• JSTS:Journal of Semiconductor Technology and Science
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• v.1 no.2
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• pp.132-139
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• 2001

We considered the uniformity of fabricated micromirror arrays by characterizing the fabrication process and calculating the appropriate driving voltages of micromirrors used as virtual photomask in maskless photolithography. The uniformity of the micromirror array in terms of driving voltage and optical characteristics is adversely affected by factors, such as the air gap between the bottom electrode and the mirror plate, the spring shape and the deformation of the mirror plate or torsion spring. The thickness deviation of the photoresist sacrificial layer, the misalignment between mirror plate and bottom electrode, the aluminum deposition condition used to produce the spring and the mirror plate, and initial mirror deflection were identified as key factors. Their importance lies in the fact that they are related to air gap deviations under the mirror plate, asymmetric driving voltages in left and right mirror directions, and the deformation of the Al sring or mirror plate after removal of the sacrificial layer. The plasma ashing conditions used for removing the sacrificial layer also contributed to the deformation of the mirror plate and spring. Driving voltages were calculated for the pixel operation of the micromirror array, and the non-uniform characteristics of fabricated micromirrors were taken into consideration to improve driving performance reliability.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.389-392
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• 2005

In the maskless photolithography based on the Digital Micromirror Device (DMD) by Texas Instruments Inc. (TI), the micromirror array works as a virtual photomask to write patterns directly onto Flat Panel Display (FPD) at high speed with low cost. However, it is neither simple to generate region-based patterns for the micromirror array nor easy to deliver sequences of patterns for the micromirror controller. Moreover, the quality of lithography yields the precise synchronization between generating sequence of patterns and irradiation rate off micromirrors. In this study, the region-based pattern generating system for maskless photolithography is devised. To verify salient features of devised functionalities, the prototype system is implemented and the system is evaluated with actual DMD based photolithography. The results show that proposed pattern generating method is proper and reliable. Moreover, the devised region-based pattern generating system is robust and precise enough to handle any possible user specified mandate and to achieve the quality of photolithography required by FPD manufacturer.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1954-1956
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• 1996

In this paper, we measured the reflectance of the $100{\mu}m{\times}100{\mu}m$ micromirror. In order to reduce the size of the HeNe laser beam, an eyepiece and an objective lens were used. CCD camera was used to the monitor the position and focusing. It was found that the diameter of the focused laser beam was about $3{\mu}m$. The reflectance of the reflectance of the micromirror was over the surface and 87% of the commercial mirror.

• Proceedings of the KIEE Conference
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• 1998.07g
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• pp.2547-2549
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• 1998

Automatic yield-test equipment for micro mirror array using image processing was developed. This computerized test equipment can classify the error states of the micromirrors. The test results are displayed on the monitor as a map which shows the error states and position. It is possible to measure yield and reliability with this test equipment for micromirror array using image processing.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.49-52
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• 2003

Single crystalline silicon (SCS) was adopted for a reliable micromirror array of biochip fabrication applications. SCS has excellent mechanical properties and smooth surface, which is the best material for micromirror devices. The mirror array has $16{\times}16$ micromirrors and each mirror has a $120{\mu}m{\times}100{\mu}m$ reflective surface. The micromirror has simple torsional beam springs and electrostatic force was used for driving. The designed tilting angle was $9.6^{\circ}$, and the tilting angles were measured according to applied voltages. The surface roughness was measured by a laser profiler. The response time was measured using He-Ne laser and position sensitive diode (PSD), and the lifetime was checked for reliability proof.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.6
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• pp.270-275
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• 2005

In order for the application of the in-vivo endoscopic biopsy, a micromirror which can be driven at a low voltage is required. In this paper, a two-step micromirror composed of bottom electrodes, moving plate and top mirror plate is proposed. Because an electrical wiring of two plates are separated, they can be actuated separately. Therefore, an intermediate moving plate plays an important role in reducing the driving voltage in half. The designed device was fabricated by the surface micromachining. Maximum rotation angle of $6.3^{\circ}$ was obtained by applying DC 48V, while a conventional one-step mirror pulled down at DC 120V. The designed structure can be used in microphotonic applications requiring low driving voltage.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.927-928
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.623-624
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• 2011

• Journal of the Korean Society for Precision Engineering
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• v.23 no.11 s.188
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• pp.116-125
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• 2006

MEMS and LIGA technologies have been used for fabricating microstructures, but their shape is not 3D because of difficulty for preparation of many masks. To fabricate 3D microstructures, microstereolithography technology based on Digital Micromirror Device($DMD^{TM}$) was introduced. It has no need of masks and is capable of fabricating high aspect ratio microstructures. In this technology, STL file is the standard format as the same of conventional rapid prototyping system, and 3D parts are fabricated by layer-by-layer according to 2D section sliced from STL file. The UV light source is illuminated to DMD which makes bitmap images of 2D section, and they are transferred and focused on resin surface. In this paper, we addressed optical design of microstereolithography system in consideration of light path according to DMD operation and image-forming on the resin surface using optical design program. To verify the performance of implemented microstereolithography system, 3D microstructures with complexity and high aspect ratio were fabricated.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.1
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• pp.98-105
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• 2000

The projectors using liquid crystal display(LCD) have faults such as low optical efficiency, low brightness and even heat generation. To solve these problems reflective-type spatial light modulators based on MEMS (Microelectromechanical Systems) technology have emerged. Digital Micromirror DeviceTM(DMDTM), which was already developed by Texas Instruments Inc., and Thin-film Micromirror ArrayTM(TMATM), which has been recently developed by Daewoo Electronics Co., are the representative examples. The display using TMATM has particularly much higher optical efficiency than other projectors. But the micromirrors manufactured by semiconductor processes have inevitable distortion because of the limitations of the manufacturing processes, so that the distortions of their surfaces have great influence on the optical efficiency of the projector. This study investigated the effects of mirror flatness on the optical performance, including the optical efficiency, of the TMATM projector. That is to say, as a part of the efforts to enhance the performance of the TMATM projector, how much influence the form errors of a micromirror surface exert on the optical efficiency and the modulation of gray scale of the projector were analyzed through a pertinent modeling and simulations.