Recent progress in molybdenum disulfide (MoS2) based flexible nanogenerators: an inclusive review

Energy consumption and structure have changed in the new era along with the growth of the Internet of Things (IoT) and artificial intelligence, and the power sources for billions of dispersed gadgets and sensors have sparked attention globally to protect the environment. Due to the rising usage of non-renewable energy sources and the resulting environmental damage, researchers are investigating alternative energy systems that can harness energy from the environment. Therefore, self-sufficient small-scale electronic systems will be possible through the use of underutilised natural waste energy sources collected in nanogenerators (NGs). The features of the materials used have a significant impact on how well NGs work. In this regard Molybdenum disulfide (MoS2), a 2D material, is one of the compounds that is discussed vastly nowadays due to its exceptional characteristics that made it useful in a variety of applications. Many research papers on the advancement and implementation of MoS2 materials have been published, but this article will give an in-depth overview. It offers an introduction and interpretation of the main properties of 2D MoS2 nanomaterials, starting with their current state, properties, and various synthesis processes. Later, the review concentrates on MoS2 applications and energy-harvesting capabilities and gives a comprehensive study of piezoelectric, triboelectric and thermometrical nanogenerators based on 2D MoS2 nanocomposite materials

Gate-all-around nanowire FET sensors with ultrahigh sensitivity and low noise

In this research work, new kinds of field-effect transistor (FET)-based sensing elements were developed to maximize the detection limits of conventional piezoresistors. These sensing elements were able to enhance the piezoresistive sensitivity and reduce the intrinsic noise, which significantly improved the detection limits and make them adaptable for lower strain detection applications. To further improve the piezoresistive sensitivity, the gate-all-around (GAA) nanowire field-effect transistor (NWFET) was presented as a novel, miniaturized and lower voltage driven piezoresistive sensing element. The piezoresistive coefficient of the NWFET enhanced up to seven times and reduction of the electronic noise improved the sensor resolution by sixteen times compared to the planar FET-based sensing element. Results showed that NWFET-based sensing elements operated at low bias with higher piezoresistance and can be used to measure lower strain values with high signal-to-noise ratio. The development of the GAA channel structure was further implemented to design and fabricate a novel junctionless nanowire field-effect transistor (JL-NWFET). The JL-NWFET operated by bulk conduction and showed significantly lower electronic noise than the NWFET counterpart. The picoampere drain current noise helped to achieve a four times better resolution for the JL-NWFET than that of the inversion mode NWFET. The preliminary results achieved in this research work indicate that the GAA JL-NWFET-based sensing element has miniaturized size, higher piezoresistive sensitivity and lower intrinsic noise and can be potentially used in ultrasensitive strain sensors.DOCTOR OF PHILOSOPHY (MAE

Piezoresistive sensing performance of junctionless nanowire FET

This letter investigates junctionless nanowire field-effect transistor (NWFET) (JL-NWFET) parameters such as piezoresistance and low-frequency noise (LFN) with respect to channel doping and gate bias. The JL-NWFET is piezoresistive, and its gauge factor (GF ) is increased from 24 to 47 by reducing the channel doping ten times from 6.7 × 1019 to 6.7 × 1018 cm-3. Significant variations of GF and LFN are observed when the JL-NWFET is operated from subthreshold to on-state regime, and resolution (minimum detectable strain) is improved four times compared to inversion-mode NWFET. The simple fabrication and superior resolution formulate JL-NWFET as a promising sensing element for miniaturized nanoelectromechanical sensors

Low-cost and reliable nanowire fabrication method for ultrasensitive pressure sensor

This paper presents piezoresistive nanowires based pressure sensor with a novel and low-cost nanowire fabrication technique. Silicon nanowire sensing element (width<100 nm) is chosen because of their higher piezoresistive coefficient compared to bulk silicon and integrated into MEMS diaphragm to measure pressure up to 2 bar. The novelty of the proposed process lies in making nanowires with controllable dimensions (CD < 100 nm) and with no dependency on the lithography tool limitations. Initially, this process is optimised for nanowires and then simulations are carried out for the pressure sensor. Simulation results are presented for a pressure sensor having a diaphragm thickness of 10 mu m and the sensor fabrication is currently ongoing. Proposed nanowire fabrication process can potentially be utilized to obtain any nano-dimension structure without using expensive masks and special lithography tools

A cantilever-based NEM nonvolatile memory utilizing electrostatic actuation and vibrational deactuation for high-temperature operation

This paper proposes a cantilever-based nanoelectromechanical (NEM) nonvolatile memory (NVM) with a novel write scheme for reliable memory operation at very high-operating temperature (up to 300 °C) in rugged electronics. The memory bit (0/1) is formed by the opening/closing of a cantilever beam. Permanent retention is obtained by adhesive force between two smooth surfaces in contact, eliminating leakage observed in all types of storage-layer-based NVMs. This allows the proposed NEM memory structure to be implemented using a simple bilayer design and easily integrated with the CMOS platform with leakage of 144 pA, which is significantly less compared with SRAM. The experimental analysis of vibrational reset is reported for the first time in this paper. An array structure using the proposed NEM memory device and CMOS devices is presented. Each bit cell consists of one NEM memory device and one nMOS transistor for realizing full random-access operation.Accepted versio

Tunable piezoresistance and noise in gate-all-around nanowire field-effect-transistor

The piezoresistance and noise of n-type gate-all-around nanowire field-effect-transistor (NWFET) is investigated as a function of gate bias. With narrow gate bias span of 0.6 V near threshold region, the piezoresistive coefficient of NWFET enhances up to seven times from 29 × 10−11 Pa−1 to 207 × 10−11 Pa−1 under compressive and tensile strain conditions. Results reveal that the low frequency noise is reduced when operated in subthreshold region. The higher piezoresistive coefficient and reduced noise improve the sensor resolution (minimum detectable strain) by sixteen times. NWFET operates at low bias with higher piezoresistance and signal-to-noise ratio and offers promising applications in strain sensors.Published versio

Design and array implementation a cantilever-based non-volatile memory utilizing vibrational reset

This paper proposes a cantilever-based memory structure for storing binary data at extreme operating temperature (up to 300 C) in rugged electronics. The memory bit (0/1) is formed by opening/closing of an electrostatic switch. Permanent retention is obtained by adhesive force between two smooth surfaces in contact, eliminating leakage observed in all types of storage-layer-based NVMs. The Reset utilizes a train of short pulses to break the adhesion between the electrodes. This allows the Nano-electromechanical switch (NEMS) memory to be implemented using a simple bi-layer design and easily integrated with CMOS platforms. We propose an array structure where each memory cell consists of a NEMS memory device and one NMOS transistor for full random-access operation.ASTAR (Agency for Sci., Tech. and Research, S’pore)Accepted versio

Molecular adhesion controlled microelectromechanical memory device for harsh environment data storage

This work demonstrates a cantilever based electrostatic microelectromechanical system device operating as a memory element. Volatile and non-volatile functions are engineered by manipulating molecular adhesion force through contact dimples and restoring force using the cantilever design. For non-volatile RESET operation, a method of detaching the cantilever with 3 V pulsating DC signal at 1 MHz is proposed. SET/RESET cycles are performed up to 103 times at 300 °C without any performance degradation. A writing speed of up to 0.94 μs is achieved, which is faster than conventional high temperature flash memories. With demonstrated attributes, the fabricated device offers excellent potential for harsh environment data storage applications.ASTAR (Agency for Sci., Tech. and Research, S’pore)Published versio