Microstructure and electrical characteristics of Ni–Cr thin films

Microstructure of thin films of different compositions of Ni–Cr alloy, over the range from 40 wt.% to 80 wt.% Ni, deposited on silicon nitride coated GaAs substrates, is investigated under Transmission Electron Microscope (TEM) in as-deposited and annealed conditions. The procedure of wet etching vias through GaAs substrates is used for preparing samples for TEM. Microstructures of as-deposited films of different Ni–Cr alloys are related to the nature of the parent alloy in the binary phase diagram. The microstructural transformations in annealed films of single and two-phase alloy materials are interpreted based on the comparison of TEM micrographs in conjunction with the X-ray diffraction and electron diffraction data. The changes in the electrical characteristics such as resistivity and temperature coefficient of resistance (TCR) of the films in relation to the microstructural transformations are discussed. The effect of superimposing a polyimide layer on the TCR of Ni–Cr films is also discussed.