• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.2
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• pp.103-106
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• 2000

ZnO is a wide-bandgap II-IV semiconductor and has a variety of potnetial applications. ZnO exhibits good piezoelectric, photoelectric and optical properties, and is a good candidate for an electroluminescence device. ZnO films have been deposited on (001) sapphire by PLD technique. Nd:YAG pulsed laser was operated at a wavelength of $\lambda=355nm$. The ZnO films were deposited at oxygen pressures from base to 500 mTorr. The substrate temperatures was increased from $200^{\circ}C\; to\;700^{\circ}C$ films showed strong UV emission by increasing the partial oxygen pressure. We have investigated the relationship between partial oxygen pressure and the intensity of UV emission.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.69-70
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• 2008

Micro resonators have been actively investigated for bio/chemical sensors and RF M/NEMS devices. Among various materials, SiC is a very promising material for micro/nano resonators since the ratio of its Young's modulus, E, to mass density, $\rho$, is significantly higher than other semiconductor materials, such as, Si and GaAs. Polycrystalline 3C-SiC cantilever with different lengths were fabricated using a surface micromachining technique. Polycrystalline 3C-SiC micro resonators were actuated by piezoelectric element and its fundamental resonance was measured by a laser vibrometer in air and vacuum at room temperature, respectively. For the cantilever with $100{\mu}m$ length, $10{\mu}m$width and $1.3{\mu}m$ thickness, the fundamental frequency appeared at 147.2 kHz.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1530-1535
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• 1992

An optical method of phase shifting interferometry is presented for the 3-dimensional profile measurement of mirror surfaces with nanometer resolution. A series of optical interferometric fringes are generated by comparing the surface to be measured with a reference flat. The fringes are captured by a CCD camera and then analyzed to obtain actual surface profile. Detailed principles are described along with necessary image processing algorithms. finally, several measurement examples are discussed which were performed on lapped surfaces, hard discs, and semiconductor wafers.

• Electrical & Electronic Materials
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• v.8 no.6
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• pp.816-822
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• 1995

본 고에서는 지구환경문제에 관련된 가스와 그들의 검지를 위한 가스센서에 관하여 살펴보고자 한다. 환경오염을 방지하려는 노력과 대책이 전세계적으로 추진되고 있는 시점에서 특히 대기오염의 주범인 환경가스에 대한 고성능 센서의 개발은 필수불가결하다. 그러나 현재에 사용되고 있는 환경가스센서는 차량의 배기계통에 사용되는 산소센서나 연소배출가스를 검지하는 소수의 가스센서외에는 아직 실용화되지 못하고 있다. 따라서 고온, 부식등의 과혹한 조건하에서 안정하고, 고성능의 센서의 개발은 물론 센서를 구동시키는데 필연적인 신호처리 등 주변기술 또한 병행해서 발달되어야 할 것이다.

• Journal of Korean Vacuum Science & Technology
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• v.3 no.2
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• pp.126-129
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• 1999

PbTio3 is a promising material with perovskite structure for pyroelectric sensor applications with its superior pyroelectric properties, low dielectric constants, and low piezoelectric constants. Growth of pyroelectric thin films in general, needs relatively higher temperatures than those of conventional Si semiconductor processing However, low growth temperature is advantageous for the device integration. We report the low temperature (350$^{\circ}C$) growth of PbTio3 thin films by 3-gun DC magnetron reactive sputtering. The effects of substrate temperature, Pb-flux, and total pressure on crystalinity and preferred orientation of PbTio3 thin films are reported.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.372-379
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• 1998

A new 6 degrees-of-freedom micro stage, based on parallel mechanisms and actuated by using piezoelectric elements, has been developed for the application of micro positioning such as semiconductor manufacturing devices, high precision optical measurement systems, and high accurate machining. The micro stage structure consists of a base platform and an upper platform(stage). The base platform can effectively generates planar motion with yaw motion, while the stage can do vertical motion with roll and pitch motions with respect to the base platform. This separated structure has an advantage of less interference among actuators. The forward and inverse kinematics of the micro stage are discussed. Also, through linearization of kinematic equations about an operating point on the assumption that the configuration of the micro stage remains essentially constant throughout a workspace is performed. To maximize the workspace of the stage relative to fixed frame, an optimal design procedure of geometric parameter is shown. Hardware description and a prototype are presented. The prototype is about 150mm in height and its base platform is approximately 94mm in diameter. The workspace of the prototype is obtained by computer simulation. Kinematic calibration procedure of the micro stage and its results are presented.

• Journal of Sensor Science and Technology
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• v.4 no.2
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• pp.7-13
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• 1995

A new FET type semiconductor pressure sensor (PSFET : pressure sensitive field effect transistor) was fabricated and its operational characteristics were investigated. A ZnO thin film as a piezoelectric layer, $5000{\AA}$ thick, was deposited on a gate oxide of FET by RF magnetron sputtering. The deposition conditions to obtain a c-axis poling structure were substrate temperature of $300^{\circ}C$, RF power of 140watt, and working pressure of 5mtorr in Ar ambience. The fabricated PSFET device showed good linearity and stability in the applied pressure range($1{\times}10^{5}\;Pa{\sim}4{\times}10^{5}\;Pa$).

• Tribology and Lubricants
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• v.33 no.2
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• pp.52-58
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• 2017

An ultra-high precise ejection process is essential in a dispensing system for fabricating various precision parts such as a semiconductor, LED, and camera module. The size of such parts has been decreasing, which implies that a precise ejecting technique is required. A phosphor-containing liquid is ejected via a dispenser using dual piezoelectric actuators that are used for generating a high-speed dispensing mechanism. The rod and nozzle continuously contact in high speed to eject the liquid. However, the high-strength filler or phosphor in the liquid causes wear on the surfaces of the rod and nozzle during the dispensing process. As a result, the ejection reliability decreases as the wear on the surfaces increases. Therefore, it is necessary to estimate the wear characteristics of the rod and nozzle via an experiment and FE analysis. Reliability rests up to 1,000 cycles are conducted under relatively severe conditions. The flow rate and surfaces roughness of the rod and nozzle are measured in each ejection cycle. The surface images and wear volume are obtained before and after the tests and the ejection reliability is confirmed by measuring the flow rate of the liquid. The experimental results show that the ejection reliability is maintained up to 1,000k cycles; these results are validated by the simulation results.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.2
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• pp.44-48
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• 2007

In recent years, the size of plane substrates and semiconductor wafers has increased. As conventional contact transportation systems composed of, for example, carrier rollers, belt conveyers, and robot hands carry these longer and wider substrates, the increased weight results in increased potential for fracture. A noncontact transportation system is required to solve this problem. We propose a new noncontact transportation system combining acoustic viscous and aerostatic forces to provide damage-free transport. In this system, substrates are supported by aerostatic force and transported by acoustic viscous streaming induced by traveling wave deformation of a disk-type stator. A ring-type piezoelectric transducer bonded on the stator excites vibration. A stator with a high Q piezoelectric transducer can generate traveling vibrations with amplitude of $3.2{\mu}m$. Prior to constructing a carrying road for substrates, we clarified the basic properties of this technique and stator vibration characteristics experimentally. We constructed the experimental equipment using a rotational disk with a 95-mm diameter. Electric power was 70 W at an input voltage of 200 Vpp. A rotational torque of $8.5\times10^{-5}Nm$ was obtained when clearance between the stator and disk was $120{\mu}m$. Finally, we constructed a noncontact transport apparatus for polycrystalline silicon wafers $(150(W)\times150(L)\times0.3(t))$, producing a carrying speed of 59.2 mm/s at a clearance of 0.3 mm between the stator and wafer. The carrying force when four stators acted on the wafer was $2\times10^{-3}N$. Thus, the new noncontact transportation system was demonstrated to be effective.

• Journal of IKEEE
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• v.17 no.1
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• pp.71-76
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• 2013

AlGaN/GaN HEMTs (High electron mobility transistors) with narrow channel were fabricated and the effect of channel scaling on the device were investigated. The devices were fabricated using e-beam lithography to have same channel length of $1{\mu}m$ and various channel width from 0.5 to $9{\mu}m$. The sheet resistance of the channel was increased corresponding to the decrease of channel width and the increase was larger at the width of sub-${\mu}m$. The threshold voltage of the HEMT with $1.6{\mu}m$ and $9{\mu}m$ channel width was -2.85 V. The transistor showed a variation of 50 mV at the width of $0.9{\mu}m$ and the variation 350 mV at $0.5{\mu}m$. The transconductance of 250 mS/mm was decreased to 150 mS/mm corresponding to the decrease of channel width. Also, the gate leakage current of the HEMT decreased with channel width. But the degree of was reduced at the width of sub-${\mu}m$. It was thought that the variation of the electrical characteristics of the HEMT corresponding to the channel width came from the reduced Piezoelectric field of the AlGaN/GaN structure by the strain relief.