Abstract. MgO thin films with either (111) or (200) preferential orientation have been prepared on (100) Si substrates by sol-gel method after a heat-treatment at 800~ The obtained (111) preferentially oriented MgO film has a dielectric constant of 7.0 with a loss factor of 5% and a dielectric strength higher than 8 • 105 V/cm. The optical refractive index, which depends on the film thickness, is 1.71 when the film thickness is 260 nm. The surface structure of the Si substrate is believed to affect the preferential orientation of the sol-gel derived MgO film. Specifically, the microstructures at the interface indicate an interdiffusion of Mg, O, and Si between the film and the substrate.
KaohsiungTo investigate the effect of reoxidation on the grainboundary acceptor-state density of reduced barium titanate, n-doped BaTiOa ceramics are sintered in a reducing atmosphere (2% H2 + 98% N2) and then annealed in oxygen.After annealing at 1150°C for different times, the experimental results show a relationship between temperatureaveraged acceptor-state density and annealing time as N, = N,,Bt'/" with n between 2 and 3. An inherent acceptorstate density N,, = 4.25 X 10" cm-' is obtained with an increase rate B = 4.8 X 10" cm-2-min-1/3, when n reaches 3. The inherent grain-boundary acceptor states in the reduced n-doped BaTi03 ceramics are believed not due to adsorbed oxygen ions. [
Semiconducting BaTiO, ceramics have been prepared by adding BN as a sintering aid. Density as high as 93% of theoretical and grain size as large as 16 pm are obtained after sintering at 1160°C. Most significant is that the semiconducting BaTiO, is obtained at sintering temperatures as low as 1100°C. The low-temperature-sintered BaTiO, exhibits a positive temperature coefficient (PTC) anomaly above 120°C with a resistivity maximum at a temperature as high as 400"C, which is much higher than that of the conventional BaTiO,. The incorporation of B into the perovskite structure is negligible. Also, the presence of B at a grain boundary after sintering is believed to enhance the PTC effect.
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