Investigation and Control of Ferroelectric / Conductor Interface Phenomena and Their Applications to Memory Devices

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The growth conditions for Pt, Ir and IrO_2 electrodes in PZT capacitors by sputtering and for PZT by MOCVD were optimized. Oriented IrO_2 films were successfuly obtained by RF sputtering using a ceramic IrO_2 target for the first time. Ferroelectric PZT thin films were also grown successfully on these electrodes.The mutual diffusion between PZT thin film and electrode materials was investigated by SIMS (Secondary Ion Mass Spectroscopy) measurements. Their measurments indicated that Ir and Ir/IrO_2 provided a much better barrier for Pb, Zr and Ti than Pt. PZT capacitors with Ir, IrO_2 and Ir/IrO_2 bottom electrodes showed a lower dielectric constant and remanent polarization, and a larger coercive field than those of PZT capacitors using both top and bottom Pt electrodes due to their poor crystalline quality. PZT capacitors with both Ir and IrO_2 top and bottom electrodes (Ir/IrO_2/PZT/Ir/IrO_2/SiO_2/Si) showed no fatigue up to a switching cycle of 10^<11>.Using the energy dispersive type total reflection X-ray diffraction method, crystalline structure and distortion of the PbTio_3 and PZT films grown on Pt/MgO were investigated.The interface between the layrs in ferroelectric/conductor/semiconductor structure was evaluated by the C-V measurement and the DLTS (Deep Level Transient Spectroscopy) method. From these measurements it was found that there exsisted some interface states at the PZT/Si interface. More details regarding the effects of photoexcitation on the interface sstate are now under investigation.