Characterization of Antenna-Coupled TES Bolometers for the Spider Experiment

We describe the transition-edge-sensors (TES's) to be employed on the Spider experiment, a balloon-based observatory whose goal is detecting the imprint of gravitational waves by mapping the polarization of the cosmic microwave background (CMB). The devices consist of Ti and Al thermistors in series sitting on a thermally isolated suspended membrane. Also on the membrane is a termination resistor coupled through a superconducting microstrip line to an on-chip, polarization sensitive, 150 GHz slot-array antenna. Several important parameters were measured. Transition temperatures were deduced by measuring the Johnson noise in the Ti thermistor. The thermal conductance between the isolated TES islands and substrate was measured by obtaining current-voltage measurements at various temperatures. The Electrical noise equivalent power was measured to sub-Hertz frequencies with varying sample geometries including those with and without normal metal bars (zebra stripes). Finally, the time constant of the devices was measured within the Al and Ti transitions where electrothermal feedback speeds up the bolometer response. This time response is compared with the natural time constant measured just above the Ti transition temperature. The results of these measurements are within the design specifications for Spider.