• KSBB Journal
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• v.6 no.3
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• pp.231-240
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• 1991

Recently, developments of large scale and high density cell culture methods have been the objects of many researches, because the demand of various pharmaceutical products produced by animal cell culture has been rapidly increasing. The cell culture equipment should have the requirements such as sufficient oxygen transfer and mixing, low shear stress and surface tension, and small foaming. In order to develop a proper bioreactor meeting these requirements simultaneously, a perfluorocarbon having high solubility of oxygen was sprayed into the medium as an oxygen carrier instead of air. Also, a new impeller was developed and combined together with the perfluorocarbon spraying system so as to design a new bioreartor for cell cultivation. The new impeller had better characteristics of mixing and oxygen transfer than the paddle and cell-lift impellers based on the same, shear rate. But, it was observed that the volumetric oxygen transfer coefficient of the new bioreactor decreased with increasing cell density during E. coli fermentation.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1249-1251
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• 1998

We have studied the properties of $GaAs_{0.35}P_{0.65}$ epitaxial films on the GaP according to doping of $NH_3$ gas using VPE method by CVD. The efficiency of $GaAs_{0.35}P_{0.65}$ epitaxial films found to be greatly enhanced by the according of nitrogen doping. The diodes were fabricated by means of Zn diffusion into vapor grown $GaAs_{0.35}P_{0.65}$ epitaxial films doped with N and Te. The effects of nitrogen doping on carrier density of epitaxial films, PL wavelength and the power out, forward voltage of diodes are discussed. In the end, The effect of electrical and optical properties is influenced by the deep level and deep level density of nitrogen doping.

• Transactions on Electrical and Electronic Materials
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• v.18 no.1
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• pp.51-54
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• 2017

TFTs (thin film transistors) were fabricated using a-SIZO (amorphous silicon-indium-zinc-oxide) channel by RF (radio frequency) magnetron sputtering at room temperature. We report the influence of various channel thickness on the electrical performances of a-SIZO TFTs and their stability, using TS (temperature stress) and NBTS (negative bias temperature stress). Channel thickness was controlled by changing the deposition time. As the channel thickness increased, the threshold voltage ($V_{TH}$) of a-SIZO changed to the negative direction, from 1.3 to -2.4 V. This is mainly due to the increase of carrier concentration. During TS and NBTS, the threshold voltage shift (${\Delta}V_{TH}$) increased steadily, with increasing channel thickness. These results can be explained by the total trap density ($N_T$) increase due to the increase of bulk trap density ($N_{Bulk}$) in a-SIZO channel layer.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.246-251
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• 1998

This paper describes the main features of an unconventional tester for high power semiconductor devices. Two application ranges are highlighted. The tester is used for the extraction of GTO parameters and their verification by measurements. The second field comprises the determination of the radial and azimuthal current density distribution of a GTO tablet. The results are compared with the carrier lifetime distribution.

• Journal of Information Display
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• v.10 no.4
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• pp.143-148
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• 2009

The theoretical current density equations for organic semiconductors was derived according to the internal carrier emission equation based on the diffusion model at the Schottky barrier contact and the mobility equation based on the field dependence model, the so-called "Poole-Frenkel mobility model." The electric field becomes constant because of the absence of a space charge effect in the case of a higher injection barrier height and a lower sample thickness, but there is distribution in the electric field because of the space charge effect in the case of a lower injection barrier height and a higher sample thickness. The transition between the injection- and bulk-limited currents was presented according to the Schottky barrier height and the sample thickness change.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.162-163
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• 2000

We have observed the short-channel effect, narrow-channel effect and small-geometry effect in terms of a variation of the threshold voltage. For a short-channel effect the threshold voltage was largely determined by the DIBL effect which stimulates more carrier injection in the channel by reducing the potential barrier between the source and channel. The effect becomes more significant for a shorter-channel device. However, the potential, field and current density distributions in the channel along the transverse direction showed a better uniformity for shorter-channel devices under the same voltage conditions. The uniformity of the current density distribution near the drain on the potential minimum point becomes worse with increasing the drain voltage due to the enhanced DIBL effect. This means that considerations for channel-width effect should be given due to the variation of the channel distributions for short-channel devices. For CCDs which are always operated at a pinch-off state the channel uniformity thus becomes significant since they often use a device structure with a channel length of > 4 ${\mu}{\textrm}{m}$ and a very high drain (or diffusion) voltage. (omitted)

• Journal of the Korean Vacuum Society
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• v.1 no.1
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• pp.212-222
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• 1992

To use polycrystalline Si Thin Film Transistor (poly-Si TFT) in high density SRAM instead of High Load Resistor (HLR), TFT is needed to show good electrical characteristics such as large carrier mobility, low leakage current, high driver current and low subthreshold swing. To satisfy these electrical characteristics, the trap state density must be reduced in the channel poly. Technological issues pertinent to the channel poly fabrication process are investigated and discussed. They are solid phase growth (SPG), Si-ion implantation, laser annealing and hydrogenation. The electrical properties of several CVD oxides used as the gate oxide of TFT are compared. The dependence of the electrical characteristics of TFT on source-drain ion-implantation dose, drain offset length and dopant lateral diffusion are also described.

• Journal of Sensor Science and Technology
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• v.24 no.6
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• pp.385-391
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• 2015

In this paper, we propose a new method to infiltrate $Fe_3O_4$-nanoparticles into a porous silicon film and a monitoring technique to detect packing density of nanoparticles within the film. Recently, research to use porous silicon as a drug carrier or a new functional sensor material by infiltrating $Fe_3O_4$-nanoparticles has been extensively performed. However, it is still necessary to enhance the packing density and to develop a monitoring technique to detect the packing density in real time. In this light, we forcibly injected a nanoparticle solution into a rugate-structured free-standing porous silicon (FPS) film by applying a pressure difference between the two sides of the film. We found that the packing density by the pressure-infiltration method proposed in this paper is enhanced, relative to that by the previous diffusion method. Moreover, a continuous shift in wavelength of the rugate reflectance peak measured from the film surface was observed while the nanoparticle solution was being injected. By exploiting this phenomenon, we could qualitatively monitor the packing density of $Fe_3O_4$-nanoparticles within the FPS film with the injection volume of the nanoparticle solution.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.9
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• pp.8-13
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• 2008

Noise in homogeneous extrinsic semiconductor samples is calculated due to distributed diffusion noise sources. As the length of the device shrinks at a fixed bias voltage, the ac-wise short-circuit noise current shows excess noise as well as thermal noise spectra. This excess noise behaves like a full shot noise when the channel length becomes very small compared with the extrinsic Debye length. For the first time, the analytic formula of the excess noise in extrinsic semiconductors from velocity-fluctuation noise sources is given for finite frequencies. This formula shows the interplay between transit time, dielectric relaxation time, and velocity relaxation time in determining the terminal noise current as well as the carrier density fluctuation. As frequency increases, the power spectral density of the excess noise rolls off. This formula sheds light on noise in nanoscale MOSFETs where quasi-ballistic transport plays an important role in carrier transport and noise.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.273-280
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• 2002

The stochiometric mix of evaporating materials for the CuGaTe$_2$ single crystal thin films was prepared from horizontal furnance. For extrapolation method of X-ray diffraction patterns for the CuGaTe$_2$ polycrystal, it was found tetragonal structure whose lattice constant a$\_$0/ and c$\_$0/ were 6.025 ${\AA}$ and 11.931 ${\AA}$, respectively. To obtain the single crystal thin films, CuGaTe$_2$ mixed crystal was deposited on throughly etched semi-insulator GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were 670 $^{\circ}C$ and 410 $^{\circ}C$ respective1y, and the thickness of the single crystal thin films is 2.1 $\mu\textrm{m}$. The crystalline structure of single crystalthin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). Hall effect on this sample was measured by the method of van der Pauw and studied on carrier density and mobility dependence on temperature. The carrier density and mobility of CuGaTe$_2$ single crystal thin films deduced from Hall data are 8.72${\times}$10$\^$23/㎥, 3.42${\times}$10$\^$-2/㎡/V$.$s at 293K, respectively. From the photocurrent spectrum by illumination of perpendicular light on the c - axis of the CuGaTe$_2$ single crystal thin film, we have found that the values of spin orbit coupling Δs.o and the crystal field splitting Δcr were 0.0791 eV and 0/2463eV at 10K, respectively. From the PL spectra at 10K, the peaks corresponding to free bound excitons and D-A pair and a broad emission band due to SA is identified. The binding energy of the free excitons are determined to be 0.0470eV and the dissipation energy of the donor -bound exciton and acceptor-bound exciton to be 0.0490eV, 0.00558eV, respectively.