Low-noise low-mass front end electronics for low-background physics experiments using germanium detectors

A low-noise resistive-feedback front-end electronics assembly has been developed for use with p-type point contact (PPC) Ge detectors in low background experiments. The front end was designed to have a low mass and potentially low radioactivity. It is fabricated on a fused silica substrate, and consists of a low-noise JFET, a feedback resistor formed from an amorphous Ge thin film, and feedback capacitor based on the stray capacitance between circuit traces. The substrate provides the appropriate thermal impedance to allow the FET to operate at the optimal temperature from self-heating when one side of the substrate is held at liquid nitrogen temperature. A noise level of 85 eV FWHM at 20 us peaking time has been observed in combination with a small PPC detector, the 1/f contribution being as low as 30 eV for the front end alone. This approach of employing ultra-low-mass and low-noise front-end electronics in combination with larger-size PPC detectors can be an enabling technology towards the observation of particles and processes such as neutrino-less double-beta, coherent neutrino scattering or cold dark matter.