An Ultralow Power Mixed Dimensional Heterojunction Transistor Based on the Charge Plasma pn Junction.

Development of a reliable doping method for 2D materials is a key issue to adopt the materials in the future microelectronic circuits and to replace the silicon, keeping the Moore's law toward the sub-10 nm channel length. Especially hole doping is highly required, because most of the transition metal dichalcogenides (TMDC) among the 2D materials are electron-doped by sulfur vacancies in their atomic structures. Here, hole doping of a TMDC, tungsten disulfide (WS2 ) using the silicon substrate as the dopant medium is demonstrated. An ultralow-power current sourcing transistor or a gated WS2 pn diode is fabricated based on a charge plasma pn heterojunction formed between the WS2 thin-film and heavily doped bulk silicon. An ultralow switchable output current down to 0.01 nA µm-1 , an off-state current of ≈1 × 10-14 A µm-1 , a static power consumption range of 1 fW µm-1 -1 pW µm-1 , and an output current ratio of 103 at 0.1 V supply voltage are achieved. The charge plasma heterojunction allows a stable (less than 3% variation) output current regardless of the gate voltage once it is turned on.

Tactile Interaction Sensor with Millimeter Sensing Acuity.

In this article we report on a 3 × 3 mm tactile interaction sensor that is able to simultaneously detect pressure level, pressure distribution, and shear force direction. The sensor consists of multiple mechanical switches under a conducting diaphragm. An external stimulus is measured by the deflection of the diaphragm and the arrangement of mechanical switches, resulting in low noise, high reliability, and high uniformity. Our sensor is able to detect tactile forces as small as ~50 mgf along with the direction of the shear force. It also distinguishes whether there is a normal pressure during slip motion. We also succeed in detecting the contact shape and the contact motion, demonstrating potential applications in robotics and remote input interfaces. Since our sensor has a simple structure and its function depends only on sensor dimensions, not on an active sensing material, in comparison with previous tactile sensors, our sensor shows high uniformity and reliability for an array-type integration.