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

摘要

Interfacial microstructures of TiNi thin films rf sputtered on to Si( 100) and post-annealed at 400-700 degreesC for 30 mins have been investigated using analytical and high-resolution transmission electron microscopy. For annealing temperatures below 600 degreesC, a very thin amorphous (Si, O)-rich layer is observed at the interface. Ni atoms are the primary diffusing species and NiSi2 forms triangularly and epitaxially towards the Si substrate. TiNi films initially crystallize after 30 min at 500 degreesC. Si and Ti atoms begin to migrate in specimens annealed at 600 degreesC for 30 min. At this temperature, a near-Ti4Ni4Si7 phase in triangular NiSi2 and a near-TiNiSi phase in the TiNi film are simultaneously nucleated and grown at the interface. For the specimens annealed at 700 degreesC for 30 min, two layers of Ti4Ni4Si7 and TiNiSi form at the interface with the sequence TiNi/TiNiSi/Ti4Ni4Si7/Si. Triangular NiSi2 islands are now embedded in the Ti4Ni4Si7 layer. A mechanism of interfacial microstructure evolution is proposed to explain the temperature effect on the interfacial reaction layers between the TiNi film and the Si(100). [References: 20]