The SAW propagation properties of apiezon wax on 128/spl deg/ Y-X lithium niobate

Apiezon W vacuum sealing wax is an excellent nonpermanent bonding agent for acoustic wave transmission between two solids. It has good compressional and shear mode properties for low-loss acoustic wave transmission. Surface acoustic wave (SAW) measurements were used to investigate the acoustic properties of the wax which was deposited on 128° Y-X lithium niobate patterned with a linear array of interdigital transducer electrodes. The measurements characterized the velocity and propagation loss of two surface wave modes, a generalized SAW (GSAW) mode and a higher velocity Pseudo-SAW (PSAW) mode. The mode characteristics were measured from 40 MHz to above 1.0 GHz. Five different film thicknesses, in the range of 40 nm to 650 nm, were developed by spin coating the wax proportionately dissolved in toluene. The GSAW velocity showed a strong decrease in value from 3900 m/s to 3800 m/s at a film-thickness to acoustic-wavelength ratios of only 0.06. The SAW propagation loss as a function of frequency for the various film thicknesses had some unique characteristics. In the three thicker films the frequency squared increase in the propagation loss in the GSAW mode up to 500 MHz was followed by a sharp decrease in the propagation loss to values at or below the bare substrate at equivalent frequencies. The PSAW mode with a velocity in the range of 4010 to 4020 m/s had a lower loss characteristic than the GSAW modes.