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3 pages, 169 KiB

Open AccessEditorial

Organic Optoelectronic Materials (Volume II)

by Nguyen-Hung Tran, Van-Chuc Nguyen and Ji-Hoon Lee

Crystals 2021, 11(11), 1327; https://doi.org/10.3390/cryst11111327 - 31 Oct 2021

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Abstract

Organic optoelectronic materials are rapidly being commercialized at present [...] Full article

(This article belongs to the Special Issue Organic Optoelectronic Materials (Volume II))

Research

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13 pages, 1921 KiB

Open AccessArticle

Reduction of Fluorine Diffusion and Improvement of Dark Current Using Carbon Implantation in CMOS Image Sensor

by Su-Young Chai and Sung-Hoon Choa

Crystals 2021, 11(9), 1106; https://doi.org/10.3390/cryst11091106 - 11 Sep 2021

Cited by 4 | Viewed by 4097

Abstract

Recently, the demand of a high resolution complementary metal-oxide semiconductor (CMOS) image sensor is dramatically increasing. As the pixel size reduces to submicron, however, the quality of the sensor image decreases. In particular, the dark current can act as a large noise source [...] Read more.

Recently, the demand of a high resolution complementary metal-oxide semiconductor (CMOS) image sensor is dramatically increasing. As the pixel size reduces to submicron, however, the quality of the sensor image decreases. In particular, the dark current can act as a large noise source resulting in reduction of the quality of the sensor image. Fluorine ion implantation was commonly used to improve the dark current by reducing the trap state density. However, the implanted fluorine diffused to the outside of the silicon surface and disappeared after annealing process. In this paper, we analyzed the effects of carbon implantation on the fluorine diffusion and the dark current characteristics of the CMOS image sensor. As the carbon was implanted with dose of 5.0 × 10¹⁴ and 1 × 10¹⁵ ions/cm² in N+ area of FD region, the retained dose of fluorine was improved by more than 131% and 242%, respectively than no carbon implantation indicating that the higher concentration of the carbon implantation, the higher the retained dose of fluorine after annealing. As the retained fluorine concentration increased, the minority carriers of electrons or holes decreased by more Si-F bond formation, resulting in increasing the sheet resistance. When carbon was implanted with 1.0 × 10¹⁵ ions/cm², the defective pixel, dark current, transient noise, and flicker were much improved by 25%, 9.4%, 1%, and 28%, respectively compared to no carbon implantation. Therefore, the diffusion of fluorine after annealing could be improved by the carbon implantation leading to improvement of the dark current characteristics. Full article

(This article belongs to the Special Issue Organic Optoelectronic Materials (Volume II))

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8 pages, 1396 KiB

Open AccessArticle

Axial Error of Spindle Measurements Using a High-Frequency-Modulated Interferometer

by Thanh-Trung Nguyen, Thanh-Tung Vu, Thanh-Dong Nguyen and Toan-Thang Vu

Crystals 2021, 11(7), 801; https://doi.org/10.3390/cryst11070801 - 9 Jul 2021

Cited by 2 | Viewed by 2349

Abstract

In this paper, a novel, compact, and high-precision axial error measurement using a frequency-modulated interferometer is developed. Normally, heterodyne interferometers are a powerful system for small displacement measurements due to their property of being less sensitive to temperature and pressure variations. However, the [...] Read more.

In this paper, a novel, compact, and high-precision axial error measurement using a frequency-modulated interferometer is developed. Normally, heterodyne interferometers are a powerful system for small displacement measurements due to their property of being less sensitive to temperature and pressure variations. However, the maximum measurement speed of the heterodyne interferometer is around 5 m/s because it is usually limited by the difference in frequency between the two components of the laser beam, which is no larger than 3 MHz or 20 MHz corresponding laser source based on the Zeeman effect and acousto-optic modulator, respectively. The proposed measuring system is realized by modulating the frequency of the laser diode source at a high modulation frequency and using lock-in amplifiers to extract the harmonics of the interference signal. The measurement speed is proportional to the modulation frequency. Thus, the higher the modulation frequency, the higher the measuring speed attains. The frequency-modulated interferometer is then applied to measure the axial error of an ultra-precision spindle. The proposed system can be a capable solution for noncontact and high-precision spindle error measurements in the machining process. Full article

(This article belongs to the Special Issue Organic Optoelectronic Materials (Volume II))

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8 pages, 2023 KiB

Open AccessCommunication

CHCl₃-Dependent Emission Color and Jumping Behavior of Cyclic Chalcone Single Crystals: The Halogen Bond Network Effect

by Zeqing Tan, Jian Zhao, Jingzhi Sun, Jiaxin Zhao, Xinrui He, Zhe Liu, Lin Zhu, Xiao Cheng and Chuanjian Zhou

Crystals 2021, 11(5), 530; https://doi.org/10.3390/cryst11050530 - 11 May 2021

Cited by 4 | Viewed by 2183

Abstract

As a conventional strategy to modulate the structure and properties of inorganic single crystals, hydration/solvation is rarely found to function in pure organic single crystal. Herein, we report chalcone single crystals with CHCl₃-dependent emission color and jumping behavior. Two crystals: a [...] Read more.

As a conventional strategy to modulate the structure and properties of inorganic single crystals, hydration/solvation is rarely found to function in pure organic single crystal. Herein, we report chalcone single crystals with CHCl₃-dependent emission color and jumping behavior. Two crystals: a pure crystal phase (1) with green-yellow emission and a CHCl₃-containing co-crystal phase (1•2CHCl₃) with orange-red emission were constructed by fine-controlling the crystallization conditions. The special halogen bond network in the crystal packing structure effectively narrows the bandgap and thereby redshift the emission of 1•2CHCl₃. 1•2CHCl₃ would revert to 1 together with emission color change when losing CHCl₃. These findings are similar to the effect of H₂O in hydrated inorganic crystals. Notably, owing to a special pre-organized “molecular pair” structure for [2 + 2] cycloaddition, the pure crystal phase 1 exhibits violently photo-induced jumping phenomenon, indicating large potentials in intelligent devices. This work would overturn the previous perception that the structurally simple solvent molecules without conjugation cannot greatly affect the structure and properties of pure organic single crystals and provide a new strategy to construct multi-colored organic fluorescent crystals. Full article

(This article belongs to the Special Issue Organic Optoelectronic Materials (Volume II))

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12 pages, 3976 KiB

Open AccessArticle

Design of New Au–NiCo MEMS Vertical Probe for Fine-Pitch Wafer-Level Probing

by Xuan Luc Le and Sung-Hoon Choa

Crystals 2021, 11(5), 485; https://doi.org/10.3390/cryst11050485 - 26 Apr 2021

Cited by 2 | Viewed by 6642

Abstract

As fine-pitch 3D wafer-level packaging becomes more popular in semiconductor industries, wafer-level prebond testing of various interconnect structures has become increasingly challenging. Additionally, improving the current-carrying capacity (CCC) and minimizing damage to the probe and micro-interconnect structures are very important issues in wafer-level [...] Read more.

As fine-pitch 3D wafer-level packaging becomes more popular in semiconductor industries, wafer-level prebond testing of various interconnect structures has become increasingly challenging. Additionally, improving the current-carrying capacity (CCC) and minimizing damage to the probe and micro-interconnect structures are very important issues in wafer-level testing. In this study, we propose an Au–NiCo MEMS vertical probe with an enhanced CCC to efficiently reduce the damage to the probe and various interconnect structures, including a solder ball, Cu pillar microbump, and TSV. The Au–NiCo probe has an Au layer inside the NiCo and an Au layer outside the surface of the NiCo probe to reduce resistivity and contact stress. The current-carrying capacity, contact stress, and deformation behavior of the probe and various interconnect structures were evaluated using numerical analyses. The Au–NiCo probe had a 150% higher CCC than the conventional NiCo probe. The maximum allowable current capacity of the 5000 µm-long Au–NiCo probe was 750 mA. The Au–NiCo probe exhibited less contact force and stress than the NiCo probe. The Au–NiCo probe also produced less deformation of various interconnect structures. These results indicate that the proposed Au–NiCo probe will be a prospective candidate for advanced wafer-level testing, with better probing efficiency and higher test yield and reliability than the conventional vertical probe. Full article

(This article belongs to the Special Issue Organic Optoelectronic Materials (Volume II))

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8 pages, 2241 KiB

Open AccessArticle

Color Glass by Layered Nitride Films for Building Integrated Photovoltaic (BIPV) System

by Akpeko Gasonoo, Hyeon-Sik Ahn, Seongmin Lim, Jae-Hyun Lee and Yoonseuk Choi

Crystals 2021, 11(3), 281; https://doi.org/10.3390/cryst11030281 - 12 Mar 2021

Cited by 11 | Viewed by 3094

Abstract

We investigated layered titanium nitride (TiN) and aluminum nitride (AlN) for color glasses in building integrated photovoltaic (BIPV) systems. AlN and TiN are among suitable and cost-effective optical materials to be used as thin multilayer films, owing to the significant difference in their [...] Read more.

We investigated layered titanium nitride (TiN) and aluminum nitride (AlN) for color glasses in building integrated photovoltaic (BIPV) systems. AlN and TiN are among suitable and cost-effective optical materials to be used as thin multilayer films, owing to the significant difference in their refractive index. To fabricate the structure, we used radio frequency magnetron deposition method to achieve the target thickness uniformly. A simple, fast, and cheap fabrication method is achieved by depositing the multilayer films in a single sputtering chamber. It is demonstrated that a multilayer stack that allows light to be transmitted from a low refractive index layer to a high refractive index layer or vice-versa can effectively create various distinct color reflections for different film thicknesses and multilayer structures. It is investigated from simulation based on wave optics that TiN/AlN multilayer offers better color design freedom and a cheaper fabrication process as compared to AlN/TiN multilayer films. Blue, green, and yellow color glasses with optical transmittance of more than 80% was achieved by indium tin oxide (ITO)-coated glass/TiN/AlN multilayer films. This technology exhibits good potential in commercial BIPV system applications. Full article

(This article belongs to the Special Issue Organic Optoelectronic Materials (Volume II))

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13 pages, 10102 KiB

Open AccessArticle

Photocontrollable Resistivity Change in Nanoparticle-Doped Liquid Crystal Alignment Layer: Voltage Holding and Discharging Properties of Fringe-Field Switching Liquid Crystal Modes

by Jeong-Hoon Ko, Jun-Chan Choi, Dong-Jin Lee, Jae-Won Lee and Hak-Rin Kim

Crystals 2021, 11(3), 268; https://doi.org/10.3390/cryst11030268 - 9 Mar 2021

Cited by 3 | Viewed by 2112

Abstract

In liquid crystal (LC) displays, deriving an optimum resistance level of an LC alignment polyimide (PI) layer is important because of the trade-off between the voltage holding and surface-discharging properties. In particular, to apply a power-saving low-frequency operation scheme to fringe-field switching (FFS) [...] Read more.

In liquid crystal (LC) displays, deriving an optimum resistance level of an LC alignment polyimide (PI) layer is important because of the trade-off between the voltage holding and surface-discharging properties. In particular, to apply a power-saving low-frequency operation scheme to fringe-field switching (FFS) LC modes with negative dielectric LC (n-LC), delicate material engineering is required to avoid surface-charge-dependent image flickering and sticking problems, which severely degrade with lowering operation frequency. Therefore, this paper proposes a photocontrolled variable-resistivity PI layer in order to systematically investigate the voltage holding and discharging properties of the FFS n-LC modes, according to the PI resistivity (ρ) levels. By doping fullerene into the high-ρ PI as the photoexcited charge-generating nanoparticles, the ρ levels of the PI were continuously controllable with a wide tunable range (0.95 × 10¹⁵ Ω∙cm to 5.36 × 10¹³ Ω∙cm) through Ar laser irradiation under the same LC and LC alignment conditions. The frequency-dependent voltage holding and discharge behaviors were analyzed with photocontrolled ρ variation. Thus, the proposed experimental scheme is a feasible approach in PI engineering for a power-saving low-frequency FFS n-LC mode without the image flickering and image sticking issues. Full article

(This article belongs to the Special Issue Organic Optoelectronic Materials (Volume II))

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8 pages, 1563 KiB

Open AccessArticle

Smart Window Based on Angular-Selective Absorption of Solar Radiation with Guest–Host Liquid Crystals

by Seong-Min Ji, Seung-Won Oh and Tae-Hoon Yoon

Crystals 2021, 11(2), 131; https://doi.org/10.3390/cryst11020131 - 28 Jan 2021

Cited by 11 | Viewed by 3113

Abstract

In this study, we analyzed angular-selective absorption in a guest–host liquid crystal (GHLC) cell for its application in smart windows. For reducing the energy consumption, angular-selective absorption is desired because the light transmitted through windows during the daytime is predominantly incident obliquely from [...] Read more.

In this study, we analyzed angular-selective absorption in a guest–host liquid crystal (GHLC) cell for its application in smart windows. For reducing the energy consumption, angular-selective absorption is desired because the light transmitted through windows during the daytime is predominantly incident obliquely from direct sunlight. Owing to the absorption anisotropy of guest dichroic dyes, a GHLC cell can absorb the obliquely incident light, while allowing people to see through windows in a normal view. Therefore, the cell can provide a comfortable environment for occupants, and reduce the energy required for cooling by blocking the solar heat incident from the oblique direction. The GHLC cell can be switched between the transparent and opaque states for a normal view. The rising (falling) time was 6.1 (80.5) ms when the applied voltage was 10 V. Full article

(This article belongs to the Special Issue Organic Optoelectronic Materials (Volume II))

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8 pages, 2663 KiB

Open AccessArticle

A Switchable Cholesteric Phase Grating with a Low Operating Voltage

by Ho-Jin Sohn, Seung-Won Oh, Yeongyu Choi, Seong-Min Ji and Tae-Hoon Yoon

Crystals 2021, 11(2), 100; https://doi.org/10.3390/cryst11020100 - 25 Jan 2021

Cited by 6 | Viewed by 2468

Abstract

We demonstrate a simple fabrication method of a uniform-lying-helix (ULH) cholesteric liquid crystal (ChLC) cell for phase grating device applications. To utilize a stable ULH state, we set the pitches of ChLCs as half of the cell gap to obtain the fingerprint texture [...] Read more.

We demonstrate a simple fabrication method of a uniform-lying-helix (ULH) cholesteric liquid crystal (ChLC) cell for phase grating device applications. To utilize a stable ULH state, we set the pitches of ChLCs as half of the cell gap to obtain the fingerprint texture with homeotropic anchoring. With the given grating period, the diffraction efficiency of the ULH cell can be maximized by optimizing the cell gap. We found that the fabricated grating device can provide a large diffraction angle of 10° and a low operating voltage of 3 V with a diffraction efficiency of 30%. We expect potential applications of the device for diffraction optics, optical interconnects, and beam steering devices. Full article

(This article belongs to the Special Issue Organic Optoelectronic Materials (Volume II))

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