Simple multifocal lens based on liquid crystals

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A biocompatible active artificial iris

A contact lens mimicking an artificial iris is presented as solution for people suffering from iris deficiencies. As this is a biomedical device, biocompatibility is a key specification for material choice and design. The presented research focusses on oxygen permeability of the lens, as the eye depends on oxygen from the environment for functioning

Accelerated hermeticity testing of biocompatible moisture barriers used for encapsulation of implantable medical devices

Acceleration protocol plays an important role on barriers reliability evaluation for encapsulation of long-term implantable medical devices. Typically, acceleration is realized by performing tests at elevated temperature: the higher the selected temperature, the higher the acceleration factor. Nevertheless, at high temperatures, reaction mechanisms might be different, resulting in false acceleration test results. Our standard barrier performance test is based on the evaluation of corrosion of copper patterns (resistivity check, Electroscopic Impedance Spectroscopy (EIS), microscopic inspection). The temperature window for accelerated testing has been investigated for our standard barrier tests. The copper patterns, protected by a barrier layer under test, are immersed in PBS (Phosphate Buffered Saline) at temperatures up to 95°C. As barriers the following material/multilayers are selected: (1) Al2O3 ALD, (2) stacked HfO2/Al2O3/HfO2 ALD (further called ALD-3), (3) polyimide, and (4) polyimide/ALD-3/polyimide. In this presentation, the results of the test protocol evaluation will be presented. As expected, the maximum applicable test temperature is dependent on the barrier under test. Furthermore, during the fine-tuning of the accelerated test protocol, we observed for some barriers a clear influence of the shape of the Cu test patterns on the barrier performance. This can be related with processing effects when fabricating the barrier on the copper patterns. This finding stresses the determination of relevant copper patterns -or test structures in general- in order to predict the barrier performance correct for each individual application

Microfabrication of a spherically curved liquid crystal display enabling the integration in a smart contact lens

A spherically curved liquid crystal display based on a guest-host liquid crystal configuration is fabricated. An asymmetric display design is introduced: two flexible display substrates with varying surface area are used, allowing for compact integration of powering and driving electronics. A matrix of spacer structures composed of photosensitive adhesive and defined by photolithography, simultaneously provides the uniform cell gap while acting as glue between both display substrates. Using poly(3,4-ethylenedioxythio phene):poly(styrenesulfonate) (PEDOT:PSS) as transparent, conductive electrode layer and obliquely evaporated SiO2as alignment layer, a functional single-pixel display was fabricated. The display can be embedded in a smart contact lens, thereby enabling applications within the emerging biomedical field. An artificial iris, for example, could be designed to help people suffering from iris deficiencies that involve hypersensitivity to light

Development of an active high-density transverse intrafascicular micro-electrode probe

In this work, the development of an active high-density transverse intrafascicular microelectrode (hd-TIME) probe to interface with the peripheral nervous system is presented. The TIME approach is combined with an active probe chip, resulting in improved selectivity and excellent signal-to-noise ratio. The integrated multiplexing capabilities reduce the number of external electrical connections and facilitate the positioning of the probe during implantation, as the most interesting electrodes of the electrode array can be selected after implantation. The probe chip is packaged using thin-film manufacturing techniques to allow for a minimally invasive electronic package. Special attention is paid to the miniaturization, the mechanical flexibility and the hermetic encapsulation of the device. A customized probe chip was designed and packaged using a flexible, implantable thin electronic package (FITEP) process platform. The platform is specifically developed for making slim, ultra-compliant, implantable complementary metal-oxide-semiconductor based electronic devices. Multilayer stacks of polyimide films and HfO2/Al2O3/HfO2 layers deposited via atomic layer deposition act as bidirectional diffusion barriers and are key to the hermetic encapsulation. Their efficacy was demonstrated both by water vapor transmission rate tests and accelerated immersion tests in phosphate buffered saline at 60 °C. Using the hd-TIME probe, an innovative implantation method is developed to prevent the fascicles from moving away when the epineurium is pierced. In addition, by transversally implanting the hd-TIME probe in the proximal sciatic nerve of a rat, selective activation within the nerve was demonstrated. The FITEP process platform can be applied to a broader range of integrated circuits and can be considered as an enabler for other biomedical applications

FITEP : a Flexible Implantable Thin Electronic Package platform for long term implantation applications, based on polymer and ceramic ALD multilayers

Within our internal FITEP technology platform (FITEP: Flexible Implantable Thin Electronic Package), a novel implantable packaging technology is under development in order to realize a very small, flexible, biomimetic package for electronic implants. This new platform enables a radical miniaturization of the final implanted device, which opens many new possibilities for the medical world, since it will be possible to insert electronic sensors in very small locations, such as arteries, nerves, glands,... The device encapsulation consists of a multilayer of biocompatible polymers and ultrathin ceramic diffusion barriers deposited using ALD techniques (ALD: atomic layer deposition) in order to fabricate a very thin and flexible but also highly hermetic device packaging. Concerning the selection of biocompatible polymers, polyimide can offer a profound mechanical support for the various device components, while Parylene with its excellent step coverage creates a highly conformal coating surrounding all components. Hermeticity can be realized by the use of ultrathin ceramic ALD layers such as Al2O3 and HfO2. An optimized ALD process will result in layers from very high quality with very good step coverage. As such, selected ALD layers of only a few tens of nm thick, can exhibit very low Water Vapor Transmission Rates (WVTR), making these ALD materials ideal as ultrathin diffusion barriers. The tested polyimide/ALD stack proved to be a very hermetic enclosure: copper patterns protected with the polyimide/ALD stack are still in perfect condition after more than 2 years of immersion in saline at 60 °C (test is still ongoing), while Cu patterns protected by the polyimide stack without ALD barriers showed first signs of damage already after 6 weeks exposure to saline. Platinum and gold are best suited for metallization of implanted electronics, but these noble metals do not adhere easily to polymers, hence dedicated measures to promote metal-polymer adhesion are essential. The FITEP platform is applied on a Si-probe for implantation in the peripheral nerves, consisting of a CMOS chip with recording and stimulation electrodes [Op de Beeck, M. 2017]. The chip is thinned down to 35um and packaged using polyimide and ALD multi-stacks, resulting in a 75um thin fully encapsulated chip, optimized to reduce the Foreign Body Reaction to obtain optimum electrode-nerve contact. Flexible interconnects are fabricated using gold and platinum sandwiched between polymers and ALD layers. For optimal charge injection, iridium oxide is used as electrode material. After this hermetic FITEP-based chip encapsulation, the CMOS chip is still fully functional, which was tested dry (in air) as well as during submersion in saline. First acute in vivo stimulation tests have shown good electrode stimulation capabilities. Mechanical bending tests on long 5um thick gold interconnects are performed, showing that even after up to 1.5 million bending cycles, no cracks occurred in the gold patterns (testing in air). Longer term immersion in saline and in-vivo testing showed some problems related to loss of adhesion and to galvanic effects of the metallization. These observations were leading to some improvements in the fabrication of the encapsulation. In a second packaging iteration of the CMOS chip, these improvements were realized and a new series of encapsulated devices is fabricated. First results are promising, showing improved metal adhesion. Longer term stability tests are on its way