• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.5
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• pp.827-834
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• 2020

In this paper, a third-order harmonic mixer is designed using frequency multiplier theory for the microwave airborne radar. Unlike the basic mixer design method, the gate bias voltage, at which the third-harmonic component of the Local frequency (LO) is the maximum, is selected using a frequency multiplier theory to maximize the third-harmonic mixing component at the intermediate frequency (IF). The proposed harmonic mixer was designed and manufactured using a commercial GaAs MESFET device in a plastic package, and it was possible to improve the high conversion loss, circuit complexity, high cost, and manufacturing complexity of the existing microwave mixer. The harmonic mixer using the proposed design method has a -8 ~ -10 dB conversion loss by pumping 11.5 GHz LO with a +5 dBm level when operating from 33.0 GHz to 36.0 GHz and the 1-dB gain compression point (P1dB) of 0 dBm.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.2
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• pp.422-427
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• 2005

In this paper, Doherty amplifier is designed by the need of improving the linearity and efficiency of wireless network and repeater for WCDMA. It is designed to maintain the high linearity and efficiency at the low efficiency period of the power amplifier after analyzing Doherty technique using the active load-pull in condition of the high efficiency power amplifier implementation according to the variation of input power. CW 1-tone experimental results at the WCDMA frequency 2.11$\~$2.17 CHz shows that Doherty amplifier, which achieves pore. add efficiency(PAE) 50$\%$ at 6dB back off the point from maximum output power 52.3dBm, obtains higher efficiency of 13.3$\%$ than class AB. finding optimum bias point after adjusted gate voltage, Doherty amplifier shows that IMD3 improves 4dB.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.10
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• pp.785-791
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• 2001

High dielectric (Ba, Sr) TiO$_3$ thin films were etched in an inductively coupled plasma (ICP) as a function of Cl$_2$/Ar mixing ration. Under Cl$_2$(20)/Ar(80), the maximum etch rate of the BST films was 400 $\AA$/mim and selectivities of BST to Pt and PR were obtained 0.4 and 0.2, respectively. Etching products were redeposited on the surface of BST and resulted in varying the nature of crystallinity. Therefore, we investigated the etched surface of BST by x-ray photoelectron spectroscopy (XPS) atomic force microscopy (AFM) and x-ray diffraction (XRD). From the result of XPS analysis, we found that residues of Ba-Cl and Ti-Cl bonds remained on the surface of the etched BST for high boiling point. The morphology of the etched surfact was analyzed by AFM. A smoothsurface(roughness ~2.8nm) ws observed under Cl$_2$(20)/Ar(80), rf power of 600 W, dc bias voltage of -250 V and pressure of 10 mTorr. This changed the nature of the crystallinity of BST. From the result of XRD analysis, the crystallinities of the etched BST film under Ar only and Cl$_2$(20)/Ar(80) were maintained as similar to as-deposited BST. However, intensity of BST(100) orientation under Cl$_2$ only plasma was abruptly decreased. This indicated that CI compounds were redeposited on the etched BST surface and resulted in changed of the crystallinity of BST during the etch process.

• JSTS:Journal of Semiconductor Technology and Science
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• v.6 no.1
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• pp.22-29
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• 2006

We demonstrate highly manufacturable Multi-channel Field Effect Transistor (McFET) on bulk Si wafer. McFET shows excellent transistor characteristics, such as $5{\sim}6 times higher drive current than planar MOSFET, ideal subthreshold swing, low drain induced barrier lowering (DIBL) without pocket implantation and negligible body bias dependency, maintaining the same source/drain resistance as that of a planar transistor due to the unique feature of McFET. And suitable threshold voltage ($V_T$) for SRAM operation and high static noise margin (SNM) are achieved by using TiN metal gate electrode.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.432.2-432.2
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• 2014

Recently, colloidal core/shell type quantum dots lighting-emitting diodes (QDLEDs) have been extensively studied and developed for the future of optoelectronic applications. In the work, we fabricate an inverted CdSe/ZnS quantum dot (QD) based light-emitting diodes (QDLED)[1]. In order to reduce work function of indium tin oxide (ITO) electrode for inverted structure, a very thin (<10 nm) polyethylenimine ethoxylated (PEIE) is used as surface modifier[2] instead of conventional metal oxide electron injection layer. The PEIE layer substantially reduces the work function of ITO electrodes which is estimated to be 3.08 eV by ultraviolet photoemission spectroscopy (UPS). From transmission electron microscopy (TEM) study, CdSe/ZnS QDs are uniformly distributed and formed by a monolayer on PEIE layer. In this inverted QD LED, two kinds of hybrid organic materials, [poly (9,9-di-n-octyl-fluorene-alt-benzothiadiazolo)(F8BT) + poly(N,N'-bis (4-butylphenyl)-N,N'-bis(phenyl)benzidine (poly-TPD)] and [4,4'-N,N'-dicarbazole-biphenyl (CBP) + poly-TPD], were adopted as hole transport layer having high highest occupied molecular orbital (HOMO) level for improving hole transport ability. At a low-operating voltage of 8 V, the device emits orange and red spectral radiation with high brightness up to 2450 and 1420 cd/m2, and luminance efficacy of 1.4 cd/A and 0.89 cd/A, respectively, at 7 V applied bias. Also, the carrier transport mechanisms for the QD LEDs are described by using several models to fit the experimental I-V data.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.838-841
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• 2012

To avoid the damage to circuit and performance degradation by temperature changes, temperature sensing circuit applicable to the IC is proposed in this paper. Temperature sensing is executed by PTAT circuit and power saving mode is activated by internal switch if internal temperature is in high. Also, characteristics of current matching are increased by using current mirror and cascode circuits. From the simulation results, this circuit is operating in action mode if input signal is in low. But it immediately goes into power saving mode if output signal is in high. It shows the output voltage of 1V at $75^{\circ}C$ and 1.75V at $125^{\circ}C$ in action mode and near 0 V(0V~ 7uV) in power saving mode.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.167-167
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• 2011

Magnetic random access memory (MRAM) is one of the prospective semiconductor memories for next generation. It has the excellent features including nonvolatility, fast access time, unlimited read/write endurance, low operating voltage, and high storage density. MRAM consists of magnetic tunnel junction (MTJ) stack and complementary metal-oxide semiconductor (CMOS). The MTJ stack is composed of various magnetic materials, metals, and a tunneling barrier layer. For the successful realization of high density MRAM, the etching process of magnetic materials should be developed. Among various magnetic materials, FePt has been used for pinned layer of MTJ stack. The previous etch study of FePt magnetic thin films was carried out using $CH_4/O_2/NH_3$. It reported only the etch characteristics with respect to the variation of RF bias powers. In this study, the etch characteristics of FePt thin films have been investigated using an inductively coupled plasma reactive ion etcher in various etch chemistries containing $CH_4$/Ar and $CH_4/O_2/Ar$ gas mixes. TiN thin film was employed as a hard mask. FePt thin films are etched by varying the gas concentration. The etch characteristics have been investigated in terms of etch rate, etch selectivity and etch profile. Furthermore, x-ray photoelectron spectroscopy is applied to elucidate the etch mechanism of FePt thin films in $CH_4$/Ar and $CH_4/O_2/Ar$ chemistries.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.390-390
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• 2012

Information technology industries has grown rapidly and demanded alternative memories for the next generation. The most popular random access memory, dynamic random-access memory (DRAM), has many advantages as a memory, but it could not meet the demands from the current of developed industries. One of highlighted alternative memories is magnetic random-access memory (MRAM). It has many advantages like low power consumption, huge storage, high operating speed, and non-volatile properties. MRAM consists of magnetic-tunnel-junction (MTJ) stack which is a key part of it and has various magnetic thin films like CoFeB, FePt, IrMn, and so on. Each magnetic thin film is difficult to be etched without any damages and react with chemical species in plasma. For improving the etching process, a high density plasma etching process was employed. Moreover, the previous etching gases were highly corrosive and dangerous. Therefore, the safety etching gases are needed to be developed. In this research, the etch characteristics of CoFeB magnetic thin films were studied by using an inductively coupled plasma reactive ion etching in $CH_4/O_2/Ar$ gas mixes. TiN thin films were used as a hardmask on CoFeB thin films. The concentrations of $O_2$ in $CH_4/O_2/Ar$ gas mix were varied, and then, the rf coil power, gas pressure, and dc-bias voltage. The etch rates and the selectivity were obtained by a surface profiler and the etch profiles were observed by a field emission scanning electron microscopy. X-ray photoelectron spectroscopy was employed to reveal the etch mechanism.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.2
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• pp.169-179
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• 1999

In this paper, a GaAs MESFET single-ended resistive mixer with high linearity and isolation is designed. The bias voltage of this mixer is applied only gate of GaAs MESFET to use the channel resistance. The LO is applied the gate and the RF is applied the drain through 7-pole hairpin bandpass filter to obtain the proper isolation thru LO-RF. The IF is extracted from the source with short circuit and lowpass filter. Using extracted equivalent circuits for LO and RF, conversion loss is calculated and compared with result of harmonic balance analysis. Measured conversion loss of this S-band down converter mixer is 8.2~10.5dB by considering the measured 3.0~3.4dB RF 7-pole hairpin bandpass filter loss and IP3in is 26.5dBm at Vg=-0.85~-1.0V in distortion performance.

• Journal of the Korean Magnetics Society
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• v.16 no.3
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• pp.186-191
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• 2006

Ferromagnetic amorphous $Ni_{16}Fe_{62}Si_8B_{14}$ and $Co_{70.5}Fe_{4.5}Si_{15}B_{10}$ layers have been devised and incorporated as free layers of magnetic tunnel junctions (MTJs) to improve MRAM reading and writing performance. The NiFeSiB and CoFeSiB single-layer film exhibited a lower saturation magnetization ($Ms=800emu/cm^3,\;and\;560emu/cm^3$, respectively) compared to that of a $Co_{90}Fe_{10}(Ms=1400emu/cm^3)$. Because amorphous ferromagnetic materials have lower Ms than crystalline ones, the MTJs incorporating amorphous ferromagnetic materials offer lower switching field ($H_{sw}$) values than that of the traditional CoFe-based MTJ. The double-barrier MTJ with an amorphous NiFeSiB free layer offered smooth surface resulting in low bias voltage dependence, and high $V_h\;and\;V_{bd}$ compared with the values of the traditional CoFe-based MTJ.