Polysilicon thin-film transistors on polymer substrates

Different approaches to fabricate low-temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) on polymer substrates are reviewed and the two main routes are discussed: (1) standard fabrication of LTPS TFTs on glass substrates followed by a transfer process of the devices on the polymeric substrate; (2) direct fabrication of the devices on the polymeric substrate. Among the different techniques we have described in more detail the process we have recently developed for the fabrication of LTPS TFTs directly on ultra-thin polyimide (PI) substrate. LTPS TFT technology is particularly suited for high performance flexible electronics applications, due to the excellent device characteristics, good electrical stability and CMOS technology. Flexible display application remains the most attractive application for LTPS technology, especially for AMOLED displays, where device stability and the possibility to integrate the driving circuits make LTPS technology superior to all the other competitive TFT technologies. Among the other applications, particularly promising is also the application to flexible smart sensors, where integration of a front-end electronics is essential. Some examples of flexible gas sensors and pressure sensors, integrated with simple readout electronics based on LTPS TFTs and fabricated on ultra-thin PI substrate, are presented.