RESEARCH INTO NEW APPROACHES FOR VHF FILTER CRYSTALS.
Abstract
Elastic wave theory for loss-less wafers includes a cut-off phenomenon, with the thickness shear resonance for the infinite wafer as the cut-off frequency. An extensive introduction discusses the significance of theory and the resulting trapped-energy modes, where the vibratory energy can be confined to the immediate vicinity of the electroded resonator on a large quartz wafer. Energy trapping gives a theoretical basis for the high Qm observed for resonators on large AT-cut quartz wafers, even when damping materials are applied at wafer edges. Confirmation of theory has been obtained qualitatively for mass-loaded and etched-mesa AT-cut resonators, and quantitatively for mechanical coupling measurements between resonator and absorbing wafer edge, and between pairs of resonators on the same wafer. Simple theory is proposed to explain existence of strong inharmonic overtone modes and also conditions for their suppression. In an idealized two-dimensional wafer, this leads to a desing criterion relating wafer thickness and electrode dimension with electrode massloading. Initial experiments with deep-etched mesa resonators have yielded improved values of Qm and interesting spurious response spectra which might be associated with inharmonic overtones. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 09, 1963
- Accession Number
- AD0426100
Entities
People
- D. J. Koneval
- Damian Curran