Research On Reliability Of Gallium Nitride Power Devices

Compared to the first generation semiconductor material silicon（Si）and the second generation semiconductor material gallium arsenide（Ga As）,the third generation semiconductor material（broadband gap semiconductor material）silicon carbide（Si C）or gallium nitride（Ga N）has better physical and chemical properties such as fast switching speed,small size,high efficiency,and fast heat dissipation.Si C and GaNhave the advantages of high power,high operating temperature,high breakdown voltage,high current density,and high-frequency characteristics which can significantly reduce the chip area,simplify peripheral circuit design,and achieve the goal of reducing the volume of modules,system peripherals,and cooling systems.Due to its unique material characteristics,gallium aluminum nitride/gallium nitride（Al Ga N/Ga N）high electron mobility transistors（HEMTs）are widely used in power electronics fields such as power amplifiers（PAs）,low noise amplifiers（LNAs）,mixers,and converter circuits（AC-DC,DC-DC）,becoming the backbone of renewable energy power conversion.Silicon power devices such as double diffused metal oxide semiconductor field effect transistors（DMOS）and insulated gate bipolar transistors（IGBTs）have reached their performance limits,and GaNhas become a choice to further reduce energy loss during power conversion.In this paper,the reliability of GaNHEMT devices was studied.The electrical and thermal performance stresses of GaNdevices were analyzed by using simulation methods,and the operating mechanism of GaNdevices was studied.The factors that cause GaNdevice failures was found,and then the parameters of GaNdevices was optimized.The improvement methods for reliability of GaNdevices were determined by testing and analysis.The reliability of GaNHEMT devices has been studied from the following aspects:（1）The key steps were discussed in the traditional Au fabrication process for GaNHEMT devices including ohmic contact in the source/drain region and Schottky metal gates.The evolution of Au free processes that incorporate CMOS compatible GaNtechnology,including the latest advances in CMOS compatible manufacturing processes for the application of new structures and materials to ohmic contact formation and gate structures,was also discussed.In addition,the relationship between GaNmanufacturing processes and GaNdevice reliability was analyzed.（2）Sil Vaco simulation software is utilized to establish a voltage breakdown model for GaNdevices,which enhances their electrical characteristics and material structure and improves reliability under high voltage conditions.The heat distribution of GaNdevices with different substrates were simulated and analyzed to solve the heat dissipation problem of GaNdevices.To investigate heat flow in device structures,thermal conductivity models and heat transfer characteristics were used to confirm the self-heating effects of Al Ga N/GaNHEMTs and to verify the heat dissipation effects of copper-filled thermal structures.Transient thermal analyses of copper-filled thermal grooves and through-holes were performed to compare and evaluate the heat dissipation effects of different structures.（3）The reliability experiments of p-GaNgrid GaNHEMT devices were carried out.From the epitaxial process of an enhanced p-GaNgrid HEMT,the bias temperature instability was evaluated and inhibited.The dynamic on-resistance R_DS-ONwas tested,and its failure mechanism was investigated.