Stabilization of phase-pure rhombohedral HfZrO4 in pulsed laser deposited thin films

Controlling the crystalline structure of Hafnium Zirconate and its epitaxial relationship to a semiconducting electrode has a high technological interest, as ferroelectric materials are key ingredients for emerging electronic devices. Using Pulsed Laser Deposition, a phase pure, ultra-thin film of HfZrO4 is grown epitaxially on a GaN (0001) / Si (111) template. Since standard microscopy techniques do not allow to determine with certitude the crystalline structure of the film due to the weak scattering of oxygen, differentiated differential phase contrast (DPC) Scanning Transmission Electron Microscopy is used to allow the direct imaging of oxygen columns in the film. Combined with X-Rays diffraction analysis, the polar nature and rhombohedral R3 symmetry of the film are demonstrated

Roadmap on ferroelectric hafnia- and zirconia-based materials and devices

Ferroelectric hafnium and zirconium oxides have undergone rapid scientific development over the last decade, pushing them to the forefront of ultralow-power electronic systems. Maximizing the potential application in memory devices or supercapacitors of these materials requires a combined effort by the scientific community to address technical limitations, which still hinder their application. Besides their favorable intrinsic material properties, HfO2–ZrO2 materials face challenges regarding their endurance, retention, wake-up effect, and high switching voltages. In this Roadmap, we intend to combine the expertise of chemistry, physics, material, and device engineers from leading experts in the ferroelectrics research community to set the direction of travel for these binary ferroelectric oxides. Here, we present a comprehensive overview of the current state of the art and offer readers an informed perspective of where this field is heading, what challenges need to be addressed, and possible applications and prospects for further development

Effets de Champ Ferroelectriques dans des dispositifs à base d'oxydes supraconducteurs HTC

In this experimental thesis, we fabricated ferroelectric field-effect devices based on high-Tc superconductors. We grew high-quality epitaxial heterostructures consisting of an ultra-thin (2 to 6 unit cells) film of YBCO and a thin ferroelectric film (BFO-Mn). We fabricated transport measurement microbridges and used a CT-AFM tip to polarise the BFO-Mn outwards or towards the BFO-Mn/YBCO interface. Due to the ferroelectric field-effect, the superconducting properties of the underlying YBCO film were consequently modified. We then used this effect locally in order to design weak links within the microbridges: two regions where the superconducting properties are enhanced are separated by a narrow region where they are depressed. We explored the conditions of existence of a Josephson coupling across this weak link.In parallel, we fabricated ferroelectric junctions. The barrier is an ultra-thin BFO-Mn film sandwiched between a high-Tc superconducting YBCO bottom electrode and a low-Tc superconducting top electrode. Both at room temperature and at low temperature, we characterised the transportproperties across the barrier and the resistive switching resulting from the polarisation of the ferroelectric barrier.Cette thèse expérimentale a pour objet la fabrication de dispositifs supraconducteurs haute température, basés sur l'effet de champ ferroelectrique. D'une part, des hétérostructures consistant en une couche ultra-fine supraconductrice (2 à 6 mailles unités d'YBCO) et un film mince ferroelectrique (30 nm de BFO-Mn) hautement épitaxiées sont fabriquées par PLD. Des microdispositifs sont ensuite lithographiés, et la polarisation du film de BFO-Mn est polée dans la direction perpendiculaire aux films, soit vers l'interface soit vers la surface du BFO-Mn, à l'aide d'un AFM à pointe conductrice (CT-AFM). L'effet de champ ferroelectrique induit une modification drastique des propriétés supraconductrices du film d'YBCO. Cet effet est ensuite utilisé localement pour définir des liens faibles en travers des microdispositifs : deux régions ou les propriétés supraconductrices sont améliorées par l'effet de champ sont séparées par une région où elle sont déprimées. Les conditions d'existence d'un couplage Josephson à travers ce lien faible sont alors étudiées.D'autre part, des jonctions ferroelectriques sont fabriquées. La barrière est alors un film ultra-fin de BFO-Mn, entre une électrode haute-Tc (un film d'YBCO) et une électrode basse Tc. Les propriétés de transport à travers cette barrière et le resistive switching résultant du poling de la barrière ferroelectrique sont étudiées à température ambiante et à basse température

Ferroelectric, Analog Resistive Switching in Back‐End‐of‐Line Compatible TiN/HfZrO4/TiOx Junctions

Due to their compatibility with complementary metal–oxide–semiconductor technologies, hafnium‐based ferroelectric devices receive increasing interest for the fabrication of neuromorphic hardware. Herein, an analog resistive memory device is fabricated with a process developed for back‐end‐of‐line integration. A 4.5 nm‐thick HfZrO4 (HZO) layer is crystallized into the ferroelectric phase, a thickness thin enough to allow electrical conduction through the layer. A TiOx interlayer is used to create an asymmetric junction as required for transferring a polarization state change into a modification of the conductivity. Memristive functionality is obtained, both in the pristine state and after ferroelectric wake‐up, involving redistribution of oxygen vacancies in the ferroelectric layer. The resistive switching is shown to originate directly from the ferroelectric properties of the HZO layer.ISSN:1862-6270ISSN:1862-625