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Ferroelectric memories have made big advancements in the last years due to the discovery of ferroelectricity in already widely used hafnium oxide. Here we investigate ferroelectric tunnel junctions (FTJ) consisting of a ferroelectric hafnium zirconium oxide layer and a dielectric aluminum oxide layer. By varying the set and reset amplitude and pulse width the fraction of reversed ferroelectric domains can be controlled. Due to the statistical distribution of the coercive voltage the current can be tuned between the minimum off-state and maximum on-state current. This leads to possible multi-level information storage in our FTJs. In this paper a detailed study of the set/reset operation and the intermediate current levels is presented. Furthermore, the endurance properties of the memory device can be directly correlated to the wake-up and fatigue phenomena in the ferroelectric layer. While the usability of the memory window is still limited by the initial polarization increase and ultimately by the hard breakdown of the device, a further optimization of the ferroelectric layer itself and the ferroelectric/dielectric interface can directly improve the viability of the tunnel junction. Finally, we show that the current of our FTJs scales as expected and reproducible results across different devices are obtained.
Max et al. (Tue,) studied this question.