  Large mass single-electron-resolution solid state detectors are desirable to
search for low mass dark matter candidates and to measure coherent elastic
neutrino nucleus scattering (CE$\nu$NS). Here, we present results from a novel
100 g phonon-mediated Si detector with a new interface architecture. This
detector gives a baseline resolution of $\sim 1 e^{-}/h^{+}$ pair and a leakage
current on the order of $10^{-16}$ A. This was achieved by removing the direct
electrical contact between the Si crystal and the metallic electrode, and by
increasing the phonon absorption efficiency of the sensors. The phonon signal
amplification in the detector shows a linear increase while the signal to noise
ratio improves with bias voltage, up to 240 V. This feature enables the
detector to operate at a low energy threshold which is beneficial for dark
matter and CE$\nu$NS like searches.
