Characteristics Of AlGaN/GaN High Electron Mobility Transistors On Metallic Substrate

GaN power electronic device has higher operating voltage,higher switching frequency,lower on-resistance and other advantages.In a new-generation highefficiency,small-size power conversion and management system,electric locomotive,new energy vehicles and other fields,it has great research significance and application prospect,which has become a research focus in various countries.At present,the mature GaN devices on the market are mostly based on sapphire or SiC.By contrast,Si substrates have the advantages of low price,high crystal quality,large size and mature process conditions,which make high-quality Si based GaN materials and devices attract much attention.However,there is lattice mismatch of 17% and thermal mismatch of 56% between GaN and Si,leading to a large mismatch stress in the epitaxial structure.And,it is easy to cause heat accumulation in the working process of the device.Therefore,the performances of GaN device such as output power density and efficiency deteriorate rapidly,even causing device failure.Due to the self-heating effect,the theoretical high output power capability of GaN HEMT is far from being developed,and the heat dissipation has become an important problem to limit the further development and application of GaN microwave power device technology.At present,to solve the heat dissipation problem,most Si based GaN devices are transferred to high heat-dissipation diamond and Al N ceramic substrate through bonding process.Since the surface electrode structure of HEMT devices is concentrated on the epitaxial surface,the temperature and pressure requirements of large-area bonding process make the bonding process very difficult and the yield is very low.In this paper,based on substrate transfer technology,GaN HEMT devices were successfully stripped from the Si substrate and transferred to Cu metal substrate with good heat dissipation performance.The surface morphologies,stress status,electrical and thermal characteristics were deeply studied.The main results are as follows:(1)In view of the high requirements of metal-substrate AlGaN/GaN HEMT on device fabrication technology,this paper redesigned and conducted in-depth research on photolithography,electrode preparation,etching,passivation and substrate transfer,and developed a complete and stable device preparation process.In addition,the corrosion effects of different corrosion fluids on Si were studied,and the efficient removal of silicon substrates without damaging was realized by optimizing the ratio and temperature of the corrosion fluids.High-quality and damage-free micron-level GaN epitaxial films were obtained.(2)Acid bright copper plating was used to prepare the metal substrate.By optimizing the process conditions and analyzing the stress distribution,Cu metal substrate with good brightness,uniformity and flatness was obtained and the metal substrate were perfectly combined with GaN HEMT devices.Besides,the graphic metal substrate was also explored.(3)In this paper,the structural,electrical and thermal performances of the devices before and after substrate transfer were deeply studied.AFM test results showed that the device surface was not damaged in the substrate transfer process.Raman test showed that the stress in the technical substrate HEMT device was effectively released.By comparing the output curve and transfer curve of two kinds of HEMT devices,it was found that the DC characteristics of Cu-substrate HEMT were basically similar to that of Si-based HEMT devices in the absence of effective heat sink preparation.We measured the heat distribution on two HEMT devices using transient infrared devices.The thermal diffusivity of HEMT devices on Cu substrates was significantly better than that of HEMT on Si substrates as clearly observed by the thermal reflection image.We also fabricated copper-substrate devices of different thickness and made micro-infrared temperature measurements.At the same voltage,when the Cu substrate thickness increased from 28 ?m to 35 ?m,the HEMT device operated at higher power and lower surface temperature.This showed that with the increase thickness,the heat dissipation capacity of copper substrate was stronger and stronger,which suggested that the Cu substrate HEMT based on electroplating process had great application potential in hightemperature and high-frequency working environment.