Dual-Polarization Sensitive MKIDs for Far Infrared Astrophysics

Abstract

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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$T_{c} \sim 4.5\ \hbox{K}$</tex></formula> . 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 ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&gt;$</tex></formula> 700 GHz). Simulations of the optical coupling show 83% co-polar and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\leq$</tex></formula> 0.3% cross-polar coupling averaged over a 400 GHz band centered on 1.2 THz. The intrapixel resonator cross-talk is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&lt;$</tex></formula> 0.01%. Arrays of dual-polarization sensitive LEKIDs (or POLEKIDs) will be deployed on the balloon-borne instrument super-BLASTPol.