This work presents a comparison of two generations of Superconducting nanowire Single-Photon Detector (SnSPD) prototypes used for Time-Resolved Emission (TRE) measurements from VLSI chips. The performance of the systems is compared in order to understand the figures of merit that a single-photon detector should have to enable the acquisition of time resolved emission waveforms for ultra-low voltage applications. We will show that measurements down to a new World record low 0.4 V supply voltage were made possible by a careful optimization of the detector front-end electronics. We also characterized the emission from devices with different threshold voltages in order to understand how the emission contributions depend on this parameter and how this affects the resulting waveform SNR.

In this paper, we present a Superconducting Nanowire Single Photon Detector (SnSPD) system and its application to ultra low voltage Time-Resolved Emission (TRE) measurements (also known as Picosecond Imaging Circuit Analysis, PICA) of scaled VLSI circuits. The 9 µm-diameter detector is housed in a closed loop cryostat and fiber coupled to an existing Emiscope III tool for collecting spontaneous emission light from the backside of integrated circuits (ICs) down to a world record 0.5 V supply voltage in a few minutes.