Papers by Author: Do Jin Kim

Abstract: A new type of gas sensor was realized by directly depositing carbon nanotube on nano channels of the anodic alumina oxide (AAO) fabricated on p-type silicon substrate. The carbon nanotubes were synthesized by thermal chemical vapor deposition at a very high temperature of 1200 oC to improve the crystallinity. The device fabrication process was also developed. The contact of carbon nanotubes and p-type Si substrate showed a Schottky behavior, and the Schottky barrier height increased with exposure to gases while the overall conductivity decreased. The sensors showed fast response and recovery to ammonia gas upon the filling (400 mTorr) and evacuation.

Abstract: We report the effects of instability with gate dielectrics of pentacene thin film transistors (OTFTs) inverter circuits. We used to the UV sensitive curable resin and poly-4-vinylphenol(PVP) by gate dielectrics. The inverter supply bias is VDD= -40 V. For a given dielectric thickness and applied voltage, pentacene OTFTs with inverter circuits measurements field effect mobility, on-off current ratio, Vth. The field effect mobility 0.03~0.07 cm2/Vs, and the threshold voltage is -3.3 V ~ -8.8 V. The on- and off-state currents ratio is about 103~106. From the OTFT device and inverter circuit measurement, we observed hysteresis behavior was caused by interface states of between the gate insulator and the pentacene semiconductor layer.

Abstract: We report on the effect of the oxygen partial pressure ratio in the sputtering gas mixture on the electrical and magnetic properties of cubic spinel ZnCo₂O₄ thin films grown by reactive magnetron sputtering. The conduction type and carrier concentration in ZnCo₂O₄ films were found to be dependent on the oxygen partial pressure ratio. The maximum electron and hole concentration at 300 K were estimated to be as high as 1.37 × 1020 cm^-3 and 2.81 × 10²⁰ cm^-3, respectively. While an antiferromagnetic coupling was found for n-type ZnCo₂O₄, a ferromagnetic interaction was observable in p-type ZnCo₂O₄, indicating hole-induced ferromagnetic transition in spinel ZnCo₂O₄.