| 초록 |
Recently, ZnO based thin film transistor is attracting great interests for transparent and flexible displays. Atomic layer deposition (ALD) can be a good deposition technique for display applications since it can produce films with good uniformity over large area at relatively low growth temperature. However, the ALD of ZnO from diethyl Zn as a precursor and water or ozone for reactant generally results in intrinsically high carrier concentration (＞ 10^17 /cm3). This is a significant drawback for the application to TFT channel material, since large off current is expected. In this research, we developed an efficient way to control the carrier concentration in the ALD ZnO films. Nitrogen doping was achieved in situ during ZnO ALD by using NH4OH as reactants. By nitrogen doping, grain size of ZnO films were reduced and, more importantly, the carrier concentrations were reduced to ＜ 10^15 /cm3. Inverted staggered type TFTs with ALD Al2O3 as a gate insulator were fabricated at low process temperatures lower than 150 °C on glass substrate. Very good device properties were achieved; usat = 7 cm2/Vs, and Ioff ＜ 3 × 10^-12 A and Ion /Ioff ＞ 10^8. Also, the hysteresis and subthreashold swing of the TFTs were low, about 0.5 V and 0.7 V/dec, respectively. ZnO:N TFT with higher saturation mobility (~20 cm2/Vs) was also fabricated on plastic substrate. |
