1,721,229 research outputs found
Deep X-ray lithography using mask with integrated electrothermal actuator
No full textWe present a deep X-ray mask with integrated bent-beam electrothermal actuator for the fabrication of 3D microstructures with curved surface. The mask absorber is electroplated on the shuttle mass, which is supported by a pair of 20-mu m-thick single crystal silicon bent-beam electrothermal. actuators and oscillated in a rectilinear direction due to the thermal expansion of the bent-beams. The width of each bent-beam is 10 mu m or 20 mu m and the length and bending angle are 1 mm and 0.1 rad, respectively, and the shuttle mass size is 1 mm X 1 mm. For 10-mu m-wide bent-beams, the shuttle mass displacement is around 15 mu m at 180 mW (3.6 V) dc input power. For 20-mu m-wide bent-beams, the shuttle mass displacement is around 19 mu m at 336 mW (4.2 V) dc input power. Sinusoidal cross-sectional PMMA microstructures with a pitch of 40 mu m and a height of 20 mu m are fabricated by 0.5 Hz, 20-mu m-amplitude sinusoidal shuttle mass oscillation
Deep X-ray mask with integrated actuator for 3D microfabrication
No full textWe present a novel method for 3D microfabrication with LIGA process that utilizes a deep X-ray mask in which a microactuator is integrated. The integrated microactuator oscillates the X-ray absorber, which is formed on the shuttle mass of the microactuator, during the X-ray exposures to modify the absorbed dose profile in X-ray resist, typically PMMA. The 3D PMMA microstructures according to the modulated dose contour are revealed after GG development. An X-ray mask with integrated comb drive actuator is fabricated using deep reactive ion etching, absorber electroplating, and bulk micromachining with silicon-on-insulator wafer. Silicon shuttle mass (1 mm x 1 mm, 20 mum thick) as a mask blank is supported by four I turn long suspension beams and is driven by the comb electrodes. A 10 mum thick, 50 mum line and spaced gold absorber pattern is electroplated on the shuttle mass before the release step. The fundamental frequency and amplitude are around 3.6 kHz and 20 mum, respectively, for a dc bias of 100 V and an ac bias of 20 V(P-P) (peak-peak). Fabricated PMMA microstructure shows 15.4 mum deep, S-shaped cross-section in the case of 1.6 kJ cm(-3) surface dose and GG development at 35 degreesC for 40 min. (C) 2003 Elsevier B.V. All rights reserved
Deep X-ray mask with integrated electro-thermal micro xy-stage for 3D fabrication
No full textWe present a novel 3D fabrication method utilizing a deep X-ray mask in which an electro-thermal micro xy-stage is integrated. The absorber of the X-ray mask is formed on the shuttle mass of the micro xy-stage and it is oscillated in x- and y-directions during exposures to modify the in-depth dose profile in the resist, usually PMMA. Curved or slanted microstructures are revealed by the modulated dose distribution and the development kinetics of the resist. The nuicro xy-stage is fabricated using a silicon-on-insulator (SOI) wafer, resulting in overhanging, 20 mum thick single-crystal silicon microstructures. It has 20 mum wide, 1 mm long bent-beam electro-thermal actuators along each axis and 10 mum wide, 1 mm long suspension beams supporting a 1.42 mm diameter shuttle mass. Displacements of the shuttle mass in x- and y-directions are both around 20 mum at 742 mW dc input power. Two-dimensional (2D) sinusoidal and tapered microstructures are fabricated through shuttle mass oscillation in two axes during exposures. (C) 2003 Elsevier B.V. All rights reserved
Hybrid neural network models for bankruptcy predictions
No full textThe objective of this paper is to develop the hybrid neural network models for bankruptcy prediction. The proposed hybrid neural network models are (1) a MDA-assisted neural network, (2) an ID3-assisted neural network, and (3) a SOFM(self organizing feature map)-assisted neural network. Both the MDA-assisted neural network and the ID3-assisted neural network are the neural network models operating with the input variables selected by the MDA method and IDS respectively. The SOFM-assisted neural network combines a backpropagation model (supervised learning) with a SOFM model (unsupervised learning). The performance of the hybrid neural network model is evaluated using MDA and IDS as a benchmark. Empirical results using Korean bankruptcy data show that hybrid neural network models are very promising neural network models for bankruptcy prediction in terms of predictive accuracy and adaptability
A NEURAL NETWORK APPROACH FOR THE IDENTIFICATION OF THE BOX-JENKINS MODEL
No full textThis study presents an artificial neural network-based paradigm for automating the controversial identification stage of the Box-Jenkins method, in which a time series is classified into an autoregressive moving average (ARMA) model. The identification stage depends on interpreting the patterns of two statistics-the autocorrelation function (ACF) and the partial autocorrelation function (PACF). The interpretation, however, requires an expertise of the Box-Jenkins method to be successfully completed. This operational drawback makes it less practical despite its theoretical elaborateness. In this paper, a neural network approach is used to extract enough useful information from the patterns of ACF and PACF to identify an appropriate ARMA model for an unknown time series. This study suggests both the neural network architecture and the training strategy that are suitable for identifying the Box-Jenkins model. Promising results were obtained through extensive computer experiments with the artificially generated time series and managerial and economic data found in the real world
A simple method for microlens fabrication by the modified LIGA process
No full textMicrolenses and microlens arrays were fabricated using a novel fabrication technology based on the exposure of a resist (usually PMMA) to deep x-rays and subsequent thermal treatment. The fabrication technology is very simple and produces microlenses and microlens arrays with good surface roughness (less than 1 nm). The molecular weight and glass transition temperature of PMMA is reduced when it is irradiated with deep x-rays. The microlenses were produced through the effects of volume change, surface tension, and reflow during thermal treatment of irradiated PMMA. The geometry of the microlens was determined by parameters such as the x-ray dose applied to the PMMA, the diameter of the microlens, along with the heating temperature, heating time and cooling rate in the thermal treatment. Microlenses were produced with diameters ranging from 30 to 1500 mum. The modified LIGA process was used to construct not only hemispherical microlenses, but also structures that were rectangular-shaped, star-shaped, etc
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