High voltage thin film transistor with second gate

Claim 1

A high voltage thin film transistor comprising a non-single crystal semiconductor charge transport layer, laterally disposed source and drain electrodes located adjacent to one surface of said charge transport layer, means for applying a constant high electrical potential to said drain electrode, a first gate dielectric layer located adjacent to an opposite surface of said charge transport layer, a first gate electrode separated from said opposite surface of said charge transport layer by said first gate dielectric layer, said first gate electrode having one edge laterally overlapping said source electrode and another edge laterally spaced from said drain electrode, and means for applying an electrical potential to said first gate electrode in a time varying manner so as to form a first accumulation channel of a given conductivity type periodically opposite to said first gate electrode in said charge transport layer, said transistor being characterized by including second gate electrode means for forming a second accumulation channel extending laterally from said first accumulation channel toward said drain electrode, said second accumulation channel of said given conductivity type being less accumulated than said first accumulation channel, and means for applying an electrical potential to said second gate electrode means for preventing depletion of charge carriers within said second accumulation channel.