Enhancement of oxide break-up by implantation of fluorine inpoly-Si emitter contacted p+-n shallow junctionformation

In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p⁺-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF₂-implanted device is much larger than that of the boron-implanted device     

Formation of n-channel polycrystalline-Si thin-film transistors by using retrograde channel scheme with double implantation

Excellent n-channel poly-Si thin-film transistors (poly-Si TFTs) have been formed by using retrograde channel scheme with channel doping implantation and extra counter-doping implantation. As compared to the conventional sample with undoped channel layer, a much smaller leakage current can be achieved by boron-doping the poly-Si channel layer, due to a significantly reduced depletion region. However, the on-state characteristics are degraded. A retrograde channel scheme, implemented by further phosphorus counter-doping the surface of the boron-doped channel layer, is proposed for lowering the channel surface doping concentration without changing the bulk channel doping concentration. By using the retrograde channel scheme, an off-state leakage current as low as that for the normal channel-doping scheme may be achieved, while yielding excellent on-state I-V transfer characteristics.     

Submicron-meter tunneling field-effect poly-Si thin-film transistors with a thinned channel layer

Submicron-meter poly-Si tunneling-effect thin-film transistor (TFT) devices with a thinned channel layer have been investigated. With reducing the gate length to be shorter than 1 μm, the poly-Si TFT device with conventional MOSFET structure is considerably degraded. The tunneling field-effect transistor (TFET) structure can be employed to alleviate the short channel effect, thus largely suppressing the off-state leakage. However, for a poly-Si channel layer of 100 nm thickness, the TFET structure causes a small on-state current, which may not provide well sufficient driving current. By reducing the channel layer thickness to be 20 nm, the on-state current for the TFET structure can be largely increased, due to the enhanced bending of energy band for a thinned channel layer. As a result, for the TFET poly-Si TFTs at a gate bias of 5 V and a drain bias of 3 V, a 20-nm channel layer leads to an on-state current of about 1 order larger than that by a 100-nm channel layer, while still keeping an off-state leakage smaller than 0.1 pA/μm. Accordingly, the submicron-meter TFET poly-Si TFT devices with a thinned channel layer would show good feasibility for implementing high packing density of poly-Si TFT devices.     

A process simplification scheme for fabricating CMOS polycrystalline-Si thin film transistors

A process simplification scheme for fabricating CMOS poly-Si thin-film transistors (TFTs) has been pro-posed, which employs large-angle-tilt-implantation of dopant through a gate sidewall spacer (LATITS). By this LATITS scheme, a lightly doped drain region under the oxide spacer is formed by low-dose tilt implantation of phosphorus (orboron) dopant through the spacer, and then the n+-source/drain (n+-S/D) (or p+-S/D) region is formed via using the same photo-mask layer during CMOS integration. For both n-TFT and p-TFT devices, as compared to the sample with conventional single n+-S/D (or p+-S/D) structure, the LATITS scheme can cause an obviously smaller leakage current, due to more gradual dopant distribution and thus smaller electric field. In addition, the resultant on-state currents only show slight degradation for the LATITS scheme, As a result, by the LATITS scheme, CMOS poly-Si TFT devices with an on/off current ratio well above 8 orders may be achieved without needing extra photo-mask layers during CMOS integration.     

A model of polyelectrolyte conductance in moist solvents as a basis of water sensors

The conductance of interpenetrated polymer networks (IPNs) containing quaternary amino groups was studied in cyclohexane, toluene, ethyl ether, ethyl acetate, and tetrahydrofurane as a function of water content by electrochemical impedance spectroscopy. IPNs were then used as sensitive materials to detect water traces in organic solvents with promising results for the construction of a moisture sensor. The detection onset for water concentration increased with the dielectric constant of the solvent. Different IPN-based sensors in the same solvent showed a detection limit at lower water concentration if their characteristic plot [conductance/relative humidity (RH%) in air] was shifted toward lower RH%. This suggests that the composition of this class of polymers can be tuned to achieve the best performance for each solvent.     

Tomography of injection and acceleration of monoenergetic electrons in a laser-wakefield accelerator

A tomographic diagnosis method was developed to systematically resolve the injection and acceleration processes of a monoenergetic electron beam in a laser-wakefield accelerator. It was found that all the monoenergetic electrons are injected at the same location in the plasma column and accelerated from 5 to 55 MeV energy in 200 microm distance. This is a direct measurement of the real acceleration gradient in a laser-wakefield accelerator, and the experimental data are consistent with the model of transverse wave breaking and beam loading for monoenergetic electron injection.     

Laser assisted ultrasound guided aspiration improves procedure time and reduces number of withdrawals

This study evaluated the performance of in-vitro freehand aspiration of a simulated cyst with ultrasound aspiration guided by a newly designed laser assisted (LA) device. The LA device was equipped with an adjustable light source generating a sector light plane. This laser light plane was parallel to and overlapped the ultrasound acoustical plane, to help with needle positioning. Five operators randomly performed 30 freehand or LA ultrasound guided aspirations of a simulated cyst. The frequency was set at 8 MHz and depth at 4 cm. Procedure time and number of syringe withdrawals were statistically compared before and after using the LA device. Both experienced and inexperienced operators required significantly less time to perform the aspiration and had fewer syringe withdrawals when using the LA device. The LA device provides a reference plane in space, allowing the operator to more accurately position and adjust needle direction. Additional in-vivo testing is required to test the clinical practicability.     

Identification of phenylpropanoids in methyl jasmonate treated Brassica rapa leaves using two-dimensional nuclear magnetic resonance spectroscopy

Metabolic analysis showed a clear increase in phenylpropanoid levels in Brassica rapa leaves after treatment with methyl jasmonate. A fraction of phenylpropanoids was prepared by Diaion HP-20 and Sephadex LH-20 column chromatography after MeOH-water extraction. Even with these purification steps, isolation of each phenylpropanoid for structure elucidation is not easy due to the low levels in the plants (ca. 0.004%). A mixture was analyzed without further purification using HPLC-electrospray ionization mass spectrometry and NMR spectroscopy. Based on the NMR results including (1)H NMR, J-resolved, correlated spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), and heteronuclear multiple bond correlation (HMBC) spectra, both (1)H and (13)C resonances of the compounds were obtained. Using these NMR data, five phenylpropanoids conjugated with malate were identified: 5-hydroxyferuloyl-, caffeoyl-, coumaroyl-, feruloyl-, and sinapoyl malate. Of the compounds, 5-hydroxyferuloyl malate is a new phenylpropanoid. In addition to the five constitutive phenylpropanoids bearing trans-configuration, their cis forms, which are believed to be artifacts formed in the course of extraction steps, were also identified in the fraction.     

Location-area partition in a cellular radio network

With an increasing population of mobile subscribers, the signalling traffic to control the subscriber mobility expands rapidly. Subscriber mobility is controlled through location registration based on the so-called location area, the basic area unit for paging which consists of a number of cells. There is a tradeoff between the two kinds of signalling traffic: paging and location updating. As location areas include a larger number of cells, the traffic volume for paging increases while that for location updating decreases. Given not only the pattern of call arrivals but also that for subscriber mobility, our problem is to minimise the total signalling traffic by optimally partitioning the whole area into location areas. We show that this problem can be transformed to the so-called clique partitioning problem (CPP). Also we demonstrate the process of implementing the algorithm for solving the CPP for real-world problems defined on the cellular network in Seoul.