Antenna Coupled MKID Performance Verification at 850 GHz for Large Format Astrophysics Arrays

Abstract

Next generation sub-mm imaging instruments require kilo-pixel focal plane arrays filled with background limited detectors. Microwave kinetic inductance detectors (MKIDs) are a state-of-the-art detector for future instruments due to their inherent multiplexing capabilities. An MKID consists of a superconducting resonator coupled to a feed-line that is used for readout. In the device presented here radiation coupling is achieved by coupling the MKID directly to a planar antenna. The antenna is placed in the focus of an extended hemispherical lens to increase the filling factor and to match efficiently to fore optics. In this paper, we present the design and the optical performance of MKIDs optimized for operation in a 100-GHz band around 850 GHz. We have measured the coupling efficiency, frequency response, and beam patterns and compare those results to simulated performance. We obtain an excellent agreement between the measured and simulated beam pattern, frequency response, and absolute coupling efficiency between a thermal calibration source and the power absorbed in the detector. Additionally, we demonstrate that antenna coupled MKIDs offer background limited radiation detection down to ∼100 aW of power absorbed in the detector.

Full characterisation of a background limited antenna coupled KID over an octave of bandwidth for THz radiation

“…Here, g rad is the radiation efficiency, defined as the fraction of the power absorbed by the central conductor of the coplanar waveguide (CPW) line in the KID, and g tap is the taper efficiency, which relates to the illumination of the lens. A detailed explanation of these efficiencies in antenna coupled KIDs can be found in Ferrari et al 11 We find g rad ¼ 0.77, g tap ¼ 0.86, and g ap ¼ 0.66 for our design.…”

“…Such sensitivities and photon noise performance are achieved with antenna coupled aluminium (Al) KIDs over a broad band 9 around 1.5 THz with poor beam quality and over a narrow band around 850 GHz. 5,11 In this paper, we extend KID technology to higher frequencies and large bandwidths using a leaky lens antenna coupled device.…”

“…To measure the NEP and coupling efficiency of the detector, we use the method developed by Ferrari et al 11 The measured NEP is given by NEP 2 ðxÞ ¼ S h ðxÞ=ðdh= dP abs Þ 2 , where S h is the power spectral density of the phase signal and dh/dP abs is the phase responsivity. We measure an optical NEP equal to 2.5 Â 10 À19 W/Hz 1=2 at the lowest loading and is shown in Fig.…”

Wideband on-chip terahertz spectrometer based on a superconducting filterbank

“…The chip couples to linearly polarized radiation using a double slot antenna, patterned using UV contact lithography and plasma etching in a SF 6 + O 2 plasma, followed by an in-situ O 2 cleaning. 21 The antenna is placed in the focus of a 8 mm extended-hemispherical Si lens, 22 which is anti-reflection coated with a 130 µmthick layer of Parylene-C. 23 The received signal is guided to the filterbank through the terahertz line: a coplanar waveguide (CPW) patterned in the NbTiN ground plane. The filterbank sorts the wideband signal into 49 sub-bands by means of narrow band pass filters.…”

“…The ground planes of the readout line, and the terahertz line, are balanced using aluminium bridges with dielectric bricks fabricated from spin-coated polyimide LTC9505 from Fujifilm. 21 As a reference for the terahertz signal power at the input of the filterbank, three 'wideband MKIDs' are placed before the filterbank; these are MKIDs that are weakly coupled to the terahertz line directly without a filter, with a nearly constant power coupling of −27 dB over the relevant frequency range. Similarly, another three wideband MKIDs are placed after the filterbank for a reference of the power that runs through the filterbank without being drawn out by the filter channels.…”