Microwave Power Characteristics Of L-band H-diamond MOSFET

The third generation semiconductor materials,mainly composed of gallium nitride(GaN),silicon carbide(SiC)and diamond,have the characteristics of large band gap,high mobility,high saturation velocity and high breakdown electric field which can meet the requirements of high frequency and high power.At present,there are some problems in making microwave power devices with diamond devices,such as small output current density and small power density.On this basis,the DC characteristics and microwave power characteristics of hydrogen terminal diamond metal-oxide-semiconductor field effect transistor(H-Diamond MOSFET)are systematically studied,and the influence of lateral scaling on microwave power characteristics is deeply analyzed.In addition,GaN high electron mobility transistor(GaN HEMT)is used as a comparison to further study the key factors limiting the microwave power characteristics of hydrogen terminal diamond MOSFET,which provides a theoretical basis for the development of high-performance hydrogen terminal diamond field effect transistors.The main research work and results of this paper are as follows:1.Based on Silvaco TCAD software,an H-diamond MOSFET with a gate length of 0.5?m and gate insulator of 25 nm was modeled.An Al GaN/GaN HEMT in same size is used as reference.The square resistance of H-diamond MOSFET is calculated as 7.31 k?/sq,two-dimensional hole gas concentration of H-diamond MOSFET is 0.946×10¹³ cm^-2.For Al GaN/GaN HEMT,the square resistance is 0.55 k?/sq,two-dimensional electron gas concentration is 0.949×10¹³ cm^-2.It is in good agreement with the experimentally reported devices.So the accuracy of these models is verified.2.Numerical simulation is carried out based on Silvaco TCAD according to the above models.The DC characteristics of the two devices are calculated.The maximum saturation current of H-diamond MOSFET is 0.703 A/mm,which is about 1/2 of the maximum saturation current(1.567 A/mm)of Al GaN/GaN HEMT.This is due to the low carrier mobility of H-diamond MOSFET.Because the series resistance of H-diamond MOSFET device is about 10 times greater than that of Al GaN/GaN HEMT,it greatly affects the transconductance.So the external transconductance of H-diamond MOSFET(50 m S/mm)is about 1/5 than that of Al GaN/GaN HEMT(260 m S/mm).It is also found that the thicker gate dielectric layer is very useful for H-diamond MOSFET devices to achieve large gate voltage swing and high gate-drain breakdown voltage and to achieve considerable transconductance at higher V_DS.3.According to the above models,the cut-off frequency of 6.4GHz and 17.4GHz were obtained by H-Diamond MOSFET and Al GaN/GaN HEMT respectively.The lower cut-off frequency of H-Diamond MOSFET are mainly due to low carrier saturation velocity.therefore,to improve the cut-off frequency of H-diamond MOSFET,saturation velocity should be improved and|V_DS|should be enlarged.The power characteristics of these two devices are also obtained by simulation.The H-diamond MOSFET achieved an output power density of 3.69 W/mm at a quiescent drain bias of-57 V,which is about one third of the Al GaN/GaN HEMT of 10.76 W/mm demonstrated at 48 V.The lower power density of the H-diamond MOSFET is mainly due to the lower voltage and current swing.According to the location of the dynamic load line of H-diamond MOSFET on the DC output characteristics,the available drain current swing has been fully utilized.To further improve the output power density of H-diamond MOSFET,higher bias point and larger dynamic swing of the drain voltage are required.That could be achieved by larger source-drain breakdown voltage and larger resistive impedance at the drain.The key factors limiting the power characteristics of diamond devices were given quantitatively for the first time in this thesis,which provided an important theoretical support for the subsequent device research.4.The influence of lateral scaling on microwave power characteristics of H-diamond MOSFET was analyzed by TCAD software for the first time.The DC and microwave power characteristics of 500 nm?100 nm gate length devices are simulated.The DC and microwave power characteristics of the device varying with the gate length are summarized.The maximum cut-off frequency of the device is 27.5 GHz at 100 nm gate length,and the output power density is 4.3 W/mm@1 GHz at 200 nm gate length.It is found that the output power of the device is improved by lateral scaling,but the linearity is decrease.In summary,based on the existing experimental studies on hydrogen-terminated diamond devices,this thesis compares and analyzes the DC and microwave power characteristics of H-diamond MOSFET and Al GaN/GaN HEMT devices,and methods to optimize the power output of H-diamond MOSFET was proposed.In addition,the influence of lateral scaling on microwave power characteristics of H-diamond MOSFET is studied.This results lays a theoretical foundation for the optimization and performance improvement of hydrogen-terminated diamond microwave power devices.