detection; furthermore, mechanisms or devices to detect other stimuli, such as strain, temperature, and humidity, may be integrated. A tactile feedback system, integrated with a prosthetic hand, was demonstrated in 1974, [2] and since then, a variety of tactile sensors have been actively developed for use in various applications, such as touch screens and robotic hands. Flexible tactile sensors capable of measuring mechanical stimuli via physical contact have attracted significant attention in the field of human-interactive systems. The utilization of tactile information can complement vision and/or sound interaction and provide new functionalities. Recent advancements in micro/nanotechnology, material science, and information technology have resulted in the development of high-performance tactile sensors that reach and even surpass the tactile sensing ability of human skin. Here, important advances in flexible tactile sensors over recent years are summarized, from sensor designs to system-level applications. This review focuses on the representative strategies based on design and material configurations for improving key performance parameters including sensitivity, detection range/linearity, response time/hysteresis, spatial resolution/crosstalk, multidirectional force detection, and insensitivity to other stimuli. System-level integration for practical applications beyond conceptual prototypes and promising applications, such as artificial electronic skin for robotics and prosthetics, wearable controllers for electronics, and bidirectional communication tools, are also discussed. Finally, perspectives on issues regarding further advances are provided.

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Flexible tactile sensors with high sensitivity have received considerable attention for their use in wearable electronics, human–machine interfaces, and health‐monitoring devices. Although various micro/nanostructured materials are introduced for high‐performance tactile sensors, simultaneously obtaining high sensitivity and a wide sensing range remains challenging. Here, a resistive tactile sensor is presented based on the hierarchical topography of carbon nanotubes (CNTs) prepared by a low‐cost and straightforward manufacturing process. The 3D hierarchical structure of the CNTs over large areas is formed by transferring vertically aligned CNT bundles to a prestrained elastomer substrate and subsequently densifying them through capillary forming, providing a monotonic increase in the contact area as applied pressure. The deformable and hierarchical structure of CNTs allows the sensor to exhibit a wide sensing range (0–100 kPa), high sensitivity (141.72 kPa−1), and low detection limit (10 Pa). Additionally, the capillary‐formed CNT structure results in increased durability of the sensor over repeated pressures. Based on these advantages, meaningful applications of tactile sensors, such as object recognition gloves and multidirectional force perceptions, are successfully realized. Given the scalable fabrication method, 3D hierarchically structured CNTs provide an essential step toward next‐generation wearable devices.

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Paper has attracted considerable interest as a promising pressure‐sensing element owing to its foldability/bendability and deformability due to its high porosity. However, paper‐based tactile sensors reported hitherto cannot achieve high sensitivity and a wide sensing range simultaneously. In this study, a resistive tactile sensor using carbon nanotube‐ and silver nanoparticle‐printed mulberry paper as a pressure‐sensing element and electrodes, respectively, is developed. The rough surface and high inner porosity of mulberry paper induce a significant change in the contact area when a multilayer‐stacked structure is used, resulting in increased sensitivity to pressure. Moreover, the enhanced mechanical robustness of mulberry paper originating from the highly bonded network of long and thick fibers affords a wide pressure‐sensing range. The sensor exhibits a high sensitivity exceeding 1 kPa−1 in an applied pressure range of 0.05–900 kPa; this achievement has not been reported among paper‐based tactile sensors. Furthermore, the sensor exhibits a fast response/relaxation time, low detection limit, high resolution, high durability, and high flexibility. The advantages of the sensor afford several applications, including a crosstalk‐free pressure sensor array, a three‐axis pressure sensor, and wearable devices for measuring signals from a user.

Layered 2D materials, owing to their unique physical and electrical properties, have significant potential for use in future nanomaterial‐based electronic devices. Among these, palladium diselenide (PdSe2) has recently emerged as a distinct 2D material with air stability and strong ambipolar property. In this study, the versatility of a PdSe2‐based split‐gate field‐effect transistor (SG‐FET) using its stable ambipolar nature is demonstrated. By applying sequentially polarized SG biases, the PdSe2 SG‐FET could be operated as a homogeneous and reconfigurable pn‐junction diode. The optimized h‐BN/PdSe2/h‐BN sandwich SG‐FET exhibits almost symmetric behaviors in the n‐ and p‐channel regions, enabling a reconfigurable single‐inversion AND (SAND) logic gate function, which can be used as a phase difference‐detection circuit composed only of a single component. It is believed that this approach to the reconfigurable diode and its circuit application paves the way for future 2D material‐based electronics.