Effect of porosity on the ferroelectric properties of sol-gel prepared lead zirconate titanate thin films

Pb(Zr_0.3Ti_0.7)O₃ (PZT) thin films are of major interest in micro-electro-mechanical systems for their ability to provide electro-mechanical coupling and pyroelectric coupling. In this work, dense, crack-free PZT thin films have been obtained on silicon substrates up to a thickness of 3 μm. Piezoelectric coefficients d_33,f and e _31,f of sol-gel processed films were investigated as a function of film thickness. Both d_33,f (- 50∼- 90 pC/N ) and e _31,f (2.5∼4 C/m² ) values have been obtained in the whole thickness range of 1-3 μm. Increasing the thickness of a single layer introduced pores into the films. Up to 700 nm porous, crack-free single layers could be obtained. It was found that the introduction of pores into the thin films decreased the dielectric constant. Therefore, it helps increase the pyroelectric performance. A dense PZT thin film (700 nm) has dielectric constant, F_d and F_v of 372, 1.02 × 10^{- 5} Pa^{- 0.5} and 0.022 m²/C, respectively, while a porous thin film (700 nm) with porosity of 3% has dielectric constant, F_d and F_v of 210, 1.32 × 10^{- 5} Pa^{- 0.5} and 0. 031 m²/C, respectively.