S. J. Noh

Poly-Si thin film transistors with a source overlap and a drain offset: leakage current characteristics

The electrical characteristics of hydrogen passivated polycrystalline-silicon p-channel metal-oxide-semiconductor thin-film transistors (poly-Si PMOS TFTs) for high density memory devices have been investigated. A lightly doped offset (LDO) structure was adopted to reduce the electric field induced in the drain region. Compared with the on-current, the off-current was reduced significantly with an LDO length. As a result, the TFT with an LDO presented the enhanced on/off current ratio. However, it still has a drawback of reducing the oncurrent due to increased parasitic resistance. To reduce this effect, a source overlap structure was introduced. Although the on current was slightly improved at a longer source overlap length due to channel length reduction, the dependence of the on/off current ratio on a source overlap length was small compared with that on an LDO length. In the measurement of leakage currents, the lower channel and gate breakdown voltages were obtained at the longer source overlap structure. 1999 Elsevier Science S.A. All rights reserved.

Low-energy D+ and H+ ion irradiation effects on highly oriented pyrolytic graphite

We have investigated the low-energy (100 eV) D+ and H+ ion irradiation effects on the structural and chemical properties of highly oriented pyrolytic graphite (HOPG). Structural disorder due to the ion irradiation was identified by the Raman spectroscopy, the D+ irradiation giving rise to greater structural disorder than the H+ irradiation. Only sp2 bonding was identified in the X-ray photoemission spectroscopy of the D+-irradiated HOPG, indicating no change in the surface chemical structure. The H+ irradiation, on the other hand, gave rise to sp3 bonding and π−π* transition, the sp3 bonding increasing with increasing irradiation dose. It is thus shown that the chemical properties of the HOPG surface may be sensitively modified by the low-energy H+ ion irradiation, but not by the low-energy D+ ion irradiation.

Design, study on the rf source for KOMAC

A study on the design of 700 MHz, 1 MW CW klystron amplifier for KOMAC (KOrea Multipurpose Accelerator Complex) proton accelerator has been carried out by KAPRA (Korea Accelerator and Plasma Research Association). A triode type electron gun including a modulating anode, six cavities including one second harmonic cavity and electromagnet for electron beam focusing were designed to produce desired output rf power. Thermal analysis at the collector according to the magnetic field profile near the collector side pole face was performed to efficiently cool the heat generated through the kinetic energy loss of the electron beam. In addition to the design study, an operation experiment of the klystron for broadcasting whose output power was 15 kW and frequency range 574 - 698 MHz was performed at 700 MHz. In this paper, the results of the design study and the operation experiment of the klystron for broadcasting at 700 MHz are presented.

Electric dipole moment in KH2PO4 systematically modified by proton irradiation

We have carried out an impedance spectroscopy study on a series of proton-irradiated KH2PO4 (KDP) systems. A systematic modification was observed in the transverse dipole moment of the proton-irradiated KDP systems, associated with hydrogen-ion displacements, as obtained from dielectric constant measurements by using a mean-field approximation. Besides, intercorrelation of the charge transport with the dielectric properties was revealed, both having closely to do with the hydrogen-bond modification.We have carried out an impedance spectroscopy study on a series of proton-irradiated KH2PO4 (KDP) systems. A systematic modification was observed in the transverse dipole moment of the proton-irradiated KDP systems, associated with hydrogen-ion displacements, as obtained from dielectric constant measurements by using a mean-field approximation. Besides, intercorrelation of the charge transport with the dielectric properties was revealed, both having closely to do with the hydrogen-bond modification.

Properties of the plasma produced by multi-cathode electron beam plasma sources

A new plasma source using the multi-cathode electron beam has been designed and manufactured. A multi-cathode was adopted to produce bulk plasmas in a large volume. Multi-cathode electron beam plasma source (MCEBPS) was found to generate stable plasmas over the wafer diameter of 300 mm or above in a low pressure regime. Over a 320 mm diameter, both the plasma potential V p and floating potential V f were uniformly maintained and the difference between V p and V f was small. The electron temperature was also sustained low. The plasma density was around 10 10 cm -3 and its variation along the radial distance was small.

RaD Status of the 700 MHz, 1MW Klystron for PEFP

KAPRA (Korea Accelerator and Plasma Research Association) are undertaking the first phase R&D for the 1 MW, CW 700 MHz klystron, which is targeting the future stage of the PEFP (Proton Engineering Frontier Project) accelerator at KAERI (Korea Atomic Energy Research Institute). The objectives of the first phase R&D are 1) setting up infra structures/procedures for the design and fabrication, 2) developing a prototype klystron for proofs of principles, and 3) making a performance test of the prototype at a reduced duty. The second phase R&D is supposed to cover full power, CW operation and reliability issues. In this paper, a summary of the R&D status during the first phase for PEFP 1 MW, 700 MHz klystron is reported.

Recent results of multi-cathode electron beam plasma source

Abstract The basic experiments of the multi-cathode electron beam plasma source (MCEBPS) were carried out recently. The MCEBPS has characteristics of uniform plasma in large area. It can be extended to produce uniform plasmas in a very large diameter of several meter with addition of the other cathodes. The plasmas are made through direct interaction of electrons and neutral gases in the wide area with a diameter of 300 mm or above. The non-uniformity of the radial plasma density must be small to be suitable for the process of next generation semiconductor devices. The MCEBPS now has seven cathodes (multi-cathode) whose array is concentric to produce uniform plasmas in a large area at the target position. The energy of extracted electron beam from cathodes is about 50 eV. This can be controlled by changing the voltages of extraction electrodes. The electron beam current can be also controlled to the desired value by adjusting the cathode temperatures. The energy and the current of the electron beam can be controlled independently. In the working chamber, plasmas for the process of target material are produced through the direct interaction of the extracted electron beam and the neutral gases which are fed from outside. The plasma density above 1×1010 cm−3 and uniformity below ±3.0% in diameter of 320 mm were achieved recently. The adoption of multi-pole or additional permanent magnets is under consideration to enhance the plasma confinement and uniformity.

Study of inductively coupled plasma effects for ZO:N thin films

ZnO has been considered in various industrial applications owing to its piezoelectric properties and wide band gap of near ultraviolet. However, its application to optoelectronic and display devices is still very limited due to the difficulty in obtaining good and stable p-type ZnO. In order to study p-type ZnO (ZO:N), we developed a plasma enhanced atomic layer deposition (PEALD) system adopting an inductively coupled plasma (ICP) source; its plasma generation was carried out and ZnO thin films were fabricated using both PEALD and ALD process. Diethylzinc was used as a zinc precursor, H2O as an oxidant, nitrogen as a dopant, and argon as a carrier and purge gas. Self-limiting growth and doping effects were investigated at various flow rates, reaction times and radio-frequency powers. The properties of thin films were investigated using field emission scanning electron microscopy (FESEM), Auger electron spectroscopy (AES), Hall measurement, photoluminescence measurement (PL), X-ray diffraction (XRD), etc. Detailed results will be presented.

The R&D status of 700MHZ 1MW CW klystron

KAPRA (Korea Accelerator and Plasma Research Association) is conducting a project of designing and making a 1 MW, 700 MHz klystron which purpose the future stage of the PEFP (Proton Engineering Frontier Project) proton accelerator at KAERI (Korea Atomic Energy Research Institute). And KAPRA has completed the proto-type klystron for proofs of principle and the performance test in first phase. The second phase is in progress at present. The goals of this phase are 1) making the new advanced klystron which was base on adjustment and repletion of previous work 2) setting up infra structure for baking, assembling, and supporting fabrication process 3) covering full power, operating CW and reliability issue 4) training the young scientists and engineers. In this paper, a summary of R&D status and results.

Test of 700MHz, 1MW proto-type klystron for PEFP

High power and RF source of 700 MHz and 1 MW klystron, which has been designed and constructed by the Korean Accelerator and Plasma Research Association, has been tested. To test the primary performance of the klystron, a pulse power supply was used to manipulate a negative high voltage. We are currently reinforcing the protection circuit, and it is going on without much trouble as originally planned. In addition, a baking furnace for the klystron is under fabrication for the ultra high vacuum with better stability. We have constructed various infrastructures such as the baking furnace for the development of the klystron.