Mobility enhancement of strained Si transistors by transfer printing on plastic substrates

Strain engineering has been utilized to overcome the limitation of geometric scaling in Si-based thin-film transistor (TFT) technology by significantly improving carrier mobility. However, current strain engineering methods have several drawbacks: they generate atomic defects in the interface between Si and strain inducers, they involve high-cost epitaxial depositions and they are difficult to apply to flexible electronics with plastic substrates. Here, we report the formation of a strained Si membrane with oxidation-induced residual strain by releasing a host Si substrate of a silicon-on-insulator (SOI) wafer. The construction of the suspended Si/SiO₂ structures induces 40.5% tensile strain on the top Si membrane. The fabricated TFTs with strained Si channels are transferred onto plastics using a roll-based transfer technique, and they exhibit a mobility enhancement factor of 1.2-1.4 compared with an unstrained Si TFT.