A New SiO2-Silicone Hybrid Insulator for Amorphous Silicon Thin Film Transistors
Speaker: Lin Han
Series: Final Public Orals
Location: Engineering Quadrangle B327
Date/Time: Thursday, March 24, 2011, 1:30 p.m. - 3:30 p.m.
Active-matrix organic light-emitting diode (AMOLED) displays will become the dominant technology for the next generation of flexible displays, due to their light weight and flexibility. Organic light-emitting diodes (OLEDs) require a permeation barrier to protect them from the rapid degradation upon exposure to moisture or oxygen. The large experience and manufacturing base of a-Si:H thin-film transistors (TFTs) make their upgrade to AMOLED displays very desirable. Each pixel of an AMOLED needs TFT switch, and a TFT that can source sufficient current to drive the OLED, and is sufficiently stable in dc operation to surpass the OLEDâs lifetime.
A SiO2-silicone hybrid material was developed as an effective permeation barrier for the protection of OLEDs. The physical and chemical properties of the hybrid material suggest that the hybrid is a homogeneous SiO2-like material with residual silicone character. It combines the electrical properties of SiO2 and the mechanical flexibility of silicone polymer. A study of hybrid growth shows that the hybrid covers trenches and similar non-uniform topographies conformably, which is very important for the uniform coverage of the relief of thin-film circuits.
The SiO2-silicone hybrid also functions well as the gate dielectric for a-Si:H TFTs. The hybrid gate dielectric enables bottom-gate inverted TFTs with reord high field-effect mobilities of 2 cm2/Vïs for electrons and 0.1 cm2/Vïs for holes. The hybrid dielectric has a breakdown field Ebd ï? 8 MV/cm and a dielectric constant of 4.0. When used in a thickness of ~100 nm, which is 1/3 of the usable thickness of the conventional 300-nm SiNx dielectric, the hybrid has ~ 1.8 the gate capacitance of SiNx. The high gate capacitance and mobility raise the transistor current to 4 times that of an otherwise identical a-Si:H/SiNx TFT.