Grain growth in Pt microheaters subjected to high current density under constant power

Abstract

When $50$ nm thick Pt microheaters of lateral dimensions $1\times10$ $\mu$m$^2$ are subjected to high electric power their resistance $R$ rises, as expected. Following an initial rise however there is a gradual decrement in $R$ while constant electric power dissipation is maintained. We find that this lowering in $R$ is accompanied by grain growth in the polycrystalline thin Pt film of our heaters. This is confirmed by XRD measurements and SEM imaging. Similar growth in grain size is observed in thin Pt films that are oven-annealed at high temperatures. Thus we argue that maintaining high power dissipation in a microheater has the same effect on its material structure as post-annealing. We observe the in-plane grain size of a $50$ nm thick as-grown Pt film/heater to be $D_\parallel=15$ nm. When post-annealed at a temperature of $T=600^\circ$C for 30 min, $D_\parallel=30$ nm, compared with when electric current is run through a heater we estimate the mean crystalline length to be $D_\parallel=35$ nm.