Scaling Properties in the Electrical and Reliability Characteristics of Lead-Zirconate-Titanate (PZT) Ferroelectric Thin Film Capacitors

Abstract

This paper investigates the issues in the scaling of thin film PZT (Lead-Zirconate-Titanate) capacitors for DRAM (Dynamic Random Access Memories) applications. The test structures used were MIM (metal-insulator-metal) capacitors with platinum electrodes and PZT deposited using a sol-gel process. Charge storage density (Q'c), leakage current density (JL), unipolar switching time to 10% decay (ts), time dependent dielectric breakdown (TDDB) and electrical fatigue have been analyzed. Unipolar switching time has been modeled as an RC time constant, where C is electric-field dependent. Q'c at a given electric field appears to remain constant over the range of film thicknesses and electrode areas studied. Leakage current density and time-to-breakdown (tBD) for a given electric field degrade with decreasing film thickness. Unipolar stressing causes considerably less fatigue than bipolar stressing, and after 2 × 1011 cycles, a 400nm film still exhibits sufficient Q'c for DRAM operation.

Leakage current mechanism and accelerated unified test of lead zirconate titanate thin film capacitors

“…In order to improve leakage current and breakdown properties for such films, the mechanisms for these phenomena should be understood extensively. Leakage current and TDDB of PZT films on Pt electrodes have been reported by some authors [5,6]. source of such conduction was investigated for PZT films on both Pt and RuO, electrodes.…”