Wafer Scale Transfer of Ultrathin Silicon Chips on Flexible Substrates for High Performance Bendable Systems

Abstract

This paper presents an innovative approach for wafer scale transfer of ultrathin silicon chips on flexible substrates. The methodology is demonstrated with various devices (ultrathin chip resistive samples, metal oxide semiconductor (MOS) capacitors and n-channel metal oxide semiconductor field effect transistors (MOSFETs)) on wafers up to 4″ diameter. This is supported by extensive electromechanical characterization and theoretical analysis, including finite element simulation, to evaluate the effect of bending and the critical breaking radius of curvature. The ultrathin chips on polyimide did not break until the radius of curvature of 1.437 mm. In the case of MOS capacitors the measured capacitance increases with increase in bending load. The changes in the transfer and output characteristics of ultrathin MOSFETs closely match with the theoretical model utilizing empirically determined parameters. Overall, the work demonstrates the efficacy of the new methodology presented here for wafer scale transfer of ultrathin chips on flexible substrates. The presented research will be useful for obtaining high performance and compact circuits needed in many futuristic flexible electronics applications such as implantable electronics and flexible displays. Further, it will open new avenues for realizing multilayered multimaterial (foil-to-foil) integrated bendable electronics.