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Choi,Chang Auck,Jang,Won Ick,Lee,Chang Seung,Hong,Youn Shik,Lee,Jong Hyun,Kwon,Oh Joon,Baek,Jong Tae,Yoo,Hyung Joun 대한전자공학회 1997 ICVC : International Conference on VLSI and CAD Vol.5 No.1
The development of the surface micromachining process for micro gyroscope fabrication is presented in this paper. The 5.3㎛ thickness of doped polysilicon actuator structures have been fabricated successfully with using multi step polysilicon deposition and POCl₃ doping process, and also by using HF gas-phase etching process for 1.5 ㎛ thickness of sacrificial oxide. After annealing and sacrificial oxide removal, the final compressive stress and stress gradient in the doped polysilicon is measured as 46 MPa and -0.5 MPa/㎛, respectively.
Dry Etching Characteristics of Indium Zinc Oxide Thin Films in Adaptive Coupled Plasma
Woo, Jong-Chang,Choi, Chang-Auck,Kim, Chang-Il The Korean Institute of Electrical and Electronic 2013 Transactions on Electrical and Electronic Material Vol.14 No.4
The etching characteristics of indium zinc oxide (IZO) in $Cl_2/Ar$ plasma were investigated, including the etch rate and selectivity of IZO. The IZO etch rate showed non-monotonic behavior with increasing $Cl_2$ fraction in the $Cl_2/Ar$ plasma, and with increasing source power, bias power, and process pressure. In the $Cl_2/Ar$ (75:25%) gas mixture, a maximum IZO etch rate of 87.6 nm/min and etch selectivity of 1.09 for IZO to $SiO_2$ were obtained. Owing to the relatively low volatility of the by-products formation, ion bombardment was required, in addition to physical sputtering, to obtain high IZO etch rates. The chemical state of the etched surfaces was investigated with X-ray photoelectron spectroscopy. These data suggested that the IZO etch mechanism was ion-enhanced chemical etching.
Woo, Jong-Chang,Choi, Chang-Auck,Kim, Chang-Il The Korean Institute of Electrical and Electronic 2014 Transactions on Electrical and Electronic Material Vol.15 No.1
In this study, we carried out an investigation of the etch characteristics of silicon (Si) film, and the selectivity of Si to $SiO_2$ in $SF_6/O_2$ plasma. The etch rate of the Si film was decreased on adding $O_2$ gas, and the selectivity of Si to $SiO_2$ was increased, on adding $O_2$ gas to the $SF_6$ plasma. The optical condition of the Si film with this work was 1,350 nm/min, at a gas mixing ratio of $SF_6/O_2$ (=130:30 sccm). At the same time, the etch rate was measured as functions of the various etching parameters. The X-ray photoelectron spectroscopy analysis showed the efficient destruction of oxide bonds by ion bombardment, as well as the accumulation of high volatile reaction products on the etched surface. Field emission auger electron spectroscopy analysis was used to examine the efficiency of the ion-stimulated desorption of the reaction products.
The Dry Etching of TiN Thin Films Using Inductively Coupled CF<sub>4</sub>/Ar Plasma
Woo, Jong-Chang,Choi, Chang-Auck,Joo, Young-Hee,Kim, Han-Soo,Kim, Chang-Il The Korean Institute of Electrical and Electronic 2013 Transactions on Electrical and Electronic Material Vol.14 No.2
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 $SiO_2$. 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 $CF_4$ content from 0 to 20 % in $CF_4$/Ar plasma. The TiN etch rate reached maximum at 20% $CF_4$ 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 $CF_4$/Ar plasma.
1.5 V Sub-mW CMOS Interface Circuit for Capacitive Sensor Applications in Ubiquitous Sensor Networks
Sungsik Lee,Ahra Lee,Chang-Han Je,Myung-Lae Lee,Gunn Hwang,Chang-Auck Choi 한국전자통신연구원 2008 ETRI Journal Vol.30 No.5
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.
Evaluation of 1/f Noise Characteristics for Si-Based Infrared Detection Materials
Hojun Ryu,Sanghoon Cheon,Seong Mok Cho,Woo Seok Yang,Chang Auck Choi,Sein Kwon 한국전자통신연구원 2009 ETRI Journal Vol.31 No.6
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.
Analytical Pinning-Voltage Model of a Pinned Photodiode in a CMOS Active Pixel Sensor
( Sung Sik Lee ),( Arokia Nathan ),( Myung Lae Lee ),( Chang Auck Choi ) 한국센서학회 2011 센서학회지 Vol.20 No.1
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.
Ko, Sang Choon,Jun, Chi-Hoon,Jang, Won Ick,Choi, Chang-Auck IOP 2006 Journal of micromechanics and microengineering Vol.16 No.10
<P>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/P<SUB>2</SUB>O<SUB>5</SUB>/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 P<SUB>2</SUB>O<SUB>5</SUB> 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 mm<SUP>2</SUP>. The sensitivity achieved was about 0.018–5.17 mV Pa<SUP>−1</SUP>. The noise level of the fabricated device was 10 µV Pa<SUP>−1</SUP>.</P>
BCl<sub>3</sub>/Ar 유도결합 플라즈마 안에 CH<sub>4</sub> 가스 첨가에 따른 건식 식각된 TaN 박막 표면의 연구
우종창,최창억,양우석,주영희,강필승,전윤수,김창일,Woo, Jong-Chang,Choi, Chang-Auck,Yang, Woo-Seok,Joo, Young-Hee,Kang, Pil-Seung,Chun, Yoon-Soo,Kim, Chang-Il 한국전기전자재료학회 2013 전기전자재료학회논문지 Vol.26 No.5
In this study, the plasma etching of the TaN thin film with $CH_4/BCl_3/Ar$ gas chemistries was investigated. The etch rate of the TaN thin film and the etch selectivity of TaN to $SiO_2$ was studied as a function of the process parameters, including the amount of $CH_4$. X-ray photoelectron spectroscopy (XPS) and Field-emission scanning electron microscopy (FE-SEM) was used to investigate the chemical states of the surface of the TaN thin film.