Wide band filter and low loss resonator have been developed using the new piezoelectric material, Langasite. The filter has about three times wider passband compared with the filter utilizing quartz crystal, and the resonator has approximately two to five times smaller equivalent series resistance than that of quartz crystal.We have developed 71MHz BAW filter for GSM base station. Since the filter is made in fundamentals mode, we have to obtain the blank of about 19,um thickness because the frequency constant is 1380kHz.mrn. We tried to obtain the required blank thickness by chemically etching the center area of the blank (thickness: 70,um) from the both sides. Special technology of langasite etching which has big differences compared with usual quartz technology was developed. We have successfully etched the blank to the required thickness using an efficient etchant. The etching area of the blank has a chemically polished surface and it is sufficient for high frequency filters.Two MCF units are used to make a 4-pole langasite filter. The size of the 4-pole langasitefilter is 10.3 X 3.5 mm and it is five times smaller than conventional filter.
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