Electrostatically variable SAW delay lines - Theory and experiment

A change in surface acoustic wave time-delay produced by applying a dc electric field is investigated theoretically and experimentally. Measurements are carried out on three high-coupling cuts of LiNbO3 and the electric field is applied in the plane of the surface with a novel electrode configuration and normal-to-the-surface- with a convolver plate. A theory is developed for the normal field configuration, where the electric field is uniform, and for the in-plane field configuration, where the field is nonuniform. It is shown that although the normal field has a higher intrinsic sensitivity than the in-plane field, the latter has lower insertion loss and dispersion and is easy to fabricate due to the noncritical substrate thickness. For a 0.16 mm thick 16.5 deg doubly rotated sample, a fractional time-delay change of 9.3 x 10 to the -7th/V is found. The time-delay change is shown to be very linear with applied voltage. Both electrode configurations yield monolithic devices that are compact, lightweight, and consume no dc power.