Gate current flow in cylindrical thyristors with partially shorted cathodes—two and three terminal operation with inner and outer gate configuration—turn-on area

Abstract

Following on the work of linear thyristors, the gate current flow in cylindrical thyristors is investigated with partially shorted cathodes. Once more the models employ single shorting “dots” (SD) for the two symmetrical configurations possible for the cylindrical geometry, inner gate—outer SD and inner SD—outer gate for a range of sheet resistance values ( ϱ/ W) for the gate region. The non-linear differential equation governing gate current flow is given by y″+ ξ −1 y′( y−1)− Cy = 0 ( y = normalised gate current, ξ = normalised radial co-ordinate) with Non-Cauchy boundary conditions and the latter difficulty is overcome both for two and three terminal operation by similar methods previously employed, when solving for y( ξ) for a variety of device geometries and ( ϱ/ W) values as well as bias conditions. The theory of turn-on area in terms of a critical cathode current density J KB is also applied to this cylindrical model and expressions are obtained for the gate drive I GD required to achieve a given turn-on area. Of particular interest are the plots of gate current flowing into the SD as a function of I GD for a variety of ( ϱ/ W) values as well as for the two possible gate/SD configurations.