| 摘要 |
PURPOSE:To make it possible to adjust easily the center frequency of a filter in the negative direction, by adjusting an applied voltage to control the thickness of the oxide film of a reed screen type Al electrode when ammonium borate solution is used as an electrolyte to subject the filter to the anodic oxidation processing. CONSTITUTION:Surface elastic wave filter 10 where film thickness h0 of a Al is 3,000Angstrom and piezoelectric substrate 11 is constituted by ST-crystal or rotation direction 42 deg.56' and a surface elastic wave filter where film thickness h0 is 2,000Angstrom and the piezoelectric substrate is constituted by ST-crystal of rotation direction 42 deg.00' are prepared and are soaked in bath 21 where ammonium borate solution is electrolyte 22, and the applied voltage is set to 0V, 50V, 100V, 150V and 200V to subject them to anodic oxidation. When insertion loss-frequency characteristic and temperature characteristic are measured for the sample dependent upon this method, the frequency is shifted to the negative direction according to the applied voltage, and the shift quantity is approximately proportional to the applied voltage, however, the temperature characteristic is hardly changed independently of formation of the oxide film. Consequently, the center frequency of the filter can be adjusted in the negative direction easily. |
