Short channel amorphous In–Ga–Zn–O thin-film transistor arrays for ultra-high definition active matrix liquid crystal displays: Electrical properties and stability

Keywords: In–Ga–Zn–O Thin-film transistor Active matrix liquid crystal display (AM-LCD) Short channel effect Tikhonov's regularization AC bias-temperature stress stability (AC BTS) a b s t r a c t The electrical properties and stability of ultra-high definition (UHD) amorphous In–Ga–Zn–O (a-IGZO) thin-film transistor (TFT) arrays with short channel (width/length = 12/3 lm) were examined. A-IGZO TFT arrays have a mobility of $6 cm 2 /V s, subthreshold swing (S.S.) of 0.34 V/decade, threshold voltage of 3.32 V, and drain current (I d) on/off ratio of <10 9 with I off below 10 À13 A. Overall these devices showed slightly different electrical characteristics as compared to the long channel devices; non-saturation of output curve at high drain-to-source voltage (V ds), negative shift of threshold voltage with increasing V ds , and the mobility reduction at high gate voltage (V gs) were observed. The second derivative method adopting Tikhonov's regularization theory is suggested for the robust threshold voltage extraction. The temperature dependency of c-value was established after taking into consideration the impact of sour-ce/drain contact resistances. The AC bias-temperature stress was used to simulate the actual operation of active matrix liquid crystal displays (AM-LCDs). The threshold voltage shift had a dependency on the magnitude of drain bias stress, frequency, and duty cycle due to the impact ionization accelerated at high temperature. This study demonstrates that the short channel effects, source/drain contact resistances and impact ionization have to be taken into account during optimization of UHD AM-LCDs. Oxide semiconductors such as an amorphous indium gallium zinc oxide (a-IGZO) have been intensively studied for past ten years especially for the application to next generation flat panel displays [1–3]. Superior characteristics of the a-IGZO thin film transistors (TFTs) as compared to the hydrogenated amorphous Si (a-Si:H) TFTs such as a high field effect mobility and transparency have increased their potential to become switching or driving transistors in next generation active matrix liquid crystal display (AM-LCD) or active matrix organic light emitting diode (AM-OLED), respectively. Today it has been already established that a-IGZO TFTs can be processed uniformly over large-size area at low temperature, and can use existing active-matrix arrays production infrastructure [4–6]. Recently, the high-end displays with the ultra-high definition (UHD > $4000 Â 2000 pixels), large-area (>70 in.), and high frame rate (>240 Hz) are being introduced to realize displays with more realistic visual images [7]. To fabricate such displays, the dimension of TFTs, …