Ni-Cr-Based Thin-Film Cryoresistors

Ni-Cr-based thin-film resistors have been fabricated and studied at temperatures of down to 50 mK. The resistivity of the films varied within (14-25)Omega*sq, depending on the additions of Cu, Al, Ge, and Mn. The minimum temperature coefficient (TC) at 4.2 K (TC = -50 middot 10 ^-6 /K) is obtained for Ni ₇₅ Cr ₂₀ CU _2.5 AI _2.5 (Evanohm alloy) doped with 2.5% Ge. At the 50-150 mK range, the TC of the alloy increases to -4.15 middot 10 ^-6 /mK. The resistors demonstrate the Kondo minimum at 20-30 K. The power coefficient of the 560-kOmega sample, which was measured at 4.2 K, was found to be les -0.008 middot 10 ^-6 /muW. Power dependence measurements at subkelvin temperatures showed an electron overheating at the power level of above 10 p W for a 500-k film resistor.