Polarity Effects of Polymer Gate Electrets on Non-Volatile Organic Field-Effect Transistor Memory

Organic non-volatile memory (ONVM) based on pentacene field-effect transistors (FETs) has been fabricated using various chargeable thin polymer gate dielectrics - termed electrets - onto silicon oxide insulating layers. The overall transfer curve of organic FETs is significantly shifted in both positive and negative directions and the shifts in threshold voltage (V-Th) can be systemically and reversibly controlled via relatively brief application of the appropriate external gate bias. The shifted transfer curve is stable for a relatively long time - more than 10(5) s. However, this significant reversible shift in V-Th is evident only in OFETs with non-polar and hydrophobic polymer electret layers. Moreover, the magnitude of the memory window in this device is inversely proportional to the hydrophilicity (determined from the water contact angle) and dielectric polarity (determined from the dielectric constant), respectively. Memory behaviors of ONVM originate from charge storage in polymer gate electret layers. Therefore, the small shifts in V-Th in ONVM with hydrophilic and polar polymers may be due to very rapid dissipation of transferred charges through the conductive channels which form from dipoles, residual moisture, or ions in the polymer electret layers. It is verified that the surface or bulk conductivities of polymer gate electret layers played a critical role in determining the non-volatile memory properties.