The Parameter Extraction And Analysis Of GaN Devices Small-Signal Equivalent Circuit

With the continuous progress of microwave technology recent years, microwave semiconductor devices have been widely used in wireless communication and telemetry system, navigation and military fields. GaN, as the representative material of the third generation of semiconductors, because of its wide band gap, high breakdown electric field, the high thermal conductivity, high electron saturation velocity, high thermal conductivity and high radiation resistance, so is widely used in radio-frequency, microwave and millimeter wave and other high frequency high power devices. Now GaN-based electronic devices and circuits have entered into the application stage, however, in the current circuit designing, most GaN HEMTs devices model are based on traditional GaAs model, such as Angelov model, TriQuint model, etc. Therefore to establish precise GaN HEMTs equivalent circuit model has great significance for circuit designing, device performance improving, especially guiding significance in large-signal modeling. This article is based on these issues, presents a detailed study in the following areas:1. We researched on a new method in AlGaN/AlN/GaN heterostructure field-effect transistor small signal equivalent circuit parameters extraction. According to the characteristics of the device, a 16 elements model was used. For parasitic inductance and capacitance extraction we adopt the radio-frequency de-embedding technology. For the most important and difficult to extract parameters in small signal extraction, parasitic resistances, we deduced the relationship between Re(Z12) and Rs. By repeated iteration calculation we solved Rs, and Rd can be calculated when we got Rs. This method avoided the defects that the parasitic resistances do not change with device bias point, and by comparing with the traditional method, fitting effect of new method is satisfactory.2. We researched on the relationship between the size of AlGaN/AlN/GaN heterostructure field-effect transistors and their cut-off frequency. And we attribute the main influence factors of cut-off frequency to transconductance and gate capacitance. Also the change rule of intrinsic parameters was studied, we found out that with the increase of frequency, the transconductance presented the downward trend. We assume the reason are as follow:at low frequency, the surface leakage current areas between gate-source and gate-drain are also modulated, which will increase the transconductance; as the frequency increases, the surface trap cannot respond the variation of signal applied on the gate, which will lower the transconductance.3. We researched on the AlGaN/AlN/GaN heterostructure field-effect transistor current collapse effect, by comparing the gate voltage pulse test of the device with dc test results; we observed obvious current collapse effect. We also found that for different gate voltage pulse widths, the shorter pulse widths were the more degree of current collapse we can observe. Because the tested devices were not passivated, in this paper, the "virtual gate" theory was used to explain the relationship between current collapse effect and surface state of devices.