Development of Aluminum-Based STJs for Phase-IV of the BeEST Experiment

The BeEST experiment is a model independent search for heavy neutrinos in the decay of 7Be implanted in superconducting tunnel junction (STJ) quantum sensors. The sensitivity goals for Phase-IV of the experiment require an increase in number of detectors, reduced backgrounds, and improved energy resolution from the STJs. To achieve this, we are currently developing arrays of aluminum-based STJs deposited on 500 nm silicon-nitride (SiN) membranes. In this talk, we present the design of these new devices as well as characterization of the signals.