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

Advances in small lasers

M.T.H was supported by an Australian Research council Future Fellowship research grant for this work. M.C.G. is grateful to the Scottish Funding Council (via SUPA) for financial support.Small lasers have dimensions or modes sizes close to or smaller than the wavelength of emitted light. In recent years there has been significant progress towards reducing the size and improving the characteristics of these devices. This work has been led primarily by the innovative use of new materials and cavity designs. This Review summarizes some of the latest developments, particularly in metallic and plasmonic lasers, improvements in small dielectric lasers, and the emerging area of small bio-compatible or bio-derived lasers. We examine the different approaches employed to reduce size and how they result in significant differences in the final device, particularly between metal- and dielectric-cavity lasers. We also present potential applications for the various forms of small lasers, and indicate where further developments are required.PostprintPeer reviewe

Selective infiltration and storage of picoliter volumes of liquids into sealed SU-8 microwells

This paper describes the selective infiltration and storage of picoliter volumes of water and IPA in arrays of sealed SU-8 microwells. Microwells, with a volume of approximately 300 picoliters, are fabricated employing photolithography and a polymer onto polymer lamination method to seal the structures with a thin cover of SU-8 and PDMS in order to suppress the evaporation of the infiltrated liquids. A glass capillary is used to punch through the SU-8/PDMS cover and to infiltrate the liquid of interest into the microwells. The influence of the mixing ratio of the PDMS and its curing agent is studied and the results show that a lower ratio of 2:1 suppresses the evaporation more when compared to the standard mixing ratio of 10:1. In regards to water and IPA, the dwell time in the reservoirs was increased by approximately 50 % and 450 % respectively. Depending on the physical properties of the microwells and the liquids, the SU-8/PDMS cover suppresses the evaporation up to 32 mins for water and 463 mins for IPA, respectively, until the microwell is completely empty again. Additionally, multiple infiltrations of the same microwell are demonstrated using two immiscible liquids IPA and paraffin oil. Based on the popular polymers SU-8 and PDMS, the sealed microwell structures are scalable and combinable with different glass capillaries according to the needs of future analytical research and medical diagnostics

Microfluidic platform for separation and extraction of plasma from whole blood using dielectrophoresis

Microfluidic based blood plasma extraction is a fundamental necessity that will facilitate many future lab-on-a-chip based point-of-care diagnostic systems. However, current approaches for providing this analyte are hampered by the requirement to provide external pumping or dilution of blood, which result in low effective yield, lower concentration of target constituents, and complicated functionality. This paper presents a capillary-driven, dielectrophoresis-enabled microfluidic system capable of separating and extracting cell-free plasma from small amounts of whole human blood. This process takes place directly on-chip, and without the requirement of dilution, thus eliminating the prerequisite of preprocessed blood samples and external liquid handling systems. The microfluidic chip takes advantage of a capillary pump for driving whole blood through the main channel and a cross flow filtration system for extracting plasma from whole blood. This filter is actively unblocked through negative dielectrophoresis forces, dramatically enhancing the volume of extracted plasma. Experiments using whole human blood yield volumes of around 180 nl of cell-free, undiluted plasma. We believe that implementation of various integrated biosensing techniques into this plasma extraction system could enable multiplexed detection of various biomarkers

Air-suspended polymer rib waveguides

In order to achieve a high refractive index contrast for air-suspended photonic devices, we present a method for laminating thin polymer films onto structured polymer layers that exhibit an air cavity. By using a flat PDMS stamp, polymer films can be transferred over areas of several hundred square microns. On top of the air-suspended slab a second layer of photoresist can be spun and subsequently every desired photonic structure can be defined by using standard photolithography. Here, to demonstrate the feasibility of our lamination method for polymer photonic devices, we present optical modeling and experimental results of air-suspended single mode rib waveguides. Waveguiding is shown for visible and infrared light and a beam profile for λ = 1550 nm is presented that underpins single mode behavior of the rib waveguide

Bonding of SU-8 films onto KMPR structures for microfluidic, air-suspended photonic and optofluidic applications

We present a method to bond unstructured and structured SU-8 films down to sub-micron thicknesses onto microchannels fabricated in KMPR using a flexible polydimethylsiloxane (PDMS) stamp. By exploiting differently casted PDMS stamps, 3D microfluidic channel networks, air-suspended photonic devices and optofluidic structures have been fabricated. First, microchannels of KMPR are patterned by photolithography and an SU-8 film is spin coated onto a prepared PDMS stamp. The stamp is then placed on top of the KMPR microchannels and the SU-8 layer is cross-linked by applying sufficient heat and pressure. After peeling off the PDMS stamp, the SU-8 layer remains bonded on the KMPR. In our experiments, we demonstrate the bonding of approximately 0.5 μm thick structured SU-8 films onto KMPR microchannels of about 500 μm width and 25 μm height. Bond strength tests demonstrated that such thin layers can withstand pressures up to 1100 hPa. The laminated SU-8 layers can enable various functionalities, e.g. sealing of microfluidic channels, realization of air-suspended photonic structures or optofluidic devices. Most importantly, the combination of fluid handling in the microchannels and air-suspended photonic structures realized in the laminated SU-8 layer enables research towards a large range of applications, such as optofluidics, biosensors, chemical and biomedical analysis, environmental investigations, and renewable energy

Optofluidic refractive index sensor based on air-suspended SU‐8 grating couplers

This work presents the design, numerical simulation, fabrication and characterization of a label-free optofluidic refractive index sensor that is based on air-suspended SU‐8 grating couplers. By exploiting a polymer-onto-polymer lamination method for thin structured SU‐8 films, waveguide grating couplers can be fabricated in a film on top of a microfluidic channel system. A capillary force valve, integrated into the microchannels, precisely positions the employed test analytes, which are different DI water based sugar solutions, below the sensing grating coupler. By performing numerical simulations, the sensing grating coupler is optimized to a center wavelength of 1550 nm in the case that pure DI water (n = 1.33) is applied to the microfluidic channel. When a supported mode, guided in the waveguide, reaches the sensing grating region, it is exposed to the test solution resulting in a change of the effective refractive index of the mode. Similar to the simulation results, the experimental characterization of the sensor structure demonstrates a refractive index sensitivity of approximately 400 nm per refractive index unit (RIU) with respect to the wavelength shift of the grating coupler response, and 17 dB RIU ‐1 with respect to the intensity decrease at the individual center wavelengths for refractive index variations between n = 1.33 and n = 1.36. Due to the combination of microfluidic channels and air-suspended grating couplers, analytes can directly be probed in-line in an integrated microfluidic channel making the presented principle suitable for low-cost, in-line polymer optofluidic and photonic sensing applications