A new approach to achieving strong ferroelectric properties in TiN/Hf_0.5Zr_0.5O₂/TiN devices

Abstract

In this paper, we propose a method to improve the performance of TiN/Hf0.5Zr0.5O2 (HZO)/TiN Nano-capacitors used in memory devices. Instead of direct fabrication of the TiN/HZO/TiN device, our method involves an intermediate step in which W metal is used as a capping material to induce a large in-plane tensile strain during rapid thermal annealing, resulting in a total suppression of the monoclinic phase and the appearance of the ferroelectric phase. Consequently, after removing the W capping electrode through an etching process and the post-deposition of a TiN top electrode at room temperature, a high remnant polarization of approximately 40 μC cm−2 and a 65% increase of coercive field were obtained. Moreover, the leakage current was reduced by an order of magnitude compared to the normal TiN/HZO/TiN capacitor; this result is attributed to the presence (absence) of the W/HZO (TiN/HZO) top interface during thermal annealing. The formation of a TiO x interfacial layer at elevated temperatures, which pulls oxygen from the HZO layer, resulting in the formation of oxygen vacancies, is the main cause of the high leakage current through the TiN/HZO/TiN stacks. It was confirmed that the re-capped TiN/HZO/TiN capacitor has a comparable endurance to a normal capacitor. Our results offer the re-capping process as a promising approach to fabricating HfO2-based ferroelectric memory devices with various electrode materials.

Stress-Memorized HZO for High-Performance Ferroelectric Field-Effect Memtransistor

“…Since the total stress value is 0, in the Type II sample, W undergoes compressive stress and induces more tensile stress in HZO, while in the Type III sample, Pt shows tensile stress, reducing the tensile stress in HZO. The Type I-a sample shows an intermediate in-plane tensile stress in HZO because the CTE of TiN is ∼7.0 × 10 –6 °C –1 , which is between those of W and Pt. , Figure c shows a clear O phase in GIXRD spectra of three types of samples after removing the capping layers. The analyzed intensity and the ratio of (111) O phase within peaks in the range 28–34° is depicted in Figure d.…”

“…Therefore, the transformation of the T phase to O phase only requires a moderate elongation of the c T axis. This transformation can be promoted with in-plane tensile stress in cooperation with a Poisson effect on the nearly (110) oriented T phase HZO, and the stress-engineered transformation can be memorized. − However, the influence of a thermal expansion mismatch with a stacked capping layer on HZO has yet to be investigated and it has not been applied to FeFET performance enhancement. In addition, the enhancement of polarization will lead to a larger built-in electric field, which will decrease the breakdown strength (BDS) .…”

Two-step deposition of TiN capping electrodes to prevent degradation of ferroelectric properties in an in-situ crystallized TiN/Hf0.5Zr0.5O2/TiN device

“…At this stage, the phase transformation is determined by a kinetic energy barrier [44,45]. In the cooling step of the RTA, a part of the t-phase is transformed into the o-phase by an in-plane tensile stress caused by the capping TiN TE [13,46]. It is generally accepted that capping electrodes also prevent twin deformation, resulting in the suppression of m-phase formation [15,21].…”

Microstructural evolution and ferroelectricity in HfO2 films

“…Furthermore, other metal electrodes, such as W, Ru and Ir, have also been used for HfO 2 FE fabrication to improve the endurance of the device or device integration ability [133][134][135][136][137][138] . Some field-induced behaviors, such as the wake-up effect and fatigue, are also related to the electrode properties [25,33] .…”