Novel fabrication techniques for ultra-thin silicon based flexible electronics

Flexible electronics offer a multitude of advantages,such as flexibility,lightweight property,portability,and high durability.These unique properties allow for seamless applications to curved and soft surfaces,leading to extensive utilization across a wide range of fields in consumer electronics.These applications,for example,span integrated circuits,solar cells,batteries,wearable devices,bio-implants,soft robotics,and biomimetic applications.Recently,flexible electronic devices have been developed using a variety of materials such as organic,carbon-based,and inorganic semiconducting materials.Silicon(Si)owing to its mature fabrication process,excellent electrical,optical,thermal properties,and cost efficiency,remains a compelling material choice for flexible electronics.Consequently,the research on ultra-thin Si in the context of flexible electronics is studied rigorously nowadays.The thinning of Si is crucially important for flexible electronics as it reduces its bending stiffness and the resultant bending strain,thereby enhancing flexibility while preserving its exceptional properties.This review provides a comprehensive overview of the recent efforts in the fabrication techniques for forming ultra-thin Si using top-down and bottom-up approaches and explores their utilization in flexible electronics and their applications.

Recent developments of emerging inorganic, metal and carbon- based nanomaterials for pressure sensors and their healthcare monitoring applications

Recently,flexible pressure sensors have gained substantial research interest in bioelectronics because they can monitor the conditions of various organs,enable early diagnosis of diseases,and provide precise medical treatment by applying them to various parts of the body.In particular,inorganic materials,metal and carbon-based materials are broadly used in novel structured pressure sensors from wearable devices to implantable devices.With the excellent electronic properties,distinctive morphologies,and remarkable mechanical and chemical stability of these materials,it is expected that these flexible pressure sensors can be the basis for new methods for human healthcare.This article covers an extensive review of the inorganic,metal and carbon-based flexible pressure sensor design strategies and sensing mechanisms studied in recent years for diverse applications such as tactile sensors,arterial pulse sensors,intracranial pressure sensors,intraocular pressure sensors,and bladder pressure sensors.Each section provides an overview by introducing the recent progress in flexible pressure sensors.

Inorganic semiconducting materials for flexible and stretchable electronics

Recent progress in the synthesis and deterministic assembly of advanced classes of single crystalline inorganic semiconductor nanomaterial establishes a foundation for high-performance electronics on bendable,and even elastomeric,substrates.The results allow for classes of systems with capabilities that cannot be reproduced using conventional wafer-based technologies.Specifically,electronic devices that rely on the unusual shapes/forms/constructs of such semiconductors can offer mechanical properties,such as flexibility and stretchability,traditionally believed to be accessible only via comparatively low-performance organic materials,with superior operational features due to their excellent charge transport characteristics.Specifically,these approaches allow integration of high-performance electronic functionality onto various curvilinear shapes,with linear elastic mechanical responses to large strain deformations,of particular relevance in bio-integrated devices and bio-inspired designs.This review summarizes some recent progress in flexible electronics based on inorganic semiconductor nanomaterials,the key associated design strategies and examples of device components and modules with utility in biomedicine.

Foldable three dimensional neural electrode arrays for simultaneous brain interfacing of cortical surface and intracortical multilayers

Challenges in the understanding of three-dimensional(3D)brain networks by simultaneously recording both surface and intracortical areas of brain signals remain due to the difficulties of constructing mechanical design and spatial limitations of the implanted sites.Here,we present a foldable and flexible 3D neural prosthetic that facilitates the 3D mapping of complex neural circuits with high spatiotemporal dynamics from the intracortical to cortical region.This device is the tool to map the 3D neural transmission through sophisticatedly designed four flexible penetrating shanks and surface electrode arrays in one integrated system.We demonstrate the potential possibilities of identifying correlations of neural activities from the intracortical area to cortical regions through continuous monitoring of electrophysiological signals.We also exploited the structural properties of the device to record synchronized signals of single spikes evoked by unidirectional total whisker stimulation.This platform offers opportunities to clarify unpredictable 3D neural pathways and provides a next-generation neural interface.

Transparent neural implantable devices:a comprehensive review of challenges and progress

The key to designing an implantable device lies in condensing the synergistic effects of diagnostic and therapeutic methods in a single tool.In conjunction with the integration of electrophysiology and optical modalities,a transparent neural interface alleviates challenges of conventional metal-based microelectrodes.In this review,the multimodal sensing and stimulation functionalities of recent research are addressed.Next,issues that arise when combining functionalities of conventional metal-based,opaque electrode arrays together with optical modalities—(1)photoelectric artifacts,(2)optical image blocking,and(3)light transmission efficiency—are introduced.Then,an introduction of advancing material candidates for transparent neural interfaces follows with the latest research.

Fully implantable and battery-free wireless optoelectronic system for modulable cancer therapy and real-time monitoring

Photodynamic therapy(PDT)is attracting attention as a next-generation cancer treatment that can selectively destroy malignant tissues,exhibit fewer side effects,and lack pain during treatments.Implantable PDT systems have recently been developed to resolve the issues of bulky and expensive conventional PDT systems and to implement continuous and repetitive treatment.Existing implantable PDT systems,however,are not able to perform multiple functions simultaneously,such as modulating light intensity,measuring,and transmitting tumor-related data,resulting in the complexity of cancer treatment.Here,we introduce a flexible and fully implantable wireless optoelectronic system capable of continuous and effective cancer treatment by fusing PDT and hyperthermia and enabling tumor size monitoring in real-time.This system exploits micro inorganic light-emitting diodes(μ-LED)that emit light with a wavelength of 624 nm,designed not to affect surrounding normal tissues by utilizing a fully programmable light intensity ofμ-LED and precisely monitoring the tumor size by Si phototransistor during a long-term implantation(2–3 weeks).The superiority of simultaneous cancer treatment and tumor size monitoring capabilities of our system operated by wireless power and data transmissions with a cell phone was confirmed through in vitro experiments,ray-tracing simulation results,and a tumor xenograft mouse model in vivo.This all-in-one single system for cancer treatment offers opportunities to not only enable effective treatment of tumors located deep in the tissue but also enable precise and continuous monitoring of tumor size in real-time.