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Past research aimed at increasing the sensitivity of capacitive pressure sensors has mostly focused on developing dielectric layers with surface/porous structures or higher dielectric constants. However, such strategies have only been effective in improving sensitivities at low pressure ranges (e.g., up to 3 kPa). To overcome this well‐known obstacle, herein, a flexible hybrid‐response pressure sensor (HRPS) composed of an electrically conductive porous nanocomposite (PNC) laminated with an ultrathin dielectric layer is devised. Using a nickel foam template, the PNC is fabricated with carbon nanotubes (CNTs)‐doped Ecoflex to be 86% porous and electrically conductive. The PNC exhibits hybrid piezoresistive and piezocapacitive responses, resulting in significantly enhanced sensitivities (i.e., more than 400%) over wide pressure ranges, from 3.13 kPa−1 within 0–1 kPa to 0.43 kPa−1 within 30–50 kPa. The effect of the hybrid responses is differentiated from the effect of porosity or high dielectric constants by comparing the HRPS with its purely piezocapacitive counterparts. Fundamental understanding of the HRPS and the prediction of optimal CNT doping are achieved through simplified analytical models. The HRPS is able to measure pressures from as subtle as the temporal arterial pulse to as large as footsteps.

Soft pressure sensors are critical components of e-skins, which are playing an increasingly significant role in two burgeoning fields: soft robotics and bioelectronics. Capacitive pressure sensors (CPS) are popular given their mechanical flexibility, high sensitivity, and signal stability. After two decades of rapid development, e-skins based on soft CPS are able to achieve human-skin-like softness and sensitivity. However, there remain two major roadblocks in the way for practical application of soft CPS: the decay of sensitivity with increased pressure and the coupled response between in-plane stretch and out-of-plane pressure. In addition to existing strategies of building porous and/or high dielectric constant soft dielectrics, are there any other promising methods to overcome those bottlenecks? Are there any further considerations for the widespread deployment of e-skins? This perspective aims to shed some light on those topics.

High-performance wearable and implantable devices capable of recording physiological signals and delivering appropriate therapeutics in real time are playing a pivotal role in revolutionizing personalized healthcare. However, the mechanical and biochemical mismatches between rigid, inorganic devices and soft, organic human tissues cause significant trouble, including skin irritation, tissue damage, compromised signal-to-noise ratios, and limited service time. As a result, profuse research efforts have been devoted to overcoming these issues by using flexible and stretchable device designs and soft materials. Here, we summarize recent representative research and technological advances for soft bioelectronics, including conformable and stretchable device designs, various types of soft electronic materials, and surface coating and treatment methods. We also highlight applications of these strategies to emerging soft wearable and implantable devices. We conclude with some current limitations and offer future prospects of this booming field.

We investigated characteristics of high performance GaN‐based laser diodes grown on LEO‐GaN/sapphire and free‐standing GaN substrates. The maximum output power was 300 mW under cw operation. The operation current and voltage were 53 mA and 4.67 V, respectively, for 30 mW‐output power. Thermal simulation and junction temperature measurement of laser diodes showed that epi‐down bonding was essential for the use of sapphire substrate. It was proposed that Mg diffusion into active layers was responsible for the degradation mechanism of GaN‐based laser diodes. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)