New challenges in thin film transistor (TFT) research

Abstract

This paper addresses the current trends in research and development for: (1) Thin film transistors (TFTs) on plastic substrates, (2) low-temperature poly-silicon (LTPS) for the pixel TFTs and for row and column drivers on glass, (3) addressing of organic light emitting diodes by silicon TFTs. For these advanced applications of TFTs the relevant issues are: (i) higher electron mobility, (ii) stability, and (iii) defect free, uniform deposition of thin silicon films and gate dielectrics at a high deposition rate (reduced cost). At Utrecht University, we are investigating hot wire (catalytic) chemical vapor deposition (CVD) as a deposition technique for novel TFTs that have a high potential to meet the above mentioned requirements. Bottom gate, inverted staggered TFTs with hot wire CVD (HWCVD) silicon films have been made with an electron mobility of 1.5 cm 2/ V s , and with field effect characteristics that are completely stable under operating conditions. Top gate, coplanar TFTs with polycrystalline silicon (poly-Si) films have been made, which showed a mobility of 4.7 cm 2/ V s . This has been obtained without any post treatment, and the hot wire technology can thus avoid expensive, time-consuming steps such as laser recrystallization as currently used in the production of the latest poly-Si lap top displays. HWCVD is also suitable for the deposition of SiN x :H gate dielectrics. TFTs with a hot wire silicon nitride gate dielectric have been deposited.