Stress-induced transfer of ultrathin silicon layers onto flexible substrates

Stress-induced cleavage was investigated as a method of transferring sizable areas of thin layers of silicon onto alternative substrates such as sapphire and flexible substrates. By bonding bulk silicon to a sapphire handle wafer using the polymer SU-8, an ultrathin layer of silicon can be transferred from the donor substrate onto the sapphire via mechanical cleavage. The thickness of the transferred silicon is essentially determined by the processing steps and the elastic properties of the composite structure. We further show that a double-flip process enables the complete transfer of ultrathin Si onto flexible substrates.