超音波顕微鏡によるSAWフィルタ用ガラス基板の評価

抄録

When we have been manufacturing ZnO/glass SAW filters, the trouble has happened that the frequency of filter changed largely when the production lot of glass sheets changed. The other trouble has happened that the SAW filters of same production lot of glass sheet had double peak frequency distribution of largely separated. Previously it has been considered that the frequency deviation in the ZnO/glass SAW filters was dependent on the elastic quality of the ZnO thin films, the thickness of the ZnO films, and soon. But, we have noticed that the frequency deviation in ZnO/glass SAW filters was dependent on the deviation of elastic quality in the glass substrates. We have measured the leaky SAW (LSAW) velocities of two kinds of glass substrates, P-glass and B-glass, by LFB acoustic microscopy technique. As the result, we have discovered the large LSAW deviation in P-glass substrates between different production lots of glass sheets, and large LSAW deviation in B-glass substrates in one production lot of glass sheets. We investigated a cause of LSAW deviation still more, discovered that large LSAW deviation in glass substrates was dependent on the heat treatments process in the production of glass sheets. We have calculated the elastic constants, C₁₁, C₁₂, C₄₄ of glass substrates of different LSAW velocity, using experimental results of LSAW velocity, longitudinal velocity, and the density of glass substrates. Consequently, it has become clear that the two glass substrates with the different LSAW velocity (both P-glass and B-glass) had different densities and more different elastic constants.