Fabrication of Ni Electroless-Plating Type Through-Silicon-Via Substrate with P-N Si Diode Array for MEMS Tactile Display Devices

For attachment to human skin of a MEMS tactile display device having arrayed actuators for mechanical stimulations, a Si substrate with arrayed through-silicon-via（TSV）electrodes and diode elements was fabricated for individual connection to each actuator without reverse current flow. After p-n junctions for the diode array were formed in a device layer of a silicon on insulator（SOI）wafer, deep holes（φ150 μm）for the TSV and 300-μm-deep large cavity were etched using a double-layered mask pattern from the substrate layer with deep reactive ion etching. After complete through etching from the device layer, sputtering and patterning of the Au/Cr seed film, Ni electroless plating was conducted to form the TSV electrode uniformly on the through-hole sidewall. A Pt/Ti/AlSi stacked thin electrode film was used to contact both the p-type and n-type Si surfaces of the diode. Instead of a long sintering process at 400 ℃ that causes shrinking and peeling of the Ni electroless-plated film, ohmic contact with low resistance was achieved between the Pt/Ti/AlSi electrode and the Si surface by rapid thermal annealing at 400 ℃ for 1 min or longer. The fabricated diode has low forward resistance and sufficiently high backward breakdown voltage greater than 35 V.