Electrical and pyroelectric properties of lithium tantalate thin films

Thin films of lithium tantalate have been deposited by RF sputtering on SiO2-coated silicon substrates. Either a planar structure with RuO2 interdigitated top electrodes or sandwich structure including a sputter-deposited RuO2 buried layer have been used. The dielectric properties and the ac resistivity of the tantalate films have been investigated as a function of frequency and of temperature. At room temperature and 1 kHz the dielectric constant is 40 and the resistivity is 2X108 Ωcm for a RuO2/tantalate/RuO2 sandwich structure. The resistivity is typically 100 times larger when measured on a planar structure. The ferroelectric and pyroelectric properties of either unpoled or poled lithium tantalate thin films have also been investigated. At room temperature, the maximum pyroelectric current and voitage response are 11μA/W and 19 V/W, respectively. In comparison with the planar structures, the sandwich structures exhibit a degraded response. This is attributed to a reaction of the tantalate layer with the RuO2 buried layer during the crystallization processing step.