Conventional rigid electronic systems use a number of metallization layers to route all necessary connections to and from isolated surface mount devices using well-established printed circuit board technology. In contrast, present solutions to prepare stretchable electronic systems are typically confined to a single stretchable metallization layer. Crossovers and vertical interconnect accesses remain challenging; consequently, no reliable stretchable printed circuit board (SPCB) method has established. This article reports an industry compatible SPCB manufacturing method that enables multilayer crossovers and vertical interconnect accesses to interconnect isolated devices within an elastomeric matrix. As a demonstration, a stretchable (260%) active matrix with integrated electronic and optoelectronic surface mount devices is shown that can deform reversibly into various 3D shapes including hemispherical, conical or pyramid.

and form factor. To the best of our knowledge, a metamorphic microphone array has not been reported. Within the field of metamorphic electronics, two fabrication strategies are commonly used. The first uses electronic devices in combination with a bendable carrier and bendable interconnects. Here origami- [2] and kirigami [3] like methods are used to fold the structure into a desired shape. The topological complexity dictates the number of folds that are required and certain topologies, for example, a sphere, and are difficult to fabricate. The microphone arrays discussed in this communication morph from a (i) concave to a (ii) planar to a (iii) convex and a (iv) cone-like topology, which would be very difficult to achieve using the origami/kirigami approach.An alternative to the origami-inspired method is to build on recent advancements in the field of stretchable electronics. Stretchable electronics incorporates electronic functions (in our case, microphones and other active and passive devices) inside or on top of a stretchable elastomeric membrane. One essential element is the requirement of stretchable electrical interconnects between the device elements. Different interconnect solutions are known today. Most of the solutions go back to the original work by Lacour, [4] Chen, [5] and Whitesides [6] and their respective co-workers who reported (i) metallization layers with topological wrinkles, [4] (ii) meander or horse-shoe designs, [5] and (iii) liquid metals, [6] as the stretchable interconnecting metal layers, respectively. A large set of applications have been demonstrated, which include smart clothing, [7] conformable photo voltaics, [8] optoelectronics, [9] digital cameras, [10] artificial electronic skins, [11] stretchable batteries, [12] robotics, [13] and mechanically soft and conformable health-monitoring devices [14] to give a few recent examples. However, considering the current state of the art, the number of interconnects to the isolated device elements has been small (2-4 connections per device), and the total number of devices continues to be limited (5-22 devices). [15] This points to scaling and robustness challenges.As a result, the desired microphone array has been difficult to fabricate using the reported methods. The array has a total number of 60 interconnects, contains 5 different device types, and a total of 25 commercially available surface mount devices (SMDs). This goes beyond the metrics previously reported in the field of stretchable electronics.This article describes the realization of a metamorphic microphone array. The array morphs from a concave to a planar and then to a convex shape. The morphing array enables a better (12×) sound source localization when compared to existing static and planar arrangements. To enable the realization, a novel stretchable (elongated up to 320% of the original length) printed circuit board fabrication process is reported. The fabrication process enables high-temperature processing, alignment, and registration. Moreover, conventional and otherw...

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Stretchable metallic interconnects are commonly designed using a meander-shaped metal track with a uniform width. This article reports on a 'stress-adaptive' metal track design which varies in width to accommodate the produced torque in the metal track during stretching. The stress-adaptive design is inspired by computational and experimental studies of two conventional meander-shape metal tracks identifying a common failure mode; specifically, the propagation of torque leading to twist and mechanical fatigue. The understanding gained led to the stress-adaptive design. The stress-adaptive structure is compared with horseshoe-and U-shaped references and shows improvements in the stress distribution, levels of twist, maximum level of elongation (>320%), and required stretch and release cycles (>6000 at 150% elongation) to cause failure in a long term cycling test.

To match the properties of a semiconductor to a desired application, it is crucial to control its crystal structure. Here, we show that, by implementing a corona discharge in a chemical vapor deposition process, the growth morphology of gallium oxide can be adjusted to produce nanowires and layerlike and columnar crystal structures. The three morphologies can be explained by the transition from a classic chemical vapor process to a corona-assisted chemical vapor process with directed transport. Specifically, the excitation of the carrier gas by the corona discharge is exploited as a switch to transition from a vapor–liquid–solid nanowire growth mechanism to a layer by layer growth mechanism. The second switching parameter is the substrate bias which affects the directed precursor transport and enhances the growth rate. While the switching of the morphology has no effect on the crystal phase, the photoluminescence properties of the three morphologies are different. The grown structures are used as optical gas sensors at room temperature. Tin-doped gallium oxide is shown to be capable of detecting trace amounts (200 ppm) of alcohols such as acetone, ethanol, and isopropanol. The layerlike morphology provides the highest response.

We demonstrate the realization of core−shell transformation-imprinted solder bumps to enable low-temperature chip assembly, while providing a route to high-temperature interconnects through transformation. The reported core−shell solder bump uses a lower melting point BiIn-based shell and a higher melting point Sn core in the initial stage. The bumps enable fluidic self-assembly and selfalignment at relatively low temperatures (60−80 °C). The bumps use the high surface free energy of the liquid shell during the self-assembly to capture freely suspended Si dies inside a heated (80 °C) water bath, leading to well-ordered defect-free chip arrays; the molten liquid shell wets the metal contact (binding site) on the chips and yields self-aligned and electrically connected devices. The solid core provides the anchor point to the substrate. After the completion of the assembly, a short reflow raises the melting point, yielding a solid electrical connection. The low melting point liquid diffuses into the high melting point core. The tuning of the material ratios leads to tailored transformation-imprinted solders with high melting points (160−206 °C) in the final structure. KEYWORDS: core−shell transformation-imprinted solder bumps, low-temperature fluidic self-assembly, high melting point interconnects, Pb-free solder bumps, self-alignment

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Parallel three-dimensional (3D) growth of different nanomaterials with submicrometer resolution is a promising approach to overcome some technological and economic limits encountered in planar integrated homogeneous films. The programmable multimaterial gas phase nanoparticle electrodeposition concept enables the fabrication of a 3D multimodal conductometric gas sensor array. The approach requires the deposition of more than one nanomaterial to achieve orthogonal sensing capabilities and multigas sensitivity and selectivity. The demonstrated "electronic nose"-like array contains 1080 self-aligning 3D nanobridge-based electrical connections of platinum, nickel oxide, and gold on a single chip. The nanobridges form through a nearest neighbor Coulombic interaction. Each gas sensitive bridge is a 3D structure composed of a porous but electrically conducting nanoparticle network. It was found that this architecture is unique, because it does not require external heating to operate. A trimodal sensor array will be demonstrated to detect various levels of ammonia (NH 3 ), carbon monoxide (CO), and hydrogen sulfide (H 2 S). A 3 × 3 transfer matrix will be discussed to correlate the recorded signals with the gas composition.