• Korean Journal of Materials Research
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• v.4 no.7
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• pp.759-766
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• 1994

Our investigation aimed to reduce the leakage current of $Ta_2O_5$ thin film capacitor by layering SnOz thin film layer under Ta thin film, thereby supplying extra oxygen ions from the $SnO_{2}$ underlayer to enhance the stoichiometry of $Ta_2O_5$ during the oxidation of Ta thin film. Tantalum was evaporated by e-beam or sputtered on p-Si wafers with various deposition temperatures and was oxidized by dry--oxygen at the temperatures between $500^{\circ}C$ and $900^{\circ}C$. Aluminum top and bottom electrodes were formed to make Al/$Ta_2O_5$/p-Si/Al or $Al/Ta_2O_5/SnO_2$p-Si/AI MIS type capacitors. LCR meter and pico-ammeter were used to measure the dielectric constants and leakage currents of the prepared thm film capacitors. XRD, AES and ESCA were employed to confirm the crystallization of the thin f~lm and the compositions of the films. Dielectric constant of $Ta_2O_5$ thin film capacitor with $SnO_{2}$ underlayer was found to be about 200, which is about 10 times higher than that of $Ta_2O_5$ thin film capacitor without $SnO_{2}$ underlayer. In addition, higher oxidation temperatures increased the dielectric constants and reduced the leakage current. Higher deposition temperature generally gave lower leakage current. $Ta_2O_5/SnO_2$ capacitor deposited at $200^{\circ}C$ and oxidized at $800^{\circ}C$ showed significantly lower leakage current, $10^{-7}A/\textrm{cm}^2$ at $4 \times 10^{5}$V/cm, compared to the one without $SnO_{2}$ underlayer. XRD showed that $Ta_2O_5$ thin film was crystallized above $700^{\circ}C$. AES and ESCA showed that initially the $SnO_{2}$, underlayer supplied oxygen ions to oxidize the Ta layer, however, Sn also diffused into the Ta thin film layer to form a new $Ta_xSn_YO_Z$ , ternary oxide layer after all.

• Journal of Korean Society of Forest Science
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• v.108 no.3
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• pp.290-295
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• 2019

This study was carried out to investigate the possibility of establishing a reproductive system for the seed of Pedicularis hallaisanensis, which is in the endangered wild species II class in Korea. The seed of P. hallaisanensis is egg-shaped, and the seed coat is dark brown. The embryo was identified as a dwarf type by the seed section. The seed length was $0.47{\pm}0.07mm$, width $0.16{\pm}0.006mm$, and thickness $0.12{\pm}0.01mm$. The weight of one seed was $0.0003{\pm}0.0001mg$, and 1000 seeds weighed $4.59{\pm}0.02mg$. The degree of seed viability was 75.33% by the tetrazolium (TZ) assay. The highest germination rate of P. hallaisanensis seed was 71% after 4 weeks of storage at $4^{\circ}C$. However, the germination rate tended to decrease gradually over a longer storage period. The germination rates after 6 or 8 weeks of storage at $4^{\circ}C$ were 64% and 60%, respectively. We used two host plants, Artemisia princeps and Dendranthema zawadskii, to determine the effect of host plants on P. hallaisanensis seed germination. The germination of P. hallaisanensis mixed with A. princeps or D. zawadskii started at 53.5 and 62.5 days after sowing, respectively. We did not find any germination 164 days postsowing with both host plants. When A. princeps and D. zawadskii were used as host plants for P. hallaisanensis seed germination, P. hallaisanensis seed germination rates were 45.5% and 19.5%, respectively. The average time to germination was 70.2 days for A. princeps, and 46.8 days for D. zawadskii.