Low Operating Voltage, Improved Breakdown Tolerance, and High Endurance in Hf_0.5Zr_0.5O₂ Ferroelectric Capacitors Achieved by Thickness Scaling Down to 4 nm for Embedded Ferroelectric Memory

Abstract

The comparatively high coercive field in Hf0.5Zr0.5O2 (HZO) and other HfO2-based ferroelectric thin films leads to two critical challenges for their application in embedded ferroelectric memory: high operating voltage due to a large thickness-field product and poor endurance due to the high operating field close to the breakdown field. In this study, we demonstrate that the thickness scaling of ferroelectric HZO down to 4 nm is a promising approach to overcome these challenges. As the coercive voltage scales down almost linearly with the film thickness, the operating voltage of 4 nm HZO is reduced to 0.6 V for one-shot operation and 1.2 V for stable memory operation, which is in the voltage range compatible with scaled silicon technologies. Furthermore, it is found that the breakdown field is substantially improved in thinner HZO since the breakdown mechanism is dominated by the stress voltage, not the stress field, resulting in improved cycle-to-breakdown by more than 4 orders of magnitude when thinning from 9.5 to 4 nm. We identify two concerns accompanying thickness scaling: the increase in crystallization temperature and the pinched hysteresis behavior, which can be addressed by carefully preparing temperature-thickness mapping and applying strong-field wake-up cycling, respectively. Our optimal 4 nm-thick HZO ferroelectric capacitor exhibits an operating voltage of 1.2 V with over 10 year data retention and 1012 endurance cycles at 100 kHz, which can be further improved to more than 1014 with a smaller capacitor size and higher operating frequency.

First direct observation of the built-in electric field and oxygen vacancy migration in ferroelectric Hf0.5Zr0.5O2 film during electrical cycling

“…These results are consistent with the wake-up phenomena commonly observed in hafnium oxide-based ferroelectrics. 32–34…”

“…These results are consistent with the wake-up phenomena commonly observed in hafnium oxide-based ferroelectrics. [32][33][34] For the sample after 1 V wake-up, the DPC-STEM images formed by subtracting the images from opposite segment detectors, namely DPC (A-C) and DPC (B-D)are shown in Fig. 3(a) and (b), respectively.…”

Toward Low-Thermal-Budget Hafnia-Based Ferroelectrics via Atomic Layer Deposition

“…The amount of dopant can be controlled by changing the number of dopant cycles inserted into the HfO 2 deposition cycles, resulting in a supercycle, which is a repeating cycle of HfO 2 and dopant cycles . Numerous researchers have employed this ALD doping technique to achieve ferroelectricity in HfO 2 using various dopants, including Al, , Si, − Y, La, , Sr, , Gd, and Zr. ,,,− Doping HfO 2 with Gd, Sr, La, Y, and Zr showed an improvement in 2 P r values compared to pure HfO 2 , as demonstrated in Figure a, satisfying the minimum switching charge density requirement (24.0 μC/cm 2 ) for FRAM applications according to International Roadmap for Devices and Systems . Moreover, the presence of Gd and Zr as dopants in HfO 2 also helped achieve ferroelectricity at temperatures compatible with the BEOL process (<450 °C).…”

“…Therefore, for low-temperature applications, precursors with ALD windows around BEOL-compatible temperatures must be utilized for self-limiting ALD reactions, as opposed to condensation or no reaction. As shown in Table , a variety of precursors, such as hafnium tetrachloride (HfCl 4 ), ,,,, tetrakis­(ethylmethylamido)hafnium (TEMA-Hf), ,,,,− ,− , tetrakis­(dimethylamido)­hafnium (TDMA-Hf), ,,,,− ,− cyclopentadienyltris­(dimethylamino)hafnium (CpHf), − and more, were used to deposit ferroelectric HfO 2 via ALD. For the deposition of HZO, similar chemicals were used for Zr, with some reports using the same type of precursor as for Hf and others mixing different types of precursors, including cocktail precursors that contain both Hf and Zr precursors in one bottle …”

Breakdown-limited endurance in HZO FeFETs: Mechanism and improvement under bipolar stress

“…HfO2-based ferroelectric thin films have been actively employed in recent electron device research thanks to their CMOS compatibility, established know-how on the fabrication process, and high scalability of thickness to 10 nm or lower (Böscke et al, 2011a;Müller et al, 2012;Park et al, 2015;Migita et al, 2018b;Kim et al, 2018;Tan et al, 2021;Toprasertpong et al, 2022a;Schroeder et al, 2022). Ferroelectric field-effect transistors (FeFETs) with HfO2-based ferroelectric thin films as gate insulators have received considerable attention, not only because of the maturity of the HfO2 deposition technology in the advanced transistor process, but also because of their low energy consumption, high speed, and satisfactory retention during their operation.…”