Observation of 45 GHz current waveforms using HTS sampler

We succeeded in observing high-frequency current waveforms up to 45 GHz using a high-temperature superconducting (HTS) sampler. In this experiment, we used a sampler circuit with a superconducting pickup coil, which magnetically detects current signals flowing through a micro-strip line on a printed board placed outside the cryochamber. This type of measurement enables non-contact current-waveform observation that seems useful for analyses of EMI, defects in LSI, etc. Computer simulation reveals that one of our latest versions of HTS sampler circuits having Josephson transmission lines with optimized biases as buffers has a potential of sampling high-frequency signals with a bandwidth above 100 GHz. To realize the circuit parameters required in the simulations, we developed an HTS circuit fabrication process employing a lower ground plane structure with SrSnO3 insulating layers. We consider that improvement of the circuit fabrication process and optimization of the pickup coil lead to much higher signal frequency observable by the sampler.