Towards High-Temperature MEMS: Two-Step Annealing Suppressed Recrystallization in Thin Multilayer Pt-Rh/Zr Films

Area of Science:

• Materials Science
• Thin Film Technology
• Microelectronic Engineering

Background:

• Platinum-based thin films are crucial for high-temperature microelectronics (>500 °C).
• Incorporating refractory oxides like ZrO2 enhances thermal stability by impeding Pt atom mobility at grain boundaries.
• The impact of annealing conditions on multiphase Pt-oxide systems remains understudied.

Purpose of the Study:

• To investigate the effect of two-step annealing on Pt-Rh/Zr multilayer films.
• To compare two-step annealing with conventional isothermal annealing for improved film morphology and stability.
• To optimize annealing protocols for high-temperature microelectronic applications.

Main Methods:

• Fabrication of 250-nm-thick Pt-Rh/Zr multilayer films.
• Two-step annealing protocol: initial low-temperature (450 °C) followed by high-temperature (800-1000 °C).
• Characterization using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS).

Main Results:

• Two-step annealing yielded uniform Pt-Rh/Zr films without voids or hillocks, unlike isothermal annealing.
• Zirconium oxidation occurred during the first annealing step (450 °C).
• Recrystallization of the Pt-Rh alloy was observed at high temperatures (800-1000 °C).
• Pt-Rh/Zr films annealed in two steps exhibited smaller grain sizes (60 ± 27 nm) and reduced <111> texture, enhancing high-temperature stability.
• Resistivity of 17 × 10^-6 Ω·m was achieved after two-step annealing at 450/900 °C.

Conclusions:

• Two-step annealing is superior to isothermal annealing for producing stable, uniform Pt-Rh/Zr thin films.
• The optimized annealing protocol enables the fabrication of thin-film MEMS devices for demanding high-temperature environments.
• This approach is suitable for devices like microheater-based gas sensors operating above 500 °C.