Schottky Barrier Controlled Conduction in Poly-Si TFTs With Metal Source and Drain

Two types of poly-Si thin-film transistors (TFTs) with the source (S) and drain (D) regions replaced by Al-metal-replaced junction TFT and self-aligned metal electrode (SAME) TFT-are characterized. Their IV characteristics are explained with a unified transport model based on the Schottky barriers at channel ends. Channel current is the sum of hole- and electron-current, which are limited by carrier injection via thermal emission or tunneling across the hole- and electron-barrier formed between poly-Si channel and metal S/D, respectively. The observed temperature dependence of transfer characteristics agrees well with the model. For SAME TFTs, barrier height of carrier transport is found to be modulated by a doped interfacial layer between the intrinsic poly-Si channel and Al electrodes at channel ends. By modulating the hole- and electron-barrier, three different types of device behaviors, such as p-type, n-type, and ambipolar TFTs can be obtained. Correlation between the doping effect and subthreshold swing and ON-state current, as well as channel length-dependent characteristics, are revealed.