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

Abstract

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. INTRODUCTIONNovel micro-and nano-technology applications encompassing plasmonic devices, field effect transistors, light-emitting diodes, sensor networks, electromagnetic components, terahertz metamaterials, energy harvesters and displays are increasingly demonstrated on flexible substrates. 1-7 These applications represent the building blocks of future flexible and transparent device technology incorporating complex circuitry and functionality. In integrating all the applications together to realise powerful and practical technology that is fully transparent, flexible and functional, two major challenges need to be overcome.First, the flexible substrate should ideally be transparent and colourless. A variety of colourless materials such as polyethylene 8 and polydimethylsiloxane (PDMS) 1 and coloured materials such as polyimide (or Kapton) 9 are widely used. The former can withstand only low processing temperatures (o100 1C), while the yellow-brown tinted polyimide can withstand up to B400 1C. The relevance of colourless substrates to flexible device technology is highlighted by the recent research focus on this area. 10,11 Second, functional oxide materials that offer tailored properties need to be integrated. These functional oxides in the form of thin films can be transparent conductive oxides for electrical conduction, ferroelectrics for memories, piezoelectrics for energy harvesting, 12 and semiconductors or dielectrics for high-performance transistors. Almost

Mechanically Tunable Dielectric Resonator Metasurfaces at Visible Frequencies

“…With recent advances in stretchable electronics fabrication, 38 brittle oxides can be integrated into elastomers through a unique transfer technique allowing for high process temperatures. 39 Using this technique, a very high resolution of the embedded features can be achieved, limited only by the lithographic patterning techniques.…”

Flexible transparent conductors based on metal nanowire networks

“…ITO films have dominated the field of photoelectronics for several decades. However, TCO materials are brittle and they often break or form cracks at small strains [8], such that they cannot be used in flexible photoelectronics where folding, stretching, twisting, or serious bending is required. Percolating networks of carbon nanotubes (CNTs) were studied for using as FTEs several years ago [9][10][11][12].…”

Indium Tin Oxide (ITO) serpentine ribbons on soft substrates stretched beyond 100%

“…Even though ITO can be sputtered and tested on Kapton, when it is sputtered on soft substrates such as polydimethylsiloxane (PDMS), ITO cannot remain intact when the soft substrate is peeled off from the sample holder. As a result, a transferring process has been developed to integrate ITO on PDMS, but the process is tedious and costly and the reported stretchability is still very limited (15%) [37].…”