Multilayer vias play a crucial role in the interconnection of different layers within electronic devices, enabling the transmission of signals and facilitating complex circuit designs. This abstract presents a comprehensive overview of the structural analysis and fabrication approach for multilayer vias, focusing on their importance, fabrication techniques, and characterization methods.

The abstract emphasizes the significance of multilayer vias as key components in modern electronic devices, enabling efficient signal transmission and improving overall circuit performance. It highlights the importance of understanding the structural properties of these vias to ensure their functionality and reliability.

The abstract also discusses various fabrication techniques employed for multilayer vias, such as deposition, lithography, and etching processes. It emphasizes the need for precise control and optimization of these fabrication steps to achieve high-quality vias with desired dimensional and geometric characteristics.

In addition, the abstract briefly mentions the characterization methods utilized to assess the structural properties of multilayer vias, such as optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). These characterization techniques provide valuable insights into the morphology, surface roughness, and dimensional accuracy of the fabricated vias.

Overall, this abstract serves as a concise overview of the structural analysis and fabrication approach for multilayer vias. It highlights the importance of understanding their structural properties, discusses key fabrication techniques, and briefly mentions the characterization methods used to assess their quality. This information provides a foundation for further research and development in the field of multilayer via technology.

Superconducting digital logic electronics based on Josephson junctions is established as the ultra-fast speed and ultra-low power consumption microelectronics device. Significant progress has been made in the development of superconducting digital circuits based on low Tc superconductors. Rapid single flux quantum (RSFQ) logic has been experimentally demonstrated to operate up to 770 GHz clock frequency with a bit-error rate close to the measurement limit. The power consumption is extremely low in such high-frequency operation, about three orders of magnitude less than that of CMOS logic. The energy dissipation of Quantum flux parametron (QFP) has been reduced to the order of zJ per transition. However, low Tc digital circuit requires more complicated cryogenic systems to operate below liquid helium temperature (sub-kelvin temperatures). An effort has been made to develop high Tc digital circuits for operation above nitrogen temperatures. Further development is needed to solve a number of problems. In order to enable circuit functionalities and complexities required for computing, a very large-scale integration of superconducting circuit is needed. Compared to the typical CMOS circuit integration scale, due to the physical limitations on the size of superconducting logic cells made by the traditional fabrication process, the present superconducting integrated circuit density is several orders of magnitude lower.

The realization of using a focused helium ion beam (FHIB) to write an over-damped Josephson junction on the material of yttrium barium copper oxide (YBCO) will further extend the digital logic technology to high Tc superconductors and allow the circuit to be tested at liquid helium temperature, which will also make the integration with nitrogen-cooled circuits easier. Furthermore, a multilayer process is presently used to make Josephson junction, which is complicated and limits the scale of the circuit. The ion irradiation technology makes the circuits simpler. It is possible to fabricate nanoscale circuits, allowing to design of more complex circuits and solving the challenge of large-scale integration. In this dissertation, we show the simulations and measurements of some basic RSFQ cells made by high Tc materials, which can monitor the propagation of signals and prove the logic function of the chip fabricated by FHIB technology. In the future, we will continue the prospects for a further increase of the operation temperature and implementation of a complex digital circuit.

Understanding superconductivity at high temperatures has been an evasive scientific hurdle. This thesis outlines efforts taken by the author to exploit recent advances in nanofabrication through helium focused ion beam (He-FIB) for the advancement of scientific and technical understanding of high-transition temperature superconductivity. He-FIB has recently been shown to be a promising technique for the fabrication of high-quality directly-written planar Josephson junctions (JJs) with tunable parameters in YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO). Herein, it is demonstrated that these He-FIB JJs are fundamental building blocks of common superconducting circuits in novel planar geometries like superconducting quantum interference devices, gradiometers, and single flux quantum logic. Furthermore, it is demonstrated that the He-FIB direct-write technique can be utilized in rare earth based cuprates, such as HoBCO, and exfoliated BSCCO, which may lead to advanced three-dimensional circuits by combining the He-FIB direct-written JJs with the intrinsic $c$-axis BSCCO JJs. I demonstrate that series arrays of closely spaced, planar long JJs are transducers of magnetic flux featuring high-dynamic range and wide-bandwidth and that they are operable at cryogenic nitrogen temperatures. For this application, a robust automated process using FIB nanolithography for layout designs with feature sizes from sub-nanometer to millimeter scales is developed. Additionally, the JJ array’s geometry and properties for magnetic flux sensing are optimized. I present a series array of long JJs fabricated in YBCO containing 2640 JJs with a critical current deviation of 30\% exhibiting a sensitivity of 1.7 mV/$\mu$T and a linear response over a range of 10 $\mu$T at 40 K, resulting in a dynamic range of 100 dB. The exact nature of the order parameter is not completely understood in cuprate materials, which can impact the performance of these devices. Direct-written planar JJs offer a novel way to characterize cuprate superconductors in their $a$-$b$ plane regarded to be the site of superconductivity in these materials. Measurements of the density of states are taken at variable angles to help determine the practical order pairing symmetry. Measurements indicate a significant $s$-wave component mixed with no more than 30\% of the prominent $d$-wave symmetry.

This dissertation reports the results of the investigation of a novel Y-Ba-Cu-O helium ion damaged Josephson junction mixer. Mixers, also known as a heterodyne detectors, are crucial tools for the study of spectroscopy, due to their ability to achieve the needed high spectral resolution to resolve the fine features in spectral lines. Current state of the art heterodyne detectors rely on low transition temperature superconductors, which have demanding cryogenic requirements. The motivation behind developing a high transition temperature superconducting mixer is their ability to be implemented in space and balloon missions where relaxed cryocooling is important. Commercially grown Y-Ba-Cu-O thin films are acquired and utilized for the fabrication and testing of devices. I have developed a large scale fabrication process that allows high yield throughput of patterned chips on a 2-inch wafer. In this process several 5 x 5 mm devices are patterned with a planar spiral antenna, then etched to prepare for implementation of the junction at the center of the antenna. The junction is created by irradiating a focused helium ion beam on the Y-Ba-Cu-O film. These Helium Ion Josephson Junctions feature unique transport properties that are dependent upon the ion dose. For low doses of helium irradiation, the junctions have metallic barriers. For higher doses of irradiation, insulator barriers are created. The direct write process involved in the fabrication of the junction allows the junction size to be aggressively scaled down to produce high impedance devices. I have measured the DC electrical transport properties of several junctions with varying doses and widths to successfully demonstrate the ability to tune the impedance of the junction to the spiral planar antenna, which has proven difficult with other Josephson Junction mixers. The ability to match the junction impedance to the antenna improves the performance of the mixer and eliminates the need for complex circuitry that is currently used for impedance matching. The mixer performance of these devices were investigated by irradiating the junction with frequencies ranging from 90 GHz -- 2.5 THz. In addition a model was developed to fit the experimental measurements and further approximate the mixer performance from existing mixer theory. I demonstrated that an existing model for Josephson junctions can be adapted to fit the experimental data for the novel type helium ion Josephson Junctions. This model is also useful for other applications outside of mixers since it can be used to determine the fundamental parameters of a junction.

This dissertation reports on experimental results on growth fabrication and electrical transport

analysis of thin film rare earth cuprate oxide (ReBCO's) superconductors with high transition temperatures. Motivation for these studies exist based on current advancements within the superconducting community with superconducting digital logic circuits. Our studies of novel films such as HoBCO exhibit high critical current densities of 3MA/cm2 and EuBCO with the highest reported transition temperature of 94K. These film properties rival the best YBCO thin films that are commercially available based upon electrical transport data and surface morphology characterization. We hope to develop improved superconducting devices based on these optimal properties. I show based on Josephson junction tunneling effect both the critical current values as well as energy gap properties within the varied ReBCO materials. Furthermore I investigate the effect of substrate matching with the new ReBCO series to show twinning boundary alignment. For film growth I show a novel method involving an oxygen plasma source used during in-situ oxide sputtering of ReBCOs which as yet has not been reported. With this technique I am able to decrease the time required at elevated grow temperatures which allows for less boundary migration between the substrate and the thin film. Also by controlling the oxygen plasma, elemental oxygen is more easily absorbed into the lattice during growth which allows us to quench our crystals to room temperature avoiding the need for a high pressure oxygen anneal.

Also mentioned is are experimental results of creating superconducting vias for multilayer device applications. Superconducting ramps that allow a-b plane electrical transport were developed to better enhance devices such as superconducting quantum interference device (SQUID) magnetometers. Through this experiment I combine previous oxygen plasma growth techniques to mitigate ground plane electrical transport degradation brought on by the elevated temperatures required for thin film cuprate growth.