SURFACE-ACOUSTIC-WAVE PROPERTIES OF ZNO FILMS ON (001)-CUT (110(-PROPAGATING GAAS SUBSTRATES

GaAs has been employed as a material for acoustic charge transport (AC T) devices principally because it is a piezoelectric semiconductor. Ho wever, because GaAs is a weakly piezoelectric material, the surface ac oustic wave (SAW) interdigital transducer (IDT) drive power required t o achieve charge transport is typically about 27 dBm. An enhancement o f the piezoelectric coupling could potentially improve device lifetime , reliability, dynamic range, and decrease device power consumption. T o this end the use of a ZnO film on top of an ACT-like substrate to en hance the piezoelectric coupling has been investigated. Moreover, the ZnO film structure would also make it possible to monolithically integ rate SAW devices and GaAs electronics. In order to provide a basis for the design of such devices, SAW properties are reported, including ve locity, effective piezoelectric coupling constant, and attenuation, me asured on ZnO films sputtered on {001}-cut [110]-propagating GaAs subs trates. The measurements have been performed for the different film th icknesses over the range of 1.6-4 mum and with films of different grai n sizes. IDTs operating between 180 and 360 MHz were fabricated, and a knife-edge laser probe was used to measure the SAW propagation. The m easured data for the velocity shows good agreement with theoretical va lues. The quality of the dc triode-sputtered films was superior to tha t of the rf magnetron-sputtered ones due to higher K2 and less attenua tion. The value of K2 for the 1.6-mum-thick dc triode-sputtered one wa s measured to be 0.75% which is comparable with 1.07% for bulk crystal line ZnO.