Dual-Polarization Sensitive MKIDs for Far Infrared Astrophysics

We present the design for arrays of dual-polarization sensitive, superconducting sensors for far infrared astrophysics. Each pixel is feedhorn-coupled and consists of orthogonal, lumped-element kinetic inductance detectors (LEKIDs) both fabricated in the same deposition layer. Each LEKID pair contains an absorptive “one-turn” inductor and a large interdigitated capacitor (IDC) made of stoichiometric titanium nitride (TiN) with T_c ~ 4.5 K. Crossovers between the two inductors are bridged with short sections of niobium. This design enables dual-polarization sensitivity at frequencies above the superconducting gap of niobium (>; 700 GHz). Simulations of the optical coupling show 83% co-polar and ≤ 0.3% cross-polar coupling averaged over a 400 GHz band centered on 1.2 THz. The intrapixel resonator cross-talk is <; 0.01%. Arrays of dual-polarization sensitive LEKIDs (or POLEKIDs) will be deployed on the balloon-borne instrument super-BLASTPol.