Human skin is capable of transducing pressures in the range of 100 Pa (light touch) to 1 MPa (full body weight bearing); common tasks such as object manipulation develop contact pressures on the order of 10 kPa. [ 21,22 ] Moreover, sensitivity of human skin to applied pressures is complex and varies widely by type of mechanoreceptor and type of stimulation (normal pressure, shear pressure, frequency, magnitude). [ 23 ] Although distributed sensing using arrays of thin-fi lm transistors on ultrathin plastic foils combined with soft mechanical sensors has also been demonstrated, [ 11,[24][25][26] most reported skin-like sensors are discrete elements. An unmet demand for truly wearable e-skin is mechanical compliance. Natural skin is soft and elastic. Electronic skins should therefore wrap over the external surface of the body and accompany movement, in particular over joints and articulations. To date, pressure sensing data gloves and tactile skins are mainly prepared with fl exible polymers [27][28][29] and conductive textiles. [ 30,31 ] These constructs conform well to developable surfaces (e.g., the arm and fi nger phalanges) but wrinkle and often fail when placed over articulations (e.g., the elbow and fi nger joints). [ 32 ] E-skins prepared entirely with stretchable materials appear as a necessary starting point. Over the last decade, multiple designs of stretchable tactile sensors using elastomers, thin fi lms, composites, [ 19,33 ] and conductive liquids [34][35][36] have been reported, but their systematic characterization in real-life conditions is often incomplete. Stretchable strain sensors are often demonstrated in complex real-life scenarios, [ 37,38 ] but in the literature related to stretchable tactile sensors, demonstrations involving dynamic states where bending and stretching of the sensors occur simultaneously are not common, likely due to the challenges of removing cross-sensitivities to strain and noise received from the body. [ 19,20,39 ] In this paper, we report on a stretchable e-skin designed to be worn over the hand, monitor live fi nger movement, and register distributed pressure along the entire length of the fi nger. The sensory skin is thin and made entirely of elastic materials, thereby can be mounted on a glove and worn without impeding hand movement ( Figure 1 ). The read-out electronics are integrated in a small printed circuit board (PCB) located immediately at the base of each fi nger. Capacitive pressure sensors combine stretchable gold thin-fi lm electrodes with porous silicone foam (Figure 1 a) and display high sensitivity across much of the large dynamic pressure range of human skin. Six adjacent pressure sensors cover the entire length of the fi nger; two soft metallic shielding layers eliminate noise and cross-sensitivity over the skin and enable multi-touch with This report demonstrates a wearable elastomer-based electronic skin including resistive sensors for monitoring fi nger articulation and capacitive tactile pressure sensors that register distributed pressure along ...

Liquid metals, encapsulated in soft materials, have therefore attracted much attention in recent years [2a,8] to manufacture soft conductors with metallic conductivity, high stretchability and reconfigurability. [9] Gallium-based alloys, rather than toxic mercury, are widely used. The high surface tension and the passivating oxide skin that spontaneously forms on the surface of these liquids hinder their patterning using conventional techniques. Alternative methods focus on injection into channels, molding and printing for rapid manufacturing of highly conductive and stretchable metal networks but none of these patterning techniques offer high-resolution batch processing over large (wafer-scale) surface areas. [10] Based on these observations, we developed a new class of stretchable electronic conductors formed of biphasic solidliquid thin metal films. A bilayer metallization sequence starting with the sputtering of an alloying gold film followed by the thermal evaporation of liquid gallium (that displays a melting point of 29.8 °C [11] ) results in a heterogeneous film composed of clusters of the solid intermetallic alloy AuGa 2 and supercool liquid gallium forming a continuous network and dispersed bulges [11b,12] (Figure 1a-c). We designed and engineered the biphasic metallic films to be compatible with large-area and standard microfabrication. Figure 1d,e shows examples of fine patterns produced at wafer scale on elastomeric substrates. Multilayered stretchable circuits can be readily integrated by covalently bonding membranes hosting patterned biphasic conductors connected through soft vias. Figure 1e displays a 4 × 4 wafer-sized hybrid array of surface mounted light emitting diodes interconnected with a two-level network of biphasic solid-liquid conductors. The array withstood demanding multiaxial inflation cycles, constantly delivering power to the optoelectronic devices (Movie S1, Supporting Information).To prepare the stretchable biphasic solid-liquid thin metal films, a two-step process was developed in which liquid gallium was evaporated on a substrate preliminarily coated with a wetting and alloying thin film. We selected poly(dimethylsiloxane) (PDMS), a silicone, as the soft carrier substrate and a gold film sputtered on the PDMS as the alloying layer. However, our process is not limited to those materials ( Figure S1 and S2, Supporting Information). Non-noble metals may be used, provided the alloying thin film is not oxidized.The high surface tension of the liquid metal prevented the formation of an evaporated continuous liquid metal film on bare silicone substrates. Instead, the surface of the elastomer was covered with a nonconducting arrangement of liquid gallium microdroplets ( Figure S3, Supporting Information). In contrast, evaporating gallium on an alloying metal film, first deposited on the silicone surface, overcame the cohesive forces Stretchable conductors are the foundation of soft electronic circuits. [1] Manufacturing elastic wiring networks to distribute and carry electrical pote...

In this manuscript, we achieve a closed-loop control over haptic feedback, first time for an entirely soft platform. We prototyped a novel self-sensing soft pneumatic actuator (SPA) with soft strain sensors, called SPA-skin, that withstands large multiaxial strains and is capable of high frequency sensing and actuation. To close-loop control the haptic feedback, the platform requires a cohesively integrated system. Our system consists of a stretchable low profile (< 500 μm) SPA and an ultra-compliant thin-metal film strain sensor that create a novel bidirectional platform for tactile sensing via force-tunable vibratory feedback. With this prototype, we demonstrated control of the actuator shape in real-time up to 100 Hz at output forces up to 1 N, maintained under variable mechanical loadings. We further characterized the SPA-skin platform for its static and dynamic behavior over a range of actuation amplitude and frequencies as well as developed an analytical model of this system to predict the actuator inflation state only using the embedded sensor's resistance. Our SPA-skin is a multifunctional multilayer system that can readily be implemented as a high-speed wearable bidirectional interface for contact sensing and vibrotactile feedback.

A new SOI/elastomer fabrication process that integrates a soft elastomer in-plane with silicon features has been developed, characterized and demonstrated. The simple three-mask process uses deep reactive ion etching of trenches in a silicon-on-insulator wafer to pattern high-aspect-ratio silicon and elastomer features from 2 μm to hundreds of micrometers in width. The elastic and adhesive properties of the fabricated elastomer have been characterized. A Young's modulus of 1.4 MPa was measured at moderate strains up to 75%, and nonlinear strain was observed beyond that. The SOI/elastomer process has been used to fabricate micromechanical thrusters to repeatedly store and release 1.3 μJ to propel a 2 mg 1.6 mm by 0.8 mm by 0.45 mm projectile 1.35 cm.

This paper presents the in situ characterization of microscale poly(dimethylsiloxane) (PDMS) springs using silicon-on-insulator-microelectromechanical systems (SOI-MEMS). PDMS samples that were 30 μm long, 20 μm thick, and 6 μm wide were fabricated on-chip along with a test mechanism that included electrostatic comb drive actuators and silicon flexures. The test mechanism allowed for applying strains up to 65%. The in situ test results were compared with results of tests on macroscale samples performed using a dynamic mechanical analyzer. The results imply that the process steps during fabrication initially led to increased crosslinking of the PDMS but that the final release of the structure in buffered hydrofluoric acid decreased the crosslink density, thereby decreasing the stiffness of the PDMS. Several implications of the results on processing PDMS in MEMS are presented. The results of this work are important for the design of MEMS devices which incorporate PDMS as a mechanical material.

In the exciting race to design and engineer biointegrated and body‐like electronic systems, many efforts concentrate on the integration of hydrogels in electronic assemblies. The versatility of hydrogels chemistry combined with their tissue‐mimicking properties inspires numerous demonstrations of hydrogel‐based touch panels, robots, and sensors over the years. However, their long‐term integration in a thin and functional electronic assembly remains a challenge: their sensitivity to both air‐drying and water swelling leads to important volume change of the network that is incompatible with the cohesion of a multilayer system, and has irreversible impact on the electronic properties of the assembly. To tackle this issue, proposed is a method to fabricate a hydrogel–elastomer micrometric bilayer with a stable interface, using of a low‐swelling type of hydrogel, i.e., poly(2‐hydroxyethyl methacrylate) and silicone rubber. The bilayer can sustain multiple hydration/dehydration cycles without delamination and can be kept for several months in its dry configuration. Combined with soft metallization technology, the bilayer can be readily integrated into a soft electronic circuit thereby opening a technological route for microfabricated, on‐demand morphing systems.

This note presents the data on the dielectric breakdown of polydimethylsiloxane (PDMS) thin films with thicknesses from 2 to 14 μm between the silicon electrodes. The results demonstrate that there is a strong dependence of the breakdown field on both the electrode gap and shape. The breakdown fields range from 250 to 635 V μm−1, depending on the electrode geometry and gap, approaching 10× the breakdown fields for air gaps of the same size. The results are critical for understanding the performance limits of PDMS thin films used in the electromechanical microsystems.

Small insects and other animals use a multitude of materials to realize specific functions, including locomotion. This paper demonstrates application of the first microfabrication process to incorporate high aspect ratio compliant elastomer structures in-plane with traditional silicon microelectromechanical systems (MEMS). By incorporating these new materials, compact energy storage systems based on elastomer springs for small jumping robots have been demonstrated. Results include a 4 mm×4 mm jumping mechanism that has reached heights of 32 cm, × 80 its own height, and an on-chip actuated mechanism that has been used to propel a 1.4 mg projectile over 7 cm.