Thin Hf_xZr_1‐xO₂ Films: A New Lead‐Free System for Electrostatic Supercapacitors with Large Energy Storage Density and Robust Thermal Stability

Abstract

still smaller than that of electrochemical capacitors due mainly to the use of the low dielectric constant ( ε r ) Al 2 O 3 thin fi lm as the dielectric layer ( ε r ≈ 9). The concurrent high-power capacitors are made mainly of linear dielectric polymers with an ESD of ≈1-2 J cm −3 . [ 3 ] Although the ε r values of linear dielectric polymers are generally small (≈2-5), their electric breakdown fi elds are quite high, thereby allowing the application of high voltages, which result in a relatively high ESD. [ 3 ] Nonetheless, their ESD values are not high enough, so many other materials have been studied for the purpose. Most previous research on this topic focused on AFE Pb(Zr,Ti)O 3 (PZT)-based fi lms because their ESD values are as large as ≈1 and ≈10-15 J cm −3 for bulk and thin fi lms, respectively. [ 3 ] An ESD value as high as ≈50 J cm −3 has been reported for thin PZT-based fi lms when a large ≈3.5 MV cm −1 electric fi eld was applied. [ 7,8 ] However, such a high electric fi eld may induce a signifi cant reliability concern for PZT fi lms. [ 9 ] In addition, the commercial use of PZT is restricted in many countries due to its environmental impact. Another signifi cant problem with PZT thin fi lms is the decrease in their ESD value by ≈20-40% when their operating temperature increases to 150 °C. [ 10,11 ] Other candidate materials are FE poly(vinylidenefl uoride) (PVDF)-based materials, which can have a large breakdown fi eld and maximum polarization. The highest ESD value of FE PVDF-based fi lms has been reported to be as high as ≈20 J cm −3 when a ≈8 MV cm −1 electric fi eld was applied. [ 3 ] However, the problem with such fi lms is that their ESD is only ≈40% of their total stored energy because PVDF is an FE material meaning that ≈60% of the total stored energy is retained in the material. The presence of remanent polarization ( P r ) prohibits the full discharge of the stored charges in any FE material. [ 3 ] In the case of AFE PVDF-based fi lms, an ESD value of ≈14 J cm −3 has been reported with a higher effi ciency of ≈70%. [ 12 ] 3D nanostructures, such as nanoholes or nanotrenches, would be needed to eventually contain an even higher ESD for practical use in electric vehicles. [ 5 ] However, both PZT-and PVDF-based materials are inappropriate for such nanostructures because they are too thick (thickness ( t f ) ≈ 10 2 -10 4 nm) to be incorporated into nanoscale structures. Therefore, a dielectric material that has an ESD value as high as that of PZT and PVDF with a high breakdown fi eld at a fi lm thickness of less than ≈10 nm must be found. The fi lm must also be well grown using the facile atomic layer deposition (ALD) technique to ensure fl uent step coverage with atomic accuracy in thickness control.FE and AFE HfO 2 -based thin fi lms with various dopants, such as Si, Al, and Zr, were recently reported, where the conventional Useful energy sources and ways to effi ciently distribute energy have been extensively studied. With the development of new energy generation and handling technologies, h...

Physical Mechanisms behind the Field‐Cycling Behavior of HfO2‐Based Ferroelectric Capacitors

“…Studies by Park et al even suggest a partial oxidation of the complete TiN. [41,42] Thus, the complete device stack consists of TiO x N y /TM-HfO x /FE-HfO 2 /TM-HfO x /TiO x sandwiched between two TiN electrodes, Figure 5b. Polycrystallinity of the HfO 2 layer was explicitly taken into account, creating the grain structure of the stack, as shown in Figure 5b.…”

Study on the internal field and conduction mechanism of atomic layer deposited ferroelectric Hf0.5Zr0.5O2 thin films

“…The N 2 atmosphere could be regarded as an inert annealing condition, and the E int of À0. 16 During the repetitive field cycling for the wake-up process, the oxygen vacancies were believed to be redistributed in the HZO films. It is notable that the N 2 -annealed sample still contained non-negligible E int of À0.09 MV cm À1 (oxygen vacancy difference of B7.5 Â 10 11 cm À2 ) even after the full wake-up, suggesting that there was another reason that caused the non-uniform distribution of the oxygen vacancies.…”

Dynamics of antipolar distortions

“…For instance, the Pnma state in ABO 3 perovskites is known to possess antipolar motions of its A cations and recent studies found that it can also adopt the double polarization-vs.-electric field hysteresis loop in some materials 13,14 that is characteristics of antiferroelectrics 15 -therefore suggesting that Pnma states in some perovskites can hold promise towards the design of energy storage devices with high energy densities and efficiencies. [16][17][18][19][20][21][22] Interestingly, all the aforementioned works on trilinear energetic couplings have been aimed at revealing and understanding resulting static properties. In other words, the effect of these original trilinear couplings on dynamics have been left out so far and are thus basically unknown, to the best of our knowledge.…”