Transforming flexible devices to stretchable oxide-based electronics, photonics, and sensors

Lightweight compact electronics are currently the most popular personal electronic devices. A trend towards wearable and body compatible smart devices is clearly indicated, creating the demand for electronics to be fully flexible and stretchable to realise next generation devices. To allow for this additional degree of freedom, strategies for fabricating these devices need to be established. The fabrication of such devices pose a challenge to materials science due to the inherent brittle nature of metals, oxides and semiconductors, the core building block for powerful electronics. This thesis explores new methods of integrating these materials into flexible and stretchable platforms. Initially a comprehensive study into metal films on flexible substrates is carried out with insights into strategies to reduce the sensitivity towards strain. Based on these insights, multilayer resonating terahertz structures on a flexible platform are presented and analysed, showcasing the ability to distinguish polarisation efficiently. The integration of a functional material namely zinc oxide into a flexible platform is demonstrated by realising a visible-blind UV imaging array capable of operating in various bending states. In order to enable an additional degree of freedom, strategies to enable stretchability of functional oxides is explored. A novel method of transferring high temperature processed oxides (indium tin oxide) is presented, to overcome process temperature limitations. Secondly, a phenomena named “micro-tectonics” which allows oxides to stretch and bend is discovered and analysed. Based on the micro-tectonic effect zinc oxide stretchable devices are demonstrated that are capable of detecting UV and gases efficiently at room temperature which outperform their rigid counterparts. Additionally high refractive index contrast devices are shown that dynamically manipulate visible light via device deformation. Multifaceted analysis provides insight into the excellent tunability of these diffractive and resonating optical devices. The thesis offers a cross-disciplinary insight into incorporation of functional oxide thin films with flexible and stretchable materials, and the potential for a new paradigm of functional devices

Strain response of stretchable micro-electrodes: Controlling sensitivity with serpentine designs and encapsulation

The functionality of flexible electronics relies on stable performance of thin film micro-electrodes. This letter investigates the behavior of gold thin films on polyimide, a prevalent combination in flexible devices. The dynamic behavior of gold micro-electrodes has been studied by subjecting them to stress while monitoring their resistance in situ. The shape of the electrodes was systematically varied to examine resistive strain sensitivity, while an additional encapsulation was applied to characterize multilayer behavior. The realized designs show remarkable tolerance to repetitive strain, demonstrating that curvature and encapsulation are excellent approaches for minimizing resistive strain sensitivity to enable durable flexible electronics

Transparent functional oxide stretchable electronics: micro-tectonics enabled high strain electrodes

Fully transparent and flexible electronic substrates that incorporate functional materials are the precursors to realising nextgeneration devices with sensing, self-powering and portable functionalities. Here, we demonstrate a universal process for transferring planar, transparent functional oxide thin films on to elastomeric polydimethylsiloxane (PDMS) substrates. This process overcomes the challenge of incorporating high-temperature-processed crystalline oxide materials with low-temperature organic substrates. The functionality of the process is demonstrated using indium tin oxide (ITO) thin films to realise fully transparent and flexible resistors. The ITO thin films on PDMS are shown to withstand uniaxial strains of 15%, enabled by microstructure tectonics. Furthermore, zinc oxide was transferred to display the versatility of this transfer process. Such a ubiquitous process for the transfer of functional thin films to elastomeric substrates will pave the way for touch sensing and energy harvesting for displays and electronics with flexible and transparent characteristics

Battery-free, fully implantable optofluidic cuff system for wireless optogenetic and pharmacological neuromodulation of peripheral nerves

Studies of the peripheral nervous system rely on controlled manipulation of neuronal function with pharmacologic and/or optogenetic techniques. Traditional hardware for these purposes can cause notable damage to fragile nerve tissues, create irritation at the biotic/abiotic interface, and alter the natural behaviors of animals. Here, we present a wireless, battery-free device that integrates a microscale inorganic light-emitting diode and an ultralow-power microfluidic system with an electrochemical pumping mechanism in a soft platform that can be mounted onto target peripheral nerves for programmed delivery of light and/or pharmacological agents in freely moving animals. Biocompliant designs lead to minimal effects on overall nerve health and function, even with chronic use in vivo. The small size and light weight construction allow for deployment as fully implantable devices in mice. These features create opportunities for studies of the peripheral nervous system outside of the scope of those possible with existing technologies.NIH Director's Transformative Research [TR01 NS081707]; NIH SPARC Award via the NIBIB of the NIH [U18EB021793, R01 NS42595]; NIMH of the NIH [R41MH116525]; NRSA [F32 DK115122]; McDonnell Center for Cellular and Molecular Neurobiology Postdoctoral Fellowship [T32 DA007261]; Medical Scientist Training Program (MSTP) [T32 GM07200]; University of Missouri-Columbia start-up fund; NINDS NRSA [F31 NS103472]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Flexible Indium-Tin Oxide Crystal on Plastic Substrates Supported by Graphene Monolayer

Flexible and crystallized indium-tin oxide (ITO) thin films were successfully obtained on plastic polyethylene terephthalate (PET) films with monolayered graphene as a platform. The highly crystalline ITO (c-ITO) was first fabricated on a rigid substrate of graphene on copper foil and it was subsequently transferred onto a PET substrate by a well-established technique. Despite the plasma damage during ITO deposition, the graphene layer effectively acted as a Cu-diffusion barrier. The c-ITO/graphene/ PET electrode with the 60-nm-thick ITO exhibited a reasonable sheet resistance of similar to 45 Omega sq(-1) and a transmittance of similar to 92% at a wavelength of 550 nm. The c-ITO on the monolayered graphene support showed significant enhancement in flexibility compared with the ITO/PET film without graphene because the atomically controlled monolayered graphene acted as a mechanically robust support. The prepared flexible transparent c-ITO/graphene/PET electrode was applied as the anode in a bulk heterojunction polymer solar cell (PSC) to evaluate its performance, which was comparable with that of the commonly used c-ITO/glass electrode. These results represent important progress in the fabrication of flexible transparent electrodes for future optoelectronics applications

Towards a digitally connected body for holistic and continuous health insight

The digitally connected body with clinical grade multimodal and multisite biosignal acquisition is a key goal of the wearable device communities, which will enable advanced diagnostics and therapeutics. Recent advances in sensor and biointerfaces have enabled insight into biomarkers and physiological states that far exceed the commercially available technologies. However, they often require intimate contact with the target organ, which is possible acutely or over days but may not translate to continuous monitoring without substantial user engagement. Holistic device ecosystems or standards are therefore required to enable a digitally connected body. Here, we discuss current barriers and highlight potential avenues to enable a seamless, almost imperceptible network, of wearable sensors to capture health comprehensively and chronically. © 2024, The Author(s).Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Visible-blind UV imaging with oxygen-deficient zinc oxide flexible devices

Flexible visible-blind UV imaging arrays tolerant to curvature are demonstrated. The functionality is enabled by crystalline oxygen-deficient zinc oxide pixels, which show high sensitivity and fast response to UV light. Such large-area, bendable imaging arrays will enable new advancements in portable and wearable electronics and sensors

Mechanically tunable high refractive-index contrast TiO2-PDMS gratings

[No abstract available

Mechanically tunable dielectric resonator metasurfaces at visible frequencies

Devices that manipulate light represent the future of information processing. Flat optics and structures with subwavelength periodic features (metasurfaces) provide compact and efficient solutions. The key bottleneck is efficiency, and replacing metallic resonators with dielectric resonators has been shown to significantly enhance performance. To extend the functionalities of dielectric metasurfaces to real-world optical applications, the ability to tune their properties becomes important. In this article, we present a mechanically tunable all-dielectric metasurface. This is composed of an array of dielectric resonators embedded in an elastomeric matrix. The optical response of the structure under a uniaxial strain is analyzed by mechanical-electromagnetic co-simulations. It is experimentally demonstrated that the metasurface exhibits remarkable resonance shifts. Analysis using a Lagrangian model reveals that strain modulates the near-field mutual interaction between resonant dielectric elements. The ability to control and alter inter-resonator coupling will position dielectric metasurfaces as functional elements of reconfigurable optical devices