Quantum tunnelling and charge accumulation in organic ferroelectric memory diodes

Non-volatile memories—providing the information storage functionality—are crucial circuit
components. Solution-processed organic ferroelectric memory diodes are the non-volatile
memory candidate for flexible electronics, as witnessed by the industrial demonstration
of a 1 kbit reconfigurable memory fabricated on a plastic foil. Further progress, however,
is limited owing to the lack of understanding of the device physics, which is required for the
technological implementation of high-density arrays. Here we show that ferroelectric diodes
operate as vertical field-effect transistors at the pinch-off. The tunnelling injection and charge
accumulation are the fundamental mechanisms governing the device operation. Surprisingly,
thermionic emission can be disregarded and the on-state current is not space charge limited.
The proposed model explains and unifies a wide range of experiments, provides important
design rules for the implementation of organic ferroelectric memory diodes and predicts an
ultimate theoretical array density of up to 1012 bit cm^-2.