An integrated cryogenic optical modulator

Integrated electrical and photonic circuits (PIC) operating at cryogenic temperatures are fundamental building blocks required to achieve scalable quantum computing, and cryogenic computing technologies. Optical interconnects offer better performance and thermal insulation than electrical wires and are imperative for true quantum communication. Silicon PICs have matured for room temperature applications but their cryogenic performance is limited by the absence of efficient low temperature electro-optic (EO) modulation. While detectors and lasers perform better at low temperature, cryogenic optical switching remains an unsolved challenge. Here we demonstrate EO switching and modulation from room temperature down to 4 K by using the Pockels effect in integrated barium titanate (BaTiO3)-based devices. We report the nonlinear optical (NLO) properties of BaTiO3 in a temperature range which has previously not been explored, showing an effective Pockels coefficient of 200 pm/V at 4 K. We demonstrate the largest EO bandwidth (30 GHz) of any cryogenic switch to date, ultra-low-power tuning which is 10^9 times more efficient than thermal tuning, and high-speed data modulation at 20 Gbps. Our results demonstrate a missing component for cryogenic PICs. It removes major roadblocks for the realisation of novel cryogenic-compatible systems in the field of quantum computing and supercomputing, and for interfacing those systems with the real world at room-temperature

Barium titanate (BaTiO3) RF characterization for application in electro-optic modulators

[EN] Barium titanate (BaTiO3 or BTO) is currently one of the most promising ferroelectric materials for enabling Pockels modulation that is compatible with silicon photonic circuits. The relative permittivity of BTO has been characterized in thin films deposited on a silicon-on-insulator (SOI) substrate. High values between 800 and 1600 have been estimated at 20 GHz. Furthermore, no substantial difference has been obtained by using BTO grown by molecular beam epitaxy and sputtering. The obtained permittivity has been used to properly design the RF electrodes for high-speed modulation in hybrid BTO/Si devices. Electrodes have been fabricated and the possibility of achieving modulation bandwidths up to 40 GHz has been demonstrated. The bandwidth is limited by the microwave propagation losses and, in this case, different losses have been measured depending on the BTO growth process.Financial support from European Commission under project FP7-ICT-2013-11-619456 SITOGA, and from TEC2016-76849-C2-2-R and NANOMET Conselleria de Educació, Cultura i Esport -PROMETEOII/2014 034 are acknowledged. Álvaro Rosa also acknowledges the Spanish Ministry of Economy and Competitiveness for funding his grant.Rosa Escutia, Á.; Tulli, D.; Castera-Molada, P.; Gutiérrez Campo, AM.; Griol Barres, A.; Baquero Escudero, M.; Vilquin, B.... (2017). Barium titanate (BaTiO3) RF characterization for application in electro-optic modulators. Optical Materials Express. 7(12):4328-4336. https://doi.org/10.1364/OME.7.004328S43284336712Hennings, D. (1987). Barium titanate based ceramic materials for dielectric use. International Journal of High Technology Ceramics, 3(2), 91-111. doi:10.1016/0267-3762(87)90031-2Sengupta, L., & Sengupta, S. (1997). 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ACS Photonics, 3(9), 1698-1703. doi:10.1021/acsphotonics.6b00350Hsu, M.-H. M., Marinelli, A., Merckling, C., Pantouvaki, M., Van Campenhout, J., Absil, P., & Van Thourhout, D. (2017). Orientation-dependent electro-optical response of BaTiO_3 on SrTiO_3-buffered Si(001) studied via spectroscopic ellipsometry. Optical Materials Express, 7(6), 2030. doi:10.1364/ome.7.002030Rabiei, P., Ma, J., Khan, S., Chiles, J., & Fathpour, S. (2013). Heterogeneous lithium niobate photonics on silicon substrates. Optics Express, 21(21), 25573. doi:10.1364/oe.21.025573Pernice, W. H. P., Xiong, C., Walker, F. J., & Tang, H. X. (2014). Design of a Silicon Integrated Electro-Optic Modulator Using Ferroelectric BaTiO3 Films. IEEE Photonics Technology Letters, 26(13), 1344-1347. doi:10.1109/lpt.2014.2322501Hu, X., Cueff, S., Romeo, P. R., & Orobtchouk, R. (2015). Modeling the anisotropic electro-optic interaction in hybrid silicon-ferroelectric optical modulator. 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Epitaxial ferroelectric oxides on silicon with perspectives for future device applications

Functional oxides on silicon have been the subject of in-depth research for more than 20 years. Much of this research has been focused on the quality of the integration of materials due to their intrinsic thermodynamic incompatibility, which has hindered the flourishing of the field of research. Nevertheless, growth of epitaxial transition metal oxides on silicon with a sharp interface has been achieved by elaborated kinetically controlled sequential deposition while the crystalline quality of different functional oxides has been considerably improved. In this Research Update, we focus on three applications in which epitaxial ferroelectric oxides on silicon are at the forefront, and in each of these applications, other aspects of the integration of materials play an important role. These are the fields of piezoelectric microelectromechanical system devices, electro-optical components, and catalysis. The overview is supported by a brief analysis of the synthesis processes that enable epitaxial growth of oxides on silicon. This Research Update concludes with a theoretical description of the interfaces and the possibility of manipulating their electronic structure to achieve the desired coupling between (ferroelectric) oxides and semiconductors, which opens up a remarkable perspective for many advanced applications. © 2021 Author(s)

Strain-Engineered Metal-to-Insulator Transition and Orbital Polarization in Nickelate Superlattices Integrated on Silicon

Epitaxial growth of SrTiO3 (STO) on silicon greatly accelerates the monolithic integration of multifunctional oxides into the mainstream semiconductor electronics. However, oxide superlattices (SLs), the birthplace of many exciting discoveries, remain largely unexplored on silicon. In this work, LaNiO3/LaFeO3 SLs are synthesized on STO-buffered silicon (Si/STO) and STO single-crystal substrates, and their electronic properties are compared using dc transport and X-ray absorption spectroscopy. Both sets of SLs show a similar thickness-driven metal-to-insulator transition, albeit with resistivity and transition temperature modified by the different amounts of strain. In particular, the large tensile strain promotes a pronounced Ni (Formula presented.) orbital polarization for the SL grown on Si/STO, comparable to that reported for LaNiO3 SL epitaxially strained to DyScO3 substrate. Those results illustrate the ability to integrate oxide SLs on silicon with structure and property approaching their counterparts grown on STO single crystal, and also open up new prospects of strain engineering in functional oxides based on the Si platform. © 2020 The Authors. Advanced Materials published by Wiley-VCH Gmb

Structural and magnetic properties of new phases related to perovskites in the La-Ti-O and Ba-(M,M')-F-Cl systems (M,M' 3D Transition element)

L'investigation du système La4TI3O12-LaTiO3 a permis de mettre en évidence une nouvelle série homologue de formulation LanTin-xO3n. Les structures de ces phases ont été caractérisées par diffraction des rayons X sur poudre et par microscopie électronique en transmission. Elles dérivent de différents polytypes de perovskites hexagonales et présentent une distorsion structurale due a la rotation coopérative des octaèdres autour de leurs axes ternaires. Une nouvelle serie de composes Ba2MM' F7Cl (M, M' = Mn, Fe, Co, Ni, Zn), dont les structures ont été déterminées par diffraction des rayons X sur monocristal, a été par ailleurs mis en évidence. Une étude comparative des propriétés structurales et magnétiques avec celles des composés de la série BaMF4 a été effectuée (filiation structurale résultant de différentes rotations coopératives des octaèdres, mesures d' aimantation sur poudre et monocristal, détermination des structures magnétiques de Ba2Co2F7Cl et Ba2Ni2F7Cl par diffraction des neutrons). Un nouveau chlorofluorure du cuivre a également été caractérise sur le plan structural et magnétique. Dans ce cas, une filiation structurale avec la structure de l'apatite et avec celle de phases derivees est proposée.non disponibl