Design and modelling of thermoformed displays for smart contact lenses

This paper explores the challenges regarding the thermoforming of a deformable guest-host liquid crystal display within a smart contact lens. Focus was given to the finite element modelling of its thermoforming, to find respective design rules. Such displays are thought to be used in vision correction applications (i.e. artificial iris)

Miniature Fresnel LC lens performance

The performance of miniature, polymer-based Fresnel liquid crystal lenses is discussed, specifically the sensitivity for non-uniformities

Miniature liquid crystal lens optimizations

Small, switchable liquid crystal based polymer Fresnel lenses are discussed, considering design optimizations for performance

Development of a thin-film stretchable electrical interconnection technology for biocompatible applications

Stretchable electronics technologies have gained a lot of interest for reasons such as user comfort and reliability. Key aspect in these technologies is the fabrication of stretchable electrical interconnections. These are realized by patterning an intrinsic, non-stretchable gold film into a sequence of horseshoe shapes, acting as "2D" springs when embedded into PDMS. Polyimide is used as a supporting material, successfully enhancing reliability during mechanical loading. This was illustrated by application of various cyclic uni-axial strains to test structures which were fabricated in this technology. A lifetime over 130'000 and 500'000 cycles has been shown at strains of respectively 20% and 10%

Thin-film stretchable electronics technology based on meandering interconnections: fabrication and mechanical performance

A new fabrication technology for stretchable electrical interconnections is presented. This technology can be used to connect various non-stretchable polyimide islands hosting conventional electronic components. The interconnections are realized by patterning a 200 nm thick sputter-deposited gold film into meandering horseshoe shapes, functioning as 'two-dimensional springs' when embedded in a silicone elastomer. Polyimide support is introduced around the meandering conductors as a means to improve the mechanical performance. Processing is done on a temporary carrier; the islands and interconnections are embedded in polydimethylsiloxane in a final stage. To this end, a release technique compatible with high temperatures up to 350 °C based on the evaporation of a 400 nm thick layer of potassium chloride is developed. Test structures consisting of stretchable interconnections with a varying polyimide support width were fabricated. These were strained up to twice their original length without compromising their functionality. Also cyclic mechanical loading at various strains was performed, indicating the influence of the polyimide support width on the lifetime. At strains of 10%, a minimum lifetime of 500 000 cycles is demonstrated. The presented technology thus provides a promising route towards the fabrication of stretchable electronic circuits with enhanced reliability

Parylene C for hermetic and flexible encapsulation of interconnects and electronic components

Flexible electronics are of a great interest for wearable and implantable medical devices due to their conformality with the body, compared to electronics made on rigid carriers. Packaging of such electronics needs to offer sufficient flexibility and in addition, has to provide good protection for the electronics inside, also in humid and harsh environments, to prevent device failure due to corrosion. Parylene C is a popular polymer due to its interesting diffusion barrier properties. Parylene C coatings are also extremely conformal, hence it offers the possibility to be used as flexibleprotecting encapsulation for electronic components and interconnects. In order to provide sufficient mechanical support for the electronic circuit, a second encapsulation in PDMS will be performed. In our work, we study the barrier properties of Parylene for long time exposure to moisture and biofluids. Since adhesion is a very important parameter to prevent corrosion, this property is studied in detail. Various substrates and various adhesion promotion treatments are evaluated. Furthermore, copper interconnects coated with parylene C are immersed in biofluids at 37 C to study corrosion. Accelerated testing is also performed at 70 C to mimic long time exposure in a harsh, humid environment. Since the Parylene barrier layers are typically 5-15 micron thick, they are highly flexible, and hence they are interesting barriers to be used in flexible/stretchable electronics. Therefore, special attention is given to the evaluation of barrier properties when Parylene is bended and stretched

Free-form 2.5D thermoplastic circuits using one-time stretchable interconnections

A technology is presented for the production of soft and rigid circuits with an arbitrary 2.5D fixed shape. The base of this technology is our proprietary technology for elastic circuits with a random shape, in which the elastic thermoset (mostly PDMS) polymer is now replaced by soft or rigid thermoplastic variants. An additional thermoforming step is required to transform the circuit from its initial flat to its final fixed 2.5D shape, but for rigid fixed shape circuits only one-time stretchability of the extensible interconnects is required, relieving the reliability requirements

Stretchable engineering technologies for the development of advanced stretchable polymeric systems

For advanced body related applications, there is a need of soft, conformable, elastic, mechanical compliant and washable systems. Smart clothes for health monitoring, sport or professional protection need washable and conformable electronic systems, which can be deformed up to 20%. Implants, like monitoring sensors, or functional implants, need softness, stretchability to comply with the human body, chemical resistance, and biocompatibility. Many technologies are already available, like polyimide or PET/PEN based flexible electronic system, or conductive yarns for textile which can be knitted or embroidered to produce textrodes or textile based electronic systems. However softness and interconnections are still problems. Polymers based electronic system or stretchable electronic systems are a possible solution. We have developed several technologies to produce stretchable electronics systems. They are based on the concept of flexible functional islands, onto which standard SMD components are soldered, interconnected with meanders shaped metallic stretchable interconnections. Metallic interconnections are made from copper or gold and are optimized using FEM analysis. Stretchable electronic systems are then molded in elastomeric (e.g. silicone rubber or polyurethane) matrix. They can sustain at least 100% of elongation and 3000 cycles at 20% of elongation. They can be integrated in textile and they are biocompatible and washable