A Highly Sensitive Capacitive-type Strain Sensor Using Wrinkled Ultrathin Gold Films

Soft strain sensors are needed for a variety of applications including human motion and health monitoring, soft robotics, and human/machine interactions. Capacitive-type strain sensors are excellent candidates for practical applications due to their great linearity and low hysteresis; however, a big limitation of this sensor is its inherent property of low sensitivity when it comes to detecting various levels of applied strain. This limitation is due to the structural properties of the parallel plate capacitor structure during applied stretching operations. According to this model, at best the maximum gauge factor (sensitivity) that can be achieved is 1. Here, we report the highest gauge factor ever achieved in capacitive-type strain sensors utilizing an ultrathin wrinkled gold film electrode. Our strain sensor achieved a gauge factor slightly above 3 and exhibited high linearity with negligible hysteresis over a maximum applied strain of 140%. We further demonstrated this highly sensitive strain sensor in a wearable application. This work opens up the possibility of engineering even higher sensitivity in capacitive-type strain sensors for practical and reliable wearable applications

High Sensitivity Tuning of Work Function of Self-Assembled Monolayers Modified Electrodes Using Vacuum Ultraviolet Treatment

We demonstrate systematic work function tuning of thiol-based SAM-modified gold electrodes with high controllability and sensitivity as high as 0.05 eV using vacuum ultraviolet technique (VUV). Under different irradiation times, both work function and wettability of the metal surface is modified. Fine tuning of the electrode work function is demonstrated by observable changes in the reverse current of a polymer Schottky diode. Additionally, the change in SAM chemical functionality validates the work function changes of VUV-irradiated electrodes. Our selective work function patterning on a single Au electrode via VUV could also reduce the required fabrication steps for more complex circuits

Ultraflexible Transparent Oxide/Metal/Oxide Stack Electrode with Low Sheet Resistance for Electrophysiological Measurements

Flexible, transparent electrodes are a crucial component for future implantable and wearable systems. For practical applications, conductivity and flexibility should be further improved to prevent signal attenuation, heat generation, and disconnection. Herein, we fabricate an ultraflexible transparent electrode with low sheet resistance (8.6 Ω/sq) using an indium-tin-oxide/Au/indium-tin-oxide (ITO) multilayer on a 1 μm thick parylene substrate. The electrodes were foldable and when compared to pristine ITO displayed greater mechanical robustness. Applicability for large-area applications was confirmed through electrochemical impedance measurements, and the compatibility of electrode arrays for in vivo applications was demonstrated with an optogenetic experiment. As a result of the ultraflexible transparent electrode’s excellent conformity to soft tissue, voltage signals induced by light stimulation directly below the electrode were successfully recorded on the moving muscle