Compact chromium oxide thin film resistors for use in nanoscale quantum circuits

We report on the electrical characterisation of a series of thin amorphous chromium oxide (CrO_x) films, grown by dc sputtering, to evaluate their suitability for use as on-chip resistors in nanoelectronics. By increasing the level of oxygen doping, the room-temperature sheet resistance of the CrO_x films was varied from 28 $Ω/◻$ to 32.6 k$Ω/◻$⁠. The variation in resistance with cooling to 4.2 K in liquid helium was investigated; the sheet resistance at 4.2 K varied with composition from 65 $Ω/◻$ to above 20 G$Ω/◻$⁠. All of the films measured displayed linear current–voltage characteristics at all measured temperatures. For on-chip devices for quantum phase-slip measurements using niobium–silicon nanowires, interfaces between niobium–silicon and chromium oxide are required. We also characterised the contact resistance for one CrO_x composition at an interface with niobium–silicon. We found that a gold intermediate layer is favourable: the specific contact resistivity of chromium-oxide-to-gold interfaces was 0.14 mΩcm², much lower than the value for direct CrO_x to niobium–silicon contact. We conclude that these chromium oxide films are suitable for use in nanoscale circuits as high-value resistors, with resistivity tunable by oxygen content.