The Role of Phase Changes in TiO2/Pt/TiO2 Filaments

This work analyses the role of phase changes in TiO₂/Pt/TiO₂ layer stacks for micro-heater application regarding their stability and reliable operation. The polycrystalline Pt layer wrapped in a TiO₂ adhesion layer underwent a continuous recrystallisation in a self-heating operation causing a drift in the resistance (R) versus temperature (T) performance. Simultaneously, the TiO₂ adhesion layer also deteriorates at high temperature by phase changes from amorphous to anatase and rutile crystallite formation, which not only influences the Pt diffusion in different migration phenomena, but also reduces the cross section of the Pt heater wire. Thorough scanning electron microscopy, energy dispersive spectroscopy, cross-sectional transmission electron microscopy (XTEM) and electron beam diffraction analysis of the structures operated at increasing temperature revealed the elemental structural processes leading to the instabilities and the accelerated degradation, resulting in rapid breakdown of the heater wire. Owing to stability and reliability criteria, the conditions for safe operation of these layer structures could be determined.