High-performance Tactile Sensors Research Articles

3D printed stretchable coaxial fiber grid for dual-mode multifunctional tactile sensor array

Tactile sensors play a critical role in the Internet of Things (IoT) and wearable devices. However, although current tactile sensors can precisely measure pressure, the simple fabrication of stretchable high-performance tactile sensors with a broad measuring range and multifunctions is still challenging. Herein, an ink-direct writing 3D printing method is developed to fabricate novel stretchable dual-mode tactile sensors with coaxial fiber structure. The 3D printed coaxial fibers have an outer skin composed of silicone rubber and polytetrafluoroethylene micropowders thixotropic agent and an inner core of an ionic conductive solution composed of polyvinyl alcohol and sodium chloride. The coaxial fibers exhibit excellent electrical conductivity (0.54 S cm−1) and outstanding stretchability, as high as 390 %. The intersection of the two fibers constitutes a dual-mode tactile sensor which can operate in triboelectric or capacitive modes with complementary measurement ranges from 0.0003 to 0.4517 N. Besides, by combining the signals from the two modes, the sensor can identify the material that comes into contact with the sensor. A 3D printed network of tactile sensor arrays made of warp-weft interwoven coaxial fibers is able to accurately detect the locations of multi-point contact with the array. This dual-mode multifunctional tactile sensor can be widely used in various applications such as the IoT and wearable devices.

A Skin-Inspired High-Performance Tactile Sensor for Accurate Recognition of Object Softness.

High-performance tactile sensors with skin-sensing properties are crucial for intelligent perception in next-generation smart devices. However, previous studies have mainly focused on the sensitivity and response range of tactile sensation while neglecting the ability to recognize object softness. Therefore, achieving a precise perception of the softness remains a challenge. Here, we report an integrated tactile sensor consisting of a central hole gradient structure pressure sensor and a planar structure strain sensor. The recognition of softness and tactile perception is achieved through the synergistic effect of pressure sensors that sense the applied pressure and strain sensors that recognize the strain of the target object. The results indicate that the softness evaluation parameter (SC) of the integrated structural tactile sensor increases from 0.14 to 0.47 along with Young's modulus of the object decreasing from 2.74 to 0.45 MPa, demonstrating accurate softness recognition. It also exhibits a high sensitivity of 10.55 kPa-1 and an ultrawide linear range of 0-1000 kPa, showing an excellent tactile sensing capability. Further, an intelligent robotic hand system based on integrated structural tactile sensors was developed, which can identify the softness of soft foam and glass and grasp them accurately, indicating human skin-like sensing and grasping capabilities.

Simulation study of ZnO nanorod geometry for the development of high-performance tactile sensors and energy harvesting devices

ZnO exhibits an excellent piezoelectric response and can transduce mechanical energy into electrical signals by applying pressure. In particular, vertically aligned ZnO nanorods were thought to be of great importance because of their higher value of piezoelectric coefficient along the z-direction. In this study, various geometries of ZnO nanorods are explored and their effect on the strength of piezoelectric output potential is simulated using COMSOL Multiphysics software. The simulation results show that out of many geometries and inclinations of ZnO nanorods, the highest piezoelectric output is demonstrated by the inclined ZnO nanorods due to the application of higher torque force or shear stress in similar applied force. The high torque force or shear stress at 60° orientation and optimized contributions from all the piezoelectric coefficients resulted in a high piezoelectric output potential close to 215 mV which is much higher than the vertically aligned ZnO nanorod which is approximately 25 mV.

(Invited) self-Powered Multifunctional Sensing and Control for Smart Wearables and Human-Machine Interfaces

Robust, high-performance tactile sensors are critical for developing soft intelligent robotics, human-machine interfaces (HMI), and wearable electronics. However, it is challenging to fabricate soft tactile sensors capable of multifunctional sensing under both fast and slow response conditions in a simple and low-cost manner. In this talk, I will present our recent efforts in developing novel self-powered sensors and HMIs for wearables and intelligent controls. I will first introduce a textile-based tactile sensor capable of multifunctional sensing (covering both dynamic and static measurements) for personalized healthcare monitoring and soft robotic control. Inspired by human skin, the tactile sensor consists of a triboelectric nanogenerator sensing layer to mimic the function of fast-adapting (FA) mechanoreceptors and a piezoresistive sensing layer to achieve the functionality of slow-adapting (SA) mechanoreceptors. Then, I will demonstrate a self-powered breath sensor to monitor the health conditions of patients and provide daily assistance for severely disabled people to control electrical household appliances and other smart systems. The new system provides the advantages of high sensitivity, good stability, low cost, and ease of use.

DotView: A Low-Cost Compact Tactile Sensor for Pressure, Shear, and Torsion Estimation

Tactile sensation is one of the most important sensing methods of humans, which helps humans complete complex decisions and actions by itself or in cooperation with other sensations. Similarly, tactile sensors are also crucial for robots to interact with the environment and fulfill dexterous object manipulation. In this study, we present DotView, a compact, low-cost, and high-performance tactile sensor that utilizes a biomimetic micro-structured soft layer to generate rich, high-resolution tactile images captured by a commercialized capacitive sensing array, which exhibits sensitive and robust responses under pressure, shear and torsion applied by different indenters. Furthermore, we utilize a neural network to estimate multiaxial contact forces and torques, and achieve good accuracy in different contact geometries. Finally, we demonstrate the capability of DotView in a dexterous manipulation scenario by performing the task of guiding a tool through a maze with only tactile feedback.

Highly Sensitive Tactile Sensor With Wide Dynamic Range Based on Multicontact Mechanism

High-performance tactile sensors have become the important part of human–machine interaction, intelligent medical monitoring, industrial robots, and many other fields. However, high sensitivity and wide range are considered as contradictory aspects, so that the trade-off is always made between parameters. How to achieve the balance between them is a huge challenge. Herein, a novel tactile sensor is introduced based on the multicontact structure, which consists of two parts: the deformable top electrode with conductive spherical surface and the bottom electrode distributed with graphite nanosheets/polyimide (GNSs/PI) resistor array. Thereafter, the sensing mechanism of this new structure is systematically analyzed, which originates from changes in the contact resistance between overlapping electrode pairs and the expansion of the parallel equivalent circuit. Notably, tactile performances can be optimized by adjusting the curvature and conductivity of the top electrode, and the distribution pattern and density of the bottom electrode, leading to an outstanding sensitivity of 15.65 kPa−1 for low pressure (0–200 kPa) and 2.99 kPa−1 for high pressure (200–1400 kPa) with linearity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{\,2}$ </tex-math></inline-formula> higher than 0.95 in both intervals. Furthermore, the sensor shows relatively low detection limit (1 g), short response time (170 ms), and the excellent repeatability and durability advantageous to prolonged use. It is proven that the sensor design concept can be used as a preferred choice for accurate collection of tactile information and gives full support for the relevant applications of intelligent electronics.

Carbon Dots-Based Ultrastretchable and Conductive Hydrogels for High-Performance Tactile Sensors and Self-Powered Electronic Skin.

Smart tactile sensing materials have excellent development prospects, including wearable health-monitoring equipment and energy collection. Hydrogels have received extensive attention in tactile sensing owing to their transparency and high elasticity. In this study, highly crosslinked hydrogels are fabricated by chemically crosslinking polyacrylamide with lithium magnesium silicate and decorated with carbon quantum dots. Magnesium lithium silicate provides abundant covalent bonds and improves the mechanical properties of the hydrogels. The luminescentproperties endowed by the carbon dots further broaden the application of hydrogels for realizing flexible electronics. The hydrogel-based strain sensor exhibits excellent sensitivity (gauge factor 2.6), a broad strain response range (0-2000%), good cyclicity, and durability (1250). Strain sensors can be used to detect human motions. More importantly, the hydrogel can also be used as a flexible self-supporting triboelectric electrode for effectively detecting pressure in the range of 1-25 N and delivering a short-circuit current (ISC ) of 2.6µA, open-circuit voltage (VOC ) of 115V, and short-circuit transfer charge (QSC ) of 29 nC. The results reveal new possibilities for human-computer interactions and electronic robot skins.

Hierarchical MXene@ZIF‐67 Film Based High Performance Tactile Sensor with Large Sensing Range from Motion Monitoring to Sound Wave Detection

AbstractConductive two‐dimensional transition metal carbides and nitrides (MXenes) as active materials have demonstrated significant promise for applications in wearable electronic devices. However, the intrinsic high conductivity and poor structural stability of MXenes severely limits its application as a high‐performance flexible tactile sensor. To overcome these disadvantages, an interlayer hierarchical MXene/MOFs film was synthesized by intercalating poorly conductive ZIF‐67s octahedron crystals between highly conductive MXene nanosheets by vacuum‐assisted filtration. The alternating MXene and MOFs layers provided a 3D, interconnected conductive network that enhanced the variation range of the conductive path. The fabricated flexible sensing device featuring the MXene/MOFs hybrid active layers exhibited excellent sensing performance, with a sensitivity of 110.0 kPa−1, a fast response/recovery time of 15 ms/15 ms, and a broad pressure‐detection range of 0.0035–100 kPa. Owing to these merits, the fabricated sensor was capable of monitoring diverse stimuli over a large pressure range, such as recognizing finger movements, eyes blinking, pulses, and vibrations from musical instruments.

Highly Sensitive Flexible Tactile Sensors in Wide Sensing Range Enabled by Hierarchical Topography of Biaxially Strained and Capillary-Densified Carbon Nanotube Bundles.

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 (0-100kPa), high sensitivity (141.72kPa-1 ), and low detection limit (10Pa). 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.

Anisotropic Shear-Sensitive Tactile Sensors with Programmable Elastomers for Robotic Manipulations.

High-performance tactile sensors are urgently demanded in various intensive interactive scenarios, e.g., texture detection, robotic interaction with fragile objects, and motion direction recognition, where dynamic conditions are involved with complex tangential forces or vibrations. Although many microstructured/porous sensors can perceive tangential forces, their isotropic structures that lack programmability lead them to be incapable of sensing the direction of forces and restrain their tunability for complex situations, e.g., a wide sensing range for large forces and high sensitivity for gentle forces. Here, by tuning the programmable microstructures (microcolumns and microfilms) of an elastomeric active layer, we propose a simple principle to flexibly tune the shear sensitivity of an anisotropic porous sensor and bring a 10-fold distinction of anisotropy with a wide range of shear sensitivity (from 0.07 to 0.7 N-1). The fabricated tactile sensors can be used in various robotic manipulations resiliently, for instance, morphology and topology identification of curved surfaces, delicate interactive manipulations, and recognizing the relative motion of two contacting objects. Our work introduces a simple and effective strategy for tailoring flexible shear-sensitive sensors for diverse dexterous robotic manipulations during complex interactions.

Stimuli-Responsive Materials from Ferrocene-Based Organic Small Molecule for Wearable Sensors.

Stimuli-responsive crystals capable of energy conversion have emerged as promising materials for smart sensors, actuators, wearable devices, and robotics. Here, a novel ferrocene-based organic molecule crystal (Fc-Cz) that possesses anisotropic piezoelectric, optical, and mechanical properties is reported. It is demonstrated that the new crystal Fc-Cz can be used as an ultrasensitive piezoelectric material in fabricating strain sensors. The flexible sensor made of crystal Fc-Cz can detect small strains/deformations and motions with a fast response speed. Analysis based on density functional theory (DFT) indicates that an external pressure can affect the dipole moment by changing the molecular configuration of the asymmetric single crystal Fc-Cz in the crystalline state, leading to a change of polarity, and thereby an enhanced dielectric constant. This work demonstrates a new artificial organic small molecule for high-performance tactile sensors, indicating its great potential for developing low-cost flexible wearable sensors.

Research on Material and Morphological Structure of Venus Flytrap Trigger Hair

Venus flytrap can sense the very small insects that touch its tactile receptors, known as trigger hairs, and thus capture prey to maintain its nutrient demand. However, there are few studies on the trigger hair and its morphological structure and material properties are not fully understood. In this study, the trigger hair is systematically characterized with the help of different instruments. Results show that trigger hair is a special cantilever beam structure and it has a large longitudinal diameter ratio. Besides, it is composed of a hair lever and a basal podium, and there is a notch near the hair base. The cross-section of the trigger hair is approximately a honeycomb structure, which is composed of many holes. Methods to measure mechanical properties of trigger hair are introduced in this paper. Based on the mechanical tests, trigger hair proved to be a variable stiffness structure and shows a high sensitivity to the external force. These features can provide supports for the understanding of the high-sensitivity sensing mechanism of trigger hairs from the perspective of structure and material, and offer inspirations for the development of high-performance tactile sensors.

Recent Advances in Flexible Tactile Sensors for Intelligent Systems.

Tactile sensors are an important medium for artificial intelligence systems to perceive their external environment. With the rapid development of smart robots, wearable devices, and human-computer interaction interfaces, flexible tactile sensing has attracted extensive attention. An overview of the recent development in high-performance tactile sensors used for smart systems is introduced. The main transduction mechanisms of flexible tactile sensors including piezoresistive, capacitive, piezoelectric, and triboelectric sensors are discussed in detail. The development status of flexible tactile sensors with high resolution, high sensitive, self-powered, and visual capabilities are focused on. Then, for intelligent systems, the wide application prospects of flexible tactile sensors in the fields of wearable electronics, intelligent robots, human-computer interaction interfaces, and implantable electronics are systematically discussed. Finally, the future prospects of flexible tactile sensors for intelligent systems are proposed.

Recent Progress in Flexible Tactile Sensors for Human-Interactive Systems: From Sensors to Advanced Applications.

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.

Recent Applications of Different Microstructure Designs in High Performance Tactile Sensors: A Review

Flexible tactile sensors have become one of the most attractive research areas because of its great application prospect in electronic skin, healthcare monitoring and artificial intelligence. However, there are still great challenges in mimicking the human skin's strong ability of tactile perception to the changes of external physical information. Nowadays, in addition to flexible polymers and conductive materials, the microstructure of sensing units is a key factor to improve the performance of tactile sensors such as sensitivity, fast response and robustness. In recent years, a variety of novel microstructure designs have been applied to applications of tactile information perception and numerous corresponding processing methods have also been developed, which provides a wealth of enlightening solutions for the production of electronic skins. Herein, a large number of research results of tactile sensor devices are systematically reviewed according to different three-dimensional geometric shapes of the microstructures which are grouped into several categories. At the same time, relevant processing technologies employed, working principles and chief performance characteristics are also briefly described. Relative merits of different types of microstructure applications are clearly elaborated through the classification and comparison of multiple microstructure geometries in this paper to provide valuable reference for sensing microstructure design and fabrication of tactile sensors in corresponding engineering applications. Moreover, current difficulties and challenges in fabrication of flexible microstructures and future investigative directions pertaining to this field have been discussed.

Energy-efficient, fully flexible, high-performance tactile sensor based on piezotronic effect: Piezoelectric signal amplified with organic field-effect transistors

Abstract Fully flexible piezoelectric tactile sensors with low power consumption and high sensitivity play an important role in artificial intelligence, advanced manufacturing, and smart wearable devices. Herein, we constructed a high-performance, energy-efficient, and fully flexible piezoelectric tactile sensor based on piezotronic effect through the integration of piezoelectric materials with the mechanical-to-electrical conversion function of β polyvinylidene fluoride (PVDF) nanorod arrays and the signal amplification function of organic field-effect transistor (OFET) devices. PVDF nanorod arrays, which considerably improve the piezoelectric properties of materials, transform the external mechanical force into piezoelectric voltage to drive the OFET. Further, the piezoelectric voltage can be effectively amplified using an OFET to improve the sensitivity of the tactile sensor. Enabled by the unique structure of sensing devices and well-defined active materials, the fabricated tactile sensor exhibited excellent pressure sensitivity, detection limit, and response time of 5.17 kPa⁻1, 175 Pa, and 150 ms, respectively. In addition, using a sophisticated fabrication process, we demonstrated a flexible integrated tactile sensor array with a 3 × 3 cell on a polyethylene terephthalate (PET) substrate to detect the bending angle of the user's wrist on which the fabricated device was mounted. This study uses piezotronic transistors to convert pressure into electrical signals without applying a gate voltage, which can substantially simplify circuit models and sensor distribution; additionally, the fabricated device provides technical support for flexible electronic skin (e-skin).

(Invited) Post-CMOS Compatible Silicon MEMS Nano-Tactile Sensor for Touch Feeling Discrimination of Materials

Semiconductor silicon has realized various kinds of valuable electron devices. CMOS technology is the present standard silicon process to fabricate integrated circuits and systems. Therefore, the word “Post-CMOS” has been an important word which means that the technology makes it possible to fabricate various kinds of MEMS sensors/actuators/passives with highly sophisticated modern CMOS devices. Also, it emphasizes that MEMS devices fabricated by post-CMOS technology has “high compatibility” with “silicon FABs” that are most universal and distributed fabrication facilities in the world. High performance devices and fine microstructures can be fabricated by universal post-CMOS fabrication processes at present.Post-CMOS compatible process is a key technology to realize ultra-high-performance silicon MEMS tactile sensors in this study. We, humans have very sophisticated sense of touch on our fingertip skin, and we can recognize and distinguish various and delicate difference of touch feelings obtained by “sweep motion” of fingertip on various kinds of materials and objects. Our fingertip skin has the highest density of force and vibration (mechanical) receptors like Meissner’s corpuscles and Merkel disks under the surface skin layer where fine pitch patterns of fingerprint are formed on. It is known that human’s fingertip has a very high spatial resolution below 100µm or less, and can recognize existence of 13nm-pitch patterns as reported recently. The high performance of our fingertip sense of touch has never been realized by any tactile sensor device. In order to reproduce artificial sense of touch like the fingertip, very high performances on “spatial resolution” and “input sensitivities” are required to integrate all on a small tactile sensor. Therefore, CMOS-compatible fabrication technology is the most suitable process to fabricate such high-performance tactile sensors with integrated functions.Based on a silicon post-CMOS compatible process, we have realized high performance silicon MEMS tactile sensor called “Nano-tactile sensor”, which is comparable to the performance of fingertip sense of touch. In this tactile sensor device, all the mechanical structures are made from single crystalline silicon which is the active layer of SOI wafers. No elastomer/polymer structures are used in the mechanical sensing structure, and softness and elasticity necessary to tactile sensing are realized by silicon micro mechanical structures. All the fine mechanical movements and sensing circuits with strain-sensitive diffusion resistors (i.e. piezoresistors) are designed by 2D-CAD, and the characteristics can be controlled by layout pattern sizes. The contactor parts of the tactile sensor have curved shape which is similarly designed to the cross-section of a fingerprint, and its suspension springs are designed to have similar spring constant with human’s fingertip skin surface.In the latest version of our “Nano-tactile sensors”, six contactors with fingerprint-like shape are integrated at a pitch of 500µm to get distributed tactile images at a high spatial resolution. The pitch of 500µm corresponds to the average value of human’s fingerprint patterns. Each fingerprint-like contactor reproduces vertical motion (by micro roughness) and horizontal motion (by frictional force) of a fingerprint closely under sweeping motion of fingertip in touch feeling measurement. Spatial resolution of our tactile sensor reaches to sub-micron (200nm) in the finest version, and its force resolution of input reaches below 50µN range. These high performances are enough high to reproduce part of our fingertip sense of touch. The Nano-tactile sensors can get touch feeling waveforms of “hair surface condition”, “skin texture and the condition”, and touch feelings of various kinds of “papers” and “clothes” at a high spatial resolution like our fingertip skin. In the lecture, experimental results of very high-resolution tactile sensing are presented, and their importance and novelty are discussed.Machine learning based on deep neural network (DNN) has become very important for sensing data analysis. We think DNN is very important to understand/reproduce human sense of touch since a trained DNN behaves similarly with human’s senses based on our experiences. Since a lot of sample data are required for such applications, we have developed a measurement system called “Touch-Feeling Scanner”. A number of tactile sensing data can be measured by the touch-feeling scanner integrating a Nano-tactile sensor device. Obtained signals with the scanner were applied to train a DNN for discrimination of different kinds of clothes. 10 kinds of cloth samples have been successfully discriminated at a correct percentage over 95% as an example. Combination of high-resolution Nano-tactile sensors and state-of-the-art machine learning (DNN) is a strong approach to reproduce human fingertip sensation for various valuable applications. Figure 1

A Deformable Foam-Layered Triboelectric Tactile Sensor with Adjustable Dynamic Range

The triboelectric effect utilizes the electric potential of materials to generate an electrical output through electrostatic induction between the two oppositely charged surfaces, which grants them unique self-powered characteristics. By utilizing this effect, self-powered tactile sensors have been studied in the previous researches. However, the conventional triboelectric tactile sensors have drawbacks of limited dynamic range due to the decreasing sensitivity under increased applied pressures. Owing to this disadvantage, the triboelectric tactile sensor has not been extensively employed in smart manufacturing applications where a consistently high sensitivity within the dynamic range is preferred. In order to address this issue, a lightweight, compact, bio-friendly and highly sensitive self-powered triboelectric tactile sensor has been investigated based on the triboelectric effect. By integration of deformable foam layer, triboelectric tactile sensor is able to shift the dynamic range by 76–98 kPa without having to employ gain adjustment circuit board or modifying the properties of the sensor (geometric, materials, etc.). The proposed tactile sensor can be employed in various smart manufacturing applications in which light, self-powered, and high-performance tactile sensors are required to reduce the weight and energy consumption.

Pressure Insensitive Strain Sensor with Facile Solution-Based Process for Tactile Sensing Applications.

Tactile sensors that can mechanically decouple, and therefore differentiate, various tactile inputs are highly important to properly mimic the sensing capabilities of human skin. Herein, we present an all-solution processable pressure insensitive strain sensor that utilizes the difference in structural change upon the application of pressure and tensile strain. Under the application of strain, microcracks occur within the multiwalled carbon nanotube (MWCNT) network, inducing a large change in resistance with gauge factor of ∼56 at 70% strain. On the other hand, under the application of pressure to as high as 140 kPa, negligible change in resistance is observed, which can be attributed to the pressure working primarily to close the pores, and hence minimally changing the MWCNT network conformation. Our sensor can easily be coated onto irregularly shaped three-dimensional objects (e.g., robotic hand) via spray coating, or be attached to human joints, to detect bending motion. Furthermore, our sensor can differentiate between shear stress and normal pressure, and the local strain can be spatially mapped without the use of patterned electrode array using electrical impedance tomography. These demonstrations make our sensor highly useful and important for the future development of high performance tactile sensors.

(Invited) 2D Materials for Wearable Electronics

Tactile sensors, in the form of conformal and embedded devices, have attracted intense research interest because of their diverse applications, from electronic skin (E-skin) for robotics to health care monitoring systems. Much effort has been made to develop large- area and high-performance tactile sensors with good sensitivity and mechanical flexibility. MoS2 semiconductors have recently attracted attention because of their outstanding mechanical and optical transmittance, high gauge factor, and tunable band gap. However, there is no report on multi-cell devices for practical applications that transcend the fabrication of a single cell. In this talk, I present an ultrathin conformal, MoS2-based tactile sensing array covering an area of 2.2 cm ´ 2.2 cm. We integrated the sensor with a graphene electrode and interconnect to achieve good mechanical flexibility and optical transmittance in the visible color range (Figure 1). This sensor shows high sensitivity, good uniformity, and linearity even after 1000 loading cycles. In addition, it provides excellent mechanical flexibility over strain of 1.98% and better than 80% transparency. Figure 1. MoS2 tactile sensor transferred on the fingertip. a-b) Optical and SEM images of the MoS2 tactile sensor on a fingertip. c) Colorized SEM images of the MoS2 strain gauge (left, yellow) and graphene electrode (right, blue). d) Pressure map detected by the MoS2 tactile sensor from contact with pens of different diameters (7 and 5 mm). e) Calculated crosstalk isolation of the MoS2 sensor array with different pen-tip sizes (D : 7,5 and 2 mm). Figure 1