Doctoral Thesis¶
PhD, Electrical Engineering and Computer Science - MIT (2025)
Superconducting Nanowire Integrated Circuits for Scalable Cryogenic Memory
Advisor: Professor Karl Berggren
Abstract:
Superconducting nanowire integrated circuits (SNICs) are a promising class of cryogenic electronics that harness the zero resistance, high kinetic inductance, and nanoscale geometry of ultrathin superconducting wires to implement logic, memory, amplification, and sensing with minimal energy dissipation. Unlike Josephson-junction-based circuits, SNICs support compact, planar layouts compatible with single-layer fabrication and operation in unshielded cryogenic environments.
This thesis develops superconducting nanowire memory (SNM) as a scalable implementation of SNICs. A modular cell architecture is introduced, exploiting hysteretic switching and inductive asymmetry to enable nonvolatile digital state storage with zero static power consumption. A hierarchical design framework is established, combining automated layout generation, electrothermal simulation in LTspice, and microscopic modeling using the time-dependent Ginzburg–Landau (TDGL) formalism.
To enable scalable integration, this work implements a row–column SNM array layout and demonstrates fabrication across full 4-inch wafers using a planar, single-layer process. Cryogenic measurements validate reliable operation in both single cells and multi-cell arrays, confirming the predictive accuracy of the design and modeling framework. Tradeoffs in bias current levels, pulse timing, and read/write conditions are systematically evaluated through cryogenic measurements, revealing their impact on bit error rate, operational margins, and energy efficiency across single cells and arrays.
Together, these contributions establish SNICs as a viable and extensible platform for cryogenic memory, providing the tools, models, and infrastructure needed to enable broader adoption in quantum computing, neuromorphic systems, and other energy-constrained cryogenic applications.
Master’s Thesis¶
MS, Electrical Engineering and Computer Science - MIT (2022)
Investigation of Thin Film Supercurrent and Photodetection in Wide Niobium Nitride Wires
Advisor: Professor Karl Berggren
Abstract: Over the past two decades, superconducting nanowire single photon detectors have become the dominant platform for detection at telecommunication wavelengths. Despite their practical success, the theoretical framework that describes the detection mechanism within the nanowire is continually evolving. Early phenomenological models suggested that a hot region forms across the superconducting strip after the arrival of a photon, producing a measurable voltage only if the diameter of the hot region extends across the width of the strip. However, predictions based on the kinetic-equation approach showed that within a certain operating regime detection no longer depends on the strip’s width. This prediction was later supported by the experimental demonstration of single photon detection in strips 1-3 𝜇m wide. The ability to fabricate detectors with larger widths would allow for higher signal to noise ratios as well as higher fabrication yield compared to narrow wires. These advantages could potentially unlock some long sought after applications of single photon detectors such as large area detectors or >kilopixel arrays of detectors. In order to produce wide wire detectors the design and material properties must be well optimized. This thesis will cover the development of wide single photon detectors using nitrogen rich niobium nitride.