Auxiliary components for kilopixel transition edge sensor arrays

We have fabricated transition edge sensor bolometer focal plane arrays sensitive to mm-submillimeter (0.1–3 THz) radiation for the Atacama Cosmology Telescope (ACT), which will probe the cosmic microwave background at 145, 215, and 280 GHz. Central to the performance of these bolometers is a set of auxiliary resistive components. Here we discuss shunt resistors, which allow for tight optimization of bolometer time constant and sensitivity. Our shunt resistors consist of AuPd strips grown atop interdigitated superconducting MoNx wires. We can tailor the shunt resistance by altering the dimensions of the AuPd strips and the pitch and width of the MoNx wires and can fabricate all of the shunts necessary for a kilopixel focal plane bolometer array on a single 4″ wafer. By modeling the resistance dependence of these parameters, a variety of different 0.75 ± 0.05 mOhm shunt resistors have been fabricated. This variety includes different shunts which have MoNx wires with wire width equal to 1.5 and 10 μm and pitch equal to 4.5 and 26 μm, respectively. Our ability to set the resistance of the shunts hints at the scalability of our design. We have also integrated a SiO2 capping layer into our shunt resistor fabrication scheme, which inhibits metal corrosion and eventual degradation of the shunt. Consequently, their robustness coupled with their high packing density makes these resistive components attractive for future kilopixel detector arrays.