Temporary bond-debond technology for high-performance transistors on flexible substrates

A processing technology based upon a temporary bond-debond approach has been developed that enables direct fabrication of high-performance electronic devices on flexible substrates. This technique facilitates processing of flexible plastic and metal-foil substrates through automated standard semiconductor and flat-panel tool sets without tool modification. The key to processing with these tool sets is rigidifying the flexible substrates through temporary bonding to carriers that can be handled in a similar manner as silicon wafers or glass substrates in conventional electronics manufacturing. To demonstrate the power of this processing technology, amorphous-silicon thin-film-transistor (a-Si:H TFT) backplanes designed for electrophoretic displays (EPDs) were fabricated using a low-temperature process (180°C) on bonded-plastic and metal-foil substrates. The electrical characteristics of the TFTs fabricated on flexible substrates are found to be consistent with those processed with identical conditions on rigid silicon wafers. These TFTs on plastic exhibit a field-effect mobility of 0.77 cm²/V-sec, on/off current ratio >10⁹ at V_ds = 10 V, sub-threshold swing of 365 mV/dec, threshold voltage of 0.49 V, and leakage current lower than 2 pA/μm gate width. After full TFT-array fabrication on the bonded substrate and subsequent debonding, the flexible substrate retains its original flexibility; this enables bending of the EPD display without loss in performance.