280 GHz Focal Plane Unit Design and Characterization for the SPIDER-2 Suborbital Polarimeter - Bergman, AS; Ade, PAR; Akers, S; Amiri, M; Austermann, JA; Beall, JA; Becker, DT; Benton, SJ; Bock, JJ; Bond, JR; Bryan, SA; Chiang, HC; et al. (JOURNAL OF LOW TEMPERATURE PHYSICS, 2018)