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The impact of Gd addition on the structural and magnetic properties of [Formula: see text]-FePt alloy thin films, which were sputter-deposited on MgO(001) substrates at 800[Formula: see text]C, was investigated. A rapid deterioration of [Formula: see text] chemical ordering along with a strong amorphization effect is observed with addition of Gd. At more than 20 at. % Gd, additional crystalline phases occur. Due to the diminishing [Formula: see text] chemical order, the perpendicular magnetic anisotropy (PMA) gets strongly reduced from about 3 down to 1 MJ/m[Formula: see text] with addition of 14 at. % Gd. For higher Gd concentrations, the easy axis of magnetization turns fully in-plane due to dominating magnetic shape anisotropy. Furthermore, the saturation magnetization gets reduced with Gd addition due to the antiferromagnetic coupling between the Fe and Gd magnetic moments. Also, the Curie temperature can be lowered. Interestingly, with addition of Gd, a change in film morphology takes place, changing from an isolated island structure to a more continuous film morphology, which is of particular interest for samples with low Gd concentration as these films exhibit still strong PMA but rather low coercive fields.

In this work, the tuning properties of hafnium zirconium oxide (HZO) metal-ferroelectric-metal (MFM) thin film varactors are investigated. It is shown that varactors with 1:1 Hf:Zr stoichiometry and 10 nm thickness, crystallized with rapid thermal annealing (RTA) at 400°C for 60 s, show a maximum capacitance tunability of 32% at room temperature without electric field pre-cycling. The cycling and accompanying wake-up effect lead to a reduction of tunability. Furthermore, the influence of the temperature on the ferroelectric properties and tunability is explored. Upon increase of measurement temperature to 200°C, the maximum tunability decreases to 24%. An elevated temperature leads to an increase in aniferroelectric-like (AFE) behavior, which is consistent with recent studies of ferroelastic nature of AFE switching.

The back-end-of-line (BEoL) integration of ferroelectric hafnium zirconium oxide (HZO) has many advantages for applications like non-volatile memories and sensors. Using transmission Kikuchi diffraction (TKD), the influence of process parameters like annealing conditions and Zr content on the microstructure are investigated here. TKD analysis allows to map the local crystallographic phase and orientations as well as grain size and shape. The results of this study present thereby no significant dependence of the grain size, shape and phase on the annealing time. However, Zr content affects the microstructure strongly, and decrease in grain size and monoclinic phase as well as changes in the crystallographic texture are observed for higher Zr content. How this affects the polarization behavior is investigated as well.

Abstract In this article, we investigate the capacitance–voltage (C–V) characteristics of $$\text {Hf}_{x}\text {Zr}_{1-x}\text {O}_{2}$$ Hf x Zr 1 - x O 2 metal-ferroelectric-metal (MFM) thin-film capacitors with various Zr doping for varactor applications. The impact of field cycling during the wake-up process on the capacitance was analyzed. In addition, the effect of antiferroelectric-like (AFE) behavior on tuning was investigated. The transition between ferroelectric (FE) and AFE regime is particularly interesting for varactor application, as a reduced bias is required for tuning. The cycle dependence of the FE and AFE properties at elevated temperatures was also investigated, where it was shown that with an increase of temperature, the tunability is reduced. Temperature measurements also comply with recent studies of ferroelastic nature of AFE behavior. Graphic abstract

In this article, we present the capacitance–voltage ( ${C}$ – ${V}$ ) characteristics of Hf x Zr1− x O2 metal–ferroelectric–metal (MFM) thin-film capacitors with various Zr doping, thicknesses, and annealing temperatures. The influence of doping, electric field cycling, and annealing temperature on tuning characteristics (tunability) was analyzed and an optimized bias region for the maximum tunability was defined. Additional focus was made on an antiferroelectric-like (AFE) behavior, which occurs for > 50% Zr doping. The presence of both the ferroelectric and the AFE phase manifests itself in specific ${C}$ – ${V}$ behavior, where a reduced bias range is required for tuning, however, at the cost of a smaller tunability. The suitability of this behavior for varactor applications is also discussed.

We demonstrate the feasibility of thermal energy recovery in the back end of line (BEoL) employing CMOS-compatible ferroelectric hafnium oxide. Efficient pyroelectric energy harvesting with a sizable power density of 92 mWcm-3 under typical thermal conditions is achieved. Our energy harvesting approach exceeds the efficiency limit of commonly-used thermoelectric materials, without using a heat switch. The low-voltage operation, scalability, and abundance in CMOS manufacturing make HfO 2 -based ferroelectrics promising candidates for integrated energy harvesting and solid-state refrigeration applications.

This paper presents a tunable 60 GHz band-pass filter, based on a coplanar waveguide (CPW) transmission line, periodically loaded with ferroelectric Hafnium Zirconium Oxide (HZO) variable metal-ferroelectric-metal (MIM) capacitors (varactors), developed for back-end-of-line (BEoL) integration. Derived from the nonlinear capacitance of hafnium zirconium oxide and implementing the method-of-moments simulation, it was shown, that with changing the bias voltage between 0.95 and -3 V, the filter’s center frequency can be tuned between 60.5 and 69,7 GHz, respectively. Hereby, a minimum insertion loss of -3.3 dB is realized. The chip area of the filter is only 0.062 mm2, making it the smallest among tunable V-band filters.

This paper presents a 60 GHz phase shifter, based on a coplanar waveguide (CPW) transmission line, loaded with ferroelectric hafnium zirconium oxide (HZO) variable metal-insulator-metal (MIM) varactors, developed for the back-end-of-line (BEoL) on-chip integration. Using the measured data of capacitance-voltage (C-V) characteristics of HZO and implementing the method-of-moments simulation, it was shown, that by changing the bias voltage between 0.95 and -3 V, the device shows a phase shift of 111° and a minimum insertion loss of -5.84 dB at 60 GHz. The chip area of the device is 0.206 mm2, making it the smallest among non-CMOS phase shifters.