Twist's Review #5 - Ferroelectric HfO2/HZO through Pulse Laser Deposition

Paper: Large enhancement of ferroelectric polarization in Hf 0.5 Zr 0.5 O 2 films by low plasma energy pulsed laser deposition

Ferroelectric HfO2 has been quite a booming topic in the electronics field as it came up as a new promising for ferroelectric devices. In the past ferroelectric devices were based on ferroelectric perovskites such as PZT (Lead Zirconium Titanate), but unfortunately were not CMOS compatible (especially with regards to its thermal budget). HfO2 though seemed more promising as it can be utilised with a more workable thermal budget with good ferroelectric characteristics.

This paper presents a method to manufacture epitaxial thin films of HZO through pulse laser deposition (PLD), but with the addition of an inert gas to produce a film with large polarization of about 55 uC/m2 (Pr = 32 uC/m2). There were challenges to face when trying to make HZO thin films with pulse laser deposition as while using a lower oxygen pressure (higher laser energy; less interaction between plasma atoms and gas atoms) benefits the ferroelectricity of the thin film, a laser that is too high in energy can reduce crystallinity while too high of ambient pressure will thermalize the plasma and degreade crystallinity.

Thus it was concluded that a balance/optimal conditions were required if we want to make comparable PLD HZO thin films (in comparison with other deposition techniques). In order to help find a balance between laser energy and gas pressure, an inert gas (Ar) was added with the purpose of reducing the plasma energy. HZO films were grown with different Ar and O2 pressure, where measurements were done such as XRD, ferroelectric polarization loops, and leakage current. A pressure of 0.05 mbar on both O2 and Ar was found to produce the best ferroelectric HZO film with a remanent polarization of 32 uC/m2 and a low leakage current of about 6 uA/cm2.

Reference:
[1] T. Song, R. Solanas, M. Qian, I. Fina, and F. Sánchez, “Large enhancement of ferroelectric polarization in Hf 0.5 Zr 0.5 O 2 films by low plasma energy pulsed laser deposition,” Journal of Materials Chemistry C, vol. 10, no. 3, pp. 1084–1089, 2022, doi: 10.1039/D1TC05387F.

I thought this paper was interesting because as far as I have seen the most common method for making HfO2/HZO films was atomic layer deposition (ALD) or sputtering. I did not know of this method and neither did I know that this method was already attempted for HfO2/HZO but with unsatisfactory results. The paper showed a good variety of results, so results from using the different pressures were clear. HfO2/HZO is a topic I am also personally interested in so learning something new about it is always exciting.

Anyway, IEDM just started today. Can’t wait for the proceedings!