Research

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11 pages, 1962 KiB

Open AccessArticle

Visible-Light-Driven Semiconductor–Metal Transition in Electron Gas at the (100) Surface of KTaO₃

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Nanomaterials 2023, 13(23), 3055; https://doi.org/10.3390/nano13233055 - 30 Nov 2023

Viewed by 177

Abstract

Two-dimensional electron gas (2DEG) at the (100) KTaO₃(KTO) surface and interfaces has attracted extensive interest because of its abundant physical properties. Here, light illumination-induced semiconductor–metal transition in the 2DEG at the KTO surface was investigated. 2DEG was formed at the surface [...] Read more.

Two-dimensional electron gas (2DEG) at the (100) KTaO₃(KTO) surface and interfaces has attracted extensive interest because of its abundant physical properties. Here, light illumination-induced semiconductor–metal transition in the 2DEG at the KTO surface was investigated. 2DEG was formed at the surface of KTO by argon ion bombardment. The 2DEG prepared with a shorter bombardment time (300 s) exhibits semiconducting behavior in the range of 20~300 K in the dark. However, it shows a different resistance behavior, namely, a metallic state above ~55 K and a semiconducting state below ~55 K when exposed to visible light (405 nm) with a giant conductivity increase of about eight orders of magnitude at 20 K. The suppression of the semiconducting behavior is found to be more pronounced with increasing light power. After removing the illumination, the resistance cannot recover quickly, exhibiting persistent photoconductivity. More interestingly, the photoresponse of the 2DEG below 50 K was almost independent of the laser wavelength, although the photon energy is lower than the band gap of KTO. The present results provide experimental support for tuning oxide 2DEG by photoexcitation, suggesting promising applications of KTO-based 2DEG in future electronic and optoelectronic devices. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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12 pages, 3275 KiB

Open AccessArticle

Super-High-Frequency Bulk Acoustic Resonators Based on Aluminum Scandium Nitride for Wideband Applications

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Nanomaterials 2023, 13(20), 2737; https://doi.org/10.3390/nano13202737 - 10 Oct 2023

Viewed by 547

Abstract

Despite the dominance of bulk acoustic wave (BAW) filters in the high-frequency market due to their superior performance and compatible integration process, the advent of the 5G era brings up new challenges to meet the ever-growing demands on high-frequency and large bandwidth. Al [...] Read more.

Despite the dominance of bulk acoustic wave (BAW) filters in the high-frequency market due to their superior performance and compatible integration process, the advent of the 5G era brings up new challenges to meet the ever-growing demands on high-frequency and large bandwidth. Al_1-xSc_xN piezoelectric films with high Sc concentration are particularly desirable to achieve an increased electromechanical coupling (K_t²) for BAW resonators and also a larger bandwidth for filters. In this paper, we designed and fabricated the Al_1-xSc_xN-based BAW resonators with Sc concentrations as high as 30%. The symmetry of the resonance region, border frame structure and thickness ratio of the piezoelectric stack are thoroughly examined for lateral modes suppression and resonant performance optimization. Benefiting from the 30% Sc doping, the fabricated BAW resonators demonstrate a large effective electromechanical coupling (K_eff²) of 17.8% at 4.75 GHz parallel resonant frequency. Moreover, the temperature coefficient of frequency (TCF) of the device is obtained as −22.9 ppm/°C, indicating reasonable temperature stability. Our results show that BAW resonators based on highly doped Al_1-xSc_xN piezoelectric film have great potential for high-frequency and large bandwidth applications. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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8 pages, 2893 KiB

Open AccessCommunication

Thermal, Mechanical, and Electrical Stability of Cu Films in an Integration Process with Photosensitive Polyimide (PSPI) Films

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Nanomaterials 2023, 13(19), 2642; https://doi.org/10.3390/nano13192642 - 26 Sep 2023

Viewed by 488

Abstract

Photosensitive polyimides (PSPIs) have been widely developed in microelectronics, which is due to their excellent thermal properties and reasonable dielectric properties and can be directly patterned to simplify the processing steps. In this study, 3 μm~7 μm thick PSPI films were deposited on [...] Read more.

Photosensitive polyimides (PSPIs) have been widely developed in microelectronics, which is due to their excellent thermal properties and reasonable dielectric properties and can be directly patterned to simplify the processing steps. In this study, 3 μm~7 μm thick PSPI films were deposited on different substrates, including Si, 50 nm SiN, 50 nm SiO₂, 100 nm Cu, and 100 nm Al, for the optimization of the process of integration with Cu films. In situ temperature-dependent resistance measurements were conducted by using a four-point probe system to study the changes in resistance of the 70 nm thick Cu films on different dielectrics with thick diffusion films of 30 nm Mn, Co, and W films in a N₂ ambient. The lowest possible change in thickness due to annealing at the higher temperature ranges of 325 °C to 375 °C is displayed, which suggests the high stability of PSPI. The PSPI films show good adhesion with each Cu diffusion barrier up to 350 °C, and we believe that this will be helpful for new packaging applications, such as a 3D IC with a Cu interconnect. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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12 pages, 1985 KiB

Open AccessArticle

Photoconduction Properties in Tungsten Disulfide Nanostructures

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Hemanth Kumar Bangolla

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Yueh-Chien Lee

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Wei-Chu Shen

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Rajesh Kumar Ulaganathan

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Raman Sankar

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He-Yun Du

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Ruei-San Chen

Nanomaterials 2023, 13(15), 2190; https://doi.org/10.3390/nano13152190 - 27 Jul 2023

Viewed by 526

Abstract

We reported the photoconduction properties of tungsten disulfide (WS₂) nanoflakes obtained by the mechanical exfoliation method. The photocurrent measurements were carried out using a 532 nm laser source with different illumination powers. The results reveal a linear dependence of photocurrent on [...] Read more.

We reported the photoconduction properties of tungsten disulfide (WS₂) nanoflakes obtained by the mechanical exfoliation method. The photocurrent measurements were carried out using a 532 nm laser source with different illumination powers. The results reveal a linear dependence of photocurrent on the excitation power, and the photoresponsivity shows an independent behavior at higher light intensities (400–4000 Wm⁻²). The WS₂ photodetector exhibits superior performance with responsivity in the range of 36–73 AW⁻¹ and a normalized gain in the range of 3.5–7.3 10⁻⁶ cm²V⁻¹ at a lower bias voltage of 1 V. The admirable photoresponse at different light intensities suggests that WS₂ nanostructures are of potential as a building block for novel optoelectronic device applications. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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16 pages, 5351 KiB

Open AccessArticle

Interface Optimization and Performance Enhancement of Er₂O₃-Based MOS Devices by ALD-Derived Al₂O₃ Passivation Layers and Annealing Treatment

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Nanomaterials 2023, 13(11), 1740; https://doi.org/10.3390/nano13111740 - 26 May 2023

Cited by 1 | Viewed by 705

Abstract

In this paper, the effect of atomic layer deposition (ALD)-derived Al₂O₃ passivation layers and annealing temperatures on the interfacial chemistry and transport properties of sputtering-deposited Er₂O₃ high-k gate dielectrics on Si substrate has been investigated. X-ray photoelectron [...] Read more.

In this paper, the effect of atomic layer deposition (ALD)-derived Al₂O₃ passivation layers and annealing temperatures on the interfacial chemistry and transport properties of sputtering-deposited Er₂O₃ high-k gate dielectrics on Si substrate has been investigated. X-ray photoelectron spectroscopy (XPS) analyses have showed that the ALD-derived Al₂O₃ passivation layer remarkably prevents the formation of the low-k hydroxides generated by moisture absorption of the gate oxide and greatly optimizes the gate dielectric properties. Electrical performance measurements of metal oxide semiconductor (MOS) capacitors with different gate stack order have revealed that the lowest leakage current density of 4.57 × 10⁻⁹ A/cm² and the smallest interfacial density of states (Dit) of 2.38 × 10¹² cm⁻² eV⁻¹ have been achieved in the Al₂O_3/Er₂O₃/Si MOS capacitor, which can be attributed to the optimized interface chemistry. Further electrical measurements of annealed Al₂O_3/Er₂O₃/Si gate stacks at 450 °C have demonstrated superior dielectric properties with a leakage current density of 1.38 × 10⁻⁹ A/cm². At the same, the leakage current conduction mechanism of MOS devices under various stack structures is systematically investigated. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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13 pages, 5739 KiB

Open AccessArticle

Humidity Sensing Properties of (In+Nb) Doped HfO₂ Ceramics

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Nanomaterials 2023, 13(5), 951; https://doi.org/10.3390/nano13050951 - 06 Mar 2023

Cited by 2 | Viewed by 1029

Abstract

(In+Nb) co-doped HfO₂ ceramics, Hf_1-x(In_0.5Nb_0.5)_xO₂ (x = 0, 0.005, 0.05, and 0.1), were prepared via a solid-state reaction method. Dielectric measurements reveal that the environmental moisture has an obvious influence on [...] Read more.

(In+Nb) co-doped HfO₂ ceramics, Hf_1-x(In_0.5Nb_0.5)_xO₂ (x = 0, 0.005, 0.05, and 0.1), were prepared via a solid-state reaction method. Dielectric measurements reveal that the environmental moisture has an obvious influence on the dielectric properties of the samples. The best humidity response was found in a sample with the doping level of x = 0.005. This sample was therefore selected as a model sample to further investigate its humidity properties. In doing so, nanosized particles of Hf_0.995(In_0.5Nb_0.5)_0.005O₂ were fabricated via a hydrothermal method and the humidity sensing properties of this material were studied in the relative humidity range of 11–94% based on impedance sensor. Our results show that the material exhibits a large impedance change of nearly four orders of magnitude over the tested humidity range. It was argued that the humidity-sensing properties were related to the defects created by doping, which improves the adsorption capacity for water molecules. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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14 pages, 15847 KiB

Open AccessArticle

Enhanced Piezoelectricity and Thermal Stability of Electrostrain Performance in BiFeO₃-Based Lead-Free Ceramics

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Nanomaterials 2023, 13(5), 942; https://doi.org/10.3390/nano13050942 - 05 Mar 2023

Cited by 2 | Viewed by 1095

Abstract

BiFeO₃–based ceramics possess an advantage over large spontaneous polarization and high Curie temperature, and are thus widely explored in the field of high–temperature lead–free piezoelectrics and actuators. However, poor piezoelectricity/resistivity and thermal stability of electrostrain make them less competitive. To address [...] Read more.

BiFeO₃–based ceramics possess an advantage over large spontaneous polarization and high Curie temperature, and are thus widely explored in the field of high–temperature lead–free piezoelectrics and actuators. However, poor piezoelectricity/resistivity and thermal stability of electrostrain make them less competitive. To address this problem, (1 − x) (0.65BiFeO₃–0.35BaTiO₃)–xLa_0.5Na_0.5TiO₃ (BF–BT–xLNT) systems are designed in this work. It is found that piezoelectricity is significantly improved with LNT addition, which is contributed by the phase boundary effect of rhombohedral and pseudocubic phase coexistence. The small–signal and large–signal piezoelectric coefficient (d₃₃ and

d_{33}^{*}

) peaks at x = 0.02 with 97 pC/N and 303 pm/V, respectively. The relaxor property and resistivity are enhanced as well. This is verified by Rietveld refinement, dielectric/impedance spectroscopy and piezoelectric force microscopy (PFM) technique. Interestingly, a good thermal stability of electrostrain is obtained at x = 0.04 composition with fluctuation η = 31% (

\frac{S_{\max}^{'} - S_{RT}}{S_{RT}} \times 100 %

), in a wide temperature range of 25–180 °C, which is considered as a compromise of negative temperature dependent electrostrain for relaxors and the positive one for ferroelectric matrix. This work provides an implication for designing high–temperature piezoelectrics and stable electrostrain materials. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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13 pages, 3359 KiB

Open AccessArticle

All-Water-Driven High-k HfO₂ Gate Dielectrics and Applications in Thin Film Transistors

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Nanomaterials 2023, 13(4), 694; https://doi.org/10.3390/nano13040694 - 10 Feb 2023

Cited by 1 | Viewed by 1081

Abstract

In this article, we used a simple, non-toxic, environmentally friendly, water-driven route to fabricate the gate dielectric on the Si substrate and successfully integrate the In₂O₃/HfO₂ thin film transistor (TFT). All the electrical properties of In₂O [...] Read more.

In this article, we used a simple, non-toxic, environmentally friendly, water-driven route to fabricate the gate dielectric on the Si substrate and successfully integrate the In₂O₃/HfO₂ thin film transistor (TFT). All the electrical properties of In₂O₃ based on HfO₂ were systematically analyzed. The In₂O₃/HfO₂ device exhibits the best electrical performance at an optimized annealing temperature of 500 °C, including a high µ_FE of 9 cm² V⁻¹ s⁻¹, a high I_ON/I_OFF of 10⁵, a low threshold voltage of 1.1 V, and a low sub-threshold of 0.31 V dec⁻¹. Finally, test the stability of the bias under positive bias stress (PBS) and negative bias stress (NBS) with threshold shifts (V_TH) of 0.35 and 0.13 V while these optimized properties are achieved at a small operating voltage of 2 V. All experimental results demonstrate the potential application of aqueous solution technology for future low-cost, energy-efficient, large-scale, and high-performance electronics. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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15 pages, 5464 KiB

Open AccessArticle

α-Fe₂O₃ Nanoparticles Aided-Dual Conversion for Self-Powered Bio-Based Photodetector

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Nanomaterials 2022, 12(7), 1147; https://doi.org/10.3390/nano12071147 - 30 Mar 2022

Cited by 3 | Viewed by 1570

Abstract

Eco-friendly energy harvesting from the surrounding environment has been triggered extensive researching enthusiasm due to the threat of global energy crisis and environmental pollutions. By the conversion of mechanical energy that is omnipresent in our environment into electrical energy, triboelectric nanogenerator (TENG) can [...] Read more.

Eco-friendly energy harvesting from the surrounding environment has been triggered extensive researching enthusiasm due to the threat of global energy crisis and environmental pollutions. By the conversion of mechanical energy that is omnipresent in our environment into electrical energy, triboelectric nanogenerator (TENG) can potentially power up small electronic devices, serves as a self-powered detectors and predominantly, it can minimize the energy crisis by credibly saving the traditional non-renewable energy. In this study, we present a novel bio-based TENG comprising PDMS/α-Fe₂O₃ nanocomposite film and a processed human hair-based film, that harvests the vibrating energy and solar energy simultaneously by the integration of triboelectric technology and photoelectric conversion techniques. Upon illumination, the output voltage and current signals rapidly increased by 1.4 times approximately, compared to the dark state. Experimental results reveal that the photo-induced enhancement appears due to the effective charge separation depending on the photosensitivity of the hematite nanoparticles (α-Fe₂O₃ nanoparticles) over the near ultraviolet (UV), visible and near infrared (IR) regions. Our work provides a new approach towards the self-powered photo-detection, while developing a propitious green energy resource for the circular bio-economy. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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Review

Jump to: Research

31 pages, 5961 KiB

Open AccessReview

Smart Triboelectric Nanogenerators Based on Stimulus-Response Materials: From Intelligent Applications to Self-Powered Systems

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Han Wu

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Xia Cao

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Ning Wang

Nanomaterials 2023, 13(8), 1316; https://doi.org/10.3390/nano13081316 - 08 Apr 2023

Cited by 3 | Viewed by 2214

Abstract

Smart responsive materials can react to external stimuli via a reversible mechanism and can be directly combined with a triboelectric nanogenerator (TENG) to deliver various intelligent applications, such as sensors, actuators, robots, artificial muscles, and controlled drug delivery. Not only that, mechanical energy [...] Read more.

Smart responsive materials can react to external stimuli via a reversible mechanism and can be directly combined with a triboelectric nanogenerator (TENG) to deliver various intelligent applications, such as sensors, actuators, robots, artificial muscles, and controlled drug delivery. Not only that, mechanical energy in the reversible response of innovative materials can be scavenged and transformed into decipherable electrical signals. Because of the high dependence of amplitude and frequency on environmental stimuli, self-powered intelligent systems may be thus built and present an immediate response to stress, electrical current, temperature, magnetic field, or even chemical compounds. This review summarizes the recent research progress of smart TENGs based on stimulus-response materials. After briefly introducing the working principle of TENG, we discuss the implementation of smart materials in TENGs with a classification of several sub-groups: shape-memory alloy, piezoelectric materials, magneto-rheological, and electro-rheological materials. While we focus on their design strategy and function collaboration, applications in robots, clinical treatment, and sensors are described in detail to show the versatility and promising future of smart TNEGs. In the end, challenges and outlooks in this field are highlighted, with an aim to promote the integration of varied advanced intelligent technologies into compact, diverse functional packages in a self-powered mode. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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30 pages, 4783 KiB

Open AccessReview

Human Body–Electrode Interfaces for Wide-Frequency Sensing and Communication: A Review

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Nanomaterials 2021, 11(8), 2152; https://doi.org/10.3390/nano11082152 - 23 Aug 2021

Cited by 11 | Viewed by 5372

Abstract

Several on-body sensing and communication applications use electrodes in contact with the human body. Body–electrode interfaces in these cases act as a transducer, converting ionic current in the body to electronic current in the sensing and communication circuits and vice versa. An ideal [...] Read more.

Several on-body sensing and communication applications use electrodes in contact with the human body. Body–electrode interfaces in these cases act as a transducer, converting ionic current in the body to electronic current in the sensing and communication circuits and vice versa. An ideal body–electrode interface should have the characteristics of an electrical short, i.e., the transfer of ionic currents and electronic currents across the interface should happen without any hindrance. However, practical body–electrode interfaces often have definite impedances and potentials that hinder the free flow of currents, affecting the application’s performance. Minimizing the impact of body–electrode interfaces on the application’s performance requires one to understand the physics of such interfaces, how it distorts the signals passing through it, and how the interface-induced signal degradations affect the applications. Our work deals with reviewing these elements in the context of biopotential sensing and human body communication. Full article

(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications)

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