The local crystal phase and orientation of ferroelectric grains inside TiN/Hf_0.5Zr_0.5O₂/TiN have been studied by the analysis of the local electron beam scattering Kikuchi patterns, recorded in transmission. Evidence was found that the ferroelectric phase of the layers is derived from an orthorhombic phase, most likely of space group Pca2₁. The orientation analysis reveals a strong out-of-plane texture of the polycrystalline film which is in accordance with a high remanent polarization P_r observed for P-V measurements. The results of this analysis help us to further optimize the ratio of ferroelectric grains and their orientation for many applications, e.g., in the field of emerging memory or infrared sensors.

The pyroelectric response of polycrystalline, Si-doped HfO₂ layers in a thickness range of 10 nm to 50 nm is investigated employing the temperature oscillation method. The largest value of the pyroelectric coefficient is obtained for the 20 nm layer with p = 84 μC m⁻²K⁻¹, which is similar to that of lithium niobate. Furthermore, the pyroelectric coefficient is analyzed with respect to field cycling and is found to increase proportionally with the remanent polarization during wake-up, providing further evidence that the hysteresis of the material is truly ferroelectric. However, for different material thicknesses, the switchable polarization and pyroelectric coefficient are not proportional, indicating that only part of the domains is pyroelectrically active, which suggests potential for further improvement of the pyroelectric response. Due to its CMOS compatibility and conformal deposition using atomic layer deposition (ALD), Si-doped HfO₂ is a promising candidate for future energy harvesting and sensor applications.

Lanthanum has been identified as a promising dopant to achieve ferroelectricity in HfO₂ thin films in recent theoretical and experimental studies. In this work, the pyroelectric properties of 10 nm thick polycrystalline La-doped HfO₂ layers manufactured by thermal atomic layer deposition are assessed employing a sinusoidal temperature profile. Compared to Si doping, La offers a broader dopant range in which ferroelectric behavior is obtained, making the material interesting for large-scale integration and deposition on area-enhanced substrates. Pyroelectric coefficients of up to −80 μC/m² K are obtained using an optimized stoichiometry, which is comparable to earlier measurements with Si-doped HfO₂ samples. Phase-sensitive evaluation of the measured current confirms the pyroelectric origin with minimal spurious contributions. The results are discussed with respect to the ferroelectric switching behavior, which is analyzed employing first-order reversal curve measurements. It is found that there is no simple linear relationship between the remanent polarization and the pyroelectric coefficient. Experimental evidence indicates that the pyroelectric response in polycrystalline thin films is modulated by internal bias fields, which can arise from charged defects. This illustrates the need for careful tuning of the manufacturing conditions and the film phase composition in future applications such as pyroelectric sensors, energy harvesting, or solid-state cooling.

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.

Capacitors based on 10 nm antiferroelectric silicon-doped hafnium oxide (Si:HfO2) thin films are investigated in terms of energy storage efficiency, cycling endurance, and reliability. Atomic layer deposition (ALD) on an area-enhanced substrate with large-scale arrays of deep-trench structures is used to significantly increase the energy density, yielding a value of 450 μJ/cm2 and an energy storage efficiency of 67% at a voltage of 3 V. High breakdown fields are obtained, and the reliability measurement indicates that more than 90% of the devices survive three years when subjected to an operating voltage of 3 V. The film stoichiometry is optimized in terms of energy storage properties to achieve an antiferroelectric-like hysteresis loop with low fatigue during electric field cycling and uniform electrical characteristics throughout the 300 mm wafer. Si:HfO2 is a promising material for novel integrated energy storage applications, as it combines CMOS compatible manufacturing, high scalability, and conformal deposition using ALD.

The in‐plane piezoelectric response of 20 nm thick Si‐doped HfO₂ is examined by exploiting thermal expansion of the substrate upon rapid temperature cycling. The sample is heated locally by a deposited metal film, and the subsequently registered pyroelectric current is found to be frequency dependent in the observed range of 5 Hz to 35 kHz. While the intrinsic response remains constant, the secondary contribution can be switched off in the high‐frequency limit due to substrate clamping. As this secondary response is generated by thermal expansion and the piezoelectric effect, this allows for extraction of the corresponding in‐plane response. By comparing pyroelectric measurements in low‐ and high‐frequency limits, a piezoelectric coefficient d₃₁ of −11.5 pm V ⁻¹ is obtained, which is more than five times larger than that of AlN. The magnitude of piezoelectric response increases upon electric field cycling, which is associated with a transition from antiferroelectric‐like behavior to a purely ferroelectric polarization hysteresis. The hafnium oxide material system is proposed as a promising candidate for future CMOS compatible piezoelectric micro‐ and nano‐electromechanical systems (MEMS and NEMS).