Comparison of Ferroelectric and Piezoelectric Properties of Sol-gel Grown and Sputter Deposited Pb(Zr, Ti)O3 Thin Films

Abstract

A new process for the sputter deposition of Pb(Zr,Ti)O₃ (PZT) thin films from a composite target has been demonstrated. PZT thin films deposited by this sputter technique are compared to those deposited by a standard sol-gel method to determine the suitability of the sputter deposition process, with its inherent advantages, for device manufacturing. Half micron PZT films were deposited by both methods onto identical substrates (Si[(100) 4 inch Cz wafer]/SiO₂/Ti/TiO₂/Pt/TiO₂) followed by sputter-deposited Pt top electrodes. PZT thickness non-uniformities of 0.759% and 0.545% (1sigma/x macr) were obtained for the sol-gel and sputtered films, respectively. While the sputtering target and sol-gel solutions were Zr-rich (Zr/Ti=1.08), RBS results revealed the films to be Ti-rich: for sol-gel, Zr/Ti=0.874, and for sputtered, Zr/Ti=0.926. X-ray diffraction indicated preferred orientations nearly exclusive to the [111] direction for the sputtered films. For the sol-gel PZT, the larger [110] and [100] peaks indicated a more randomly textured film. SEM cross-sections showed both types of PZT to be void-free and homogeneous. The remnant polarization (P_r) and coercive field (E_c) values of the sol-gel films were slightly higher than for their sputtered analogue: for sol-gel, P_r = 27.9 muCldrcm^-2 and E_c = 70.7 kVldrcm^-1, and for sputtered, P_r = 26.5 muCldrcm^-2 and E_c = 63.3 kVldrcm^-1. The sputtered films exhibited a higher dielectric constant, epsiv₃₃ ^sputtered = 858 compared to epsiv₃₃ ^sol-gel = 776. Piezoelectric coefficients, d₃₃, for the sputtered films were found to be 86 pCldrN^-1, in the range of those measured for typical sol-gel films (between 70 and 100 pCldrN^-1). The advantages and disadvantages of both techniques will be discussed in greater detail.