Development of the Low Frequency Telescope Focal Plane Detector Modules for LiteBIRD

LiteBIRD is a JAXA-led strategic large-class satellite mission designed to measure the polarization of the cosmic microwave background and Galactic foregrounds from 34 to 448 GHz across the entire sky from L2 in the late 2020s. The scientific payload includes three telescopes which are called the low-, mid-, and high-frequency telescopes each with their own receiver that covers a portion of the mission's frequency range. The low frequency telescope will map synchrotron radiation from the Galactic foreground and the cosmic microwave background. We discuss the design, fabrication, and characterization of the low-frequency focal plane modules for low-frequency telescope, which has a total bandwidth ranging from 34 to 161 GHz. There will be a total of 4 different pixel types with 8 overlapping bands to cover the full frequency range. These modules are housed in a single low-frequency focal plane unit which provides thermal isolation, mechanical support, and radiative baffling for the detectors. The module design implements multi-chroic lenslet-coupled sinuous antenna arrays coupled to transition edge sensor bolometers read out with frequency-domain mulitplexing. While this technology has strong heritage in ground-based cosmic microwave background experiments, the broad frequency coverage, low optical loading conditions, and the high cosmic ray background of the space environment require further development of this technology to be suitable for LiteBIRD. In these proceedings, we discuss the optical and bolometeric characterization of a triplexing prototype pixel with bands centered on 78, 100, and 140 GHz.Comment: SPIE Astronomical Telescope + Instrumentation (AS22

Controlled sacrificial sidewall surface micromachining for the release of high length-to-thickness as

A surface micromachining technique for the release of high length-to-thickness aspect ratio (800:1) bridge structures is presented. During a timed etch release, the remaining side wall geometry of the sacrificial layer provides intrinsic support for the structural layer. The micromachining process itself is an equipment limited procedure in which the wet etchant for the sacrificial layer is replaced in solution (i.e., in situ) with a supportive photoresist layer. Once in solid form, the photoresist is removed via ashing in an oxygen plasma. This combination of controlling the sidewall etch profile of the sacrificial layer and its removal technique results in the successful release of bridge structures, which are 4000 μm long and 5 μm thick, with a 2 μm suspension gap

Integrated heaters for the thermal tuning of Bragg grating filters on silicon-on-insulator rib waveguides

The thermal tuning of a Bragg grating filter on silicon-on-insulator rib waveguides has been demonstrated with integrated resistive heaters.The thermal sensitivity is 82 pm/ × - °C with an efficiency of 4.5 nm/W. A technique for indirectly measuring the temperature of the integrated heaters is also demonstrated