Phase Transition and Microstructural Changes of Sol–Gel Derived ZrO₂/Si Films by Thermal Annealing: Possible Stability of Tetragonal Phase without Transition to Monoclinic Phase

Abstract

Stabilization of high-temperature phases such as tetragonal (t-) or cubic phases has been a pivotal issue for technological applications of polymorphic ZrO2. In this work, we fabricated ZrO2/Si films using a sol–gel deposition route and investigated the phase transformation, microstructural evolution, surface morphological changes, and interfacial chemical structures by thermal annealing. The ZrO2 precursor solution was prepared using a zirconium acetylacetonate, coated, dried on Si substrates, and finally annealed at 300–950 °C in ambient air. The sol–gel-derived ZrO2 layer crystallized into the t-phase as the annealing temperature increased. Despite high-temperature annealing, the t-phase was stabilized without a noticeable transition to the monoclinic phase, probably because of the relatively low film thickness (∼15 nm), enlarged surface/interface area due to thermal grooving, and strain effects. The probable t(112) orientation was developed after annealing at ≥800 °C, which could be related to minimization of the sum of the surface, interface, and strain energies. High-temperature thermal annealing resulted in the contraction of the ZrO2 layer as a result of the pyrolysis of the remnant organics, surface roughening by thermal grooving, and thickening of the amorphous interface layer (predominantly SiO x ) between the ZrO2 and Si.

Fabrication of Porous ZrO2 Nanostructures with Controlled Crystalline Phases and Structures via a Facile and Cost-Effective Hydrothermal Approach

“…When the calcination temperature is elevated to 800 °C, the t -ZrO 2 phase can be completely transformed to the pure m -ZrO 2 phase. It is well-known that the thermodynamically metastable t- ZrO 2 phase is easily transformed to the m- ZrO 2 phase, and the common phase transformation temperature is in the range of 600–700 °C. , In our case, in situ HT-XRD results (Figure S2) reveal that the accurate transition temperature of t- ZrO 2 to m -ZrO 2 for ZrO 2 obtained is in the range of 700–775 °C. The aforementioned results demonstrate the high stability of the t -ZrO 2 phase synthesized under hydrothermal treatment conditions at 150 °C using NaBH 4 as the precipitant.…”

Fast and Tunable Synthesis of ZrO2 Nanocrystals: Mechanistic Insights into Precursor Dependence

“…Sol-gel methods and some solvothermal methods produce poorly crystalline particles and require an additional crystallization step at high temperatures, giving rise to highly agglomerated ZrO2 NCs. 5,[14][15][16][17][18][19] Other methods suffer from the formation of mixed ZrO2 phases 5,20 and in general high temperatures and/or long reaction times 2,4,9,21 are required. These drawbacks depend on a combination of different factors: the selected synthesis method, presence or absence of pressure, difference in precursor solution or pH… One of the most appealing synthesis routes was introduced by Niederberger et al and uses a solvothermal autoclave method in benzyl alcohol to create a variety of crystalline metal oxide NCs (ZrO2, HfO2, In2O3, Ga2O3 …) at moderate temperatures.…”

“…Various ZrO 2 synthesis methods are described in the literature. Sol–gel methods and some solvothermal methods produce poorly crystalline particles and require an additional crystallization step at high temperatures, giving rise to highly agglomerated ZrO 2 NCs. ,− Other methods suffer from the formation of mixed ZrO 2 phases, , and generally high temperatures and/or long reaction times ,,, are required. These drawbacks are dependent on a combination of different factors: the selected synthesis method, the presence or absence of pressure, differences in precursor solution or pH, etc.…”

Microstructure, optical and electrical properties of solution-derived peroxo-zirconium oxide gate dielectrics for CMOS application

“…To address these issues, we herein introduce a simple solution-based fabrication process with many advantages, such as simplicity, low processing temperature, low cost, stoichiometry control and its ability to produce uniform, chemically homogeneous film over large areas, for a solution-processed ZrO 2 gate insulator [17,18]. Although some reports on the investigation of solution-based gate dielectrics, little work on the evolution of optical and electrical properties of solution-based ZrO 2 gate dielectrics modulated by annealing temperature has been reported.…”