Polarity and Area Dependence of Reliability Characteristics of Sputitered and Sol-Gel Derived Thin Plzt Films for Dram Applications

Abstract

AbstractThe reliability properties of sputtered and sol-gel derived lanthanum doped lead-zirconatetitanate (Pb1-xLax(Zr,Ti)O3) have been studied for DRAM applications. A strong polarity dependence for times-to-breakdown (tbd) and significant space charge effects are observed under constant voltage stressing, and are understood to be related to the movement of oxygen vacancies in the d.c. field. The equilibrium current density attained during d.c. stressing appears to be Schottky emission limited. The endurance of lanthanum doped films to high voltage d.c. stressing improves with increasing lanthanum content and a linear extrapolation of log(tbd) with reciprocal electric field indicates a lifetime of ∼10 years. The low-voltage polarizability of fresh sputtered films depends strongly on the polarity; a.c. stressing leads to hysteresis relaxation. The asymmetry in the response to a.c. stressing is possibly due to the structural asymmetry of the device. Neither tbd nor the fatigue-rate seem to depend on the capacitor area for the areas studied.