Room Temperature Bonding of Diamond and GaN with Ti/Ag Intermediate Layer
Wafer bonding has become the mainstream technology for developing GaN-on-Diamond devices. Room temperature bonding technology can avoid lattice mismatch and differences in thermal expansion coefficients caused by high temperature growth process,and there is no need to consider the low thermal conductivity of the nucleation layer. The use of diamond with high thermal conductivity as a bonding material can maximize the heat dissipation capacity. Therefore,the work aims to study the bonding technology between polycrystalline diamond and GaN with Ti/Ag intermediate layer at room temperature. Firstly,5 mm×5 mm diamond and GaN samples were ultrasonically cleaned. Afterwards,Ti adhesion layer,Ti/Ag gradient layer,and Ag nano-layer were deposited on the surface of polished free-standing polycrystalline diamond wafers and GaN wafers by magnetron sputtering,forming a Ti/Ag transition layer composite structure. The thickness of each layer was about 5 nm,with a total thickness of 5 nm. The Ti/Ag gradient layer with component transition was formed by controlling the deposition power. Finally,the deposited film sides of the two samples were attached and fixed,and diamond and GaN were successfully bonded through a vacuum bonding system at room temperature and certain pressure conditions. By means of scanning electron microscope (SEM),atomic force microscope (AFM),X-ray diffraction (XRD),and X-ray photoelectron spectroscopy (XPS),the morphology and structure of the sample surface were analyzed. The bonding rate and strength after bonding were evaluated with scanning acoustic microscope (SAM) and tensile mechanical testing system. With the help of Ti/Ag intermediate layer,good bonding between diamond and GaN was successfully achieved at room temperature. The use of metal film as the intermediate bonding layer had a high tolerance for the roughness of the wafer surface,and good bonding could be achieved at room temperature through diffusion,with a bonding rate of 95.5％ at room temperature. Through tensile strength testing,the bonding strength reached 13.7 Mpa,and the Ti/Ag gradient layer formed by controlling process parameters effectively improved the bonding strength. The high surface activity of nanoparticles is the key issue to achieving room temperature fusion of the bonding interface. The good adhesion characteristics of Ti substrate,the deposition of Ti/Ag gradient layer,and the formation of intermetallic compounds between Ti and Ag through diffusion reactions are key factors in improving the bonding quality between diamond and GaN.
diamondGaNTi/Ag intermediate layerroom temperature bondingintermetallic compounds
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