Multilayer Flexible SU8-Gold Microelectrode Arrays for Wearable Bioelectronics

Year 2023, Volume 27, Issue 1, 56 - 67, 28.02.2023

Murat Kaya YAPICI

https://doi.org/10.16984/saufenbilder.1108035

Abstract

Wearable health trackers for vital signs monitoring are becoming ever more important especially due to the global coronavirus pandemic (COVID-19) caused by the SARS‑CoV‑2 virus which severely affect the respiratory system and can cause cardiac manifestations. Particularly, wearable solutions which can seamlessly monitor heart activity are critical to facilitate personal preventive and remote healthcare, as well as to allow early diagnosis of cardiac dysfunctions. A fundamental enabler of wearable bioelectronics is the sensing bioelectrode which is used to record surface biopotentials. While a plethora of attempts have been reported to realize skin-conformal dry electrodes and electronic skin patches, oftentimes a very critical aspect of the electrode i.e., the actual electrical interfacing of the wearable electrode to readout circuits without disturbing the skin-electrode contact, is overlooked. To address this issue, this paper reports a unique tri-layer, polymer-metal-polymer skin-conformal microelectrode design with sidewall metal coating to achieve vertical interconnect accesses (VIAs) and realize contact pads for external interfacing. The novel and optimized process flow reported herein allows repeatable fabrication of flexible electrodes in arrayed format with yields exceeding 90%. Functionality of the microfabricated electrodes were demonstrated by successful acquisition of the electrocardiogram in lead-I configuration with clear detection of the P-QRS-T complex.

Keywords

Microelectrode, wearable, biopotential, mems, ecg

References

• [1] C. Chitrakar, E. Hedrick, L. Adegoke, M. Ecker, “Flexible and stretchable bioelectronics,” Materials, vol. 15, no.5, pp. 1664, 2022.
• [2] S. Lee, J. Park, S. Kim, J. Ok, J. I. Yoo, Y. S. Kim, Y. Ahn, T-i. Kim, H. C. Ko, J. Y. Lee, “High-Performance implantable bioelectrodes with immunocompatible topography for modulation of macrophage responses,” ACS Nano, vol. 16, no.5, pp. 7471–7485, 2022.
• [3] Z. Wang, H. Bai, W. Yu, Z. Gao, W. Chen, Z. Yang, C. Zhu, Y. Huang, F. Lv, S. Wang, “Flexible bioelectronic device fabricated by conductive polymer–based living material,” Science Advances, vol.8, no.25, pp. eabo1458, 2022.
• [4] Y. Chen, Y. Zhang, Z. Liang, Yu Cao, Zhiyuan Han, Xue Feng, “Flexible inorganic bioelectronics,” npj Flexible Electronics, vol.4, no.2, pp. 1-20, 2020.
• [5] L. Zhang, K. S. Kumar, H. He, C. J. Cai, X. He, H. Gao, S. Yue, C. Li, R.C-S. Seet, H. Ren, J. Ouyang “Fully organic compliant dry electrodes self-adhesive to skin for long-term motion-robust epidermal biopotential monitoring”, Nature Communications, vol. 11, no. 4683, pp. 1-13, 2020.
• [6] D. H. Kim, N. Lu, R. Ma, Y. S. Kim, R. H. Kim, S. Wang, J. Wu, S. M. Won, H. Tao, A. Islam, K. J. Yu, T. I. Kim, R. Chowdhury, M. Ying, L. Xu, M. Li, H. J. Chung, H. Keum, M. McCormick, P. Liu, Y. W. Zhang, F. G. Omenetto, Y. Huang, T. Coleman, J. A. Rogers “Epidermal electronics,” Science, vol. 333, no. 6044, pp. 838-843, 2011.
• [7] J. Viventi, D. H. Kim, J. D. Moss, Y. S. Kim, J. A. Blanco, N. Annetta, A. Hicks, J. Xiao, Y. Huang, D. J. Callans, J. A. Rogers, B. Litt “A conformal, bio-interfaced class of silicon electronics for mapping cardiac electrophysiology,” Science Translational Medicine, vol. 2, no. 24, pp. 24ra22, 2010.
• [8] M. Ferguson, D. Sharma, D. Ross, F. Zhao, ‘‘A Critical Review of Microelectrode Arrays and Strategies for Improving Neural Interfaces,” Advanced Healthcare Materials, vol.8, pp. 1900558, 2019.
• [9] S. Moussa, J. Mauzeroll, “Review—Microelectrodes: An Overview of Probe Development and Bioelectrochemistry Applications from 2013 to 2018,” Journal of the Electrochemical Society, vol. 166, no. 6, pp. G25-G38, 2019.
• [10] T. I. Oh, S. Yoon, T. E. Kim, , H. Wi, K. J. Kim, E. J. Woo, R. J. Sadleir, “Nanofiber web textile dry electrodes for long-term biopotential recording,” IEEE Transactions on Biomedical Circuits and Systems, vol. 7, no. 2, pp. 204-211, 2013.
• [11] Y. Wang, Y. Qiu, S. K Ameri, H. Jang, Z. Dai, Y. A. Huang, N. Lu, “Low-cost, μm-thick, tape-free electronic tattoo sensors with minimized motion and sweat artifacts,” npj Flexible Electronics, vol.2, no.6, 2018.
• [12] G. Paul, R. Torah, S. Beeby, J. Tudor, “The development of screen printed conductive networks on textiles for biopotential monitoring applications,” Sensors and Actuators A: Physics, vol.206, pp. 35–41, 2014.
• [13] F. Stauffer, M. Thielen, C. Sauter, S. Chardonnens, S. Bachmann, K. Tybrandt, C. Peters, C. Hierold, J. Vörös, “Skin Conformal Polymer Electrodes for Clinical ECG and EEG Recordings,” Advanced Healthcare Materials, vol. 7, pp. 1700994, 2018.
• [14] M. A. Yokus, T. Songkakul, V. A. Pozdin, A. Bozkurt, M. A. Daniele, “Wearable multiplexed biosensor system toward continuous monitoring of metabolites,” Biosensors and Bioelectronics, vol. 153, pp. 12038, 2020.
• [15] N. X. Williams, A. D. Franklin, “Electronic Tattoos: A Promising Approach to Real-time Theragnostics,” Journal of Dermatology and Skin Science, vol. 2, 1, pp. 5-16, 2020.
• [16] C. Wang, K. He, J. Li, X. Chen, “Conformal electrodes for on‐skin digitalization,” SmartMat, vol.2, pp.252-262, 2021.
• [17] J. Alberto, C. Leal, C. Fernandes, P. A. Lopes, H. Paisana, A. T de Almeida, M. Tavakoli, “Fully Untethered Battery-free Biomonitoring Electronic Tattoo with Wireless Energy Harvesting,” Scientific Reports, vol.10, no. 5539, pp. 1-11, 2020.
• [18] B. F. E. Matarèse, P. L. C. Feyen, A. Falco, F. Benfenati, P. Lugli, J. C. DeMello, “Use of SU8 as a stable and biocompatible adhesion layer for gold bioelectrodes,” Scientific Reports, vol. 8, no. 5560, pp.1-12, 2018.
• [19] H. Lorenz, M. Despont, N. Fahrni, N. LaBianca, P. Renaud, P. Vettiger, “SU-8: a low-cost negative resist for MEMS,” Journal of Micromechanics and Microengineering, vol. 7, no. 3, pp.121–4, 1997.
• [20] T. A. Anhoj, A. M. Jorgensen, D. A. Zauner, Jörg Hübner, “The effect of soft bake temperature on the polymerization of SU-8 photoresist,” Journal of Micromechanics and Microengineering, vol. 16, pp. 1819, 2006.
• [21] R. Feng, R. J. Farris, “Influence of processing conditions on the thermal and mechanical properties of SU8 negative photoresist coatings,” Journal of Micromechanics and Microengineering, vol.13, no. 1, pp. 80–88, 2003.
• [22] S. Keller, G. Blagoi, M. Lillemose, D. Haefliger, A. Boisen, “Processing of thin SU-8 films”, Journal of Micromechanics and Microengineering, vol. 18, pp. 125020, 2008.
• [23] G. Hass, J. E. Waylonis, “Optical Constants and Reflectance and Transmittance of Evaporated Aluminum in the Visible and Ultraviolet,’’ Journal of the Optical Society of America, vol. 51, pp. 719-722, 1961.
• [24] S. Banerjee, R. Gupta, M. Mitra, “Delineation of ECG characteristic features using multiresolution wavelet analysis method,” Measurement, vol. 45, no. 3, pp. 474-487, 2012.
• [25] S. Asgari, A. Mehrnia, “A novel low-complexity digital filter design for wearable ECG devices,” PLoS One, vol.12, no. 4, pp. e0175139, 2017.