Busan, South Korea
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Kwon H.-J.,University of Maryland University College | Kim J.-H.,Korea Research Institute of Standards and Science | Choi W.-C.,Fabrication Center
Microsystem Technologies | Year: 2011

In this paper, we propose a flexible three-axial tactile sensor array for measuring both normal and shear loads. The sensor array has 16 tactile sensor units based on piezoresistive strain gauge. It is constructed on a Kapton polyimide film using advanced polymer micromachining technologies. Thin metal strain gauges are embedded in polyimide to measure normal and shear loads, which are tested by applying forces from 0 to 1 N. The developed sensor unit had a hysteresis error of about 9% and repeatability error of about 1.31%. The sensor showed a good resulting image when pressed by a circle-shaped object with 10 N loads. The proposed flexible three-axial tactile sensor array can be applied in a curved or compliant surface that requires slip detection and flexibility, such as a robotic finger. © Springer-Verlag 2011.


Lee Y.W.,Pukyong National University | Kim E.-S.,Korea University | Shin B.-S.,Pusan National University | Lee S.-M.,Fabrication Center
Journal of Electrical Engineering and Technology | Year: 2012

In this paper, a high-performance optical gating in a junction device based on a vanadium dioxide dioxide (VO2) thin film grown by a sol-gel method was experimentally demonstrated by directly illuminating the VO2 film of the device with an infrared light at ~1554.6 nm. The threshold voltage of the fabricated device could be tuned by ~76.8 % at an illumination power of ~39.8 mW resulting in a tuning efficiency of ~1.930 %/mW, which was ~4.9 times as large as that obtained in the previous device fabricated using the VO2 thin film deposited by a pulsed laser deposition method. The rising and falling times of the optical gating operation were measured as ~50 ms and ~200 ms, respectively, which were ~20 times as rapid as those obtained in the previous device.reakdown.


Moon H.-S.,The Bump | Kim S.-E.,Fabrication Center | Choi W.-C.,Fabrication Center
Transactions on Electrical and Electronic Materials | Year: 2012

A low power methane gas sensor with microheater was fabricated by silicon bulk micromachining technology. In order to heat up the sensing layer to operating temperature, a platinum (Pt) micro heater was embedded in the gas sensor. The line width and gap of the microheater was 20 μm and 4.5 μm, respectively. Zinc oxide (ZnO) nanowhisker arrays were grown on a sensor from a ZnO seed layer using a hydrothermal method. A 200 ml aqueous solution of 0.1 mol zinc nitrate hexahydrate, 0.1 mol hexamethylenetetramine, and 0.02 mol polyethylenimine was used for growing ZnO nanowhiskers. Temperature distribution of the sensor was analyzed by infrared thermal camera. The optimum temperature for highest sensitivity was found to be 250°C although relatively high (64%) sensitivity was obtained even at as low a temperature as 150°C. The power consumption was 72 mW at 250°C, and only 25 mW at 150°C. © 2012 KIEEME. All rights reserved.


Lim J.-H.,Pukyong National University | Ryu J.-Y.,Pukyong National University | Choi W.-C.,Fabrication Center
Transactions on Electrical and Electronic Materials | Year: 2013

This paper describes the highly productive process technologies of microprobe arrays, which were used for a probe card to test a Dynamic Random Access Memory (DRAM) chip with fine pitch pads. Cantilever-type microprobe arrays were fabricated using conventional micro-electro-mechanical system (MEMS) process technologies. Bonding material, gold-tin (Au-Sn) paste, was used to bond the Ni-Co alloy microprobes to the ceramic space transformer. The electrical and mechanical characteristics of a probe card with fabricated microprobes were measured by a conventional probe card tester. A probe card assembled with the fabricated microprobes showed good x-y alignment and planarity errors within ±5 μm and ±10 μm, respectively. In addition, the average leakage current and contact resistance were approximately 1.04 nA and 0.054 ohm, respectively. The proposed highly productive microprobes can be applied to a MEMS probe card, to test a DRAM chip with fine pitch pads. © 2013 KIEEME. All rights reserved.


Kim Y.,Pukyong National University | Noh T.K.,Pukyong National University | Lee Y.W.,Pukyong National University | Kim E.-S.,Busan University of Foreign Studies | And 2 more authors.
Journal of the Korean Physical Society | Year: 2013

In this study, we have demonstrated a fiber-optic hydrogen sensor using a polarization-diversity loop interferometer composed of a polarization beam splitter, two quarter-wave plates, and a polarization-maintaining fiber coated with palladium whose thickness was ~400 nm. One dip in the output interference spectrum of the proposed sensor, chosen as a sensor indicator, was observed to spectrally shift with increasing hydrogen concentration. At a hydrogen concentration of 4%, the sensing indicator showed a wavelength shift of ~2. 48 nm. The response time of the proposed sensor was measured as 10-12. 5 s and did not show significant dependence on the hydrogen concentration except for a hydrogen concentration of 4%. In particular, compared with other hydrogen sensors based on side-polished fibers or fiber gratings, the proposed sensor is much more durable because UV illumination or physical/chemical etching process is not necessary for the optical fiber and thus is highly resistant to external stress applied on a transverse axis of an optical fiber. © 2013 The Korean Physical Society.


Choi W.-C.,Fabrication Center | Ryu J.-Y.,Pukyong National University
Journal of Semiconductor Technology and Science | Year: 2011

This paper presents a new programmable compensation circuit (PCC) for a System-on-Chip (SoC). The PCC is integrated with 0.18-μm BiCMOS SiGe technology. It consists of RF Design-for- Testability (DFT) circuit, Resistor Array Bank (RAB) and digital signal processor (DSP). To verify performance of the PCC we built a 5-GHz low noise amplifier (LNA) with an on-chip RAB using the same technology. Proposed circuit helps it to provide DC output voltages, hence, making the RF system chain automatic. It automatically adjusts performance of an LNA with the processor in the SoC when it goes out of the normal range of operation. The PCC also compensates abnormal operation due to the unusual PVT (Process, Voltage and Thermal) variations in RF circuits.


Choi W.-C.,Fabrication Center | Ryu J.-Y.,Pukyong National University
Microsystem Technologies | Year: 2012

This paper describes the design and fabrication of a guide block and micro probes, which were used for avertical probe card to test a chip with area-arrayed solder bumps. The size of the fabricated guide block was 10 mm 9 6 mm. The guide block consisted of 172 holes to insert micro probes, 2 guide holes for exact alignment, and 4 holes for bolting between the guide block and the housing of a PCB. Pitch and size of the inserting holes were 80 lm, and 90 lm 9 30 lm, respectively. A silicon on insulator wafer was used as the substrate of the guide block to reduce micro probes insertion error. The micro probes were made of nickel-cobalt (Ni-Co) alloy using an electroplating method. The length and thickness of the micro probes were 910 and 20 lm, respectively. A vertical probe card assembled with the fabricated guide block and micro probes showed good x-y alignment and planarity errors within ±4 and ±3 lm, respectively. In addition, average leakage current and contact resistance were approximately 0.35 nA and 0.378 ohm, respectively. The proposed guide block and micro probes can be applied to a vertical probe card to test a chip with area-arrayed solder bumps. © 2012 Springer-Verlag.


Choi W.-C.,Fabrication Center
Microsystem Technologies | Year: 2011

This paper describes the design and fabrication of a MEMS guide plate, which was used for a vertical probe card to test a wafer level packaged die wafer. The size of the fabricated MEMS guide plate was 10.6 × 10.6 cm. The MEMS guide plate consisted of 8,192 holes to insert pogo pins, and four holes for bolting between the guide plate and the housing. To insert pogo pins easily, an inclined plane was defined at the back of each hole. Pitch and diameter of the hole were 650 and 260 μm, respectively. In order to define inserting holes and inclined planes at an exact position, silicon MEMS technology was used such as anisotropic etching, deep reactive etching and more. Silicon was used as the material of the guide plate to reduce alignment mismatch between the pogo pins and solder bumps during a high temperature testing. A combined probe card with the fabricated MEMS guide plate showed good x-y alignment and planarity errors within ±9 and ±10 μm at room temperature, respectively. In addition, x-y alignment and planarity are ±20 and ±16 μm at 125°C, respectively. The proposed MEMS guide plate can be applied to a vertical probe card for burn-in testing of a wafer level packaged die wafer because the thermal expansion coefficient of the MEMS guide plate and die wafer is same. © 2010 Springer-Verlag.


Kim S.-E.,Fabrication Center | Choi W.-C.,Fabrication Center
Transactions on Electrical and Electronic Materials | Year: 2012

This paper proposes a micro gas sensor for measuring H 2S gas. This is based on a SnO 2-CuO multi-layer thin film. The sensor has a silicon diaphragm, micro heater, and sensing layers. The micro heater is embedded in the sensing layer in order to increase the temperature to an operating temperature. The SnO 2-CuO multi layer film is prepared by the alternating deposition method and thermal oxidation which uses an electron beam evaporator and a thermal furnace. To determine the effect of the number of layers, five sets of films are prepared, each with different number of layers. The sensitivities are measured by applying H 2S gas. It has a concentration of 1 ppm at an operating temperature of 270°C. At the same total thickness, the sensitivity of the sensor with multi sensing layers was improved, compared to the sensor with one sensing layer. The sensitivity of the sensor with five layers to 1 ppm of H 2S gas is approximately 68%. This is approximately 12% more than that of a sensor with one-layer. © 2012 KIEEME. All rights reserved.


Choi W.-C.,Fabrication Center | Choi H.-J.,Fabrication Center
IEEE Transactions on Components, Packaging and Manufacturing Technology | Year: 2012

This paper presents a simple and low-cost 3-D process technology for the wafer-level packaging (WLP) of microelectromechanical system (MEMS) devices. A small-sized WLP (1.0 × 1.0 ×0.35 mm) with a hermetically sealed cavity for the moving parts of MEMS devices was fabricated by using specially designed processes. The WLP was developed using three key techniques: through-wafer interconnection, wafer bonding, and bilateral face-MEMS fabrication. The expense and complexity of processes such as silicon deep reactive ion etching and electroplating that arise from bilateral processing for through-wafer interconnection were overcome by using bulk micromachining technology. The fabricated WLP chips with a bonding area of 0.314 mm 2 showed an average shear strength of 9.74 kg/mm 2 and a leak rate less than 7 × 10 -10.cc/sec. In addition, the chips had less than 0.1 dB insertion loss before and after reliability testing. This newly developed 3-D process technology is a good candidate for WLP MEMS fabrication because it is simple and cost-effective. © 2011-2012 IEEE.

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