Electrically Conductive Pt-Zr-B and Pt-Si Thin Films for Use in High Temperature Harsh Environments

Abstract

ABSTRACTStable, electrically conductive, thin film materials are key components for high temperature sensors operating in harsh environments. In this work, nanocomposite Pt-Zr-B and Pt-Si thin film materials were grown to a nominal thickness of 200 nm on both r-cut sapphire (α-Al2O3) substrates using e-beam evaporation, and their structure, morphology, and chemical composition was characterized following thermal treatments in an air laboratory furnace up to 1300°C. In the Pt-Zr-B system, oxidation of a nanolaminate architecture consisting of ZrB2 and pure Pt layers leads to boron oxide evaporation and the formation of Pt grains decorated by tetragonal-ZrO2 nanocrystallites at high temperature. Electrical conductivity measurements with a 4-point probe show that this nanocomposite film structure can maintain a film conductivity > 1x106 S/m up to 1300°C, depending on the Pt/ZrB2 layer thickness ratio. In the Pt-Si system, film compositions were varied to yield either nanocrystalline Pt3Si, Pt2Si, or PtSi phases depending on the Pt-Si ratio, or an amorphous phase at high Si content. Above 1000°C in air, Pt-oxide and Si-oxide phases form and coexist with the Pt-Si phases, and some Pt-Si film conductivities remain as high as 1x106 S/m after annealing at 1000°C for 6 hours. It was found that a 100 nm thick amorphous alumina capping layer grown by atomic layer deposition (ALD) aids in limiting film oxidation, but film stress leads to regions of delamination.