Synthesis and Guided Self-Assembly of Mixed-Metal Oxide Arrays from Undercooled Liquid Metal

In the Information Age, inexorable progression of big data demands rapid upgradation of modern electronics. Internet of Things (IoT), for example, requires numerous “communicable” electronics and powerful central processing units to build a “smart” world, where every physical object is digitally connected. With vast amount of high-performance electronics in-need, advancement of nanofabrication technologies become pivotal. Contradiction between better performance and lower cost, however, has long been unreconciled for electronic fabrication, and Moore’s law is an exemplary case of facing such challenge. While Moore’s law has inspired disparate advances in Complementary Metal Oxide Semiconductor (CMOS) devices (&gt;20 doubling in transistors per chip every year), the scaling approach that drives these advances is predicted to stall after ~27 doubling events. This scaling approach faces a triple challenge in: i) continued miniaturization with concomitant need for more tools, characterization, metrology, among others, transitioning Moore’s law into ‘more’ law. ii) a looming fabrication challenge as we approach the sub nanometer-length (atomic) scale per component, and iii) global demand for more computation presents an energy and supply challenge unless new, rapid, energy efficient fabrication methods are realized. New paradigm(s) in multiscale manufacturing of microelectronics is therefore needed, among which interface-based (43 more doublings) and/or self-assembled organic (&gt;100 doublings) post-CMOS devices pertains great potential. This calls for a significant shift in microelectronic fabrication with an emphasis to the introduction of new chemistries, composition and functionality while maintaining energy efficiency and low-cost through a device lifecycle.<br/>Liquid metal particles bear great potential to reduce energy and capital cost in functional array fabrication since they can act as a controlled reservoir for metal ions. Exploiting partial miscibility of organometallic adducts in aqueous media, steady-state kinetics <i>ad-infinitum</i> living polymerization was demonstrated using liquid metal particles as an infinitely large metal ion reservoir – the so-called HetMet reaction. This reaction led to synthesis of high aspect ratio self-assembled beams that were then translated to graphitic-carbon coated metal oxides with tunable band gaps. Herein, we extend this work by coupling the HetMet reaction with confinement from nanograting templates to separate the metal particles from the self-assembling adducts. Using molds bearing channels with desired dimensions and periodicity enables deposition of desired arrays, and exploiting fluidic dynamics of this process allows us to control both the nucleation point and the rate of ion transport to the growing seed. Driven by capillary action and solution evaporation, large-area, high-quality organometallic nanowire arrays were fabricated by D-Met, of which an in-air heat-treatment conveniently transformed the organic wires into mixed-metal oxide without compromising wire continuity or array periodicity. Besides planar patterns, fabrication of multi-layer nanostructures such as 2-layer arrays were also achieved, which is promising for design and fabrication of 3D electronics. With the high structural precision of D-Met fabricated wire arrays, we demonstrate unique electrical and optical properties including diode behavior and guided wave resonance.