Anomalous behaviors of FeFETs based on polar polymers with high glass temperature (Conference Presentation)

Abstract

The low processing temperature of polymeric materials and their wide range of applications make polar polymer based ferroelectric memory very promising and attractive. The typical configuration of the ferroelectric memory cell is the FeFET (Ferroelectric field-effect-transistor) with the polar polymer incorporated in the gate dielectric stack. The memory effect in these devices originates from the polarization of the ferroelectric polymer film and results in a hysteresis of the Id-Vg characteristics. In this study, we fabricated FeFETs based on ultrathin poly-Si channel and CP1- polymer (glass-transition temperature (Tg ~260 C) as the gate dielectric. We investigated the hysteresis of the Id-Vg curves over a wide range of temperatures and frequencies. We observed the effects of thermocycling on the device, such as the change of the hysteresis loop direction at temperatures close to Tg (associated with the change of the dominant hysteresis mechanism), and the simultaneous significant decrease in gate leakage current (which may indicate significant reduction of active defects in the polymer layer). The reversibility of the observed phenomena was also investigated through consecutive thermocycles. Soaking the chip in warm water (60 C) for 3 hours changes the magnitude of the hysteresis loop without changing the direction. The gate leakage current also remains very low. Thus, humidity may play some role in the hysteresis magnitude but not the loop direction, nor does it play any role in the leakage current. In this paper, we will discuss possible explanations of these observations.