Silicon-based antenna-coupled polarization-sensitive millimeter-wave bolometer arrays for cosmic microwave background instruments

Abstract

We describe feedhorn-coupled polarization-sensitive detector arrays that utilize monocrystalline silicon as the dielectric substrate material. Monocrystalline silicon has a low-loss tangent and repeatable dielectric constant, characteristics that are critical for realizing efficient and uniform superconducting microwave circuits. An additional advantage of this material is its low specific heat. In a detector pixel, two Transition-Edge Sensor (TES) bolometers are antenna-coupled to in-band radiation via a symmetric planar orthomode transducer (OMT). Each orthogonal linear polarization is coupled to a separate superconducting microstrip transmission line circuit. On-chip filtering is employed to both reject out-of-band radiation from the upper band edge to the gap frequency of the niobium superconductor, and to flexibly define the bandwidth for each TES to meet the requirements of the application. The microwave circuit is compatible with multi-chroic operation. Metalized silicon platelets are used to define the backshort for the waveguide probes. This micro-machined structure is also used to mitigate the coupling of out-of-band radiation to the microwave circuit. At 40 GHz, the detectors have a measured efficiency of ∼90%. In this paper, we describe the development of the 90 GHz detector arrays that will be demonstrated using the Cosmology Large Angular Scale Surveyor (CLASS) ground-based telescope.

The CLASS 150/220 GHz Polarimeter Array: Design, Assembly, and Characterization

“…The optical signal on the microstrip transmission lines coming from the OMTs is separated into two bands by a diplexer plus on-chip filters and terminated on the TES bolometers. For a single frequency band, the detector architecture is similar to the CLASS 90 GHz design described in [3,4]. (Color figure online.)…”

“…Similar to the 90 GHz architecture described in [2][3][4], the HF wafer package consists of three separate wafers hybridized together: a photonic choke wafer, a detector wafer, and a backshort assembly. The photonic choke [7] acts as a waveguide interface between the feedhorn array and the detectors.…”

“…The photonic choke [7] acts as a waveguide interface between the feedhorn array and the detectors. The backshort assembly [8], among its many functions [4], forms a quarter-wavelength short for the OMT antenna probes. The middle detector wafer contains the detectors fabricated on single-crystal silicon that has excellent microwave and thermal properties [4].…”

“…The backshort assembly [8], among its many functions [4], forms a quarter-wavelength short for the OMT antenna probes. The middle detector wafer contains the detectors fabricated on single-crystal silicon that has excellent microwave and thermal properties [4]. The hybridized wafer package is mounted to the CE7 feedhorn array as a single assembly.…”

“…The HF focal plane array consists of three detector modules, seen in Figure 1, with 255 dichroic dual-polarization pixels in total. Each pixel consists of four transition edge sensor (TES) bolometers that couple to light through a planar orthomode transducer (OMT) [3,4] fed by a smooth-walled feedhorn array made from an aluminum-silicon (CE7) alloy. 1 Here we describe the design and assembly, and present lab characterization of the HF detector array.…”