Flexible IGZO TFT SPICE Model and Design of Active Strain-Compensation Circuits for Bendable Active Matrix Arrays

摘要

The detailed measurement and characterization of strain-induced performance variations in flexible InGaZnO thin-film transistors (IGZO TFTs) resulted in a SPICE TFT model able to simulate tensile and compressive bending. This model was used to evaluate a new concept, namely, the active compensation of strain-induced performance variations in pixel driving circuits for bendable active matrix arrays. The designed circuits can compensate the mobility and threshold voltage shifts in IGZO TFTs induced by bending. In a single TFT, a drain current of 1mA varies byn$83~mu text{A}$nper percent of mechanical strain. The most effective compensation circuit design, comprising one additional TFT and two resistors, reduces the driving current variation ton$1.1~mu text{A}$nper percent of strain. The compensation circuit requires no additional control signals and increases the power consumption by onlyn$235~mu text{W}$n(corresponds to 4.7%). Finally, switching operation is possible for frequencies up to 200 kHz. This opens a way toward the fabrication of flexible displays with constant brightness even when bent.