INTERFACE ACOUSTIC MODES OF TWISTED SI(001) WAFERS

Interface acoustic waves at the (001) boundary of twisted single-cryst al silicon wafers are studied using analytical and numerical technique s. A secular equation of the problem in an explicit form is derived fo r the propagation directions along the twist-angle bisectrix and a com plete numerical solution is calculated for arbitrary propagation. A ne w mode of leaky-wave type is predicted. This leaky mode has a low prop agation loss and distinct near-interface localization at small twist a ngles. The leaky wave is purely longitudinal at the interface in the b isectric case. A mode without leakage is found only in the vicinity of the bisectrix directions. Its feature is a rotating movement of inter face particles in the plane normal to the propagation direction in the bisectrix case. The sector of azimuthal angles permitted for the prop agation of the nonleaky mode has an unusual jumplike behavior as a fun ction of the twist angle. (C) 1998 American Institute of Physics.