Effect of dead layers on the ferroelectric property of ultrathin HfZrOx film

Abstract

In this study, we investigate the effects of various electrodes on the ferroelectric properties of ultrathin HfZrOx (HZO) films. The ferroelectric polarization is totally suppressed in the HZO films with TiN and W bottom electrodes when the film thickness is below 5 nm. These results can be attributed to the formation of a dead layer at the bottom electrode/HZO interface during the atomic layer deposition (ALD) and annealing processes. On the other hand, the HZO film with a Pt bottom electrode shows an excellent P–E loop with a very high switchable polarization (2Pr) of 42.5 μC/cm2 even at a film thickness of 2.5 nm. Through the short pulse switching technique, we confirm the formation of a thick dead layer in the HZO films with TiN and W electrodes, which inhibits the formation of the orthorhombic phase in these ultrathin HZO films. This implies that the ferroelectric property of ultrathin HZO films can be improved by choosing an appropriate electrode material capable of suppress ing the formation of a dead layer.

Hafnium Oxide (HfO2) – A Multifunctional Oxide: A Review on the Prospect and Challenges of Hafnium Oxide in Resistive Switching and Ferroelectric Memories

“…[281,283,[292][293][294][295] This approach introduced a substantial improvement in the dielectric properties of HfO 2 -based thin films. In fact, the discovery of ferroelectricity and anti-ferroelectricity in HfO 2 -ZrO 2 (HZO) solid solution thin films [246][247][248][249][250][251][252][253][254][255][256][257][258][259][260][261][262] paved the way for enhancing dielectric properties through MPB, which will be discussed later in Section 8.…”

“…[356] Moreover, the formation of an insulating interfacial layer with the oxygen-metal reaction, which causes incomplete screening of polarization charges, can create depolarizing field against ferroelectric polarization. [248] This field can directly cause a reduction in the net polarization and indirectly cause the injection of electrons from metal electrodes inside the insulating film, which degrades ferroelectric polarization under cycling field. [357,358] Capacitors with conductive oxide electrodes such as SrRuO 3 , LaNiO 3 , LaSrMnO 3 , IrO 2 , LaSrCaO 3 , YBa 2 Cu 3 O x , and RuO 2 are generally free from fatigue.…”

“…Moreover, the discovery of ferroelectricity in a ≈ 10-nm doped HfO 2 thin film has unleashed the perspective of ferroelectric memory for future electronics. [245,246] Interestingly, HfO 2 has resolved the scaling issues, and ferroelectricity is not only maintained [247][248][249] but also enhanced in a few monolayers of doped HfO 2 , which is highly promising for the miniaturization of emergent devices. [250][251][252] While conventional ferroelectric materials such as Pb(Zr 1-x Ti x )O 3 (PZT) and BaTiO 3 (BTO) are considerably affected by scaling down film thickness, [254][255][256] the HfO 2 -based materials show excellent ferroelectric properties at nanoscale.…”

“…[250][251][252] While conventional ferroelectric materials such as Pb(Zr 1-x Ti x )O 3 (PZT) and BaTiO 3 (BTO) are considerably affected by scaling down film thickness, [254][255][256] the HfO 2 -based materials show excellent ferroelectric properties at nanoscale. [247][248][249]257,258] Interestingly, ferroelectricity is hardly observed in relatively thick HfO 2based films, [259][260][261] which is in favor of the miniaturization of electronic devices. It is worth mentioning that the negative aspects of conventional ferroelectrics caused a considerable lack of interest in the industrial research communities; however, the decade-old discovery of ferroelectricity in an HfO 2 -based thin film [245] dramatically revived the declining interest in theoretical and experimental research on ferroelectrics.…”

Advances in dielectric performance of atomically engineered perovskite nanosheet thin films

“…In addition, these materials are signi cantly affected by intrinsic size effects involving the particle and grain sizes. The size effect is often attributed to the low-k interfacial 'dead layer', which is caused by the degradation of the dielectric/electrode interface layer during post-annealing, the growth-induced defects, and the strain introduced from electrodes [4][5][6]. In addition, the lm fabrication process is complicated and requires a post-annealing process which causes cracks and defects in thin lms [7].…”