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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.

BaTiO3 films of various thicknesses were grown on doped and undoped SrTiO3(100) substrates and on (La, Sr)2CuO4 films by a pulse laser deposition method. Both BaTiO3 and (La, Sr)2CuO4 films were smooth and free of particulates. X-ray diffractometry showed that all materials were three-dimensionally aligned with the cube-on-cube epitaxial relationship, and that the films obtained on SrTiO3(100) were of a c-axis-oriented tetragonal phase contrary to previous studies using metal bottom electrodes. As the film thickness decreased, the tetragonality of these films increased and the dielectric constant along the c-axis decreased rapidly, despite reduction of disorder at the interface by use of perovskite electrodes. The 2000-Å-thick BaTiO3 grown on (La, Sr)2CuO4 film had the remnant polarization of about 1.5 µ C/cm2. The results were discussed using a surface layer model.