Lead-free piezoelectric films prepared by sol-gel and potential applications in MEMS

Les composés à base du plomb sont très utilisés dans l'industrie microélectronique en raison de leurs propriétés ferroélectriques et piézoélectriques. Cependant, en raison de la toxicité du plomb, la recherche est dirigée vers le développement des matériaux piézoélectriques « écologiques » (sans plomb). L’objectif de ce travail consiste donc à synthétiser par procédé sol-gel un matériau piézoélectrique écologique : le Bi0.5Na0.5TiO3 (BNT). Les films minces ont été déposés à l’aide d’une tournette sur des substrats de Pt/TiOx/SiO2/Si. Une étape de séchage sur plaque est appliquée à 100ºC après chaque dépôt. L’utilisation du procédé thermique rapide (RTP) permet la densification et la cristallisation de BNT. Ainsi une pyrolyse est appliquée après le séchage pour densifier le film ; la température a été fixée à 200ºC. Enfin un recuit à 700ºC a permis la cristallisation des films dans la structure pérovskite. Les résultats de caractérisations électriques macroscopiques ainsi que les caractérisations à l’échelle locale ont mis en évidence des performances diélectrique, ferroélectrique et piézoélectrique encourageantes.Lead based materials are widely used in microelectronic industry due to their ferroelectric and piezoelectric properties. However, due to lead toxicity, it has recently desired to develop lead-free piezoelectric materials for environmental protection. The aim of this work is to synthesize a lead-free piezoelectric material by sol-gel method: Bi0.5Na0.5TiO3. BNT films were deposited by spin coating on Pt/TiOx/SiO2/Si substrate. The films were dried at 100ºC on a hot-plate after each layer deposition. Rapid thermal process (RTP) was used for the densification and crystallization of BNT films. Thus a pyrolysis step is applied to densify the dried film; the temperature was set at 200ºC. The film annealed at 700ºC is well crystallized in the perovskite phase. Macroscopic and local electrical characterizations showed promising dielectric, ferroelectric and piezoelectric properties

Films piézoélectriques sans plomb par une approche sol gel et applications potentielles dans les MEMS

Lead based materials are widely used in microelectronic industry due to their ferroelectric and piezoelectric properties. However, due to lead toxicity, it has recently desired to develop lead-free piezoelectric materials for environmental protection. The aim of this work is to synthesize a lead-free piezoelectric material by sol-gel method: Bi0.5Na0.5TiO3. BNT films were deposited by spin coating on Pt/TiOx/SiO2/Si substrate. The films were dried at 100ºC on a hot-plate after each layer deposition. Rapid thermal process (RTP) was used for the densification and crystallization of BNT films. Thus a pyrolysis step is applied to densify the dried film; the temperature was set at 200ºC. The film annealed at 700ºC is well crystallized in the perovskite phase. Macroscopic and local electrical characterizations showed promising dielectric, ferroelectric and piezoelectric properties.Les composés à base du plomb sont très utilisés dans l'industrie microélectronique en raison de leurs propriétés ferroélectriques et piézoélectriques. Cependant, en raison de la toxicité du plomb, la recherche est dirigée vers le développement des matériaux piézoélectriques « écologiques » (sans plomb). L’objectif de ce travail consiste donc à synthétiser par procédé sol-gel un matériau piézoélectrique écologique : le Bi0.5Na0.5TiO3 (BNT). Les films minces ont été déposés à l’aide d’une tournette sur des substrats de Pt/TiOx/SiO2/Si. Une étape de séchage sur plaque est appliquée à 100ºC après chaque dépôt. L’utilisation du procédé thermique rapide (RTP) permet la densification et la cristallisation de BNT. Ainsi une pyrolyse est appliquée après le séchage pour densifier le film ; la température a été fixée à 200ºC. Enfin un recuit à 700ºC a permis la cristallisation des films dans la structure pérovskite. Les résultats de caractérisations électriques macroscopiques ainsi que les caractérisations à l’échelle locale ont mis en évidence des performances diélectrique, ferroélectrique et piézoélectrique encourageantes

Local Pressure of Supercritical Adsorbed Hydrogen in Nanopores

An overview is given of the development of sorbent materials for hydrogen storage. Understanding the surface properties of the adsorbed film is crucial to optimize hydrogen storage capacities. In this work, the lattice gas model (Ono-Kondo) is used to determine the properties of the adsorbed hydrogen film from a single supercritical hydrogen isotherm at 77 K. In addition, this method does not require a conversion between gravimetric excess adsorption and absolute adsorption. The overall average binding energy of hydrogen is 4.4 kJ/mol and the binding energy at low coverage is 9.2 kJ/mol. The hydrogen film density at saturation is 0.10 g/mL corresponding to a local pressure of 1500 bar in the adsorbed phase

Properties of adsorbed supercritical methane film in nanopores

Adsorbed natural gas technology is an efficient technology for storing natural gas at low pressure and room temperature. This work investigates the properties of the adsorbed methane film in nanopores where methane is adsorbed by strong van der Waals forces in pores of few molecular diameter as a high-density fluid. BET surface area, porosity, and pore size distribution were measured using sub-critical nitrogen adsorption. The adsorbed film thickness, the film density, specific surface area, and methane average binding energy were extracted from a single supercritical methane adsorption isotherm using Langmuir and Ono-Kondo models. In addition, this method does not require a conversion between gravimetric excess adsorption and absolute adsorption. The adsorbed film thickness is between 4.2 and 4.4 Å and the density of the adsorbed film at maximum capacity is between 302 and 340 g/L. Specific surface areas obtained from supercritical isotherms are consistent with BET surface areas from subcritical nitrogen adsorption. The binding energies obtained from the two models are compared to the ones obtained from Clausius-Clapeyron method

Synthesis and characterization of BNT thin films

Polycrystalline piezoelectric lead-free Bi0.5Na0.5TiO3 (abbreviated as BNT) thin films were deposited on glass substrates by an optimized Sol-Gel process using the Electrospray technique. X-ray Diffraction (XRD) analysis showed that after heating the films at 650˚C for 1 hour, dense and well crystallized BNT films in the rhombohedral perovskite phase were formed. Polyhedral shaped primary particles, with an average size of approximately 200 nm and a smooth surface of 1.8 nm average roughness (Ra), were detected using AFM analysis. The deconvolution of Raman spectrum had confirmed our first results of XRD about the crystallization of BNT films due to the appearance of Raman peaks corresponding to the bending vibrations of Bi-O, Na-O and TiO6 bonds

Synthesis and characterization of BNT thin films

Polycrystalline piezoelectric lead-free Bi0.5Na0.5TiO3 (abbreviated as BNT) thin films were deposited on glass substrates by an optimized Sol-Gel process using the Electrospray technique. X-ray Diffraction (XRD) analysis showed that after heating the films at 650˚C for 1 hour, dense and well crystallized BNT films in the rhombohedral perovskite phase were formed. Polyhedral shaped primary particles, with an average size of approximately 200 nm and a smooth surface of 1.8 nm average roughness (Ra), were detected using AFM analysis. The deconvolution of Raman spectrum had confirmed our first results of XRD about the crystallization of BNT films due to the appearance of Raman peaks corresponding to the bending vibrations of Bi-O, Na-O and TiO6 bonds