Tag: 2021

Impact of La Concentration on Ferroelectricity of La-Doped HfO2 Epitaxial Thin Films

T. Song, H. Tan, R. Bachelet, G. Saint-Girons, I. Fina,* F. Sánchez*

ACS Appl. Electron. Mater. 2021, 3, 11, 4809–4816;  DOI: doi.org/10.1021/acsaelm.1c00672

 

Epitaxial thin films of HfO2 doped with La have been grown on SrTiO3(001) and Si(001), and the impact of the La concentration on the stabilization of the ferroelectric phase has been determined. Films with 2–5 at. % La doping present the least amount of paraelectric monoclinic and cubic phases and exhibit the highest polarization, having a remanent polarization above 20 μC/cm2. The dopant concentration results in an important effect on the coercive field, which is reduced with increasing La content. Combined high polarization, high retention, and high endurance of at least 1010 cycles is obtained in 5 at. % La-doped films.

Large enhancement of ferroelectric polarization in Hf0.5Zr0.5O2 films by low plasma energy pulsed laser deposition

T. Song, R. Solanas, M. Qian, I. Fina,* F. Sánchez*

Journal of Materials Chemistry C, 2021;  DOI: doi.org/10.1039/D1TC05387F

 

The ferroelectric phase of HfO2 is generally stabilized in polycrystalline films, which typically exhibit the highest polarization when deposited using low oxidizing conditions. In contrast, epitaxial film grown by pulsed laser deposition show low or suppressed polarization if low oxygen pressure is used. Epitaxial films are essential to better understand physical properties, and obtaining films that have intrinsic polarization is of great importance. In order to advance towards this objective, we have carried out a systematic study of the epitaxial growth of Hf0.5Zr0.5O2 combining inert Ar gas with oxidizing O2 gas. This allows us controlling the oxidizing conditions (through O2 partial pressure) and the energy of the pulsed laser deposition plasma (through the total pressure of O2 and Ar). A pressure of Ar high enough to significantly reduce plasma energy and low enough O2 to reduce oxidation conditions is found to allow a large increase in ferroelectric polarization up to 32 μC/cm2, representing an increase of around 50% respect films grown by conventional pulsed laser deposition. This simple growth process, with high impact in the development of ferroelectric HfO2, can be also beneficial in the growth of thin films of other materials by pulsed laser deposition.

Efficient spin pumping into metallic SrVO3 epitaxial films

Ferran Macià, Mathieu Mirjolet and Josep Fontcuberta

J. Magnetism and Magnetic Materials 546, 168871, 15 March 2022; DOI: doi.org/10.1016/j.jmmm.2021.1688716

 

Spin-charge conversion requires materials with a large spin-orbit coupling, which is typically obtained in heavy metal (Pt, etc.) ions.

Here we demonstrate spin pumping across interfaces between metallic SrVO3, where V is a 3d1 ion, epitaxial thin films and ferromagnetic Ni80Fe20. Data shows an efficient spin pumping with a spin mixing conductance value (11.8 × 1018 m−2). These results demonstrate that heavy ions are not longer required and illustrated an yet undisclosed relevance of density of states at the Fermi level and suggest new toggles to tune spin-mixing conductance across interfaces.

 

Bulk photovoltaic effect in hexagonal LuMnO3 single crystals

Yunwei Sheng, Ignasi Fina,* Marin Gospodinov, Aaron M. Schankler Andrew M. Rappe, and Josep Fontcuberta,*

Physical ReviewB 104, 184116 (2021);  DOI: doi.org/10.1103/PhysRevB.104.184116

 

When illuminating a non-centrosymmetric material with light of energy higher than the bandgap, a net current appears because the electrons do not see the same electronic environment in one direction and the opposite direction, thus they hold a net momentum. This is the bulk photovoltaic effect (BPE), which depends on the light polarization. Here we report for the first time, in hexagonal manganites h-LuMnO3 which is ferroelectric with a narrow bandgap of ≈ 1.5 eV, that the short circuit photocurrent density (Jsc) is dependent on the direction of the polarization plane of the linearly polarized incoming light, indicating its contribution of BPE. It is found the BPE tensor elements and Glass coefficients are significantly larger than in BiFeO3, suggesting possible advantages for photoconversion.

 

 

Positive Effect of Parasitic Monoclinic Phase of Hf0.5Zr0.5O2 on Ferroelectric Endurance

Tingfeng Song, Saúl Estandía, Huan Tan, Nico Dix, Jaume Gàzquez, Ignasi Fina,* Florencio Sánchez*

Inorb. Adv. Electron. Mater. 2021, 2100420;  DOI: doi.org/10.1002/aelm.202100420

 

Endurance of ferroelectric HfO2 needs to be enhanced for its use in commercial memories. This work investigates fatigue in epitaxial Hf0.5Zr0.5O2 (HZO) instead of polycrystalline samples. Using different substrates, the relative amount of orthorhombic (ferroelectric) and monoclinic (paraelectric) phases is controlled. Epitaxial HZO films almost free of parasitic monoclinic phase suffer severe fatigue. In contrast, fatigue is mitigated in films with a greater amount of paraelectric phase.
This suggests that fatigue can be intrinsically pronounced in ferroelectric HZO. It is argued that the enhancement of endurance in films showing coexisting phases results from the suppression of pinned domain propagation at ferroelectric–paraelectric grain boundaries, in contrast with a rapid increase of the size of the pinned domains in single ferroelectric regions.

High-Temperature Synthesis and Dielectric Properties of LaTaON2

Augustin Castets, Ignasi Fina, Jhonatan R. Guarín, Judith Oró-Solé, Carlos Frontera, Clemens Ritter, Josep Fontcuberta*, and Amparo Fuertes*

Inorg. Chem. 2021, 60, 16484−16491;  DOI: doi.org/10.1021/acs.inorgchem.1c02325

 

The development of new synthetic methodologies of perovskite oxynitrides is challenging but necessary for the search of new compounds and the investigation of their properties. Here, we report on the synthesis of LaTaO1+xN2-x under N2 at 1500 °C, that allows to obtain highly sintered compounds with x ≤ 0.35, suitable for dielectric characterization. It is found that of LaTaO1+xN2-x crystallizes in the monoclinic space group I2/m. In contrast to earlier reports, two anion sites show strongly preferred occupancy by nitride indicating a dependence of the anion distribution on the synthetic approach. The dielectric permittivity for LaTaON2 (εr ≈ 200), reported for the first time, is similar to that observed in perovskites with one nitrogen per formula

 

OPEN CALL FOR PhD FELLOWSHIP

 

DEADLINE FOR APPLICATION: 11th November 2021

 

Project Title: “Symmetry and Low-Dimensionality Mine-and-Craft for Efficient Spin Manipulation and Photoconversion (SymDim) (SIMETRIA Y BAJA DIMENSIONALIDAD COMO PLATAFORMA PARA MATERIALES ESPINTRONICOS Y FOTOCONVERSION)

Project number PID2020-118479RB-I00

Profile of the candidate: We seek for a candidate desiring to get a multidisciplinary training on transport properties and optical (ellipsometry, plasmonics, etc.) measurements, and understanding of electron-correlated metallic systems and thin film growth. This combination should provide a solid scientific broad background. The candidate’s scientific education will be framed within the PhD program of “Materials Science “ of UAB (Universitat Autònoma de Barcelona) and complemented with participation to appropriate Schools to boost the education and networking skills. Other courses will include training on a) IPR protection, b) Communication skills and c) Building leadership and team management. Regular presentations at weekly group’s meeting and International conferences shall provide adequate training.

Please, address any questions to:

fontcuberta@icmab.cat

gherranz@icmab.cat

jgazqueza@gmail.com

Ignasi Fina crazy about physics

Ignasi Fina delivers a hands on work lecture to high school students crazy about physics. Crazy about physics (Bojos per la física) is a program for high school students.

Switchable photovoltaic response in hexagonal LuMnO3 single crystals

Yunwei Sheng, Ignasi Fina, Marin Gospodinov, and Josep Fontcuberta

Appl. Phys. Lett. 118, 232902 (2021);  DOI: doi.org/10.1063/5.0053379

 

Hexagonal manganites, such as h-LuMnO3, are ferroelectric with its polar axis along the hexagonal axis and have a narrow electronic bandgap (≈1.5 eV). Using Pt electrodes, h-LuMnO3 single crystals display a strong rectification, characteristic of a Schottky diode, and a large photoresponse. It is found that the short circuit photocurrent density Jsc along the polar axis is modulated (up to 25%) by the direction of the ferroelectric polarization P, leading to a short circuit photocurrent loop that mimics the ferroelectric polarization. However, a non-switchable Jsc persists. Diffusion photocurrent is shown to dominate current-in-plane measurements and contributes to the non-switchable Jsc. This observation illustrates the dramatic role of the large optical absorption in hexagonal manganites. The accompanying optical dichroism might challenge disentangling a genuine bulk photovoltaic response in h-LuMnO3 single crystals, contributing to the non-switchable Jsc. Epitaxial thin films may offer a suitable alternative.
 
 

Orbital occupancy and hybridization in strained SrVO3 epitaxial films

Mathieu Mirjolet , Hari Babu Vasili, Adrian Valadkhani, José Santiso , Vladislav Borisov, Pierluigi Gargiani, Manuel Valvidares, Roser Valentí , and Josep Fontcuberta

Phys Rev. Materials 5, 095002 (2021),  DOI:10.1103/PhysRevMaterials.5.09500212K

Strain is a knob that allows tuning the electronic bandwidth or the electronic distribution within the atomic orbitals is solids, to promote dramatic changes of their properties or even to induce emerging ones, such as metal-insulator transitions, ferroelectricity, ferromagnetism or superconductivity, to mention a few.

SrVO3 is an excellent metal of the highest interest in technology. Epitaxial strain affects the electronic conductivity supposedly by changing the electronic distribution within the 3d(t2g) orbitals and their corresponding bandwidth.

Here, we show that the role of strain is more involved. It turns out that the V-O hybridization is substantially modified by unbalancing the 3d(t2g)-2p molecular orbital mixtures. It follows that not only the orbital hierarchy of the (xy, xz and yz) orbitals of the t2g manifold is modified but also the amount of electrons at 3d(t2g) orbitals of the metal ion also change with strain. In other words, a rigid band picture does not hold even in this seemingly simple metallic oxide

Thickness effect on ferroelectric properties of La-doped HfO2 epitaxial films down to 4.5 nm

Tingfeng Song, Romain Bachelet, Guillaume Saint-Girons, Nico Dix, Ignasi Fina and Florencio Sanchez

J. Mater. Chem. C, 2021,  DOI: doi.org/10.1039/D1TC02512K

Stabilization of the orthorhombic phase of HfO2 with La allows very high polarization and endurance. However, these properties have not been confirmed yet in films having thickness of less than 10 nm. We have grown (111)-oriented La (2 at%) doped epitaxial HfO2 films on SrTiO3(001) and Si(001) substrates, and we report on the thickness dependence of their ferroelectric properties.
Films of less than 7 nm have a high remanent polarization of about 30 µC cm-2, show slight wake-up, endurance of at least 1010 cycles and retention of more than 10 years, both latest properties measured at the same poling voltage. La-doped HfO2 films even as thin as 4.5 nm also show robust ferroelectric properties.
 

Congratulations Dr. Mathieu Mirjolet!

Doctor Mathieu Mirjolet from the Laboratory of Multifunctional Thin Films and Complex Structures (MULFOX) group at ICMAB, defended his PhD thesis titled “Transparent Conducting Oxides Based on Early Transition Metals: From Electrical and Optical Properties of Epitaxial Thin Films, to Integration in All-Oxide Photoabsorbing Heterostructures.” on Friday, 23 July 2021 in an online session. Congrats!

 

Electron–Phonon Coupling and Electron–Phonon Scattering in SrVO3

M. Mirjolet, F. Rivadulla, P. Marsik, V. Borisov, R. Valentí, J. Fontcuberta,

J. Adv. Sci. 2021, 2004207. https://doi.org/;      DOI:doi.org/10.1002/advs.202004207

 

 
  • The nature of electron-electron and electron-lattice interactions in metallic oxides is revised. The common wisdom is that the strong correlations among electrons determine their properties.
  • Here we argue that the unavoidable coupling between free electrons and the lattice in ionic materials leads to the formation of polarons. These are carriers dressed by a lattice distortion that travel with them and largely determine the transport and some optical properties.
  • Moreover, we argue that in early transition metal oxides, the Fermi surface has a cylindrical shape that limits the phonons available for scattering.
  • Taking SrVO3as illustrative example of a Fermi liquids, we demonstrate that both mechanisms can contribute to the ubiquitously observed quasi-T2temperature dependence of the electrical resistivity in many metallic oxides.
  • A new twist on the physics of Fermi liquids in ionic lattices.

Optical Plasmon Excitations in Transparent Conducting SrNbO3 and SrVO3 Thin Films

Mathieu Mirjolet, Mikko Kataja, Tommi K. Hakala, Philipp Komissinskiy, Lambert Alff, Gervasi Herranz, Josep Fontcuberta,

Adv. Opt. Materials First published: 14 June 2021;      DOI:doi.org/10.1002/adom.202100520

From catalysis and flat panel displays to photovoltaics, transparent and conducting transition metal oxides are gaining momentum toward more sustainable and cost-efficient applications.

Here it is shown that, without using phase-matching arrangements, bulk plasmons can be excited in continuous epitaxial films of metallic SrVO3 and SrNbO3, with plasma absorption edges at visible range, and tuned mainly by electron correlations and phonon dressing.

Films can be made reflective or transparent at whish.

Stabilization of the Ferroelectric Phase in Epitaxial Hf1–xZrxO2 Enabling Coexistence of Ferroelectric and Enhanced Piezoelectric Properties

Tingfeng Song, Huan Tan, Nico Dix, Rahma Moalla, Jike Lyu, Guillaume Saint-Girons, Romain Bachelet, Florencio Sánchez, and Ignasi Fina

ACS Appl. Electron. Mater. 2021, 3, 5, 2106–2113 (2021);      DOI:doi.org/10.1021/acsaelm.1c00122

Systematic studies on polycrystalline Hf1–xZrxO2 films with varying Zr contents show that HfO2 films are paraelectric (monoclinic). If the Zr content is increased, films become ferroelectric (orthorhombic) and then antiferroelectric (tetragonal). HfO2 shows very good insulating properties and it is used in metal-oxide-semiconductor field-effect devices, while ZrO2 shows good piezoelectric properties, but it is antiferroelectric. In between, Hf0.5Zr0.5O2 shows good ferroelectric properties at the expense of poorer insulating and piezoelectric properties than HfO2 and ZrO2, respectively.
Here, we explore the ferroelectric, insulating, and piezoelectric properties of a series of epitaxial films of Hf1–xZrxO2 with different compositions. We show that epitaxial growth permits the stabilization of the ferroelectric phase in a whole range of Zr content (from x = 0 to x = 1). In epitaxial ZrO2 films, ferroelectricity coexists with better piezoelectric and insulating properties than Hf0.5Zr0.5O2, and in HfO2 epitaxial films, ferroelectricity coexists with better insulating properties than Hf0.5Zr0.5O2. For the case of ZrO2 films, large electroresistance is also observed. In both cases, the ferroelectric endurance is poorer than that for Hf0.5Zr0.5O2.

Saúl Estandía defens his PhD Thesis

Nanoscale Study of Epitaxial Ferroelectric Hf0.5Zr0.5O2 Thin Films and BaTiO3/SrTiO3 Superlattices

Date: Friday, 28 May 2021
Time: 11 am

Abstract: This thesis focuses on the characterization of ferroelectric Hf0.5Zr0.5Othin films and BaTiO3/SrTiOsuperlattices by combining scanning transmission electron microscopy, which allows to image the structure and chemistry locally with atomic resolution, with ferroelectric and structure measurements as x-ray diffraction. The first block revealed the ferroelectric dipole configurations in ferroelectric/paraelectric BaTiO3/SrTiO3 superlattices of different periods. A distinct configuration was found in the longest period BaTiO3/SrTiO3 superlattice (10 unit cell-BaTiO3/10 unit cell-SrTiO3), where unforeseen rotations of the polarization were directly imaged. The second block studied the stabilization of ferroelectric Hf0.5Zr0.5Oon perovskite substrates. Since the discovery of ferroelectricity in HfO2-based materials in 2011 these materials have attracted much attention, given their CMOS compatibility and robust nanoscale ferroelectricity, which bears profound advantages for applications. The strong effects of the bottom electrode and the epitaxial stress on the ferroelectricity of Hf0.5Zr0.5Othin films were studied in detail. 

Supervisors:

  • Florencio Sánchez, MULFOX group, ICMAB-CSIC
  • Jaume Gázquez, MULFOX group, ICMAB-CSIC

 

 

Critical Effect of Bottom Electrode on Ferroelectricity of Epitaxial Hf0.5Zr0.5O2 Thin Films

Saúl Estandía, Jaume Gazquez, Maria Varela, N. Dix, Mengdi Qian, Raul Solanas, Ignasi Fina and Florencio Sanchez

J. Mater. Chem. C, 9, 3486 – 3492 (2021);      DOI:doi.org/10.1039/D0TC05853J

Epitaxial orthorhombic Hf0.5Zr0.5O2 (HZO) films on La0.67Sr0.33MnO3 (LSMO) electrodes show robust ferroelectricity, with high polarization, endurance and retention. However, no similar results have been achieved using other perovskite electrodes so far. Here, LSMO and other perovskite electrodes are compared.
A Small amount of orthorhombic phase and low polarization is found in HZO films grown on La-doped BaSnO3 and Nb-doped SrTiO3, while null amounts of orthorhombic phase and polarization are detected in films on LaNiO3 and SrRuO3.The critical effect of the electrode on the stabilized phases is not consequence of differences in the electrode lattice parameter. The interface is critical, and engineering the HZO bottom interface on just a few monolayers of LSMO permits the stabilization of the orthorhombic phase. Furthermore, while the specific divalent ion (Sr or Ca) in the manganite is not relevant, reducing the La content causes a severe reduction of the amount of orthorhombic phase and the ferroelectric polarization in the HZO film.

Epitaxial Ferroelectric HfO2 Films: Growth, Properties, and Devices

Ignasi Fina* and Florencio Sánchez*

ACS Appl. Electron. Mater. 2021, 3, 4, 1530-1549;      DOI:doi.org/10.1021/acsaelm.1c00110

About ten years after ferroelectricity was first reported in doped HfO2 polycrystalline films, there is tremendous interest in this material and ferroelectric oxides are once again in the spotlight of the memories industry. Great efforts are being made to understand and control ferroelectric properties. Epitaxial films, which have fewer defects and a more controlled microstructure than polycrystalline films, can be very useful for this purpose. Epitaxial films of ferroelectric HfO2 have been much less investigated, but after the first report in 2015 significant progress has been achieved.
This review summarizes and discusses the main advances on epitaxial HfO2, considering growth, study of structural and ferroelectric properties, identification of the ferroelectric phase, and fabrication of devices. We hope this review will help researchers investigating epitaxial HfO2. It can also help extend the interest of the ferroelectric HfO2 community, now basically focused on polycrystalline samples, to epitaxial films.
 

Milena Sulzbach

My name is Milena Sulzbach and I am from Brasil. There, I studied physics and acquired my Bachelor´s and Master´s degree from Universidade Federal do Rio Grande do Sul (UFRGS). Now, I have started my PhD in ICMAB under the supervision of Prof. Fontcuberta in the Multifunctional Oxides and Complex Structures group. In my free time, I enjoy walking, listen music, reading and travelling to new places with my friends.

Milena Cervo Sulzbach defens his PhD Thesis

Resistive Switching in Hf0.5Zr0.5O2 ferroelectric tunnel junctionecs

Date: Wednesday, 26 May 2021
Time: 3 pm

Abstract: HfO2-based oxides have been explored as ReRAM elements due to their resistance change caused by redox reactions. However, the discovery of ferroelectricity in doped-HfO2 opens doors to use polarization reversal as a phenomenon to control the resistance. Here, Hf0.5Zr0.5O2 epitaxial ferroelectric tunnel junctions with thickness smaller than 5 nanometers are studied. Electrical and structural analyses have allowed identifying the coexistence of genuine ferroelectric switching and ionic-like motion as mechanisms to induce resistance change in the same junction. By engineering the film’s microstructure, the ferroelectric switching was optimized and the ionic motion was suppressed. In addition, its memristive behavior were. The results presented indicate HZO tunnel junctions are feasible alternatives for application in non-volatile memories.

Supervisors:

  • Josep Fontcuberta, MULFOX, ICMAB, CSIC

 

 

Josep Fontcuberta, Florencio Sánchez and Ignasi Fina deliver regular talks in the main ferroelectric conference.

The annual International Symposium on Applications of Ferroelectrics (ISAF) is sponsored by the IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society (UFFC-S). The first ISAF meeting was held in 1968; since that time, meetings have been hosted all around the world. The first ISAF meeting held in Japan was in the year 2002 (Nara) and again in 2007.

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Pep Fontcuberta delivers a Lecture at BeMAGIC

Pep Fontcuberta delivers a Lecture on “Oxide materials for electronics: oxitronics  ” at the BeMAGIC Summer School: Setting gateway to academia University of Cambridge 7-9 April 2021 (Workshop)

Anne-Claire Robert starting the master thesis with us!

 
Hello! My name is Anne-Claire and I’m from France! I’m a materials chemistry student at Rennes1 University. I’m working with Dr.Florencio Sanchez and Dr.Ignasi Fina to complete my Master degree. After work I enjoy playing video games with friends, travelling, sewing, doing SFX makeup… I don’t have recent picture without mask but I guess that Versailles’ gardens are au good place to represent France! See you!
 

Non-volatile optical switch of resistance in photoferroelectric tunnel junctions

Xiao Long, Huan Tan, Florencio Sánchez, Ignasi Fina, Josep Fontcuberta

Nature Communications volume 12, Article number: 382 (2021);      DOI:10.1038/s41467-020-20660-9

In the quest for energy efficient and fast memory elements, optically controlled ferroelectric memories are promising candidates. Here, we show that, by taking advantage of the imprint electric field existing in the nanometric BaTiO3 films and their photovoltaic response at visible light, the polarization of suitably written domains can be reversed under illumination. We exploit this effect to trigger and measure the associate change of resistance in tunnel devices. We show that engineering the device structure by inserting an auxiliary dielectric layer, the electroresistance increases by a factor near 2 × 103%, and a robust electric and optic cycling of the device can be obtained mimicking the operation of a memory device under dual control of light and electric fields.

 

 

Ignasi Fina Three receives an i-Link+ grant for International collaborations

Ignasi FinaFlorencio SánchezHuan Tan, and Tingfeng Song, from the Multifunctional Thin Films and Complex Structures (MULFOX) group, are joining forces with the Politecnico di Milano and the University of Cambridge to aid in the ongoing efforts in device miniaturization. They are doing so by trying to face one of the main bottlenecks in the process: heating.

As miniaturized devices become more powerful, it becomes more and more important to find solutions to dissipate the extra heat that comes with it. This team is trying to develop solid materials that can refrigerate the device using the electrocaloric effects that are very pronounced in ferroelectric materials. Ferroelectricity has been recently discovered in hafnium oxide, a CMOS compatible material, but its electrocaloric properties are yet to be investigated.

To further study the properties and applications of hafnium oxide films, Ignasi Fina’s group is pitching in their experience in ferroelectric characterization and material development. They will join the University of Cambridge’s group (UK), led by Xavier Moya, who has experience in the characterization of electrocaloric effects, and the one from Politecnico di Milano (Italy), led by Christian Rinaldi, with experience in device fabrication, in order to reduce the heating and power consumption of small devices.

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