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Open Access Publications from the University of California

Scholarly Works (15 results)

  • Article
  • Peer Reviewed
UC Berkeley Previously Published Works (2024)
    Cover page: Study of Jupiter’s interior: Comparison of 2, 3, 4, 5, and 6 layer modelsCreative Commons 'BY' version 4.0 license
    • Thesis
    • Peer Reviewed
    UCLA Electronic Theses and Dissertations (2017)

    Transmission electron microscopy (TEM) is one of the few techniques capable of imaging nanoscale systems in situ. We developed in situ TEM device architectures that allow for TEM imaging without sacrificing device function in order to study device novel nanoelectronic devices. Our slant-vertical device architecture enabled us to observe resistive memory switching cycles for the first time.

    While TEM is capable of unparalleled spatial resolution, conventional TEM contrast is determined only by the physical structure of samples; TEM contrast is blind to the electronic structure of devices. We developed novel scanning TEM electron beam-induced current (STEM EBIC) imaging modes and, for the first time, demonstrated its use for qualitative thermal and connectivity mapping as well as quantitative potential and thickness measurements. We demonstrated these STEM EBIC modes with sub-nanometer spatial resolution.

    We used conventional TEM imaging along with STEM EBIC to observe functioning conductive bridge (CBRAM) and valence change (VCM) resistive memory elements as well as the metal-insulator transition in NbO2. We also used a nanoscale electron energy loss spectroscopy (EELS) thermometry technique we developed to demonstrate cooling in 2D Bi2Te3/Sb2Te3 thermoelectric coolers. The fabrication and imaging techniques reported here are broadly applicable and can be used to study virtually any nanoelectronic device in which operation alters the thermal or electronic state of the device.

    • 3 supplemental images
    Cover page: Visualizing the Invisible in Functioning Nanoelectronic Devices
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2019)
    An electron microscope's primary beam simultaneously ejects secondary electrons (SEs) from the sample and generates electron beam-induced currents (EBICs) in the sample. Both signals can be captured and digitized to produce images. The off-sample Everhart-Thornley detectors that are common in scanning electron microscopes (SEMs) can detect SEs with low noise and high bandwidth. However, the transimpedance amplifiers appropriate for detecting EBICs do not have such good performance, which makes accessing the benefits of EBIC imaging at high-resolution relatively more challenging. Here we report lattice-resolution imaging via detection of the EBIC produced by SE emission (SEEBIC). We use an aberration-corrected scanning transmission electron microscope (STEM), and image both microfabricated devices and standard calibration grids.
      Cover page: Electron beam-induced current imaging with two-angstrom resolution
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2016)
        Cover page: STEM Video of Electronically-Driven Metal-Insulator Transitions in Nanoscale NbO 2 Devices
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2018)
          Cover page: STEM Imaging with Beam-Induced Hole and Secondary Electron Currents
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2015)
          Conductive bridge random access memory (CBRAM) is a leading candidate to supersede flash memory, but poor understanding of its switching process impedes widespread implementation. The underlying physics and basic, unresolved issues such as the connecting filament's growth direction can be revealed with direct imaging, but the nanoscale target region is completely encased and thus difficult to access with real-time, high-resolution probes. In Pt/Al2O3/Cu CBRAM devices with a realistic topology, we find that the filament grows backward toward the source metal electrode. This observation, consistent over many cycles in different devices, corroborates the standard electrochemical metallization model of CBRAM operation. Time-resolved scanning transmission electron microscopy (STEM) reveals distinct nucleation-limited and potential-limited no-growth periods occurring before and after a connection is made, respectively. The subfemtoampere ionic currents visualized move some thousands of atoms during a switch and lag the nanoampere electronic currents.
          • 1 supplemental PDF
          Cover page: Nanofilament Formation and Regeneration During Cu/Al2O3 Resistive Memory Switching
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2015)
          Modern microelectronic devices have nanoscale features that dissipate power nonuniformly, but fundamental physical limits frustrate efforts to detect the resulting temperature gradients. Contact thermometers disturb the temperature of a small system, while radiation thermometers struggle to beat the diffraction limit. Exploiting the same physics as Fahrenheit's glass-bulb thermometer, we mapped the thermal expansion of Joule-heated, 80-nanometer-thick aluminum wires by precisely measuring changes in density. With a scanning transmission electron microscope and electron energy loss spectroscopy, we quantified the local density via the energy of aluminum's bulk plasmon. Rescaling density to temperature yields maps with a statistical precision of 3 kelvin/hertz(-1/2), an accuracy of 10%, and nanometer-scale resolution. Many common metals and semiconductors have sufficiently sharp plasmon resonances to serve as their own thermometers.
            Cover page: Thermal measurement. Nanoscale temperature mapping in operating microelectronic devices.
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2017)
              Cover page: STEM EBIC Mapping of the Metal-Insulator Transition in Thin-film NbO2
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2022)
                Cover page: Imaging Dielectric Breakdown in Valence Change MemoryCreative Commons 'BY' version 4.0 license
                • Article
                • Peer Reviewed
                UCLA Previously Published Works (2021)
                With continued scaling toward higher component densities, integrated circuits (ICs) contain ever greater lengths of nanowire that are vulnerable to failure via electromigration. Previously, plastic electromigration driven by the "electron wind" has been observed, but not the elastic response to the wind force itself. Here we describe mapping, via electron energy-loss spectroscopy, the density of a lithographically defined aluminum nanowire with sufficient precision to determine both its temperature and its internal pressure. An electrical current density of 108 A/cm2 produces Joule heating, tension upwind, and compression downwind. Surprisingly, the pressure returns to its ambient value well inside the wire, where the current density is still high. This spatial discrepancy points to physics that are not captured by a classical "wind force" model and to new opportunities for optimizing electromigration-resistant IC design.
                  Cover page: Visualizing the Electron Wind Force in the Elastic RegimeCreative Commons 'BY' version 4.0 license
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