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Research

12 pages, 2475 KiB

Open AccessArticle

Effect of Hot Junction Size on the Temperature Measurement of Proton Exchange Membrane Fuel Cells Using NiCr/NiSi Thin-Film Thermocouple Sensors

by Huijin Guo, Zhihui Liu, Tengda Guo, Yi Sun, Kai Shen, Bi Wang, Yongjun Cheng, Yuming Wang, Tiancai Ma, Zixi Wang and Wanyu Ding

Micromachines 2024, 15(11), 1375; https://doi.org/10.3390/mi15111375 - 14 Nov 2024

Viewed by 490

Abstract

In the process of using thin-film thermocouples for contact measurement of the reaction temperature in proton exchange membrane fuel cells (PEMFC), the impact of thin-film thermocouple volume on the system’s reaction temperature field variation, reaction efficiency, and the lifespan of thermocouples under these [...] Read more.

In the process of using thin-film thermocouples for contact measurement of the reaction temperature in proton exchange membrane fuel cells (PEMFC), the impact of thin-film thermocouple volume on the system’s reaction temperature field variation, reaction efficiency, and the lifespan of thermocouples under these conditions is not thoroughly studied. Using magnetron sputtering technology, NiCr/NiSi thin-film thermocouples (NiCr/NiSi TFTCs) with different junction sizes were fabricated on the proton exchange membrane (PEM). These NiCr/NiSi TFTCs exhibit excellent compactness, with thickness and planar dimensions in the micrometer range. When PEMFCs are equipped with built-in NiCr/NiSi TFTCs of different hot junction sizes, the time required for the system to reach a steady state varies with the size of the hot junction, with smaller hot junction sizes reaching a steady state more quickly. In a 500-h continuous operation test, the failure rates of NiCr/NiSi TFTCs also vary based on the hot junction size. Both smaller and larger hot junction sizes have relatively higher failure rates, whereas medium-sized junctions have a lower failure rate. These extensive and repetitive comparative experiments provide significant reference value for the size design of TFTCs operating inside PEMFCs, promoting both industrial production and scientific research. Full article

(This article belongs to the Special Issue Advanced Thin-Films: Design, Fabrication and Applications, 2nd Edition)

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17 pages, 15109 KiB

Open AccessArticle

Indirect Enhancement of ALD Thin-Film Properties Induced by the ECAP Modification of an As-Extruded Mg-Ca Alloy

by Pi-Chen Lin, Jun-Yu Li, Hou-Jen Chen, Kaifan Lin, Miin-Jang Chen, Kun-Ming Lin and Hsin-Chih Lin

Micromachines 2024, 15(8), 1006; https://doi.org/10.3390/mi15081006 - 3 Aug 2024

Viewed by 1085

Abstract

The purpose of this study is to investigate the indirect effects on the properties of ZrO₂ films deposited by atomic layer deposition (ALD) when an Mg-Ca alloy is modified through equal-channel angular pressing (ECAP) following extrusion. The study aims to understand how [...] Read more.

The purpose of this study is to investigate the indirect effects on the properties of ZrO₂ films deposited by atomic layer deposition (ALD) when an Mg-Ca alloy is modified through equal-channel angular pressing (ECAP) following extrusion. The study aims to understand how the increase in CaO content in the native oxide layer of the Mg-Ca alloy influences the crystallinity and defect density of the ZrO₂ film. Consequently, the corrosion protection performance of the ZrO₂ film is enhanced by 1.2 to 1.5 times. A reduction in the anti-scratch property of the ZrO₂ film was also observed, with a critical load reduction of 34 μN. This research provides a detailed analysis of the modifications induced by ECAP on the as-extruded Mg-Ca alloy and its subsequent impact on the properties of the ZrO₂ film. Full article

(This article belongs to the Special Issue Advanced Thin-Films: Design, Fabrication and Applications, 2nd Edition)

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12 pages, 4757 KiB

Open AccessArticle

Structural and Optical Characterization of Porous NiV₂O₆ Films Synthesized by Nebulizer Spray Pyrolysis for Photodetector Applications

by Ahmed Kotbi, Islam M. El Radaf, Ilham Hamdi Alaoui, Anna Cantaluppi, Andreas Zeinert and Abdelilah Lahmar

Micromachines 2024, 15(7), 839; https://doi.org/10.3390/mi15070839 - 28 Jun 2024

Viewed by 721

Abstract

NiV₂O₆ thin films were grown on glass slides with varying thicknesses using nebulizer spray pyrolysis. The impact of thickness on the thin films’ optical, structural, morphological, and electrical characteristics was systematically investigated. X-ray diffraction and micro-Raman analysis confirmed the formation [...] Read more.

NiV₂O₆ thin films were grown on glass slides with varying thicknesses using nebulizer spray pyrolysis. The impact of thickness on the thin films’ optical, structural, morphological, and electrical characteristics was systematically investigated. X-ray diffraction and micro-Raman analysis confirmed the formation of the triclinic NiV₂O₆ system. Surface morphology and roughness variations in the as-deposited NiV₂O₆ films were studied using scanning electron microscopy (SEM) and a profilometer. Optical properties, including optical band gap (Eg), extinction coefficient (k), absorption coefficient (α), and refractive index (n), were determined through optical reflectance and transmittance measurements. The optical energy gap of the as-deposited NiV₂O₆ films decreased from 2.02 eV to 1.58 eV with increased layer thickness. Furthermore, the photo-detectivity of the films demonstrated an enhancement corresponding to the prolonged spray time. The sensitivity values obtained for visible irradiation were 328, 511, and 433 for samples S1, S2, and S3, respectively. The obtained results can be imputed to the specific porous microstructure. Full article

(This article belongs to the Special Issue Advanced Thin-Films: Design, Fabrication and Applications, 2nd Edition)

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11 pages, 3764 KiB

Open AccessArticle

Enhancing the Uniformity of a Memristor Using a Bilayer Dielectric Structure

by Yulin Liu, Qilai Chen, Yanbo Guo, Bingjie Guo, Gang Liu, Yanchao Liu, Lei He, Yutong Li, Jingyan He and Minghua Tang

Micromachines 2024, 15(5), 605; https://doi.org/10.3390/mi15050605 - 30 Apr 2024

Viewed by 1203

Abstract

Resistive random access memory (RRAM) holds great promise for in-memory computing, which is considered the most promising strategy for solving the von Neumann bottleneck. However, there are still significant problems in its application due to the non-uniform performance of RRAM devices. In this [...] Read more.

Resistive random access memory (RRAM) holds great promise for in-memory computing, which is considered the most promising strategy for solving the von Neumann bottleneck. However, there are still significant problems in its application due to the non-uniform performance of RRAM devices. In this work, a bilayer dielectric layer memristor was designed based on the difference in the Gibbs free energy of the oxide. We fabricated Au/Ta₂O₅/HfO₂/Ta/Pt (S3) devices with excellent uniformity. Compared with Au/HfO₂/Pt (S1) and Au/Ta₂O₅/Pt (S2) devices, the S3 device has a low reset voltage fluctuation of 2.44%, and the resistive coefficients of variation are 13.12% and 3.84% in HRS and LRS, respectively, over 200 cycles. Otherwise, the bilayer device has better linearity and more conductance states in multi-state regulation. At the same time, we analyze the physical mechanism of the bilayer device and provide a physical model of ion migration. This work provides a new idea for designing and fabricating resistive devices with stable performance. Full article

(This article belongs to the Special Issue Advanced Thin-Films: Design, Fabrication and Applications, 2nd Edition)

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12 pages, 5028 KiB

Open AccessArticle

Wafer-Scale Characterization of 1692-Pixel-Per-Inch Blue Micro-LED Arrays with an Optimized ITO Layer

by Eun-Kyung Chu, Eun Jeong Youn, Hyun Woong Kim, Bum Doo Park, Ho Kun Sung and Hyeong-Ho Park

Micromachines 2024, 15(5), 560; https://doi.org/10.3390/mi15050560 - 24 Apr 2024

Cited by 3 | Viewed by 1298

Abstract

Wafer-scale blue micro-light-emitting diode (micro-LED) arrays were fabricated with a pixel size of 12 μm, a pixel pitch of 15 μm, and a pixel density of 1692 pixels per inch, achieved by optimizing the properties of e-beam-deposited and sputter-deposited indium tin oxide (ITO). [...] Read more.

Wafer-scale blue micro-light-emitting diode (micro-LED) arrays were fabricated with a pixel size of 12 μm, a pixel pitch of 15 μm, and a pixel density of 1692 pixels per inch, achieved by optimizing the properties of e-beam-deposited and sputter-deposited indium tin oxide (ITO). Although the sputter-deposited ITO (S-ITO) films exhibited a densely packed morphology and lower resistivity compared to the e-beam-deposited ITO (E-ITO) films, the forward voltage (V_F) values of a micro-LED with the S-ITO films were higher than those with the E-ITO films. The V_F values for a single pixel and for four pixels with E-ITO films were 2.82 V and 2.83 V, respectively, while the corresponding values for S-ITO films were 3.50 V and 3.52 V. This was attributed to ion bombardment damage and nitrogen vacancies in the p-GaN layer. Surprisingly, the V_F variations of a single pixel and of four pixels with the optimized E-ITO spreading layer from five different regions were only 0.09 V and 0.10 V, respectively. This extremely uniform V_F variation is suitable for creating micro-LED displays to be used in AR and VR applications, circumventing the bottleneck in the development of long-lifespan and high-brightness organic LED devices for industrial mass production. Full article

(This article belongs to the Special Issue Advanced Thin-Films: Design, Fabrication and Applications, 2nd Edition)

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17 pages, 4936 KiB

Open AccessArticle

Analysis of a Flexible Photoconductor, Manufactured with Organic Semiconductor Films

by Luis Alberto Cantera Cantera, María Elena Sánchez Vergara, Leon Hamui, Isidro Mejía Prado, Alejandro Flores Huerta and Teresa Lizet Martínez Plata

Micromachines 2024, 15(4), 446; https://doi.org/10.3390/mi15040446 - 27 Mar 2024

Viewed by 1508

Abstract

This work presents the evaluation of the electrical behavior of a flexible photoconductor with a planar heterojunction architecture made up of organic semiconductor films deposited by high vacuum evaporation. The heterojunction was characterized in its morphology and mechanical properties by scanning electron microscopy [...] Read more.

This work presents the evaluation of the electrical behavior of a flexible photoconductor with a planar heterojunction architecture made up of organic semiconductor films deposited by high vacuum evaporation. The heterojunction was characterized in its morphology and mechanical properties by scanning electron microscopy and atomic force microscopy. The electrical characterization was carried out through the approximations of ohmic and SCLC (Space-Charge Limited Current) behaviors using experimental J–V (current density–voltage) curves at different voltages and under different light conditions. The optimization of the photoconductor was carried out through annealing and accelerated lighting processes. With these treatments, the Knoop Hardness of the flexible photoconductor has reached a value of 8 with a tensile strength of 5.7 MPa. The ohmic and SCLC approximations demonstrate that the unannealed device has an ohmic behavior, whereas the annealed device has an SCLC behavior, and after the optimization process, an ohmic behavior and a maximum current density of 0.34 mA/mm² were obtained under blue light. The approximations of the device’s electron mobility (

μ_{n}

) and free carrier density (

n_{0}

) were performed under different light conditions, and the electrical activation energy and electrical gap were obtained for the flexible organic device, resulting in appropriate properties for these applications. Full article

(This article belongs to the Special Issue Advanced Thin-Films: Design, Fabrication and Applications, 2nd Edition)

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8 pages, 2729 KiB

Open AccessCommunication

Origin of the High Density of Oxygen Vacancies at the Back Channel of Back-Channel-Etched a-InGaZnO Thin-Film Transistors

by Shimin Ge, Juncheng Xiao, Shan Li, Dong Yuan, Yuhua Dong and Shengdong Zhang

Micromachines 2024, 15(3), 400; https://doi.org/10.3390/mi15030400 - 16 Mar 2024

Cited by 2 | Viewed by 1337

Abstract

This study reveals the pronounced density of oxygen vacancies (Vo) at the back channel of back-channel-etched (BCE) a-InGaZnO (a-IGZO) thin-film transistors (TFTs) results from the sputtered deposition rather than the wet etching process of the source/drain metal, and they are distributed within approximately [...] Read more.

This study reveals the pronounced density of oxygen vacancies (Vo) at the back channel of back-channel-etched (BCE) a-InGaZnO (a-IGZO) thin-film transistors (TFTs) results from the sputtered deposition rather than the wet etching process of the source/drain metal, and they are distributed within approximately 25 nm of the back surface. Furthermore, the existence and distribution depth of the high density of Vo defects are verified by means of XPS spectra analyses. Then, the mechanism through which the above Vo defects lead to the instability of BCE a-IGZO TFTs is elucidated. Lastly, it is demonstrated that the device instability under high-humidity conditions and negative bias temperature illumination stress can be effectively alleviated by etching and thus removing the surface layer of the back channel, which contains the high density of Vo defects. In addition, this etch method does not cause a significant deterioration in the uniformity of electrical characteristics and is quite convenient to implement in practical fabrication processes. Thus, a novel and effective solution to the device instability of BCE a-IGZO TFTs is provided. Full article

(This article belongs to the Special Issue Advanced Thin-Films: Design, Fabrication and Applications, 2nd Edition)

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17 pages, 9913 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hollow Microcavity Electrode for Enhancing Light Extraction

by Seonghyeon Park, Byeongwoo Kang, Seungwon Lee, Jian Cheng Bi, Jaewon Park, Young Hyun Hwang, Jun-Young Park, Ha Hwang, Young Wook Park and Byeong-Kwon Ju

Micromachines 2024, 15(3), 328; https://doi.org/10.3390/mi15030328 - 27 Feb 2024

Viewed by 2040

Abstract

Luminous efficiency is a pivotal factor for assessing the performance of optoelectronic devices, wherein light loss caused by diverse factors is harvested and converted into the radiative mode. In this study, we demonstrate a nanoscale vacuum photonic crystal layer (nVPCL) for light extraction [...] Read more.

Luminous efficiency is a pivotal factor for assessing the performance of optoelectronic devices, wherein light loss caused by diverse factors is harvested and converted into the radiative mode. In this study, we demonstrate a nanoscale vacuum photonic crystal layer (nVPCL) for light extraction enhancement. A corrugated semi-transparent electrode incorporating a periodic hollow-structure array was designed through a simulation that utilizes finite-difference time-domain computational analysis. The corrugated profile, stemming from the periodic hollow structure, was fabricated using laser interference lithography, which allows the precise engineering of various geometrical parameters by controlling the process conditions. The semi-transparent electrode consisted of a 15 nm thick Ag film, which acted as the exit mirror and induced microcavity resonance. When applied to a conventional green organic light-emitting diode (OLED) structure, the optimized nVPCL-integrated device demonstrated a 21.5% enhancement in external quantum efficiency compared to the reference device. Further, the full width at half maximum exhibited a 27.5% reduction compared to that of the reference device, demonstrating improved color purity. This study presents a novel approach by applying a hybrid thin film electrode design to optoelectronic devices to enhance optical efficiency and color purity. Full article

(This article belongs to the Special Issue Advanced Thin-Films: Design, Fabrication and Applications, 2nd Edition)

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