89 results on '"Chang Auck Choi"'
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2. A p Small-Signal Model of MEMS Series Switches Based on the Parameter- Extraction Method.
- Author
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Jaewoo Lee, Woo-Seok Yang, Changhee Hyoung, Sungweon Kang, and Chang-Auck Choi
- Published
- 2004
- Full Text
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3. The Fabrication of an Applicative Device for Trench Width and Depth Using Inductively Coupled Plasma and the Bulk Silicon Etching Process
- Author
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Chang Auck Choi, Jong-Chang Woo, and Chang-Il Kim
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Materials science ,Fabrication ,business.industry ,Process (computing) ,Electrical engineering ,Creative commons ,Engineering physics ,Electronic, Optical and Magnetic Materials ,Etching (microfabrication) ,Trench ,Electrical and Electronic Engineering ,Inductively coupled plasma ,business ,Silicon etching ,Electronic materials - Abstract
Copyright 2014 KIEEME. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN: 1229-7607 eISSN: 2092-7592 DOI: http://dx.doi.org/10.4313/TEEM.2014.15.1.49 TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS Vol. 15, No. 1, pp. 49-54, February 25, 2014
- Published
- 2014
4. Low power consumption micro C2H5OH gas sensor based on micro-heater and screen printing technique
- Author
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Hyung-Kun Lee, Seok-Hwan Moon, Woo Seok Yang, J.J. Jong, D.-J. Yoo, J. Kim, Choi Nj, Joon-Ki Lee, and Chang Auck Choi
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Microelectromechanical systems ,Materials science ,business.industry ,Direct current ,Metals and Alloys ,Analytical chemistry ,Condensed Matter Physics ,Tin oxide ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Power (physics) ,Surface micromachining ,Semiconductor ,CMOS ,Screen printing ,Materials Chemistry ,Optoelectronics ,Electrical and Electronic Engineering ,business ,Instrumentation - Abstract
Micro C2H5OH gas sensor based on micro-heater and tin oxide thick film was fabricated by using complementary metal-oxide semiconductor (CMOS) compatible micro electro mechanical systems (MEMS) process, which showed low power consumption and high response. Semiconducting SnO2 nano-powders were synthesized via co-precipitation method, and to increase the sensitivity for alcohol gas rare metal dopants were added. Bridge type micro-heater based on Si substrate was fabricated by surface micromachining technique and in the structure of micro-heater, the resistances of two semi-circled Pt heaters are connected to the spreader for thermal uniformity. The response of the micro gas sensor was 0.78 for 2 ppm alcohol with lower power consumption (35 mW) than that of the commercial alcohol gas sensor. The mechanical stability of the sensor was tested under the higher direct current (DC) power than that of the normal operation power and the variation rate of the micro-heater resistance was below 2% after 105 times repetitive 35 mW pulse operations.
- Published
- 2013
5. Use of Gas-Sensor Array Technology in Lung Cancer Diagnosis
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Won Ik Jang, Byeong Jun Lee, Yar Kyeon Kim, Han Young Yu, Youngjun Kim, Chang Geun Ahn, Chang Auck Choi, Ji Eun Lim, Yong Sun Yoon, Jeong-Ho Park, In Bok Baek, and Bong Kuk Lee
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Materials science ,Research groups ,Cellular metabolism ,Sensor array ,Electronic nose ,medicine ,Cancer ,Nanotechnology ,Lung cancer ,medicine.disease - Abstract
Gas-sensor array technology, which has been much utilized in the field of food technology by the name of 'electronic nose' is drawing attention in diagnosing lung cancer based on the analysis of the exhaled human breath. Much understanding has been accomplished about the composition of the volatile organic compounds (VOCs) of the human exhaled breath, in spite of some variations depending on research groups due mainly to lack of the standardization of the sensing procedures. Since VOCs may be produced during the process of cellular metabolism, difference in the cellular metabolism between healthy cells and lung cancer cells are expected to be reflected on the composition variation of the exhaled VOCs. Several studies have attempted to apply the gas-sensor array technology to lung cancer analysis using many different types of sensors including metal oxide, carbon black-polymer composite, surface acoustic wave, and gold nanoparticles. In this mini-review VOC as biomarkers, sensor array technology and application of the array technology for the diagnosis of cancer disease have been described.
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- 2013
6. A Study on the Surface of the Dry Etched TaN Thin Film by Adding The CH4Gas in BCl3/Ar Inductively Coupled Plasma
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Pil-Seung Kang, Chang-Il Kim, Jong-Chang Woo, Young-Hee Joo, Yoon-Soo Chun, Woo Seok Yang, and Chang Auck Choi
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Crystallinity ,Materials science ,Annealing (metallurgy) ,Sputtering ,Electrical resistivity and conductivity ,Surface roughness ,Analytical chemistry ,Transmittance ,Substrate (electronics) ,Thin film - Abstract
Al:ZnO thin films were deposited using the radio frequency magnetron sputtering technique at various temperatures and sputtering powers. With the increase in the deposition temperature and the decrease in the radio frequency sputtering power, the crystallinity was increased and the surface roughness was decreased, which lead to the decrease in the electrical resistivity of the film. It is also clearly observed that, the intensity of the (002) XRD peak increases with increasing the substrate temperature [1, 2]. The electrical resistivity and optical transmittance of the Al:ZnO thin film were analyzed as a function of the post-annealing temperature. It can be seen that with the annealing temperature set at 400℃, the resistivity decreases to a minimum value of 4.1×10-3 Ωcm and the transmittance increases to a maximum value of 85% of the Al:ZnO thin film.
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- 2013
7. The Dry Etching of TiN Thin Films Using Inductively Coupled CF4/Ar Plasma
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Han-Soo Kim, Chang-Il Kim, Jong-Chang Woo, Chang Auck Choi, and Young-Hee Joo
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Materials science ,Analytical chemistry ,chemistry.chemical_element ,Plasma ,Isotropic etching ,Chemical reaction ,Electronic, Optical and Magnetic Materials ,X-ray photoelectron spectroscopy ,chemistry ,Etching (microfabrication) ,Torr ,Dry etching ,Electrical and Electronic Engineering ,Tin - Abstract
In this study, we changed the input parameters (gas mixing ratio, RF power, DC bias voltage, and process pressure), and then monitored the effect on TiN etch rate and selectivity with . When the RF power, DC-bias voltage, and process pressure were fixed at 700 W, - 150 V, and 15 mTorr, the etch rate of TiN increased with increasing content from 0 to 20 % in /Ar plasma. The TiN etch rate reached maximum at 20% addition. As RF power, DC bias voltage, and process pressure increased, all ranges of etch rates for TiN thin films showed increasing trends. The analysis of x-ray photoelectron spectroscopy (XPS) was carried out to investigate the chemical reactions between the surfaces of TiN and etch species. Based on experimental data, ion-assisted chemical etching was proposed as the main etch mechanism for TiN thin films in /Ar plasma.
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- 2013
8. Surface Micromachined Pressure Sensor with Substrate Internal Vacuum Cavity
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Chang Han Je, Woo Seok Yang, Sung Q Lee, and Chang Auck Choi
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Microelectromechanical systems ,Surface (mathematics) ,Materials science ,General Computer Science ,business.industry ,020206 networking & telecommunications ,02 engineering and technology ,Substrate (printing) ,021001 nanoscience & nanotechnology ,Pressure sensor ,Electronic, Optical and Magnetic Materials ,0202 electrical engineering, electronic engineering, information engineering ,Optoelectronics ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Piezoresistive pressure sensors - Abstract
A surface micromachined piezoresistive pressure sensor with a novel internal substrate vacuum cavity was developed. The proposed internal substrate...
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- 2016
9. Analytical Pinning-Voltage Model of a Pinned Photodiode in a CMOS Active Pixel Sensor
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Sungsik Lee, Chang Auck Choi, Arokia Nathan, and Myung Lae Lee
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Materials science ,Cmos active pixel sensor ,business.industry ,Doping ,Process (computing) ,Hardware_PERFORMANCEANDRELIABILITY ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Photodiode ,law.invention ,law ,Condensed Matter::Superconductivity ,Hardware_INTEGRATEDCIRCUITS ,Optoelectronics ,business ,Voltage - Abstract
An analytical pinning-voltage model of a pinned photodiode has been proposed and derived. The pinning-voltage is calculated using doping profiles based on shallow- and exponential-junction approximations. Therefore, the derived pinning-voltage model is analytically expressed in terms of the process parameters of the implantation. Good agreement between the proposed model and simulated results has been obtained. Consequently, the proposed model can be used to predict the pinning-voltage and related performance of a pinned photodiode in a CMOS active pixel sensor.
- Published
- 2011
10. Evaluation of 1/f Noise Characteristics for Si-Based Infrared Detection Materials
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Sein Kwon, Hojun Ryu, Woo Seok Yang, Seong M. Cho, Sang-Hoon Cheon, and Chang Auck Choi
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Amorphous silicon ,Materials science ,General Computer Science ,Silicon ,business.industry ,chemistry.chemical_element ,Microbolometer ,Chemical vapor deposition ,Specific detectivity ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,Antimony ,Sputtering ,Plasma-enhanced chemical vapor deposition ,Electronic engineering ,Optoelectronics ,Electrical and Electronic Engineering ,business - Abstract
Silicon antimony films are studied as resistors for uncooled microbolometers. We present the fabrication of silicon films and their alloy films using sputtering and plasma-enhanced chemical vapor deposition. The sputtered silicon antimony films show a low 1/f noise level compared to plasma-enhanced chemical vapor deposition (PECVD)-deposited amorphous silicon due to their very fine nanostructure. Material parameter K is controlled using the sputtering conditions to obtain a low 1/f noise. The calculation for specific detectivity assuming similar properties of silicon antimony and PECVD amorphous silicon shows that silicon antimony film demonstrates an outstanding value compared with PECVD Si film.
- Published
- 2009
11. Uncooled amorphous silicon 16x16 infrared focal plane arrays development
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Ki-Dong Yang, Seong-M. Cho, Byoung-Gon Yu, Woo Seok Yang, Sang-Hoon Cheon, Chang Auck Choi, and Hojun Ryu
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Amorphous silicon ,Materials science ,business.industry ,Microbolometer ,Biasing ,Noise-equivalent temperature ,Noise figure ,Noise (electronics) ,Responsivity ,chemistry.chemical_compound ,Optics ,chemistry ,Optoelectronics ,business ,Temperature coefficient - Abstract
This paper describes the design and fabrication of 1616 microbolometer infrared focal plane arrays based on iMEMS technology. Amorphous silicon was used for infrared-sensitive material, and it showed the resistance of 18 Mohm and the temperature coefficient of resistivity of -2.4 %. The fabricated sensors exhibited responsivity of 78 kV/W and thermal time constant of 8.0 msec at a bias voltage of 0.5 V. The array performances had satisfactory uniformity less than 5 % within one-sigma. Also, 1/f noise of pixel was measured and the noise factor of was extracted. Finally, we obtained detectivity of and noise equivalent temperature difference of 200 mK at a frame rate of 30 Hz.
- Published
- 2009
12. 1.5 V Sub-mW CMOS Interface Circuit for Capacitive Sensor Applications in Ubiquitous Sensor Networks
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Ahra Lee, Gunn Hwang, Chang Auck Choi, Sungsik Lee, Myung-Lae Lee, and Chang-Han Je
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Engineering ,General Computer Science ,business.industry ,Interface (computing) ,Capacitive sensing ,Diode-or circuit ,Hardware_PERFORMANCEANDRELIABILITY ,Electronic, Optical and Magnetic Materials ,CMOS ,Hardware_INTEGRATEDCIRCUITS ,Electronic engineering ,Wireless ,Electrical and Electronic Engineering ,business ,Wireless sensor network ,Reset (computing) ,Hardware_LOGICDESIGN ,Voltage - Abstract
In this paper, a low-power CMOS interface circuit is designed and demonstrated for capacitive sensor applications, which is implemented using a standard 0.35-μm CMOS logic technology. To achieve low-power performance, the low-voltage capacitance-to-pulse-width converter based on a self-reset operation at a supply voltage of 1.5 V is designed and incorporated into a new interface circuit. Moreover, the external pulse signal for the reset operation is made unnecessary by the employment of the self-reset operation. At a low supply voltage of 1.5 V, the new circuit requires a total power consumption of 0.47 mW with ultra-low power dissipation of 157 μW of the interfacecircuit core. These results demonstrate that the new interface circuit with self-reset operation successfully reduces power consumption. In addition, a prototype wireless sensor-module with the proposed circuit is successfully implemented for practical applications. Consequently, the new CMOS interface circuit can be used for the sensor applications in ubiquitous sensor networks, where low-power performance is essential.
- Published
- 2008
13. Fabrication and Properties of Vanadium Oxide Thin Films for Microbolometer by using Plasma Atomic Layer Deposition Method
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Byoung-Gon Yu, Kwang Ho Kim, Soon-Won Jung, Chang Auck Choi, Sang-Hyun Jeong, and Hyeong-Seon Yun
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Fabrication ,Materials science ,Inorganic chemistry ,Bolometer ,Analytical chemistry ,chemistry.chemical_element ,Vanadium ,Microbolometer ,Oxygen ,Vanadium oxide ,law.invention ,Atomic layer deposition ,chemistry ,law ,Phase (matter) - Abstract
The fabrication of vanadium oxide films directly on Si(100) substrates by plasma atomic layer deposition(ALD) with vanadium oxytriisopropoxide(VOIP) and oxygen as the reactants have been performed at temperature ranging from 250 to . Growth rate of vanadium oxide was /cycle at defined as ALD acceptable temperature window, Vanadium oxide has been shown the different phases at and more than . It has been confirmed that the phase of the films deposited at type and that of the films above type measured at room temperature, respectively. A large change in resistance and small temperature hysteresis corresponding to a temperature has been observed in the vanadium oxide film deposited at temperature .
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- 2008
14. Micromachined air-gap structure MEMS acoustic sensor using reproducible high-speed lateral etching and CMP process
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Sang Choon Ko, Won Ick Jang, Chang Auck Choi, and Chi-Hoon Jun
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Microelectromechanical systems ,Materials science ,Silicon ,business.industry ,Mechanical Engineering ,Electrical engineering ,Oxide ,chemistry.chemical_element ,Capacitance ,Electronic, Optical and Magnetic Materials ,Printed circuit board ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Chemical-mechanical planarization ,Optoelectronics ,Electrical and Electronic Engineering ,business ,Sound pressure ,Air gap (plumbing) - Abstract
This paper presents a micromachined air-gap structure microelectromechanical systems (MEMS) acoustic sensor, which is fabricated via assisted high-speed lateral etching and chemical mechanical polishing (CMP). A sandwich structure (LTO/P2O5/LTO) as a sacrificial layer for the releasing process is proposed to produce an air-gap structure MEMS acoustic sensor. This sandwich structure can be etched selectively in a specific patterned P2O5 layer. In addition, the sandwich structure proved superior to using only low temperature oxide (LTO) layer for the releasing process. We confirmed that the proposed releasing method assisted by lateral etching and CMP is very effective for creating a clean air-gap cavity in MEMS devices. In this work, the air-gap structure MEMS acoustic sensor is based on the capacitance change of a movable thin poly-silicon membrane. A high-gain impedance converter was mounted on a printed circuit board (PCB) with a silicon MEMS acoustic sensor to transform the electrical signal for input acoustic pressure. The membrane size of the MEMS acoustic sensor was 1.5 × 1.5 mm2. The sensitivity achieved was about 0.018–5.17 mV Pa−1. The noise level of the fabricated device was 10 µV Pa−1.
- Published
- 2006
15. A low-loss single-pole six-throw switch based on compact RF MEMS switches
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Chang Auck Choi, Chang Han Je, Sung-Weon Kang, and Jaewoo Lee
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Microelectromechanical systems ,Radiation ,Materials science ,RF switch ,business.industry ,Electrical engineering ,Insertion loss ,Port (circuit theory) ,Electrical and Electronic Engineering ,Condensed Matter Physics ,business - Abstract
A low-loss single-pole six-throw (SP6T) switch using very compact metal-contact RF microelectromechanical system (MEMS) series switches is presented. The metal-contact MEMS switch has an extremely compact active area of 0.4 mm /spl times/ 0.3 mm, thus permitting the formation of an SP6T MEMS switch into the RF switch with a total area of 1 mm/sup 2/. The MEMS switch shows an effective spring constant of 746 N/m and an actuation time of 8.0 /spl mu/s. It has an isolation loss from -64.4 to -30.6dB and an insertion loss of 0.08-0.19 dB at 0.5-20 GHz. Furthermore, in order to evaluate RF performances of the SP6T MEMS switch, as well as those of the single-pole single-throw RF MEMS series switch, we have performed small-signal modeling based on a parameter-extraction method. Accurate agreement between the measured and modeled RF performances demonstrates the validity of the small-signal model. The SP6T switch performed well with an isolation loss from -62.4 to -39.1dB and an insertion loss of 0.19-0.70 dB from dc to 6 GHz between the input port and each output port.
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- 2005
16. A Low Power Analog CMOS Vision Chip for Edge Detection Using Electronic Switches
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Jang-Kyoo Shin, Minho Lee, Hong-Bae Park, Jung-Hwan Kim, Sungho Suh, Jae-Sung Kong, and Chang Auck Choi
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Signal processing ,Engineering ,General Computer Science ,business.industry ,Hardware_PERFORMANCEANDRELIABILITY ,Chip ,Edge detection ,Electronic, Optical and Magnetic Materials ,Electronic switch ,CMOS ,Hardware_INTEGRATEDCIRCUITS ,Vision chip ,Electronic engineering ,Electrical and Electronic Engineering ,Full custom ,business ,Electronic circuit - Abstract
An analog CMOS vision chip for edge detection with power consumption below 20 mW was designed by adopting electronic switches. An electronic switch separates the edge detection circuit into two parts: one is a logarithmic compression photocircuit, and the other is a signal processing circuit for edge detection. The electronic switch controls the connection between the two circuits. When the electronic switch is off, it can intercept the current flow through the signal processing circuit and restrict the magnitude of the current flow below several hundred nA. The estimated power consumption of the chip, with 128 × 128 pixels, was below 20 mW. The vision chip was designed using 0.25 µm 1-poly 5-metal standard full custom CMOS process technology.
- Published
- 2005
17. Miniaturized Electronic Nose System Based on Personal Digital Assistant
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Chang Auck Choi, Yong Shin Kim, Yoon Seok Yang, Hyeon-Bong Pyo, and Seung-Chul Ha
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chemistry.chemical_classification ,Materials science ,General Computer Science ,Electronic nose ,business.industry ,Polymer ,Chip ,Polyimide substrate ,Electronic, Optical and Magnetic Materials ,Data acquisition ,Sensor array ,chemistry ,Electronic engineering ,Optoelectronics ,Electrical and Electronic Engineering ,business ,Electronic circuit - Abstract
A small electronic nose (E-Nose) system has been developed using an 8-channel vapor detection array and personal digital assistant (PDA). The sensor array chip, integrated on a single microheater-embedded polyimide substrate, was made of carbon black-polymer composites with different kinds of polymers and plasticizers. We have successfully classified various volatile organic compounds such as methanol, ethanol, i-propanol, benzene, toluene, n-hexane, n-heptane, and c-hexane with the aid of the sensor array chip, and have evaluated the resolution factors among them, quantitatively. To achieve a PDA-based E-Nose system, we have also elaborated small sensor-interrogating circuits, simple vapor delivery components, and data acquisition and processing programs. As preliminary results show, the miniaturized E-Nose system has demonstrated the identification of essential oils extracted from mint, lavender, and eucalyptus plants.
- Published
- 2005
18. A portable electronic nose (E-Nose) system using PDA device
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Seung-Chul Ha, Seong-Mok Cho, Hyeon-Bong Pyo, Yoon Seok Yang, Yong-Jun Kim, Chang Auck Choi, and Yong-Shin Kim
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Engineering ,Reproducibility ,Electronic nose ,Sensor array ,business.industry ,Embedded system ,Pattern recognition (psychology) ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,Application specific ,Polymer composites ,business ,Computer hardware ,Plastic packaging - Abstract
The electronic nose (e-nose) has been used in food industry and quality controls in plastic packaging. Recently it finds its applications in medical diagnosis, specifically on detection of diabetes, pulmonary or gastrointestinal problem, or infections by examining odors in the breath or tissues with its odor characterizing ability. Moreover, the use of portable e-nose enables the on-site measurements and analysis of vapors without extra gas-sampling units. This is expected to widen the application of the e-nose in various fields including point-of-care-test or e-health. In this study, a PDA-based portable e-nose was developed using micro-machined gas sensor array and miniaturized electronic interfaces. The rich capacities of the PDA in its computing power and various interfaces are expected to provide the rapid and application specific development of the diagnostic devices, and easy connection to other facilities through information technology (IT) infra. For performance verification of the developed portable e-nose system, Six different vapors were measured using the system. Seven different carbon-black polymer composites were used for the sensor array. The results showed the reproducibility of the measured data and the distinguishable patterns between the vapor species. Additionally, the application of two typical pattern recognition algorithms verified the possibility of the automatic vapor recognition from the portable measurements. These validated the portable e-nose based on PDA developed in this study.
- Published
- 2005
19. Surface micromachined thermally driven micropump
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Chi Hoon Jun, Won Ick Jang, Chang Auck Choi, Masayoshi Esashi, and Youn Tae Kim
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Microheater ,Microchannel ,Materials science ,Metals and Alloys ,Analytical chemistry ,Micropump ,Diaphragm (mechanical device) ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Surface micromachining ,Plasma-enhanced chemical vapor deposition ,Etching (microfabrication) ,Stiction ,Electrical and Electronic Engineering ,Composite material ,Instrumentation - Abstract
This paper presents the design, fabrication, and testing of a thermally driven micropump fabricated by surface micromachining. The micropump consists of a membrane of a corrugated diaphragm, a sealed cavity filled with air and buried with n + polysilicon microheater and a microchannel with a pair of nozzle and diffuser valves. The polysilicon membrane was used as a structural layer and low-temperature oxide (LTO) and plasma enhanced chemical vapor deposition (PECVD) oxide as a sacrificial layer. Using gas-phase etching (GPE) process with anhydrous hydrogen fluoride (HF) gas and isopropyl alcohol (IPA) vapor, we successfully fabricated the thermally driven micropmump with no virtually process-induced stiction. The flow rate of the micropump is measured at the applied voltage of 25 V with the duty cycle of 50%. The maximum flow rate of the micropump with the corrugated diaphragm is about 3.1 μl/min at 5 Hz.
- Published
- 2004
20. A self-aligned vertical comb-drive actuator on an SOI wafer for a 2D scanning micromirror
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Chang Auck Choi, Chi-Hoon Jun, Dooyoung Hah, and Chang-Kyu Kim
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Materials science ,Silicon ,business.industry ,Mechanical Engineering ,Silicon on insulator ,chemistry.chemical_element ,Electronic, Optical and Magnetic Materials ,Optics ,Tilt (optics) ,chemistry ,Mechanics of Materials ,Comb drive ,Etching (microfabrication) ,Deep reactive-ion etching ,Wafer ,Electrical and Electronic Engineering ,Actuator ,business - Abstract
A self-aligned vertical comb-drive actuator for a two-axis tilt scanning micromirror is presented. Self-alignment between moving and fixed fingers is essential in order to avoid lateral instability leading to an in-plane rotational pull-in during an actuation. Multilayered masking films have been utilized to fabricate the self-aligned comb fingers. To generate high electrostatic torque, high-aspect ratio comb-drive actuators with 40 µm thick fingers have been realized on a silicon-on-insulator (SOI) wafer utilizing deep reactive ion etching (DRIE) technology. A delay-mask process (DMP) was employed in an etching step of a silicon device layer to assist etching of a buried oxide (BOX) layer at the bottom of narrow (5 µm) and deep (40 µm) silicon trenches. The DC mechanical scan angles of the actuators employed in the two-axis tilt, gimbal-configured micromirror were measured as ±2.1° at 48 V around an inner axis and ±1.8° at 44 V around an outer axis, respectively. The fabricated micromirror with a mirror area of 1 mm × 1 mm has mechanical resonant frequencies of 1.2 kHz around the inner axis (a mirror only) and 0.9 kHz around the outer axis (a frame and the mirror), respectively.
- Published
- 2004
21. Fabrication of MEMS devices by using anhydrous HF gas-phase etching with alcoholic vapor
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Myung Lae Lee, Chi Hoon Jun, Youn Tae Kim, Won Ick Jang, and Chang Auck Choi
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Microelectromechanical systems ,Materials science ,Silicon ,Mechanical Engineering ,chemistry.chemical_element ,Isotropic etching ,Electronic, Optical and Magnetic Materials ,Surface micromachining ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Silicon nitride ,Mechanics of Materials ,Etching (microfabrication) ,Plasma-enhanced chemical vapor deposition ,Electronic engineering ,Electrical and Electronic Engineering ,Phosphosilicate glass - Abstract
In silicon surface micromachining, anhydrous HF GPE process was verified as a very effective method for the dry release of microstructures. The developed gas-phase etching (GPE) process with anhydrous hydrogen fluoride (HF) gas and alcoholic vapor such as methanol, isopropyl alcohol (IPA) was characterized and its selective etching properties were discussed. The structural layers are P-doped multi-stacked polysilicon and silicon-on-insulator (SOI) substrates and sacrificial layers are tetraethylorthosilicate (TEOS), low-temperature oxide (LTO), plasma enhanced chemical vapor deposition (PECVD) oxide, phosphosilicate glass (PSG) and thermal oxides on silicon nitride or polysilicon substrates. We successfully fabricated and characterized micro electro mechanical system (MEMS) devices with no virtually process-induced stiction and no residues. The characteristics of the MEMS devices for microsensor and microactuator, microfluidic elements and optical MEMS application were evaluated by experiment.
- Published
- 2002
22. Effects of phosphorus on stress of multi-stacked polysilicon film and single crystalline silicon
- Author
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Kwangsoo No, Chang Seung Lee, Dang-Moon Wee, Jong Hyun Lee, and Chang Auck Choi
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Materials science ,Silicon ,Dopant ,Mechanical Engineering ,chemistry.chemical_element ,Mineralogy ,engineering.material ,Electronic, Optical and Magnetic Materials ,Stress (mechanics) ,Polycrystalline silicon ,chemistry ,Mechanics of Materials ,Residual stress ,Stress relaxation ,engineering ,Crystalline silicon ,Electrical and Electronic Engineering ,Composite material ,Stress concentration - Abstract
In multi-stacked polysilicon films, the stress was examined in terms of dopant distribution and the polysilicon/polysilicon interface at which phosphorus and oxygen atoms were piled up. The phosphorus dopant introduced the compressive stress in the films. The thin oxidized layer formed at the interface was an important factor governing the stress gradient in the multi-stacked film. This interface effect could be minimized using symmetrical stacking of polysilicon films and resulted in a low stress gradient of -0.15 MPa µm-1 for a 5.3 µm thick polysilicon layer. In single crystalline silicon, the phosphorus dopant induced the tensile stress. The lattice dilation coefficient of 4.5 × 10-24 cm3 for phosphorus was measured using a high-resolution x-ray rocking curve. A stress model was introduced on the basis of the lattice dilation theory to calculate the stress and stress gradient induced by the dopant.
- Published
- 1999
23. Development and application of a laterally driven electromagnetic microactuator
- Author
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Youn Tae Kim, Jong Soo Ko, Dae-Sik Lee, Chang Auck Choi, and Myung Lae Lee
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Microelectromechanical systems ,Microactuator ,Optics ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Etching (microfabrication) ,Leaf spring ,Silicon on insulator ,Wafer ,Reactive-ion etching ,business ,Optical switch - Abstract
A laterally driven electromagnetic microactuator (LaDEM) is introduced, and a micro-optical switch is designed and fabricated as an application. LaDEM offers parallel movement of the microactuator to the silicon substrate surface (in-plane mode). Polysilicon-on-insulator wafers and a reactive ion etching process were used to fabricate high-aspect-ratio vertical microstructures, which allowed the equipping of vertical micromirrors. A fabricated single leaf spring had a width of 1.2 μm, thickness of 16 μm, and length of 920 μm. The resistance of the fabricated leaf spring for the optical switch was 5 Ω. The deflection of the leaf spring started to profoundly increase at about 400 mA, and it showed snap-through phenomenon over that current value. Owing to the snap-through phenomenon, a large deflection of 60 μm was detected at 566 mA.
- Published
- 2002
24. Z-axis capacitive MEMS accelerometer with moving ground masses
- Author
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Chang Han Je, Sungsik Lee, Myung Lae Lee, Woo Seok Yang, Jaewoo Lee, and Chang Auck Choi
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Physics ,Microelectromechanical systems ,Acceleration ,business.industry ,Capacitive sensing ,Acoustics ,Electrode ,Electrical engineering ,Accelerometer ,business ,Capacitance ,Reference electrode ,Displacement (vector) - Abstract
We design, fabricate and characterize a noble high sensitivity z-axis capacitive type MEMS accelerometer which has moving ground masses. The previous MEMS capacitive accelerometers detect the acceleration by measuring the capacitance change between fixed reference electrode and movable sensing electrode. However, capacitive MEMS accelerometer for sensing out-of-plane acceleration shows relatively low sensitivity due to its small displacement. In this paper, we increase the relative displacement between reference electrode and sensing electrode by using movable ground masses. In this way, the reference and sensing electrodes move to an opposite direction for the applied out-of-plane acceleration. The capacitance of the fabricated accelerometer is changed from −135.1 to 140.7fF with average standard deviation of 0.77fF at 0V bias and from −190 to 211.6fF with average standard deviation of 0.74fF at 1V bias for the applied gravitational force (from −1g to 1g). Nonlinearity is 0.1% at 0V bias and 0.23% at 1V bias, respectively.
- Published
- 2010
25. Chip scale packaging with surface mountable solder ball terminals for microsensors
- Author
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Sunghae Jung, Chang Han Je, Ahra Lee, Sungsik Lee, Myoung-Lae Lee, Sangchul Lee, Byoung-Gon Yu, Chang Auck Choi, and Gunn Hwang
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Microelectromechanical systems ,Surface-mount technology ,Materials science ,Chip-scale package ,Bumping ,Mechanical engineering ,Wafer ,Actuator ,Wafer-level packaging ,Flip chip - Abstract
This paper presents a simple and low-cost flip chip bumping method with vertical feedthroughs for MEMS WLCSP. The vertical feedthroughs are fabricated on glass wafer using sand-blasting, and these provide inherent aligning jig for micro-ball arrangement. The experimental evaluations using MEMS accelerometer are also presented. The proposed method can be a more cost-effective solution by eliminating the conventional expensive and complex process including electroplating or ball-aligning jig. The feasibility of WLCSP is experimentally demonstrated by testing the developed devices.
- Published
- 2009
26. Sensitivity tunable capacitive type micro accelerometer
- Author
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Sungsik Lee, Ahra Lee, Byoung Gon Yu, Myung Lae Lee, Gunn Hwang, Chang Auck Choi, Chang Han Je, and Sunghae Jung
- Subjects
Microelectromechanical systems ,Bulk micromachining ,Engineering ,business.industry ,Capacitive sensing ,Electrical engineering ,Optoelectronics ,business ,Accelerometer ,Capacitance ,Sensitivity (electronics) ,Voltage ,DC bias - Abstract
In this paper, we present a novel sensitivity tunable capacitive type micro accelerometer which could adjust its sensitivity. The previous bulk-micromachined accelerometer is hard to make a pattern which is smaller than 1 um with high aspect ratio because of ICP etching errors such as loading effect and footing. In this paper, by making movable ground electrodes which have MEMS actuators, we present a high sensitivity micro accelerometer with a narrow sensing gap under 1 um using conventional bulk micromachining. Unlike previous capacitive type MEMS accelerometers which have anchored ground electrodes, the proposed micro accelerometer has movable ground electrodes. By simply applying DC bias to MEMS actuators, the ground electrodes are moved to the sensing electrodes. The fabricated sensing gap is 1.9 um and it could be reduced to 0.8 um according to the actuation voltage, VDD. The working sensitivity of the micro accelerometer is 0.410 pF/g at VDD=1.0 V, which is higher than 0.125 pF/g with no actuation, VDD=0 V.
- Published
- 2008
27. Sputtered silicon antimony thin film for the infrared detection layer of microbolometer
- Author
-
Byoung Gon Yu, Woo Seok Yang, Se In Kwon, Sang Hoon Cheon, Hojun Ryu, Myung Lae Lee, Seong M. Cho, and Chang Auck Choi
- Subjects
Amorphous silicon ,Materials science ,Silicon ,business.industry ,chemistry.chemical_element ,Microbolometer ,Chemical vapor deposition ,chemistry.chemical_compound ,chemistry ,Antimony ,Sputtering ,Plasma-enhanced chemical vapor deposition ,Electronic engineering ,Optoelectronics ,Thin film ,business - Abstract
We have studied on the sputtered silicon antimony thin film for bolometric materials of mid-IR range application. In order to obtain high detectivity of infrared sensors, the infrared detection materials which have been using today as a resistor must have a high temperature coefficient of resistance (TCR) and low noise. We fabricated silicon films and their alloy films by sputtering and plasma-enhanced chemical vapor deposition. PECVD deposited silicon film has been found to exhibit high level of 1/f noise but having reasonable TCR. On the other hand silicon antimony alloy films have a good TCR comparing to the VO2 and very low levels of 1/f noise than PECVD Si films. Moreover the silicon antimony films have low resistivity and been expected to be the best CMOS compatible material for a high performance microbolometer having high TCR and low 1/f noise.
- Published
- 2008
28. Deformation Reduction of a MEMS Sensor by Stress Balancing of Multilayer
- Author
-
Woo Seok Yang, Seong M. Cho, Byoung Gon Yu, Sang Hoon Cheon, Hojun Ryu, and Chang Auck Choi
- Subjects
Stress (mechanics) ,Microelectromechanical systems ,Surface micromachining ,Cantilever ,Silicon ,chemistry ,Computer science ,Residual stress ,chemistry.chemical_element ,Composite material ,Deformation (meteorology) ,Polyimide - Abstract
Stress balancing of a multilayer is presented to reduce out-of-plane deformation of a MEMS structure for infrared (IR) sensor application. The MEMS structure is designed to have a suspended membrane with two supporting legs, and fabricated by surface micromachining using a sacrificial polyimide. The uncontrolled stress of Si3N4/a-Si:H/Si3N4 multilayer resulted in a large deformation of the membrane, likely causing problems in IR absorption and thermal isolation of the sensor. Flat membrane was successfully achieved by minimizing the residual stress of individual films and adjusting their relative thickness and distribution. Based on simple stress analyses, the deformation of sensor structure is suggested to be dominated by gradient stress rather than mean stress of the multilayer, likewise that of a monitoring cantilever.
- Published
- 2008
29. Sensing gap reconfigurable capacitive type MEMS accelerometer
- Author
-
Sunghye Jung, Chang Han Je, Sungsik Lee, Chang Auck Choi, Gunn Hwang, and Myung-Lae Lee
- Subjects
Microelectromechanical systems ,Materials science ,business.industry ,Capacitive sensing ,Electronic engineering ,Deep reactive-ion etching ,Optoelectronics ,Silicon on insulator ,Accelerometer ,business ,Actuator ,Capacitance ,DC bias - Abstract
A novel sensing gap reconfigurable capacitive type MEMS accelerometer with high sensitivity and high resolution is designed, fabricated and characterized. The present MEMS accelerometer is fabricated by using simple SOI process-DRIE. However, conventional Silicon on Insu lator (SOI) process is hard to make patterns which is smaller than 1 um because of its high aspect ratio and ICP etching error such as loading-effect and under-cutting. So we have adopted a simple idea of the MEMS actuator-stopper system to modulate the sensing gap pr ecisely. Unlike previous capacitive type MEMS accelerometer which has an anchored reference comb electrodes, the proposed accelerometer has a movable reference comb with MEMS electrostatic actuators and stoppers. By simply applying DC bi as to MEMS actuators, the reference comb electrode is moved to the sensing comb structure until the actuators contacting the stoppers. The gap between sensing comb fingers and reference comb fingers is reduced by the gap between actuators and stoppers. In this paper, the initial sensing gap is 1.5um and it reduced to 0.5um, when working. Then, the overall capacitance and sensitivity is simple increased. The capacitance is increased from 3.47pF at the OFF state to 5.35pF at the ON state by applying 2V DC bias. Keyword : capacitive, MEMS, Microelectromechanical system, accelerometer, acceleration
- Published
- 2007
30. Design, Fabrication, and Characterization of a Readout Integrated Circuit (ROIC) for Capacitive MEMS Sensors
- Author
-
Chang Han Je, Chang Auck Choi, Myung Lae Lee, Gunn Hwang, Sungsik Lee, and Sung Hae Jung
- Subjects
Engineering ,business.industry ,Capacitive sensing ,Clock rate ,Electrical engineering ,Signal ,Capacitance ,Phase-locked loop ,Readout integrated circuit ,CMOS ,Hardware_INTEGRATEDCIRCUITS ,Hardware_ARITHMETICANDLOGICSTRUCTURES ,business ,Sensitivity (electronics) - Abstract
A novel readout integrated circuit (ROIC) with tunable sensitivity, variable resolution, and especially multiple and selectable input ranges is designed, fabricated, and characterized for various capacitive MEMS sensors. The ROIC was fabricated by using 0.35 mum 3.3 V CMOS process and consisted of a capacitance-to-time (C-T) converter, a high speed signal counter, a phase-locked loop (PLL), control logics and synchronous peripheral interfaces (SPI). By using SPI, the clock frequency (fCLK) of the ROIC can be changed from 10 MHz to 160 MHz, which results in resolutions up to 14 bit. The measured minimum detectable capacitance of the ROIC were 2.86 fF for fCLK = 10 MHz and 180 aF for fCLK = 160 MHz, which were equivalent to 9 bit and 14 bit resolutions, respectively.
- Published
- 2007
31. A π Small-Signal Model of MEMS Series Switches Based on the Parameter- Extraction Method
- Author
-
Chang-Hee Hyoung, Sung-Weon Kang, Woo Seok Yang, Chang Auck Choi, and Jaewoo Lee
- Subjects
Microelectromechanical systems ,Physics ,Small-signal model ,Series (mathematics) ,Mathematical analysis ,Electrode ,Contact resistance ,Electronic engineering ,Range (statistics) ,Extraction methods ,Capacitance - Abstract
A novel π small-signal model of MEMS series switches is presented based on a parameter-extraction method, which can determine a fringing capacitance (C_f) in the end of each signal line as well as a contact resistance (R_c). For an on-state modeling, the average error of S₁₁ for the π model is 5.1% in the range of 5~35 GHz, whereas that of the conventional model of two-port series-impedance without C_f is 167.2 %. It is noted that the conventional model is not valid anymore for the on-state model and C_f should be taken into account. The small-signal modeling by the proposed π model demonstrates the validity of the approach.
- Published
- 2006
32. Monolithic Electronic Nose System Fabricated by Post CMOS Micromachining
- Author
-
Sang Choon Ko, Young Jun Kim, Seong M. Cho, Hyeon-Bong Pyo, Yoon Seok Yang, Seung-Chul Ha, Chang Auck Choi, and Yong Shin Kim
- Subjects
Microelectromechanical systems ,Bulk micromachining ,Materials science ,business.industry ,Integrated circuit ,law.invention ,Surface micromachining ,CMOS ,Etching (microfabrication) ,law ,Electronic engineering ,Optoelectronics ,Dry etching ,business ,Electronic circuit - Abstract
A monolithic electronic nose system, which has 12 independent channels, was fabricated by post CMOS micromachining process. Read-out integrated circuits were fabricated with the standard CMOS processes with design rule of 0.8 mum. And, the MEMS parts of the electronic nose were fabricated by hybrid etching, composed of bulk micromachining with TMAH (tetramethy lammonium hydroxide) and deep dry etching, on the backside of the wafer after the CMOS processes. Resistance matching circuit, instrumentation amplifier, multiplexer, and transducer circuits with bridge structure were included in the read-out circuitry. And, heat control circuits were also implanted in the monolithic circuit to maintain the temperature of the MEMS sensing parts as constant. Carbon black-polymer composites and Au nano-particles were used as sensor materials. The MEMS parts of the electronic nose were designed to have well-shaped structures. These structures are considered to be suitable for drop coating procedure
- Published
- 2006
33. Sub-ppm Detection of Gold Nanoparticle Transducer Toward Carboxyl Functionality
- Author
-
Hyeon-Bong Pyo, Chang Auck Choi, Young Jun Kim, and Suk-Hyung Cho
- Subjects
Materials science ,Silicon ,chemistry ,Transmission electron microscopy ,Colloidal gold ,Scanning electron microscope ,Electrode ,Analytical chemistry ,Substrate (chemistry) ,Nanoparticle ,chemistry.chemical_element ,Fourier transform infrared spectroscopy ,Nuclear chemistry - Abstract
Gold nanoparticles functionalized with methyl 3-mercaptopropionate (MMP) were synthesized and used as sensor materials to detect acetic acid in the sub-ppm range. The success of the MMP gold nanoparticles was confirmed by high resolution TEM and FTIR. The average diameter was characterized by TEM to be 3.1 nm. Transducer film was formed on a glass or a silicon substrate mounted with interdigitated gold electrodes. Highly porous morphology with sub-micron porosity was observed by SEM images of the nanoparticle film. The nanoparticle sensor was able to reproducibly detect around 50 ppb of acetic acid. Moreover linear relationship between response amplitude and analyte concentration was observed at least from 40 ppb to 2000 ppb
- Published
- 2006
34. Multiplexed polymer surface plasmon sensor with integrated optical coupler
- Author
-
Se Ho Park, Hyeon-Bong Pyo, Chang Auck Choi, and Kwang Hyo Chung
- Subjects
Materials science ,business.industry ,Surface plasmon ,Fresnel equations ,Laser ,Ray ,Collimated light ,law.invention ,Optics ,law ,Prism ,Surface plasmon resonance ,business ,Refractive index - Abstract
In this paper, we describe a novel multiplexed surface plasmon resonance (SPR) sensor which is made of cyclic olefin copolymers (COCs, TOPASTM). This material has excellent chemical resistance, low water uptake (< 0.01%), and high refractive index (nHe-Ne=1.53) suitable to use as an optical coupler (prism) as well as a sensor substrate. We fabricated a standard slide glass sized, prism integrated, and injection molded COC-SPR sensor which are being applied toward the multiplexed detection of DNA single nucleotide polymorphism (SNP). To evaluate the sensitivity of COC-SPR sensor, we first patterned MgF2 on gold-coated COC-SPR sensor and observed the shift of minimum reflectivity (SPR dip) in pixel address. As incident light source we used an expanded, collimated, rectangular shaped He-Ne laser, with a diffuser for beam homogenization. With expanded laser beam we varied incident angle so that the angular shift is expressed as the darkest pixel shift on CCD. For optimized SPR characteristics and sensor configuration, analytical calculations (Fresnel equation) were performed, and the best SPR conditions were found to be dAu~48 nm at wavelength λ=633 nm with respected resonance angle at θSPR =44.2° for COC-SPR sensor.
- Published
- 2005
35. Diversifying chemical selectivity using mixed-ligand gold nanoparticles
- Author
-
Chang Auck Choi, Young Jun Kim, Hyeon-Bong Pyo, and Seong M. Cho
- Subjects
Detection limit ,Analyte ,Thermogravimetric analysis ,Colloidal gold ,Chemistry ,Ligand ,Analytical chemistry ,Molecule ,Nanoparticle ,Selectivity - Abstract
A novel method for systematic variation of chemical selectivity is introduced using mixed-ligand gold nanoparticles. We have shown that altering the composition of ligand molecules attached on the nanoparticle surface affected interaction of the nanoparticle sensors with the analyte vapors. A gold nanoparticle flinctionalized with 4-methylbenzenethiol (4-MBT, -SC/sub 6/H/sub 4/CH/sub 3/) was synthesized and used to produce a series of mixed-ligand nanoparticles of 4-MBT and 4-mercatophenol (4-MP, -SC/sub 6/H/sub 4/OH) with varying ligand composition. High resolution transmission microscopy (HREM) analysis of the nanoparticles confirmed that the ligand-exchange reaction to produce binary-ligand nanoparticles did not affect the size of the resulting nanoparticle diameter (/spl sim/2.3 nm). Thermal gravimetric analysis (TGA) revealed that the amount organic ligand comprising the nanoparticles ranged from 10.4 to 11.3 weight % of the mixed ligand nanoparticles. Especially the two-step mode in weight loss observed in the binary-ligand particles was correlated with the ligand composition. The compositional variation of the ligands in the nanoparticles was well reflected on the selectivity variation as was confirmed by diversified amplitude and response time in the signals. Fairly impressive signal reproducibility was observed at least for ethanol vapor. At least 10 ppm detection limit was observed toward ethanol. S3 showed reasonable linearity ranging from 10 ppm to 100 ppm of ethanol.
- Published
- 2005
36. Wafer-level fabrication of polymer microsensors with integrated heat control
- Author
-
Chang Auck Choi, Dae-Sik Lee, Kwang Hyo Chung, Hyeon-Bong Pyo, Haesik Yang, and Se Ho Park
- Subjects
Atomic layer deposition ,Microelectrode ,Fabrication ,Materials science ,Semiconductor ,business.industry ,Electrode ,Optoelectronics ,Wafer ,Nanotechnology ,business ,Layer (electronics) ,Micropatterning - Abstract
This paper described a novel wafer-level fabrication of polymer microsensors on the injection-molded thin polymer membrane with integrated heat control by conventional semiconductor processing techniques including standard photolithographic methods. A COC 5-in. wafer (1 mm thickness) is fabricated using injection molding method, in which polymer membranes (ca. 130 /spl mu/m thick and 3 mm /spl times/ 6 mm in area) are implemented simultaneously to reduce local thermal mass around micropatterned heaters and temperature sensors. The highly polished surface (ca. 4-nm) of the COC wafer makes it possible to use the standard photolithographic protocols. Gold micropatterns are fabricated for making microheaters, temperature sensors, and microelectrodes. An insulating layer of aluminum oxide (Al/sub 2/O/sub 3/) is prepared by using atomic layer deposition and micropatterning for the electrode contacts. The microdevice for heating and temperature sensing shows improved performance of thermal isolation, and microelectrodes display good electrochemical performances for electrochemical sensors.
- Published
- 2005
37. A single-pole 6-throw (SP6T) antenna switch using metal-contact RF MEMS switches for multi-band applications
- Author
-
Chang Auck Choi, Jaewoo Lee, Chang-Han Je, and Seongweon Kang
- Subjects
Microelectromechanical systems ,Physics ,Multi band ,business.industry ,Stiction ,Transmitter ,Electrical engineering ,Insertion loss ,Antenna (radio) ,business ,Chip ,Voltage - Abstract
A single-pole 6-throw (SP6T) antenna switch using metal-contact RF micro-electro-mechanical system (MEMS) series switches has been developed for multi-band applications. The fabricated metal-contact MEMS switch with a broad signal line gap of 140 /spl mu/m shows a very high isolation loss of -51 dB at 2 GHz because its center-wedge (CW) can control a membrane stiction problem due to the anchor role. The pull-down voltage (V/sub P/) of the MEMS switch is 27.5 V and its leakage current is 26.1 /spl mu/A at V/sub P/. The SP6T antenna switch, which has six SPST MEMS switches, is comprised of two transmitter (Tx) ports and four receiver (Rx) ports for quad-band application. The chip area is very compact to 1 mm/sup 2/ (1.3 mm /spl times/ 0.8 mm). This antenna switch has an isolation loss of -48 dB and an insertion loss of -0.27 dB at 2 GHz between the antenna (ANT) port and transmitter portl (T/spl times/1) at V/sub A/ = 36V.
- Published
- 2005
38. A Π small-signal model of MEMS series switches based on the parameter-extraction method
- Author
-
null Jaewoo Lee, null Woo-Seo Yang, null Chaghee Hyoung, null Sungweon Kang, and null Chang-Auck Choi
- Published
- 2004
39. Novel lithography process for extreme deep trench by using laminated negative dry film resist
- Author
-
Won Ick Jang, Chi Hoon Jun, Youn Tae Kim, Moon-Youn Jung, Myung Rae Lee, and Chang Auck Choi
- Subjects
Microelectromechanical systems ,Fabrication ,Materials science ,Resist ,business.industry ,Trench ,Optoelectronics ,Nanotechnology ,Photomask ,Photoresist ,Edge (geometry) ,business ,Lithography - Abstract
For the fabrication of MEMS(micro electro mechanical system) devices such as HAR(high-aspect-ratio) microstructures with an extreme deep trench, a novel lithography method was newly developed in this study. In the case of the deep trench, the liquid photoresist is not or very thinly coated at edge parts of the trench boundary. And, if a very thick resist coated, it is nearly impossible to develop the photoresist in the deep trench. To solve these problems, it is capped by laminating negative DFR(dry film resist) film on the cavity opening of the deep trench. Then positive photoresist is conventionally coated and patterned by the same photomask for the deep trench. To apply electric signals from outside to inside of the trench, aluminum on sidewall and bottom of the deep trench was successfully patterned by newly developed lithography method.
- Published
- 2004
40. Packaging technology for wavelength tunable filter based on optical MEMS
- Author
-
Yong-Sung Eom, Jongdeog Kim, Byung-Suk Choi, Myung-Lae Lee, Jong-Hyun Lee, Jong-Tae Moon, Ho-Gyeong Yun, Kwang-Seong Choi, Chang Auck Choi, and Chi-Hoon Jun
- Subjects
Microelectromechanical systems ,Materials science ,Optics ,Packaging engineering ,business.industry ,Filter (video) ,Wavelength-division multiplexing ,Optical communication ,Optoelectronics ,Integrated circuit packaging ,business ,Optical filter ,Flip chip - Abstract
One of the key components for the WDM optical communication is a wavelength tunable filter. The packaging technology of the tunable filter with Fabry-Perot cavity based on optical MEMS is investigated for the low power consumption and mass production. The flip chip process with Au-20(wt.%)Sn solder was conducted to integrate two DBR mirrors in parallel with a constant distance for the simple design of packaging structure. TEC fiber was used to achieve a wide range of the optical alignment tolerance for the high coupling efficiency.
- Published
- 2004
41. A self-aligned vertical comb-drive actuator using surface micromachining for scanning micromirrors
- Author
-
Chi-Hoon Jun, Chang Auck Choi, Dooyoung Hah, and Youn Tae Kim
- Subjects
Surface micromachining ,Optical scanners ,Tilt (optics) ,Materials science ,Optics ,Optical testing ,Comb drive ,business.industry ,Actuator ,business - Abstract
A self-aligned vertical comb-drive actuator fabricated using surface micromachining is presented. One- and two-axis tilt scanning micromirrors with the actuators were fabricated and tested. A mechanical tilt angle of /spl plusmn/1.4/spl deg/ at 66 V/sub DC/ was achieved for a 1-mm-diameter micromirror.
- Published
- 2004
42. An iridium oxide reference electrode for use in microfabricated biosensors and biochips
- Author
-
Hyokyum Kim, Chang Auck Choi, Yong Shin Kim, Youn Tae Kim, Sun Kil Kang, Dong-Ho Shin, and Haesik Yang
- Subjects
Blood Glucose ,Working electrode ,Materials science ,Silver ,Time Factors ,Polyurethanes ,Biomedical Engineering ,Bioengineering ,Nanotechnology ,Biosensing Techniques ,Iridium ,Biochemistry ,Reference electrode ,Quinhydrone electrode ,Electrochemistry ,Humans ,Glucose oxidase ,Electrodes ,Polytetrafluoroethylene ,Platinum ,biology ,General Chemistry ,Hydrogen-Ion Concentration ,Palladium-hydrogen electrode ,Electrode ,biology.protein ,Potentiometry ,Biosensor ,Electrode potential - Abstract
In this paper we argue for the use of iridium oxide (IrO(x)) electrodes as quasi-reference electrodes in microfabricated biosensors and biochips that operate in buffered solutions. The simple microfabrication of these electrodes consists of a one-step electrodeposition of IrO(x) onto a microfabricated platinum (Pt) electrode. The IrO(x) electrode potential was found to vary less than 20 mV over 9 days after stabilization for 1 day in a phosphate-buffered saline (PBS) solution; this behavior of the electrode potential was found to be easily reproduced. Moreover, the electrode potential was found to vary by less than 15 mV in the initial hour of its use; this behavior of the electrode potential was also found to be reproducible. The performance of a microfabricated glucose sensor employing an IrO(x) reference electrode is characterized in this paper in order to evaluate the usefulness of this new IrO(x) electrode as a quasi-reference electrode. The glucose sensor consists of a recessed microfabricated Pt electrode array, an electrodeposited IrO(x) film, an inner layer composed of an electropolymerized poly(m-phenylenediamine)/glucose oxidase (PMPD/GOx) film, and an outer or protective layer composed of Teflon and polyurethane (PU) films. The response of this sensor was found to be equivalent to the response of the same sensor employing a commercial Ag/AgCl reference electrode. These results show that a microfabricated IrO(x) electrode can be used as a quasi-reference electrode in microfabricated biosensors and biochips operating in buffered solutions.
- Published
- 2004
43. An independent, temperature-controllable microelectrode array
- Author
-
Haesik Yang, Chang Auck Choi, Kwang Hyo Chung, Chi-Hoon Jun, and Youn Tae Kim
- Subjects
Microelectromechanical systems ,Microheater ,Temperature control ,Fabrication ,business.industry ,Chemistry ,Analytical chemistry ,Multielectrode array ,Temperature measurement ,Analytical Chemistry ,Microelectrode ,Optoelectronics ,Thermal mass ,business - Abstract
Rapid, localized temperature control and negligible power consumption are key requisites for realizing effective parallel and sequential processing in the miniaturized, integrated biomedical microdevices where temperature-dependent biochemical reactions and fluid flow occur. In this study, an independent, temperature-controllable microelectrode array, with excellent temperature control rates and minimal power consumption, has been developed using microelectromechanical systems technology. The microfabricated array consists of Pt microelectrodes (100-microm diameter), with n-doped polysilicon microheaters (1.4-k Omega resistance), and vacuum-sealed cavities of depth 6.2 microm and diameter 200 microm. The thermal characteristics of each microelectrode were evaluated electrochemically through surface temperature measurements. The large heater power coefficient (2.1 +/- 0.1 degrees C mW(-1)) and the short heating and cooling times (less than 0.2 s for T(0.95)) are consequences of the vacuum-sealed cavities, which facilitate good thermal isolation and low thermal mass. The temperature of each microelectrode is independently controlled by a dedicated microheater, without thermally influencing the adjacent microelectrodes significantly.
- Published
- 2004
44. Glucose sensor using a microfabricated electrode and electropolymerized bilayer films
- Author
-
Chang Auck Choi, Hee Chan Kim, Taek Dong Chung, Youn Tae Kim, Haesik Yang, and Chi Hoon Jun
- Subjects
Materials science ,Biomedical Engineering ,Biophysics ,Enzyme electrode ,Analytical chemistry ,chemistry.chemical_element ,Biosensing Techniques ,Phenylenediamines ,Permeability ,chemistry.chemical_compound ,Electrochemistry ,Polyamines ,Glucose oxidase ,Electrodes ,Polytetrafluoroethylene ,Acetaminophen ,biology ,Bilayer ,General Medicine ,Hydrogen-Ion Concentration ,Glucose ,chemistry ,Chemical engineering ,Electrode ,biology.protein ,Tetrafluoroethylene ,Platinum ,Biosensor ,Layer (electronics) ,Biotechnology - Abstract
A new type miniaturized glucose sensor with good selectivity and stable current response has been developed. The structure consists of a recessed rectangular microfabricated platinum electrode, inner layer of two electropolymerized nonconducting films, and outer bilayer of poly(tetrafluoroethylene) (Teflon) and polyurethane (PU) films. Glucose oxidase (GOx) is entrapped during the electropolymerization of a poly( m -phenylenediamine) (PMPD) film in an acetate buffer (AB) solution, on which a highly interference-resistive PMPD film is deposited in a phosphate buffered saline (PBS) solution. The second PMPD film causes no significant decrease in accessibility of glucose to GOx. The inner layer maintains less than 1% permeability to acetaminophen for 12 days. The fairly adhesive outer layer allows stable current response. Due to high permeability, the information about enzyme activity can be obtained without serious error in spite of outer layer intervening between enzymes and solution. The apparent Michaelis–Menten constant and the maximum steady-state current density were 24 mM and 80 μA cm −2 , respectively.
- Published
- 2002
45. Surface properties of ZrO2thin film under Cl2/Ar plasma using angle-resolved X-ray photoelectron spectroscopy
- Author
-
Chang Auck Choi, Chang-Il Kim, Jong-Chang Woo, Yoon-Soo Chun, and Woo Seok Yang
- Subjects
Diffraction ,Physics and Astronomy (miscellaneous) ,Chemistry ,technology, industry, and agriculture ,General Engineering ,Analytical chemistry ,General Physics and Astronomy ,Plasma ,Crystal structure ,Chemical reaction ,Carbon film ,X-ray photoelectron spectroscopy ,Thin film ,Volatility (chemistry) - Abstract
ZrO2 thin films were investigated by surface characterization in a Cl2/Ar gas mixture adaptively coupled plasma system. The plasmas were characterized by optical emission spectroscopy analysis. The crystal structures of the films etched with gases at various mixing ratios were observed by X-ray diffraction. The results can show the damage caused by ion bombardment and chemical reaction of plasma on the crystalline structure of the ZrO2 surface. The chemical reactions of the etched ZrO2 films were investigated by angle-resolved X-ray photoelectron spectroscopy. The etching mechanism of ZrO2 thin films could be explained as Zr interacting with the Cl radical upon adding Cl2, but remaining at the surface owing to the low volatility of ZrClx. From the experimental results, the etching mechanism of ZrO2 was described as ion-assisted chemical reaction.
- Published
- 2014
46. Fabrication of highly sensitive thermal microflow sensor with surface-micromachined vacuum platform for gas and liquid applications
- Author
-
Youn Tae Kim, Won Ick Jang, Chi-Hoon Jun, and Chang Auck Choi
- Subjects
Surface micromachining ,Fabrication ,Materials science ,Microchannel ,business.industry ,Microfluidics ,Thermoelectric effect ,Optoelectronics ,Heat sink ,business ,Thermoelectric materials ,Thermopile - Abstract
For realization of a highly sensitive thermal microflow sensor with small active area of 100 X 100 micrometers 2, a main interest is focused on decreasing thermal loss due to a substrate and air medium. A basic microstructure that was composed of a vacuum cavity with 6.2 micrometers depth and a stacked membrane was formed by the DECTOR (deep cavity using trench oxidation and release) process using silicon surface micromachining. On the vacuum platform, a n+-doped heater and two n+/p+-doped thermopiles with 1.0-micrometers -width poly-Si lines and Pt RTDs as major parts of the flow sensor were subsequently implemented by CMOS processing. The completed sensor had a microfluidics with a microchannel of 500(w) X 200(d) micrometers 2. The thermopiles as main temperature sensors showed fast thermal response time of 68 microsecond(s) and maximum thermoelectric responsivity of 25 mV/mW. Flow measurements up to 430 sccm for air and 80 (mu) l/min for water revealed that the sensor outputs were significantly enhanced with the increase of the heater power and decrease of the distance between the heater and thermopile hot junction. Irrespective of a much smaller active area compared to bulk-micromachined thermal flow sensors, a high sensitivity of about 3.08 X 10-2 mV/mW/sccm and 2.3 X 10-2 mV/mW/((mu) l/min) was achieved for air and water as working fluid, respectively. Thanks to the vacuum platform and optimized sensor configuration, it is possible to improve flow sensitivity and to extend a linear flow range, accompanying with a reduced sensor size and low power consumption.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
- Published
- 2001
47. Temperature-Addressable Microelectrode Array
- Author
-
Chang Auck Choi, Chi-Hoon Jun, Haesik Yang, and Youn Tae Kim
- Subjects
Microheater ,Materials science ,business.industry ,technology, industry, and agriculture ,Analytical chemistry ,Multielectrode array ,Electrolyte ,Microelectrode ,Surface micromachining ,Power consumption ,Trench ,Electrode ,Optoelectronics ,business - Abstract
A new temperature-addressable microelectrode array with low power consumption has been developed using surface micromachining. It consists of 96 temperature-controllable microelectrodes, and each microelectrode contains a vacuum-sealed cavity, an n+-doped poly-Si microheater, and an electrically isolated electrode. The vacuum-sealed cavity was employed for thermal isolation and low power consumption and was fabricated by using the DECTOR (DEep Cavity using Trench Oxidation and Release) process. The performance of the microelectrode was evaluated electrochemically. The microelectrode in electrolytes showed better heating/cooling characteristics.
- Published
- 2001
48. Formation of low-stress multilayered thick polysilicon films for fabrication of microsystems
- Author
-
Won Ick Jang, Youn Tae Kim, Myung-Lae Lee, and Chang Auck Choi
- Subjects
Surface micromachining ,Materials science ,Structural material ,Dopant ,Annealing (metallurgy) ,Doping ,Dry etching ,Chemical vapor deposition ,Composite material ,Microstructure - Abstract
The effects of impurity doping and heat treatments on the characteristics of thick polysilicon films were studied for development of the structural materials in the MEMS. In this study, 8-15 layers of 6.5-12 micrometers thickness polysilicon films were deposited to have a symmetrical structure using low-pressure chemical vapor deposition with a novel stacking method. We have measured the physical and structural characteristics using micromachined test patterns to verify the minimal stress and stress gradient in the polysilicon layers, according to the film stacking, doping, and thermal treatment methods. The multilayer film revealed the complex orientation composed of (100), (220) and (311) grains after annealing and showe4d a higher doping concentration induced a higher compressive stress of 70 Mpa since phosphorus gave rise to a compressive stress in a polysilicon film. However, the doping method for the most uniform distribution of phosphorus induced the lowest stress gradient among all samples. A polysilicon microresonator with thickness of 6.5 micrometers were manufactured by the symmetrical stacking and optimum doping method in which the dopant concentration was lowered and annealing at 1000 degrees C. The film had a low stress of 7.6 MPa and a low stress gradient of -0.15 MPa/micrometers and revealed good slopes of sidewalls after dry etching. The fabricated test structure for a micro gyroscope showed that the driving resonant frequency and the sensitivity was measured as 9,175 Hz and 5 mV-sec/deg under the condition of a static angular velocity, respectively.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
- Published
- 2000
49. Silicon surface micromachining of a deep vacuum cavity structure and its application to a microflow sensor
- Author
-
Chi-Hoon Jun, Youn Tae Kim, Won Ick Jang, and Chang Auck Choi
- Subjects
Microelectromechanical systems ,Materials science ,Silicon ,Precision engineering ,business.industry ,chemistry.chemical_element ,Nanotechnology ,Dielectric ,Thermopile ,Surface micromachining ,chemistry ,Thermal ,Optoelectronics ,Dielectric loss ,business - Abstract
Main interests for MEMS devices are to reduce thermal, dielectric and magnetic loss in active areas due to a substrate and an air medium. For this purpose, deep vacuum cavity structures with planarized stacked membranes were fabricated by the DECTOR process based on silicon surface micromachining. We discuss details of the developed process, especially the effects of a Si trench geometry, post- annealing of the poly-Si layer and HF release conditions on completion of the vacuum structure. To identify validity of the proposed microstructures, thermal microflow sensors having an n+-doped heater and two n+- /p+-doped thermopiles with poly-Si lines were implemented on the various cavity structures of 100 by 100 by 6.2 micrometers 3 using additional CMOS batch processing. The heating efficiency of the sensor on the vacuum cavity is increased by a factor of 5.8 and 1.7 compared to the structures with residual oxides and the air cavity, respectively. It is also found that the sensitivity using the downstream thermopile of 2.5 M(Omega) , 1.53 by 10-1 mV/(m/s)/mW under 10 mW input power, is about ten and three times higher than corresponding values with residual oxides and the air cavity. Therefore, the configuration employing the deep vacuum cavity structure has advantages of low power consumption and the high sensitivity. These results support versatile MEMS applications.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
- Published
- 2000
50. Fabrication of surface-micromachined thermally driven micropump by anhydrous HF gas-phase etching with 2-propanol
- Author
-
Chi Hoon Jun, Myung Lae Lee, Chang Auck Choi, Won Ick Jang, and Youn Tae Kim
- Subjects
Surface micromachining ,Materials science ,Silicon ,chemistry ,Chemical engineering ,Plasma-enhanced chemical vapor deposition ,Etching (microfabrication) ,Stiction ,Anhydrous ,Micropump ,chemistry.chemical_element ,Chemical vapor deposition - Abstract
In silicon surface micromachining, the HF GPE process was verified as a very effective method for the dry release of microstructures. The developed GPE system with anhydrous HF gas and 2-propanol vapor was characterized and its selective etching properties were discussed. The polysilicon membrane was used as a structural layer and LTO and PECVD oxide as a sacrificial layer. We successfully fabricated the surface micromachined microstructures of a thermally driven micropump with no virtually process-induced stiction and no residues after the GPE of sacrificial oxides on polysilicon substrates.
- Published
- 2000
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