The gate electrode of a polysilicon gate MOS transistor--the transistor
having either a thin film polysilicon substrate or a bulk monocrystalline
substrate--has a pair of contiguous regions: a heavily doped gate
electrode region near the source, and a lightly doped gate electrode
region near the drain. The gate electrode region near the drain is thus
doped significantly more lightly, in order to reduce electric fields in
the channel region in the neighborhood of the drain (and hence reduce
field induced leakage currents) when voltages are applied to turn
transistor OFF. At the same time, sufficient impurity doping is introduced
into the gate electrode region near the source in order to enable the
transistor to turn ON when other suitable voltages are applied.
Other References
Hayashi, F. et al., "A High Performance Polysilicon TFT Using RTA and
Plasma Hydrogenation Applicable to Highly Stable SRAMs of 16Mbit and
Beyond," 1992 Symp. on VLSI tech. Digest of Tech. Papers, pp. 36-37.
Tanaka, K. et al., "Characteristics of Offset-Structure
Polycrystalline-Silicon Thin-Film Transistors," IEEE Electron Device
Lett., vol. 9, No. 1, Jan. 1988, pp. 23-25.
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