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Nanotechnology in Electronics, Materials Properties, and Devices: State of the Art and Future Challenges

P. M. Visakh1 and Raneesh Balakrishnan2

1Faculty of Electronic Engineering, Department of Physical Electronics, TUSUR University, Tomsk 634050, Russia

2Department of Physics, Catholicate College, Pathanamthitta, Kerala, 689645, India

1.1 Graphene-based Nanoelectronic Biosensors

Graphene is the thinnest, strongest material, with one-particle thickness, and is 200 times stronger than steel. Graphene exhibits outstanding electrical and thermal conductivity with remarkable light absorption capability. Graphene is a material that could change the world in the true sense, with its infinite potential for integration practically in any industry. Graphene has diverse forms and can be combined with other materials to form various materials of extraordinary characteristics. Researchers are very keen to explore and patent graphene and gain expertise about its various properties and potential applications, mainly in cells, transistors, computer chips, supercapacitors, energy production, etc.

The common graphene derivatives are pristine graphene, reduced graphene oxide, graphene quantum dots (GQDs), and polycrystalline graphene, which are extensively used in biosensing applications. Pristine graphene consists of single crystalline grains that have flawless lattices made up of defect-free hexagonal ring networks of sp2 hybridized carbons atoms [1]. Graphene oxide also mainly consists of covalently bonded sp2-hybridized carbon atoms but has some defects due to the following reasons: disrupted sp3-hybridized carbon atoms and the oxygen functional groups like carboxyl group located at the edges and the basal plane are saturated with hydroxyl and epoxy groups [2]. The presence of these groups makes graphene oxide hydrophilic depending on their oxidation state [3].

Nanoelectronic devices are made up of nanomaterials such as nanowires, graphene, carbon nanotubes (CNTs), and transition metal dichalcogenides. These nanomaterials must possess extraordinary characteristics such as high surface-area-to-volume ratio, low power consumption, high charge mobility, and excellent compatibility to fit in modern electronic devices. As nanomaterials display unusual properties that are not obtainable at the micro scale, nanoelectronics holds significant importance. Graphene is a recently discovered nanomaterial known for its outstanding mechanical, electrical, and optical properties [4-6]. To develop an efficient graphene-based electrochemical biosensor, the graphene oxide nanosheets were decorated with Au NPs by aryldiazonium bridges fabricated on glassy carbon electrode (GCE). Then, the glucose oxidase enzyme was immobilized on the graphene oxide-Au NP nanocomposites. The biosensor showed a high sensitivity of about 42 µA mM-1 cm-2 with a wide detection range of 0.3-20 mM. This glucose biosensor showed excellent selectivity for glucose detection [7].

N-doped graphene-chitosan-glucose oxidase biosensors showed an excellent sensitivity of 226.24 µA mM-1 M-2 120 due to high porosity of graphene and high conductivity of graphene sheets, which facilitate enhanced electron transfer. The CuO nanoparticle (NP) composites with graphene oxide have shown a high sensitivity of 262.52 µA mM-1 cm-2 with an LOD of 0.69 µM. This biosensor was also used for human serum detection and showed a sensitivity of 285.38 µA mM-1 cm-2 [8]. Similarly, biosensors based on Pt-NiO-reduced graphene oxide nanocomposites showed a sensitivity of 832.95 µA mM-1 cm-2 and an LOD of 2.67 µM. This high performance was attributed to porosity of Pt-NiO-reduced graphene oxide nanocomposites [9]. Moreover, the Cu-Co-reduced graphene oxide nanocomposites were electrochemically deposited over the pencil graphite electrode and showed a high sensitivity of 240 µA mM-1 cm-2 and an LOD of 0.15 µM [10].

1.2 Zinc Oxide Piezoelectric Nanogenerators for Low-frequency Applications

Nanoparticles can be fabricated through solid-phase, liquid-phase, and gas-phase methods. Chemical bath deposition [11], green chemistry synthesis [12], and wet chemical methods [13] are other recently used techniques for the synthesis of ZnO NPs. Vertical ZnO nanorods were grown hydrothermally on a gold-coated PTFE (polytetrafluoroethylene). Spin coating was used to deposit 0.005 M zinc acetate dehydrated in ethanol on the surface of gold-coated PTFE film. Then, the substrate was heated at 90 °C for 30 minutes. The seed layer was uniformly deposited in a two-step process of deposition and decomposition to cover the substrate. ZnO nanorods were hydrothermally grown on the seed layer. Zinc nitrate hexahydrate and hexamethylenetetramine (HMT) were used to hold the seed layer at 90 °C for three hours [14].

Masuda et al. [15] demonstrated a simple liquid-phase synthesis method to control the morphology and crystal size of ZnO. ZnO nanowires of 100 nm long and about 50 nm wide were successfully synthesized at 50 °C. They also found that nanowires had no branches without aggregations. Several techniques have been explored to synthesize and develop both direct and alternating current zinc oxide piezoelectric nanogenerators [16]. Controlled precipitation is typically used to produce ZnO NPs in large quantities with reproducible properties for use in industrial products. In this process, zinc salt solution is spontaneously reduced by a reducing agent. Breaking down of agglomerations is an important process in this method. Therefore, temperature, pH, type of aqueous media, time of precipitation, and the raw materials are most important parameters in the precipitation of ZnO NPs, which have impact on the size and final characteristics of the nanoparticles [17]. Aladpoosh et al. [18] used the ZnO-controlled precipitation method, a green synthesis method using natural plant source, namely, Keliab and zinc acetate. Wurtzite structure and nanorod shapes result from in situ synthesis of ZnO on the cellulosic chains of cotton using the green synthesis method. The principle of nanogenerators was first used by Wang's research group in 2006 [19]. They used a conductive tip of an atomic force microscope (AFM) to deflect the aligned semiconductor ZnO nanowires and successfully obtained a measurable piezoelectric voltage output of around 10 mV. They grew ZnO nanorods on a sapphire substrate using a vapor-liquid solid method, which caused the gold particles to remain on the top of each rod after their growth.

A Schottky contact was formed between the conductive AFM tip and the semiconductor ZnO nanowires, which is a key factor in current generation by piezoelectric nanogenerators. The stretched side of the rod with a positive potential produced a reverse bias with the Schottky junction, leading to no current to screen the polarization. When the contact between the tip and the compressed, negatively polarized side of the rod was disconnected, the junction was forward biased, and the current was able to flow and screen the polarization. Monitoring the open-circuit voltage reflects an uncertainty in the measurement of this type of device [20]. Zinc oxide is an environmentally friendly multifunctional semiconductor possessing outstanding piezoelectric effect, piezoelectric coupling coefficient, and thermal and mechanical stability at room temperature. Owing to its non-centrosymmetric hexagonal wurtzite crystal structure and polar Zn-O bonds, ZnO has unique piezoelectric properties as the core of studies in the ceramic industry [21, 22]. For the first time in 2009, Xi and coworkers [23] fabricated a ZnO-nanotube-based piezoelectric nanogenerator. They used a solution chemical method to synthesize hexagonal ZnO nanotube arrays at temperatures below 100 °C.

ZnO-based nanogenerators can be incorporated into various substrates. In 2012, Khan et al. [24] grew ZnO nanorods on a silver-coated cotton fabric using a low-temperature, aqueous chemical growth method. An external force was applied on ZnO nanorods via an AFM tip, where the flow of charges was taken into account and a Schottky barrier formed between the electrode and the nanorods.

1.3 Investigation of the Hot Carrier-induced Degradation in Nanoscale Junctionless MOSFETs: A Reliability-based Analysis

In the past decades, reliability of MOSFET devices was a major concern in the electronics industry: the aging phenomenon degraded the device operation and lifetime severely. Extensive research has been carried out to identify the causes of aging and to seek viable solutions. Channel and substrate hot carrier injection (HCI and SCI), channel hot electron/hole (CHE/H), drain avalanche injection, and radiation were found to be the main degradation mechanisms[25-31]. Hot carrier-induced degradation is of prime interest for designers as the process aggravates with downscaling. Degradation is essentially due to the enhancement of the...