The Electrode‐Ferroelectric Interface as the Primary Constraint on Endurance and Retention in HZO‐Based Ferroelectric Capacitors

Abstract

Ferroelectric hafnium‐zirconium oxide is one of the most relevant CMOS‐compatible materials for next‐generation, non‐volatile memory devices. Nevertheless, performance reliability remains an issue. With TiN electrodes (the most reported electrode material), Hf‐Zr‐based ferroelectric capacitors struggle to provide reliable retention due to electrode‐ferroelectric interface interactions. Although Hf‐Zr‐based ferroelectric capacitors are fabricated with other electrodes, the focus is predominantly directed toward obtaining a large ferroelectric response. The impact of the electrodes on data retention for these ferroelectrics remains underreported and greater insight is needed to improve device reliability. Here, a comprehensive set of electrodes are evaluated with emphasis on the core ferroelectric memory reliability metrics of endurance, retention, and imprint. Metal‐ferroelectric‐metal capacitors comprised of a Hf0.5Zr0.5O2 layer deposited between different combinations of nitride (TiN, TiAlN, and NbN), pure metal (W), and oxide (MoO2, RuO2, and IrO2) top and bottom electrodes are fabricated for the investigation. From the electrical, physical, and structural analysis, the low reactivity of the electrode with the ferroelectric is found to be key for improved reliability of the ferroelectric capacitor. This understanding of interface properties provides necessary insight for the broad implementation of Hf‐Zr‐based ferroelectrics in memory technology and, overall, boosts the development of next‐generation memories.

Modulation of Oxygen Content and Ferroelectricity in Sputtered Hafnia‐Zirconia by Engineering of Tungsten Oxide Bottom Electrodes

“…After this development, the focus of optimizing the FeCap was shifted to the electrode and interface engineering, which was also done recently for ALD‐deposited HfO 2 ‐based ferroelectrics. [ 15,16 ] A material screening for the bottom electrode (BE) has been accomplished by testing TiN, W/TiN, W, and Pt. In this work, all the sputtered HZO layers have the same Hf to Zr ration of 3:1.…”

“…[ 17,18 ] It is believed that a high P r value induced by the W BE results from its small thermal expansion coefficient, inducing more stress to the HZO film during annealing. [ 15,17,19 ] Meanwhile, the potential reason for the poor endurance is the oxygen scavenging and the detrimental interface between the HZO and W layer. [ 15,17 ] In order to improve endurance and maintain a good P r value, a feasible solution would be to modify the oxygen scavenging and the interface between the BE and HZO materials.…”

“…[ 15,17,19 ] Meanwhile, the potential reason for the poor endurance is the oxygen scavenging and the detrimental interface between the HZO and W layer. [ 15,17 ] In order to improve endurance and maintain a good P r value, a feasible solution would be to modify the oxygen scavenging and the interface between the BE and HZO materials. Back in the perovskite FE era, a similar reliability issue was circumvented by utilizing oxide electrodes like IrO x.…”

“…The difference E c shift in the positive and negative states is associated with the work function of TE and BE, charge and defect states at both interfaces. [ 15 ] Combining both enhanced P r value, higher number of endurance cycles, and reduced imprint shift rate, WO x indeed advances the HZO FeCap FE properties by modifying the oxygen content inside HZO films. Those results are consistent with the structure investigation from GIXRD results and the proposed model.…”

Influence of Biaxial Strain and Interfacial Layer Growth on Ferroelectric Wake-Up and Phase Transition Fields in ZrO2

“…14,15 Significant progress has been made in demonstrating improve-ments in the ferroelectric properties and reliability of fluoritestructured ferroelectric capacitors by incorporating different dopants, 16,17 varying film growth process parameters, 18,19 and using different electrodes. 20 However, a critical issue in bringing capacitors from the laboratory to the industrial scale is that the ferroelectric behavior is strongly influenced by small differences in the parameters used during film growth. For example, 10 nm-thick La-doped HfO 2 films processed with different atomic layer deposition (ALD) tools exhibit distinctly different ferroelectric behaviors.…”