The long-term stability of polymer-encapsulated CMOS integrated circuits (ICs) is essential for mm-size active implantable medical devices (AIMDs), where hermetic packaging is impractical. Validating robust, biocompatible, implantable IC encapsulation is a prerequisite for chip-scale polymeric bioelectronic implants. This study presents the first long-term validation of a design strategy combining medical-grade silicone, plasma surface treatment for adhesion, and foundry-manufactured CMOS ICs. These ICs feature a perforated shield layer (top metal layer) and a double-layer wall-of-vias to reduce moisture ingress and mechanical delamination. Test structures with silicon oxide/nitride passivation were encapsulated using implant-compatible processes and immersed in saline under accelerated ageing conditions (47 °C, 67 °C, and 87 °C) for up to 4.3 years, under DC and biphasic biases. Throughout the study, electrochemical impedance spectroscopy (EIS) showed no insulation failures. Minor visual corrosion was confined to wire bonds and solder pads, with no correlation to electrical degradation. These results demonstrate the robustness to biofluid exposure of modern IC passivation when combined with well-adhered silicone encapsulation. To our knowledge, this is the longest and most comprehensive accelerated ageing study of its kind, and the first to establish a scalable, industry-compatible encapsulation method for implanted ICs. Our findings provide critical evidence supporting the integration of CMOS ICs into next-generation bioelectronic implants. ... Read more

Correction to: Nature Communicationshttps://doi.org/10.1038/s41467-024-55298-4, published online 02 January 2025 In this article the following sentence was omitted from the acknowledgements section, ‘This research was funded by the following projects: Project CANDO (Controlling Network Dynamics with Optogenetics), funded by UK EPSRC (grant ref: NS/A000026/1) and the Wellcome Trust (contract ref: 102037/Z/13/Z)’. The original article has been corrected. ... Read more

Silicon integrated circuits (ICs) are central to the next-generation miniature active neural implants, whether packaged in soft polymers for flexible bioelectronics or implanted as bare die for neural probes. These emerging applications bring the IC closer to the corrosive body environment, raising reliability concerns, particularly for chronic use. Here, we evaluate the inherent hermeticity of bare die ICs, and examine the potential of polydimethylsiloxane (PDMS), a moisture-permeable elastomer, as a standalone encapsulation material. For this aim, the electrical and material performance of ICs sourced from two foundries was evaluated through one-year accelerated in vitro and in vivo studies. ICs featured custom-designed test structures and were partially PDMS coated, creating two regions on each chip, uncoated “bare die” and “PDMS-coated”. During the accelerated in vitro study, ICs were electrically biased and periodically monitored. Results revealed stable electrical performance, indicating the unaffected operation of ICs even when directly exposed to physiological fluids. Despite this, material analysis revealed IC degradation in the bare regions. PDMS-coated regions, however, revealed limited degradation, making PDMS a suitable IC encapsulant for years-long implantation. Based on the new insights, guidelines are proposed that may enhance the longevity of implantable ICs, broadening their applications in the biomedical field. ... Read more