Bio-Inspired Dynamically Morphing Microelectronics toward High-Density Energy Applications and Intelligent Biomedical Implants.

Choreographing the adaptive shapes of patterned surfaces to exhibit designable mechanical interactions with their environment remains an intricate challenge. Here, a novel category of strain-engineered dynamic-shape materials, empowering diverse multi-dimensional shape modulations that are combined to form fine-grained adaptive microarchitectures is introduced. Using micro-origami tessellation technology, heterogeneous materials are provided with strategic creases featuring stimuli-responsive micro-hinges that morph precisely upon chemical and electrical cues. Freestanding multifaceted foldable packages, auxetic mesosurfaces, and morphable cages are three of the forms demonstrated herein of these complex 4-dimensional (4D) metamaterials. These systems are integrated in dual proof-of-concept bioelectronic demonstrations: a soft foldable supercapacitor enhancing its power density (≈108 mW cm-2 ), and a bio-adaptive device with a dynamic shape that may enable novel smart-implant technologies. This work demonstrates that intelligent material systems are now ready to support ultra-flexible 4D microelectronics, which can impart autonomy to devices culminating in the tangible realization of microelectronic morphogenesis.

A Photolithographable Electrolyte for Deeply Rechargeable Zn Microbatteries in On-Chip Devices.

Zn batteries show promise for microscale applications due to their compatibility with air fabrication but face challenges like dendrite growth and chemical corrosion, especially at the microscale. Despite previous attempts in electrolyte engineering, achieving successful patterning of electrolyte microscale devices has remained challenging. Here, successful patterning using photolithography is enabled by incorporating caffeine into a UV-crosslinked polyacrylamide hydrogel electrolyte. Caffeine passivates the Zn anode, preventing chemical corrosion, while its coordination with Zn2+ ions forms a Zn2+-conducting complex that transforms into ZnCO3 and 2ZnCO3·3Zn(OH)2 over cycling. The resulting Zn-rich interphase product significantly enhances Zn reversibility. In on-chip microbatteries, the resulting solid-electrolyte interphase allows the Zn||MnO2 full cell to cycle for over 700 cycles with an 80% depth of discharge. Integrating the photolithographable electrolyte into multilayer microfabrication creates a microbattery with a 3D Swiss-roll structure that occupies a footprint of 0.136 mm2. This tiny microbattery retains 75% of its capacity (350 µAh cm-2) for 200 cycles at a remarkable 90% depth of discharge. The findings offer a promising solution for enhancing the performance of Zn microbatteries, particularly for on-chip microscale devices, and have significant implications for the advancement of autonomous microscale devices.

Microbatteries with twin-Swiss-rolls redefine performance limits in the sub-square millimeter range.

To maintain the downscaling of microelectronic devices with footprints less than one square millimeter, next-generation microbatteries should occupy the same area and deliver adequate energy for running a new generation of multi-functional microautonomous systems. However, the current microbattery technology fails in accomplishing this task because the micrometer-sized electrodes are not compatible with on-chip integration protocols and technologies. To tackle this critical challenge, an on-chip Swiss-roll microelectrode architecture is employed that exploits the self-assembly of thin films into ultra-compact device architectures. A twin-Swiss-roll microelectrode on a chip occupies a footprint of 0.045 mm2 and delivers an energy density up to 458 µW h cm-2. After packaging, the footprint of a full cell increases to 0.11 mm2 with a high energy density of 181 µW h cm-2. The volumetric energy density excluding the chip thickness is 16.3 mW h cm-3. These results open opportunities for deploying microbatteries as energy and power sources to drive smart dust microelectronics and microautonomous systems.

A new dimension for magnetosensitive e-skins: active matrix integrated micro-origami sensor arrays.

Magnetic sensors are widely used in our daily life for assessing the position and orientation of objects. Recently, the magnetic sensing modality has been introduced to electronic skins (e-skins), enabling remote perception of moving objects. However, the integration density of magnetic sensors is limited and the vector properties of the magnetic field cannot be fully explored since the sensors can only perceive field components in one or two dimensions. Here, we report an approach to fabricate high-density integrated active matrix magnetic sensor with three-dimensional (3D) magnetic vector field sensing capability. The 3D magnetic sensor is composed of an array of self-assembled micro-origami cubic architectures with biased anisotropic magnetoresistance (AMR) sensors manufactured in a wafer-scale process. Integrating the 3D magnetic sensors into an e-skin with embedded magnetic hairs enables real-time multidirectional tactile perception. We demonstrate a versatile approach for the fabrication of active matrix integrated 3D sensor arrays using micro-origami and pave the way for new electronic devices relying on the autonomous rearrangement of functional elements in space.

Electronically integrated microcatheters based on self-assembling polymer films.

Existing electronically integrated catheters rely on the manual assembly of separate components to integrate sensing and actuation capabilities. This strongly impedes their miniaturization and further integration. Here, we report an electronically integrated self-assembled microcatheter. Electronic components for sensing and actuation are embedded into the catheter wall through the self-assembly of photolithographically processed polymer thin films. With a diameter of only about 0.1 mm, the catheter integrates actuated digits for manipulation and a magnetic sensor for navigation and is capable of targeted delivery of liquids. Fundamental functionalities are demonstrated and evaluated with artificial model environments and ex vivo tissue. Using the integrated magnetic sensor, we develop a strategy for the magnetic tracking of medical tools that facilitates basic navigation with a high resolution below 0.1 mm. These highly flexible and microsized integrated catheters might expand the boundary of minimally invasive surgery and lead to new biomedical applications.

Creating Ferroic Micropatterns through Geometrical Transformation.

The functionality of a ferroic device is intimately coupled to the configuration of domains, domain boundaries, and the possibility for tailoring them. Exemplified with a ferromagnetic system, we present a novel approach which allows the creation of new, metastable multidomain patterns with tailored wall configurations through a self-assembled geometrical transformation. By preparing a magnetic layer system on a polymeric platform including swelling layer, a repeated self-assembled rolling into a multiwinding tubular structure and unrolling of the functional membrane is obtained. When polarizing the rolled-up 3D structure in a simple homogeneous magnetic field, the imprinted configuration translates into a regularly arranged multidomain configuration once the tubular structure is unwound. The process is linked to the employed magnetic anisotropy with respect to the surface normal, and the geometrical transformation connects the angular with the lateral degrees of freedom. This combination offers unparalleled possibilities for designing new magnetic or other ferroic micropatterns.

Self-sufficient self-oscillating microsystem driven by low power at low Reynolds numbers.

Oscillations at several hertz are a key feature of dynamic behavior of various biological entities, such as the pulsating heart, firing neurons, or the sperm-beating flagellum. Inspired by nature's fundamental self-oscillations, we use electroactive polymer microactuators and three-dimensional microswitches to create a synthetic electromechanical parametric relaxation oscillator (EMPRO) that relies on the shape change of micropatterned polypyrrole and generates a rhythmic motion at biologically relevant stroke frequencies of up to ~95 Hz. We incorporate an Ag-Mg electrochemical battery into the EMPRO for autonomous operation in a nontoxic environment. Such a self-sufficient self-oscillating microsystem offers new opportunities for artificial life at low Reynolds numbers by, for instance, mimicking and replacing nature's propulsion and pumping units.

Nano-biosupercapacitors enable autarkic sensor operation in blood.

Today's smallest energy storage devices for in-vivo applications are larger than 3 mm3 and lack the ability to continuously drive the complex functions of smart dust electronic and microrobotic systems. Here, we create a tubular biosupercapacitor occupying a mere volume of 1/1000 mm3 (=1 nanoliter), yet delivering up to 1.6 V in blood. The tubular geometry of this nano-biosupercapacitor provides efficient self-protection against external forces from pulsating blood or muscle contraction. Redox enzymes and living cells, naturally present in blood boost the performance of the device by 40% and help to solve the self-discharging problem persistently encountered by miniaturized supercapacitors. At full capacity, the nano-biosupercapacitors drive a complex integrated sensor system to measure the pH-value in blood. This demonstration opens up opportunities for next generation intravascular implants and microrobotic systems operating in hard-to-reach small spaces deep inside the human body.

Imperceptible Supercapacitors with High Area-Specific Capacitance.

Imperceptible electronics will make next-generation healthcare and biomedical systems thinner, lighter, and more flexible. While other components are thoroughly investigated, imperceptible energy storage devices lag behind because the decrease of thickness impairs the area-specific energy density. Imperceptible supercapacitors with high area-specific capacitance based on reduced graphene oxide/polyaniline (RGO/PANI) composite electrodes and polyvinyl alcohol (PVA)/H2 SO4 gel electrolyte are reported. Two strategies to realize a supercapacitor with a total device thickness of 5 µm-including substrate, electrode, and electrolyte-and an area-specific capacitance of 36 mF cm-2 simultaneously are implemented. First, the void volume of the RGO/PANI electrodes through mechanical compression is reduced, which decreases the thickness by 83% while retaining 89% of the capacitance. Second, the PVA-to-H2 SO4 mass ratio is decreased to 1:4.5, which improves the ion conductivity by 5000% compared to the commonly used PVA/H2 SO4 gel. Both advantages enable a 2 µm-thick gel electrolyte for planar interdigital supercapacitors. The impressive electromechanical stability of the imperceptible supercapacitors by wrinkling the substrate to produce folds with radii of 6 µm or less is demonstrated. The supercapacitors will be meaningful energy storage modules for future self-powered imperceptible electronics.

Digital Electrochemistry for On-Chip Heterogeneous Material Integration.

Many modern electronic applications rely on functional units arranged in an active-matrix integrated on a single chip. The active-matrix allows numerous identical device pixels to be addressed within a single system. However, next-generation electronics requires heterogeneous integration of dissimilar devices, where sensors, actuators, and display pixels sense and interact with the local environment. Heterogeneous material integration allows the reduction of size, increase of functionality, and enhancement of performance; however, it is challenging since front-end fabrication technologies in microelectronics put extremely high demands on materials, fabrication protocols, and processing environments. To overcome the obstacle in heterogeneous material integration, digital electrochemistry is explored here, which site-selectively carries out electrochemical processes to deposit and address electroactive materials within the pixel array. More specifically, an amorphous indium-gallium-zinc oxide (a-IGZO) thin-film-transistor (TFT) active-matrix is used to address pixels within the matrix and locally control electrochemical reactions for material growth and actuation. The digital electrochemistry procedure is studied in-depth by using polypyrrole (PPy) as a model material. Active-matrix-driven multicolored electrochromic patterns and actuator arrays are fabricated to demonstrate the capabilities of this approach for material integration. The approach can be extended to a broad range of materials and structures, opening up a new path for advanced heterogeneous microsystem integration.

A Patternable and In Situ Formed Polymeric Zinc Blanket for a Reversible Zinc Anode in a Skin-Mountable Microbattery.

Owing to their high safety and reversibility, aqueous microbatteries using zinc anodes and an acid electrolyte have emerged as promising candidates for wearable electronics. However, a critical limitation that prevents implementing zinc chemistry at the microscale lies in its spontaneous corrosion in an acidic electrolyte that causes a capacity loss of 40% after a ten-hour rest. Widespread anti-corrosion techniques, such as polymer coating, often retard the kinetics of zinc plating/stripping and lack spatial control at the microscale. Here, a polyimide coating that resolves this dilemma is reported. The coating prevents corrosion and hence reduces the capacity loss of a standby microbattery to 10%. The coordination of carbonyl oxygen in the polyimide with zinc ions builds up over cycling, creating a zinc blanket that minimizes the concentration gradient through the electrode/electrolyte interface and thus allows for fast kinetics and low plating/stripping overpotential. The polyimide's patternable feature energizes microbatteries in both aqueous and hydrogel electrolytes, delivering a supercapacitor-level rate performance and 400 stable cycles in the hydrogel electrolyte. Moreover, the microbattery is able to be attached to human skin and offers strong resistance to deformations, splashing, and external shock. The skin-mountable microbattery demonstrates an excellent combination of anti-corrosion, reversibility, and durability in wearables.

Impedimetric Microfluidic Sensor-in-a-Tube for Label-Free Immune Cell Analysis.

Analytical platforms based on impedance spectroscopy are promising for non-invasive and label-free analysis of single cells as well as of their extracellular matrix, being essential to understand cell function in the presence of certain diseases. Here, an innovative rolled-up impedimetric microfulidic sensor, called sensor-in-a-tube, is introduced for the simultaneous analysis of single human monocytes CD14+ and their extracellular medium upon liposaccharides (LPS)-mediated activation. In particular, rolled-up platinum microelectrodes are integrated within for the static and dynamic (in-flow) detection of cells and their surrounding medium (containing expressed cytokines) over an excitation frequency range from 102 to 5 × 106  Hz. The correspondence between cell activation stages and the electrical properties of the cell surrounding medium have been detected by electrical impedance spectroscopy in dynamic mode without employing electrode surface functionalization or labeling. The designed sensor-in-a-tube platform is shown as a sensitive and reliable tool for precise single cell analysis toward immune-deficient diseases diagnosis.

A Rotating Spiral Micromotor for Noninvasive Zygote Transfer.

Embryo transfer (ET) is a decisive step in the in vitro fertilization process. In most cases, the embryo is transferred to the uterus after several days of in vitro culture. Although studies have identified the beneficial effects of ET on proper embryo development in the earlier stages, this strategy is compromised by the necessity to transfer early embryos (zygotes) back to the fallopian tube instead of the uterus, which requires a more invasive, laparoscopic procedure, termed zygote intrafallopian transfer (ZIFT). Magnetic micromotors offer the possibility to mitigate such surgical interventions, as they have the potential to transport and deliver cellular cargo such as zygotes through the uterus and fallopian tube noninvasively, actuated by an externally applied rotating magnetic field. This study presents the capture, transport, and release of bovine and murine zygotes using two types of magnetic micropropellers, helix and spiral. Although helices represent an established micromotor architecture, spirals surpass them in terms of motion performance and with their ability to reliably capture and secure the cargo during both motion and transfer between different environments. Herein, this is demonstrated with murine oocytes/zygotes as the cargo; this is the first step toward the application of noninvasive, magnetic micromotor-assisted ZIFT.

Wafer-Scale High-Quality Microtubular Devices Fabricated via Dry-Etching for Optical and Microelectronic Applications.

Mechanical strain formed at the interfaces of thin films has been widely applied to self-assemble 3D microarchitectures. Among them, rolled-up microtubes possess a unique 3D geometry beneficial for working as photonic, electromagnetic, energy storage, and sensing devices. However, the yield and quality of microtubular architectures are often limited by the wet-release of lithographically patterned stacks of thin-film structures. To address the drawbacks of conventionally used wet-etching methods in self-assembly techniques, here a dry-release approach is developed to roll-up both metallic and dielectric, as well as metallic/dielectric hybrid thin films for the fabrication of electronic and optical devices. A silicon thin film sacrificial layer on insulator is etched by dry fluorine chemistry, triggering self-assembly of prestrained nanomembranes in a well-controlled wafer scale fashion. More than 6000 integrated microcapacitors as well as hundreds of active microtubular optical cavities are obtained in a simultaneous self-assembly process. The fabrication of wafer-scale self-assembled microdevices results in high yield, reproducibility, uniformity, and performance, which promise broad applications in microelectronics, photonics, and opto-electronics.

Stress-Actuated Spiral Microelectrode for High-Performance Lithium-Ion Microbatteries.

Miniaturization of batteries lags behind the success of modern electronic devices. Neither the device volume nor the energy density of microbatteries meets the requirement of microscale electronic devices. The main limitation for pushing the energy density of microbatteries arises from the low mass loading of active materials. However, merely pushing the mass loading through increased electrode thickness is accompanied by the long charge transfer pathway and inferior mechanical properties for long-term operation. Here, a new spiral microelectrode upon stress-actuation accomplishes high mass loading but short charge transfer pathways. At a small footprint area of around 1 mm2 , a 21-fold increase of the mass loading is achieved while featuring fast charge transfer at the nanoscale. The spiral microelectrode delivers a maximum area capacity of 1053 µAh cm-2 with a retention of 67% over 50 cycles. Moreover, the energy density of the cylinder microbattery using the spiral microelectrode as the anode reaches 12.6 mWh cm-3 at an ultrasmall volume of 3 mm3 . In terms of the device volume and energy density, the cylinder microbattery outperforms most of the current microbattery technologies, and hence provides a new strategy to develop high-performance microbatteries that can be integrated with miniaturized electronic devices.

Self-Assembly of Integrated Tubular Microsupercapacitors with Improved Electrochemical Performance and Self-Protective Function.

Inspired by origami art, we demonstrate a tubular microsupercapacitor (TMSC) by self-assembling two-dimensional (2D) films into a "swiss roll" structure with greatly reduced footprint area. A polymeric framework consisting of swelling hydrogel and polyimide layers ensures excellent ion transport between poly(3,4-ethylenedioxythiophene) (PEDOT)-based electrodes and provides efficient self-protection of the TMSC against external compression up to about 30 MPa. Such TMSCs exhibit an areal capacitance of 82.5 mF cm-2 at 0.3 mA cm-2 with a potential window of 0.8 V, an energy density and power density of 7.73 µWh cm-2 and 17.8 mW cm-2 (0.3 and 45 mA cm-2), and an improved cycling stability with a capacitance retention up to 96.6% over 5000 cycles. Furthermore, as-fabricated TMSC arrays can be detached from their surface and transferred onto target substrates. The connection of devices in parallel/series greatly improves their capacity and voltage output. Overall, our prototype devices and fabrication methodology provide a promising route to create integratable microscale tubular energy storage devices with an efficient self-protection function and high performance for future miniaturized electronics.

Magnetic origami creates high performance micro devices.

Self-assembly of two-dimensional patterned nanomembranes into three-dimensional micro-architectures has been considered a powerful approach for parallel and scalable manufacturing of the next generation of micro-electronic devices. However, the formation pathway towards the final geometry into which two-dimensional nanomembranes can transform depends on many available degrees of freedom and is plagued by structural inaccuracies. Especially for high-aspect-ratio nanomembranes, the potential energy landscape gives way to a manifold of complex pathways towards misassembly. Therefore, the self-assembly yield and device quality remain low and cannot compete with state-of-the art technologies. Here we present an alternative approach for the assembly of high-aspect-ratio nanomembranes into microelectronic devices with unprecedented control by remotely programming their assembly behavior under the influence of external magnetic fields. This form of magnetic Origami creates micro energy storage devices with excellent performance and high yield unleashing the full potential of magnetic field assisted assembly for on-chip manufacturing processes.

Self-assembly of highly sensitive 3D magnetic field vector angular encoders.

Novel robotic, bioelectronic, and diagnostic systems require a variety of compact and high-performance sensors. Among them, compact three-dimensional (3D) vector angular encoders are required to determine spatial position and orientation in a 3D environment. However, fabrication of 3D vector sensors is a challenging task associated with time-consuming and expensive, sequential processing needed for the orientation of individual sensor elements in 3D space. In this work, we demonstrate the potential of 3D self-assembly to simultaneously reorient numerous giant magnetoresistive (GMR) spin valve sensors for smart fabrication of 3D magnetic angular encoders. During the self-assembly process, the GMR sensors are brought into their desired orthogonal positions within the three Cartesian planes in a simultaneous process that yields monolithic high-performance devices. We fabricated vector angular encoders with equivalent angular accuracy in all directions of 0.14°, as well as low noise and low power consumption during high-speed operation at frequencies up to 1 kHz.

Magnetosensitive e-skins with directional perception for augmented reality.

Electronic skins equipped with artificial receptors are able to extend our perception beyond the modalities that have naturally evolved. These synthetic receptors offer complimentary information on our surroundings and endow us with novel means of manipulating physical or even virtual objects. We realize highly compliant magnetosensitive skins with directional perception that enable magnetic cognition, body position tracking, and touchless object manipulation. Transfer printing of eight high-performance spin valve sensors arranged into two Wheatstone bridges onto 1.7-µm-thick polyimide foils ensures mechanical imperceptibility. This resembles a new class of interactive devices extracting information from the surroundings through magnetic tags. We demonstrate this concept in augmented reality systems with virtual knob-turning functions and the operation of virtual dialing pads, based on the interaction with magnetic fields. This technology will enable a cornucopia of applications from navigation, motion tracking in robotics, regenerative medicine, and sports and gaming to interaction in supplemented reality.

Magnetic Suspension Array Technology: Controlled Synthesis and Screening in Microfluidic Networks.

Information tagging and processing are vital in information-intensive applications, e.g., telecommunication and high-throughput drug screening. Magnetic suspension array technology may offer intrinsic advantages to screening applications by enabling high distinguishability, the ease of code generation, and the feasibility of fast code readout, though the practical applicability of magnetic suspension array technology remains hampered by the lack of quality administration of encoded microcarriers. Here, a logic-controlled microfluidic system enabling controlled synthesis of magnetic suspension arrays in multiphase flow networks is realized. The smart and compact system offers a practical solution for the quality administration and screening of encoded magnetic microcarriers and addresses the universal need of process control for synthesis in microfluidic networks, i.e., on-demand creation of droplet templates for high information capacity. The demonstration of magnetic suspension array technology enabled by magnetic in-flow cytometry opens the avenue toward point-of-care multiplexed bead-based assays, clinical diagnostics, and drug discovery.