METHODS OF IMPROVING TURN-OFF CHARACTERISTICS OF THYRISTOR USING CONTROL OF ANODE-SIDE EMITTER

摘要

The present invention provides appropriate methods for improving the turn- off characteristics of power semiconductor thyristors, especially where the observed delayed turn-off is not attributable to the usual causes related to the recombination rate of electrons and holes. The invention studies the impacts of anode-side n+ layer formed during the doping processes as well as silicon wafer thickness on turn-off time of thyristors. The cause of delayed turn-off is clearly established as incomplete replacement of the anode-side n+ with p+ formed during the brazing of anode-side of silicon wafer with molybdenum plate. The invention recommends to avoid n+ layer on anode-side for thyristors with silicon wafers up to ~500-μm thick. On the contrary, the invention insists on formation of n+ layer on anode-side for thicker wafers (~500-μm thick) in order to achieve the on-state conduction drop within specified limits and recommends to enhance brazing temperature to ensure complete replacement of n+ by p+. The manufacturing yield and the long-term product reliability of thyristors are improved by the recommended methods that have been successfully adapted in industrial manufacturing process.