Performance of a microcalorimeter with a superconducting transition edge thermometer

The performance of a single-pixel microcalorimeter is described and analyzed. The microcalorimeter has a Cu absorber which is isolated from the heat bath by means of a SixNy membrane and is connected to a voltage-biased Ti/Au proximity bilayer thermometer with a transition temperature of about 150 mK. The measured FWHM energy resolution for 5.9 keV X-ray photons is 12.4 eV for this sensor while 2.36(kBT2C)1/2 equals 9.1 eV. The detector time constant is about 1 ms. The measured current-voltage characteristic and current noise spectra are analyzed in detail in the context of the energy resolution. High frequency excess noise is measured in the superconducting transition and is briefly discussed