The POLARBEAR-2 and Simons Array Focal Plane Fabrication Status

Abstract

We present on the status of POLARBEAR-2 A (PB2-A) focal plane fabrication. The PB2-A is the first of three telescopes in the Simons Array, which is an array of three cosmic microwave background polarization-sensitive telescopes located at the POLARBEAR site in Northern Chile. As the successor to the PB experiment, each telescope and receiver combination is named as PB2-A, PB2-B, and PB2-C. PB2-A and -B will have nearly identical receivers operating at 90 and 150 GHz while PB2-C will house a receiver operating at 220 and 270 GHz. Each receiver contains a focal plane consisting of seven close-hex packed lenslet-coupled sinuous antenna transition edge sensor bolometer arrays. Each array contains 271 dichroic optical pixels, each of which has four TES bolometers for a total of 7588 detectors per receiver. We have produced a set of two types of candidate arrays for PB2-A. The first we call Version 11 (V11) uses a silicon oxide (SiO$_x$) for the transmission lines and crossover process for orthogonal polarizations. The second we call Version 13 (V13) uses silicon nitride (SiN$_x$) for the transmission lines and cross-under process for orthogonal polarizations. We have produced enough of each type of array to fully populate the focal plane of the PB2-A receiver. The average wirebond yield for V11 and V13 arrays is 93.2% and 95.6%, respectively. The V11 arrays had a superconducting transition temperature ($T_\mathrm{c}$) of $452 \pm \,15$ mK, a normal resistance ($R_\mathrm{n}$) of $1.25 \pm 0.20~\Omega$, and saturation powers of $5.2 \pm 1.0$ pW and $13 \pm 1.2$ pW for the 90 and 150 GHz bands, respectively. The V13 arrays had a superconducting transition temperature ($T_\mathrm{c}$) of $456 \pm 6$ mK, a normal resistance ($R_\mathrm{n}$) of $1.1 \pm 0.2~\Omega$, and saturation powers of $10.8 \pm 1.8$ pW and $22.9 \pm 2.6$ pW for the 90 and 150 GHz bands, respectively. Production and characterization of arrays for PB2-B are ongoing and are expected to be completed by the summer of 2018. We have fabricated the first three candidate arrays for PB2-C but do not have any characterization results to present at this time.