Study On Testing For Gate Resistance Of Vertical Double-diffused MOSFET

Vertical Double-diffused MOSFET(VDMOSFET) is a main type among current Power MOSFET's. For VDMOSFET, the switching performance is quite important for its application and mainly depends on the product of the equivalent Gate resistance Rg between Gate and Source and input capacitance Ciss. This paper will present the advantages and applications of VDMOSFET and its structure, working principle, manufacturing process and equivalent circuit model. This paper will describe each component of Gate resistance Rg and Gate capacitance Cg based on the VDMOSFET device, and give an analysis of the effect of Gate resistance on the switching performance of VDMOSFET device during gate Charge-discharge and introduce how to decrease the Gate resistance and Gate capacitance. This paper will present also several kinds of testing method and testing equipments on impedance, two testing equipments HP4285A and Ip Test Mostrak can be selected to test the Gate resistance Rg and Gate capacitance Cg, it will analyze the effect on testing of Rg and Cg under different testing frequency and DC bias VGS based on the MIS C-V curve. Through a series of testing experiments with variable DC bias VGS, frequency and AC signal input, an optimum Rg testing methodology is developed for device characterization. Under such conditions, with enough negative DC bias for N type VDMOSFET and positive DC bias for P type VDMOSFET, the device is in accumulation state, and providing a small AC signal input with the frequency 1MHz, stable value of Rg and Cg can be obtained. Using this Rg testing method, some of the chip fabrication and package processes induced defects can be successfully identified.This paper will describe some of the device fabrication related issues, such as improper ion implantation of gate doping and the metal contact defects, and the wire bonding problems in the packaging process, such as bonding lift and heel crack of the gate wire for VDMOSFET. These defects are difficult to discover through a general DC measurement method but can be identified through the Rg testing this paper described.