No abstract

No abstract

Electromagnetic device design and flexible electronics fabrication are combined to demonstrate mechanically tunable metamaterials operating at terahertz frequencies. Each metamaterial comprises a planar array of resonators on a highly elastic polydimethylsiloxane substrate. The resonance of the metamaterials is controllable through substrate deformation. Applying a stretching force to the substrate changes the inter-cell capacitance and hence the resonance frequency of the resonators. In the experiment, greater than 8% of the tuning range is achieved with good repeatability over several stretching-relaxing cycles. This study promises applications in remote strain sensing and other controllable metamaterial-based devices.

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

Planar metamaterials consisting of subwavelength resonators have been recently proposed for thin dielectric film sensing in the terahertz frequency range. Although the thickness of the dielectric film can be very small compared with the wavelength, the required area of sensed material is still determined by the diffraction-limited spot size of the terahertz beam excitation. In this article, terahertz near-field sensing is utilized to reduce the spot size. By positioning the metamaterial sensing platform close to the sub-diffraction terahertz source, the number of excited resonators, and hence minimal film area, are significantly reduced. As an additional advantage, a reduction in the number of excited resonators decreases the inter-cell coupling strength, and consequently the resonance Q factor is remarkably increased. The experimental results show that the resonance Q factor is improved by more than a factor of two compared to the far-field measurement. Moreover, for a film with a thickness of λ/375 the minimal area can be as small as 0.2λ × 0.2λ. The success of this work provides a platform for future metamaterial-based sensors for biomolecular detection.