Processing and Switching Mechanisms of Materials for Memory Devices in Flexible Electronics

  • Author / Creator
    Almadhoun, Mahmoud
  • Current trends in Big Data are driving industries towards new innovations for data acquisition and processing. Among these trends is the concept of the Internet of Things (typically abbreviated as IOT), which will result in the collection of very large amounts of data from sensors and microelectronic devices integrated in household appliances, wearable electronics for health, vehicles, and manufacturing facilities, among others. Many of these devices and sensors will need to be interfaced directly with living, natural, and other non-rigid surfaces, thus, an enormous field has emerged that falls under the umbrella term of flexible hybrid electronics (FHE). Global standards for FHE currently are being developed and are propelling research support and advances in new materials. The focus of this dissertation will be to investigate the processing of materials used for memory and the mechanism of operation of these materials, which then can be integrated onto flexible substrates.

    In the second chapter, metal-assisted chemical etching of Si substrates is used to fabricate freestanding Si pillars via different patterning techniques to create devices with different architectures. Then, a specialty ferroelectric polymer, poly(vinylidenefluoride-co-trifluoroethylene) P(VDF-TrFE), will be interfaced with the silicon structures to explore resistive switching that is driven by polarization of the polymer.

    The third chapter demonstrates how to process the commodity polymer, PVDF, which is 10 times less expensive than P(VDF-TrFE), as an alternative to achieving robust memory properties. However, transforming PVDF into ferroelectric phases has proven to be challenging in a manner that is amenable to large-scale commercial applications. Here, it is shown that PVDF can be transformed from the α-phase into the desired ferroelectric β-phase using microsecond pulses of UV irradiation. Under optimal pulse durations, typical characteristics of dipolar and reversible hysteresis loops appear in ferroelectric PVDF, reaching a remnant polarization of 5.4 µC/cm2 and a coercive field around 120 MV/m. Potentially, this single-step method can open a wide range of opportunities for high-throughput roll-to-roll annealing of plastic electronics.

    Flexible electronic devices assembled upon a platform of liquid gallium and related alloys are of interest due to their mouldability, negligible toxicity, and high conductivity of these materials. In Chapter 4, the eutectic Ga-In alloy (EGaIn) and its surface oxide, gallium oxide, are utilized as electrode and electrolyte materials, respectively. The native oxide is positioned between bulk gallium and degenerately doped p-type silicon to form junctions that show memristive behavior. When cycled between –2.5 and 2.5 V, an abrupt insulator–metal transition is observed that is reversible when the polarity is reversed. The ON/OFF ratio between the high and low resistive states in these junctions can reach values on the order of 108, retain the ON and OFF resistive states for up to 105 s, and with an endurance exceeding 100 cycles. A nanoscale interface of gallium oxide is the critical feature intrinsic to these devices, through which reversible formation and rupture of Ga filaments occur via electrochemical metallization.

    In the last chapter, Chapter 5, follow-up directions of research are provided that are backed with preliminary data. This includes the design of new device architectures for hybrid ferroelectric diodes, light processing of PVDF on plastic substrates, the role of electrodes and the thickness of gallium oxide on resistive switching, and in-situ XPS analysis of resistive switching across gallium oxide/p-type Si interfaces.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.