Low-Power Liquid Lens Having Si Cylinder Chamber for Capsule Endoscope
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1075-J07-13
Low-Power Liquid Lens Having Si Cylinder Chamber for Capsule Endoscope Sangwon Seo1,2, Seungoh Han3, Jun-Ho Seo2, Young-Mok Kim2, Moon-Sik Kang2, Nam-Gi Min2, Woo-Bum Choi1, and Man-Young Sung2 1 BNP Science CO., LTD., Paju-City, 413-843, Korea, Republic of 2 Korea University, Seoul, 136-713, Korea, Republic of 3 Hoseo University, Asan-City, 336-795, Korea, Republic of ABSTRACT The liquid lens based on MEMS technology can be an appropriate solution to improve the imaging capability of a capsule endoscope because it can be realized small enough and also consume negligible power. In this paper, a cylinder-type liquid lens was designed to minimize the dead area and then fabricated with MEMS technology combining the silicon thin-film process and the wafer bonding process where the multiple dielectric layer of Teflon, silicon nitride and thermal oxide was formed on the cylinder wall. The focal length of the lens module including the fabricated liquid lens was changed reproducibly as a function of the applied voltage. With the change of 30V in the applied bias, the focal length of the constructed lens module could be tuned in the range of about 42cm. The fabricated liquid lens was also proven to be small enough to be adopted in the capsule endoscope, which means the liquid lens can be utilized for the imaging capability improvement of the capsule endoscope.
INTRODUCTION During the past few years, MEMS-based liquid lenses have attracted the attention more and more for digital imaging applications. Among them, the capsule endoscope emerges as a new digital imaging field [1]. Currently it adopts a simple imaging system but demands the improved image quality by using auto-focusing and/or zoom-in capabilities. As the power consumption and the allowable space are the key limitations in the capsule endoscope, the MEMS-based liquid lens can be a right-on solution for the required high optical performance. This paper presents the minimized dead area by incorporating the cylinder-type liquid chamber made of a silicon wafer. In order to reduce the power consumption, the leakage current was measured with several dielectric materials and then the silicon nitride was selected.
DEVICE DESIGN AND FABRICATION Most liquid lenses operate based on the electrowetting phenomenon [2] and several compact liquid lenses have been published with MEMS technology [3~5]. The electrowetting phenomenon, come from the electrocapillary, can be explained as the contact angle change in the conducting liquid when an electric potential is applied between the conducting liquid and the solid electrode. Due to the thin dielectric layer between the conducting liquid and the solid electrode, the system consisting of conducting liquid, dielectric layer and solid electrode can be modeled as a capacitor. The electric field due to the applied electric bias results in the charge
distribution in the conducting liquid which changes the free energy of the liquid and therefore causes the liquid to spread over the surface of the dielectric layer. Through th
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