[Show abstract][Hide abstract] ABSTRACT: State of the art packaging for implantable devices uses metal or glass housings that are reliable but limited from a miniaturisation viewpoint as well as cost-intensive. We suggest a hermetic and biocompatible thin film packaging based on alternating organic/inorganic coatings for further miniaturisation of smart implantable MEMS devices that can be applied for long-term implantation. The combination of high intrinsic molecular density silicon oxide (SiOx) and pinhole-free and stress releasing poly-para-xylylene (parylene-C) thin films creates a new composite material, which is optimal for hermetic and biocompatible packaging. A novel single-chamber thin film deposition process was developed for the fabrication of SiOx/parylene thin film multilayer structures, using a modified chemical vapour deposition (CVD) process. According to permeation and conformity aspects, the inorganic layer is the crucial layer of the coating. Permeation measurements the highly ceramic SiOx material revealed a low helium gas permeation and a non-critical cracking thickness up to 300 nm. The morphology of the multilayer structure was analysed by scanning electron microscopy; an algorithm for defining ideal layer conformity was established and no local thickness deficiencies of deposited SiOx layers could be observed. To evaluate the corrosion protection, an adapted calcium mirror test based on water droplet permeation was developed, and the water permeation of conventional parylene-C layers (4.5 μm) was compared to multilayer stacks composed of 3 SiOx interlayers (4.7 μm).
In this paper, it could be shown that by tailoring the thickness ratio between the involved layers, the percolative pathway and thereby, the permeation for direct water exposure could be considerably reduced compared to conventional parylene-C single layers with the same thickness.
[Show abstract][Hide abstract] ABSTRACT: State of the art packaging for long-term implantable electronic devices generally uses reliable metal and glass housings; however, these are limited in the miniaturization potential and cost reduction. This paper focuses on the development of biocompatible hermetic thin-film packaging based on poly-para-xylylene (Parylene-C) and silicon oxide (SiOx) multilayers for smart implantable microelectromechanical systems (MEMS) devices. For the fabrication, a combined Parylene/SiOx single-chamber deposition system was developed. Topological aspects of multilayers were characterized by atomic force microscopy and scanning electron microscopy. Material compositions and layer interfaces were analyzed by Fourier transform infrared spectrometry and x-ray photoelectron spectroscopy. To evaluate the multilayer corrosion protection, water vapor permeation was investigated using a calcium mirror test. The calcium mirror test shows very low water permeation rates of 2 × 10−3 g m−2 day−1 (23 °C, 45% RH) for a 4.7 µm multilayer, which is equivalent to a 1.9 mm pure Parylene-C coating. According to the packaging standard MIL-STD-883, the helium gas tightness was investigated. These helium permeation measurements predict that a multilayer of 10 µm achieves the hermeticity acceptance criterion required for long-term implantable medical devices.
Journal of Micromechanics and Microengineering 05/2013; 23(7):075001. DOI:10.1088/0960-1317/23/7/075001 · 1.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An implantable transducer for monitoring the flow of Cerebrospinal fluid (CSF) for the treatment of hydrocephalus has been developed which is based on measuring the heat dissipation of a local thermal source. The transducer uses passive telemetry at 13.56 MHz for power supply and read out of the measured flow rate. The in vitro performance of the transducer has been characterized using artificial Cerebrospinal Fluid (CSF) with increased protein concentration and artificial CSF with 10% fresh blood. After fresh blood was added to the artificial CSF a reduction of flow rate has been observed in case that the sensitive surface of the flow sensor is close to the sedimented erythrocytes. An increase of flow rate has been observed in case that the sensitive surface is in contact with the remaining plasma/artificial CSF mix above the sediment which can be explained by an asymmetric flow profile caused by the sedimentation of erythrocytes having increased viscosity compared to artificial CSF. After removal of blood from artificial CSF, no drift could be observed in the transducer measurement which could be associated to a deposition of proteins at the sensitive surface walls of the packaged flow transducer. The flow sensor specification requirement of +-10% for a flow range between 2 ml/h and 40 ml/h. could be confirmed at test conditions of 37 degrees C.
[Show abstract][Hide abstract] ABSTRACT: An implantable thermal flow sen treatment of hydrocephalus has been developed.The sensor uses passive telemetry at 13.56 MHz
for power supply and read out of the measured flow rate. The in vitro performance of the sensor has been characterized using
artificial Cerebrospinal Fluid (CSF) with increased protein concentration and artificial CSF with 10% fresh blood. No drift
could be observed in the flow sensor measurement which could be associated to a deposition of proteins at the sensitive surface
walls of the packaged flow sensor.
Keywordsimplant–flow sensor–hydrocephalus–protein adsorption