Measurements of AlMn TES bolometers well described by simple electrothermal model

Cosmic microwave background (CMB) polarization experiments utilize arrays of low temperature detectors, such as superconducting transition-edge sensor (TES) bolometers. Voltage-biased TES bolometers must be embedded in a readout circuit that allows for stable operation. To ensure stability and to test our physical and electrothermal model of these devices, measurements aimed at characterizing the dynamics of the sensor over the range of detector bias and loading conditions relevant to our application are carried out for multiple bolometer designs. In this work, we present bolometer electrothermal properties derived from current-voltage curves, effective electrothermal time constant measurements, and complex impedance measurements of AlMn TES bolometers intended for the Ali CMB Polarization Telescope (AliCPT). All bolometers consist of 385nm thick 1400 ppma AlMn film with measured superconducting critical temperature Tc = 480 mK. The bolometers are well-described by a simple, one-pole electrothermal model with a natural time constant τ0 that we adjust by varying the leg geometry and the amount of PdAu thermal ballast on the bolometer island. From these measurements, we determine that the volumetric heat capacity of sputtered PdAu (atomic percentages 67.6%/32.4%) at 480mK is 0.22 fJ/(K·μm3). Finally, we present the TES parameters as a function of operational resistance and over a range of loading conditions.