Liquid Encapsulation by Bonding-In-Liquid Technique
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1222-DD05-15
Liquid Encapsulation by Bonding-In-Liquid Technique
Yoshiyuki Okayama1, Keijiro Nakahara1, Takeshi Ninomiya1, Yasuaki Matsumoto1 and Norihisa Miki1 1 Keio University, Kouhoku-ku Yokohama, Kanagawa, Japan
ABSTRACT We propose and demonstrate Bonding-in-Liquid Technique (BiLT) for encapsulation of liquid in MEMS devices. Liquid encapsulation enables innovative MEMS devices with various functions. Interfusion of air bubbles, heterogeneity of the liquid quantity, and leakage of the encapsulated liquid must be averted not to deteriorate device performances. In BiLT, two structural layers are passively aligned and brought into contact in solution, where the encapsulation cavities are uniformly filled up with the liquid without air bubbles. A UV-curable resin is used as an adhesive that does not require heat or vacuum environment but UV to bond the two layers. We successfully achieved encapsulation of DI water and glycerin in silicon structural layers. Since conventional aligners are not applicable to BiLT, we experimentally evaluated the accuracy of the passive alignment process in solution that makes use of matching concave and convex structures. INTRODUCTION Wafer bonding has been frequently used as a packaging technique of MEMS devices [1-5]. A MEMS component can be encapsulated in either vacuum or a certain gas at designated pressure. The packaging gas determines the performance of MEMS devices [6, 7]. Wafer bonding is also an effective method to create complex three-dimensional structures by bonding multiple wafers with a good accuracy of alignment that have been processed by conventional MEMS processes to have prismatic structures [8, 9]. MEMS devices that encapsulate liquid inside have been proposed to achieve various attractive applications. In optical applications, deformable lens and scanning micro mirror was developed by encapsulating droplets of silicone oil by depositing parylene [10]. Non-volatile silicone oils maintain the shapes of droplets throughout the low vacuum deposition processes of parylene. Parylene deposits on the substrate as well as the droplets conformably. This technique was used to fabricate hydraulic amplification mechanism [11]. Although the liquid encapsulating process using parylene and silicone oil is a well developed and effective one, in some applications, more flexible membranes and volatile liquid are more preferable. For example, our group used largely deformable polydimethyl siloxane (PDMS) membrane to encapsulate glycerin to achieve a high hydraulic amplification [12]. The largely deformable PDMS has low Young’s modulus of about 32kPa. Since it is gas permeable, glycerin was used to be encapsulated.
We herein propose a liquid encapsulating method using bonding-in-liquid technique (BiLT). This method allows us to use various sealing material and liquid to be encapsulated. UV curable resin is used as the intermediate layer. First, a structural layer containing chambers to encapsulate liquid is prepared. UV curable resin is coated onto the bonding surface. A sealing
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