Our study investigates heterogeneous co-doped HfO2 thin films integrated into metal-ferroelectric-metal stacks, achieved by incorporating multiple layers doped with various species during the atomic layer deposition process. This approach creates an artificial crystallization temperature gradient across the HfO2 film, influencing the preferred nucleation sites of HfO2 during rapid thermal processing. Our findings demonstrate that the phase composition of the annealed HfO2 film is primarily determined by heterogeneous or homogeneous crystallization processes. In cases of heterogeneous crystallization, where crystallization initiates from nuclei formed at electrode/HfO2 interfaces, grains predominantly crystallize in the orthorhombic phase. Conversely, grains are more likely to crystallize in the monoclinic phase if they originate from nuclei formed at the center of the HfO2 film. Additionally, we observe correlations between the texture of the HfO2 film and the texture of the electrodes.

In this study, a range of miniaturized Ag/AgCl reference electrodes with various layouts were successfully fabricated on wafer-level silicon-based substrates with metallic intermediate layers by precisely controlling the electrochemical deposition of Ag, followed by electrochemical chlorination of the deposited Ag layer. The structure, as well as the chemical composition of the electrode, were characterized with SEM & EDS. The results showed that the chlorination is very sensitive to the applied electric field and background solution. Potentiostatic chlorination, in combination with an adjusted mushroom-shaped Ag sealing deposition, enabled the formation of electrochemical usable Ag/AgCl layers. The stability of the electrodes was tested using open circuit potential (OCP) measurement. The results showed that the reference electrodes stayed stable for 300 s under 3 M KCl solution. The first stage study showed that the stability of the Ag/AgCl reference electrode in a chip highly depends on chip size design, chlorination conditions, and a further protection layer.

A novel machine learning (ML)-assisted approach is proposed for investigating the variability of ferroelectric field-effect transistor (FeFET) to shorten the loop of technology pathfinding. To quantify the ferroelectric (FE) domain variation, the atomic intragranular misorientation of Si-doped HfO2 thin film is measured by transmission Kikuchi diffraction (TKD) and is transformed into a polarization map. With the metrology data, polarization variation (PV) of FE domains on the gate-stack is modeled in technology computer-aided design (TCAD) to assess the impact of PV on the FeFET performance and to obtain datasets for ML-assisted analysis. A neural network model is trained using the datasets (input: polarization maps; output: high/low threshold voltage, ON-state current, and subthreshold slope) for the 28-nm bulk FeFET analysis. Our trained network, if used for inference to obtain three-sigma statistics, shows >98% of accuracy of the device features and significantly faster simulation time than TCAD. In addition, we used the transfer learning technique to reduce the number of training datasets by 83% for the fully depleted silicon-on-insulator (FDSOI) FeFET by applying the pretrained model from the bulk FeFET.

The rising interest in increased manufacturing maturity of quantum processing units is pushing the development of alternative superconducting materials for semiconductor fab process technology. However, these are often facing CMOS process incompatibility. In contrast to common CMOS materials, such as Al, TiN, and TaN, reports on the superconductivity of other suitable transition-metal nitrides are scarce, despite potential superiority. Here, we demonstrate fully CMOS-compatible fabrication of HfN and ZrN thin films on state-of-the-art 300 mm semiconductor process equipment, utilizing reactive DC magnetron sputtering on silicon wafers. Measurement of mechanical stress and surface roughness of the thin films demonstrates process compatibility. We investigated the materials phase and stoichiometry by structural analysis. The HfN and ZrN samples exhibit superconducting phase transitions with critical temperatures up to 5.84 and 7.32 K, critical fields of 1.73 and 6.40 T, and coherence lengths of 14 and 7 nm, respectively. A decrease in the critical temperature with decreasing film thickness indicates mesoscopic behavior due to geometric and grain-size limitations. The results promise a scalable application of HfN and ZrN in quantum computing and related fields.

We proposed a novel machine learning (ML)-assisted methodology to analyze the variability of ferroelectric field-effect transistor (FeFET) with raw data from the metrology. Transmission Kikuchi diffraction (TKD) measurement was performed on grown Si-doped HfO 2 (Si:HfO 2 ) thin film. An experimentally acquired polarization map was employed to generate the polarization variation of a ferroelectric gate stack. FeFETs with the multi-domains are simulated in TCAD to generate the training dataset. We trained a neural network using the polarization maps as inputs and the high/low threshold voltage, on-state current, and subthreshold slope as outputs. The trained model with 3,000 data points shows >98% of accuracy and is more than 10 6 times faster than performing TCAD to obtain statistics for 10,000 test samples.

The ferroelectric properties of hafnium oxide films are strongly influenced by the crystallization process due to the interaction of thermodynamics, kinetics, and mechanical stress. In this work, the influence of annealing temperature on the crystallographic properties and microstructure of Si-doped hafnium oxide thin films as well as their ferroelectric properties are investigated by X-ray diffraction, transmission Kikuchi diffraction, and electrical characterization. The findings reveal the emergence of a [100] and [110] out-of-plane texture for metal-ferroelectric-metal (MFM) and metal-ferroelectric-insulator-semiconductor (MFIS) capacitor structures with increasing annealing temperature, respectively. In combination with observed stress relaxation at higher temperatures and the evolution of the wake-up behavior, insights into the crystallization process and the influence of the interplay of microstructure and stress on the ferroelectric properties of hafnium oxide thin films are given.

Applying transmission Kikuchi diffraction (TKD) allows us to fundamentally investigate the Si-doped-hafnium-oxide (HSO) microstructure that results from the interface layer present in ferroelectric field-effect transistors. In addition to the predominant orthorhombic phase, dendritic HSO grains larger than 100nm govern the microstructure composition. Furthermore, the observed strong out-of-plane texture aligned along the [110] and [011] axis clearly differs from features found in hafnium oxide thin films grown on TiN layers. Our TKD analysis shows that the texture intensity strongly varies for samples annealed at different temperatures. Additionally, intra-granular misorientation and chemical composition analyses of the layers provide insight into the crystallization process of these ferroelectric thin films.

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.

Recently, ferroelectric field-effect transistors (Fe-FETs) based on hafnium oxide (HfO2) have been shown to be promising candidates for synaptic devices in neuromorphic applications. The polycrystalline structure of the ferroelectric layer strongly impacts the memory storage as well as the synaptic device performance, especially for highly scaled FeFETs. Therefore, detailed understanding of the transition behavior for synaptic potentiation and depression cases is essential. Combining the measurement results of grain structure, crystallographic phases and texture obtained by means of transmission Kikuchi diffraction (TKD) with a current percolation path (CPP) simulation model scaling trends for FeFETs suitable for neuromorphic applications can be explained. Results show that after overcoming a grain size dependent minimum channel length (L) width (W) scaling is the key factor to control the switching transition slope.

The present study investigates the cyclic deformation behavior of a new metastable β-type Ti–40Nb alloy (wt%) in two different microstructural conditions. Severe cold rolling followed by recrystallization annealing were performed on cast and homogenized Ti–40Nb rods to obtain a single β-phase microstructure at room temperature. Additional aging at 573 K was carried out to generate isothermal ω-phase precipitates in the β-matrix. Fatigue tests at cycles up to 2 × 106 and a stress ratio of R = −1 were realized with samples with electrochemically polished surfaces. EBSD analysis was carried out after the fatigue tests. Furthermore, detailed fractographic investigations as well as TEM analysis were executed. Results revealed significant differences in the cyclic deformation behavior and a higher fatigue strength for the aged condition. Reasons for superior fatigue properties of the aged condition are a pronounced precipitation hardening effect of the ω-phase as well as a complete suppression of stress-induced martensite formation and deformation twinning due to a barrier function of the ω-precipitates. In the vicinity of the fatigue crack tip, where the localized plastic zone dominates the damage evolution, precipitation-depleted channels can be observed. Within these ω-depleted channels dislocations have an increased mobility, allowing highly localized plastic deformation. Signs of other deformation features with increasing distance to the fatigue crack are not observed. EBSD analysis of the recrystallized samples with initial single β-phase showed on the contrary changes in the microstructure caused by the cyclic loading and the high instability of the β-phase. A dominant development of stress-induced α’’-martensite towards a full martensitic microstructure dependent on the applied stress amplitudes and cycles as well as additional isolated {332} <113> twinning were detected.

The study presented investigates the fatigue strength of the (α+β) Ti-6Al-4V-ELI titanium alloy processed by laser cutting with and without mechanical post-processing. The surface quality and possible notch effects as a consequence of non-optimized intermediate cutting parameters are characterized and evaluated. The microstructural changes in the heat-affected zone (HAZ) are documented in detail and compared to samples with a mechanically post-processed (barrel grinding, mechanical polishing) surface condition. The obtained results show a significant increase (≈50%) in fatigue strength due to mechanical post-processing correlating with decreased surface roughness and minimized notch effects when compared to the surface quality of the non-optimized laser cutting. The martensitic α’-phase is detected in the HAZ with the formation of distinctive zones compared to the initial equiaxial α+β microstructure. The HAZ could be removed up to 50% by means of barrel grinding and up to 100% through mechanical polishing. A fracture analysis revealed that the fatigue cracks always initiate on the laser-cut edges in the as-cut surface condition, which could be assigned to an irregular macro and micro-notch relief. However, the typical characteristics of the non-optimized laser cutting process (melting drops and significant higher surface roughness) lead to early fatigue failure. The fatigue cracks solely started from the micro-notches of the surface relief and not from the dross. As a consequence, the fatigue properties are dominated by these notches, which lead to significant scatter, as well as decreased fatigue strength compared to the surface conditions with mechanical finishing and better surface quality. With optimized laser-cutting conditions, HAZ will be minimized, and surface roughness strongly decreased, which will lead to significantly improved fatigue strength.

This study examined the fatigue properties of a newly developed cast and thermomechanical processed (β)-Ti-40Nb alloy for a possible application as biomedical alloy due to exceptional low Young’s modulus (64-73 GPa), high corrosion resistance and ductility (20-26%). Focusing on the influence of two microstructural states with fully recrystallized β-grain structure as well as an aged condition with nanometer-sized ω-precipitates, tension-compression fatigue tests (R=-1) were carried out under lab-air and showed significant differences depending on the β-phase stability under cyclic loading. Present ω- precipitates stabilized the β-phase against martensitic α’’ phase transformations leading to an increased fatigue limit of 288 MPa compared to the recrystallized state (225 MPa), where mechanical polishing and subsequent cyclic loading led to formation of α’’-phase due to the metastability of the β-phase. Additional studied commercially available (β)-Ti-45Nb alloy revealed slightly higher fatigue strength (300 MPa) and suggest a change in the dominating cyclic deformation mechanisms according to the sensitive dependence on the Nb-content. Further tests in simulated body fluid (SBF) at 37°C showed no decrease in fatigue strength due to the effect of corrosion and prove the excellent corrosion fatigue resistance of this alloy type under given test conditions.

This research work focuses on the fatigue behavior of a new metastable Ti-40Nb alloy (wt.%) with a single ß-phase microstructure and a low Young’s modulus of 60GPa. Samples were manufactured by laser cutting and subsequently subjected to an anodized (Type III) surface condition which is currently an industrial standard (Stryker Trauma GmbH). Accompanied by detailed analysis of the fractured surfaces by means of scanning electron microscopy (SEM) including cross section preparation by means of focused ion beam (FIB) at the crack initiation area, the experimental results reveal a large scatter and a fatigue strength of 150MPa at 2×106 cycles (R=−1). In-depth surface evaluation before and after the fatigue tests show a variety of large notches distributed along the complete sample radius as a consequence of the laser cutting process. Stress concentration on these surface flaws together with the notch sensitivity of titanium alloys are the major reason for the pronounced scatter of fatigue results accompanied by crack initiation always starting from the surface. Equally tested cp-titanium (ASTM Grade 4) reference samples exhibit a fatigue strength of 200MPa at 2×106cycles. Additionally studied osteosynthesis plates of Ti-40Nb and cp-4 titanium (hand surgery sector – same surface condition) showed even lower fatigue strength compared to the standard fatigue specimens.