Direct Correlation of Ferroelectric Properties and Memory Characteristics in Ferroelectric Tunnel Junctions

Benjamin Max,Thomas Mikolajick,Michael Hoffmann,Stefan Slesazeck

doi:10.1109/jeds.2019.2932138

Benjamin Max, Thomas Mikolajick + Show 2 more

Open Access

https://doi.org/10.1109/jeds.2019.2932138

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Abstract

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.

Highlights

The ever-increasing need for high density and fast data storage has become prevalent in all sectors in the last years due to the rise of smart hard- and software (Internetof-Things, Industry 4.0, big data, etc.) [1]–[3]
After the thermal anneal during sample preparation, the typical grain size inside the ferroelectric layer films is in the range of about 10-30 nm [20]
We have investigated ferroelectric tunnel junctions that utilize a ferroelectric HZO film as the memory layer and a dielectric Al2O3 layer that serves as the tunneling barrier for the current through the device

Summary

INTRODUCTION

The ever-increasing need for high density and fast data storage has become prevalent in all sectors in the last years due to the rise of smart hard- and software (Internetof-Things, Industry 4.0, big data, etc.) [1]–[3]. The discovery of ferroelectricity in hafnium-based dielectrics in 2011 [10] led to new promising results for the aforementioned memory applications, as well as other areas, such as logic-inmemory [11], negative capacitance [12] and neuromorphic computing [13] Besides these common research fields, ferroelectric tunnel junctions (FTJ) have gained popularity in the last years [14]–[16]. Due to the internal band bending related to the imperfectly screened charges at the ferroelectric/dielectric interface, an asymmetry in the band diagram for opposite polarization states is achieved The novelty of this MFIM stack was proposed and proven first by Meyer et al in 2004 as a ferroresistive RAM cell [17].

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CONCLUSION