Influence of W and TiN Electrodes on Ferroelectric ALD-(Hf,Zr)O₂ Capacitors at Cryogenic Temperatures

Atomic layer deposited ferroelectric (Hf,Zr)O₂ (HZO) thin films have been applied in a wide range of fields, including next-generation memories, due to their advantages such as compatibility with CMOS processes, low power consumption, fast switching speed, and sub-10 nm scaling [1,2]. Recently, with the rapid development of cloud computing, quantum computing, and space electronics applications, the demand for high-performance memories that can operate stably at cryogenic temperatures has grown substantially, and memory devices utilizing ferroelectric HZO materials have attracted great attention as promising candidates for cryogenic electronics [3]. However, since most studies have investigated the ferroelectric properties of TiN/HZO/TiN capacitors above room temperature, analyses at cryogenic temperatures are insufficient. Meanwhile, it is well known that HZO thin films show excellent ferroelectricity in structures sandwiched with TiN top and bottom electrodes [1]. Nonetheless, the TiN electrodes can induce chemical reactions with the HZO thin film, which may cause defects in the HZO thin film and generate unwanted interface layers, thereby degrading the device reliability. Therefore, in this study, TiN/HZO/TiN and W/HZO/W capacitors were fabricated using the same process as well described in our previous reports [4,5], and the electrical characteristics of these devices were measured and analyzed from -180°C to room temperature using a vacuum probe station equipped with a semiconductor parameter analyzer (Keithley 4200A-SCS) connected to a pulse measurement unit (4225-PMU). As a result, in both TiN/HZO/TiN and W/HZO/W capacitors, the remanent polarization slightly decreased as the measurement temperature decreased. This polarization reduction is attributed to the diminished mobility of dipoles within the ferroelectric material at cryogenic temperatures. Additionally, the external electric field required to switch the polarization direction, i.e., the coercive field, was found to increase as the measurement temperature decreased. It should be noted that the W/HZO/W capacitors exhibited relatively low leakage current and high breakdown characteristics regardless of the measurement temperature. These results highlight the feasibility of ferroelectric HZO thin films as cryogenic memory applications and also provide useful insights into the properties of ferroelectric materials. In particular, the use of W electrodes offers distinct advantages in terms of reduced leakage current and enhanced breakdown field.

This research was supported by the Nano & Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (RS-2024-00450836). This work was also partially supported by Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea government (MOTIE) (P0017011 and P0020966, HRD Program for Industrial Innovation).

[1] S. J. Kim et al., JOM 71, 246 (2019).
[2] J.-H. Kim et al., ACS Appl. Electron. Mater. 5, 4726 (2023).
[3] J. Hur et al., IEEE J. Explor. Solid-State Comput. Devices Circuits 7, 168 (2021).
[4] S. J. Kim et al., Appl. Phys. Lett. 111, 242901 (2017).
[5] S. Lee et al., Solid-State Electron. 216, 108911 (2024).