Polarization and Resistive Switching in Epitaxial 2 nm Hf_0.5Zr_0.5O₂ Tunnel Junctions

Abstract

In the quest for reliable and power-efficient memristive devices, ferroelectric tunnel junctions are being investigated as potential candidates. Complementary metal oxide semiconductor-compatible ferroelectric hafnium oxides are at the forefront. However, in epitaxial tunnel devices with thicknesses around ≈4−6 nm, the relatively high tunnel energy barrier produces a large resistance that challenges their implementation. Here, we show that ferroelectric and electroresistive switching can be observed in ultrathin 2 nm epitaxial Hf 0.5 Zr 0.5 O 2 (HZO) tunnel junctions in large area capacitors (≈300 μm 2 ). We observe that the resistance area product is reduced to about 160 and 65 Ω•cm 2 for OFF and ON resistance states, respectively. These values are 2 orders of magnitude smaller than those obtained in equivalent 5 nm HZO tunnel devices while preserving a similar OFF/ON resistance ratio (210%). The devices show memristive and spike-timing-dependent plasticity behavior and good retention. Electroresistance and ferroelectric loops closely coincide, signaling ferroelectric switching as a driving mechanism for resistance change.

Enhanced electroresistance endurance of capped Hf0.5Zr0.5O2 ultrathin epitaxial tunnel barriers

“…It can be observed [insets in Fig. 1(d)] that in agreement with earlier reports, 17 the resistance increases after voltage training. A similar trend is observed in the STO//HZO/STO1 capped samples (see the supplementary material, S2), and a less perceptible resistance increase is observed in the GSO//HZO and GSO//HZO/STO1 films (see the supplementary material, S3).…”

“…Samples grown on GSO have been characterized in detail elsewhere. 17 The samples with STO capping (1 nm) are named STO//HZO/STO1 and GSO//HZO/STO1.…”

“…Further details are described elsewhere. 17 The electric cycling of the junctions (named training in this work) was carried out using bipolar square pulses of indicated number (N C = 10 4 times) at 5 kHz and 2.5 V amplitude.…”

Ferroelectrics Based on HfO2 Film

“…Therefore, using PLD can greatly contribute to understanding the structural and physical properties of HfO 2 . In addition, it is expected that fabricating devices based on epitaxial HfO 2 will further understanding of ferroelectric HfO 2 [16,43,44].…”

“…HfO 2 has already been used in high-k metal gate (HKMG) technology for logic transistors, and its compatibility and scalability with CMOS technology have supported its potential for ferroelectric devices in mass-produced semiconductor components. Accordingly, ferroelectric HfO 2 based devices have been studied in various fields of application, including next-generation memory devices and logic devices such as FRAM [12][13][14], FTJ [15][16][17][18][19], and FeFET [20][21][22].…”