Low-temperature metal/Zerodur heterogeneous bonding through gas-phase processed adhesion promoting interfacial layers

Abstract

The bonding of ceramic to metal has been challenging due to the dissimilar nature of the materials, particularly different surface properties and the coefficients of thermal expansion (CTE). To address the issues, gas phase-processed thin metal films were inserted at the metal/ceramic interface to modify the ceramic surface and, therefore, promote heterogeneous bonding. In addition, an alloy bonder that is mechanically and chemically activated at as low as 220 °C with reactive metal elements was utilized to bond the metal and ceramic. Stainless steel (SS)/Zerodur is selected as the metal/ceramic bonding system where Zerodur is chosen due to the known low CTE. The low-temperature process and the low CTE of Zerodur are critical to minimizing the undesirable stress evolution at the bonded interface. Sputtered Ti, Sn, and Cu (300 nm) were deposited on the Zerodur surface, and then dually activated molten alloy bonders were spread on both surfaces of the coated Zerodur and SS at 220 °C in air. The shear stress of the bonding was tested with a custom-designed fixture in a universal testing machine and was recorded through a strain indicator. The mechanical strength and the bonded surface property were compared as a function of interfacial metal thin film and analyzed through thermodynamic interfacial stability/instability calculations. A maximum shear strength of bonding of 4.36 MPa was obtained with Cu interfacial layers, while that of Sn was 3.53 MPa and that of Ti was 3.42 MPa. These bonding strengths are significantly higher than those (∼0.04 MPa) of contacts without interfacial reactive thin metals.