Ignacio Ruiz

Major: Electrical Engineering

Mentors: Michael Arena, Ben Mazin

On-Chip Superconducting Diplexers for Quantum-Limited Amplifiers in the MKID Exoplanet Camera 

Microwave kinetic inductance detector (MKID) arrays require low-noise readout to resolve individual photon energies, and traveling-wave parametric amplifiers (TWPAs) are central to achieving the necessary sensitivity in the MEC readout chain. However, integrating TWPAs into a multiplexed readout system requires isolating the amplifier's pump and signal bands without introducing excess loss or reflections that degrade detector performance. The goal of our research is to design an on-chip superconducting diplexer that separates these bands while preserving signal integrity for TWPA readout. To test our design approach, we used electromagnetic simulation in Sonnet and circuit-level modeling in Keysight ADS to model inverted microstrip diplexer geometries fabricated from titanium nitride, niobium, and amorphous silicon dielectric layers, and developed a Python-based layout and simulation workflow to iterate on device designs and extract S-parameters. We developed a low-pass filter to route signals from the MKIDs; with optimization, this filter achieved 20 dB return loss across 4–8 GHz while rejecting pump frequencies (10–11 GHz) at 20 dB. Work is currently underway on the high-pass/bandpass filter, with a promising geometry identified that should allow the filter to be completed. Once both filters are realized, they can be combined into a full diplexer for the MEC readout chain. These results indicate that the proposed geometry can achieve sufficient band isolation 46 for integration into the MEC readout chain. This work supports the broader effort to scale TWPA-based readout for large-format MKID arrays, improving energy resolution for next-generation astronomical instrumentation.