Device physics and nanostructuring of organic ferroelectric memory diodes
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Abstract
Organic ferroelectric memory diodes are promising data storage devices for flexible electronics. They strongly depend on the interface between the polymer semiconductor poly(9,9-octylfluorene) (PFO) and the ferroelectric polymer P(VDF-TrFE). Therefore, a technique called solution micromolding was established in this work to obtain well-defined bilinear arrays of PFO and P(VDF-TrFE), which were stacked between two electrodes. The resulting diodes showed excellent memory characteristics including data retention. Moreover, downscaling the feature dimensions of the array using solution micromolding led to an unexpected performance improvement.
The device physics of the memory diodes was analyzed with a numerical device simulator. The derived operational mechanism can be summarized as follows: since the injecting bottom electrode forms a Schottky contact with PFO, the current density is normally low: the diode is in the Off-state (Boolean “0”).
If P(VDF-TrFE) is fully polarized, a stray electric field between the polarization charges and the resulting image charges in the electrode rises, which enables efficient charge injection into the semiconducting PFO via barrier tunnelling. The injected charges form a strong accumulation layer along the PFO/P(VDF-TrFE) interface, which governs the high current density On-state (Boolean “1”). Although being a two terminal device, the memory diode works like a field-effect transistor.