Blocking of Conducting Channels Widens Window for Ferroelectric Resistive Switching in Interface‐Engineered Hf_0.5Zr_0.5O₂ Tunnel Devices

Abstract

Films of Hf 0.5 Z 0.5 O 2 (HZO) contain a network of grain boundaries. In (111) HZO epitaxial films on (001) SrTiO 3, for instance, twinned orthorhombic (o-HZO) ferroelectric crystallites coexist with grain boundaries between o-HZO and a residual paraelectric monoclinic (m-HZO) phase. These grain boundaries contribute to the resistive switching response in addition to the genuine ferroelectric polarization switching and have detrimental effects on device performance. Here, it is shown that, by using suitable nanometric capping layers deposited on HZO film, a radical improvement of the operation window of the tunnel device can be achieved. Crystalline SrTiO 3 and amorphous AlO x are explored as capping layers. It is observed that these layers conformally coat the HZO surface and allow to increase the yield and homogeneity of functioning ferroelectric junctions while strengthening endurance. Data show that the capping layers block ionic-like transport channels across grain boundaries. It is suggested that they act as oxygen suppliers to the oxygen-getters grain boundaries in HZO. In this scenario it could be envisaged that these and other oxides could also be explored and tested for fully compatible CMOS technologies.

Non-volatile optical switch of resistance in photoferroelectric tunnel junctions

“…Moreover, whereas two critical ( V + C-LOW and V + C-HIGH ) fields, related to polarization reversal and ionic motion, respectively, were observed in LSMO/BTO junctions, only the V + C-LOW remains apparent in the R ( V W ) loops of the LSMO/STO/BTO hybrid junctions. This observation confirms that the STO layer contributes to suppress the ionic channel and the HRS ION state 64 (Supplementary Note 18 and Supplementary Fig. 18 ).…”

“…This enhancement results from the larger asymmetry of the electronic potential profile across the device. A similar approach had been used earlier to improve ER in ferroelectric tunnel barriers 9,64 . Moreover, whereas two critical (V + C-LOW and V + C-HIGH ) fields, related to polarization reversal and ionic motion, respectively, were observed in LSMO/BTO junctions, only the V + C-LOW remains apparent in the R(V W ) loops of the LSMO/STO/BTO hybrid junctions.…”

Epitaxial Ferroelectric HfO2 Films: Growth, Properties, and Devices

“…Electroresistance (ER) loops were soon measured in epitaxial HZO films a few nanometers thick. 76,81,83,87 Sulzbach et al 87 reported electroresistance loops with the same coercive voltage (Figure 13a) than the corresponding polarization loops (Figure 13b), indicating the close relation between ferroelectric switching and electroresistance. The Brinkman model was used to fit I-V characteristics pointing to tunneling current as predominant conduction mechanism.…”

“…Thus, genuine tunneling ER resulting from ferroelectric switching can be accompanied by ER resulting from other transport mechanisms. They are associated to ions motion, and cause huge ER values up to 10 5 % 87 or even 10 6 %. 83 Noheda and coworkers 83,86 proposed that the huge ER is connected to oxygen vacancy migration between bottom LSMO electrode and HZO film.…”

Interplay between oxygen defects and dopants: effect on structure and performance of HfO2-based ferroelectrics

“…Accordingly, FTJ performance could be drastically improved. 117 The benefit of single layer stacks 118 is the low non-polar interface layer thickness generating lower depolarization fields and an improved retention behavior. In contrast, the low barrier thickness causes only about 100 field cycles before breakdown and a high FTJ capacitance, which makes the tunnel current difficult to read by the sensing circuit.…”