Nonvolatile transistor memory devices using high dielectric constant polyimide electrets

Abstract

We report on the nonvolatile memory characteristics of pentacene-based organic field-effect transistors (OFETs) using polyimides, PI(6FDA-TPA-CN), PI(DSDA-TPA-CN), and PI(BTDA-TPA-CN), consisting of electron-donating 4,4′-diamino-4′′-cyanotriphenylamine (TPA-CN) and different electron-accepting dianhydrides as polymer electrets. The dielectric constants of PI(BTDA-TPA-CN), PI(DSDA-TPA-CN), and PI(6FDA-TPA-CN) are 3.44, 3.52, and 3.70, respectively, higher than those (∼3) of common polyimides. Among the polymer electrets, the OFET memory device based on PI(6FDA-TPA-CN) exhibits the highest OFET mobility of 0.5 cm² V⁻¹ s⁻¹ due to the formation of a pentacene film of large grain size by the hydrophobic surface. The OFET memory devices with the configuration of n+Si/SiO₂/PI/pentacene/Au show excellent nonvolatile memory behaviors for bistable switching. The stability for ON and OFF states can be maintained for 10⁴ s with a I_on/I_off current ratio of 10⁴ for PI(6FDA-TPA-CN). Moreover, the higher dipole moment and larger torsion angle result in the more stable charge transfer complex, accompanied by the largest memory window of 84 V for the fabricated device. The write–read–erase–read (WRER) cycles can be operated over 100 cycles. The present study suggests that the high dielectric constant polyimide electrets with the enhanced capabilities for storing the charges have great potential applications for advanced OFET memory devices.