Characterization of a bonding-in-liquid technique for liquid encapsulation into MEMS devices

• Published in: Journal of micromechanics and microengineering Vol. 20; no. 9; p. 095018
• Main Authors: Okayama, Yoshiyuki, Nakahara, Keijiro, Arouette, Xavier, Ninomiya, Takeshi, Matsumoto, Yasuaki, Orimo, Yoshinori, Hotta, Atsushi, Omiya, Masaki, Miki, Norihisa
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.09.2010; Institute of Physics
• Subjects: Air bubbles; Alignment; Applied sciences; Bonding; Condensed matter: structure, mechanical and thermal properties; Devices; Electronics; Encapsulation; Exact sciences and technology; Fluid surfaces and fluid-fluid interfaces; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Leakage; Liquids; Mechanical engineering. Machine design; Mechanical instruments, equipment and techniques; Microelectronic fabrication (materials and surfaces technology); Micromechanical devices and systems; Phosphates; Physics; Precision engineering, watch making; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Surface energy (surface tension, interface tension, angle of contact, etc.); Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Water; Encapsulation; Cavities; Bubbles; Adhesives; Ultraviolet irradiation; Photopolymerization; Adhesive joint; Surface tension; Microelectromechanical device; Leaks
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/20/9/095018

We demonstrate and characterize a new bonding-in-liquid technique (BiLT) for the encapsulation of liquids in MEMS devices. Liquid encapsulation enables innovative MEMS devices with various functions exploiting the unique characteristics of liquids, such as high deformation and spherical shape due to surface tension. Interfusion of air bubbles, variation of the liquid quantity and leakage of the encapsulated liquid must be avoided, or device performance will deteriorate. In BiLT, two structural layers are passively aligned and brought into contact in a solution, and the encapsulation cavities are filled uniformly with liquid, without air bubbles. A UV-curable resin is used as an adhesive that does not require heat or vacuum to bond the layers, but UV irradiation. DI water, glycerin and phosphate buffer saline were successfully encapsulated in silicon structural layers with PDMS membranes. We experimentally evaluated the bond strengths and alignment accuracy of BiLT in order to provide crucial information for the application of this process to the packaging and/or manufacturing of MEMS devices. Since conventional aligners are not applicable to BiLT, we experimentally evaluated the accuracy of an in-solution passive alignment process, which made use of matching concave and convex structures.