Acoustic-bulk-wave resonators and filters operating in the fundamental mode at frequencies greater than 100 MHz
A localised ion-beam milling has been used to increase the fundamental frequency of acoustic-bulk-wave resonators. Monolithic filters in lithium niobate (Y+37°) and lithium tantalate (X) operating, respectively, at 220 and 230 MHz have been realised. The relative bandwidth is equal to 1% and the insertion loss is about 4 dB. An a.t.-cut quartz resonator working in the fundamental mode at 270 MHz with a Q-factor of 12 000 has also been obtained. In this case, the vibrating membrane is 6 μm thick, with a centre portion of diameter 2.5 mm.
