Fink, C. W.Watkins, S. L.Aramaki, T.Brink, P. L.Camilleri, J.Defay, X.Ganjam, S.Kolomensky, Y. G.Mahapatra, R.Mirabolfathi, N.Page, W. A.Partridge, R.Platt, M.Pyle, M.Sadoulet, B.Serfass, B.Zuber, S.2021-06-042021-06-042021-01-110003-695122601http://hdl.handle.net/10919/103606We present the design and characterization of a large-area Cryogenic PhotoDetector designed for active particle identification in rare event searches, such as neutrinoless double beta decay and dark matter experiments. The detector consists of a 45.6 cm 2 surface area by a 1-mm-thick 10.6 g Si wafer. It is instrumented with a distributed network of Quasiparticle-trap-assisted Electrothermal feedback Transition-edge sensors with superconducting critical temperature T c = 41.5 mK to measure athermal phonons released from interactions with photons. The detector is characterized and calibrated with a collimated Fe-55 x-ray source incident on the center of the detector. The noise equivalent power is measured to be 1 x 10 - 17 W / <mml:msqrt> Hz</mml:msqrt> in a bandwidth of 2.7 kHz. The baseline energy resolution is measured to be sigma E = 3.86 +/- 0.04 ( stat . ) - 0.00 + 0.19</mml:msubsup> ( syst . ) eV. The detector also has an expected timing resolution of sigma t = 2.3 mu s for 5 <mml:msub> sigma E events.application/pdfenCreative Commons Attribution 4.0 InternationalArticle - Refereedhttps://doi.org/10.1063/5.003237211821077-3118