Thermal-type micro sensor array on PI film substrate having wet-etched through-holes for interconnection

We proposed an ultra-thin structure of thermal-type micro sensor array having excellent thermal isolation and sensitivity by using 25/spl sim/50-/spl mu/m-thick polyimide (PI) film as the substrate. The device also has the attractive features of mechanical flexibility allowing three-dimensional packaging. For vertical interconnects, microvia holes (diameter<100 /spl mu/m) were made by PI film wet etching. Arrayed heater elements with 0.1-/spl mu/m-thick nickel film were formed by using lift-off technology, and electrical feed-through with 2-/spl mu/m-thick Cu film were formed by electroless Cu-plating. Heater elements (front side) and electrical feed-through (backside) were interconnected through the fabricated microvia holes using electroless Cu-plating. Fabricated heater elements (Ni) showed good adhesion with the PI film substrate, and its temperature coefficient of resistance (TCR) was 2600 ppm. Because of the small thermal capacity and good thermal isolation, the sensor also showed high thermal response of less than 0.4 /spl mu/s when 280 mV/10 /spl mu/s of pulse voltage was applied to the heater elements.