPZT圧電体層５ａ、PbリーンPZT圧電体層５ｂを積層することにより、PbリッチPZT圧電体層５ａの鉛酸化物によってリークパスＬＰが発生してもPbリーンPZT圧電体層５ｂによって分断して耐電圧特性を大きくできる。 FIG. 9 is a sectional view showing a third conventional piezoelectric actuator (see FIG. 1 of Patent Document 5). In FIG. 9, a plurality of Pb-excess (Pb-rich) PZT piezoelectric layers 5a and Pb-deficient (Pb-lean) PZT piezoelectric layers 5b are used instead of the piezoelectric layer 5 of FIG. PZT piezoelectric layers 5 ′ that are alternately stacked are provided. That is, if the PZT piezoelectric layer is formed only with a PZT piezoelectric layer having a perovskite structure with a Pb higher than the stoichiometric composition in a lead-rich atmosphere, the process margin increases, but the PbT-rich PZT piezoelectric layer In many cases, it has lead oxide having good conductivity at the grain boundary, so that the withstand voltage characteristic is lowered. On the other hand, if a PZT piezoelectric layer is formed only of a PZT piezoelectric layer having a perovskite structure with a Pb slightly less than the stoichiometric composition in a lead-lean atmosphere, a heterogeneous phase such as ZrO2 is likely to grow, so the process margin However, since the proportion of lead oxide in the crystal grain boundary is small, the withstand voltage characteristics are improved. For this reason, in the PZT piezoelectric layer 5 ′, the Pb-rich PZT piezoelectric layer 5a and the Pb-lean PZT piezoelectric layer 5b are stacked, so that a leak path LP is generated by the lead oxide of the Pb-rich PZT piezoelectric layer 5a. However, the withstand voltage characteristic can be increased by dividing by the Pb-lean PZT piezoelectric layer 5b.
しかしながら、図９の圧電アクチュエータにおいては、PbリッチPZT圧電体層５ａ、PbリーンPZT圧電体層５ｂの結晶成長が不連続となる。この結果、この不連続な部分、つまり、PbリッチPZT圧電体層５ａとPbリーンPZT圧電体層５ｂの界面部分に圧電アクチュエータの駆動による機械的振動による割れ・剥離が発生し、圧電アクチュエータが破損する恐れがある。 However, in the piezoelectric actuator of FIG. 9, the crystal growth of the Pb-rich PZT piezoelectric layer 5a and the Pb-lean PZT piezoelectric layer 5b is discontinuous. As a result, the discontinuous portion, that is, the interface portion between the Pb-rich PZT piezoelectric layer 5a and the Pb-lean PZT piezoelectric layer 5b is cracked and peeled off due to mechanical vibrations driven by the piezoelectric actuator, and the piezoelectric actuator is damaged. There is a fear.
図１０は第４の従来の圧電アクチュエータを示す断面図である（参照：特許文献６）。図１０においては、リーク電流を低減するために、図６のPZT圧電体層５の代りに、Zr及びTiを膜厚方向に漸増もしくは漸減により濃度勾配させたPZT圧電体層５”を設けてある。PZT圧電体層５”においては、Zr/(Zr+Ti)組成比xを結晶構造の安定なZrリッチ領域もしくはTiリッチ領域へずらすことにより高い圧電性能を示すモルフォトロピック相境界（MPB）を通過させて圧電特性を向上させる。尚、図１０の参照番号１’は振動板を示す。 FIG. 10 is a cross-sectional view showing a fourth conventional piezoelectric actuator (see Patent Document 6). In FIG. 10, in order to reduce the leakage current, a PZT piezoelectric layer 5 ″ in which the concentration gradient of Zr and Ti is gradually increased or decreased in the film thickness direction is provided instead of the PZT piezoelectric layer 5 of FIG. In the PZT piezoelectric layer 5 ″, the morphotropic phase boundary (MPB) exhibiting high piezoelectric performance by shifting the Zr / (Zr + Ti) composition ratio x to the stable Zr-rich region or Ti-rich region of the crystal structure. To improve the piezoelectric characteristics. Note that reference numeral 1 ′ in FIG. 10 indicates a diaphragm.
しかしながら、図１０の圧電アクチュエータにおいては、Zrリッチ領域では、圧電特性が向上するも、誘電損失係数が大きくなる。誘電損失係数が大きくなると、圧電アクチュエータに交流電圧を印加した場合に電気エネルギーの一部が熱として喪失してエネルギー変換効率が低下する。また、熱による特性変動、寿命劣化を招く。さらに、リークパスLPが発生して絶縁破壊を招き、耐電圧特性が低下する。 However, in the piezoelectric actuator of FIG. 10, in the Zr rich region, the piezoelectric characteristics are improved, but the dielectric loss coefficient is increased. When the dielectric loss coefficient increases, when an AC voltage is applied to the piezoelectric actuator, a part of the electric energy is lost as heat and the energy conversion efficiency decreases. Moreover, the characteristic fluctuation | variation by heat and lifetime deterioration are caused. Furthermore, a leak path LP is generated, causing dielectric breakdown, and the withstand voltage characteristics are degraded.
図１１は第５の従来の圧電アクチュエータを示す断面図である（参照：特許文献７、８、９）。図１１においては、PZTの圧電特性および耐電圧特性を向上させるために、図６に示すPZT圧電体層５の代りに、Zr/(Zr+Ti)組成比xは高い圧電性能を示すと言われているモルフォトロピック相境界（MPB）近傍かつ一般的に耐電圧特性が高いと言われている正方晶構造を有する組成領域（PbZrxTi1-xO3においてMPBはx=0.52付近、x<0.52において正方晶構造を持つと言われている）のPZT圧電体層５Ａを設けてある。このPZT圧電体層５Ａは、図１１の圧電アクチュエータの製造方法を説明するためのフローチャートである図１２のADRIP工程１２０１において、モルフォトロピック相境界（MPB）近傍の正方晶構造を有するPZT圧電体層５Ａをアーク放電反応性イオンプレーティング（ADRIP）法を用いて形成している。 FIG. 11 is a cross-sectional view showing a fifth conventional piezoelectric actuator (refer to Patent Documents 7, 8, and 9). In FIG. 11, it is said that the Zr / (Zr + Ti) composition ratio x shows high piezoelectric performance instead of the PZT piezoelectric layer 5 shown in FIG. 6 in order to improve the piezoelectric characteristics and withstand voltage characteristics of PZT. In the composition region with a tetragonal structure that is said to be near the morphotropic phase boundary (MPB), which is generally said to have high withstand voltage characteristics (in PbZr x Ti 1-x O 3 , MPB is near x = 0.52, x PZT piezoelectric layer 5A (which is said to have a tetragonal structure at <0.52) is provided. This PZT piezoelectric layer 5A is a PZT piezoelectric layer having a tetragonal crystal structure in the vicinity of the morphotropic phase boundary (MPB) in the ADRIP step 1201 of FIG. 12, which is a flowchart for explaining the manufacturing method of the piezoelectric actuator of FIG. 5A is formed using an arc discharge reactive ion plating (ADRIP) method.
図１２のADRIP工程１２０１におけるADRIP法は、スパッタリング法に比較してPZT圧電体層の堆積速度が大きいという利点を有し、また、有機金属化学的気相成長（MOCVD）法に比較して基板温度が低く、製造コストが低く、有毒な有機金属ガスを用いないので、対環境性がよく、また、原料の利用効率がよいという利点を有する。このADRIP法に用いられるADRIP装置を図１３を参照して説明する。 The ADRIP method in the ADRIP step 1201 of FIG. 12 has an advantage that the deposition rate of the PZT piezoelectric layer is higher than that of the sputtering method, and the substrate is higher than that of the metal organic chemical vapor deposition (MOCVD) method. Since the temperature is low, the production cost is low, and no toxic organometallic gas is used, there are advantages in that the environment is good and the utilization efficiency of raw materials is good. An ADRIP apparatus used for the ADRIP method will be described with reference to FIG.
図１３において、真空チャンバ１３０１内の下方側に、Pb、Zr、Tiを独立に蒸発させるためのPb蒸発源１３０２−１、Zr蒸発源１３０２−２、Ti蒸発源１３０２−３が設けられる。Pb蒸発源１３０２−１、Zr蒸発源１３０２−２、Ti蒸発源１３０２−３上には、蒸気量センサ１３０２−１Ｓ、１３０２−２Ｓ、１３０２−３Ｓが設けられている。真空チャンバ１３０１内の上方側に、ウェハ１３０３ａを載置するためのヒータ付ウェハ回転ホルダ１３０３が設けられる。 In FIG. 13, a Pb evaporation source 1302-1, a Zr evaporation source 1302-2, and a Ti evaporation source 1302-3 for evaporating Pb, Zr, and Ti independently are provided on the lower side in the vacuum chamber 1301. Vapor amount sensors 1302-1S, 1302-2S, and 1302-3S are provided on the Pb evaporation source 1302-1, the Zr evaporation source 1302-2, and the Ti evaporation source 1302-3. On the upper side in the vacuum chamber 1301, a wafer rotating holder with heater 1303 for placing the wafer 1303a is provided.
また、真空チャンバ１３０１の上流側には、アーク放電を維持するために不活性ガスたとえば数sccmのArガスおよび数100sccmのHeガスを導入する圧力勾配型プラズマガン１３０４及びPZT圧電体層５の酸素原料となる酸素（O2）ガスを導入するO2ガス導入口１３０５が設けられる。他方、真空チャンバ１３０１の下流側には、真空ポンプ（図示せず）に接続された排気口１３０６が設けられる。 Further, on the upstream side of the vacuum chamber 1301, an oxygen gas in the pressure gradient plasma gun 1304 and the PZT piezoelectric layer 5 into which an inert gas such as Ar gas of several sccm and He gas of several hundred sccm is introduced in order to maintain arc discharge. An O 2 gas introduction port 1305 for introducing oxygen (O 2 ) gas as a raw material is provided. On the other hand, an exhaust port 1306 connected to a vacuum pump (not shown) is provided on the downstream side of the vacuum chamber 1301.
図１３のADRIP装置において図１２のADRIP工程１２０１を行う場合、圧力勾配型プラズマガン１３０４によって導入されたArガスおよびHeガスによって高密度・低電子温度の放電電流約80Ａのアーク放電プラズマ１３０７を発生させ、そしてO2ガス導入口から約250sccmのO2ガスを導入し真空チャンバ１３０１内に発生している高密度・低電子温度のアーク放電プラズマ１３０７でO2ガスを励起させることによって、真空チャンバ１３０１内に多量の酸素ラジカルを主とする活性原子、分子が生成される。他方、Pb蒸発源１３０２−１、Zr蒸発源１３０２−２及びTi蒸発源１３０２−３より発生したPb蒸気、Zr蒸気及びTi蒸気が上述の活性原子、分子と反応し、所定温度たとえば約500℃に加熱されたウェハ１３０３ａ上に付着し、この結果、Zr/(Zr+Ti)組成比xのPbZrxTi1-xO3が形成されることになる。尚、Pb蒸気、Zr蒸気、Ti蒸気は蒸気量センサ１３０２−１Ｓ、１３０２−２Ｓ、１３０２−３Ｓによって検出される。 When the ADRIP process 1201 of FIG. 12 is performed in the ADRIP apparatus of FIG. 13, the arc discharge plasma 1307 having a high-density, low-electron-temperature discharge current of about 80 A is generated by the Ar gas and He gas introduced by the pressure gradient plasma gun 1304. by exciting the O 2 gas is allowed, and O 2 gas inlet O 2 gas is introduced to about 250sccm from high density and low electron temperature is generated within the vacuum chamber 1301 arc discharge plasma 1307, the vacuum chamber In 1301, active atoms and molecules mainly including a large amount of oxygen radicals are generated. On the other hand, Pb vapor, Zr vapor, and Ti vapor generated from the Pb evaporation source 1302-1, Zr evaporation source 1302-2, and Ti evaporation source 1302-3 react with the above-mentioned active atoms and molecules, and a predetermined temperature, for example, about 500 ° C. As a result, PbZr x Ti 1-x O 3 having a Zr / (Zr + Ti) composition ratio x is formed. Pb vapor, Zr vapor, and Ti vapor are detected by vapor amount sensors 1302-1S, 1302-2S, and 1302-3S.
図１１の圧電アクチュエータのモルフォトロピック相境界（MPB）近傍の正方晶構造を有するPZT圧電体層５Ａの走査型電子顕微鏡（SEM）写真を図１４に示す。図１４はきれいな柱状構造を示し、従って、良好な配向性つまり良好な圧電特性を示す。 FIG. 14 shows a scanning electron microscope (SEM) photograph of the PZT piezoelectric layer 5A having a tetragonal structure near the morphotropic phase boundary (MPB) of the piezoelectric actuator of FIG. FIG. 14 shows a clean columnar structure, and therefore good orientation, ie good piezoelectric properties.
しかしながら、図１１の圧電アクチュエータにおいては、モルフォトロピック相境界（MPB）近傍の正方晶構造を有するPZT圧電体層５Ａの成膜を行うと、表面ラフネスが大きくなってしまう。従って、モルフォトロピック相境界（MPB）近傍の正方晶構造を有するPZT圧電体層５Ａ上のPt上部電極層６の表面ラフネスも大きくなる。この結果、Pt上部電極層６とPt下部電極層４との間に交流電圧を印加すると、局所的に電場が集中して破壊し易く、これにより、PZT圧電体層５Ａ側のPt上部電極層６の凸部に対応するPZT圧電体層５Ａに生じた結晶粒界に、図１１に示すごとく、リークパスＬＰが発生し、絶縁破壊を招き、耐電圧特性を低下させる。 However, in the piezoelectric actuator of FIG. 11, when the PZT piezoelectric layer 5A having a tetragonal structure near the morphotropic phase boundary (MPB) is formed, the surface roughness becomes large. Accordingly, the surface roughness of the Pt upper electrode layer 6 on the PZT piezoelectric layer 5A having a tetragonal structure in the vicinity of the morphotropic phase boundary (MPB) is also increased. As a result, when an AC voltage is applied between the Pt upper electrode layer 6 and the Pt lower electrode layer 4, the electric field is locally concentrated and easily broken, and thereby the Pt upper electrode layer on the PZT piezoelectric layer 5 A side. As shown in FIG. 11, a leak path LP is generated at the crystal grain boundary generated in the PZT piezoelectric layer 5A corresponding to the convex portion 6 to cause dielectric breakdown, thereby lowering the withstand voltage characteristic.
図１５は第６の従来の圧電アクチュエータを示す断面図である（参照：特許文献１０）。図１５においては、図１１のPZT圧電体層５Ａ上にPZT圧電体層５Ａより比誘電率の低いTiリッチなPZT圧電体層５Ｂを形成し、二重構造のPZT圧電体層を実現している。尚、PZT圧電体層５ＡのZr/(Zr+Ti)組成比xはモルフォトロピック相境界（MPB、一般的にはx=0.52）近傍、かつ一般的に耐電圧特性が高いと言われている正方晶構造をもつ組成領域（x<0.52）である。 FIG. 15 is a cross-sectional view showing a sixth conventional piezoelectric actuator (see Patent Document 10). In FIG. 15, a Ti-rich PZT piezoelectric layer 5B having a relative dielectric constant lower than that of the PZT piezoelectric layer 5A is formed on the PZT piezoelectric layer 5A of FIG. Yes. Incidentally, it is said that the Zr / (Zr + Ti) composition ratio x of the PZT piezoelectric layer 5A is near the morphotropic phase boundary (MPB, generally x = 0.52) and generally has high withstand voltage characteristics. This is a composition region (x <0.52) having a tetragonal structure.
図１５においては、比誘電率の高いPZT圧電体層５Ａの表面ラフネスは大きいが、それよりも比誘電率が低いTiリッチなPZT圧電体層５Ｂの表面ラフネスは小さい。この結果、PZT圧電体層５Ｂ上のPt上部電極層６の表面ラフネスも小さくなる。従って、Pt上部電極層６とPt下部電極層４との間に交流電圧を印加しても、局所的に電場が集中しにくく、しかも、PZT圧電体層５Ｂ側のPt上部電極層６の凸部に対応するPZT圧電体層５Ｂの結晶粒界に、図１５に示すごとく、リークパスＬＰはほとんど発生せず、耐電圧特性を向上できる。 In FIG. 15, the surface roughness of the PZT piezoelectric layer 5A having a high relative dielectric constant is large, but the surface roughness of the Ti-rich PZT piezoelectric layer 5B having a lower relative dielectric constant is smaller. As a result, the surface roughness of the Pt upper electrode layer 6 on the PZT piezoelectric layer 5B is also reduced. Therefore, even if an AC voltage is applied between the Pt upper electrode layer 6 and the Pt lower electrode layer 4, the electric field is not easily concentrated locally, and the Pt upper electrode layer 6 on the PZT piezoelectric layer 5B side is convex. As shown in FIG. 15, the leakage path LP hardly occurs at the crystal grain boundary of the PZT piezoelectric layer 5B corresponding to the portion, and the withstand voltage characteristic can be improved.
図１６は図１５の圧電アクチュエータの製造方法を説明するためのフローチャートである。図１６においては、図１２のフローチャートにPZT圧電体層５ＡよりもTiリッチなPZT圧電体層５Ｂを形成するためのADRIP工程１６０１を付加してある。この場合、高誘電率PZT圧電体層５Ａを形成するためのADRIP工程１２０１とTiリッチな低流電率PZT圧電体層５Ｂを形成するためのADRIP工程１６０１とは同一のADRIP装置を用いて連続的に実行される。従って、プロセスマージンの狭小化を防ぐことができる。また、図１５の圧電アクチュエータにおいては、高誘電率PZT圧電体層５Ａ及びTiリッチな低流電率PZT圧電体層５Ｂの結晶成長が連続となり、この結果、この組成比が連続的に変化する界面部分が圧電アクチュエータの駆動による機械的振動によって割れ、圧電アクチュエータが破損することを防止できる。 FIG. 16 is a flowchart for explaining a method of manufacturing the piezoelectric actuator of FIG. In FIG. 16, an ADRIP process 1601 for forming a PZT piezoelectric layer 5B richer in Ti than the PZT piezoelectric layer 5A is added to the flowchart of FIG. In this case, the ADRIP process 1201 for forming the high dielectric constant PZT piezoelectric layer 5A and the ADRIP process 1601 for forming the Ti-rich low current PZT piezoelectric layer 5B are continuously performed using the same ADRIP apparatus. Is executed automatically. Accordingly, it is possible to prevent the process margin from being narrowed. Further, in the piezoelectric actuator of FIG. 15, the crystal growth of the high dielectric constant PZT piezoelectric layer 5A and the Ti-rich low current PZT piezoelectric layer 5B is continuous, and as a result, the composition ratio changes continuously. It is possible to prevent the interface portion from cracking due to mechanical vibration caused by driving the piezoelectric actuator and damaging the piezoelectric actuator.
しかしながら、上述の第６の従来の圧電アクチュエータでは、表面ラフネスの小さいTiリッチなPZT圧電体層５Ｂを成膜する圧電体層全体のうち表面層にあたる部分のみ成膜を行ってもPZT圧電体層５Ａの大きな表面ラフネスを補償できず、表面ラフネスが依然として大きい。この結果、リークパスの発生を抑制できず、耐電圧特性の向上が不充分であるという課題がある。また、PZT圧電体層５ＡのZr/(Zr+Ti)組成比はモルフォトロピック相境界ＭＰＢに近く、TiリッチのPZT圧電体層５Ｂを合わせても、圧電特性（図２の（Ａ）参照）は向上しないという課題もある。 However, in the sixth conventional piezoelectric actuator, the PZT piezoelectric layer is formed even if only the portion corresponding to the surface layer is formed in the entire piezoelectric layer for forming the Ti-rich PZT piezoelectric layer 5B having a small surface roughness. The large surface roughness of 5A cannot be compensated, and the surface roughness is still large. As a result, there is a problem that the occurrence of a leak path cannot be suppressed and the withstand voltage characteristics are insufficiently improved. Moreover, the Zr / (Zr + Ti) composition ratio of the PZT piezoelectric layer 5A is close to the morphotropic phase boundary MPB, and even when the Ti-rich PZT piezoelectric layer 5B is combined, the piezoelectric characteristics (see FIG. 2A) There is also a problem that does not improve.
上記の課題を解決するために、本発明に係る圧電アクチュエータは、下部電極層と、下部電極層上に設けられた第１のZr/(Zr+Ti)組成比を有する第１のPZT圧電体層と、第１のPZT圧電体層上に設けられた前記第１のZr/(Zr+Ti)組成比より大きい第２のZr/(Zr+Ti)組成比を有する第２のPZT圧電体層と、PZT圧電体層上に設けられた第２のZr/(Zr+Ti)組成比より小さい第３のZr/(Zr+Ti)組成比を有する第３のPZT圧電体層と、第３のPZT圧電体層上に設けられた上部電極層とを具備し、第１、第３のZr/(Zr+Ti)組成比はモルフォトロピック相境界値より大きくしたものである。 In order to solve the above problems, a piezoelectric actuator according to the present invention includes a lower electrode layer and a first PZT piezoelectric body having a first Zr / (Zr + Ti) composition ratio provided on the lower electrode layer. And a second PZT piezoelectric material having a second Zr / (Zr + Ti) composition ratio greater than the first Zr / (Zr + Ti) composition ratio provided on the first PZT piezoelectric material layer A third PZT piezoelectric layer having a third Zr / (Zr + Ti) composition ratio smaller than the second Zr / (Zr + Ti) composition ratio provided on the PZT piezoelectric layer; 3 and an upper electrode layer provided on the PZT piezoelectric layer, and the first and third Zr / (Zr + Ti) composition ratios are larger than the morphotropic phase boundary value.
また、本発明に係る圧電アクチュエータの製造方法は、アーク放電イオンプレーティング法によってPb蒸発量、Zr蒸発量及びTi蒸発量を制御して下部電極層上に第１のZr/(Zr+Ti)組成比を有する第１のPZT圧電体層を形成する第１の圧電体層形成工程と、アーク放電イオンプレーティング法によってPb蒸発量、Zr蒸発量及びTi蒸発量を制御して第１のPZT圧電体層上に第１のZr/(Zr+Ti)組成比より大きい第２のZr/(Zr+Ti)組成比を有する第２のPZT圧電体層を形成する第２の圧電体層形成工程と、アーク放電イオンプレーティング法によってPb蒸発量、Zr蒸発量及びTi蒸発量を制御して第２のPZT圧電体層上に第２のZr/(Zr+Ti)組成比より小さい第３のZr/(Zr+Ti)組成比を有する第３のPZT圧電体層を形成する第３の圧電体層形成工程とを具備し、第１、第３のZr/(Zr+Ti)組成比はモルフォトロピック相境界値より大きくしたものである。 In addition, the piezoelectric actuator manufacturing method according to the present invention controls the Pb evaporation amount, Zr evaporation amount, and Ti evaporation amount by the arc discharge ion plating method to form the first Zr / (Zr + Ti) on the lower electrode layer. A first piezoelectric layer forming step for forming a first PZT piezoelectric layer having a composition ratio, and a Pb evaporation amount, a Zr evaporation amount and a Ti evaporation amount are controlled by an arc discharge ion plating method to control the first PZT piezoelectric layer. Forming a second PZT piezoelectric layer having a second Zr / (Zr + Ti) composition ratio larger than the first Zr / (Zr + Ti) composition ratio on the piezoelectric layer; A third PdT piezoelectric layer with a second Zr / (Zr + Ti) composition ratio smaller than the second Zr / (Zr + Ti) composition ratio by controlling the Pb evaporation amount, Zr evaporation amount and Ti evaporation amount by the arc discharge ion plating method. And a third piezoelectric layer forming step of forming a third PZT piezoelectric layer having a Zr / (Zr + Ti) composition ratio, wherein the first and third Zr / (Zr + Ti) composition ratios are provided. Is It is made larger than Gandolfo lyotropic phase boundary values.
本発明によれば、Zr/(Zr+Ti)組成比の大きい第２のPZT圧電体層の小さな表面ラフネスによってZr/(Zr+Ti)組成比の小さい第１、第３のPZT圧電体層の大きな表面ラフネスを補償することによりリークパスの発生を抑制するので、耐電圧特性を大幅に向上できる。 According to the present invention, the first and third PZT piezoelectric layers having a small Zr / (Zr + Ti) composition ratio due to the small surface roughness of the second PZT piezoelectric layer having a large Zr / (Zr + Ti) composition ratio. Since the occurrence of a leak path is suppressed by compensating the large surface roughness, the withstand voltage characteristics can be greatly improved.
図１は本発明に係る圧電アクチュエータの実施の形態を示す断面図である。図１においては、図１２のPZT圧電体層５Ａを2層のPZT圧電体層５Ａ−１、５Ａ−２とし、PZT圧電体層５Ａ−１、５Ａ−２間にZr/(Zr+Ti)組成比xが大きいZrリッチなPZT圧電体層５Ｂ’を挿入して、三重構造のPZT圧電体層を実現している。尚、PZT圧電体層５Ａ−１、５Ｂ’、５Ａ−２のいずれも同一のADRIP装置によって形成される。 FIG. 1 is a sectional view showing an embodiment of a piezoelectric actuator according to the present invention. In FIG. 1, the PZT piezoelectric layer 5A shown in FIG. 12 is replaced with two PZT piezoelectric layers 5A-1 and 5A-2, and Zr / (Zr + Ti) is interposed between the PZT piezoelectric layers 5A-1 and 5A-2. A triple-structured PZT piezoelectric layer is realized by inserting a Zr-rich PZT piezoelectric layer 5B ′ having a large composition ratio x. Note that all of the PZT piezoelectric layers 5A-1, 5B 'and 5A-2 are formed by the same ADRIP apparatus.
たとえば、PZT圧電体層５Ａ−１、５Ａ−２のZr/(Zr+Ti)組成比xはモルフォトロピック相境界値（ｘ＝0.52）より大きくし、0.55〜0.60たとえば0.58である。従って、図２の（Ａ）に示すごとく、圧電定数-d31は大きく圧電特性は良好であり、また、図２の（Ｂ）、（Ｃ）に示すごとく、比誘電率εは大きくかつ誘電損失係数tanδは小さい。しかし、図２の（Ｄ）、（Ｅ）に示すごとく、平均粗さRaは小さくなく、従って、表面ラフネスは大きくかつ耐電圧特性が悪い。 For example, the Zr / (Zr + Ti) composition ratio x of the PZT piezoelectric layers 5A-1 and 5A-2 is larger than the morphotropic phase boundary value (x = 0.52), and is 0.55 to 0.60, for example 0.58. Accordingly, as shown in FIG. 2A, the piezoelectric constant -d 31 is large and the piezoelectric characteristics are good, and as shown in FIGS. 2B and 2C, the relative dielectric constant ε is large and the dielectric constant is low. The loss factor tanδ is small. However, as shown in FIGS. 2D and 2E, the average roughness Ra is not small, and thus the surface roughness is large and the withstand voltage characteristic is poor.
他方、PZT圧電体層５ＢのZr/(Zr+Ti)組成比xは0.61〜0.65たとえば0.64であり、PZT圧電体層５Ａ−１、５Ａ−２に比較してZrリッチである。従って、図２の（Ａ）に示すごとく、圧電定数-d31はより大きく圧電特性はより良好であり、また、図２の（Ｄ）、（Ｅ）に示すごとく、平均粗さRaは小さく、従って、表面ラフネスは小さく、また耐電圧特性は良好である。しかし、図２の（Ｂ）、（Ｃ）に示すごとく、比誘電率εが大きくかつ誘電損失係数tanδが大きくなる。 On the other hand, the Zr / (Zr + Ti) composition ratio x of the PZT piezoelectric layer 5B is 0.61 to 0.65, for example, 0.64, which is richer in Zr than the PZT piezoelectric layers 5A-1 and 5A-2. Therefore, as shown in FIG. 2A, the piezoelectric constant -d 31 is larger and the piezoelectric characteristics are better, and as shown in FIGS. 2D and 2E, the average roughness Ra is small. Therefore, the surface roughness is small and the withstand voltage characteristic is good. However, as shown in FIGS. 2B and 2C, the relative dielectric constant ε is large and the dielectric loss coefficient tan δ is large.
従って、第１層であるPZT圧電体層５Aの厚さは、たとえば、PZT圧電体層５Ａ−１、５Ｂ’、５Ａ−２の全体の４０％〜５０％たとえば４５％の厚さとすると、表面ラフネスが大きい膜となる。また、第２層であるPZT圧電体層５Ｂの厚さは、たとえば、PZT圧電体層５Ａ−１、５Ｂ’，５Ａ−２の全体の５〜１５％たとえば１０％の厚さとすると、PZT圧電体層５Ａ−１をそのまま形成した場合に比較して、PZT圧電体層５Ｂ’によってその表面ラフネスは小さくなる。さらに、第３層であるPZT圧電体層５Ａ−２の厚さは、たとえば、PZT圧電体層５Ａ−１、５Ｂ’，５Ａ−２の全体の４０％〜５０％たとえば４５％の厚さとすると、PZT圧電体層５Ａ−１をそのまま形成した場合に比較して、PZT圧電体層５Ｂの小さな表面ラフネスの影響を受けてPZT圧電体層５Ａ−１の表面ラフネスは小さくなる。 Accordingly, the thickness of the PZT piezoelectric layer 5A as the first layer is, for example, 40% to 50%, for example, 45% of the entire PZT piezoelectric layer 5A-1, 5B ′, 5A-2. The film has a large roughness. Further, if the thickness of the PZT piezoelectric layer 5B as the second layer is, for example, 5 to 15%, for example, 10% of the entire PZT piezoelectric layer 5A-1, 5B ', 5A-2, the PZT piezoelectric layer Compared with the case where the body layer 5A-1 is formed as it is, the surface roughness is reduced by the PZT piezoelectric layer 5B ′. Furthermore, the thickness of the PZT piezoelectric layer 5A-2 as the third layer is, for example, 40% to 50%, for example, 45% of the entire PZT piezoelectric layer 5A-1, 5B ′, 5A-2. Compared with the case where the PZT piezoelectric layer 5A-1 is formed as it is, the surface roughness of the PZT piezoelectric layer 5A-1 is reduced by the influence of the small surface roughness of the PZT piezoelectric layer 5B.
上述のごとく、PZT圧電体層５Ａ−１、５Ｂ’，５Ａ−２の厚さ比を４５％、１０％、４５％とすれば、実質的なZr/(Zr+Ti)組成比ｘは０．５８６であり、従って、図２の(A)、(B)、(C)に示すごとく、圧電特性、比誘電率ε、誘電損失係数tanδは余り変化がない。特に、誘電損失係数tanδは0.02程度と小さく、熱による特性変動、寿命劣化は少なく、耐電圧特性の向上にも寄与する。また、図２の（Ｄ）に示すごとく、表面ラフネスは僅かに向上し、従って、図１に示すごとく、リークパスＬＰは図１５の圧電アクチュエータに比較してもほとんど発生しない。この結果、図２の（Ｅ）に示すごとく、耐電圧特性は大幅に向上する。 As described above, if the thickness ratio of the PZT piezoelectric layers 5A-1, 5B ′, 5A-2 is 45%, 10%, and 45%, the substantial Zr / (Zr + Ti) composition ratio x is 0. Therefore, as shown in FIGS. 2A, 2B, and 2C, the piezoelectric characteristics, the relative permittivity ε, and the dielectric loss coefficient tan δ are not significantly changed. In particular, the dielectric loss coefficient tan δ is as small as about 0.02, and there are few characteristic fluctuations and life deterioration due to heat, which contributes to improvement of withstand voltage characteristics. Further, as shown in FIG. 2D, the surface roughness is slightly improved. Therefore, as shown in FIG. 1, the leak path LP hardly occurs even when compared with the piezoelectric actuator of FIG. As a result, as shown in FIG. 2E, the withstand voltage characteristic is greatly improved.
図３は図１の圧電アクチュエータの製造方法を説明するためのフローチャートである。図３においては、図１６のフローチャートにおけるADRIP工程に１２０１、１６０１の代わりに、PZT圧電体層５Ａ−１を形成するためにADRIP工程３０１ZrリッチなPZT圧電体層５Ｂを形成するためのADRIP工程３０２及びPZT圧電体層５Ａ−１と同一のPZT圧電体層５Ａ−２を形成するためのADRIP工程３０３を設けてある。この場合、PZT圧電体層５Ａ−１を形成するためのADRIP工程３０１、ZrリッチなPZT圧電体層５Ｂ’を形成するためのADRIP工程３０２及びPZT圧電体層５Ａ−２を形成するためのADRIP工程３０３は、図１２のADRIP 工程１２０１と同様のADRIP装置を用いて連続的に実行される。従って、プロセスマージンの狭小化を防ぐことができる。また、図１の圧電アクチュエータにおいては、PZT圧電体層５Ａ−１、ZrリッチなPZT圧電体層５Ｂ’及びPZT圧電体層５Ａ−２の結晶成長が連続となり、この結果、この組成比が連続的に変化する界面部分が圧電アクチュエータの駆動による機械的振動によって割れ、圧電アクチュエータが破損することを防止できる。 FIG. 3 is a flowchart for explaining a method of manufacturing the piezoelectric actuator of FIG. In FIG. 3, instead of 1201 and 1601 in the ADRIP process in the flowchart of FIG. 16, an ADRIP process 301 for forming the PZT piezoelectric layer 5B is formed in order to form the PZT piezoelectric layer 5A-1. And an ADRIP step 303 for forming the same PZT piezoelectric layer 5A-2 as the PZT piezoelectric layer 5A-1. In this case, an ADRIP process 301 for forming the PZT piezoelectric layer 5A-1, an ADRIP process 302 for forming the Zr-rich PZT piezoelectric layer 5B ', and an ADRIP for forming the PZT piezoelectric layer 5A-2. Step 303 is continuously performed using an ADRIP apparatus similar to the ADRIP step 1201 of FIG. Accordingly, it is possible to prevent the process margin from being narrowed. In the piezoelectric actuator shown in FIG. 1, the crystal growth of the PZT piezoelectric layer 5A-1, the Zr-rich PZT piezoelectric layer 5B ', and the PZT piezoelectric layer 5A-2 is continuous. As a result, this composition ratio is continuous. Therefore, it is possible to prevent the interface portion that changes with time from being broken by mechanical vibration caused by driving of the piezoelectric actuator and damaging the piezoelectric actuator.
次に、図３のADRIP工程３０１、３０２，３０３の具体例を説明する。 Next, a specific example of the ADRIP steps 301, 302, and 303 in FIG. 3 will be described.
ADRIP工程３０１において、ADRIP装置を用いてZr/(Zr+Ti)組成比x=0.58、Pb/(Zr+Ti)=1.24となるように、Pb蒸気、Zr蒸気及びTi蒸気を制御し、PZT圧電体層５Ａ−１を厚さ0.9μmで形成する。そして基板シャッタ（図示せず）を閉じてADRIP工程３０２に進む。 In the ADRIP step 301, the Pr vapor, the Zr vapor and the Ti vapor are controlled using the ADRIP apparatus so that the Zr / (Zr + Ti) composition ratio x = 0.58 and the Pb / (Zr + Ti) = 1.24. The piezoelectric layer 5A-1 is formed with a thickness of 0.9 μm. Then, the substrate shutter (not shown) is closed and the process proceeds to the ADRIP step 302.
次に、ADRIP工程３０２にて、基板シャッタを開け、同一ADRIP装置を用いてZr/(Zr+Ti)組成比ｘ＝0.64、Pb/(Zr+Ti)＝1.24となるように、Pb蒸気、Zr蒸気、及びTi蒸気を制御し、PZT圧電体層５Ｂ’を厚さ0.2μmで形成する。そして、基板シャッタ（図示せず）を閉じてADRIP工程３０３に進む。 Next, in the ADRIP step 302, the substrate shutter is opened, and using the same ADRIP apparatus, Pb vapor, so that Zr / (Zr + Ti) composition ratio x = 0.64, Pb / (Zr + Ti) = 1.24, Zr vapor and Ti vapor are controlled to form a PZT piezoelectric layer 5B ′ with a thickness of 0.2 μm. Then, the substrate shutter (not shown) is closed and the process proceeds to the ADRIP step 303.
最後に、ADRIP工程３０３にて、基板シャッタを開け、同一ADRIP装置を用いてZr/(Zr+Ti)組成比ｘ＝0.58、Pb/(Zr+Ti)＝1.24となるように、Pb蒸気、Zr蒸気、及びTi蒸気を制御し、PZT圧電体層５Ａ−２を厚さ0.9μmで形成する。そして、基板シャッタを閉じる。 Finally, in the ADRIP step 303, the substrate shutter is opened, and the same ADRIP apparatus is used to make the Pr vapor, so that the Zr / (Zr + Ti) composition ratio x = 0.58 and Pb / (Zr + Ti) = 1.24. Zr vapor and Ti vapor are controlled to form the PZT piezoelectric layer 5A-2 with a thickness of 0.9 μm. Then, the substrate shutter is closed.
尚、上述のADRIP工程３０１，３０２，３０３においてZr蒸気のみを変化させたのは、Zrはゲッタリング効果がないので、成膜圧力の変動がなく、Pb、Ti蒸気量に影響を及ぼすおそれがないからである。 The reason why only the Zr vapor was changed in the above ADRIP steps 301, 302, and 303 is that Zr has no gettering effect, so there is no fluctuation in the film forming pressure, and there is a possibility of affecting the amount of Pb and Ti vapor. Because there is no.
このようにして得られた三層のPZT圧電体層による圧電アクチュエータによれば、耐電圧特性は25.4V/μmであり、Pt上部電極層６の表面ラフネスの平均粗さ（Ra）は49Åであった。 According to the piezoelectric actuator using the three PZT piezoelectric layers thus obtained, the withstand voltage characteristic is 25.4 V / μm, and the average roughness (Ra) of the surface roughness of the Pt upper electrode layer 6 is 49 mm. there were.
これに対し、図１２の圧電アクチュエータにおいて、ADRIP装置を用いて、PZT圧電体層５Ａを厚さ2.0μmで形成した。この結果、耐電圧特性は15.1V/μmであり、Pt上部電極層６の表面ラフネスの平均粗さ（Ra）は60Åであった。また、図１５の圧電アクチュエータにおいて、ADRIP装置を用いて、PZT圧電体層５Ａを厚さ2.5μmで形成し、TiリッチのPZT圧電体層５Ｂを厚さ0.3μmで形成した。この結果、耐電圧特性は22.78V/μmであり、Pt上部電極層６の表面ラフネスの平均粗さ（Ra）は65Åであった。 In contrast, in the piezoelectric actuator of FIG. 12, the PZT piezoelectric layer 5A was formed to a thickness of 2.0 μm using an ADRIP device. As a result, the withstand voltage characteristic was 15.1 V / μm, and the average roughness (Ra) of the surface roughness of the Pt upper electrode layer 6 was 60 mm. Further, in the piezoelectric actuator of FIG. 15, the ADRIP apparatus was used to form the PZT piezoelectric layer 5A with a thickness of 2.5 μm and the Ti-rich PZT piezoelectric layer 5B with a thickness of 0.3 μm. As a result, the withstand voltage characteristic was 22.78 V / μm, and the average roughness (Ra) of the surface roughness of the Pt upper electrode layer 6 was 65 mm.
このように、図１２、図１５の圧電アクチュエータと比較して図１の圧電アクチュエータの表面ラフネスは抑制されるので、リークパスの発生は抑止でき、この結果、耐電圧特性を大幅に向上できる。 Thus, since the surface roughness of the piezoelectric actuator of FIG. 1 is suppressed as compared with the piezoelectric actuator of FIGS. 12 and 15, the occurrence of a leak path can be suppressed, and as a result, the withstand voltage characteristics can be greatly improved.
尚、上述の実施の形態においては、PZT圧電体層５Ａ−１、５Ａ−２のZr/(Zr+Ti)組成比ｘは同一である必要はなく、ＭＰＢ値(x=0.52付近)より大きくかつPZT圧電体層５Ｂ’のZr/(Zr+Ti)組成比ｘより小さければよい。 In the above-described embodiment, the Zr / (Zr + Ti) composition ratio x of the PZT piezoelectric layers 5A-1 and 5A-2 does not need to be the same, and is larger than the MPB value (near x = 0.52). In addition, it may be smaller than the Zr / (Zr + Ti) composition ratio x of the PZT piezoelectric layer 5B ′.
また、本発明は、上述の実施の形態の自明の範囲のいかなる変更にも適用し得る。 Further, the present invention can be applied to any change in the obvious range of the above-described embodiment.
本発明に係る圧電アクチュエータは、光スキャナイングジェックプリンタヘッド、ジャイロセンサ等に利用できる。 The piezoelectric actuator according to the present invention can be used for an optical scanner ink jet printer head, a gyro sensor, and the like.
１：単結晶シリコン基板
１’：振動板
２：酸化シリコン層
３：Ti密着層
４：Pt下部電極層
５、５’：PZT圧電体層
５ａ：PbリッチPZT圧電体層
５ｂ：PbリーンPZT圧電体層
５Ａ、５Ａ−１、５Ａ−２：PZT圧電体層
５Ｂ：TiリッチPZT圧電体層
５Ｂ’：ZrリッチPZT圧電体層
６：Pt上部電極層
１３０１：真空チャンバ
１３０２−１：Pb蒸発源
１３０２−２：Zr蒸発源
１３０２−３：Ti蒸発源
１３０２−１Ｓ、１３０２−２Ｓ、１３０２−３Ｓ：蒸気量センサ
１３０３：ヒータ付ウェハ回転ホルダ
１３０３ａ：ウェハ
１３０４：圧力勾配型プラズマガン
１３０５：O2ガス導入口
１３０６：排気口
1: Single crystal silicon substrate
1 ': Diaphragm 2: Silicon oxide layer
3: Ti adhesion layer
4: Pt lower electrode layer 5, 5 ': PZT piezoelectric layer 5a: Pb rich PZT piezoelectric layer 5b: Pb lean PZT piezoelectric layer 5A, 5A-1, 5A-2: PZT piezoelectric layer 5B: Ti rich PZT Piezoelectric layer 5B ': Zr rich PZT piezoelectric layer 6: Pt upper electrode layer
1301: Vacuum chamber 1302-1: Pb evaporation source 1302-2: Zr evaporation source 1302-3: Ti evaporation source 1302-1S, 1302-2S, 1302-3S: Vapor amount sensor 1303: Wafer rotating holder with heater
1303a: Wafer 1304: Pressure gradient type plasma gun
1305: O 2 gas inlet
1306: Exhaust port
Claims (9)
前記下部電極層上に設けられた第１のZr/(Zr+Ti)組成比を有する第１のPZT圧電体層と、
前記第１のPZT圧電体層上に設けられた前記第１のZr/(Zr+Ti)組成比より大きい第２のZr/(Zr+Ti)組成比を有する第２のPZT圧電体層と、
前記PZT圧電体層上に設けられた第２のZr/(Zr+Ti)組成比より小さい第３のZr/(Zr+Ti)組成比を有する第３のPZT圧電体層と、
前記第３のPZT圧電体層上に設けられた上部電極層と
を具備し、前記第１、第３のZr/(Zr+Ti)組成比はモロフォトロピック相境界値より大きい圧電アクチュエータ。 A lower electrode layer;
A first PZT piezoelectric layer having a first Zr / (Zr + Ti) composition ratio provided on the lower electrode layer;
A second PZT piezoelectric layer having a second Zr / (Zr + Ti) composition ratio greater than the first Zr / (Zr + Ti) composition ratio provided on the first PZT piezoelectric layer; ,
A third PZT piezoelectric layer having a third Zr / (Zr + Ti) composition ratio smaller than the second Zr / (Zr + Ti) composition ratio provided on the PZT piezoelectric layer;
An upper electrode layer provided on the third PZT piezoelectric layer, wherein the first and third Zr / (Zr + Ti) composition ratios are larger than the morphotropic phase boundary value.
アーク放電イオンプレーティング法によってPb蒸発量、Zr蒸発量及びTi蒸発量を制御して前記第１のPZT圧電体層上に前記第１のZr/(Zr+Ti)組成比より大きい第２のZr/(Zr+Ti)組成比を有する第２のPZT圧電体層を形成する第２の圧電体層形成工程と、
アーク放電イオンプレーティング法によってPb蒸発量、Zr蒸発量及びTi蒸発量を制御して前記第２のPZT圧電体層上に前記第２のZr/(Zr+Ti)組成比より小さい第３のZr/(Zr+Ti)組成比を有する第３のPZT圧電体層を形成する第３の圧電体層形成工程と
を具備し、前記第１、第３のZr/(Zr+Ti)組成比はモロフォトロピック相境界値より大きい圧電アクチュエータの製造方法。 The first PZT piezoelectric layer having the first Zr / (Zr + Ti) composition ratio is formed on the lower electrode layer by controlling the Pb evaporation amount, Zr evaporation amount and Ti evaporation amount by the arc discharge ion plating method. A first piezoelectric layer forming step,
A Pb evaporation amount, a Zr evaporation amount, and a Ti evaporation amount are controlled by an arc discharge ion plating method, and a second larger than the first Zr / (Zr + Ti) composition ratio is formed on the first PZT piezoelectric layer. A second piezoelectric layer forming step of forming a second PZT piezoelectric layer having a Zr / (Zr + Ti) composition ratio;
A Pb evaporation amount, a Zr evaporation amount, and a Ti evaporation amount are controlled by an arc discharge ion plating method, and a third Zr / (Zr + Ti) composition ratio smaller than the second Zr / (Zr + Ti) composition ratio is formed on the second PZT piezoelectric layer. And a third piezoelectric layer forming step of forming a third PZT piezoelectric layer having a Zr / (Zr + Ti) composition ratio, wherein the first and third Zr / (Zr + Ti) composition ratios are provided. Is a method of manufacturing a piezoelectric actuator larger than the morphotropic phase boundary value.
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| CN111355460A (en) * | 2018-12-20 | 2020-06-30 | 中国电子科技集团公司第十三研究所 | Method for manufacturing resonator |
| WO2020153289A1 (en) * | 2019-01-25 | 2020-07-30 | Tdk株式会社 | Piezoelectric element |
| EP3846231A4 (en) * | 2018-08-30 | 2021-10-13 | FUJIFILM Corporation | Piezoelectric device and method of manufacturing piezoelectric device |
| US11984864B2 (en) | 2018-12-20 | 2024-05-14 | The 13Th Research Institute Of China Electronics Technology Group Corporation | Method for manufacturing resonator |
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| EP3846231A4 (en) * | 2018-08-30 | 2021-10-13 | FUJIFILM Corporation | Piezoelectric device and method of manufacturing piezoelectric device |
| CN111355460A (en) * | 2018-12-20 | 2020-06-30 | 中国电子科技集团公司第十三研究所 | Method for manufacturing resonator |
| US11984864B2 (en) | 2018-12-20 | 2024-05-14 | The 13Th Research Institute Of China Electronics Technology Group Corporation | Method for manufacturing resonator |
| WO2020153289A1 (en) * | 2019-01-25 | 2020-07-30 | Tdk株式会社 | Piezoelectric element |
| JP2020120028A (en) * | 2019-01-25 | 2020-08-06 | Tdk株式会社 | Piezoelectric element |
| JP7010247B2 (en) | 2019-01-25 | 2022-01-26 | Tdk株式会社 | Piezoelectric element |
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| JP6271333B2 (en) | 2018-01-31 |
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