Han‐Cheol Ryu

Sahmyook University

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Su‐Jae Lee

Hanyang University

Seung Eon Moon

Electronics and Telecommunications Research Institute

Min-Hwan Kwak

Electronics and Telecommunications Research Institute

Young‐Tae Kim

Samsung (South Korea)

Sang-Pil Han

Hanyang University

Kyung Hyun Park

Electronics and Telecommunications Research Institute

Hyunsung Ko

Central Michigan University

Min Yong Jeon

Chungnam National University

Namje Kim

Electronics and Telecommunications Research Institute

Kwang‐Yong Kang

Electronics and Telecommunications Research Institute

Cooperative Institutions

Electronics and Telecommunications Research Institute

102

Seoul National University

Yonsei University

University of Würzburg

Korea Advanced Institute of Science and Technology

Chinese Academy of Sciences

Sahmyook University

Chungnam National University

Changwon National University

Pusan National University

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Microwave Performance of Distributed Analog Phase Shifter Using Ferroelectric (Ba,Sr)TiO₃ Thin Films

Integrated ferroelectrics (2003)

Han‐Cheol Ryu Seung Eon Moon Su‐Jae Lee Min-Hwan Kwak Young‐Tae Kim

Abstract This work presents the design, fabrication and microwave performance of distributed analog phase shifter (DAPS) fabricated on (Ba,Sr)TiO3 (BST) thin films for X-band applications. Ferroelectric BST thin films were deposited on MgO substrates by pulsed laser deposition. The DAPS consists of high impedance coplanar waveguide (CPW) and periodically loaded tunable BST interdigitated capacitors (IDC). In order to reduce the insertion loss of DAPS and to remove the alteration of unloaded CPW properties according to an applied dc bias voltage, BST layer under transmission lines were removed by photolithography and RF-ion milling. The measured results are in good agreement with the simulated results at the frequencies of interest. The measured differential phase shift based on BST thin films was 24° and the insertion loss decreased from −1.1 dB to −0.7 dB with increasing the bias voltage from 0 to 40 V at 10 GHz. Keywords: Ferroelectric thin films distributed analog phase shifter coplanar waveguide interdigitated capacitor phased array antenna

Phase shift module

10.1080/714040718

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Citations (5)

Analysis of the THz Resonance Characteristics of H-shaped Metamaterials with Varying Width

Current Optics and Photonics (2021)

Han‐Cheol Ryu

The resonance characteristics of H-shaped metamaterials, whose widths were varied while keeping the height constant, were investigated in the terahertz (THz) frequency range. The H-shaped metamaterials were numerically analyzed in two modes in which the polarization of the incident THz electric field was either parallel or perpendicular to the width of the H-shaped structure. The resonant frequency of the metamaterial changed stably in each mode, even if only the width of the H shape was changed. The resonant frequency of the metamaterial operating in the two modes increases without significant difference regardless of the polarization of the incident electromagnetic wave as the width of the H-shaped metamaterial increases. The electric field distribution and the surface current density induced in the metamaterial in the two modes were numerically analyzed by varying the structure ratio of the metamaterial. The numerical analysis clearly revealed the cause of the change in the resonance characteristics as the width of the H-shaped metamaterial changed. The efficacy of the numerical analysis was verified experimentally using the THz-TDS (time-domain spectroscopy) system. The experimental results are consistent with the simulations, clearly demonstrating the meaningfulness of the numerical analysis of the metamaterial. The analyzed resonance properties of the H-shaped metamaterial in the THz frequency range can be applied for designing THz-tunable metamaterials and improving the sensitivity of THz sensors.

Metamaterial antenna

Split-ring resonator

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A Band-Switchable and Tunable THz Metamaterial Based on an Etched Vanadium Dioxide Thin Film

Photonics (2022)

Jun‐Hwan Shin Kyung Hyun Park Han‐Cheol Ryu

A band-switchable and tunable terahertz (THz) metamaterial based on a vanadium dioxide (VO2) thin film was proposed in the THz frequency regime. The VO2 thin film with a high conductivity change rate and smooth phase transition characteristics was deposited. To obtain band switching characteristics and reduce THz wave loss, the VO2 thin film was etched in the form of a line. Two rectangular C-shaped resonators were configured to face each other, with an etched VO2 thin film line in between. When the VO2 thin film was in the insulator phase, the two resonators individually resonated, and when the VO2 thin film was in the metal phase, they were connected and resonated as one, showing band switching characteristics. According to the state of the VO2 thin film, the fabricated metamaterial resonated at 1.29 THz when the two resonators were electrically separated and resonated at 0.65 THz when the two resonators were electrically connected. In the band-switching process, the THz wave transmission characteristics were continuously tunable. The measurement results of the proposed structure clearly showed that the rectangular C-shaped metamaterial based on the etched VO2 thin film is capable of band switching and continuous transmission control. In the near future, band-switchable and tunable THz metamaterials based on etched VO2 thin films can be employed as key devices in THz wave 6G wireless communication technology.

Split-ring resonator

10.3390/photonics9020089

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Generation and Detection of Terahertz Waves Using Low-Temperature-Grown GaAs with an Annealing Process

ETRI Journal (2014)

Kiwon Moon Jeong‐Yong Choi Jun‐Hwan Shin Sang-Pil Han Hyunsung Ko

Photoconductivity

10.4218/etrij.14.0213.0319

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Citations (21)

DESIGN OF A Ka-BAND COUPLED MICROSTRIP LINE FERROELECTRIC PHASE SHIFTERS

Integrated ferroelectrics (2005)

Han‐Cheol Ryu Seung Eon Moon Su‐Jae Lee Min-Hwan Kwak Young‐Tae Kim

ABSTRACT We report on the design, fabrication and microwave performance of coupled microstrip line phase shifters (CMPS) based on (Ba,Sr)TiO3 (BST) thin films for Ka-band phased array antenna. Single phase BST thin films were deposited by pulsed laser deposition (PLD) on (001) MgO substrates. The CMPS were analyzed and designed by using an exact analysis in terms of even and odd mode phase velocities rather than the approach in which the velocities are averaged. These CMPS were tested in Ka-band, at room temperatures, and between the bias ranges of 0∼200 V. The measured differential phase shift was 458° and the insertion loss varied between 7.8 dB and 10.5 dB at 29 GHz in the bias ranges of 5∼200 V. The CMPS exhibited a figure of merit of about 44°/dB.

Ka band

Phase shift module

Figure of Merit

Line (geometry)

10.1080/10584580500414317

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Citations (2)

CAIR: Fast and Lightweight Multi-scale Color Attention Network for Instagram Filter Removal

Lecture notes in computer science (2023)

Woon-Ha Yeo Wang-Taek Oh Kyungsu Kang Young-Il Kim Han‐Cheol Ryu

Code (set theory)

10.1007/978-3-031-25063-7_45

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Citations (4)

A Phased Array Antenna Using Ferroelectric CPW Phase Shifter Active Modules

Ferroelectrics (2010)

Han‐Cheol Ryu Su‐Jae Lee Seung Eon Moon Min-Hwan Kwak Mun‐Cheol Paek

Abstract A phased array antenna using ferroelectric coplanar waveguide (CPW) phase shifter active modules is presented based on a Ba0.6Sr0.4TiO3 (BST) thin film. The ferroelectric BST thin film was deposited on an MgO substrate by using pulsed laser deposition. The active module amplifies an RF signal with low noise and changes the phase of a received RF signal to control the main beam of the array antenna. It is composed of low noise amplifier (LNA), dc block, and ferroelectric CPW phase shifter. The prototype of 6×12 phased array patch antenna with the active modules using a ferroelectric phase shifter is proposed. The proposed array antenna continuously scanned its main beam in elevation plane to 32° from its broadside direction at 11.85 GHz by applying the continuous dc voltage to the ferroelectric phase shifter. Keywords: Ferroelectric phase shiftercoplanar waveguide (CPW)active modulenoise figureimpedance matchingphased array antennamaximum beam scan angle Acknowledgments This work was supported by the IT R&D program of MKE/KEIT [2006-S-005-04, Development of THz-wave oscillation/modulation/detection module and signal source technology].

Phase shift module

Coplanar waveguide

10.1080/00150193.2010.484707

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Citations (2)

Microwave properties of compositionally graded (Ba, Sr)TiO3 thin films according to the direction of the composition gradient for tunable microwave applications

Applied Physics Letters (2003)

Su‐Jae Lee Seung Eon Moon Han‐Cheol Ryu Min-Hwan Kwak Young‐Tae Kim

Compositionally graded (Bax, Sr1−x)TiO3 (BST) thin films were deposited on MgO substrates by pulsed laser ablation. The microwave properties of the graded BST thin films were investigated at microwave frequencies with coplanar waveguide (CPW) meander-line phase shifters as a function of the direction of the composition gradient with respect to the substrate at room temperature. CPW phase shifters using graded BaTiO3(BT)→SrTiO3(ST) and ST→BT thin films exhibited a differential phase shift of 73° and 22° at 10 GHz with a dc bias voltage of 150 V, respectively. The figure of merit of the phase shifters at 10 GHz was 14.6 deg/dB for the graded BT→ST film, and 10 deg/dB for the graded ST→BT film. The graded BT→ST thin films showed a larger phase tuning than the ST→BT thin films. The microwave properties of the graded BST films depended strongly on the crystalline structure and the direction of the composition gradient with respect to the substrate.

Coplanar waveguide

Figure of Merit

10.1063/1.1565705

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Citations (75)

Terahertz radiation based on fiber-pigtailed InGaAs photoconductive antenna pumped by 1030-nm mode-locked Yb-doped fiber laser

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2017)

Ji Su Kim Sang-Pil Han Kiwon Moon Han‐Cheol Ryu Kyung Hyun Park

We present a terahertz (THz) radiation pumped by a passively mode-locked Yb-doped fiber laser using two fiberpigtailed log-spiral-based low-temperature-grown (LTG) InGaAs photoconductive antenna (PCA) modules. The modelocked fiber laser produces over 220 mW of the average optical power with positively chirped of 1.49 ps pulses. In order to generate THz radiation using the fiber-pigtailed PCA modules, the mode-locked optical pulses are pre-chirped with 538 fs using two diffraction gratings. We successfully achieved THz radiation over 2.0 THz using the pre-chirped pulses. We successfully observed the various absorption lines of water vapor dips in the free space of 120 mm.

10.1117/12.2265379

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Direct evidence on Ta-Metal Phases Igniting Resistive Switching in TaOx Thin Film

Scientific Reports (2015)

Min Yang Hyunsu Ju Gun Hwan Kim Jeon-Kook Lee Han‐Cheol Ryu

Abstract A Ta/TaO x /Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform distribution of resistive switching operational parameters, highly promising endurance and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaO x mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaO x thin film at the LRS.

Resistive touchscreen

High resistance

Tetragonal crystal system

10.1038/srep14053

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Citations (32)