Research On Negative Differential Regime Of SOI LIGBT

Lateral insulated gate bipolar transistor(LIGBT) is a kind of composite power device, which is made up of power MOS field effect Transistor and a Bipolar Transistor. it has the characteristics of both high input impedance and low voltage drop, so LIGBT device is widely used in various power electronics system. Silicon On Insulator(SOI) material has the advantage of lower parasitic capacitance, and higher integration,the object of this paper analyzes is SOI LIGBT device. However, due to SOI LIGBT device is a bipolar device so it can reduce on-resistance when the device is turned on. but when the device is turned off, because the drift region storages a large number of non-equilibrium carriers, it can reduce the turn-off speed and increase the loss of the device. Researcher usually used anode-shorted SOI LIGBT structure to improve the turn-off speed of the device, but this structure will produce Negative Differential Regime during the transition from LDMOS model to LIGBT model.In this paper, basing on the analysis of the mechanism of Negative Differential Regime, we propose two kinds of new SOI LIGBT structures to improve the turn-off speed,at the same time suppress Negative Differential Regime when the device is turned on. The first structure is a anode-shorted SOI LIGBT with a higher N+ region than conventional anode-shorted SOI LIGBT.this structure can change the electrons flow path, reduce anode voltage that can turn on anode P+ / n-buffer junction, so that the device can enters the LIGBT mode earlier, achieving the purpose of suppressing Negative Differential Regime, while N+ anode region still plays a role in reducing the turn-off time because it can offer a way of extracting electrons when the device is turned off. The second structure is the SOI LIGBT which combines the dielectric isolation technology and junction isolation technology.The specific measure of this structure is joining the insulation groove between the anode P+ region and N+ region, adding p-buffer region below the anode N+ region, p-buffer region not completely surrounding anode N+ region.This structure firstly can change flow path of electrons, the p-buffer region can hinder electrons into the anode N+ region from the n-drift region,thereby suppressing the Negative Differential Regime; secondly when the device is turned off, the triode that is made up of anode N+, p-buffer and N-drift open.because the triode can extract electrons from the drift region, so the structure can get a high turn-off speed.