In this work we will report our recent progress in the control of the interface quality between b... more In this work we will report our recent progress in the control of the interface quality between buffer layers and YBCO thin films grown by the trifluoroacetates route (TFA) and how it influences the critical current of the coated conductors. We have mainly focused on vacuum and metalorganic deposited (MOD) fluorite-like CeO2 buffer layers and on MOD perovskite SrTiO3 buffer layers. We will show that for vacuum CeO2 buffer layers, microcracks at the surface can be controlled by the means of thermal treatments. Coated conductors TFA-YBCO/CeO2sputt/YSZ/CeO2/Ni with Jc(77K)˜1MA/cm2 can be grown even in the presence of these microcracks. For MOD SrTiO3 we will show that growing the buffer layer at low temperature reduces surface roughness and multilayers with high critical currents can be achieved. An all-chemical coated conductor has been grown TFA-YBCO/SrTiO3MOD/BaZrO3MOD/NiO-SOE/Ni with promising in-plane texture, Δ φYBCO=6.6°. For MOD CeO2 buffer layers, thermal annealings in oxidizi...
Modern microelectronics and micromachining are based on crystalline silicon. The increasing deman... more Modern microelectronics and micromachining are based on crystalline silicon. The increasing demand for sensors able to operate in harsh environment, as temperature above 300°C, high pressures, intense vibrations or corrosive liquids, has stimulated the research for alternatives to silicon. Particularly due to its superior electrical, mechanical and chemical properties, silicon carbide is a material that has attracted much attention. Some
CAS 2005 Proceedings. 2005 International Semiconductor Conference, 2005., 2005
The development of high quality 3C-SiC layers on Si free of residual stress opens the possibility... more The development of high quality 3C-SiC layers on Si free of residual stress opens the possibility to use SiC for microsystems fabrication and to combine them with Si devices for sensor applications. A new front-side micromachining process technology for 3C-SiC layers on Si resonators has been developed. To show it feasibility several resonator cantilever or bridge test structures of various dimensions have been fabricated. The main advantage of SiC in comparison with Si lies on its higher Young's modulus (almost three times higher), which results in higher resonance frequencies and higher quality factors
A high field-effect mobility peak (50 cm2/Vs) has been extracted in (0001) Si face 4HSiC MOSFETs ... more A high field-effect mobility peak (50 cm2/Vs) has been extracted in (0001) Si face 4HSiC MOSFETs with oxidized Ta2Si (O-Ta2Si) high-k dielectric (k~20) as gate insulator, with their gates in the strong inversion regime. The interface state density (Dit) has not been particularly reduced in O-Ta2Si capacitors. This anomalous mobility enhancement is explained in terms of Coulomb scattering reduction and quantified using a physical model based on the Lombardi mobility model. The anomalous mobility increase is closely related to the leakage current, and also to the gate breakdown mechanism. We propose a model for which the observed interfacial SiO2 tunnel current combined with Poole-Frenkel mechanisms at the O-Ta2Si gate generates a sufficiently low abrupt transition in gate breakdown to obtain an effective passivation of the interface traps. Under these conditions, the increase of free carriers in the inversion layer induced by the gate leakage diminishes the effect of the interface tr...
ABSTRACT Zr-doped ceria thin films were prepared by spin-coating metalorganic solutions containin... more ABSTRACT Zr-doped ceria thin films were prepared by spin-coating metalorganic solutions containing polyvinylpyrrolidone (PVP), which serves as a relaxing agent to relieve the strong mechanical stresses developed during the thermal decomposition step. The precursor solutions were deposited on silicon substrates and subsequently heated in air at 500 °C. The complete decomposition of organics was checked by infrared spectroscopy with attenuated total reflectance. The molar ratio between PVP and total metal ions was varied between zero and one. Furthermore, the effect of using two different PVP molecular weights was also investigated. For the high molecular weight of PVP, crack-free films as high as 150 nm could be obtained compared to 30 nm when no PVP is added. Thickness after spin-coating and after thermal decomposition were determined by profilometry and correlated with the polymer concentration in the precursor solution, showing a linear dependence with PVP concentration in both cases. The main controlling parameter of the final thickness is the viscosity, with similar power law dependencies both before and after thermal treatment, which would indicate that the porosity fraction remains essentially constant in the final films. Furthermore, AFM analysis was used to investigate the flatness and surface porosity of the films after the thermal treatment.
Abstract. An alternative dielectric for MIS structures, using SiC as semiconductor, have been ana... more Abstract. An alternative dielectric for MIS structures, using SiC as semiconductor, have been analysed. Ta2Si films have been deposited by direct sputtering on 6H-SiC and 4H-SiC samples, and oxidized in dry environment at 950C during 90min. Ta2O5 films have been evidenced by X-Ray diffraction analysis. SIMS depth profiling analysis has revealed a considerable thickness increase of the remaining insulator after the Ta2Si oxidation, as well as the presence of an interfacial region composed by a Si-Ta-O mixture between the Ta2O5 films and the semiconductor interface. This last result has been reported in Ta2O5/Si interface previous studies. C-V and I-V measurements have been used to demonstrate the correct dielectric behaviour of the oxidized Ta2Si films, and to extract their interface properties.
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any fo... more All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 66.249.71.12-20/05/11,18:14:33) ... 894 Silicon Carbide and Related Materials - 1999
In this study, a SiC on insulator growth is optimized, in order to electrically isolate the activ... more In this study, a SiC on insulator growth is optimized, in order to electrically isolate the active structural layer towards the substrate. High quality single crystalline SiC was grown on SOI and SIS substrates. Smooth surface, low stress and bowing, confirmed by microscopy techniques, SEM, AFM, X-Ray diffraction and Raman spectroscopy, have been obtained. SiC electrostatic resonators on insulated substrates were also fabricated, and electrically driven. These results demonstrate that this material is very promising for MEMS application requiring isolation from the substrate and operation in harsh ambient.
In this work we will report our recent progress in the control of the interface quality between b... more In this work we will report our recent progress in the control of the interface quality between buffer layers and YBCO thin films grown by the trifluoroacetates route (TFA) and how it influences the critical current of the coated conductors. We have mainly focused on vacuum and metalorganic deposited (MOD) fluorite-like CeO2 buffer layers and on MOD perovskite SrTiO3 buffer layers. We will show that for vacuum CeO2 buffer layers, microcracks at the surface can be controlled by the means of thermal treatments. Coated conductors TFA-YBCO/CeO2sputt/YSZ/CeO2/Ni with Jc(77K)˜1MA/cm2 can be grown even in the presence of these microcracks. For MOD SrTiO3 we will show that growing the buffer layer at low temperature reduces surface roughness and multilayers with high critical currents can be achieved. An all-chemical coated conductor has been grown TFA-YBCO/SrTiO3MOD/BaZrO3MOD/NiO-SOE/Ni with promising in-plane texture, Δ φYBCO=6.6°. For MOD CeO2 buffer layers, thermal annealings in oxidizi...
Modern microelectronics and micromachining are based on crystalline silicon. The increasing deman... more Modern microelectronics and micromachining are based on crystalline silicon. The increasing demand for sensors able to operate in harsh environment, as temperature above 300°C, high pressures, intense vibrations or corrosive liquids, has stimulated the research for alternatives to silicon. Particularly due to its superior electrical, mechanical and chemical properties, silicon carbide is a material that has attracted much attention. Some
CAS 2005 Proceedings. 2005 International Semiconductor Conference, 2005., 2005
The development of high quality 3C-SiC layers on Si free of residual stress opens the possibility... more The development of high quality 3C-SiC layers on Si free of residual stress opens the possibility to use SiC for microsystems fabrication and to combine them with Si devices for sensor applications. A new front-side micromachining process technology for 3C-SiC layers on Si resonators has been developed. To show it feasibility several resonator cantilever or bridge test structures of various dimensions have been fabricated. The main advantage of SiC in comparison with Si lies on its higher Young's modulus (almost three times higher), which results in higher resonance frequencies and higher quality factors
A high field-effect mobility peak (50 cm2/Vs) has been extracted in (0001) Si face 4HSiC MOSFETs ... more A high field-effect mobility peak (50 cm2/Vs) has been extracted in (0001) Si face 4HSiC MOSFETs with oxidized Ta2Si (O-Ta2Si) high-k dielectric (k~20) as gate insulator, with their gates in the strong inversion regime. The interface state density (Dit) has not been particularly reduced in O-Ta2Si capacitors. This anomalous mobility enhancement is explained in terms of Coulomb scattering reduction and quantified using a physical model based on the Lombardi mobility model. The anomalous mobility increase is closely related to the leakage current, and also to the gate breakdown mechanism. We propose a model for which the observed interfacial SiO2 tunnel current combined with Poole-Frenkel mechanisms at the O-Ta2Si gate generates a sufficiently low abrupt transition in gate breakdown to obtain an effective passivation of the interface traps. Under these conditions, the increase of free carriers in the inversion layer induced by the gate leakage diminishes the effect of the interface tr...
ABSTRACT Zr-doped ceria thin films were prepared by spin-coating metalorganic solutions containin... more ABSTRACT Zr-doped ceria thin films were prepared by spin-coating metalorganic solutions containing polyvinylpyrrolidone (PVP), which serves as a relaxing agent to relieve the strong mechanical stresses developed during the thermal decomposition step. The precursor solutions were deposited on silicon substrates and subsequently heated in air at 500 °C. The complete decomposition of organics was checked by infrared spectroscopy with attenuated total reflectance. The molar ratio between PVP and total metal ions was varied between zero and one. Furthermore, the effect of using two different PVP molecular weights was also investigated. For the high molecular weight of PVP, crack-free films as high as 150 nm could be obtained compared to 30 nm when no PVP is added. Thickness after spin-coating and after thermal decomposition were determined by profilometry and correlated with the polymer concentration in the precursor solution, showing a linear dependence with PVP concentration in both cases. The main controlling parameter of the final thickness is the viscosity, with similar power law dependencies both before and after thermal treatment, which would indicate that the porosity fraction remains essentially constant in the final films. Furthermore, AFM analysis was used to investigate the flatness and surface porosity of the films after the thermal treatment.
Abstract. An alternative dielectric for MIS structures, using SiC as semiconductor, have been ana... more Abstract. An alternative dielectric for MIS structures, using SiC as semiconductor, have been analysed. Ta2Si films have been deposited by direct sputtering on 6H-SiC and 4H-SiC samples, and oxidized in dry environment at 950C during 90min. Ta2O5 films have been evidenced by X-Ray diffraction analysis. SIMS depth profiling analysis has revealed a considerable thickness increase of the remaining insulator after the Ta2Si oxidation, as well as the presence of an interfacial region composed by a Si-Ta-O mixture between the Ta2O5 films and the semiconductor interface. This last result has been reported in Ta2O5/Si interface previous studies. C-V and I-V measurements have been used to demonstrate the correct dielectric behaviour of the oxidized Ta2Si films, and to extract their interface properties.
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any fo... more All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 66.249.71.12-20/05/11,18:14:33) ... 894 Silicon Carbide and Related Materials - 1999
In this study, a SiC on insulator growth is optimized, in order to electrically isolate the activ... more In this study, a SiC on insulator growth is optimized, in order to electrically isolate the active structural layer towards the substrate. High quality single crystalline SiC was grown on SOI and SIS substrates. Smooth surface, low stress and bowing, confirmed by microscopy techniques, SEM, AFM, X-Ray diffraction and Raman spectroscopy, have been obtained. SiC electrostatic resonators on insulated substrates were also fabricated, and electrically driven. These results demonstrate that this material is very promising for MEMS application requiring isolation from the substrate and operation in harsh ambient.
Uploads
Papers by N. Mestres