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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.

The discovery of ferroelectric (FE) properties in binary oxides has enabled CMOS compatible and scalable FE memories. Recently, we reported a simple approach to introduce non-volatility into state-of-the-art dynamic random-access memory stacks that show anti-FE (AFE) behavior. By employing a pair of electrodes with different work functions, a built-in bias is generated. Consequently, this bias modulates the energy potential of the AFE and enables two stable non-volatile states. Using this approach, a significant endurance improvement compared to hafnia-based FE memories can be obtained. In this paper, we investigate the possibility to bypass the usage of asymmetric workfunction electrodes. Using the interface-engineering approach, based on fixed charge or dipole formation, we show two additional methods for built-in bias generation within AFE layer stacks. By characterizing the film properties and performance of AFE capacitors, we compare and investigate retention and endurance of both work function-difference-based and interface-based AFE non-volatile memory. Finally, for the first time we present the concept of a binary oxide-based AFE tunnel junction that leverages both an interface and work function engineered AFE stack.