Seong-Hyun Jin

High-Performance Homojunction a-IGZO TFTs With Selectively Defined Low-Resistive a-IGZO Source/Drain Electrodes

We report high-performance homojunction amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with low-resistive a-IGZO source/drain (S/D) electrodes. The a-IGZO S/D electrodes are selectively treated with high-power NF3 plasma, which reduces their resistivity from ~16 to 5.5×10-3 Ω · cm. X-ray photoelectron spectroscopy indicates an increase in weakly bonded oxygen and a substantial amount of indium-fluorine and zinc-fluorine bonds at the a-IGZO top surface (extending to ~7 nm into the bulk) after plasma treatment. Temperature-dependent conductivity measurements show metallic behavior of the a-IGZO after treatment. It is concluded that fluorine atoms substitute for oxygen atoms-generating free electrons in the process and/or occupy oxygen vacancy sites-eliminating electron trap sites. As a result, the homojunction TFTs show good ON-state characteristics with typical field-effect mobility, subthreshold gate-voltage swing, and turn-ON voltage of 19 ± 1 cm2/V·s, 178 ± 30 mV/decade, and -3.2 ± 1.5 V, respectively. Good stability at high temperature and under bias and light stress are also exhibited by the homojunction TFTs, verifying a stable doping effect by the NF3 plasma treatment.

Reduction of Positive-Bias-Stress Effects in Bulk-Accumulation Amorphous-InGaZnO TFTs

We report an abnormal negative threshold-voltage shift (ΔVTH) in bulk-accumulation (dual-gate driven) amorphous-InGaZnO (a-IGZO) thin-film transistors (TFTs) after application of positive-bias-stress (PBS). In devices annealed at 250°C for 2 h in vacuum, the negative ΔVTH is accompanied with subthreshold swing degradation, consistent with PBS-induced defect creation. Negative-bias-stress induces negligible ΔVTH, ruling out ion migration in the gate-insulator. By varying the top-gate length, it is found that the negligible ΔVTH is a function of bulk-accumulation. However, after vacuum annealing at 250°C for 100 h, PBS induces negligible ΔVTH, verifying that the negative ΔVTH in short-time annealed devices is related to defects in the bulk a-IGZO. Therefore, good PBS stability can be achieved in bulk-accumulation dual-gate a-IGZO TFTs by long-time vacuum anneal.

Lateral Grain Growth of Amorphous Silicon Films With Wide Thickness Range by Blue Laser Annealing and Application to High Performance Poly-Si TFTs

We report high performance p-type poly-Si thin-film transistors (TFTs) achieved by lateral grain growth of amorphous silicon (a-Si) by using a continuous-wave blue diode laser of wavelength 445 nm. The blue laser beam is efficiently absorbed into the a-Si film, such that full melting and lateral crystallization is achieved in all thicknesses investigated, 50-200 nm. TFTs fabricated with 75-, 100-, and 125-nm-thick poly-Si films laterally grown by the blue laser annealing exhibited field-effect mobility of 108 ± 7, 104 ± 9, and 134 ± 12 cm2/V · s, and subthreshold swing of 210±51, 191±16, and 193±53 mV/decade, respectively, and high ON/OFF current ratio of ~108.

P‐8: a‐Si:H TFT‐LCD with Single Organic Passivation Layer

A novel photosensitive organic material is used as the single organic passivation layer for the conventional back channel etched thin film transistors. We find that the leakage current of the a-Si:H TFTs with single organic passivation layer is lower than that of the conventional transistors with silicon nitride passivation layers and the adhesion strength between the organic layers and the pixel electrode is sufficiently strong so that the overlap between the ITO pixel electrode and the data lines can be formed. Using the novel materials, 1.9″ qCIF AMLCD with single organic passivation layer was successfully fabricated with reduced process steps.

P-31: Thin and Light Integrated TSP with Enhanced Display Qualities

We have developed an innovative liquid crystal display (LCD) which includes a resistive type touch screen system — integrated touch screen panel (iTSP). It can detect touch events and locate touch positions by measuring voltage at the contact point between indium tin oxide (ITO) coated color filter glass and ITO conductive isotropic film. iTSP shows not only better display qualities outside but also considerable decreases in weight and thickness compared to conventional resistive touch screen panel which consists of ITO glass and conductive film. In this paper, main characteristics of 7.0″ WVGA LCD Panel integrated with the touch screen function were presented and the optical characteristics also were discussed.