Direct Bonded Aluminum/Alumina using Various Elements as Interlayer for High Power Device Substrate

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Direct bonded copper (DBC) substrates have been widely used in power electronics and insulated gate bipolar transistors (IGBT) modules. However, poor thermal cycling reliability of DBC substrates restrict its applications. Direct bonded aluminum (DBA) substrates have been developed to replace DBC substrates due to its superior reliability. In this study, nickel, copper, germanium, silicon has been deposited on Al2O3 substrate as the interlayer between Al/Al2O3. The specimens were heated above their eutectic temperature, the eutectic liquid phase formed at Al/Al2O3 interface to obtain better wettability. Since these elements could lower the melting point of aluminum, the bonding process could be realized at lower temperature. The DBA substrates were annealed at 640 oC for 60 minutes in argon atmosphere to prevent aluminum from oxidization. The aim of present study is to analyze and comparing Ni, Cu, Ge, Si with each other as interlayer between Al and Al2O3, including analyze microstructure of Al/Al2O3 interface and aluminum layer. Furthermore, scanning acoustic tomography (SAT) is used to reveal the voids distribution of Al/Al2O3 bonding layer for the purpose of evaluating the quality of DBA substrate. The interfacial strength of Al/Al2O3 interfaces were measured by shear strength test. The thermal conductivity of the Al/Al2O3 specimens were measured by laser flash method. The results indicated that the interfacial strength of Al/Al2O3 interfaces and thermal conductivity of DBA substrates were better as deposited element is nickel. The thermal conductivity of Ni-DBA specimen was 42.3 Wm-1K-1 and the maximum shear strength is 33.74MPa. This result shows that Ni-DBA has potential to be applied as substrate of high power device.