Polymer-sandwiched ultra-thin silicon(100) layer for flexible electronics

Flexible electronics has gained increasing attention for biomedical engineering applications, solar cell and so on. In this paper, an SU-8/silicon(100)/SU-8 flexible composite sandwich structure is studied. Besides preventing corrosion to the underneath thin silicon membrane, SU-8 photoresist coated on the silicon membrane improves its flexibility as shown by a finite element (FE) simulation utilizing ANSYS software. Using plasma enhanced chemical vapor deposited SiO2/Si3N4 composite film as an etching mask, a 4" silicon(100) wafer was thinned to 26μm without rupture in a 30 wt.% KOH solution. The thinned wafer was coated on both sides with 20μm of SU-8 photoresist and cut into strips. And then the strips were bent by a caliper to measure its radius of curvature. A sector model of bending deformation was adopted to estimate the radius of curvature. The determined minimal bending radius of the polymer-sandwiched ultra-thin silicon layer is no more than 3.3mm. The polymer-sandwiched ultra-thin silicon(100) layer can be used as a flexible substrate. And the fabrication of this sandwich structure is compatible with conventional microelectronic fabrication processing. It can be used as a post-fabrication process for high performance flexible electronics.