A Conductivity Modulated Polysilicon Thin-Film Transistor
This paper reports a novel high voltage Conductivity Modulated Thin-Film Transistor (CMTFT) fabricated using polycrystalline silicon. The transistor uses the idea of conductivity modulation in the offset region to obtain a significant reduction in on-state resistance. Experimental on-state and off-state current-voltage characteristics of the CMTFT have been compared with those of the conventional offset drain device. Results show that the CMTFT has six times to more than three orders of magnitude higher on-state current handling capability for operating at drain voltages ranging from 15 V to 5 V while still maintaining low leakage current and providing even faster switching speed. The CMTFT devices can be fabricated using a low temperature process (620/spl deg/C) which is highly desirable for large area electronic applications.<<ETX>>
A simpler 100-V polysilicon TFT with improved turn-on characteristics
An improved polysilicon high-voltage thin-film transistor (HVTFT) structure for eliminating the current-pinching phenomenon often observed in the conventional offset-gate polysilicon HVTFTs is discussed. The device employs, in lieu of implantation, a metal field plate overlapping the entire offset region to control the conductivity of the offset region. By properly biasing the field plate to distribute the drain electric field at both ends, high-voltage operation of up to 100 V, suitable for many large-area applications, is achieved. Good turn-on characteristics without current pinching effects are consistently obtained. The structure also eliminates the lightly doped drain implant required in conventional offset-gate HVTFTs, resulting in a simpler and more reproducible process.<<ETX>>
p-Channel MOSFET's in LPCVD PolySilicon
p-channel MOSFET's have been fabricated in LPCVD polysilicon. A 5000-Å n+poly acts as the gate electrode on which a 500-Å thermal oxide is grown to act as the gate insulator. Then a 1500-Å LPCVD polysilicon layer is deposited at 620°C and is subsequently boron doped to form the conductive channel. Devices with channel length as small as 2 µm show well-behaved transistor characteristics. The drive current and leakage current are as suitable for usage as load element in memory applications. At large gate voltages the accumulation hole mobility is 9 cm2/V.s. The drain-to-source breakdown voltage exceeds -20 V.