(Invited) Ferroelectric (Hf,Zr)O2 Films

Abstract

Since the first report on the ferroelectricity in ultra-thin Si-doped HfO2 film [1], the unexpected ferroelectricity in doped HfO2 and (Hf,Zr)O2 solid solution films are attracting a great deal of attention from the ferroelectric community.[2] Compared to the conventional ferroelectrics based on perovskite structure, HfO2-based ferroelectrics can be extremely thin with mature deposition process such as atomic layer deposition, environmentally benign with lead-free nature, and Si-compatible.[2] Especially, the ferroelectricity and antiferroelectricity in (Hf,Zr)O2 solid solution are considered highly promising for various electronic and energy applications.[2] The ferroelectric Hf0.5Zr0.5O2 film could have remanent polarization value higher than 20 mC/cm2, and could endure more than 109 times of electric field cycling, meaning that it is a promising candidate for the future memory applications.[2] The high coercive field of ~1 MV/cm enables even 10 nm-thick films can have sufficiently large memory window.[2] The antiferroelectric Hf0.2Zr0.8O2 film could harvest 11.5 J/cm3 cycle from its pyroelectricity, and could show adiabatic temperature change of 13.4 K for solid state cooling.[3] As a electrostatic capacitor, Hf0.3Zr0.7O2 film could store 46 J/cm3 of electric energy.[4] On the other hand, the academic researches to understand this unexpected ferroelectricity is also under rapid progress. The two step polarization switching based on the involvement of intermediate nonpolar phase in Hf0.4Zr0.6O2 film was also reported, which could be understood based on the classical first order phase transition theory.[5] The so-called “wake-up” effect, which generally means the depinching of the pinched ferroelectric hysteresis in pristine state in (Hf,Zr)O2 film, is another interesting topic in this field. The wake-up effect is now ascribed to the involvement of the complicated polymorphisms in (Hf,Zr)O2 films being related with the motion of charged defects such as oxygen vacancies.[6] In this talk, the recent progresses in the ferroelectric performance of (Hf,Zr)O2 thin films will be comprehensively reviewed based on both theoretical and experimental studies. [1] T. S. Boescke et al., Appl. Phys. Lett. 99, 102903 (2011). [2] M. H. Park et al., Adv. Mater. 27, 1811 (2015). [3] M. H. Park et al., Nano Energy 12, 131 (2015). [4] M. H. Park et al., Adv. Energy Mater. 4, 1400610 (2014). [5] M. H. Park and H. J. Kim et al., Nanoscale, DOI: 10.1039/c5nr08346j [6] H. J. Kim et al., Nanoscale 8, 1383 (2016).