Interfacial microstructures of rf-sputtered TiNi shape memory alloy thin films on (100) silicon

Abstract

Interfacial microstructures of TiNi thin ®lms rf sputtered on to Si(100) and post-annealed at 400±7008C for 30 mins have been investigated using analytical and high-resolution transmission electron microscopy. For annealing temperatures below 6008C, a very thin amorphous (Si, O)-rich layer is observed at the interface. Ni atoms are the primary diOE using species and NiSi2 forms triangularly and epitaxially towards the Si substrate. TiNi ®lms initially crystallize after 30 min at 5008C. Si and Ti atoms begin to migrate in specimens annealed at 6008C for 30 min. At this temperature, a near-Ti 4 Ni 4 Si 7 phase in triangular NiSi2 and a near-TiNiSi phase in the TiNi ®lm are simultaneously nucleated and grown at the interface. For the specimens annealed at 7008C for 30 min, two layers of Ti4Ni4Si7 and TiNiSi form at the interface with the sequence TiNi/TiNiSi/Ti 4 Ni 4 Si 7= Si. Triangular NiSi 2 islands are now embedded in the Ti4Ni4Si7 layer. A mechanism of interfacial microstructure evolution is proposed to explain the temperature eOE ect on the interfacial reaction layers between the TiNi ®lm and the Si(100).