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This paper presents the simulated performance assessment of an artificial iris embedded on a scleral contact lens using real data from an aniridia patient. The artificial iris is based on guest–host liquid crystal cells (GH-LCD) in order to actively modify the transmittance of the lens and effective pupil size. Experimental validation of the GH-LCD spectrum and iris contrast (determined to be 1:2.1) enabled the development of optical models that include the effect of a small pupil on image quality and visual quality on an optical system with aniridia characteristics. Visual simulations at different light conditions (high/low photopic and mesopic) demonstrated the theoretical capacity of the customized artificial iris smart contact lens to expand the depth-of-focus and decrease the optical aberrations (in particular, the spherical aberration). The visual modelling suggests a maximum depth-of-focus value for a 2-mm pupil diameter for both eyes as follows: 3D (1,000 cd/m2), 2D (10 cd/m2) and 0.75D (1 cd/m2). This work demonstrates the beneficial optical effects of an active artificial iris, based on visual simulations in response to different light levels, and enables further experimental investigation on patients to validate the dynamic light attenuation and visual performance of smart contact lenses with GH-LCD.

In a normally functioning eye, the iris controls the pupil diameter to regulate the amount of light reaching the retina. Various iris deficiencies exist, manifesting as defects in the iris or an absence of one which result in too much light reaching the retina. Some iris deficiencies, such as aniridia or leiomyoma, can be mitigated with fixed or adaptive artificial irises. As an alternative, adaptive transparency glasses may also alleviate this situation, however, both solutions do not mimic the other normal functionality of the natural iris: adaptive aperture. To address this, we developed a fully encapsulated, self-contained artificial iris embedded in a smart contact lens. The control ASIC of the contact lens is developed in 0.18- $\mu \text{m}$ 16-V BCD TSMC and has a typical power consumption of 1.9 $\mu \text{W}$ from a 3-V supply voltage at office light condition.

Many of today’s stretchable interconnection technologies make extensive use of meandered interconnections, these provide 2-D in-plane springs capable of extending and compressing as the need arises. While a significant quantity of research work exists on these interconnects, few generic methodologies exist to design circuits in a consistent manner. This shortfall leads to questionable design practices, which can negatively affect reliability and performance. Presented within this paper is a method to quickly determine which meander fits within a given area based on common geometric boundary conditions.

In a functional eye, the iris controls the pupil diameter to regulate the exposure of the retina. While iris deficiencies such as aniridia or leiomyoma can be mitigated with fixed or adaptive artificial irises [1] and adaptive transparency glasses exist to alleviate this situation, they do not mimic the normal functionality of the natural iris. To address this, a fully encapsulated, self-contained artificial iris embedded in a smart contact lens is proposed. A control ASIC is developed in 0.18 μm 16 V BCD TSMC with typ. 1.9 μw current consumption from 3 V supply voltage at office light condition.

An electrochemical smart contact lens (ESCL) capable of real-speed spatiotemporal electrochemical sensing across the surface of the eye is demonstrated. Four microelectrode arrays, each comprising 33 gold microdiscs of 30 μm diameter, and a distributed common gold counter electrode, are integrated into a soft smart contact lens platform based on polyimide and thermoplastic polyurethane. Using a novel fast-switching chronoamperometric method, an electrochemical ‘video’ of concentration variation in a model eye under flow conditions is produced, in which the introduction, progress, mixing and drainage of fluid of varying concentration can be observed. The device builds on previous work towards a platform suitable for clinical use and has proven to be robust under expected use conditions, with sensing performance remaining unchanged after thermoforming and repeated mechanical deformation. This work represents a significant step forward in ESCL design, and constitutes significant progress towards a technology with real clinical utility.

We demonstrate a real-speed spatiotemporal electrochemical map showing both time- and position-varying concentration of an analyte in contact with a flexible microelectrode array. A polymer-based device of 11 μm in thickness comprising patterned gold metallisation on a polyimide substrate was fabricated, with eight individually addressable working electrodes (diameter 30 μm) and an integrated counter electrode. We performed a repeated sequence of high-speed chronoamperometric measurements at each electrode and processed the data to generate a spatiotemporal concentration map, in which a number of fluid effects, including bulk flow, diffusive mixing and homogenisation of two miscible fluids of different concentration were observed. This device was fabricated using processes compatible with an existing smart contact lens platform, with a view to develop integrated sensors in future work. We believe this technique has significant potential in the field of electrochemical smart contact lenses, both in introducing new functionality and in improving our ability to draw accurate and clinically-relevant conclusions from measurements made in the tear film.

Nowadays, smart contact lenses (SCLs) display interesting features for healthcare monitoring; however, their comfort and practical usability strongly depend on the outermost material in contact with the eye. In this publication, the embedding of a custom-made and thermoformed Near-Field Communication based circuit in a conventional soft CL is presented. The circuit is composed of gold tracks on polyimide between thermoplastic polyurethane layers (insert), while the lens is based on industry standard double-molding process of poly(2-hydroxyethyl methacrylate) with proven compatibility with corneal tissue. The lens shows stable geometrical parameters (bevel landing area) thus enabling a practical implementation. Finite element method models are used to optimize the thermoforming process in order to provide a stable and desired curvature of the insert before the embedding process. While the insert is designed to allow oxygen transmission at the center of the lens, a custom-made ultra-compact radio-frequency antenna provides communication and wireless power transfer both in air and inside saline solutions. The successful combination of the intrinsic soft mechanical properties of the wirelessly powered electronic insert with conventional hydrogel materials and manufacturing processes delivers a practical solution for SCLs. This enables non-invasive applications in fields such as vision correction and/or biomedical sensing.

In this paper we report on the fabrication of spin-coated biodegradable polylactic acid (PLA) thin films to be used as substrates for the realisation of all-solution-processed organic electronic devices. The full mechanical and electrical characterisation of these substrates shows that they exhibit good mechanical and dielectric properties and are therefore suitable for the fabrication of disposable electronics. To demonstrate practically the functionality of such PLA thin films, organic electronic devices were realised on the top of them, exclusively by means of solution-process fabrication techniques and in particular inkjet-printing. Also, a photonic curing procedure is here presented as a means for sintering the conductive inks without heating up the PLA substrates. Two types of organic transistors were fabricated on the top of PLA: organic field-effect transistors (OFETs), where the PLA film was used not only as a substrate but also as the gate dielectric, and all-inkjet-printed organic electrochemical transistors (OECTs). The second typology of transistors exhibited one of the highest transconductance reported so far in the literature (up to 2.75 mS). This study opens an avenue for the fabrication of disposable, low-cost organic electronic devices. (C) 2014 Elsevier B.V. All rights reserved.

This paper presents an automated test bench, based on a rigorous measurement procedure, used to fully characterize vibration energy harvesters including determination of the resonance frequency, impedance, optimal load, and output power as a function of both frequency and acceleration. The potential of this method and the performance of the automated test bench allows systematic data acquisition which is essential for a good comparison of all harvesters. A dedicated automation circuit was designed and fabricated. It uses stepper motors to mechanically control trimmers to vary the resistive load and reed relays to switch between the measurement sequences. With this, the setup is able to determine the optimal load of the device-under-test at its resonant frequency for a given acceleration. The test bench was used to fully characterize several types of vibration harvesters fabricated on both silicon and polymeric substrates. A comparison of the characterized devices is discussed using a figure of merit proposed here. A survey and compilation of current practices used to benchmark vibration harvesters is also reported.

This paper describes and compares two integration methods to structurally laminate and interconnect foil-based components with flexible polymeric substrates. The first method uses isotropic conductive adhesives (ICA) confined in laser-ablated through foil vias (TFV), while the second one uses an anisotropic conductive adhesive (ACA). Both procedures were successfully demonstrated by interconnecting silverbased inkjet printed and gold-sputtered interdigitated capacitive humidity sensors onto flexible PEN carrier substrates, showing functionality, high process yield and low-complexity. The robustness of the assemblies was tested and compared for adhesion, bending, high humidity and temperature cycling. Confined ICA vias show higher mechanical robustness to bending, while both methods remained functional after more than 900 h of environmental ageing. Finally, the interconnections were fully validated at different levels of relative humidity (RH) by comparing the sensor response to that of a commercial sensor. (C) 2013 Elsevier B.V. All rights reserved.

In this paper, a woven textile containing temperature and humidity sensors realized on flexible, plastic stripes is presented. The authors introduce two different sensors fabrication techniques: the first one consists of a conventional photolithography patterning technique; the second one, namely inkjet-printing, is here presented as an effective, low-cost alternative. In both cases, we obtain temperature and humidity sensors that can be easily integrated within a fabric by using a conventional weaving machine. All the sensors are fully characterized and the performances obtained with the two different fabrication techniques are compared and discussed, pointing out advantages and drawbacks resulting from each fabrication technique. The bending tests performed on these sensors show that they can be successfully woven without being damaged. A demonstrator, consisting of a mechanical support for the e-textile, a read-out electronic circuit, and a graphical PC interface to monitor the acquisition of humidity and temperature values, is also presented and described. This paper opens an avenue for real integration between printed electronics and traditional textile technology and materials. Printing techniques may be successfully used for the fabrication of e-textile devices, paving the way for the production of large area polymeric stripes and thus enabling new applications that, at the moment, cannot be developed with the standard lithography methods.

A stretchable platform with spherical-shaped electronics based on thermo- plastic polyurethane (TPU) is introduced for soft smart contact lenses. The low glass transition temperature of TPU, its relatively low hardness, and its proven biocompatibility (i.e., protection of exterior body wounds) fulfill the essential requirements for eye wearable devices. These requirements include optical transparency, conformal fitting, and flexibility comparable with soft contact lenses (e.g., hydrogel-based). Moreover, the viscoelastic nature of TPU allows planar structures to be thermoformed into spherical caps with a well-defined curvature (i.e., eye’s curvature at the cornea: 9 mm). Numerical modeling and experimental validation enable fine-tuning of the thermo - forming parameters and the optimization of strain-release patterns. Such tight control is proven necessary to achieve oxygen permeable, thin, nonde- velopable, and wrinkle-free contact lenses with integrated electronics (silicon die, radio-frequency antenna, and stretchable thin-film interconnections). This work paves the way toward fully autonomous smart contact lenses potentially for vision correction or sensing applications, among others.

This study presents the mechanical characterization of the dry film photoresist PerMX and its adhesion properties when laminated onto Kapton (R) E (PI) and Melinex (R) ST506 (PET). Additionally, the processing temperature, the adhesion strength, and the neutral plane position are investigated and optimized. A relatively low-temperature (85 degrees C) process is developed to protect the integrity of the polymers with low glass transition temperature and reduce the thermal mismatch stress. Reduction in processing temperature led to a decrement in the adhesion strength. To counteract this unwanted effect, surface treatments (oxygen plasma) are performed on the polymer surface before lamination. Using the latter techniques, adhesion of PerMX to PET (hard bake: 1 h at 85 degrees C) is increased from 0.07 to 0.26 N mm1 (variation of 270%). Finally, the mechanical robustness is investigated and increased by tuning the position of the neutral plane, after 50,000 bending cycles and a radius of curvature of 2.5 mm. (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

We show an active artificial iris based on solely thin-film components, wherein several LCD elements are controlled a metal-oxide TFT and by powered by thin-film photovoltaics (TFPV). Key aspects for the driver are size and low power consumption. We demonstrate power consumption down to 25μW for the full iris.

The emergence of the fields of wearable devices, e-textiles and smart packaging brings new requirements on electronics and sensing systems. One or a combination of the following properties can be desired for their proper operation and to meet the functionalities required by the application in order to improve market penetration. Very low-cost, thin, large area, lightweight, flexibility, conformability, transparency, stretchability are some of the characteristics that can be offered by making sensors on polymeric foil. We propose printing processes for the fabrication of these devices to mainly reduce their production cost and to improve the environmental friendliness of their manufacturing. In this communication, we discuss the benefits, drawbacks, potential, and challenges of printing sensors on plastic substrates illustrated with some examples of technical developments performed in our laboratory. We present environmental sensors fabricated on plastic foil and the associated flexible encapsulation method at the foil level. Integration of printed sensing devices on smart RFID tags is also discussed. By using thin polymeric substrates, very small bending radius of curvature can be achieved. Besides the challenges linked to the large area printing of the sensing devices on flexible foil and the reliability of these devices under mechanical cycling, new developments are required on the interconnectivity of these devices with other electronics components to achieve efficient system integration. (C) 2011 Published by Elsevier Ltd.

This paper reports a study on the dynamics of foil-based functional component self-alignment onto patterned test substrates and its demonstration when integrating a flexible sensor onto a printed circuitry. We investigate the dependence of alignment time and final precision of stacking of mm- and cm-sized foil dies on a number of system parameters, such as amount of assembly medium dispensed on target positions, size and weight of assembling dies and their initial misalignment. Using water as a medium for direct self-alignment, mm- and cm-sized square-shaped pre-marked foil dies were aligned with accuracy down to 30 μm and smaller, which reflects a high precision relatively to their lateral dimensions on patterned marked carriers. High-speed camera stage and image recognition tools were used for analyzing rapid capillary-driven self-alignment processes of marked foil dies. It is shown that there is a definite range of initial misalignment values allowing dies to align with high accuracy and yield within the same time window, whereas both under smaller and larger initial offsets, i.e. with dies correspondingly too close or too far from their target positions, yield and alignment precision is significantly lower. The high-alignment accuracy of mm- to cm-sized functional foils was demonstrated by means of the integration of an interdigitated electrodes (IDE) capacitive sensor to a flexible polymeric substrate. Additionally, high-yield electrical interconnection was performed using anisotropic conductive adhesives (ACA). The latter opens the perspective of efficiently assembling interesting new systems such as separately manufactured sensors, paper batteries and RFIDs components through the direct capillary-driven self-alignment approach and ACA electrical interconnection.

The design optimization through modeling of a thinned bulk-PZT-based vibration energy harvester on a flexible polymeric substrate is presented. We also propose a simple foil-level fabrication process for their realization, by thinning the PZT down to 50 mu m and laminating it via dry film photoresist onto a PET substrate at low temperature (

This work presents an approach for increasing operational bandwidth of a vibration energy harvester in low-frequency environments by effectively exploiting contact-based frequency up-conversion. It was implemented by a couple of low-frequency resonators with appropriately spaced natural frequencies impacting high-frequency piezoelectric generators when the device is harmonically excited in 10-40 Hz range. A proof of concept was designed, modeled, fabricated and characterized, demonstrating improved power and bandwidth performance (up to 37 μW and 9 Hz at 1g) with respect to traditional single-resonator designs. © 2014 The Authors. Published by Elsevier Ltd.

This communication presents an overview on our activities on the development of printed sensors on flexible polymeric foil for RFID. We are envisioning the direct printing of sensors on different types of products such as smart labels and RFID tags. This technology could bring sensors where there is no sensor at the moment by significantly reducing their production cost and by adding new functionalities. The integration of these sensors fabricated on plastic foil with electronics, communication and powering capabilities will be addressed. The realization of cost-effective smart objects can be one of the key enabling technologies for the deployment of the Internet of Things (IoT).

International audience; Conducting polyaniline-based chemiresistors on printed polymeric micro-hotplates were developed, showing sensitive and selective detection of ammonia vapor in air. The devices consist of a fully inkjet-printed silver heater and interdigitated electrodes on a polyethylene naphthalate substrate, separated by a thin dielectric film. The integrated heater allowed operation at elevated temperatures, enhancing the ammonia sensing performance. The printed sensor designs were optimized over two different generations, to improve the thermal performance through careful design of the shape and dimension of the heater element. A vapor-phase deposition polymerization technique was adapted to produce polyaniline sensing layers doped with poly(4-styrenesulfonic acid). The resulting sensor had better thermal stability and sensing performance when compared with conventional polyaniline-based sensors, and this was attributed to the polymeric dopant used in this study. Improved long-term stability of the sensors was achieved by electrodeposition of gold on the silver electrodes. Response to sub-parts-per-million concentrations of ammonia even under humid conditions was observed.

In this paper, a low temperature flip-chip integration technique for Si bare dies is demonstrated on flexible PET substrates with screen-printed circuits. The proposed technique is based on patterned blind vias in dry film photoresist (DP) filled with isotropic conductive adhesive (ICA). The DP material serves to define the vias, to confine the ICA paste (80 mu m-wide and potentially 25 mu m-wide vias), as an adhesion layer to improve the mechanical robustness of the assembly, and to protect additional circuitry on the substrate. The technique is demonstrated using gold-bumped daisy chain chips (DCCs), with electrical vias resistances in the order to hundreds of milliohms, and peel/shear adhesion strengths of 0.7 N mm(-1) and 3.2 MPa, respectively, (i.e. at 1.2 MPa of bonding pressure). Finally, the mechanical robustness to bending forces was optimized through flexural mechanics models by placing the neutral plane at the DCC/DP adhesive interface. The optimization was performed by reducing the Si thickness from 400 to 37 mu m, and resulted in highly robust integrated assemblies withstanding 10 000 cycles of dynamic bending at 40 mm of radius, with relative changes in vias resistance lower than 20%. In addition, the electrical vias resistance and adhesion strengths were compared to samples integrated with anisotropic conductive adhesives (ACAs). Besides the low temperature and high integration resolution, the proposed method is compatible with large area fabrication and multilayer architectures on foil.

This paper presents the printing of resistive and interdigitated (IDE) capacitive devices for temperature and humidity sensing applications, respectively, on biodegradable polylactic acid (PLA) substrates. Inkjet and gravure printing were evaluated to transfer silver-based nanoparticles inks. Flash photonic ink sintering methodologies were employed to maintain the PLA mechanical integrity due to its low glass transition temperature (58 degrees C). Between the two printing techniques investigated, gravure-printed devices on 200 mu m-thick PLA sheets were shown to have better resolution and higher sensitivities to temperature and humidity (1100 ppmK(-1) and 5.6 fF/%RH). Additionally, we demonstrated the inkjet printing of IDE onto thin (25 mu m) dissolved-PLA spin-coated substrates, to enhance the mechanical flexibility and to reduce the response time to humidity (from 238 s to 70 s). Finally, a low temperature encapsulation is proposed by embedding the printed structures within PLA sheets.