Bongsik Choi

Cutter-location data optimization in 5-axis surface machining

Abstract A method of generating ‘optimal’ cutter-location data for 5-axis NC contour milling from given cutter-contact data is presented in the paper. The cutter-location data-optimization problem is formulated as a 2D constrained minimization problem. The cutter orientation angles consisting of the tilt angle α and yaw angle β are used as decision variables. An analytic expression for approximate cusp heights is derived as a function of α, β (for a given path interval) to be used as a measure of optimality. The proposed optimization scheme has been successfully applied in the 5-axis face milling of large marine propellers.

Triangulation of scattered data in 3D space

Abstract Triangular interpolants are widely used to construct smooth surfaces from scattered data in 3D. To apply smooth triangular interpolants, the input 3D points have to be triangulated. This paper presents an algorithmic procedure for 3D triangulation. Relevant algorithms and datastructures are described in detail. Existing methods of 2D triangulation are based on Thiessen polygonization, which is an optimal partitioning of a geometric domain. To obtain an optimal triangular grid on the domain, the max-min angle criterion is frequently used. As there is no domain for 3D points, a new criterion called the smoothness criterion is proposed.

Sweep surfaces modelling via coordinate transformations and blending

Abstract A method for constructing mathematical models r ( r, v ) of ‘sweep-type’ sculptured surfaces by using coordinate transformations and blending is described. The surface modelling scheme is based on the logic of describing sweep surfaces on conventional engineering drawings. A smooth sculptured surface that is best described as a trajectory of cross-section curves swept along profile curves is called a sweep surface. A sweep surface is regarded as a tuple consisting of cross-section curves, profile curves, and a sweeping rule. The sweeping rules considered are parallel sweeping, rotational sweeping, spined sweeping, and synchronized sweeping. Also considered is a generalized spined sweeping where cross-section curves are allowed to rotate around the spine curve. For all the sweeping rules, the model r( u, v ) of the sweep surface has the same mathematical structure.

A Highly Responsive Silicon Nanowire/Amplifier MOSFET Hybrid Biosensor

This study demonstrates a hybrid biosensor comprised of a silicon nanowire (SiNW) integrated with an amplifier MOSFET to improve the current response of field-effect-transistor (FET)-based biosensors. The hybrid biosensor is fabricated using conventional CMOS technology, which has the potential advantage of high density and low noise performance. The biosensor shows a current response of 5.74 decades per pH for pH detection, which is 2.5 × 105 times larger than that of a single SiNW sensor. In addition, we demonstrate charged polymer detection using the biosensor, with a high current change of 4.5 × 105 with a 500 nM concentration of poly(allylamine hydrochloride). In addition, we demonstrate a wide dynamic range can be obtained by adjusting the liquid gate voltage. We expect that this biosensor will be advantageous and practical for biosensor applications which requires lower noise, high speed, and high density.

Pattern Recognition Using Carbon Nanotube Synaptic Transistors with an Adjustable Weight Update Protocol

Recent electronic applications require an efficient computing system that can perform data processing with limited energy consumption. Inspired by the massive parallelism of the human brain, a neuromorphic system (hardware neural network) may provide an efficient computing unit to perform such tasks as classification and recognition. However, the implementation of synaptic devices (i.e., the essential building blocks for emulating the functions of biological synapses) remains challenging due to their uncontrollable weight update protocol and corresponding uncertain effects on the operation of the system, which can lead to a bottleneck in the continuous design and optimization. Here, we demonstrate a synaptic transistor based on highly purified, preseparated 99% semiconducting carbon nanotubes, which can provide adjustable weight update linearity and variation margin. The pattern recognition efficacy is validated using a device-to-system level simulation framework. The enlarged margin rather than the linear weight update can enhance the fault tolerance of the recognition system, which improves the recognition accuracy.

Flammable carbon nanotube transistors on a nitrocellulose paper substrate for transient electronics

Transient electronics represent an emerging class of technology comprising materials that can vanish in a controlled manner in response to stimuli. In contrast to conventional electronic devices that are designed to operate over the longest possible period, transient electronics are defined by operation typically over a short and well-defined period; when no longer needed, transient electronics undergo self-deconstruction and disappear completely. In this work, we demonstrate the fabrication of thermally triggered transient electronic devices based on a paper substrate, specifically, a nitrocellulose paper. Nitrocellulose paper is frequently used in acts of magic because it consists of highly flammable components that are formed by nitrating cellulose by exposure to nitric acid. Therefore, a complete and rapid destruction of electronic devices fabricated on nitrocellulose paper is possible without producing any residue (i.e., ash). The transience rates can be modified by controlling radio frequency signal-induced voltages that are applied to a silver (Ag) resistive heater, which is stamped on the backside of the nitrocellulose paper. The Ag resistive heater was prepared by a simple, low-cost stamping fabrication, which requires no harsh chemicals or complex thermal treatments. For the electronics on the nitrocellulose paper substrate, we employed semiconducting carbon nanotube (CNT) network channels in the transistor for superior electrical and mechanical properties.

Transparent, Flexible Strain Sensor Based on a Solution-Processed Carbon Nanotube Network

The demands for transparent, flexible electronic devices are continuously increasing due to their potential applications to the human body. In particular, skin-like, transparent, flexible strain sensors have been developed to realize multifunctional human-machine interfaces. Here, we report a sandwich-like structured strain sensor with excellent optical transparency based on highly purified, solution-processed, 99% metallic CNT-polydimethylsiloxane (PDMS) composite thin films. Our CNT-PDMS composite strain sensors are mechanically compliant, physically robust, and easily fabricated. The fabricated strain sensors exhibit a high optical transparency of over 92% in the visible range with acceptable sensing performances in terms of sensitivity, hysteresis, linearity, and drift. We also found that the sensitivity and linearity of the strain sensors can be controlled by the number of CNT sprays; hence, our sensor can be applied and controlled based on the need of individual applications. Finally, we investigated the detections of human activities and emotions by mounting our transparent strain sensor on various spots of human skins.

TCAD-Based Simulation Method for the Electrolyte–Insulator–Semiconductor Field-Effect Transistor

A simulation method for the electrolyte-insulator-semiconductor field-effect transistor (EISFET)-type sensor is proposed based on a well-established commercialized semiconductor 3-D technology computer-aided design simulator. The proposed method relies on the fact that an electrolyte can be described using a modified intrinsic semiconductor material because of the similarity between the electrolyte and the intrinsic semiconductor. The electrical double layer of the electrolyte is characterized in the simulation using the Gouy-Chapman-Stern model. Using the proposed simulation method, we extract the Debye lengths depending on phosphate buffered saline solutions with various concentrations and demonstrate that it is possible to simulate the screening effect. Furthermore, we investigate the responses of the EISFET-type silicon nanowire pH sensor based on our simulation method, which shows good agreement with the reported Nernst limit value.

A novel SiNW/CMOS hybrid biosensor for high sensitivity/low noise

A novel silicon nanowire (SiNW)/CMOS hybrid biosensor was produced for the first time. The hybrid biosensor features a complementary SiNW block and CMOS logic inverter readout circuitry. The proposed hybrid biosensor shows remarkably sensitive output voltage (Δ1.2 V/Δ0.4 pH and Δ1.2 V/Δ200 fM DNA) without noise or fluctuations.

Comprehensive evaluation of early retention (fast charge loss within a few seconds) characteristics in tube-type 3-D NAND flash memory

A fast charge loss within a few seconds, which is referred to as early retention, was observed in tube-type 2y word-line stacked 3-D NAND flash memory for the first time, and the origin of the early retention was comprehensively evaluated. Using a fast-response pulse I-V system, the early retention characteristics from microseconds to seconds were thoroughly investigated, and the correlations with various program and erase levels were examined using solid and checkerboard patterns. Our findings indicate that the early retention mainly originates from the lateral charge loss through the shared charge trap layers and suggest that the program and erase levels should be balanced and optimized to reduce the early retention.