Structural and functional characterization of (110)-oriented epitaxial La2/3Ca1/3MnO3 electrodes and SrTiO3 tunnel barriers

La2/3Ca1/3MnO3 (LCMO) films have been deposited on (110)-oriented SrTiO3 (STO) substrates. X-ray diffraction and high-resolution electron microscopy reveal that the (110) LCMO films are epitaxial and anisotropically in-plane strained, with higher relaxation along the [1¿10] direction than along the [001] direction; x-ray absorption spectroscopy data signaled the existence of a single intermediate Mn3+/4+ 3d-state at the film surface. Their magnetic properties are compared to those of (001) LCMO films grown simultaneously on (001) STO substrates It is found that (110) LCMO films present a higher Curie temperature (TC) and a weaker decay of magnetization when approaching TC than their (001) LCMO counterparts. These improved films have been subsequently covered by nanometric STO layers. Conducting atomic-force experiments have shown that STO layers, as thin as 0.8 nm, grown on top of the (110) LCMO electrode, display good insulating properties. We will show that the electric conductance across (110) STO layers, exponentially depending on the barrier thickness, is tunnel-like. The barrier height in STO (110) is found to be similar to that of STO (001). These results show that the (110) LCMO electrodes can be better electrodes than (001) LCMO for magnetic tunnel junctions, and that (110) STO are suitable insulating barriers

(001) and (110) La⅔Ca⅓MnO₃ epitaxial ferromagnetic electrodes : a comparative study = Elèctrodes epitaxials ferromagnètics (001) i (110) La⅔Ca⅓MnO₃ : un estudi comparatiu / :

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Effect of bottom electrodes on HZO thin film properties

International audienceThe discovery of memristor, theorized in 1971 by L. Chua, has led to the development of novel artificial neuromorphic concepts and devices, including ferroelectric-based ones. Ferroelectric Tunnel Junction (FTJ) type memristors based on zirconium-doped hafnium oxide, Hf_0.5 Zr_0.5 O_2 (HZO) have recently displayed to have synaptic learning capabilities [1]. In addition, HZO processes are already fully compatible with silicon CMOS industry with oxide layers thinner than 10 nm. In the present work, the HZO layer is realized by room temperature magnetron sputtering of a Hf_0.5 Zr_0.5 O_2 ceramic target and subsequently crystallized by rapid thermal annealing [2]. Using different bottom electrode (germanium, titanium nitride, platinum) layers grown on silicon and different substrates (n-doped silicon, n-doped germanium), we studied the effect on the stabilized crystalline phase and microstructure (Fig), band structure alignment and electrical properties of thin HZO films. Furthermore, we explored the effect of ultra-thin buffer layers between the electrodes and the HZO layer, including their material, insertion position and thickness. We exploited X-ray photoemission spectroscopy to analyze the chemistry and the electronic state of the electrodes/HZO interface. X-ray reflectometry and grazing incidence X-ray diffraction (GIXRD) were used to probe the thickness and structural characteristics of the HZO layer, whose ferroelectricity is associated to the polar orthorhombic phase. We will discuss our results in the framework of structural, chemical and physical properties of the different electrode/ferroelectric interfaces and their effect on the electrical properties of thin HZO-based junctions.References:[1] L. Chen et al. Nanoscale, vol. 10, no. 33, pp. 15826–15833, 2018.[2] J Bouaziz, et al., ACS Applied Electronic Materials 1 (9), 1740-1745, 2019

Développement de capteurs environnementaux ultra-basse consommation à base de SnO2

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How to play on the fabrication process of HfZrO2 ferroelectric thin film to enhance its physical properties

International audienceVarious applications have been suggested for fluorite-structure ferroelectrics due to their advantages over the conventional perovskite-structure ferroelectrics [1]. We focus on (Hf,Zr)O2 (HZO) thin films deposition for the capacitor of Ferroelectric Random Access Memories (FRAM) in the 1Transitor-1Capacitor (1T-1C) model. (Hf,Zr)O2 thin films are studied to either fully understand the stabilization of the ferroelectric phase (f-phase) or to fit with industrial requirements. Changing the pressure in our sputtering chamber during the room temperature deposition lead to the deposition of crystalline or amorphous films at room temperature. After a Rapid Thermal Annealing (RTA), only the amorphous films crystallize in the f-phase. Samples are stacks of Si/TiN/Hf0.5Zr0.5O/TiN/Pt. The samples are called NM, and M: NM and M refers to two different architectures, respectively non-mesa and mesa structures. Fabrication and architecture details can be found in reference [2]. The set-up for electrical measurements have been described in reference [3]. We report the fabrication of two samples deposited by magnetron sputtering. Pr values are among the highest for samples deposited by sputtering. Although the N-sample and NM-samples show very close Pr values, the two samples show completely different electrical behaviors. During cycling, the increase of Pr value for the NM-sample is more than an order of magnitude higher than the M-sample. It is accompanied by a decrease of the endurance which is two order of magnitude higher for the NM-sample than for the M-sample. The origins of the different electrical behaviors come from the micro-crystalline structures of the two samples, according to GIXRD results. The crystallization takes place during the annealing step. During annealing, M-sample is built with a TiN TE fully covering the HZO layer whereas the TiN covers only partially the HZO layer in case of the NM-sample. It induces different stress states which lead to two different micro-crystalline patterning. The M-sample shows no monoclinic peak, whereas the NM-sample shows many monoclinic orientations. It can explain the huge reduction of the wake-up effect. A correlation between long-term retention properties and the wake-up effect is also established: the sample with a reduced wake-up effect has a higher extrapolated polarization value and a smaller retention loss after ten years [4]. [1] M.H. Park, et al. MRS Commun. 1 (2018). [2] J. Bouaziz, et al., ACS Appl. Electron. Mater. 1, 1740 (2019). [3] J. Bouaziz, et al., APL Mater. 7, 081109 (2019). [4] J. Bouaziz, et al., Appl. Phys. Lett. 118, 082901 (2021)

Mixtures of hyaluronic acid and liposomes for drug delivery: Phase behavior, microstructure and mobility of liposomes

International audienceHyaluronic acid liposomal gels have previously demonstrated in vivo their great potential for drugdelivery. Elucidating their phase behavior and structure would provide a better understanding of theiruse properties. This work evaluates the microstructure and the phase behavior of mixtures of hyaluronicacid (HA) and liposomes and their impact on the vesicle mobility. HA concentration and surfaceproperties of liposomes (positively or negatively charged, neutral, with a polyethylene glycol corona) arevaried while the liposome concentration remains constant. Below the entanglement concentration of HA(0.4%), the mixtures exhibit a depletion phase separation except for positively charged liposomes thatinteract with anionic HA through attractive electrostatic interactions. At high HA concentration, nomacroscopic phase separation is observed, except a slight syneresis with cationic liposomes. Themicrostructure shows aggregates of liposomes homogeneously distributed into a HA network except forPEGylated liposomes, which seem to form bicontinuous interpenetrating networks. The diffusion ofliposomes is controlled by HA concentration and their surface properties. Finally, PEGylated liposomesdisplay the highest mobility at high HA concentration (2.28%) both macro- and microscopically. Themicrostructure of HA-liposomes mixtures and the diffusion of liposomes are key parameters that must betaken into account for drug delivery

Comparative Study of sub-8 nm HZO-Based Ferroelectric Tunnel Junctions with Enhanced Ferroelectricity

International audienceThe synthesis of sub-8 nm HZO films that exhibit robust ferroelectricity is a challenging task. Interface engineering is a promising method to improve the electrical performances and the scalability of HZO-based devices. In this work, we propose a comparative study of 6 nm HZO-based ferroelectric tunnel junctions with enhanced ferroelectricity, which will be considered for the demonstration of synaptic learning mechanisms for neuromorphic applications

Study of Polarisation and Conduction Mechanisms in Ferroelectric Hf0.5Zr0.5O2 Down to Deep Cryogenic Temperature 4.2 K

International audienceTwo structures, TiN/HZO/TiN and TiN/HZO/AlOx(2nm)/TiN, were fabricated and their electrical properties were studied down to 4.2 K. Low voltage IVs were carried out as well as polarisation-voltage curves at each temperature steps. The aim was to study and compare the evolution of ferroelectric switching and conduction in HZO for both structures. A systematic study of possible charge transport mechanisms was carried out

Influence of the electrode interface on the properties of ferroelectric HfZrO2

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