Electrical Properties of Background-Limited Membrane-Isolation Transition-Edge Sensing Bolometers for Far-IR/Submillimeter Direct-Detection Spectroscopy

Abstract

We built and measured the electrical properties of membrane-isolation transition-edge sensing bolometers (TESs) suitable for background-limited far-IR/submillimeter direct-detection spectroscopy. Each TES consists of a Mo/Au bilayer patterned onto a suspended, thermally isolated absorber that is connected to the substrate through four SixNy beams deposited by low pressure chemical vapor deposition (LPCVD). We fabricated TESs with straight and meander support beams. The dimensions of the meander (straight) support beams are 700 μm (700 μm) long by 0.25 μm (0.5 μm) thick by 0.35 μm (0.5 μm) wide. We measured I–V characteristics for these TESs and determined that the thermal conductance G equals 72 fW/K (straight) and 19 fW/K (meander) for our best devices. The thermal conductance exhibits a T1/2 dependence with temperature which is evidence of effective elastic scattering of the acoustic phonon modes. The transition temperatures Tc for the same TESs are Tc=137 mK (straight) and Tc=71 mK (meander). If we assume the TESs are temperature-fluctuation noise limited, then the derived noise equivalent power (NEP) equals 1.9×10−19 W/Hz1/2 (straight) and 6.1×10−20 W/Hz1/2 (meander), using our measured values for G and Tc. The meander-beam TES has a derived NEP that is close to two orders of magnitude lower than the state-of-the-art. Finally, we measured an effective time constant τ of about 300 ms (straight) and 400 ms (meander) using electrical and optical pulses. These values for the NEP and τ for the meander-beam TES meet the requirements for the Background-Limited far-IR/Submillimeter Spectrograph (BLISS), a proposed NASA instrument.