Improved switching endurance of lead zirconate-titanate capacitors for nonvolatile memory applications

Abstract

For nonvolatile memory applications, thin-film ferroelectric capacitors having high level of switching endurance (or ferroelectric fatigue limit) are required. This paper presents results that demonstrate improved endurance characteristics in our semiconductor-device quality, sol-gel derived lead zirconate-titanate (PZT) capacitors compared to other published results under comparable test conditions. These improved endurance characteristics have been obtained through continued developments in the PZT film deposition process, electrode metallization and capacitor fabrication techniques. Capacitors with top electrode of gold, platinum or palladium film and bottom electrode of platinum-titanium film were tested for endurance and related properties of transient current response, leakage current density, and small-signal capacitance-voltage and conductance-voltage characteristics. An alloying heat treatment of the gold or platinum top electrode to the PZT film significantly improved the endurance characteristics, apparently by decreasing the leakage current density. Capacitors with Pt top electrode that were alloyed at a lower than optimum temperature exhibited abnormal hysteresis loop changes after mid-109 cycles. Some evidence indicated that these changes were related to an increase in the leakage current density.