George A. Hernandez

Flexible superconducting Nb transmission lines on thin film polyimide for quantum computing applications

We describe progress and initial results achieved towards the goal of developing integrated multi-conductor arrays of shielded controlled-impedance flexible superconducting transmission lines with ultra-miniature cross sections and wide bandwidths (dc to >10 GHz) over meter-scale lengths. Intended primarily for use in future scaled-up quantum computing systems, such flexible thin-film Nb/polyimide ribbon cables provide a physically compact and ultra-low thermal conductance alternative to the rapidly increasing number of discrete coaxial cables that are currently used by quantum computing experimentalists to transmit signals between the low-temperature stages (from ~ 4 K down to ~ 20 mK) of a dilution refrigerator. S-parameters are presented for 2-metal layer Nb microstrip structures with lengths ranging up to 550 mm. Weakly coupled open-circuit microstrip resonators provided a sensitive measure of the overall transmission line loss as a function of frequency, temperature, and power. Two common polyimide dielectrics, one conventional and the other photo-definable (PI-2611 and HD-4100, respectively) were compared. Our most striking result, not previously reported to our knowledge, was that the dielectric loss tangents of both polyimides are remarkably low at deep cryogenic temperatures, typically 100

Cryogenic microwave characterization of Kapton polyimide using superconducting resonators

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Electrical characteristics and density of states of thin-film transistors based on sol-gel derived ZnO channel layers with different annealing temperatures

smaller than corresponding room temperature values. This enables fairly long-distance transmission of microwave signals without excessive attenuation and permits usefully high rf power levels to be transmitted without creating excessive dielectric heating. We observed loss tangents as low as 2.2

Through Si vias using liquid metal conductors for re-workable 3D electronics

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Preserving Nb Superconducvity in Thin Film Flexible Structures

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Flip chip based on compliant double helix interconnect for high frequency applications

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Microwave Loss Measurements of Copper-Clad Superconducting Niobium Microstrip Resonators on Flexible Polyimide Substrates

at 20 mK. Our fabrication techniques could be extended to more complex structures such as multiconductor, multi-layer stripline or rectangular coax, and integrated attenuators and thermalization structures.

Influence of fatigue and bending strain on critical currents of niobium superconducting flexible cables containing Ti and Cu interfacial layers

Half-wavelength, capacitively-coupled superconducting microstrip resonators have been constructed on 50.8 μm (2 mil) thick flexible Kapton polyimide substrates. The metal stack-up on each side was a 50 nm Ti adhesion layer followed by a 250 nm Nb layer. These resonators yield high quality factors (loaded Q as high as 4110) at 1.2 K in the 2-10 GHz frequency range, implying a loss tangent of less than 0.000275 at 2 GHz. This work provides complex dielectric permittivity information for Kapton materials that have not previously been reported for this temperature (1-6 K) and frequency range. Furthermore it provides confidence that commercially available flexible Kapton is potentially useful as a substrate material for flexible superconducting interconnects or cables, which are of great interest for use in cryogenic electronics systems.

Embedded Niobium Using PI-2611 for Superconducting Flexible Cables

We report on the fabrication and electrical characterization of bottom gate thin-film transistors (TFTs) based on a sol-gel derived ZnO channel layer. The effect of annealing of ZnO active channel layers on the electrical characteristics of the ZnO TFTs was systematically investigated. Photoluminescence (PL) spectra indicate that the crystal quality of the ZnO improves with increasing annealing temperature. Both the device turn-on voltage (Von) and threshold voltage (VT) shift to a positive voltage with increasing annealing temperature. As the annealing temperature is increased, both the subthreshold slope and the interfacial defect density (Dit) decrease. The field effect mobility (μFET) increases with annealing temperature, peaking at 800 °C and decreases upon further temperature increase. An improvement in transfer and output characteristics was observed with increasing annealing temperature. However, when the annealing temperature reaches 900 °C, the TFTs demonstrate a large degradation in both transf...

Microwave Performance of Niobium/Kapton Superconducting Flexible Cables

This paper describes the design and fabrication of liquid metal interconnects (vias) for 2.5D and 3D integration. The liquid metal is gallium indium eutectic (78.6% Ga, 21.4% In) with a melting temperature of approximately 15.7 °C, which is introduced into via openings of a silicon interposer. This liquid metal interconnect technology can be integrated with existing interposer technologies, including capacitors and traditional (solid metal) through-silicon vias (TSVs). We anticipate that liquid metal interconnects can better accommodate thermal stresses and provide re-workability in case of chip failure or upgrade. We determined the liquid metal resistance to be 1.67 KΩ at room temperature and observed an increase in the resistance to 5.6 KΩ at 37°C.