JP2005039343A - Method for designing surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for designing a surface acoustic wave device that can make shorter and lower the time and cost needed for device designing in a simple method and also predict device characteristics with high precision. <P>SOLUTION: The method for designing the surface acoustic wave device has a virtual value calculation step for calculating a virtual value of a specified device characteristic of the surface acoustic wave device, a measured value measurement step for measuring a measured value of the specified device characteristic, a specified material constant calculation step for finding a correction value for the specified material constant obtained by equalizing the virtual value to the measured value or an approximate value obtained based upon the measured value by varying the specified material constant among material constants of thin films used to calculate the virtual value, and a device designing step for designing the surface acoustic wave device by using the correction value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

が成立する。これをｍ組のΔｖを適用したｍ行の行列式にて表現すると、
Ｙ［ｍ］＝Ｆ［ｍｎ］・Ｘ［ｎ］ …（６）
となる。ここで、Ｙはｍ組の偏差Δｖを示すｍ行のベクトル、Ｆはｎ列の伝播速度ｖの変化率δｖｃ_ｉｊ＝δｖ／δＣ_ｉｊのｍ組を示すｍ行ｎ列の行列、Ｘはｎ列の弾性係数の変化量ΔＣ_ｉｊを示すベクトルである。ここで、ｍは計算に用いる測定値（近似値）の数であり、ｎは弾性定数Ｃ_ｉｊのうち独立な弾性係数の数（すなわち未知数の数）である。ｍ≧ｎとすれば、最小二乗法などによって弾性係数の変化量を求めることができる。
【００４０】
例えば、六方晶系の圧電体ＺｎＯの弾性定数のテンソル表示は６行６列の行列で表されるが、行列要素のうちの図６に示す独立な４つの弾性係数Ｃ_１１、Ｃ_１３、Ｃ_３３、Ｃ_４４の変化量ΔＣ_１１、ΔＣ_１３、ΔＣ_３３、ΔＣ_４４を求める場合には、上記（６）式のｎが４となるため、ｍを４以上とすることによって算出することが可能になる。例えば、ｍ＝４としたときには、４種の膜厚ｋｈ＝ｄ，ｅ，ｆ，ｇにおける偏差Ｙ［Δｖ_ｄ，Δｖ_ｅ，Δｖ_ｆ，Δｖ_ｇ］、並びに、各弾性係数及び各膜厚ｋｈに対応する変化率Ｆ［δｖｃ_１１−ｄ（＝δｖ_ｄ／δＣ_１１）、δｖｃ_１１−ｅ（＝δｖ_ｅ／δＣ_１１）、δｖｃ_１１−ｆ（＝δｖ_ｆ／δＣ_１１）、δｖｃ_１１−ｇ（＝δｖ_ｇ／δＣ_１１）；δｖｃ_１３−ｄ（＝δｖ_ｄ／δＣ_１３）、δｖｃ_１３−ｅ（＝δｖ_ｅ／δＣ_１３）、δｖｃ_１３−ｆ（＝δｖ_ｆ／δＣ_１３）、δｖｃ_１３−ｇ（＝δｖ_ｇ／δＣ_１３）；δｖｃ_３３−ｄ（＝δｖ_ｄ／δＣ_３３）、δｖｃ_３３−ｅ（＝δｖ_ｅ／δＣ_３３）、δｖｃ_３３−ｆ（＝δｖ_ｆ／δＣ_３３）、δｖｃ_３３−ｇ（＝δｖ_ｇ／δＣ_３３）；δｖｃ_４４−ｄ（＝δｖ_ｄ／δＣ_４４）、δｖｃ_４４−ｅ（＝δｖ_ｅ／δＣ_４４）、δｖｃ_４４−ｆ（＝δｖ_ｆ／δＣ_４４）、δｖｃ_４４−ｇ（＝δｖ_ｇ／δＣ_４４）］を用いる。これにより最小二乗法によって弾性係数の変化量Ｘ［ΔＣ_１１、ΔＣ_１３、ΔＣ_３３、ΔＣ_４４］を求めることができる。すなわち、弾性表面波の伝播速度の仮想値を測定値（近似値）に合わせ込むために必要な弾性定数の変化量は、上記のようにして求めた弾性係数の変化量Ｘ［ΔＣ_１１、ΔＣ_１３、ΔＣ_３３、ΔＣ_４４］によって表される。
【００４１】
最後に、上記伝播速度ｖの仮想値を求めるのに用いた弾性係数の仮定値をＣ_ｉｊ ^０と、上記のようにして求めた弾性表面波の伝播速度の変化量ΔＣ_ｉｊを用いて、弾性係数の修正値Ｃ_ｉｊ ^０＋ΔＣ_ｉｊを求める。
【００４２】
上記のようにして、弾性表面波の伝播速度ｖの仮想値を測定値或いは近似値に合わせ込んだときの弾性定数若しくはその変化量を求めたが、このように仮想値を測定値或いは近似値に合わせ込んだときの伝播速度ｖの膜厚ｋｈ依存性を図８に示す。この図に示すように、仮想値を示す曲線Ａに較べて測定値に近い曲線Ｃとなっていることがわかる。
【００４３】
図９には、上記のようにして得た、仮想値を測定値若しくは近似値に合わせ込むために必要な弾性係数の変化量ΔＣ_ｉｊの膜厚ｋｈ依存性を示す。ここで、各膜厚ｋｈにおける変化量ΔＣ_ｉｊの算出には、その膜厚ｋｈの近傍のｍ＝４組の異なる膜厚ｋｈにおける上記変化率δｖｃ_ｉｊ及び偏差Δｖの値を用いている。この図によれば、膜厚ｋｈが１．０を下回り、さらに低下していくと急激に各弾性係数の変化量が大きくなることがわかる。これは、薄膜１０２の内部応力に対して強い相関を示しているものと思われる。通常、薄膜１０２の内部応力は、基板１０１との間の格子定数や結晶構造の相違に起因して膜厚が小さくなるほど大きくなる。そして、薄膜１０２の膜厚が小さいと薄膜の表面が基板１０１との界面に近づくため、薄膜１０２の表面を伝播する弾性表面波の伝播速度ｖは薄膜１０２と基板１０１との間の界面部分の影響を受けやすくなることから、薄膜１０２の弾性定数はバルク材料の弾性定数の値から大きく離れることになる。逆に、薄膜１０２の膜厚が大きくなると薄膜１０２の表面は上記界面から離れていくとともに、表面近傍の内部応力も小さくなっていくものと考えられるので、薄膜１０２の表面を伝播する弾性表面波の伝播速度ｖは薄膜１０２と基板１０１との間の界面の影響を受けにくくなることから、薄膜の弾性定数はバルク材料の弾性定数に近づくものと考えられる。したがって、図９に示す本実施例の結果は、このような薄膜の内部応力に起因する特性を正しく反映しているものと思われる。また、この実施例では、各弾性係数の変化量ΔＣ_ｉｊの大きさによって、薄膜１０２の内部応力がどの方向に生じているかを知ることができる。
【００４４】
図１０には、本実施例の薄膜１０２の各材料定数の値を１０％変化させたときの弾性表面波デバイスの伝播速度ｖの変化量Δｖを示す。ここで、弾性定数、圧電定数、誘電率は全ての係数を一律に１０％変化させてある。この図に示すように、圧電定数や弾性定数を変化させたときにはいずれも伝播速度ｖが大きく変化している。また、圧電定数や弾性定数の伝播速度ｖへの影響度合は、薄膜１０２の膜厚ｋｈによって変化することがわかる。したがって、上記方法において、弾性定数の代わりに特定材料定数として圧電定数を用いても、上記と同様に有用な材料定数の修正値を得ることができる。
【００４５】
また、上記特定デバイス特性としては、上記の弾性表面波の伝播速度ｖ以外に、弾性表面波の電気機械結合係数ｋ^２、弾性表面波の伝播損失などを用いることも可能である。また、これらの特定デバイス特性のパラメータとしては、上記の薄膜の膜厚だけでなく、たとえば、弾性表面波の周波数などを用いることができる。
【００４６】
次に、上記のようにして算出した弾性定数の修正値を用いて、弾性表面波の上記伝播速度以外のデバイス特性を予測する。この特性予測は、本実施例では弾性表面波デバイス１００のフィルタ特性（挿入損失の周波数特性）について行い、この特性を予測するために等価回路法を用いる。等価回路法は、薄膜１０２上に電極１０４Ｓ，１０４Ｔが形成されている構造の等価回路を設定し、この等価回路からデバイス特性を導出する方法である。
【００４７】
まず、上記等価回路としては、例えば、図１１に示すスミスの等価回路と呼ばれているものを用いる。この等価回路は、上記の文献１にも記載されており、ＩＤＴ構成部１１０，１２０の基本構成（一対の電極１０４Ｓ，１０４Ｔの配列構造）に対応するものである。ここで、等価回路は音響入力端子１、音響出力端子２及び電気端子３を備えている。１対を越える数の電極が設けられる場合には、上記等価回路における一つの電極に対応する部分を、音響端子を縦続に、電気端子は並列に接続する態様で、１対を越える電極数に応じて付加すればよい。そして、この等価回路の回路定数Ｚ_１、Ｚ_２、Ｃ_Ｓ変成比γ_ｐなどを求めることによって特性予測が可能になる。これらの回路定数は、有限要素法（ＦＥＭ）を用いて決定することができる。この決定方法は、ニューセラミックス（１９９５） Ｎｏ．１０ Ｐ．６７ 「弾性表面波デバイスの等価回路定数の理論的決定法［１］−基本的な考え方−」、Ｎｏ．１１ Ｐ．４７ 「弾性表面波デバイスの等価回路定数の理論的決定法［２］−有限要素法の導入−」、Ｎｏ．１２ Ｐ．６０ 「弾性表面波デバイスの等価回路定数の理論的決定法［３］−等価回路定数の実際−」、以上すべて小柴 正則 著に詳細に説明されている。
【００４８】
なお、上記の等価回路定数の決定において、弾性定数については上記修正値を用い、その他の材料定数については仮想値を算出したときに用いた値（バルク材料の値）を用いた。
【００４９】
次に、上記のようにして決定された等価回路定数に基づいて弾性表面波デバイス１００の挿入損失の周波数特性を求めた。挿入損失は、フィルタである弾性表面波デバイス１００の入力信号と出力信号の振幅比に相当する。その結果を図１２に示す。上記弾性定数について仮想値を求める際に用いた仮定値を用いて求めた挿入損失の周波数特性を図中一点鎖線の仮想値曲線ＰＡで示し、弾性表面波デバイス１００に対して実際に測定した挿入損失の周波数特性を図中破線の測定値曲線ＰＢで示し、本実施例の上記修正値を用いて求めた挿入損失の周波数特性を図中実線の修正値曲線ＰＣで示す。この図に示されるように、仮想値曲線ＰＡは測定値曲線ＰＢと大きく異なる周波数帯域にピーク位置を有するが、修正値曲線ＰＣは測定値曲線ＰＢとほぼ一致したピーク位置を有し、しかも、測定値曲線ＰＢとほぼ同様の曲線形状を有している。
【００５０】
上記のように、本実施形態のデバイス設計方法では、特定デバイス特性の仮想値と測定値との相違を特定材料定数に反映させることによって特性材料定数の修正値を求め、この修正値を用いて特性予測を行うことができる。そして、この特性予測によって得られた特性は、上記実施例で示したように実際の弾性表面波デバイスのデバイス特性の測定値にほぼ一致する。したがって、上記のような特性予測によって弾性表面波デバイスの種々の特性を予想し、これを望まれる特性に合わせるようにデバイス構造を設定したり、或いは、特定デバイス特性を計測するために既に形成したデバイス構造を修正したりすることが可能になる。
【００５１】
なお、上記実施形態では、基板１０１上に単層の圧電体の薄膜１０２が形成された層構造を有するものについて説明したが、本発明はこのような層構造を備えたものに限らず、基板上に硬質薄膜を形成した後に圧電体薄膜を形成したもの、基板上の圧電体薄膜上にさらに誘電体薄膜を形成し、その上に電極を形成したもの、基板上に電極を形成し、その上に圧電体薄膜を形成したものなど、種々の層構造を有するものに適用可能である。
【図面の簡単な説明】
【図１】基板上に薄膜を備えた弾性表面波デバイスの概略構成を示す断面図。
【図２】基板上の薄膜の特性、バルク材料の材料定数及び薄膜の材料定数の関係を示す説明図。
【図３】実施形態の弾性表面波デバイスの設計方法を示す説明図。
【図４】実施例のデバイス設計手順を示す概略フローチャート。
【図５】弾性表面波の伝播速度ｖの仮想値、測定値及び近似値を示すグラフ。
【図６】各弾性係数を変化させたときの伝播速度の変化量ｄｖを示すグラフ。
【図７】伝播速度ｖの仮想値と近似値の偏差Δｖを示すグラフ。
【図８】伝播速度ｖの仮想値、測定値及びフィッティング値を示すグラフ。
【図９】フィッティングによって得られた弾性係数の変化量ΔＣ_ｉｊを示すグラフ。
【図１０】各材料定数を変化させたときの伝播速度ｖの変化量ｄｖを示すグラフ。
【図１１】弾性表面波デバイスの基本単位の等価回路図。
【図１２】弾性表面波デバイスの挿入損失の周波数特性について、特定材料定数の仮定値を用いて予測した仮想値、計測した測定値、特定材料定数の修正値を用いて予測した修正値をそれぞれ比較して示すグラフ。
【図１３】弾性表面波デバイスの構成を模式的に示す概略斜視図。
【図１４】弾性表面波デバイスの伝播速度を計測する方法を示す説明図。
【符号の説明】
１００…弾性表面波デバイス、１０１…基板、１０２…薄膜、１０４Ｓ，１０４Ｔ…電極、１１０，１２０…ＩＤＴ構成部、１１０Ｓ，１１０Ｔ…電極パターン、ｖ…伝播速度、Δｖ…偏差、Ｃ…弾性定数、Ｃ_ｉｊ…弾性係数、ΔＣ_ｉｊ…変化量、δｖｃ_ｉｊ…変化率、ｋｈ…膜厚[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for designing a surface acoustic wave device, and more particularly to a design method for accurately obtaining desired device characteristics of a surface acoustic wave device.
[0002]
[Prior art]
In general, many electronic devices using a thin film formed on a substrate as a functional layer are created, and various products using such electronic devices are commercially available. For example, surface acoustic wave devices using a piezoelectric body are often used in high-frequency elements such as TV filters in electronic devices and communication devices. In this surface acoustic wave device, a surface acoustic wave is generated on the surface of a piezoelectric body, and various characteristics are obtained through the surface acoustic wave. In particular, in recent years, many devices with a piezoelectric thin film formed on a substrate have been proposed in order to improve the performance of the device. For example, the quality of the thin film is improved, a hard material is used for the substrate, Device characteristics have been improved by devising the structure.
[0003]
Various design tools that can be used for the design of various electronic devices have been known. However, due to the recent progress in device performance enhancement, it is possible to accurately evaluate constituent materials regardless of which design tool is used. There is a strong demand to do. Conventionally, as a material evaluation method, a large number of samples are mainly prepared by forming a thin film on a substrate, and X-ray diffraction, atomic absorption analysis, differential thermal analysis, etc. are performed on the thin film of this sample. Evaluation using various analysis methods has been performed. These analysis methods are all for specifying the crystallinity and composition ratio of the material.
[0004]
On the other hand, not the method of directly identifying the material configuration as described above, but also a method of estimating a material property by a predetermined theoretical formula based on various properties of the material or calculating by a numerical calculation is also known. (For example, refer to Patent Document 1 and Non-Patent Document 1 below). However, unlike bulk materials, the characteristics of the thin film formed on the substrate are not only the type and structure of the substances that make up the thin film, but also the combination with the underlying substrate, film formation conditions, film thickness, and device usage conditions. It is greatly influenced by many factors such as. More specifically, the characteristics of the thin film greatly change due to internal stress due to lattice mismatch with the substrate, thermal stress, crystal defects, warpage due to stress, and the like. For this reason, since the material characteristics greatly change as compared with the bulk material, it is necessary to evaluate the thin film formed on the substrate. As a method for evaluating the thin film in this way, for example, a method is known in which the elastic constant of the thin film is obtained by obtaining the velocity of the surface acoustic wave using laser light (for example, see Non-Patent Document 2 below). .
[0005]
[Patent Document 1]
JP 2002-267640 A [Non-Patent Document 1]
IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS AND FREQUENCY CONTROL, VOL. 49, NO. 7, JULY 2002, p. 893
[Non-Patent Document 2]
50th Applied Physics Related Conference Lecture Proceedings NO. 2 p. 919 29p-ZG-8 “Determination of Young's modulus of LOW-k film using surface acoustic wave”
[0006]
[Problems to be solved by the invention]
In the above conventional surface acoustic wave device design method, since it is necessary to repeatedly prepare and measure a variety of thin film samples, it takes a lot of time and effort in the basic stage of device design, and the burden is great in terms of time and cost. There is a problem. In addition, since it is not necessary to measure the characteristics of the thin film itself for device design, the above-described basic stage work may not be directly linked to the device characteristics and is wasteful.
[0007]
On the other hand, surface acoustic wave device design methods such as numerical simulations and simulations based on modeling reflect thin film effects that can be directly related to the device characteristics of actually created surface acoustic wave devices, or are caused by device structures. Calculations that take into account additional effects are extremely difficult, and the device characteristics cannot be predicted with high accuracy, and as a result, it is not a substitute for the above-mentioned steady and costly evaluation method as described above. There is a point. In particular, the internal stress and warpage of the piezoelectric thin film have a significant effect on the device characteristics. However, the calculation that reflects the state of such a thin film is extremely complicated, and it is not possible to calculate the device characteristics with high accuracy. Almost impossible.
[0008]
Therefore, the present invention solves the above-mentioned problems, and the problem is that it is possible to reduce the time and cost required for device design by a simple method and to be able to predict device characteristics with high accuracy. The object is to provide a method for designing a surface acoustic wave device.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, a surface acoustic wave device design method according to the present invention is a surface acoustic wave device design method including a piezoelectric thin film formed on a substrate. A virtual value calculating step for calculating a virtual value of the measured value, a measured value measuring step for measuring the measured value of the specific device characteristic, and a specific material constant among the material constants of the thin film used for calculating the virtual value is changed. A specific material constant calculating step for obtaining a correction value of the specific material constant obtained by adjusting the virtual value to the measurement value or an approximate value obtained based on the measurement value, and using the correction value And a device design step for designing the surface acoustic wave device.
[0010]
According to this invention, by changing the specific material constant, the virtual value of the specific device characteristic is matched with the measured value of the specific device characteristic measured in the measurement value measurement step or the approximate value obtained based on the measured value. Include. Then, the correction value of the characteristic material constant is calculated based on the amount of change in the specific material constant necessary for this adjustment. This is equivalent to obtaining the corrected value of the specific material constant on the assumption that the deviation between the virtual value of the specific device characteristic and the measured value or approximate value is caused only by the error of the assumed value of the specific material constant. In this way, the correction value of the specific material constant obtained is different from the specific material constant of the thin film itself, but it includes the influence of the state of the thin film and the device structure, so this correction value is used. This makes it possible to predict device characteristics with higher accuracy. Further, since it is not necessary to create a simple thin film sample having no device configuration, it is possible to avoid waste of time and cost in the basic stage of device design.
[0011]
In the present invention, in the specific material constant calculation step, a change rate of the specific device characteristic with respect to a change in the specific material constant and a deviation of the virtual value with respect to the measured value or the approximate value are obtained, and the change rate and the It is preferable to calculate the correction value using a deviation. According to this, the change amount of the specific material constant for eliminating the deviation of the virtual value from the measured value or the approximate value can be derived very easily by using the change rate of the specific device characteristic of the specific material constant. Therefore, the correction value corresponding to this can be derived easily.
[0012]
In the present invention, it is preferable that in the device design step, device characteristics are predicted using the correction value, and device design is performed based on the result. When the device characteristics are predicted based on the correction value as described above, it is possible to know the coincidence / non-coincidence and the degree of difference with the required device characteristics, so that the device design can be performed based on the result. For example, a surface acoustic wave device having desired device characteristics can be designed by comparing expected device characteristics with required device characteristics and modifying the device structure based on the comparison. As a method for predicting the device characteristics, an equivalent circuit method described later can be used. That is, in a surface acoustic wave device, electromechanical coupling characteristics such as an excitation structure for generating a surface acoustic wave by an electrical signal such as IDT, a detection structure for electrically detecting a surface acoustic wave, etc. Therefore, the structure portion can be expressed by an equivalent circuit. Then, the device characteristics can be calculated by determining the equivalent circuit constant using the correction value and obtaining the characteristics of the equivalent circuit.
[0013]
In the present invention, in the measurement value measurement step, the specific device characteristic is preferably measured with respect to a device structure including an electrode. Since the measurement method of the specific device characteristic described above may be a method that can obtain a measurement value corresponding to the specific device characteristic of the surface acoustic wave device, it is not always necessary to complete the surface acoustic wave device and perform measurement. However, by actually measuring the device structure including the electrodes of the surface acoustic wave device, it is possible to obtain measurement values including the effects of the electrode structure (electrode pattern shape, etc.) Device design becomes possible.
[0014]
In the present invention, the specific device characteristic is preferably a propagation speed of a surface acoustic wave. The propagation speed of surface acoustic waves is easy to measure among the device characteristics of surface acoustic wave devices, and has a strong correlation with the material constants of thin films, so that a correction value for specific material constants can be obtained appropriately. Therefore, highly accurate device design is possible.
[0015]
In the present invention, in the measurement value measurement step, the surface acoustic wave is generated by irradiating the thin film with laser light, and the propagation velocity is measured by observing the surface acoustic wave by laser interferometry. Is preferred. According to this, surface acoustic waves can be generated without providing an electrode structure, and measurement can be performed in a non-contact state with high accuracy at an arbitrary position. In addition, since it is possible to excite surface acoustic waves with an appropriate wavelength without depending on the electrode structure, it is possible to measure by changing the surface acoustic wave wavelength, making it more useful and more informational in device design. A value can be obtained.
[0016]
In the present invention, it is preferable to use a material constant of a bulk material as an assumed value of the specific material constant for calculating the virtual value. The material constant of the bulk material can be easily known in general and is an ideal value that does not include the influence of the thin film state. Therefore, as an assumed value of a specific material constant, that is, a parameter for calculating a virtual value of a specific device characteristic Most suitable to use.
[0017]
In the present invention, the specific material constant is preferably an elastic constant of the thin film. The elastic constant is a material constant that directly affects the composition, crystal state, internal stress, and the like of the thin film, and is therefore an appropriate parameter for reflecting the state of the thin film through which the surface acoustic wave propagates. In particular, since it has a large correlation with the propagation speed of the surface acoustic wave, it is most preferable when the specific device characteristic is the propagation speed of the surface acoustic wave.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a method for designing a surface acoustic wave device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram schematically showing a surface acoustic wave device structure including a thin film which is a design target of the embodiment. In this device structure, a thin film 102 having a thickness Tp is formed on the surface of a substrate 101. The thin film 102 is composed of a piezoelectric body. On the surface of the thin film 102, electrodes 104S and 104T made of a metal such as Al are alternately formed. The electrodes 104S and 104T are configured as interdigital electrodes (IDT), for example. Here, a surface acoustic wave having a wavelength λ corresponding to the electrode pitch can be generated on the surface of the thin film 102 by applying a predetermined voltage between the electrodes 104S and 104T. Further, when a surface acoustic wave propagates through the surface of the thin film 102, a fluctuating voltage corresponding to the amount of surface displacement due to the surface acoustic wave is generated between the electrodes 104S and 104T.
[0019]
The substrate 101 and the thin film 102 can have various combinations. For example, examples of the substrate 101 include glass such as Pyrex (registered trademark), quartz, Si, quartz, sapphire, and diamond. Examples of the piezoelectric thin film 102 include ZnO, PZT, KNbO ₃ , LiTaO ₃ , and LiNbO ₃ .
[0020]
FIG. 2 shows the relationship between the thin film properties on the substrate and the material constants of the bulk material and the thin film. The thin film characteristics on the substrate largely depend on the composition, crystal structure, crystal state, etc. of the material constituting the thin film, but the thin film does not necessarily have the same characteristics as the bulk material having the same composition, crystal structure, crystal state, etc. It does not show. This is because the thin film is greatly influenced by the structure of the base substrate and the film thickness of the substrate. More specifically, thin film characteristics are greatly affected by differences in lattice constants and crystal structures between the thin film and the base substrate, hardness of the base substrate, crystal defects, internal stress, warpage, etc. in the thin film. Therefore, in order to evaluate the characteristics of the thin film, it is necessary to obtain the material constant of the thin film corresponding to the characteristics of the thin film, in addition to the material constant of the bulk material.
[0021]
FIG. 3 is a conceptual diagram showing a design procedure of the surface acoustic wave device of the present embodiment. A change in the characteristics of the thin film 102 on the substrate 101 means that there is a change in the material constant of the thin film 102. When the material constant of the thin film 102 varies, the device characteristics of the device including the thin film 102 also vary.
[0022]
In general, surface acoustic wave devices can find a plurality of device characteristics, such as surface acoustic wave propagation velocity, electromechanical coupling coefficient, propagation loss, etc., and these device characteristics are mutually related to the thin film 102. The dependence on material constants is different. Here, a certain device characteristic among the device characteristics is set as a specific device characteristic. Various theoretical correlations are conceivable between the specific device characteristics and the material constant of the thin film 102. For this reason, by setting an appropriate value as a material constant of the thin film 102 as an assumed value, the material constant of the thin film 102 and parameters other than the thin film as necessary can be set based on an appropriate calculation method. A virtual value can be calculated. The specific device characteristics can be actually measured by actually creating a device including the thin film 102 and performing measurement.
[0023]
Since the specific device characteristics described above are usually related to a plurality of material constants of the thin film 102, the correlation mode is complicated. Therefore, in the present embodiment, it is assumed that the variation in the specific device characteristics is caused by a variation in some of the plurality of material constants of the thin film 102. And let this part be a specific material constant. As the specific material constant, it is desirable to select one that is considered to have the strongest influence on the specific device characteristics, but it may be two or more.
[0024]
In addition, based on the calculation method when the virtual value is calculated, or an appropriate calculation method different from that, how much the specific device characteristics are affected when the specific material constant selected as described above is changed. You can calculate what to give. For example, the ratio between the fluctuation amount of the specific device characteristic and the fluctuation amount of the specific material constant corresponding thereto can be obtained as the change rate. Here, the material constants other than the specific material constant are typically constant. However, other material constants may be set so as to change in a predetermined change mode in accordance with the fluctuation of the specific material constant.
[0025]
Using the rate of change obtained as described above, the virtual value of a specific device characteristic is matched with the measured value or approximate value (approximate curve obtained by an appropriate fitting method such as the least squares method based on the measured value). It is possible to calculate the amount of change in the specific material constant when it is included. For example, a deviation between a virtual value of a specific device characteristic and a measured value or an approximate value is obtained, and a change amount of a specific material constant necessary for the adjustment can be obtained from the deviation and the change rate. . That is, the relationship of change amount of specific material constant × change rate = deviation is used. Thereby, the correction value of the specific material constant can be obtained by the correction value = assuming + change amount. Further, the specific material constant corrected by the above fitting can be directly obtained from the deviation and the change rate and the assumed value of the specific material constant. That is, the relationship of (corrected value−assumed value) × change rate = deviation is used.
[0026]
The above correction value is not the value of the specific material constant of the thin film itself, but merely reflects the influence of the specific device characteristics on the specific material constant. Therefore, in addition to the influence due to the characteristics of the thin film, this correction value includes the influence of material constants other than the specific material constant, the influence due to the device structure, and the like. In addition, the thin film 102 as a component of a surface acoustic wave device can also be evaluated by using the above-described change amount and correction value.
[0027]
Finally, device design is performed using the correction values of the specific material constants. In this device design, device characteristics are derived (predicted) by an appropriate method using the correction values described above, compared with the reference characteristics, or device settings are corrected to obtain the required device characteristics. Design the device structure you have. At this time, as a method of deriving device characteristics using the correction value, an equivalent circuit method described later can be cited. At this stage, the device characteristics to be predicted may be the specific device characteristics or other device characteristics. However, for the specific device characteristics, it is meaningful to predict a device structure different from the actually measured surface acoustic wave device 100.
[0028]
【Example】
Next, a more specific configuration of the embodiment will be described with reference to FIGS. FIG. 4 is a flowchart showing an outline of the design procedure of the surface acoustic wave device according to this embodiment. First, the device structure is provisionally set. The design object of this embodiment is a surface acoustic wave device having a thin film 102 formed on the same substrate 101. Here, a specific device characteristic of the surface acoustic wave device is set, and the dependence of the specific device characteristic on a certain parameter is observed. In this case, it is preferable that all the components other than the thin film 102 are the same, and it is also preferable that the thin film 102 is the same except for one parameter. For example, in the embodiments described below, it is assumed that all the components other than the thin film 102 are the same, and the composition and manufacturing method of the thin film 102 are the same, but the case where only the film thickness of the thin film 102 is changed is considered.
[0029]
The surface acoustic wave device of the present embodiment is a filter, and the surface acoustic wave device 100 includes a pair of IDT components 110 and 120 on a thin film 102 as shown in FIG. The IDT components 110 and 120 are provided with electrode patterns 110S and 120S having an electrode 104S and electrode patterns 110T and 120T having an electrode 104T. The IDT components 110 and 120 have electrodes 104S and 104T, respectively. Are alternately formed on the thin film 102. In addition, sound absorbing materials 130 are formed on both sides of the IDT components 110 and 120, that is, on both sides in the arrangement direction in which the electrodes 104S and 104T are alternately arranged.
[0030]
In the surface acoustic wave device 100 of this embodiment, the substrate 101 is a silicon substrate, the thin film 102 is a ZnO thin film (c-axis orientation), and the electrode is an Al thin film. Here, the wavelength λ of the surface acoustic wave corresponding to the electrode pitch is set to 16 to 24 μm. The thin film 102 can be formed by a sputtering method, for example, a high frequency magnetron sputtering apparatus. In this example, the sputtering power was 200 to 600 W, the target was ZnO, the substrate temperature was about 300 ° C., the degree of vacuum was 5 Pa or less, the Ar flow rate was 50 SCCM, and the O 2 flow rate was 50 SCCM. The formed thin film 102 had a sheet resistance value of several MΩ · cm or more.
[0031]
Next, a virtual value of the specific device characteristic is calculated based on the setting of the device structure. As this specific device characteristic, in this embodiment, the propagation velocity v of the surface acoustic wave generated in the surface acoustic wave device is used. The virtual value of the propagation velocity v of the surface acoustic wave can be obtained according to a predetermined calculation formula. In general, a tensor expression describing a sound wave propagating through an anisotropic piezoelectric medium is as follows. Here, (1) is an equation of motion, (2) is a definition equation of linear strain, (3) is an equation indicating a quasi-static assumption, and (4) is a linear piezoelectric basic formula. In each equation, T is stress, ρ is density, u is displacement, S is strain, D is electrical displacement, E is an electric field, C is an elastic constant, and φ is an electric potential.
[0032]
δT _ij / δx _i = ρ · δ ² u _j / δt ² (1)
S _km = 1/2 (δu _k / δx _m + δu _m / δx _k ) (2)
δD _i / δx _i = 0, E _i = −δφ / δx _i (3)
T _ij = C _ij · S−e _ij · E, D = e · S + ε · E (4)
[0033]
Based on this equation, a surface traveling wave that propagates at the phase velocity v along the x ₁ direction, that is, along the surface of the thin film 102, and has an attenuation coefficient exp [−αωx ₃ / v] in the x ₃ direction, that is, the thickness direction. Assuming that u _i = β _i e ^{−αωx3 / v} · e ^{jω (t−x1 / v)} (i = 1,2,3) and substituting boundary conditions into this, a transcendental equation is obtained, A virtual value of the propagation velocity v of the surface acoustic wave can be obtained by repeatedly performing calculation based on the computer. For each material constant used here, the value of the bulk material of the thin film 102 can be used. In the present embodiment, the elastic constant C among the material constants is a specific material constant. In addition, the calculation method used here is New Ceramics (1993) No. 7 p. 61 “Introduction to Surface Acoustic Wave Engineering-A Simple Equivalent Circuit of IDT” Toshihiro Kojima (hereinafter simply referred to as “Document 1”).
[0034]
FIG. 5 shows a hypothetical value of the propagation velocity v of the surface acoustic wave obtained as described above and the normalized film thickness kh (= 2πTp / λ; where Tp is the thickness of the thin film 102. The solid line A indicates the relationship between λ and the wavelength of the surface acoustic wave.
[0035]
On the other hand, the actual propagation velocity v of the surface acoustic wave of the surface acoustic wave device 100 as shown in FIG. 13 is measured. This measured value is indicated by a triangular point in FIG. As a method of measuring the propagation velocity v, an input signal is applied to the IDT component 110 of the surface acoustic wave device 100 as shown in FIG. 13 to generate a surface acoustic wave having a wavelength λ on the surface of the thin film 102, and the IDT component The time until it is detected at 120 is measured. Unlike the case of FIG. 13 (filter), the surface acoustic wave device has a structure including one input / output IDT and a pair of reflectors arranged on both sides thereof (for example, a resonator). In the case of configuration), the propagation velocity v can be obtained by measuring the propagation time from the input of the signal to the input / output IDT until the detection of the surface acoustic wave of wavelength λ.
[0036]
Further, as shown in FIG. 14, a surface acoustic wave having a wavelength λ is generated by irradiating the surface of the thin film 102 with laser light, and then the surface acoustic wave is generated at an appropriate position by a laser interferometer or the like. It is also possible to obtain it by measuring the time until it is detected. In FIG. 14, 10 is a laser oscillator, 11 is a deflection mirror, 12 is a condenser, 13 is a laser interferometer, and 14 is an oscilloscope. As described above, in the present invention, even when the surface acoustic wave device 100 is not necessarily in a completed state, for example, without forming an electrode pattern, it is assumed that the surface acoustic wave device 100 is formed. What is necessary is just to measure the propagation speed of the surface acoustic wave of wavelength (lambda). However, the measurement may be performed on a structure provided with an electrode pattern. Here, the wavelength λ of the surface acoustic wave to be excited can be controlled by the pulse width of the laser light. Note that a phase velocity scanning method can also be used as a surface acoustic wave excitation method using laser light.
[0037]
In the present embodiment, an approximate curve B shown in FIG. 5 is obtained by using the least square method or the like based on the measured value of the propagation velocity v obtained by the above measurement. For example, the least square method is applied to each measurement point for v = a · exp [−b · kh + c], and the coefficients a, b, and c are obtained. In this case, one or two of the three coefficients may be appropriately fixed, and the remaining coefficients may be obtained by a least square method or the like. Hereinafter, in this embodiment, an approximate value on the approximate curve B is used instead of the measured value. In this way, various parameter values (thickness kh = 2πTp / λ in this embodiment) can be obtained without trial manufacture of a large number of devices (surface acoustic wave device 100) with different thicknesses kh of the thin film 102. The characteristics of the provided thin film can be easily evaluated.
[0038]
Next, the virtual value of the propagation velocity v that is the specific device characteristic when the elastic constant C _ij that is the specific material constant of the thin film 102 is changed by the method for obtaining the virtual value of the propagation velocity v of the surface acoustic wave. Change rate δvc _ij = δv / δC _ij is calculated. The tensor representation [C _ij ] of the elastic constant of the hexagonal piezoelectric material ZnO is represented by a matrix of 6 rows and 6 columns. FIG. 6 shows four independent matrix elements (C ₁₂ = C _{12). 21} , C ₆₆ do not affect the velocity) assumed elastic modulus C ₁₁ (= C ₂₂ ), C ₁₃ (= C ₂₃ ), C ₃₃ , C ₄₄ (= C ₅₅ ) (for example, the value of the above bulk material) These values are used to obtain the above imaginary value.) The difference between the propagation speed when the value obtained by multiplying 0.9 is used and the propagation speed when the value obtained by multiplying 1.1 is used. That is, the change rate dv of the propagation speed is shown. Here, it can be seen that the elastic coefficients C ₁₁ and C ₁₃ greatly affect the propagation velocity v. Further, regarding the elastic coefficients C ₁₁ and C ₁₃ , the rate of change δvc _ij = δv / δC _ij shows a relatively large dependence on the value of the film thickness hk.
[0039]
On the other hand, the deviation Δv between the virtual value and the approximate value is obtained for the propagation velocity v of the surface acoustic wave. FIG. 7 shows the relationship between the deviation Δv and the film thickness kh of the thin film 102. Then, using this deviation Δv and the change rate δvc _ij = δv / δC _ij , the amount of change in the elastic constant necessary for fitting (fitting) the virtual value of the propagation velocity v to the approximate value is obtained. Can do. This calculation process is roughly as follows. First, assuming that the change amount of the elastic constant C _ij corresponding to the deviation Δv is ΔC _ij ,

Is established. When this is expressed by a determinant of m rows to which m sets of Δv are applied,
Y [m] = F [mn] · X [n] (6)
It becomes. Here, Y is an m-row vector indicating m sets of deviations Δv, F is an m-row n-column matrix indicating m sets of propagation rates v of δ columns δvc _ij = δv / δC _ij , and X is n It is a vector which shows the variation | _{change_quantity} (DELTA) _Cij of the elasticity coefficient of a row | line _| column. Here, m is the number of measured values (approximate values) used in the calculation, and n is the number of independent elastic coefficients (that is, the number of unknowns) among the elastic constants C _ij . If m ≧ n, the change amount of the elastic coefficient can be obtained by the least square method or the like.
[0040]
For example, the tensor display of the elastic constant of a hexagonal piezoelectric material ZnO is represented by a matrix of 6 rows and 6 columns, but four independent elastic coefficients C ₁₁ , C ₁₃ , C shown in FIG. _33, the change amount [Delta] C ₁₁ of _{C 44,} [Delta] C _13, [Delta] C _33, when obtaining the [Delta] C _44, since n of the equation (6) is 4, can be calculated by a 4 or more m become. For example, when the m = 4, the four thickness kh = d, e, f, deviation in _{g Y [Δv d, Δv e} , Δv f, Δv g], as well as the elastic modulus and the respective film thickness kh the rate of change F [δvc _11-d corresponding to _{(= δv d / δC 11)} , δvc 11-e (= δv e / δC 11), δvc 11-f (= δv f / δC 11), δvc 11-g (= Δv _g / δC ₁₁ ); δvc _13-d (= δv _d / δC ₁₃ ), δvc _13-e (= δv _e / δC ₁₃ ), δvc _13-f (= δv _f / δC ₁₃ ), δvc _{13 −g} (= δv _g / δC ₁₃ ); δvc _33-d (= δv _d / δC ₃₃ ), δvc _33-e (= δv _e / δC ₃₃ ), δvc _33-f (= δv _f / δC ₃₃ ), δvc _33-g (= δv _g / δC ₃₃ ); δvc _44-d (= δv _{d / δC 44), δvc 44} -e (= δv e / δC 44), δvc 44-f (= δv f / δC 44), δvc 44-g (= δv g / δC 44)] is used. Accordingly, the elastic coefficient change amount X [ΔC ₁₁ , ΔC ₁₃ , ΔC ₃₃ , ΔC ₄₄ ] can be obtained by the method of least squares. That is, the amount of change in the elastic constant required to match the virtual value of the propagation velocity of the surface acoustic wave to the measured value (approximate value) is the amount of change X [ΔC ₁₁ , ΔC of the elastic coefficient obtained as described above. ₁₃ , ΔC ₃₃ , ΔC ₄₄ ].
[0041]
Finally, the assumed elastic modulus value used to determine the virtual value of the propagation velocity v is C _ij ⁰ and the surface acoustic wave propagation velocity variation ΔC _ij determined as described above is used to determine the elasticity. The coefficient correction value C _ij ⁰ + ΔC _ij is obtained.
[0042]
As described above, the elastic constant or the amount of change when the virtual value of the propagation velocity v of the surface acoustic wave is matched with the measured value or the approximate value is obtained. In this way, the virtual value is measured or approximated. FIG. 8 shows the dependence of the propagation velocity v on the film thickness kh when adjusted to. As shown in this figure, it can be seen that the curve C is closer to the measured value than the curve A indicating the virtual value.
[0043]
FIG. 9 shows the film thickness kh dependence of the change amount ΔC _ij of the elastic coefficient necessary for fitting the virtual value to the measured value or approximate value obtained as described above. Here, in calculating the change amount ΔC _ij at each film thickness kh, the values of the change rate δvc _ij and the deviation Δv at m = 4 different film thicknesses kh in the vicinity of the film thickness kh are used. According to this figure, it can be seen that as the film thickness kh falls below 1.0 and further decreases, the amount of change in each elastic coefficient increases rapidly. This seems to show a strong correlation with the internal stress of the thin film 102. Usually, the internal stress of the thin film 102 increases as the film thickness decreases due to a difference in lattice constant and crystal structure with the substrate 101. When the thickness of the thin film 102 is small, the surface of the thin film approaches the interface with the substrate 101. Therefore, the propagation velocity v of the surface acoustic wave propagating through the surface of the thin film 102 is that of the interface portion between the thin film 102 and the substrate 101. Since the film is easily affected, the elastic constant of the thin film 102 is greatly different from the value of the elastic constant of the bulk material. Conversely, when the thickness of the thin film 102 increases, the surface of the thin film 102 moves away from the interface and the internal stress in the vicinity of the surface also decreases. Is less susceptible to the influence of the interface between the thin film 102 and the substrate 101, the elastic constant of the thin film is considered to approach the elastic constant of the bulk material. Therefore, the result of the present embodiment shown in FIG. 9 seems to correctly reflect the characteristics resulting from the internal stress of such a thin film. Further, in this embodiment, it is possible to know in which direction the internal stress of the thin film 102 is generated according to the magnitude of the change amount ΔC _ij of each elastic coefficient.
[0044]
FIG. 10 shows the amount of change Δv of the propagation velocity v of the surface acoustic wave device when the value of each material constant of the thin film 102 of this example is changed by 10%. Here, the elastic constant, piezoelectric constant, and dielectric constant are all changed by 10% uniformly. As shown in this figure, when the piezoelectric constant and the elastic constant are changed, the propagation velocity v changes greatly. Further, it can be seen that the degree of influence of the piezoelectric constant and the elastic constant on the propagation speed v changes depending on the film thickness kh of the thin film 102. Therefore, in the above method, even if the piezoelectric constant is used as the specific material constant instead of the elastic constant, a useful correction value of the material constant can be obtained similarly to the above.
[0045]
In addition to the surface acoustic wave propagation velocity v, the surface acoustic wave electromechanical coupling coefficient k ² , surface acoustic wave propagation loss, and the like can be used as the specific device characteristics. Further, as the parameters of the specific device characteristics, not only the film thickness of the thin film but also, for example, the frequency of the surface acoustic wave can be used.
[0046]
Next, device characteristics other than the propagation velocity of the surface acoustic wave are predicted using the correction value of the elastic constant calculated as described above. In the present embodiment, this characteristic prediction is performed for the filter characteristic (frequency characteristic of insertion loss) of the surface acoustic wave device 100, and an equivalent circuit method is used to predict this characteristic. The equivalent circuit method is a method of setting an equivalent circuit having a structure in which the electrodes 104S and 104T are formed on the thin film 102 and deriving device characteristics from the equivalent circuit.
[0047]
First, as the equivalent circuit, for example, a so-called equivalent circuit of Smith shown in FIG. 11 is used. This equivalent circuit is also described in the above-mentioned document 1, and corresponds to the basic configuration of the IDT components 110 and 120 (the arrangement structure of the pair of electrodes 104S and 104T). Here, the equivalent circuit includes an acoustic input terminal 1, an acoustic output terminal 2, and an electrical terminal 3. When more than one pair of electrodes is provided, the portion corresponding to one electrode in the above-mentioned equivalent circuit is connected in a manner that the acoustic terminals are connected in cascade and the electrical terminals are connected in parallel. What is necessary is just to add according to. Then, it is possible to characteristics predicted by obtaining such circuit constants Z _1, Z _2, C _S transformation ratio gamma _p of the equivalent circuit. These circuit constants can be determined using the finite element method (FEM). This determination method is described in New Ceramics (1995) No. 10 P.M. 67 “Theoretical Determination Method of Equivalent Circuit Constant of Surface Acoustic Wave Device [1] —Basic Concept” —No. 11 P.M. 47 “Theoretical Determination Method of Equivalent Circuit Constant of Surface Acoustic Wave Device [2] —Introduction of Finite Element Method” —No. 12 P.M. 60 “Theoretical determination of equivalent circuit constants of surface acoustic wave devices [3] —Estimation of equivalent circuit constants” is described in detail by Masanori Koshiba.
[0048]
In the determination of the equivalent circuit constants, the modified values were used for the elastic constants, and the values (bulk material values) used when calculating the virtual values were used for the other material constants.
[0049]
Next, the frequency characteristic of the insertion loss of the surface acoustic wave device 100 was obtained based on the equivalent circuit constant determined as described above. The insertion loss corresponds to the amplitude ratio between the input signal and the output signal of the surface acoustic wave device 100 that is a filter. The result is shown in FIG. The insertion loss actually measured with respect to the surface acoustic wave device 100 is shown by the phantom value curve PA of the dashed line in the figure showing the frequency characteristic of the insertion loss obtained by using the assumed value used when obtaining the virtual value for the elastic constant. The frequency characteristic of the loss is indicated by a measured value curve PB indicated by a broken line in the figure, and the frequency characteristic of the insertion loss obtained using the correction value of the present embodiment is indicated by a corrected value curve PC indicated by a solid line in the figure. As shown in this figure, the virtual value curve PA has a peak position in a frequency band that is greatly different from the measurement value curve PB, but the correction value curve PC has a peak position that substantially matches the measurement value curve PB, and It has a curve shape substantially similar to the measured value curve PB.
[0050]
As described above, in the device design method of the present embodiment, the correction value of the characteristic material constant is obtained by reflecting the difference between the virtual value of the specific device characteristic and the measurement value in the specific material constant, and this correction value is used. Characteristic prediction can be performed. And the characteristic obtained by this characteristic prediction substantially corresponds to the measured value of the device characteristic of the actual surface acoustic wave device as shown in the above-mentioned embodiment. Therefore, various characteristics of the surface acoustic wave device are predicted by the characteristic prediction as described above, and the device structure is set so as to match the desired characteristic, or already formed to measure a specific device characteristic. It becomes possible to modify the device structure.
[0051]
In the above-described embodiment, the single-layer piezoelectric thin film 102 is formed on the substrate 101. However, the present invention is not limited to such a layer structure. A piezoelectric thin film formed after a hard thin film is formed thereon, a dielectric thin film is further formed on the piezoelectric thin film on the substrate, an electrode is formed thereon, and an electrode is formed on the substrate. The present invention can be applied to those having various layer structures such as a piezoelectric thin film formed thereon.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic configuration of a surface acoustic wave device including a thin film on a substrate.
FIG. 2 is an explanatory diagram showing a relationship among characteristics of a thin film on a substrate, a material constant of a bulk material, and a material constant of a thin film.
FIG. 3 is an explanatory diagram showing a method for designing a surface acoustic wave device according to an embodiment.
FIG. 4 is a schematic flowchart showing a device design procedure of the embodiment.
FIG. 5 is a graph showing virtual values, measured values, and approximate values of the propagation velocity v of surface acoustic waves.
FIG. 6 is a graph showing a change rate dv of the propagation velocity when each elastic coefficient is changed.
FIG. 7 is a graph showing a deviation Δv between a virtual value of propagation velocity v and an approximate value.
FIG. 8 is a graph showing a virtual value, a measured value, and a fitting value of the propagation velocity v.
FIG. 9 is a graph showing a change amount ΔC _ij of an elastic coefficient obtained by fitting.
FIG. 10 is a graph showing a change amount dv of the propagation velocity v when each material constant is changed.
FIG. 11 is an equivalent circuit diagram of a basic unit of a surface acoustic wave device.
FIG. 12 shows the hypothetical value predicted using the assumed value of the specific material constant, the measured value measured using the assumed value of the specific material constant, and the corrected value predicted using the corrected value of the specific material constant for the frequency characteristics of the insertion loss of the surface acoustic wave device. The graph shown in comparison.
FIG. 13 is a schematic perspective view schematically showing a configuration of a surface acoustic wave device.
FIG. 14 is an explanatory diagram showing a method for measuring the propagation velocity of a surface acoustic wave device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 ... Surface acoustic wave device, 101 ... Substrate, 102 ... Thin film, 104S, 104T ... Electrode, 110, 120 ... IDT component, 110S, 110T ... Electrode pattern, v ... Propagation velocity, [Delta] v ... Deviation, C ... Elastic constant, C _ij ... elastic coefficient, ΔC _ij ... change amount, δvc _ij ... change rate, kh ... film thickness

Claims (8)

In a method for designing a surface acoustic wave device including a piezoelectric thin film formed on a substrate,
A virtual value calculating step of calculating a virtual value of a specific device characteristic of the surface acoustic wave device;
A measurement value measuring step for measuring a measurement value of the specific device characteristic;
It was obtained by changing a specific material constant of the material constants of the thin film used for calculating the virtual value and adjusting the virtual value to the measured value or an approximate value obtained based on the measured value. A specific material constant calculating step for obtaining a correction value of the specific material constant;
A device design step of designing the surface acoustic wave device using the correction value;
A method for designing a surface acoustic wave device, comprising: In the specific material constant calculation step, a change rate of the specific device characteristic with respect to a change in the specific material constant and a deviation of the virtual value with respect to the measured value or the approximate value are obtained, and the change rate and the deviation are used. The surface acoustic wave device design method according to claim 1, wherein the correction value is calculated. 3. The surface acoustic wave device design method according to claim 1, wherein in the device design step, device characteristics are predicted using the correction value, and device design is performed based on the result. 4. The surface acoustic wave device design method according to claim 1, wherein in the measurement value measurement step, the specific device characteristic is measured for a device structure including an electrode. 5. The surface acoustic wave device design method according to claim 1, wherein the specific device characteristic is a surface acoustic wave propagation velocity. In the measurement value measuring step, the surface acoustic wave is generated by irradiating the thin film with laser light, and the propagation velocity is measured by observing the surface acoustic wave by laser interferometry. A method for designing a surface acoustic wave device according to claim 5. The method for designing a surface acoustic wave device according to any one of claims 1 to 6, wherein a material constant of a bulk material is used as an assumed value of the specific material constant for calculating the virtual value. The method for designing a surface acoustic wave device according to any one of claims 1 to 7, wherein the specific material constant is an elastic constant of the thin film.

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