Microstrip-coupled TES bolometers for CLOVER

Clover aims to detect the signature of gravitational waves from inflation by measuring the B-mode polarization of the cosmic microwave background. We have produced microstrip-coupled TES detectors for Clover. The dark NEP of these detectors is dominated by the fundamental phonon-noise limit and we have measured high optical detection efficiencies in these devices with two completely different RF architectures: a finline transition and a four-probe OMT. Clover consists of two telescopes: one operating at 97 GHz, and one with a combined 150/220-GHz focal plane. The 220-and 150-GHz detectors use waveguide probes while the 97-GHz detectors use finline transitions to couple waveguide modes into the microstrip. Each detector is fabricated as a single chip to ensure a 100% operational focal plane. The detectors are mounted in eightpixel modules and the focal planes are populated using 12 detector modules per detection frequency. Each detector module contains a time-division SQUID multiplexer to read out the detectors. Further amplification of the multiplexed signals is provided by SQUID series arrays. We describe the design of the Clover detectors and present measurements of the prototype detectors' performance showing that they satisfy the requirement of photon-noise limited operation on Clover.