Leaky SAW with reduced TCF on LT42/Silicon substrates

Abstract

This work is devoted to the reduction of temperature coefficient of frequency (TCF) of leaky-surface-acoustic-wave (LSAW) on (YXl)/42° Lithium Tantalate. Compound single crystal substrates based on LiTaO3 wafers bonded onto Silicon and thinned down to some tens μm are manufactured in that way. The leading idea consists in impeding the natural Tantalate thermal expansion using Silicon limited expansion. 2 GHz resonators have been built on these compound wafers to demonstrate the principle. Temperature-controlled tip-probing tests show on-trench absolute TCF smaller than 7 pmm.K-1. A representative set of resonator has been packaged and tested in a climatic chamber, yielding evidence of TCF much smaller than the one of the single-crystal substrate and even temperature compensation. Perspective and further developments of this work are discussed as a conclusion.