Kwangseok Seo

Seoul National University, Sŏul, Seoul, South Korea

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Publications (26)16.24 Total impact

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    ABSTRACT: Size-optimized AlGaN/GaN HEMTs on Si-substrate are investigated for millimeter-wave power amplifier (PA) MMICs. The number of finger (2, 4, 8) and the unit finger width (25, 37.5, 50, 75, 100 μm) of devices are split in the AlGaN/GaN HEMTs process on Si-substrate. For searching the best suitable size for millimeter-wave PA, the RF performances such as Fmax and MAG (Maximum Available Gain) are investigated through S-parameter measurements and small signal model parameter extractions. Moreover, thermal resistances are extracted through pulsed IV measurement to evaluate thermal degradation on GaN HEMTs. Through these experiments and parametric analyses, 4×37.5 μm or 8 × 37.5 μm GaN HEMTs show the best RF performance keeping not larger thermal resistances (Rth). Thermal resistance and MAG are dependent on the gate pitch of GaN HEMTs. The selection of the proper gate pitch parameter of device is expected to bring the optimal power device performance in the millimeter-wave frequencies.
    Microwave Conference Proceedings (APMC), 2013 Asia-Pacific; 01/2013
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    ABSTRACT: AbstractA broadband watt‐level power amplifier in a metamorphic high electron mobility transistor (mHEMT) technology is presented at K‐band. The quadruple‐stacked transistor is used to overcome the low breakdown voltage limit of mHEMTs and achieve watt‐level output powers. The fabricated power amplifier using 130‐nm mHEMTs shows an output power of 1.3 W at 18 GHz with a 3‐dB power bandwidth of 58%. To the best of our knowledge, this is the first report of watt‐level single‐chip power amplifiers in mHEMT technology. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2624–2626, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27140
    Microwave and Optical Technology Letters 01/2012; 54(11). · 0.59 Impact Factor
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    ABSTRACT: A broadband power amplifier (PA) with a 3 dB power bandwidth of 72% is presented using metamorphic high electron mobility transistors (mHEMTs). A stacked FET structure, where transistors are series connected to combine voltage swings, is employed to overcome relatively low breakdown voltages of mHEMTs. Series-connected PA's show much higher load impedance compared to the parallel combined transistors, which allows output matching to be realized in the low quality (Q)-factor region, providing the broadband performance. The fabricated PA using quadruple-stacked 130 nm mHEMTs has a gain of 21.2 dB and saturated output power of 26.4 dBm with power added efficiency (PAE) of 33% at the design frequency of 18 GHz. The 3 dB output power bandwidth is from 10 to 23 GHz.
    IEEE Microwave and Wireless Components Letters 01/2010; · 1.78 Impact Factor
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    ABSTRACT: An active single-ended 77 GHz frequency tripler MMIC based on a 130 nm In<sub>0.8</sub>GaP/In<sub>0.4</sub>AlAs/In<sub>0.35</sub>GaAs metamorphic high electron mobility transistors (MHEMTs) technology has been developed. The frequency tripler MMIC demonstrates a maximum conversion gain of 1 dB for an input power of 0 dBm with 77 GHz output buffer amplifier and 3 dB output power bandwidth of 10 GHz.
    Infrared, Millimeter, and Terahertz Waves, 2009. IRMMW-THz 2009. 34th International Conference on; 10/2009
  • Chan Sei Yoo, Sangsub Song, Kwangseok Seo
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    ABSTRACT: The novel multilayer thin-film substrate using BCB as a dielectric was suggested in the paper. 3-metals and 2-BCB layers were used in this technology for the evaluation of passive devices. The band pass filter for W-band application with unique circuit and structure was designed and implemented. The implemented filter has an insertion loss below 1.5 dB, and return loss over 20 dB in the passband of 90~100 GHz. The attenuation is over 40 dB and 20 dB at the first and second harmonic frequencies, respectively and this response is adequate for the tripler application. The W-band tripler with a novel band pass filter in output part was evaluated on the thin-film substrate using commercial 0.15 um GaAs pHEMT from WIN foundry, and occupies the area of 2.5 x 1.5 mm. The measured response shows the conversion gain of -20dB and the spurious suppressions are 20 dBc and 10 dBc for the first and second harmonics, respectively due to the operation of the band pass filter.
    Microwave Conference, 2008. APMC 2008. Asia-Pacific; 01/2009
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    ABSTRACT: The development of cross-coupled bandpass filters and a duplexer for W-band transceiver applications on a thin-film substrate is presented. The filter is designed at 94 GHz using the cross-coupling method on a planar thin-film microstrip (TFMS) line platform and fabricated with a thin-film multichip module technology. The developed filter has an insertion loss of 2.5 dB with a 3-dB fractional bandwidth of 12.8%. Combining two cross-coupled filters with T-junction matching, a simple W-band duplexer is developed. The two channels of the duplexer are centered at 80 GHz and 94 GHz having channel bandwidth of 6.5 GHz and 6.7 GHz, respectively, with insertion loss less than 4.3 dB in both channel. The developed passives are compact and show good matching, selectivity, and isolation characteristics, and are suitable for low-cost W-band front-end integration.
    Proceedings - Electronic Components and Technology Conference 01/2009;
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    ABSTRACT: This paper proposed the symmetry Rotman Lens which is enabled beam steering at mm-wave. The Lens which has four beam ports and eight array ports has four dummy ports at beam curve in order to reduce multi reflection from the inside of the lens, and the side wall of the lens was minimized. Also the array curve is designed without a dummy port in order to reduce insertion loss. The lens has been employed as a feeder of eight linear array antennas with spaced 0.5lambda (2.5 mm), showing beam steering angle of -20deg, -6deg, +4deg, +18deg and HPBW of 11deg~13.5deg. The beam steering antenna module is mounted a antipodal fin line transition, SP4T switch, and PA on metal jig, showing gain of 17.3 dB~18 dB and SLL of 7.3 dBc.
    Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE; 08/2008
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    ABSTRACT: Embedded capacitors with available capacitances up to ˜80 nF have been implemented on a thin-film multichip module-deposited (MCM-D) substrate. By cost-effective silicon wet etching, a new metal-insulator-metal (MIM) structure named quasi-three-dimensional MIM capacitor has been realized. The groove structure formed by silicon wet etching increases effective capacitance area, thus enhancing capacitance density by 1.5 times. No additional mask or process step is required to form the groove structure since it is simultaneously patterned and etched with ground bumps that are for effective interconnection. The implemented capacitors have capacitances from 2 to 78 nF with a scalable density of 3.6 nF/mm2, indicating that they are excellent candidates for high-power decoupling application.
    Japanese Journal of Applied Physics 04/2008; 47(4):2535-. · 1.07 Impact Factor
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    ABSTRACT: Ultra-short-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) have been successfully fabricated with nano-gate fabrication technology and epitaxial optimization. We obtained an extrinsic maximum transconductance (G<sub>m,max</sub>) of 1.65 S/mm and a current gain cutoff frequency (f<sub>T</sub>) of 610 GHz for 15-nm-gate HEMTs on GaAs substrates. Through a delay time analysis, the ultrahigh f<sub>T</sub> of this work is explained by an enhanced average electron velocity under the gate (V<sub>ave</sub>) of 4.3 x 10<sup>7</sup> cm/s, which was a result of reduction of gate length (L<sub>g</sub>) and epitaxial engineering. This report is the first experimental demonstration of 15 nm InAlAs/TnGaAs metamorphic HEMTs (MHEMTs) with an extremely high f<sub>T</sub> of 610 GHz.
    Electron Devices Meeting, 2007. IEDM 2007. IEEE International; 01/2008
  • Hyungtae Kim, Kwangseok Seo
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    ABSTRACT: We demonstrate the novel and compact implementation of a monostable-to-bistable transition logic element (MOBILE) using only three resonant tunneling diodes (RTDs). The proposed circuit consists of only three RTDs and one resistor, with the configuration of a series-connected RTD pair and a series-connected RTD and resistor. The RTD pair is used for the MOBILE core circuit, and the RTD and resistor pair is used for current modulation. We also designed a frequency divider using the proposed MOBILE circuits. Test circuits are fabricated using InP-based RTD technology. The operation of the fabricated circuits is demonstrated up to 12.5 Gbits/s.
    Japanese Journal of Applied Physics 01/2008; 47:2854-2857. · 1.07 Impact Factor
  • Seongjin Yeon, Kwangseok Seo
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    ABSTRACT: We fabricated 50 nm InAlAs/InGaAs metamorphic high electron mobility transistors (HEMTs) with a very thin barrier. Through the reduction of the gate-channel distance (dGC) in the epitaxial structure, a channel aspect ratio (\mathit{AR}C) of over three was achieved when Lg was 50 nm. We inserted a thin InGaAs layer as a protective layer, and tested various gate structures to reduce surface problems induced by barrier shrinkage and to optimize the device characteristics. Through the optimization of the gate structure with the thin InGaAs layer, the fabricated 50 nm metamorphic HEMT exhibited high DC and RF characteristics, Gm of 1.5 S/mm, and fT of 490 GHz.
    Japanese Journal of Applied Physics 01/2008; 47:2868-2871. · 1.07 Impact Factor
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    Hyungtae Kim, Kwangseok Seo
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    ABSTRACT: We demonstrate the novel and compact implementation of literal gates with one literal window and two literal windows using only resonant tunneling diodes (RTDs). The proposed circuit consists of only three RTDs and one resistor for one literal window and four RTDs and one resistor for two literal windows, with the configuration of a series-connected RTD pair and a series-connected RTD and a resistor. The operation of the newly proposed literal gate is based on a monostable-to-bistable transition logic element (MOBILE). The RTD pair is used for the MOBILE core circuit and the RTD and resistor pair is used for current modulation. The circuit configuration is markedly reduced compared with conventional literal gates using complementary metal oxide semiconductor (CMOS) or previously reported RTD-based literal gates.
    Japanese Journal of Applied Physics 01/2008; 47:3340-3345. · 1.07 Impact Factor
  • Hyungtae Kim, Seongjin Yeon, Kwangseok Seo
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    ABSTRACT: We demonstrate a novel and compact implementation of high-speed and low-power source-coupled-field-effect transistor (FET)-logic (SCFL)-type non-return-to-zero (NRZ) delayed flip-flop circuit using resonant tunneling diode (RTD)/high electron mobility transistor (HEMT) integration technology on an InP substrate. The proposed circuit has several advantages of reduced device count, low power consumption, and reduced clock loading over previously reported circuits. The operations of the fabricated circuit was successfully confirmed up to 12.5 Gbits/s with a very low power consumption of about 11 mW.
    Japanese Journal of Applied Physics 01/2008; 47:2877-2879. · 1.07 Impact Factor
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    Hyungtae Kim, Seongjin Yeon, Kwangseok Seo
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    ABSTRACT: In this paper, we present new resonant tunneling bistable-to-monostable-to-bistable transition logic element with non-return-to-zero (NRZ) mode output. The proposed circuit is composed of resonant tunneling diode (RTD)/high electron mobility transistor (HEMT) series connection (RHS) and RTD/HEMT parallel connection (RHP). Novel high-speed and low-power NRZ delayed flip-flop (D-F/F) operation has been successfully achieved using RTD/HEMT integration technology on an InP substrate. The operation of the fabricated circuit was confirmed up to 36 Gb/s with a very low power dissipation of about 3 mW at a power supply voltage of 0.9 V.
    Nanotechnology, 2007. IEEE-NANO 2007. 7th IEEE Conference on; 09/2007
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    ABSTRACT: This paper proposed a microstrip Rotman lens which is enables beam steering at mm-wave. The lens which has three beam ports and five array ports has two dummy ports at beam curve in order to reduce multi reflection from inside of the Lens, and side wall of the Lens was minimized. Also array curve is designed without a dummy port in order to reduce insertion loss. The lens which has magnitude deviation less than plusmn2 dB and phase aberration less than plusmn5deg over 58 GHz- 62 GHz has been employed as a feeder of five linear array antennas with spaced 0.6lambda (3 mm), showing beam steering angle of -7deg, 0deg, +7deg and HPBW of 15deg.
    Antennas and Propagation Society International Symposium, 2007 IEEE; 07/2007
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    ABSTRACT: In this paper, a novel low-damage silicon nitride passivation for 100 nm In0.45AlAs/In0.4GaAs MHEMTs has been developed using remote ICPCVD. The silicon nitride deposited by ICPCVD showed higher quality, higher density, and lower hydrogen concentration than those of silicon nitride deposited by PECVD. In particular, we successfully minimized the plasma damage by separating the silicon nitride deposition region remotely from ICP generation region, typically with distance of 34 cm. The silicon nitride passivation with remote ICPCVD has been successfully demonstrated on GaAs MHEMTs with minimized damage. The passivated devices showed considerable improvement in DC characteristics and also exhibited excellent RF characteristics (fT of 200 GHz).The devices with remote ICPCVD passivation of 50 nm silicon nitride exhibited 22 % improvement (535 mS/mm to 654 mS/mm) of a maximum extrinsic transconductance and 20 % improvement (551 mA/mm to 662 mA/mm) of a maximum saturation drain current compared to those of unpassivated ones, respectively. The results achieved in this work demonstrate that remote ICPCVD is a suitable candidate for the next-generation MHEMT passivation technique.
    ECS Transactions 04/2007; 6(3).
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    Hyungtae Kim, Seongjin Yeon, Kwangseok Seo
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    ABSTRACT: A high-speed and low-power delayed flip-flop circuit with non-return-to-zero mode output using a new negative differential resistance logic element is proposed and fabricated using resonant tunneling diode (RTD)/high electron mobility transistor (HEMT) integration technology on an InP substrate. The number of devices used in the delayed flip-flop and the power dissipation has been significantly reduced by using the proposed scheme. The operation of the fabricated delayed flip-flop is demonstrated up to 26 Gb/s with a very low power dissipation of about 2.8 mW at a power supply voltage of 0.9 V.
    Japanese Journal of Applied Physics 03/2007; 46:2300. · 1.07 Impact Factor
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    ABSTRACT: Gate length reduction technology was developed for pseudomorphic high-electron-mobility transistors (P-HEMTs) applicable to nano-HEMTs. This technology utilizes various reactions between plasmas and dielectrics. Using optimum conditions for reducing gate length through pattern transfer in dielectric etching, we fabricated HEMTs having a sub-30 nm gate length reduced from the initial gate length of 0.13 mum. A HEMT with this technology has merits of both fine length definition beyond the limit of an electron beam (e-beam) lithography system and overcoming the metal filling problem caused by a high aspect ratio. The fabricated devices have high DC and RF performance characteristics, a transconductance of 1.35 S/mm, a maximum saturated current of 800 mA/mm and a cutoff frequency fT of 450 GHz.
    Japanese Journal of Applied Physics 01/2007; 46:2296-2299. · 1.07 Impact Factor
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    ABSTRACT: In0.4AlAs/In0.35GaAs metamorphic high-electron-mobility transistors (MHEMTs) have been successfully fabricated. In order to reduce the surface effects on the barrier layer, Si3N4 layer passivation by remote plasma-enhanced chemical vapor deposition (PECVD) is utilized, which might suppress the surface trap density in side-recessed region and reduce the parasitic resistance. The device simulation was performed to derive the effects of surface trap in the side-recessed region. As the surface trap density decreases, ID.max increases because of the stabilization of the surface states in the side-recessed region. This result indicates that the increases of gm.max and ID.max are related with both the reduction of parasitic resistance and the gate-sinking effect. The fabricated 100 nm MHEMTs with the passivated of Si3N4 layer exhibited excellent characteristics such as a maximum extrinsic gm.max of 740 mS/mm and a cut off frequency ( fT) of 210 GHz.
    Japanese Journal of Applied Physics 01/2007; 46:2341-2343. · 1.07 Impact Factor
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    ABSTRACT: In this work, the authors demonstrate a compact 77GHz single-chip transceiver for an automotive radar system. The transceiver consists of a low noise amplifier, mixer, doubler and power amplifier. The MMIC chip set is fabricated using a 120nm-gate-length In<sub>0.4</sub>AlAs/In<sub>0.35</sub>GaAs mHEMT. The low noise amplifier demonstrated a small signal gain of 19dB at 77GHz. The resistive mixer achieved a -11dB conversion gain. The doubler achieved 0.4dBm output power, a -5.6dB conversion gain and a difference of 18.4dBc between the 77GHz output and the fundamental output. The power amplifier demonstrated a small signal gain of 21.4dB at 77GHz with 12.3dBm output power. The single-chip transceiver demonstrated 9.3dBm output power at the transmitter and a 5dB conversion gain at the receiver
    Compound Semiconductor Integrated Circuit Symposium, 2006. CSIC 2006. IEEE; 12/2006

Publication Stats

46 Citations
16.24 Total Impact Points

Institutions

  • 2006–2012
    • Seoul National University
      • • School of Electrical Engineering and Computer Sciences
      • • School of Computer Science and Engineering
      • • Department of Electrical and Computer Engineering
      Sŏul, Seoul, South Korea