Donaldson, N;
Lamont, C;
Shah Idil, A;
Mentink, M;
Perkins, T;
(2018)
Apparatus to investigate the insulation impedance and accelerated life-testing of neural interfaces.
Journal of Neural Engineering
, 15
(6)
, Article 066034. 10.1088/1741-2552/aadeac.
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Abstract
OBJECTIVE: Neural interfaces and other implantable micro-devices that use polymer-encapsulated integrated circuits will only be allowed in medical devices when their lifetimes can be estimated from experimental data. An apparatus has been developed and tested that allows hundreds of insulation samples (interdigitated combs) to be aged under accelerated conditions of high temperature and voltage stress. Occasionally, aging is interrupted while the sample's impedance is measured; the impedance spectrogram shows degradation as it progresses before failure. Approach. The design was based on practical considerations which are reviewed. A Solartron Modulab provides the frequency response analyser and the femtoammeter. The apparatus can accommodate batches of samples at several temperatures and with different aging voltage waveforms. It is important to understand features of the spectra that are not due to comb-comb leakage; these have been observed and investigated using SPICE. Main results. The design is described in detail and tests show that it is capable of making measurements over long periods, at least up to 67°C. Despite the size of the apparatus, background capacitance is about 1 pF and comb-comb capacitances of about 30 pF can be measured down to 10 mHz. an impedance of about 100GΩ. An important discovery was the advantage of grounding the bathing solution, mainly because it raises the measurement ceiling. Observation and SPICE simulation show that leakage from the substrate to the bathing solution can give phase lags >90°, in contrast to comb-comb leakage which reduces phase lag to <90°. Significance. We think that the value of this paper is that it will facilitate research into the endurance of small implanted devices because, given a description of proven apparatus, researchers can start building their own apparatus relatively quickly and with confidence.
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| Type: | Article |
|---|---|
| Title: | Apparatus to investigate the insulation impedance and accelerated life-testing of neural interfaces |
| Location: | England |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1088/1741-2552/aadeac |
| Publisher version: | http://doi.org/10.1088/1741-2552/aadeac |
| Language: | English |
| Additional information: | Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Although reasonable endeavours have been taken to obtain all necessary permissions from third parties to include their copyrighted content within this article, their full citation and copyright line may not be present in this Accepted Manuscript version. Before using any content from this article, please refer to the Version of Record on IOPscience once published for full citation and copyright details, as permission may be required. All third party content is fully copyright protected, and is not published on a gold open access basis under a CC BY licence, unless that is specifically stated in the figure caption in the Version of Record. |
| Keywords: | Accelerated tests, Apparatus, Electrochemical Impedance Spectroscopy, Encapsulation, Impedance Spectroscopy, Integrated circuit, Life-testing |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10055809 |
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