Characterization of Zero-Bias Microwave Diode Power Detectors at   Cryogenic Temperature
  We present the characterization of commercial tunnel diode low-level microwave power detectors at room and cryogenic temperatures. The sensitivity as well as the output voltage noise of the tunnel diodes are measured as functions of the applied microwave power, the signal frequency being 10 GHz. We highlight strong variations of the diode characteristics when the applied microwave power is higher than few microwatt. For a diode operating at ${4}$ K, the differential gain increases from ${1,000}$ V/W to about ${4,500}$ V/W when the power passes from ${-30}$ dBm to ${-20}$ dBm. The diode present a white noise floor equivalent to a NEP of ${0.8}$ pW/ ${\sqrt{\mathrm{Hz}}}$ and ${8}$ pW/${ \sqrt{\mathrm{Hz}}}$ at 4 K and 300 K respectively. Its flicker noise is equivalent to a relative amplitude noise power spectral density ${S_{\alpha}(1~\mathrm{Hz})=-120}$~dB/Hz at ${4}$ K. Flicker noise is 10 dB higher at room temperature. 
Vincent Giordano, Christophe Fluhr, Beno\^it Dubois and Enrico Rubiola
physics.ins-det