Development of the Low Frequency Universal Focal Plane Modules for the Simons Observatory

The Simons Observatory is a state of the art cosmic microwave background experiment deploying a series of telescopes to Cerro Toco in Northern Chile. The project will begin deployment and operations in 2023 with the installation of the first of three small aperture telescopes. These SATs are sensitive to the large angular scales of the cosmic microwave background with a primary focus on b-mode inflationary science. In addition, SO will deploy a large aperture telescope sensitive to smaller angular scales to help with foreground cleaning and provide a wide variety of astrophysical science. In total, SO will operate ~60,000 detectors spread across six frequency bands ranging from 27 to 285 GHz with angular resolutions ranging from 1 arcminute to tens of degrees. The six bands are divided into 3 groups of modules which we refer to as low-, mid-, and high-frequency (LF, MF, and HF respectively) universal focal plane modules (UFMs). In this work we present on the development of the LF modules which will observe the CMB from both a SAT and the LAT platforms. A UFM consists of a detector optical stack and universal microwave multiplexing module and is compatible with either telescope. Each LF DOS is an array of borosilicate-coated silicon lenselts mated to an array of sinuous antenna arrays coupled to transition edge sensor bolometers. The UMM contains the cold readout hardware for the microwave squid multiplexing used by SO. In these proceedings, we present on the design, fabrication, and characterization of the modules in preparation for deployment in late 2023.