Electrical properties of ferroelectric thin-film capacitors with hybrid (Pt,RuO2) electrodes for nonvolatile memory applications

Abstract

For Pb(ZrxTi1−x)O3 (PZT) thin-film capacitors to be used in ferroelectric nonvolatile memories, they must have low polarization fatigue and low leakage currents. PZT capacitors fabricated in our laboratory with RuO2 electrodes exhibit excellent polarization fatigue characteristics, but they have large and variable leakage currents (typically 10−3–10−4 A/cm2 at 1 V). On the other hand, PZT capacitors with Pt electrodes have low leakage currents (typically <10−9 A/cm2 at 1 V), but they undergo severe polarization fatigue. New (Pt,RuO2) hybrid electrodes which result in PZT capacitors that combine the excellent fatigue behavior of RuO2/PZT/RuO2 with the low leakage currents of Pt/PZT/Pt capacitors have been developed. The hybrid electrodes studied are of two main types: one type consisted of Pt/RuO2 or RuO2/Pt double layers, while the other consisted of a codeposited Pt–RuO2 layer. All capacitors discussed here had an RuO2/PZT/hybrid electrode/MgO heterostructure. It will be shown that capacitors with negligible fatigue (up to 1011 switching cycles) and with leakage currents that are two to four orders of magnitude lower than those of RuO2/PZT/RuO2 capacitors can be achieved. In addition, the capacitors with hybrid electrodes have very small retention loss.