Jae-Seob Lee

The influence of the gate dielectrics on threshold voltage instability in amorphous indium-gallium-zinc oxide thin film transistors

We investigated the threshold voltage (Vth) instability for various gate dielectrics (SiNx and SiOx) in amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs). The a-IGZO TFTs with SiNx 150 °C exhibited reasonable electrical performance (field-effect mobility of 8.1 cm2/V s and Ion/off ratio of >108) but showed huge Vth shift under positive gate bias. The TFTs with SiOx dielectrics exhibit smaller Vth instability than those of SiNx dielectrics. This behavior can be explained by using simple charge trapping into the gate insulators and the difference of Vth instability on various dielectrics may be originated from the hydrogen contents, providing high density of charge traps in gate dielectrics.

Flexible Full-Color AMOLED on Ultrathin Metal Foil

Full-color active-matrix organic light-emitting diode panels, driven by poly-Si thin-film transistors (poly-Si TFTs), were successfully fabricated on thin metal foil substrates. The p-channel poly-Si TFTs on metal foil showed a field-effect mobility of 82.9 cm2/Vmiddots, subthreshold slope of 0.34 V/dec, threshold voltage of -1.67 V, and off-current of 6.6times10-14 A/mum. The 5.6-in panel had 160 times RGB times 350 pixels, each of which had a pixel circuit of two TFTs and one capacitor

47.2: 2.8‐inch WQVGA Flexible AMOLED Using High Performance Low Temperature Polysilicon TFT on Plastic Substrates

This paper reports a low-temperature polycrystalline silicon (LTPS) fabrication process on plastic substrate for a flexible AMOLED display. Characteristics of fabricated TFTs showed excellent performance with field effect mobility of 124.1 cm2/V-s, on/off ratio of >108, subthreshold slope of 0.30V/dec, and threshold voltage of −2.03V. Internal scan drive circuits, 1:3 demux, and compensation circuits were successfully integrated on the backplane of a 166ppi 2.8″ WQVGA flexible AMOLED panel.

16.2: World-Best Performance LTPS TFTs with Robust Bending Properties on AMOLED Displays

This study reported a low temperature polycrystalline silicon LTPS thin film transistor TFT fabrication process on plastic substrates for flexible display applications. Polycrystalline silicon poly-Si films were formed by excimer laser annealing ELA method. It was found by ELA thermal simulation that there was around 70 □ on plastic surface during ELA crystallization process. The excimer laser irradiated film was analyzed by using various spectroscopic methods such as X-ray diffraction, scanning electron microscopy, and atomic force microscopy. Dehydrogenation and activation processes were performed by a conventional LTPS method without causing any plastic substrate distortion. The fabricated poly-Si TFT on a flexible backplane shows a very good performance with field effect mobility of 95.3 cm2/Vs, on/off ratio current ratio > 108, and threshold voltage of −1.6 V. Bending tests after a delamination process were also performed with TFT backplane samples.

Nonstoichiometric Solution-Processed BaTiO3 Film for Gate Insulator Applications

Solution processed barium titanate (BTO) was used to fabricate an Al/BaTiO3/p-Si metal-insulator-semiconductor (MIS) structure, which was used as a gate insulator. Changes in the electrical characteristics of the film were investigated as a function of the film thickness and post deposition annealing conditions. Our results showed that a thickness of 5 layers and an annealing temperature of 650 °C produced the highest electrical performance. BaxTi1-xO3 was altered at x = 0.10, 0.30, 0.50, 0.70, 0.90, and 1.0 to investigate changes in the electrical properties as a function of composition. The highest dielectric constant of 87 was obtained for x = 0.10, while the leakage current density was suppressed as Ba content increased. The lowest leakage current density was 1.34×10-10 A/cm2, which was observed at x = 0.90. The leakage current was related to the resistivity of the film, the interface states, and grain densification. Space charge limited current (SCLC) was the dominant leakage mechanism in BTO films based on leakage current analysis. Although a Ba content of x = 0.90 had the highest trap density, the traps were mainly composed of Ti-vacancies, which acted as strong electron traps and affected the film resistivity. A secondary phase, Ba2TiO4, which was observed in cases of excess Ba, acted as a grain refiner and provided faster densification of the film during the thermal process. The absence of a secondary phase in BaO (x = 1.0) led to the formation of many interface states and degradation in the electrical properties. Overall, the insulator properties of BTO were improved when the composition ratio was x = 0.90.