Kyung Haeng Lee

Preparations of PZT Thin Film Capacitors on PtRhOx Electrodes With Various Conducting Barriers for High Density Ferroelectric Memories

We have investigated the high quality electrode-barriers for Pb(Zr0.35Ti0.65)O3 (PZT) thin film capacitors to contact directly on W-plug for COB (capacitor-over-bit line) structured high density ferroelectric memories (FRAM). A conducting oxide of 40-nm-thickness PtRhOx was used as a fatigue free electrode for PZT capacitors. Various materials, such as Ta, NiCr (Ni with 20 wt% Cr), Cr and PtRh (Pt with 10 wt% Rh), were investigated as conducting oxygen diffusion barriers between PtRhOx bottom electrode and W-plug. It was found that PZT capacitors with Ta-barriers of 30-nm-thickness showed superior thermal stability up to 630°C, whose remanent polarization and coercive field were typically 30 μ C/cm2 and 86 kV/cm, respectively. However, their polarization fatigue behaviors are associated with the oxygen content in PtRhOx electrodes.

PREPARATION OF Pb(Zr0.35Ti0.65)O3 FILMS ON CONDUCTING OXIDE Ga-DOPED ZnO FILMS FOR TRANSPARENT FERROELECTRIC THIN-FILM TRANSISTORS

ABSTRACT We have investigated the feasibility of the deposition of ferroelectric PZT films on transparent conducting Ga-doped ZnO (GZO) films, for transparent ferroelectric thin-film transistors. Low resistive and high c-axis oriented GZO films are prepared at the substrate temperature of 250°C using the dc magnetron sputtering method. PZT films are deposited at low substrate temperature and subsequently crystallized by means of the rapid annealing process in a high vacuum to minimize the reaction of PZT with GZO films. Various vacuum-annealing conditions are investigated to get high-quality PZT films, which show single perovskite phase with a random orientation. The optimized PZT/GZO capacitors have somewhat unsaturated P-E hysteresis loops with the values of remanent polarization and coercive field of about 4.5 μC/cm2 and 145 kV/cm, respectively.

Characteristics of ferroelectric Pb(Zr/sub 1-x/Ti/sub x/)O/sub 3/ thin film capacitors deposited on PtRhO/sub y/ electrode barriers

We present the feasibility of single-layer PtRhO/sub y/ thin films as electrode barriers for ferroelectric Pb(Zr/sub 1-x/Ti/sub x/)O/sub 3/ (PZT) (x = 0.2 to 0.8) thin film capacitors. PtRhO/sub y/ thin films were deposited directly on n+ Si wafers by means of the reactive sputtering method. PtRhO/sub y//PZT/PtRhO/sub y//n+ Si capacitors showed well-saturated P-E hysteresis loops. The remanent polarizations, as well as the polarization loss after the switching repetitions, were varied with the ratio of Zr/Ti. Especially, Pb(Zr/sub 0.4/Ti/sub 0.6/)O/sub 3/ thin film capacitor showed the superior ferroelectric properties, such as the shape of P-E hysteresis loops and the behaviors of the polarization fatigue. The typical remanent polarization and the coercive field of this capacitor were 22 /spl mu/C/cm/sup 2/ and 87 kV/cm, respectively, and the polarization loss was only less than 5 % after 10/sup 11/ switching repetitions. The chemical binding states of PtRhO/sub y/ films affected mainly the shape of P-E hysteresis loops. From the measurement of the depth profile and the microstructure of this capacitor, it could be convinced that single-layer PtRhO/sub x/ films behaved as high quality electrode barriers for PZT thin film capacitors.

Photo-induced changes of thermally stimulated conductivity spectra in undoped hydrogenated amorphous silicon

Abstract The changes in the gap state distributions produced by light soaking in undoped a-Si:H prepared by remote-plasma chemical vapour deposition were determined from the simultaneous measurement of thermally stimulated conductivity and low-intensity photoconductivity. The temperature dependence and the changes of the product of the microscopic mobility and the recombination lifetime, μ m τ r , produced by light soaking were also determined. In the gap profiles in the energy interval between 0.2 and 0.8 eV below the conduction band edge, at least two electron traps are found at 0.30 ± 0.02 and 0.54 ± 0.02 eV. The density of the trap located at 0.54 eV due to the doubly occupied dangling bond, D − , is increased by light soaking together with a simultaneous decrease of traps located at 0.30 eV due to the weak bonds. These effects are interpreted as defect creation and annealing, respectively. The temperature dependence of the μ m τ r product is found to be due to that of μ m , and thermal quenching and light quenching of μ m τ r are mainly due to those of τ r .