Fabrication strategies that pursue "simplicity" for the production process and "functionality" for a device, in general, are mutually exclusive. Therefore, strategies that are less expensive, less equipment-intensive, and consequently, more accessible to researchers for the realization of omnipresent electronics are required. Here, this study presents a conceptually different approach that utilizes the inartificial design of the surface roughness of paper to realize a capacitive pressure sensor with high performance compared with sensors produced using costly microfabrication processes. This study utilizes a writing activity with a pencil and paper, which enables the construction of a fundamental capacitor that can be used as a flexible capacitive pressure sensor with high pressure sensitivity and short response time and that it can be inexpensively fabricated over large areas. Furthermore, the paper-based pressure sensors are integrated into a fully functional 3D touch-pad device, which is a step toward the realization of omnipresent electronics.

The fundamental challenge in designing transparent pressure sensors is the ideal combination of high optical transparency and high pressure sensitivity. Satisfying these competing demands is commonly achieved by a compromise between the transparency and usage of a patterned dielectric surface, which increases pressure sensitivity, but decreases transparency. Herein, a design strategy for fabricating high-transparency and high-sensitivity capacitive pressure sensors is proposed, which relies on the multiple states of nanoparticle dispersity resulting in enhanced surface roughness and light transmittance. We utilize two nanoparticle dispersion states on a surface: (i) homogeneous dispersion, where each nanoparticle (≈500 nm) with a size comparable to the visible light wavelength has low light scattering; and (ii) heterogeneous dispersion, where aggregated nanoparticles form a micrometer-sized feature, increasing pressure sensitivity. This approach is experimentally verified using a nanoparticle-dispersed polymer composite, which has high pressure sensitivity (1.0 kPa ), and demonstrates excellent transparency (>95%). We demonstrate that the integration of nanoparticle-dispersed capacitor elements into an array readily yields a real-time pressure monitoring application and a fully functional touch device capable of acting as a pressure sensor-based input device, thereby opening up new avenues to establish processing techniques that are effective on the nanoscale yet applicable to macroscopic processing.

A thermochromic-based interactive sensor that can generate local color switching and pressure mapping is developed using a 2D array of resistive pressure sensor switch. This thermochromic-based interactive sensor will enable the visualization of localized information in arbitrary shapes with dynamic responses in the context of serial/parallel pressure mapping and quantifying capability without optoelectronic arrays.

In addition to the demand for stimuli‐responsive sensors that can detect various vital signals in epidermal skin, the development of electronic skin displays that quantitatively detect and visualize various epidermal stimuli such as the temperature, sweat gland activity, and conductance simultaneously are of significant interest for emerging human‐interactive electronics used in health monitoring. Herein, a novel interactive skin display with epidermal stimuli electrode (ISDEE) allowing for the simultaneous sensing and display of multiple epidermal stimuli on a single device is presented. It is based on a simple two‐layer architecture on a topographically patterned elastomeric polymer composite with light‐emitting inorganic phosphors, upon which two electrodes are placed with a certain parallel gap. The ISDEE is directly mounted on human skin, which by itself serves as a field‐responsive floating electrode of the display operating under an alternating current (AC). The AC field exerted on the epidermal skin layer depends on the conductance of the skin, which can be modulated based on a variety of physiological skin factors, such as the temperature, sweat gland activity, and pressure. Conductance‐dependent field‐induced electroluminescence is achieved, giving rise to an on‐hand sensing display platform where a variety of human information can be directly sensed and visualized.

Simultaneous sensing and visualization of pressure provides a useful platform to obtain information about a pressurizing object, but the fabrication of such interactive displays at the single-device level remains challenging. Here, we present a pressure responsive electroluminescent (EL) display that allows for both sensing and visualization of pressure. Our device is based on a two-terminal capacitor with six constituent layers: top electrode/insulator/hole injection layer/emissive layer/electron transport layer/bottom electrode. Light emission upon exposure to an alternating current field between two electrodes is controlled by the capacitance change of the insulator arising from the pressure applied on top. Besides capacitive pressure sensing, our EL display allows for direct visualization of the static and dynamic information of position, shape, and size of a pressurizing object on a single-device platform. Monitoring the pressurized area of an elastomeric hemisphere on a device by EL enables quantitative estimation of the Young's modulus of the elastomer, offering a new and facile characterization method for the mechanical properties of soft materials.