CHARGE TRAPPING AND DEVICE BEHAVIOR IN FERROELECTRIC MEMORIES

The electric field emanating from the surface of a poled ferroelectric (FE) can control the conduction properties of an overlying semiconduc ting (SC) film; this combination of materials can thus serve as a nond estructive readout (NDRO), nonvolatile memory device. We have characte rized prototypes of these devices which utilize semiconducting In2O3 d eposited on thin film lead zirconate titanate and bulk BaTiO3 FEs. The remanent state SC resistance in thin film FE NDRO devices is often op posite to that predicted from the known direction of FE polarization. In these cases charge injected from the SC him into the FE and trapped near the interface appears to control the electric field at the SC/FE interface. By contrast, the response of SC films on bulk FEs is large ly controlled by just the FE remanent polarization. The measured SC re sistance values in the ''up'' and ''down'' polarization states can be fairly accurately predicted by calculating the accumulation and deplet ion charge densities from the measured carrier concentrations, mobilit ies, and FE hysteresis behavior. We also observe a correlation between charge trapping in bulk and thin film of NDRO memory devices and the presence or absence of temperature-bias-stress-induced voltage shifts (imprint) of the FE hysteresis curves. We suggest that the presence of near-interfacial traps in the FE controls both imprint and NDRO memor y response. (C) 1996 American Institute of Physics.