Yoshiyuki Okayama

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

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.

Dynamic Characteristics of a Hydraulic Amplification Mechanism for Large Displacement Actuators Systems

We have developed a hydraulic displacement amplification mechanism (HDAM) and studied its dynamic response when combined with a piezoelectric actuator. The HDAM consists of an incompressible fluid sealed in a microcavity by two largely deformable polydimethylsiloxane (PDMS) membranes. The geometry with input and output surfaces having different cross-sectional areas creates amplification. By combining the HDAM with micro-actuators, we can amplify the input displacement generated by the actuators, which is useful for applications requiring large deformation, such as tactile displays. We achieved a mechanism offering up to 18-fold displacement amplification for static actuation and 12-fold for 55 Hz dynamic actuation.

MEMS Tactile Display with Hydraulic Displacement Amplification Mechanism

Tactile displays mechanically stimulate tactile receptors on a finger pad. They require a micro-actuator array capable of generating displacement greater than 100 ¿m. We propose a MEMS-based tactile display with hydraulic displacement amplification mechanisms (HDAM). HDAM contains micro-cavities that have different cross-sectional areas between at the contact and the drive parts and encapsulate incompressive glycerin with largely-deformable thin PDMS (polydimethylsiloxane) membranes. Displacement applied to the drive part is amplified at the contact part associated with the ratio of cross-sectional areas of the drive to the contact parts. HDAM was fabricated and achieved a seven-fold of amplification. We successfully demonstrated rewritable Braille codes.

A peristaltic micropump using traveling waves on a polymer membrane

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.

A peristaltic micropump using traveling waves of polymer membranes driven by a single actuator

We demonstrate a peristaltic micropump that utilizes traveling waves of polymer membranes to transport liquids. This micropump does not require any valves and more importantly, the traveling waves can be generated by a single actuator. The micropump contains hydraulic displacement amplification mechanism (HDAM) that encapsulates incompressible glycerin in a micro chamber that has different cross-sectional area at the top and the bottom to amplify the amplitude of the traveling waves. The manufactured micropump achieved a flow rate of 1.3 ml/min, which was by far more efficient than a micropump without HDAM.

Vibrational Braille code display with MEMS-Based hydraulic diplacement amplification mechanism

We demonstrate an efficient vibrational Braille code display with large-displacement MEMS actuator arrays. The large displacement is realized by hydraulic displacement amplification mechanisms (HDAM). Static and dynamic characteristics of HDAM were investigated and 18- and 11-fold amplification were achieved in static and dynamic (at 70 Hz) actuation, respectively. We applied actuator arrays consisting of HDAM and piezoelectric actuators to Braille code display. Owing to the characteristics of finger tactile receptors being more sensitive to vibrational stimuli than static ones and the natural frequency of HDAM, vibrational actuation at 70 Hz, which required a low voltage of 30V for subjects to detect the code, were more efficient than static actuation, which required 65V, and vibrational actuation at other frequencies.