PROCEEDINGS ARTICLE | July 19, 2016
Proc. SPIE. 9914, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VIII
KEYWORDS: Bolometers, Sensors, Silicon, Physics, Receivers, Detector arrays, Antennas, Niobium, Technetium, Semiconducting wafers
Detectors for cosmic microwave background (CMB) experiments are now essentially background limited, so a
straightforward alternative to improve sensitivity is to increase the number of detectors. Large arrays of multichroic
pixels constitute an economical approach to increasing the number of detectors within a given focal plane area. Here, we
present the fabrication of large arrays of dual-polarized multichroic transition-edge-sensor (TES) bolometers for the
South Pole Telescope third-generation CMB receiver (SPT-3G). The complete SPT-3G receiver will have 2690 pixels,
each with six detectors, allowing for individual measurement of three spectral bands (centered at 95 GHz, 150 GHz and
220 GHz) in two orthogonal polarizations. In total, the SPT-3G focal plane will have 16140 detectors. Each pixel is
comprised of a broad-band sinuous antenna coupled to a niobium microstrip transmission line. In-line filters are used to
define the different band-passes before the millimeter-wavelength signal is fed to the respective Ti/Au TES sensors.
Detectors are read out using a 64x frequency domain multiplexing (fMux) scheme. The microfabrication of the SPT-3G
detector arrays involves a total of 18 processes, including 13 lithography steps. Together with the fabrication process, the
effect of processing on the Ti/Au TES’s Tc is discussed. In addition, detectors fabricated with Ti/Au TES films with Tc
between 400 mK 560 mK are presented and their thermal characteristics are evaluated. Optical characterization of the
arrays is presented as well, indicating that the response of the detectors is in good agreement with the design values for
all three spectral bands (95 GHz, 150 GHz, and 220 GHz). The measured optical efficiency of the detectors is between
0.3 and 0.8. Results discussed here are extracted from a batch of research of development wafers used to develop the
baseline process for the fabrication of the arrays of detectors to be deployed with the SPT-3G receiver. Results from
these research and development wafers have been incorporated into the fabrication process to get the baseline fabrication
process presented here. SPT-3G is scheduled to deploy to the South Pole Telescope in late 2016.
