| 摘要 |
PURPOSE:To improve the temperature characteristics of filter without deteriorating the conversion efficiency of comb type electrode, in surface acoustic wave element having the reflector such as ring type surface acoustic filter. CONSTITUTION:Electric signal fed to the terminal 3 is converted into the surface acoustic waves 12, 15 with the input comb type electrode 1 made on the piezoelectric substrate 5, they are reflected orthogonally on the reflectors 6 and 8 to constitute the surface acoustic waves 13, 16, and become the waves 14, 17 with orthogonal reflection on the reflectors 7 and 9 again. They are converted into electric signal at the output comb type electrode 2 and picked up from the terminal 4. On the other hand, the thin film layers 10, 11 made of the material having inverse delay time versus temperature coefficient are constituted so that they can at least cover the reflectors 6-9 except the comb type electrodes 1, 2. Since the filtering performance of the filter is determined with the reflector, the temperature coefficient of filter can sufficiently be improved and the formation of the thin film layer on the comb type electrode is avoided. |
