Research On Key Techniques For Gan Power Transistor With Working Frequency Over 90 GHz

Owing of short wavelength,wide frequency bandwidth and narrow beam,adopting millimeter wave can greatly improve the detection accuracy of radar and the data capacity of communication,providing more non-interference channels.In addition,in the millimeter-wave band(30 to 300 GHz),there have large bandwith for the spectrum absorption and attenuation,providing guarantees to high-precision radar and large-capacity secure communication.Millimeter wave technology has become an important means to improve the combat capability of the next generation weapon system.Moreover,millimeter wave is also the application frequency band for 5 G communication.Therefore,the research of millimeter wave has important value for military and industrial application.For working frequency over 90 GHz,the output power of the chip based on the traditional GaAs and InP semiconductor materials can hardly reach the watt level,limited by their own characteristics.This greatly limits the development and application of millimeter wave in the equipment and communication technology.As a typical third generation semiconductor material,GaN material has much better characteristics such as wider band gap,higher critical breakdown field strength and higher carrier saturation drift velocity.The output power density of GaN-based microwave power devices is 10 times higher than that of GaAs,and watt-level output power can been obtained in the W band(75-110 GHz).Thus,GaN-based microwave power devices can meet the needs of high-power millimeter-wave frequency for radar,satellite communication,information communication and electronic countermeasures.GaN-based microwave power devices have been drawn great attention for military and civil applications by many countries in the world.Although there have been many reports on GaN High Electron Mobility Transistor(HEMT)and Monolithic Microwave Integrated Circuit(MMIC)power amplifier with working frequency over 90 GHz,the research is still at the early stage and there have many technical difficulties and scientific problems need being investigated.Therefore,the research on key techniques of GaN power devices over 90 GHz has important scientific research value and engineering significance.In this paper,the key technologies of GaN power devices above 90 GHz are studied.The main contents and conclusions of this research include:(1)The physical simulation model of GaN HEMT device is established.The influence of material and device parameters on frequency,output power and thermal characteristics of AlGaN/GaN HEMT device is simulated and analyzed.The optimum values of material and device structure parameters for realizing the operation above90 GHz band are proposed.At the same time,the material and device parameters for the novel InAlN/GaN HEMT are simulated and analyzed.The optimum range of material and device structure parameters is proposed to guide the improvement of device frequency characteristics.(2)The key techniques for GaN heterostructure growth and high-frequency device fabrication are investigated,focusing on regrown n⁺GaN non-alloy contact with low ohmic resistance,high density passivation with double-T-shaped gate,and 40-nm T-shaped gate.By processing optimization of dry etching and n⁺-GaN regrowth,a low ohmic contact resistance of 0.05?.mm is obtained,which is a recorded value regrown by metal organic chemical vapor deposition(MOCVD).Based on High Density Plasma Chemical Vapor Deposition(HDPCVD),novel Si N passivation is adopted to suppress the surface states.The current collapse drops about 15 times,compared with the traditional passivation by PECVD.In additional,double-T-shaped gate is fabricated to reduce the gate parasitic capacitance and resistance,and to improve the device frequency.Double exposure and development are employed to suppress the neighbor effect,and 40-nm T-shaped gate is fabricated.(3)Combined with the optimization design of material devices and key techniques of device fabrication,the maximum oscillation frequency(f_max)of fabricated AlGaN/GaN HEMT devices reaches 205 GHz,which meets the requirement of power amplifiers with working frequency above 90 GHz.Based on a novel ultra-thin InAlN/GaN heterostructure,by reducing the source-to-drain distance to 600 nm,the fabricated InAlN/GaN HEMT with 40-nm T-shaped gate shows a maximum oscillation frequency(f_max)of 405 GHz,which is a recorded result reported for InAlN/GaN HEMTs.In addition,34-nm rectangular gate is adopted,and the fabricated InAlN/GaN HEMT shows a current cut-off frequency(f_T)of 350 GHz,which is a recorded result reported for GaN-based HEMTs in domestic.(4)A 90-96 GHz AlGaN/GaN MMIC power amplifier is designed and fabricated based on the developed AlGaN/GaN high-frequency HEMT device.The 90-96 GHz GaN MMIC power amplifier has a saturated output power of more than 2 W in the frequency range of 90-96 GHz.At frequency of 91 GHz,the output power reaches 3W.In addition,infrared thermal resistance test demonstrates that there is no unusual high-temperature spot or region on the MMIC surface.Junction temperature is evenly distributed,which indicates that the fabricated MMIC power amplifier has high reliability.