Fabrication of Concave-Shaped Ultra-Thinned FDSOI CMOS Circuit for Curved Image Sensor

A high-performance flexible image sensor is useful for acquiring various types of image information around us. Particularly, if the image sensor is curved, lens aberrations can be directly corrected and high-quality images can be acquired. An ultra-thin complementary metal oxide semiconductor circuit and photoconversion film were transferred onto a flexible substrate to realize a curved image sensor with high performance and flexibility. Fully depleted silicon on insulator circuits were prepared to eliminate a thick silicon substrate using xenon difluoride etching and only
$6-\mu\mathrm{m}-\text{thick}$
thinned silicon circuits were bonded to a flexible substrate. In this study, we established a method for transferring a thin silicon circuit to a flexible substrate after removing a thick silicon substrate, and transistors operated properly in silicon circuits bent into a uniaxial cylindrical surface with a radius of curvature of 15 mm. Furthermore, we used a stretchable substrate to form a concave shape like a part of a sphere demonstrating that the thin silicon device can change shape flexibly.