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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2020)

Internet of Things (IoT) is becoming pervasive in our daily lives. Wearable technologies will expand the connectivity of IoT and will increase the interaction between technology and human body. Micro Electro-Mechanical Systems (MEMS) microfabrication techniques that involve bulk Si micromachining and thin film processing have allowed us to develop electronic systems that are based on Si and other advanced materials that are flexible, wearable, and implantable. Wearable and implantable electronics equipped with sensors enable us to perform real-time health monitoring from above and below the skin, respectively, and can replace conventional bulky electrophysiological monitoring devices and systems.

Research efforts in wearables and implantables have intensified in the last decade tackling several aspects of the sensor technology, embedded signal processing and conditioning, energy harvesting, connectorization, functionality, longevity and reliability. However, there are still technical challenges that impose restrictions for their widespread adoption. On top of these challenges is the power source for the wearable or implantable device. Energy harvesting is expected to replace conventional battery systems that power wearables and implantables. In this dissertation, we focus on solar energy as an energy source for self-powered electronics.

In Chapter 1, the motivation of the dissertation together with a brief survey of state of the art in flexible and wearable electronics with energy harvesting system and implantable medical devices are discussed.

In Chapter 2, we disclose our parametric studies on solar cells with different microwire surface and array morphologies to understand the effect of surface passivation, surface crystal orientation on surface recombination and carrier collection on SiMW solar cells with radial p-n junctions as well as their emitter series resistances with an overall goal of maximizing their power conversion efficiencies.

In Chapter 3, we present an approach for self-powered wearable electronics by means of the monolithic integration of SiMW solar cells with Si MOSFETs on a Silicon on Insulator (SOI) wafer that is subsequently transferred to flexible substrates. The fabrication details and its application to a voltage-controlled oscillator and electrophysiological monitoring are discussed.

In Chapter 4, we discuss the details of the novel fabrication processes for the development of a stylet guided depth/laminar probe and of a surface electrocorticography (ECoG) grid that is fabricated with bio-compatible polymers (Polyimide and Parylene C) including their electrochemical characterization and their use in vivo for electrophysiological recordings in rats.

    Cover page: Advanced Microfabrication Technologies for Wearable Solar Energy Harvesting and Electrophysiology Monitoring Devices
    • Article
    • Peer Reviewed
    UC Lab Fees Research Program (LFRP) Funded Publications (2018)
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2015)
      Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale.
        Cover page: Atomic scale analysis of the enhanced electro- and photo-catalytic activity in high-index faceted porous NiO nanowires.Creative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC Lab Fees Research Program (LFRP) Funded Publications (2017)
        We report a new hybrid integration scheme that offers for the first time a nanowire-on-lead approach, which enables independent electrical addressability, is scalable, and has superior spatial resolution in vertical nanowire arrays. The fabrication of these nanowire arrays is demonstrated to be scalable down to submicrometer site-to-site spacing and can be combined with standard integrated circuit fabrication technologies. We utilize these arrays to perform electrophysiological recordings from mouse and rat primary neurons and human induced pluripotent stem cell (hiPSC)-derived neurons, which revealed high signal-to-noise ratios and sensitivity to subthreshold postsynaptic potentials (PSPs). We measured electrical activity from rodent neurons from 8 days in vitro (DIV) to 14 DIV and from hiPSC-derived neurons at 6 weeks in vitro post culture with signal amplitudes up to 99 mV. Overall, our platform paves the way for longitudinal electrophysiological experiments on synaptic activity in human iPSC based disease models of neuronal networks, critical for understanding the mechanisms of neurological diseases and for developing drugs to treat them.
          Cover page: High Density Individually Addressable Nanowire Arrays Record Intracellular Activity from Primary Rodent and Human Stem Cell Derived Neurons
          • Article
          • Peer Reviewed
          UCOP Previously Published Works (2017)
            Cover page: High Density Individually Addressable Nanowire Arrays Record Intracellular Activity from Primary Rodent and Human Stem Cell Derived Neurons
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2017)
              Cover page: High Density Individually Addressable Nanowire Arrays Record Intracellular Activity from Primary Rodent and Human Stem Cell Derived Neurons
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2024)
              Over the past decade, stereotactically placed electrodes have become the gold standard for deep brain recording and stimulation for a wide variety of neurological and psychiatric diseases. Current electrodes, however, are limited in their spatial resolution and ability to record from small populations of neurons, let alone individual neurons. Here, we report on an innovative, customizable, monolithically integrated human-grade flexible depth electrode capable of recording from up to 128 channels and able to record at a depth of 10 cm in brain tissue. This thin, stylet-guided depth electrode is capable of recording local field potentials and single unit neuronal activity (action potentials), validated across species. This device represents an advance in manufacturing and design approaches which extends the capabilities of a mainstay technology in clinical neurology.
                Cover page: Flexible, scalable, high channel count stereo-electrode for recording in the human brain
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2022)
                We report innovative scalable, vertical, ultra-sharp nanowire arrays that are individually addressable to enable long-term, native recordings of intracellular potentials. Stable amplitudes of intracellular potentials from 3D tissue-like networks of neurons and cardiomyocytes are obtained. Individual electrical addressability is necessary for high-fidelity intracellular electrophysiological recordings. This study paves the way toward predictive, high-throughput, and low-cost electrophysiological drug screening platforms.
                  Cover page: Ultra‐Sharp Nanowire Arrays Natively Permeate, Record, and Stimulate Intracellular Activity in Neuronal and Cardiac Networks
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