Noise characteristics of YBCO c-axis microbridge junctions

We present measurements of the noise properties of YBCO c-axis Microbridge (CAM) Junctions. The junctions have been characterised in terms of their electrical and noise properties over range of temperature and frequency. The methods used provide both very high sensitivity measurements in a narrow frequency band (60 kHz), and moderate sensitivity measurements in a broad band (0.01-10 kHz). The normalised levels of critical current fluctuations and normal resistance fluctuations are found to be comparable to earlier measurements carried out on grain boundary junctions at both 100 Hz and 60 kHz. The 60 kHz results can be modelled reasonably successfully with the same model developed to describe grain boundary junctions. The frequency dependence is close to 1/f, but has some Lorentzian shaped deviations appearing for many of the junctions examined. These structures are both temperature and bias current dependent.