The Curvature Effect On The Effective Role Of The Pn Junction Breakdown Voltage

PN junction is the foundation of almost all the power devices. The avalanche breakdown voltage of PN junction determines the work voltage range of related power devices. The practical PN junction is not parallel planner junction. It is widely accepted that the curvature of PN junction reduces the breakdown voltage. A series of junction termination technology such as Field plate, Field ring, Bevel edge, Contour etching and VLD are developed to avoid the curvature.The ideal electric field of depletion region is analyzed in this paper. It is claimed in the paper that the curvature of PN junction is sometimes good for the breakdown voltage, when the curvature is called effective curvature. The curvature in ideal cylindrical junctions and spherical junctions is analyzed, and how the breakdown voltage is affected by the effective curvature is analyzed. The essential of effective curvature and the doping of drift region are discussed. In addition, 2 essentials of effective curvature is carried out in the PT N+N-P+/ P+P-N+ junctions with random shape.The PiN diode and SOI LDMOS are introduced to show the effective curvature's effect of enhancing the breakdown voltage of power devices. The other parameters such as speed, switching loss are analyzed when the device is constructed with effective curvature. It is proved that effective curvature is valuable in practical power devices.In the end of this article, analytical conclusion is carried out to point out when the effective curvature is useful and how much the breakdown voltage is increased. The PN junction with effective curvature is compared with the parallel planner junction that has the same doping and drifts region length. The practical curvature is usually local curvature and the critical Electrical Field is not a constant, so the breakdown voltage is decreased in a smaller proportion than the ideal one.The main purpose of this article is to show the curvature can be good for the breakdown voltage. Related Conditions, examples and analytical calculations is worked out. The conclusion of this article can be regarded as a proof for the effective curvature used in power devices. When the effective curvature is realized the analytical calculation can be used.