Effect of ferroelectric and interface films on the tunneling electroresistance of the Al₂O₃/Hf_0.5Zr_0.5O₂ based ferroelectric tunnel junctions

Abstract

Ferroelectric random-access memory (FRAM) based on conventional ferroelectric materials is a non-volatile memory with fast read/write operations, high endurance, and 10 years of data retention time. However, it suffers from destructive read-out operation and lack of CMOS compatibility. HfO 2 -based ferroelectric tunnel junctions (FTJ) may compensate for the shortcomings of FRAM by its CMOS compatibility, fast operation speed, and non-destructive readout operation. In this study, we investigate the effect of ferroelectric and interface film thickness on the tunneling electroresistance or ON/OFF current ratio of the Hf 0.5 Zr 0.5 O 2 /Al 2 O 3 based FTJ device. Integrating a thick ferroelectric layer (i.e. 12 nm Hf 0.5 Zr 0.5 O 2 ) with a thin interface layer (i.e. 1 nm Al 2 O 3 ) resulted in an ON/OFF current ratio of 78. Furthermore, to elucidate the relationship between ON/OFF current ratio and interfacial properties, the Hf 0.5 Zr 0.5 O 2 -Al 2 O 3 films and Ge-Al 2 O 3 interfaces are examined via time-of-flight secondary ion mass spectrometry depth profiling mode. A bilayer oxide heterostructure (Hf 0.5 Zr 0.5 O 2 /Al 2 O 3 ) is deposited by atomic layer deposition (ALD) on the Ge substrate. The ON/OFF current ratio is enhanced by an order of magnitude when the Hf 0.5 Zr 0.5 O 2 film deposition mode is changed from exposure (H 2 O) ALD to sequential plasma (sequential O 2 -H 2 ) ALD. Moreover, the interfacial engineering approach based on the in situ ALD H 2 -plasma surface pre-treatment of Ge increases the ON/OFF current ratio from 9 to 38 by reducing the interfacial trap density state at the Ge-Al 2 O 3 interface and producing Al 2 O 3 with fewer oxygen vacancies as compared to the wet etch (HF+H 2 O rinse) treatment of the Ge substrate. This study provides evidence of strong coupling between Hf 0.5 Zr 0.5 O 2 and Al 2 O 3 films in controlling the ON/OFF current ratio of the FTJ.

Effect of Al Concentration on Ferroelectric Properties in HfAlOx‐Based Ferroelectric Tunnel Junction Devices for Neuroinspired Applications

“…However, when the pulse interval was 1 s, the maximum value of the current returned to 92.70% of the initial set. Moreover, in the case of [84] HZO (12 nm) Al 2 O 3 (2 nm) Ti/p þ Si 5 Ryu et al [40] HZO (8.4 nm) Al 2 O 3 (1 nm) TiN/p þ Ge 14 Shekhawat et al [85] HZO (6 nm) None TiN/p þ Ge 30 Goh et al [25] HZO (12 nm) Al 2 O 3 (1 nm) TiN/p þ Ge 78 Shekhawat et al [85] HZO (4.5 nm) None TiN/p þ Si 80 Mikheev et al [86] HAO (8 nm) None TiN/n þ Si 120 This work 2 s, it returned to 97.26%. As the gap between pulses increased, it could be interpreted that local switching occurred, as the polarization vectors aligned by the first pulse were returned by the depolarization field (E dep ).…”

Physics, Structures, and Applications of Fluorite‐Structured Ferroelectric Tunnel Junctions

“…The majority of papers concentrate on methods for enhancing TER effects through the engineering of device structure, [51][52][53] ferroelectric barrier, [54][55][56] and interfacial characteristics. [51,[57][58][59][60][61] Additionally, some prospective uses for fluorite FTJ have been introduced. [62][63][64][65] However, the review paper that systematically organizes all fluorite ferroelectric FTJ in terms of physics, structure, applications, and device difficulties has not yet been published, despite the fact that there have been many investigations of fluorite FTJ.…”

Electrodes as the protagonists in composite barrier Ferroelectric Tunnel Junctions

“…Wang et al experimentally obtained quite an enhanced TER effect for a CB-FTJ system with the composite barrier consisting of a perovskite BaTiO 3 (BTO) ferroelectric and a nonpolar dielectric (quantum Para electric) SrTiO 3 (STO) [29]. A 12 nm thick Hf 0.5 Zr 0.5 O 2 in contact with a 1 nm Al 2 O 3 interface layer was reported to exhibit an ON/OFF current ratio of 78 [30]. A metalferroelectric-insulator-semiconductor (MFIS) composite structure in a Si-doped HfO 2 -based FTJ was proposed to maximize the TER effect [31].…”