Lawrence Berkeley National Laboratory

Next-generation neutrinoless double-beta ( $\mathbf {0}\boldsymbol { u }\boldsymbol {\beta }\boldsymbol {\beta }$ ) decay searches require a large detector/isotope mass and very low radioactive backgrounds. The upcoming LEGEND-1000 experiment (Large Enriched Germanium Experiment for Neutrinoless double-beta Decay) constitute a ton-scale array of several hundred high-purity germanium (HPGe) detectors enriched in 76Ge, the isotope of interest. It aims to reach a sensitivity beyond $10\mathbf {^{28}}$ years on the $\mathbf {0}\boldsymbol { u }\boldsymbol {\beta }\boldsymbol {\beta }$ decay half-life of 76Ge, necessitating an order of magnitude reduction in background with respect to the state of the art. This will require the implementation of a dedicated application specific integrated circuit (ASIC) preamplifier that will significantly lower background contribution compared to the conventional low-mass front end (LMFE) employed in the Majorana Demonstrator and LEGEND-200 experiments while maintaining or improving energy resolution and other performance parameters. Features include a high (9 MeV) dynamic range with noise low enough to achieve a trigger threshold of $\mathbf {\lt }1$ keV, a single power supply to reduce background-inducing cabling, and a differential output to maintain signal integrity over several meters of transmission line. The chip would be optimized to operate in liquid argon (87 K) and be able to do so reliably for ten years. Following on from an earlier 180-nm prototype, we have developed a differential-output charge-sensitive preamplifier ASIC fabricated in a 65-nm process, $1\times 2$ mm in size, that addresses these needs. We present recent results from the successful testing and characterization of the first version of this device.