Abstract
This paper is to fabricate a three-dimensional(3D) thermopile with 64 in-series thermocouple coated on polyimide(PI) substrate. By using wet-etching technology to etch through PI with thickness 25μm, the cold and hot junction of thermocouple are then located at the surface and bottom of PI. The device is made with 64 Cu-Ni thermocouples connected in series and can be used as thermal sensor on curved-surfaced. The optimal etching PI condition can be determined from various degree of the mixture of KOH and C2H7NO. In order to find larger etching rate, we vary KOH and C2H7NO concertration and the etching temperature is controlled at eighty degrees. From the results of the experiment, etchant is composed of 7M~9M KOH and 2M~4M C2H7NO has larger etching rate. In order to reduce PI surface roughness after etching, we spin ~1μm photoresist(PR) on above etched surface, then deposit Cu and Ni to accomplish 64 thermocouples on PR. For sensitivity measurement, by using hotplat to supply heat for thermopile and using digital thermometer to measure the truth temperature of hot and cold junction, we record the relationship between truth temperature difference and output voltage. The sensitivity of 3D thermopile is 0.4412mV/oC. Finally, the 3D thermopile was pasted on the surface of the notebook, beaker, and desk lamp, we measure output voltage and determine temperature. From our data, the measured temperature of 3D thermopile is closing to that of digital thermometer. Therefore, we succeed to fabricate 3D thermopile and use it as thermal sensor on curved surface.