[Show abstract][Hide abstract] ABSTRACT: Progress in the development of active neural interface devices requires a very compact method for protecting integrated circuits (ICs). In this paper, a method of forming micropackages is described in detail. The active areas of the chips are sealed in gas-filled cavities of the cap wafer in a wafer-bonding process using Au–Si eutectic. We describe the simple additions to the design of the IC, the post-processing of the active wafer and the required features of the cap wafer. The bonds, which were made at pressure and temperature levels within the range of the tolerance of complementary metal–oxide–semiconductor ICs, are strong enough to meet MIL STD 883G, Method 2019.8 (shear force test). We show results that suggest a method for wafer-scale gross leak testing using FTIR. This micropackaging method requires no special fabrication process and is based on using IC compatible or conventional fabrication steps.
Journal of Micromechanics and Microengineering 06/2013; 23(7):075021. · 1.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objective. We investigate the ability of the method of velocity selective recording (VSR) to determine the fibre types that contribute to a compound action potential (CAP) propagating along a peripheral nerve. Real-time identification of the active fibre types by determining the direction of action potential propagation (afferent or efferent) and velocity might allow future neural prostheses to make better use of biological sensor signals and provide a new and simple tool for use in fundamental neuroscience. Approach. Fibre activity was recorded from explanted Xenopus Laevis frog sciatic nerve using a single multi-electrode cuff that records whole nerve activity with 11 equidistant ring-shaped electrodes. The recorded signals were amplified, delayed against each other with variable delay times, added and band-pass filtered. Finally, the resulting amplitudes were measured. Main Result. Our experiments showed that electrically evoked frog CAP was dominated by two fibre populations, propagating at around 20 and 40 m/s, respectively. The velocity selectivity, i.e. the ability of the system to discriminate between individual populations was increased by applying band-pass filtering. The method extracted an entire velocity spectrum from a 10 ms CAP recording sample in real time. Significance. Unlike the techniques introduced in the 1970s and subsequently, VSR requires only a single nerve cuff and does not require averaging to provide velocity spectral information. This makes it potentially suitable for the generation of highly-selective real-time control-signals for future neural prostheses. In our study, electrically evoked CAPs were analysed and it remains to be proven whether the method can reliably classify physiological nerve traffic.
Journal of Neural Engineering 05/2013; 10(3):036016. · 3.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We developed an implantable wireless, hermetically sealed brain-computer interface which is intended to stay functional within the body for decades. Such an ambitious task demands interconnection technologies of high reliability and reproducibility. Investigating soft-soldering, poor wetting behavior of SnAg solder and destructive influences of additional fluxing materials excluded the lead-free compound from our list of suitable sealing and interconnection materials. We developed a robust and reliable welded interconnection method, which allows us to join a multichannel electrode array, even if materials such as MP35N are involved, which are inherently difficult to solder. For solder-sealing of the implant package with leakage rates in the desired range of
Neural Engineering (NER), 2013 6th International IEEE/EMBS Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Strong permanent adhesion between thin-film polyimide (BPDA-PPD) and silicone rubber (MED-1000) was achieved through deposition of a chemically-transitive intermediate adhesion promoting layer. Plasma-enhanced chemical vapor deposition (PECVD) of SiC and SiO2 was used to grow a thin 50 nm layer directly on a 5 μm thin polyimide substrate. The deposition at low pressures permitted the fabrication of an adaptive covalent bond transition from sp2-hybridized carbon (in polyimide) towards the sp3 bonding in SiC, continuing to SiO2 which provides a good bonding partner for one-component poly-dimethyl siloxane (PDMS). The fabricated laminates together with reference probes containing no adhesion promoting layer were subjected to intense accelerated aging at 125°C and 130 kPa (pressure cooker) over 96 hrs in phosphate buffered saline solution. While the reference polyimide-PDMS laminates failed just after 30 min in the pressure cooker, no failure was detected on samples using the proposed adhesion promoter technique. Mechanical loading of the samples resulted in cohesive crack formation at the polyimide, propagating across the bulk with no evidence of adhesive failure between any of the materials. The strong permanent adhesion brings the fabrication of hybrid neural interfaces one step forward, achieving the combination of thin-film manufacturing and PDMS.
Neural Engineering (NER), 2013 6th International IEEE/EMBS Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Iridium oxide is known for its superior charge injection capacity, required for high-performance implantable stimulation electrodes. We integrated sputtered iridium oxide films into an electrode fabrication process based on laser-micromachining, suitable for production of neural electrodes for human use. In comparison to traditional electrode material MP35N (recording) and PtIr (stimulation), our iridium oxide electrodes provide a lower noise floor in recording settings and a much larger injectable charge in stimulation settings.
Neural Engineering (NER), 2013 6th International IEEE/EMBS Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Micro-packages based on alumina ceramics hermetically sealed with glass solder were fabricated and tested over a 1.5 years period under accelerated aging at 85 °C. A device for sealing the 1.2 mm high, and ø10mm packages while cooling the critical centre of the package containing the electronics was developed. Heating of the rim up to 550 °C while maintaining the package centre below 300°C was successful, allowing a symmetrical heating of the device during the sealing procedure. The fabricated packages with an inner volume of 0.05 cc were backfilled with helium and tested for hermeticity with a fine leak tester. Samples passing the fine leak (1•10(-12) atm•cc/s) test were attached to a larger chamber containing a humidity sensor. Some devices covered in PDMS and some directly exposed were stored at 85 °C in water to measure the humidity intrusion into the device due to deterioration of glass solder. 1 out of the 8 successfully fabricated devices failed after 5 years extrapolated lifetime. Two of the devices have kept constant humidity levels while others gradually rise. Nevertheless, 7 out of 8 have maintained a level below 17000 ppm humidity. Furthermore, the deterioration of glass solder was electrically and optically studied over a year's period showing no corrosion of glass if properly coated in PDMS.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:2784-7.
[Show abstract][Hide abstract] ABSTRACT: In the past we developed a method for the fabrication of neural electrodes based on laser-structuring metal foil to form tracks and electrode sites within a silicone rubber substrate. Here, this process was refined by an additional coating of the laser-patterned metal tracks to improve their mechanical properties. Parylene C has been found to be the coating material of choice due to excellent electrical and mechanical characteristics and its well known biocompatibility. An almost ten times increased tensile strength compared to uncoated tracks could be achieved. Investigating the electrical properties of parylene C and silicone rubber attested both materials excellent insulating capabilities by withstanding voltages of more than 400 V(DC) for layer thicknesses as intended to be used in electrode array fabrication (some 10 µm). This paper outlines the feasibility of the manufacturing process using a 1064 nm Nd:YAG laser in the nanosecond pulse regime. However, an improvement of the whole processing was demonstrated when a 355 nm Nd:YVO(4) laser in the picosecond regime is used. Benefits of this short pulse duration range from ablating materials independent of their optical properties to increased manufacturing speed and superior processing quality.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:5130-3.
[Show abstract][Hide abstract] ABSTRACT: Miniaturization of implantable devices while drastically increasing the number of stimulation channels is one of the greatest challenges in implant manufacturing because a small but hermetic package is needed that provides reliable protection for the electronics over decades. Retinal vision prostheses are the best example for it. This paper presents a miniaturized 232-channel vision prosthesis, summarizing the studies on the individual technologies that were developed, improved and combined to fabricate a telemetrically powered retinal device sample. The implantable unit, which is made out of a high temperature co-fired alumina ceramic package containing hermetic feedthroughs, electronic circuitry and a radio frequency coil for powering is manufactured through a modified screen-printing/lasering process. The package is sealed with solder glass to provide unaffected inductive coupling to the telemetric transmitter. A 0.05 cc inner volume allows helium leak testing and mathematical lifetime estimations for moisture-induced failure of up to 100 years. The feedthroughs contact a thin-film polyimide electrode array that utilizes DLC and SiC coatings for improved interlayer adhesion of the metallic tracks to the polymer carrier. Two metal layers allow integrated wiring of the electrode array within the very limited space.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:2796-9.
[Show abstract][Hide abstract] ABSTRACT: Future brain-computer-interfaces (BCIs) for severely impaired patients are implanted to electrically contact the brain tissue. Avoiding percutaneous cables requires amplifier and telemetry electronics to be implanted too. We developed a hermetic package that protects the electronic circuitry of a BCI from body moisture while permitting infrared communication through the package wall made from alumina ceramic. The ceramic package is casted in medical grade silicone adhesive, for which we identified MED2-4013 as a promising candidate.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:3886-9.
[Show abstract][Hide abstract] ABSTRACT: Thin-film electrode arrays for neural implants are necessary when large integration densities of stimulating or recording channels are required. However, delamination of the metallic layers from the polymer substrate leads to early failure of the device. Based on new adhesion studies of polyimide to SiC and diamond-like carbon (DLC) the authors successfully fabricated a 232-channel electrode array for retinal stimulation with improved adhesion. Layers of SiC and DLC were integrated into the fabrication procedure of polyimide-platinum (Pt) arrays to create fully coated metal wires, which adhere to the polyimide substrate even after 1 year of accelerated aging in saline solution. Studies on the inter-diffusion of Pt and SiC were conducted to establish an optimal thickness for a gold core of the platinum tracks, which is used for reducing the electrical track resistance. Furthermore, the electrochemical behaviour of the stimulating contacts coated with IrOx were studied in a long-term pulse tests over millions of pulses showing no deterioration of the coating.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:5134-7.
[Show abstract][Hide abstract] ABSTRACT: Complex prosthetic limbs, the bionic eye, or brain-computer interfaces implement microelectrode arrays to connect the nervous system to an electronic device. The aim is to partly restore lost body functions or to gather bioelectrical activity from the nervous system. Microelectrode arrays are fabricated to have specific electrical and mechanical properties to match the biological requirements of the intended application. Polyimide and parylene-C are favorable polymers for substrate and insulation layers in thin-film applications. This article reviews the materials and the mechanical and electrical properties of electrode arrays. It emphasizes the often ignored but crucial influence of adhesion of the thin-film layers on the device’s longevity and reliability. Adhesion promotion techniques using layers of silicon carbide (SiC) are also discussed. Even though the main focus is on thin-film devices fabricated using traditional methods of micromachining based on lithography, an alternative to thin films, laser-patterned silicone/metal foil microelectrode arrays, is also presented. Characterization as well as application examples of these devices are also presented.
[Show abstract][Hide abstract] ABSTRACT: This paper describes the improvements to the theory of velocity selective recording and some simulation results. In this method, activity in different groups of axons is discriminated by their propagation velocity. A multi-electrode cuff and an array of amplifiers produce multiple neural signals; if artificial delays are inserted and the signals are added, the activity in axons of the matched velocity are emphasized. We call this intrinsic velocity selective recording. However, simulation shows that interpreting the time signals is then not straight-forward and the selectivity Q(v) is low. New theory shows that bandpass filters improve the selectivity and explains why this is true in the time domain. A simulation study investigates the limits on the available velocity selectivity both with and without additive noise and with reasonable sampling rates and analogue-to-digital conversion parameters. Bandpass filters can improve the selectivity by factors up to 7 but this depends on the speed of the action potential and the signal-to-noise ratio.
Medical & Biological Engineering 02/2012; 50(3):309-18. · 1.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Neural prostheses are technical systems that interface nerves to treat
the symptoms of neurological diseases and to restore sensory of motor
functions of the body. Success stories have been written with the
cochlear implant to restore hearing, with spinal cord stimulators to
treat chronic pain as well as urge incontinence, and with deep brain
stimulators in patients suffering from Parkinson's disease. Highly
complex neural implants for novel medical applications can be
miniaturized either by means of precision mechanics technologies using
known and established materials for electrodes, cables, and hermetic
packages or by applying microsystems technologies. Examples for both
approaches will be introduced and discussed. Electrode arrays for
recording of electrocorticograms during presurgical epilepsy diagnosis
have been manufactured using approved materials and a marking laser to
achieve an integration density that is adequate in the context of brain
machine interfaces, e.g. on the motor cortex. Microtechnologies have to
be used for further miniaturization to develop polymer-based flexible
and light weighted electrode arrays to interface the peripheral and
central nervous system. Polyimide as substrate and insulation material
will be discussed as well as several application examples for nerve
interfaces like cuffs, filament like electrodes and large arrays for