Fabrication of Tactile Display Mechanism Using Arrayed SMA Thick Film Actuator and Si TSV Layer with Individually Connecting Diode

Abstract

This paper describes the fabrication of a tactile display with a shape memory alloy (SMA) thick film actuator array bonded to an Si substrate using through-substrate-via (TSV) electrodes and diode elements to realize individual connection without reverse current flow. The SMA actuator array (5×5 array, 2 mm pitch) was fabricated from a flash-evaporated SMA thick film while the TSV substrate was fabricated using a different Si substrate. After large through holes and cavities were etched for the vibrating SMA actuator, the TSV electrodes were formed by double-side sputtering and lift-off processes. The fabricated diode element exhibited a sufficient backward breakdown voltage above 36 V and low forward resistance of 15 Ω. On the fabricated SMA and TSV substrates with through holes, 10-µm and 5-µm-thick SU-8 patterns were uniformly formed, respectively, and then, the substrates were bonded using the patterned SU-8 layers with a bonding strength above 3.5 MPa. Simultaneously, in the bonding process, the electrodes on the SMA and TSV substrates were electrically connected via an Ag paste dispensed in the opening of the SU-8 pattern. Using the proposed processes, we successfully completed the tactile display mechanism with the arrayed SMA actuator , including the TSV substrate with diode elements.