Asymmetric Electrical Properties of Half Corbino Hydrogenated Amorphous Silicon Thin-Film Transistor and Its Applications to Flat Panel Displays

Abstract

The half-Corbino hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were fabricated with a five-photomask process used in the processing of the active matrix liquid-crystal displays (AM-LCD). We showed that the a-Si:H half-Corbino TFTs have the asymmetric electrical characteristics under different drain-bias conditions. In comparison to half-Corbino TFT with unpatterned gate electrode, the device parasitic capacitance can be significantly reduced by patterning the gate electrode for same device dimension, while the sub-threshold swing and threshold voltage remain identical for same bias condition. The OFF-current remains below 0.1 pA for all device configurations. Finally, we discuss their potential applications as a driving or switching TFT to various flat panel displays.

Channel Shape Effects on Device Instability of Amorphous Indium–Gallium–Zinc Oxide Thin Film Transistors

“…Even though a-IGZO TFTs has been developed to such an extent that they can be applied to commercialized backplanes in flat panel displays such as active-matrix liquid-crystal display (AMLCD) and active-matrix organic light-emitting diode (AMOLED) [ 7 , 8 ], the reliability issues associated with electrical field, temperature, and light induced instabilities are still challenging issues for the mass production of reliable active-matrix flatpanel displays (AMFPDs) based on a-IGZO TFTs [ 9 , 10 , 11 , 12 , 13 , 14 ]. Among the various parameters that determine the reliability of a-IGZO TFTs, the geometrical shape of the channel for a-IGZO TFTs can be one of the key design parameters to determine the electrical reliability of a-IGZO TFTs [ 15 , 16 , 17 , 18 , 19 , 20 ]. Up until now, comb-shaped electrodes for amorphous silicon solar cells and interdigitated (e.g., fork-shaped) electrodes in TFTs have been predominantly studied for reduction of gate-to-source capacitance which is one of the key requirements for reduction of kick-back voltage.…”

“…This is one of the core parameters in determining image quality in FPDs during operation [ 18 ]. In addition, ring-shaped (or circular type) electrodes, which are one of the variations in the family of Corbino TFTs, were also studied for the enhancement on insights related to device reliability, which might have the strong dependency on asymmetrical electrical characteristics associated with geometrical configuration on electrodes in TFTs [ 15 , 18 ]. Thus, among a variety of channel shapes, U-type channel for pixel transistors in flat panel display backplanes, do have strong merits for achieving low gate-to-source capacitance (C gs ) per area, thereby, the U-shape of channel in pixel transistors has been predominately adopted in AMFPD pixel designs, compared with that of the I-type channel [ 21 , 22 , 23 ].…”

Electrical Stability of Power Efficient Half Corbino Hydrogenated Amorphous Silicon Thin-Film Transistors

“…Detailed process steps can be found in the previous publication. 9) As shown in Fig. 1(b), the fabricated half-Corbino a-Si:H TFT consists of rod-shape inner electrode (radius R 1 ¼ 5 m) and half-circle shape outer electrode (radius R 2 ¼ 11 m) while fork-shaped a-Si:H TFT [ Fig.…”

“…11) Then, we changed the drain bias condition (drain current on rod shape electrode), and repeated the same CTS measurement for both TFTs. Using the effective channel width calculated by Lee et al, 9,10) we extracted the threshold voltages using the maximum slope method over the stress time for each drain bias condition. 9) The threshold voltage shift (ÁV th ) is defined as follows:…”

“…Using half-Corbino geometry, we can achieve a larger W=L by about 1.6 times than fork-shaped TFT over the similar device area. 9) In general, when the TFT is used as a driving transistor in AMOLED pixel circuit, it always suffers electrical stress by the OLED current since OLED is a current-driven device. Therefore, by using half-Corbino TFT as a driving TFT in the pixel circuit, we can expect a large enhancement in the electrical stability of pixel circuit for AMOLED due to the reduction of the effective channel width of transistor.…”