| 학회 | 한국재료학회 |
| 학술대회 | 2010년 가을 (11/11 ~ 11/12, 무주리조트) |
| 권호 | 16권 2호 |
| 발표분야 | F. Display and optic Materials and processing(디스플레이 및 광 재료) |
| 제목 | Analysis of the activation energy of the subthreshold current in oxide-based thin film transistors |
| 초록 | Recently, ZnO-based wide band gap semiconductors are promising alternatives to a-Si TFTs that relatively low field effect mobility. Especially, most of research groups are concentrated on employing a-IGZO thin films as an active channel layer due to the high mobility, uniformity, transparency, and low temperature process. However, they still have some limitation such as instability under external conditions to apply into commercial products. In other words, in order to make a-IGZO TFTs acceptable for various applications, the temperature-dependent instability, and the sensitivity to optical illumination is very important problems. First, in this study, we tried to employ the new oxide-based materials as an active channel layer of TFTs. Sn was introduced into ZnO system as an amorphizer with Zn/Sn=3 ratio. In order to obtain the higher and more stable device performance, we used Hf doping method as a role of stabilizer which could be suppressed to generate oxygen vacancies and zinc interstitials. Also, threshold voltage stability was examined under negative bias temperature stress for a-Hf-Zn-Sn-O (a-HZTO) TFTs deposited at room temperature and annealing with different temperatures in wet air atmosphere. In order to compare device characteristics between a-HZTO TFTs and the others, we fabricated intrinsic ZnO (i-ZnO) and Hf-doped ZnO (HZO) TFTs. Analysis of the thermal and gate-voltage dependences of the current in the subthreshold region is performed on the i-ZnO, HZO, and a-HZTO TFTs. Temperature measurements are made at first in order to extract the variations of the activation energy (EA) of the drain current with the gate voltage. The subthreshold current in oxide-based TFTs described by the thermally activated Arrhenius model, where it is assumed that thermally activated electrons from the deep level trap sites into the conduction band move quickly toward the drain electrode. Hence, the rate-limiting process would be the thermal excitation of the trapped charge and the conductance EA can be calculated as a function of VGS in the forbidden band gap from the fitting of the temperature-dependent log (IDS) versus 1/T curve. From the variation of falling rate of EA in the oxide-based TFTs, we can verify that total trap density including the semiconductor bulk gap-state density (NSS) and interfacial trap density (Nit). Moreover, this result is strongly corroborated by the fact that Nit values of oxide-based TFTs, where these values were calculated form subthreshold swing values. |
| 저자 | Yeon-Keon Moon1, Woong-Sun Kim2, Kyung-Taek Kim1, Se-Young Shin2, Jong-Wan Park1 |
| 소속 | 1Department of Materials Science and Engineering, 2Hanyang Univ. |
| 키워드 | oxide-based TFT; amorphous HfZnSnO; stabiliy; trap density; activation energy |
