Three-dimensional microfabrication process using Bi electrodeposition for a highly sensitive X-ray imaging sensor

A microscale Bi electrodeposition process was developed and applied to the three-dimensional fabrication of a highly sensitive X-ray imaging sensor, so called X-ray microcalorimeter, which has an array of sensing elements with a mushroom-shaped X-ray absorber. The composition and operating conditions for Bi electrodeposition were optimized and flat, smooth Bi deposits were obtained by applying additives such as diethylenetriamine pentaacetic acid (DTPA) and sodium n-dodecyl sulfate (SDS). The results of ultraviolet (UV)-visible absorption spectroscopy and polarization curves from the Bi electrodeposition solution indicated that the formation of a DTPA-Bi(III) complex and an increase of overpotential for Bi electrodeposition in the presence of SDS improved the solution stability as well as the surface morphology of the deposited film. The mold for the mushroom-shaped microstructure array was formed from a single-layered photoresist coating by applying sequential exposure steps for the “stem” part and the “roof” part. The absorber array was successfully fabricated by the Bi electrodeposition into the mold, precise polishing, and mold removal processes.