Processing and patterning of soft semiconductors for wearable bioelectronics

Abstract

Human-centric healthcare increasingly relies on wearable bioelectronics capable of continuous monitoring and analyzing physiological signals, essential for personalized health management. Organic electrochemical transistors (OECTs) have emerged as promising devices due to their high sensitivity, low-voltage operation, and efficient ionic-to-electronic signal conversion, ideal for biosensing and bio-computing. However, conventional OECTs, typically fabricated on rigid substrates, exhibit mechanical mismatch with soft biological tissues, severely limiting their effectiveness in wearable applications. Transitioning these devices onto stretchable platforms remains challenging due to compatibility issues with traditional semiconductor processing methods. Consequently, innovations in materials science, device design, and fabrication methods are critical to realizing the potential of fully stretchable electronics. In this thesis, we introduce several significant advances toward robust, stretchable OECTs optimized for wearable bioelectronics. First, stretchable OECTs often suffer from poor performance while the reason has been unexplored. In this work, we have identified that the oxygen trapped in soft substrates is a critical parameter influencing the performance of soft semiconductors.Our work demonstrates that selecting substrates with reduced oxygen permeability significantly enhances the transistor’s electrical performance, achieving metrics comparable to rigid counterparts. This insight underscores the importance of substrate engineering to minimize unintended doping and ensure consistent device operation. Second, the lack of scalable fabrication methods for high-density, miniaturized stretchable OECT arrays restricts their widespread integration into wearable systems. To address this limitation, we developed a standardized inkjet printing protocol for fabricating intrinsically stretchable OECT arrays with high resolution, reproducibility, and yield. Leveraging a supramolecular adhesion layer to enhance the robustness of the soft semiconductor film under strain, we successfully demonstrated high-uniformity stable stretchable transistor arrays suitable for real-time, on-body sensing and in-sensor computing. This scalable approach marks significant progress toward practical wearable electronic systems capable of direct signal processing at the point of measurement. Third, current soft semiconductors still exhibit significant modulus and dimensional mismatch with biological tissues, restricting their ability to fully emulate tissue-level mechanical properties. To address this gap, we introduced a hydrogel-based soft semiconductor that supports volumetric ionic-electronic modulation at thicknesses exceeding conventional limits (~1 mm). By carefully controlling phase separation and creating a stable three-dimensional polymer network, our devices maintain effective ionic-electronic transport across significant volumes, closely resembling biological tissues in terms of mechanics and functionality. This advancement opens new pathways for integrating bioelectronics into complex, three-dimensional biological environments, advancing tissue engineering and biomedical applications. The processing and patterning strategies for soft semiconductors investigated in this thesis advances the field of stretchable bioelectronics by addressing core challenges—substrate-induced doping, scalable device fabrication, and mechanical mismatches—through innovative substrate design, processing optimization, and novel materials development. These achievements represent crucial steps toward realizing truly wearable, high-performance bioelectronic devices, enabling next-generation healthcare technologies and providing powerful tools for future biological research.