Titanium nitride films for ultrasensitive microresonator detectors

Titanium nitride (TiNx) films are ideal for use in superconducting microresonator detectors for the following reasons: (a) the critical temperature varies with composition (0 < T-c <5 K); (b) the normal-state resistivity is large, p(n) similar to 100 mu Omega cm, facilitating efficient photon absorption and providing a large kinetic inductance and detector responsivity; and (c) TiN films are very hard and mechanically robust. Resonators using reactively sputtered TiN films show remarkably low loss (Q(i)>10(7)) and have noise properties similar to resonators made using other materials, while the quasiparticle lifetimes are reasonably long, 10-200 mu s. TiN microresonators should therefore reach sensitivities well below 10(-19) W Hz(-1/2). (C) 2010 American Institute of Physics. [doi: 10.1063/1.3480420]