Degradation in molybdenum thin films and Mo/AuPd bilayers and its reduction by sidewall passivation

Abstract

Molybdenum is a common material for superconducting thin films used, for example, in transition edge sensors as Mo/metal bilayers. For such applications long term stability of the superconducting parameters is essential, especially the critical temperature and the transition width. Our analysis of the effect of film oxidation on these parameters for Mo/AuPd bilayers shows that even slight oxidation will have a significant effect. A direct comparison shows the potential of sidewall passivation to reduce the degradation and stabilize these parameters.

Study of long-term stability of Mo–Cu bilayer films

“…in [21], which also helps protect the edges of the devices from corrosion. For the bilayer sample under monitoring, the measured T c variation is much smaller, compared with case in [17], probably due to a more moderate environment (air/vacuum vs water). Our results imply that oxidation enhanced the superconductivity of the bilayer film, in contrast to the case of the bare Mo film.…”

“…The best-fit value of T c0 is significantly higher than the measured T c of our pure Mo films. We note that the Mo film was likely oxidized [15][16][17], when stored in the laboratory environment, while the Mo layer in bilayer films is well protected by the overlying Cu layer against oxidation. Our results imply that oxidation suppressed the superconductivity of the Mo film.…”

“…This could explain the apparent break in the rate of increase and also the subsequent evolution. The effects of oxidation on T c and ∆T c have been studied in detail for Mo/AuPd bilayers [17], with the film samples immersed in water for different time duration or treated with sidewall passivation. The samples without sidewall passivation were found to exhibit significant changes in T c (more than 50 mK within 17 h), and to show a reduced rate of T c variation after the formation of an oxide barrier along edge, illustrating the effects of edge corrosion.…”

Optimization of radiation sensors for a passive terahertz video camera for security applications

“…The relation of the observed degradation to the superconductivity parameters of the bilayer is discussed in section 3.3.5. The results of these analyses were published in [65].…”