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 >0.5% 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. Strained thin-film transistors have been made by releasing the silicon layer of a silicon-on-insulator (SOI) wafer to realize better devices. Stretching a silicon thin film by a transfer process makes it easier for electrons to flow through the film and hence improves the performance of electronic devices. Jong-Hyun Ahn from Yonsei University and colleagues have realized a simple and cost-effective way for achieving this. After fabricating devices on a SOI wafer, they etched the handle silicon layer of a SOI wafer to leave a suspended silicon–silicon dioxide membrane. Residual oxidation-induced compressive strain in the buried oxide layer of the wafer created the desired strain and introduced it to the top silicon layer. This transfer-process-based approach reduced the number of defects in silicon and enabled devices to be transferred to plastic substrates to realize flexible devices. Formation of a strained Si membrane with oxidation-induced residual strain by releasing a host Si substrate of a silicon-on-insulator (SOI) wafer is demonstrated. To do this, we construct suspended Si/SiO2 structures and induce over 0.5% tensile strain on the top Si membrane. The fabricated thin-film transistor (TFTs) with strained Si channels are transferred on plastics using a roll-based transfer technique, and they exhibit a mobility enhancement factor of 1.2–1.4 in comparison with an unstrained Si TFT.