Human skin has different types of tactile receptors that can distinguish various mechanical stimuli from temperature. We present a deformable artificial multimodal ionic receptor that can differentiate thermal and mechanical information without signal interference. Two variables are derived from the analysis of the ion relaxation dynamics: the charge relaxation time as a strain-insensitive intrinsic variable to measure absolute temperature and the normalized capacitance as a temperature-insensitive extrinsic variable to measure strain. The artificial receptor with a simple electrode-electrolyte-electrode structure simultaneously detects temperature and strain by measuring the variables at only two measurement frequencies. The human skin–like multimodal receptor array, called multimodal ion-electronic skin (IEM-skin), provides real-time force directions and strain profiles in various tactile motions (shear, pinch, spread, torsion, and so on).

Conductive and stretchable electrodes that can be printed directly on a stretchable substrate have drawn intensive attention for wearable electronics and electronic skins. Printable inks containing liquid metal (LM) are strong candidates for these applications, but the insulating oxide skin forming around LM particles limits their conductivity. This study reveals that hydrogen doping (H-doping) introduced by ultrasonication in the presence of aliphatic polymers makes the oxide skin highly conductive and deformable. X-ray photoelectron spectroscopy and atom probe tomography confirms hydrogen doping, and first-principles calculations are used to rationalize the obtained conductivity. Printed circuit lines show metallic conductivity (25,000 S/cm), excellent electromechanical decoupling at 500% uniaxial stretching, mechanical resistance to scratches, and long-term stability in wide ranges of temperature and humidity. The self-passivation of the printed lines allows direct printing of 3D circuit lines and double-layer planar coils that are used as stretchable inductive strain sensors.Stretchable electronic devices have received widespread attention for potential uses in healthcare monitoring 1-3 , electronic skins 4,5 , and wearable haptic devices 6,7 . One of the key technological issues in stretchable electronics is the fabrication of stretchable circuit lines, for which several characteristics are requested simultaneously; metallic conductivity, negligible resistance changes under deformations, electrical stability in harsh environments, printing of complicated circuit designs, passivation 8 , and good adhesion to elastomeric substrates 9 . Serpentine and buckled metal interconnections have achieved a few of the above requests such as metallic conductivity, small resistance changes, some degree of deformability, and environmental stability 10 . Other progress has been with conductive elastomer composites with respect to high

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Wang et al. fabricated a 100 × 100 pressure sensor matrix with a resolution of 100 dpi that could detect a wide pressure range. [32] You et al. made a flexible pressure sensor array of 100 pixels cm −2 without having electrical crosstalks between the pixels. [33] Kim et al. have demonstrated a carbonbased piezocapacitive pressure sensor array which could perceive a low pressure (0.4 Pa). [34] Li et al. fabricated a 4 × 4 matrix of supercapacitive pressure sensors using the ion-electronic interface and showed a high pressure-to-capacitance sensitivity (114 nF kPa -1 ). [35] In contrast to the intensive studies on the pressure sensors, shear sensors have been rarely investigated. It is because of the structural complexity of the shear sensor required for detecting different horizontal shear directions and the angles to the normal direction. Another technological difficulty in shear sensor fabrication is the need for deformability requested to prevent the slip of an object.So far, tactile shear force recognition has proceeded in three approaches; i) fabrication of a unit shear sensor, ii) profiling relative strain distribution by analyzing strain distribution obtained from a strain sensor array, and iii) direct mapping of shear forces by using a shear sensor array. The unit sensors are relatively large and designed to detect the shear forces applied from four directions. Viry et al. made a three-axial force sensor by using fluorosilicone and air gap between top and bottom electrodes. [36] Although the sensor could quantitatively measure shear forces, it could not provide the shear force distribution over a large area. Hua et al. implemented a 10 × 10 strain sensor array showing the shear force distribution through the piezoresistive sensor network. [37] Unfortunately, the quantitative value of shear force was difficult to obtain through the strain distribution approach. A shear sensor array is expected to simultaneously provide the shear force distribution and the quantitative force values. Cheng et al. fabricated a shear sensor array based on capacitance change upon air gap deformation. [38] Because of the small capacitance of the air gap, this type of capacitive sensor requires a large sensing area to obtain reliable sensing signals, thus fabrication of a miniaturized array sensor is difficult through this approach.In this work, we propose a deformable shear sensor array (3 × 3) in 27 mm × 27 mm, in which each sensor can An array of shear sensors is essential in tactile sensation as well as the pressure sensors. Surprisingly, however, the shear sensor array is rarely investigated mainly due to the structural complexity to measure the horizontal forces from various directions and also due to the mechanical softness required for preventing the slip of an object. Here, an array of small shear sensors that can recognize both shear force and shear rotational angle is fabricated. All the device components are made of deformable materials to acquire the softness of the sensor. This work presents a novel design for the sm...