A floating gate negative capacitance MoS2 phototransistor with high photosensitivity.

Monolayer MoS2 exhibits interesting optoelectronic properties that have been utilized in applications such as photodetectors and light emitting diodes. For image sensing applications, improving the light sensitivity relies on achieving a low dark current that enables the detection weak light signals. Although previous reports on improving the detectivity have been explored with heterostructures and pn junction devices, some of these approaches lack CMOS compatibility processing and sufficient low dark current suppression. Steep slope transistors that overcome the Boltzmann tyranny can further enhance the performance in photodetectors by providing efficient extraction of photogenerated charges. Here, we report a monolayer MoS2 floating gate negative capacitance phototransistor with the integration of a hafnium-zirconium oxide ferroelectric capacitor. In this study, a SSmin of 30 mV dec-1, very low dark currents of 10-13-10-14 A, and a high detectivity of 7.2 × 1015 cm Hz1/2 W-1 were achieved under weak light illumination due to an enhancement in the photogating effect. In addition, its potential as an optical memory and as an optical synapse with excellent long-term potentiation characteristics in an artificial neural network was also explored. Overall, this device structure offers high photosensitivity to weak light signals for future low-powered optoelectronic applications.

A Highly Sensitive Capacitive-type Strain Sensor Using Wrinkled Ultrathin Gold Films.

Soft strain sensors are needed for a variety of applications including human motion and health monitoring, soft robotics, and human/machine interactions. Capacitive-type strain sensors are excellent candidates for practical applications due to their great linearity and low hysteresis; however, a big limitation of this sensor is its inherent property of low sensitivity when it comes to detecting various levels of applied strain. This limitation is due to the structural properties of the parallel plate capacitor structure during applied stretching operations. According to this model, at best the maximum gauge factor (sensitivity) that can be achieved is 1. Here, we report the highest gauge factor ever achieved in capacitive-type strain sensors utilizing an ultrathin wrinkled gold film electrode. Our strain sensor achieved a gauge factor slightly above 3 and exhibited high linearity with negligible hysteresis over a maximum applied strain of 140%. We further demonstrated this highly sensitive strain sensor in a wearable application. This work opens up the possibility of engineering even higher sensitivity in capacitive-type strain sensors for practical and reliable wearable applications.

Mechanically Durable and Highly Stretchable Transistors Employing Carbon Nanotube Semiconductor and Electrodes.

Mechanically durable stretchable trans-istors are fabricated using carbon nanotube electrical components and tough thermoplastic elastomers. After an initial conditioning step, the electrical characteristics remain constant with strain. The strain-dependent characteristics are similar in orthogonal stretching directions. Devices can be impacted with a hammer and punctured with a needle while remaining functional and stretchable.