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.
We demonstrate a peristaltic micropump that utilizes traveling waves on polymer membranes to transport liquids. This micropump requires no valves and, more importantly, the traveling waves can be generated by a single actuator. These features enable the design of simple, compact devices. This micropump has a hydraulic displacement amplification mechanism (HDAM) that encapsulates an incompressible fluid with flexible polymer membranes made of polydimethyl siloxane. A microchannel is attached to the top side of the HDAM. We used a cantilever-type piezoelectric actuator to oscillate the flexible membrane at the bottom of the HDAM, while the top-side membrane drives the liquid in the channel. This format enables rectangular parallelepiped micropumps as compact as 36 mm long, 10 mm wide and several millimeters high, depending on the channel height. Experiments using the fabricated micropumps equipped with microchannels of various heights revealed that the flow rate was dependent on the ratio of the amplitude of the traveling waves to the height of the fluidic channel. The manufactured micropump could successfully generate a maximum flow rate of 1.5 ml min−1 at 180 mW.
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.
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