Macro Model And Test Of Gan Hemts Device Equivalent Circuit Analysis

GaN based high electron mobility transistors(HEMT) that offer a good microwave power characteristic are extensively pursued for potential applications in high frequency and high power. But the standard FET model can not represent the characteristics of GaN HEMT infected with current collapse or self-heat effects, needing to build up urgently a precision model for GaN HEMT.This thesis aims at above mentioned problems. An equivalent circuit marco-model are built, based on thorough analysis about physical mechanism of GaN HEMT, which is making up of equivalent circuit structure and component parameter. Taking into account the GaN HEMT characteristic, confirmed the equivalent circuit structure and extract the component parameters of small-signal equivalent circuit model from measured S parameters. Then the small-signal equivalent circuit model is accomplished.According to experiment testing datasheet, there is a BARITT diode between the gate and the drain in GaN HEMT, then model the diode. The third class FET model is adopted to express the basis device characteristic of voltage control current source. In order to promise model accuracy and calculation efficiency, behavioral model is adopted to deal with GaN HEMT intrinsic nonlinear resistance and correct output character. Then the whole dc large-signal equivalent circuit model is accomplished. Taking into account current collapse, typical device is simulated by using the built model. The simulated results are basic similar with experiment data.Base on experiment results, the mechanism of current collapse are different under DC and high frequency. The collapse under DC large-signal is dependent on the electronics trap in the buffer layer. Along with the increase of drain voltage, electric field between gate and drain and 2-DEG electron energy increase, then part of electron excite to GaN buffer layer, depletion the channel, reduce the drain current, induce the current collapse. The collapse under high frequency is dependent on surface state between gate and drain. The charging and discharging of surface state form virtual gate in the surface, which extend depletion layer, deduce the concentration of 2-DEG, reduce the drain current, induce the current collapse.