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The hafnium oxide (HfO2) material system offers a unique combination of outstanding physical properties, that enable a manifold of novel integrated ferroelectric, piezoelectric, and pyroelectric applications. Long-term stability is an essential concern for nonvolatile memory devices, sensors, and nanoelectromechanical systems. Herein, the aging effects of the pyroelectric response in polycrystalline Si-doped HfO2 thin films in the field-free case are reported. It is observed that aging effects are accelerated by high temperatures, lower film thicknesses, and higher dopant concentration. The decay of the pyroelectric coefficients and the dielectric permittivity exhibits a logarithmic time dependence. The full pyroelectric response is restored by repeated electric field cycling (i.e., deaging). After the aging process, a significant internal bias field is observed. It is concluded that the migration of positively charged oxygen vacancies in the films is responsible for this aging process.

The "zero-strain" Li4Ti5O12 is an attractive anode material for 3D solid-state thin-film batteries (TFB) to power upcoming autonomous sensor systems. Herein, Li4Ti5O12 thin films fabricated by atomic layer deposition (ALD) are electrochemically evaluated for the first time. The developed ALD process with a growth per cycle of 0.6 Å cycle−1 at 300 °C enables high-quality and dense spinel films with superior adhesion after annealing. The short lithium-ion diffusion pathways of the nanostructured 30 nm films result in excellent electrochemical properties. Planar films reveal 98% of the theoretical capacity with 588 mAh cm−3 at 1 C. Substrate-dependent film texture is identified as a key tuning parameter for exceptional C-rate performance. The highly parallel grains of a strong out-of-plane (111)-texture allow capacities of 278 mAh cm−3 at extreme rates of 200 C. Outstanding cycle performance is demonstrated, resulting in 97.9% capacity retention of the initial 366 mAh cm−3 after 1000 cycles at 100 C. Compared to other deposition techniques, the superior performance of ALD Li4Ti5O12 is a breakthrough towards scalable high-power 3D TFBs.

On-chip integration of solid-state thin-film lithium-ion batteries (LIBs) can be a feasible solution for integrating energy storage devices directly into microchips. Constituting an energy source in such devices requires an implementation of the battery on a silicon substrate and prevent lithium ions diffusing from the active battery materials into other components. In this paper, we compare 10 nm titanium nitride, deposited with two techniques: thermal atomic layer deposition (ALD) and pulsed chemical vapor deposition (pCVD). TiN films feasibility as a barrier layer is investigated before and after electrochemical cycling by time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy. The results show the superior performance of the TiN prepared with ALD in comparison to pCVD. This drawback of pCVD identify the dependency of TiN stability on the composition ratio between nitrogen and oxygen, and the co-existence of surface/interface impurities. Moreover, 35 nm films prepared with pCVD compared with 10 nm films to show the effectiveness of increasing the thickness. Finally, we show that the concentration of oxygen atoms at grain boundaries can be a leading cause of TiN abruption. For the pCVD sample, this can be related to the higher number of crystal defects in comparison to ALD.

Piezoelectric thin films are of current interest in science and industry for highly integrated nano-electro-mechanical-systems and sensor devices. In this study, the dependence of the piezoelectric properties on the doping concentration in Si:HfO2 thin films and their crystallographic origin are investigated. The Si:HfO2 films with a thickness of 20 nm and various Si doping concentrations in the range of 2.7-5.6 cat.% were examined. The relationship between the piezoelectric displacement and remanent polarization is studied during wake-up from the antiferroelectric-like pristine state until the cycled ferroelectric state, which reveals an application-dependent optimal doping concentration. Furthermore, the piezoelectric and ferroelectric properties, as well as the relative permittivity, were measured over wake-up, thus giving a glimpse at the underlying mechanism of the transition from a pristine antiferroelectric-like behavior to a ferroelectric/piezoelectric one, revealing a pre-existing polar phase that is reorienting during wake-up. The studied samples show a strong displacement and polarization dependence on the doping concentration. Hence, the stoichiometry is an excellent parameter for the application-specific adjustment of complementary metal-oxide-semiconductor compatible piezoelectric thin films.

In this Letter, we report the percentage of the ferroelectric phase in a 10-nm-thick Hf0.5Zr0.5O2 (HZO) film deposited in a metal-insulator-metal stack by atomic layer deposition. The ferroelectric behavior was confirmed by polarization measurements and piezoresponse force microscopy. Ferroelectric behavior in this material has been attributed most likely to the formation of the polar non-centrosymmetric orthorhombic phase [Müller et al., Appl. Phys. Lett. 99, 102903 (2011)], which is difficult to distinguish from the tetragonal phase in x-ray diffraction due to peak overlap. Using a model for each of the crystal phases of hafnia-zirconia, the phase percentages were estimated using a Rietveld refinement method applied to grazing incidence x-ray diffraction data and a linear combination fit analysis procedure [McBriarty et al., Phys. Status Solidi 257, 1900285 (2020)] applied to grazing incidence extended x-ray absorption fine structure data. Using these methods, it was found that the tetragonal (P42/nmc) phase is the most prevalent at 48-60% followed by the polar non-centrosymmetric orthorhombic (Pca21) phase at 35%-40% with the remainder consisting of the monoclinic (P21/c) phase. Understanding the details of the effect of the phase structure on the electrical properties of these materials is extremely important for device engineering of HZO for logic and emerging nonvolatile memory applications. V.M. acknowledges TEL Technology Center, America, LLC, for funding support. V.M. thanks Dr. Martin McBriarty for detailed discussion regarding the EXAFS analysis procedure. The authors also acknowledge Dr. Bruce Ravel from NIST for the use of XAS end-station at 6-BM, NSLS-II. This work is based on research done at 6-BM, of the NSLS II, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by BNL under Contract No. DE-SC0012704.

The accurate determination of electrocaloric coefficients in nanometer-thin, polycrystalline doped HfO2 is challenging and has led to very different values reported in the literature. Here, we apply two different methods in order to compare and analyze reversible and irreversible or metastable contributions to the electrocaloric effect. The indirect method is based on temperature-dependent ferroelectric hysteresis characteristics. Furthermore, we apply a direct method, where electrocaloric temperature variations are observed using a specialized test structure. A comparison of both methods reveals that the indirect method dramatically overestimates the response due to thermal fatigue effects, which are caused by the migration of charged defects to the electrode interfaces. The partial transition to the antiferroelectric-like tetragonal phase is not immediately reversed to the polar Pca21 phase upon cooling. An electrocaloric coefficient of −107 mC m−2 K−1 is determined for a 20 nm thick Si-doped HfO2 film with the direct method, which corresponds to a DT of 4.4 K.

ZrO2 is of very high interest for various applications in semiconductor industry especially as high-k dielectric in metal insulator metal (MIM) capacitor devices. Further improvement of deposition processes, of material properties, and of integration schemes is essential in order to meet the strict requirements of future devices. In this paper, the authors describe a solution to solve one of the key challenges by reducing the process time of the bottle neck high-k atomic layer deposition (ALD). The authors extensively optimized the most common ALD process used for the ZrO2 deposition (TEMAZ/O-3) resulting now in a doubled growth rate compared to the published growth rates of maximum 1 angstrom/cycle. Chemical reactions explaining the origin of the high growth rate are proposed by theoretical process modelling. At the same time, the outstanding electrical properties of ZrO2 thin films could be preserved. Finally, the integration of the ZrO2 process in MIM capacitor devices with TiN electrodes was evaluated. Thereby, the known effect of TiN bottom electrode oxidation by the O-3 process was analyzed and significantly reduced by different integration approaches including wet chemical treatments and ALD process variations. The resulting MIM capacitors show low leakage current and high polarity symmetry.

Metal-Insulator-Metal capacitors, with ZrO2/Al2O 3/ZrO2 (ZAZ)-nanolaminate thin-films as a dielectric layer, exhibit reduced leakage currents compared to corresponding capacitors based on pure ZrO2 while maintaining a sufficiently high dielectric constant for the DRAM application. This work is a comparative study demonstrating how the incorporation of a small amount of Al is responsible for the suppression of crystallization during deposition. Extensive electrical characterization leads to the identification of a defect band which conductive atomic force microscopy shows to be formed along crystallite grain boundaries, extending through the entire ZrO2-film. The incorporation of a sub-layer of Al2O3 prevents these grain boundaries resulting in an effective reduction of leakage currents, despite the film being in the nanocrystalline phase, necessary for it to exhibit the required high dielectric constant. A transport model based on phonon assisted trap to trap tunneling is proposed.

Thin ZrO2 films are of high interest as high-k material in dynamic random access memory (DRAM), embedded dynamic random access memory, and resistive random access memory as well as for gate oxides. Actually, ZrO2 is predicted to be the key material in future DRAM generations below 20 nm. Profound knowledge of pure and doped ZrO2 thin films, especially of the structural properties, is essential in order to meet the requirements of future devices. This paper gives a detailed overview about the structural properties of ZrO2 films in dependence of various process parameters. The study of atomic layer deposition (ALD) growth mechanisms of ZrO2 on a TiN-substrate in comparison to a Si-substrate covered with native oxide exhibits significant differences. Furthermore, the structural properti es crystallinity, surface roughness, and film stress are studied after the ALD deposition in dependence of the process parameters deposition temperature, layer thickness, and underlying substrate. Remarkable dependencies of the ZrO2 crystallization temperatures on the substrates are figured out. The structural properties after various annealing steps are monitored as well. The influence of doping by SiO2 and Al2O3 is studied, which is primarily used to keep the thin films amorphous during deposition.

ZrO2-based metal-insulator-metal capacitors are used in various volatile and nonvolatile memory devices as well as for buffer capacitors or radio frequency applications. Thus, process optimization and material tuning by doping is necessary to selectively optimize the electrical performance. The most common process for dielectric fabrication is atomic layer deposition which guarantees high conformity in three dimensional structures and excellent composition control. In this paper, the C-V and J-V characteristics of ZrO2 metal-insulator-metal capacitors with TiN electrodes are analyzed in dependence on the O3 pulse time revealing the optimum atomic layer deposition process conditions. Moreover, a detailed study of the leakage current mechanisms in undoped ZrO2 compared to SiO2- or Al2O3-dope d ZrO2 is enclosed. Thereby, the discovered dependencies on interfaces, doping, layer thickness, and crystalline phase's enable the detailed understanding and evaluation of the most suitable material stack for dynamic random access memory devices below the 20 nm generation.

We assess the impact of structural relaxation of defects upon charging on trap-assisted tunneling in high- dielectric materials. ZrO 2/Al 2O 3/ZrO2 thin films are taken as an exemplary system. In our completely different approach, a first-principles defect model is derived from Hedins GW approximation calculations, which is then coupled to kinetic Monte Carlo charge transport simulations. Comparison between simulation and experiment demonstrates that it is often imperative to take structural relaxation processes into account when modeling nanoscale transport across defect states.

In order for sub-10 nm thin films of ZrO2 to have a dielectric constant larger than 30 they need to be crystalline. This is done by either depositing the layer at higher temperatures or by a postdeposition annealing step. Both methods induce high leakage currents in ZrO2 based dielectrics. In order to understand the leakage a thickness series of ultrathin ZrO2 and nanolaminate ZrO2 / Al2 O3 / ZrO2 (ZAZ) films, deposited by atomic layer deposition, was investigated. After deposition these films were subjected to different rapid thermal annealing (RTA) processes. Grazing incidence x-ray diffraction and transmission electron microscopy yield that the crystallization of ZrO 2 during deposition is dependent on film thickness and on the presence of an Al2 O3 sublayer. Moreover, the incorporation of Al2 O3 prevents crystallites from spanning across the entire film during RTA. C-V and I-V spectroscopies show that after a 650 °C RTA in N2 the capacitance equivalent oxide thickne ss of 10 nm ZAZ films is reduced to 1.0 nm while maintaining low leakage currents of 3.2× 10-8 A/ cm2 at 1 V. Conductive atomic force microscopy studies yield that currents are not associated with significant morphological features in amorphous layers. However, after crystallization, the currents at crystallite grain boundaries are increased in ZrO2 and ZAZ films.

Leakage currents in TiN/high-K-ZrO2/TiN capacitors were simulated by using a novel kinetic Monte Carlo algorithm specially designed to describe tunneling transport of charge carriers in high-K dielectrics, including defect-assisted transport mechanisms. Comparing simulation results with experimental data, a model for electronic transport was established and validated. Transport was found to be dominated by Poole-Frenkel emission from positively charged bulk trap states at medium voltages and trap-assisted tunneling at high voltages. Information on the conduction band offset at the TiN/ZrO2 interface as well as on the trap depth was extracted. The model accurately describes the scaling of the leakage current with temperature and with thickness of the dielectric film, and it provides insight into the mutual interdependence of the competing transport mechanisms.