Daniel Popovici - Academia.edu (original) (raw)
Papers by Daniel Popovici
Journal of the American Ceramic Society, May 3, 2011
Aerosol deposition method was used as an alternative deposition technique in crystalline electrol... more Aerosol deposition method was used as an alternative deposition technique in crystalline electrolyte deposition process. Crystalline Li1.3Al0.3Ti1.7(PO4)3 thick layers were successfully deposited on stainless‐steel substrates and X‐ray diffractometry, scanning electron microscopy, transmission electron microscopy, and AC impedance techniques were used to characterize these films. The density of the deposited films was between 83% and 86% of the theoretical density and Vickers hardness was calculated to have values between 260 and 280 Hv. Bulk and total conductivities were 3.62 × 10−3 and 1.12 × 10−6 S/cm, respectively, and DC conductivity was <10−10 S/cm for a wide range of film thicknesses. Improvement in total conductivity of the Li1.3Al0.3Ti1.7(PO4)3 samples is still needed to make these films more suitable for all‐solid‐state Li‐ion batteries.
Journal of Applied Physics, Mar 15, 2009
The effect of thermal treatment on physical properties of (Ba0.6,Sr0.4)TiO3 (BST60) ferroelectric... more The effect of thermal treatment on physical properties of (Ba0.6,Sr0.4)TiO3 (BST60) ferroelectric thick films deposited by aerosol deposition (AD) technique has been investigated by x-ray photoelectron spectroscopy (XPS) and complex impedance spectroscopy (CIS) to explain the leakage current behavior of the films. The leakage current increases when the thermal treatment temperature was increased. By XPS analysis it was found that the films are not formed entirely of BST60 phase. Carbonates of Ba or/and Sr and TiO2 coexist with the BST phase, and it is believed to play an important role in the properties of the AD-deposited BST60 thick films. CIS analysis revealed that the grain boundary region becomes less resistive with the increase in thermal treatment temperature. Also, it has been observed after comparing the electric modulus of green and thermally treated samples that the activation energy for electron-hole formation becomes smaller with the increase in thermal treatment temperature above 600 °C. Decrease in resistivity at the grain boundary regions and activation energy is believed to be caused by the diffusion from the highly conductive isolated areas present in the grain boundary toward the entire grain boundary area with increase in thermal treatment temperature.
センサ・マイクロマシンと応用システムシンポジウム講演概要集, 2003
Sensors and Materials, 2004
Ferroelectric Ba(Ti Sn )O (BTS ) thin film is newly prepared on the Pt/Ti/SiO /Si substrate by me... more Ferroelectric Ba(Ti Sn )O (BTS ) thin film is newly prepared on the Pt/Ti/SiO /Si substrate by metal-organic decomposition. The firing condition is determined by thermogravi- metric and differential thermal analysis. The BTS thin film with a flat surface and uniform thickness is obtained by spin coating in N atmosphere that avoids moisture. The BTS film has a per- ovskite phase and a preferential (110) texture. It is also found that the crystalline structure is cubic at 24 C with a lattice constant of 4.01 , and a grain size of about 30 nm was estimated by Scherrer equation and SEM image. From - hysteresis loop at 20 C, the polarization at and the electric field at are found to be 1.07 C/cm and 24.0 kV/cm, respectively. It is observed that the dielectric constant decreases monotonously from about 830 to 630 with increasing temperature ranging from 20 Ct o 50 C. Fi- nally, it is found that the BTS thin film shows a sufficient ferro- electricity and is an attractive material for funct...
IEEE MTT-S International Microwave Symposium Digest, 2005.
We have newly designed and fabricated both Ba x Sr 1-x TiO 3 (BST) ferroelectric thin film tunabl... more We have newly designed and fabricated both Ba x Sr 1-x TiO 3 (BST) ferroelectric thin film tunable phase shifter and pseudomorphic HEMT MMIC digital 360-degree phase shifter. A low loss BST thin film was obtained on MgO substrate by preparation of initial layer by pulsed laser deposition (PLD) and following metal-organic-decomposition (MOD) method. For the interdigital capacitors with finger spacing of 10 μm, dielectric loss was found to be as low as 0.002 to 0.004 when applied surface electric field was from m40 to ±40 kV/cm at measuring frequency of 1 MHz, where tunability was about 12%. Moreover, it increases up to about 40% in a Pt/BST/Pt stacked capacitor structure when the applied electric field was from m170 to ±170 kV/cm at the same frequency. When applying dc bias voltage of 0 to 60 V to the electrodes of the CPW pattern (width:60 μm, gap:10 μm, length:2.5 mm), a differential phase shift of 18 degree was obtained at 20 GHz with insertion loss of about -2 dB for Au/Cr interconnection. A 3-stage LC-ladder-type phase shifter with variable capacitors of BST film was designed to have a differential phase shift of about 40 degrees at 20 GHz. A fabricated phase shifter shows successfully the shift of 40 degree at 20GHz with bias of 60 V. The HEMT MMIC also shows a digital 360-degree phase shift with 11.25 degree interval, thus the BST phase shifter can be usable for phase adjustment of the MMIC. Finally it is found that the new BST film process is very promising for realizing a micro and millimeter-wave tunable device.
MRS Proceedings, 2004
ABSTRACTBarium Strontium Titanate (BST) thin films have been deposited on (100)-oriented MgO subs... more ABSTRACTBarium Strontium Titanate (BST) thin films have been deposited on (100)-oriented MgO substrate by combining preparation of initial layer by Pulsed Laser Deposition and main layer by Metal-Organic-Decomposition method. Films with an initial layer of 20, 30 and 40 nm thickness and final thickness of 400, 650 and 800 nm have been obtained. Physical and dielectric properties of the BST thin films have been characterized from the viewpoint of frequency-agile micro and millimeter wave circuit applications. The results reveal that Ba0.6Sr0.4TiO3 thin films have a good crystallinity with characteristic orientation that is affected by the deposition conditions of the initial layer. Interdigital capacitor with a gap of 10 μm has been characterized and the dielectric loss and tunability are as low as 0.002 to 0.004 and 12%, respectively, at frequency of 1 MHz for the applied voltage from -/+40V to +/-40V. At microwave frequencies, classical coplanar waveguide lines formed on BST/(100)M...
2008 17th IEEE International Symposium on the Applications of Ferroelectrics, 2008
ABSTRACT The aerosol deposition (AD) technique is unique among today??s film growing technologies... more ABSTRACT The aerosol deposition (AD) technique is unique among today??s film growing technologies because ceramic thick films can be fabricated at room temperature. Thick (Ba0.6,Sr0.4)TiO3 films have been fabricated on Si/SiO2/Ti/Pt substrates by AD method. As-deposited films and films postannealed at different temperatures have been investigated by SEM, XRD, XPS, UV-PYS and impedance spectroscopy. UV-PYS measurements showed that Fermi level is found closer to the valence band when postannealing temperature has been increased, suggesting that the films are acting more strongly like a p-type semiconductor as postannealing temperature increases. Leakage currents have been found to increase with increase in postannealing temperature and it is believed that this effect is caused by increase in the conductance of grain boundary as revealed by impedance spectroscopy measurements. A secondary phase is observed in XRD patterns of the samples annealed at temperatures of 7000C or above. The decrease in grain boundary resistance observed by impedance spectroscopy measurements with increase of annealing temperature is explained by a reduced potential barrier at the grain-grain boundary interface by annealing.
Key Engineering Materials, 2009
(Ba0.6,Sr0.4)TiO3 thick films have been fabricated on various substrates and their physical and e... more (Ba0.6,Sr0.4)TiO3 thick films have been fabricated on various substrates and their physical and electrical properties were analyzed. The effect of primary powder condition on the quality of the BST fabricated films using aerosol deposition technique has been investigated keeping in mind results shown in the literature for BST films fabricated with classical deposition techniques. Presence of carbonates and TiO2 has been demonstrated by XPS analysis and the leakage current behavior has linked to the presence of TiO2 at the grain boundaries. The films showed good insulating properties, with small leakage densities being on the order of 10-6 A/cm2 for an applied electric field of 150 kV/cm.
Journal of the American Ceramic Society, 2011
ABSTRACT
Journal of Applied Physics, 2009
ABSTRACT
Japanese Journal of Applied Physics, 2010
(Ba0.6,Sr0.4)TiO3 (BST60) thick films were fabricated on Cu substrates by aerosol deposition (AD)... more (Ba0.6,Sr0.4)TiO3 (BST60) thick films were fabricated on Cu substrates by aerosol deposition (AD) method. The quality of the raw powder was checked and optimized to increase the dielectric constant of the fabricated films without the need of a post-film-formation annealing procedure. The carbonate phase has been observed in the raw powder and it was successfully reduced by thermally treating the powder at 900 °C. The AD-fabricated films obtained from the 900 °C thermally-treated powder show a dielectric constant of 200, which is much higher than that of the AD-fabricated films obtained from the raw powders. The leakage currents in the films fabricated from 900 °C thermally-treated powders stay below 10-7 A/cm2 when the applied electric field is less than 500 kV/cm, being at least one order of magnitude smaller than the leakage values in the AD-fabricated films obtained from the raw powder. The above results indicate that thermally treating the powder at 900 °C is a satisfactory method of improving the electrical properties of the AD-fabricated BST60 thick films.
Japanese Journal of Applied Physics, 2008
ABSTRACT
Integrated Ferroelectrics, 2005
ABSTRACT
Integrated Ferroelectrics, 2006
Barium strontium titanate, (Ba0.6,Sr0.4)TiO3, thin films have been deposited on (100)-orientated ... more Barium strontium titanate, (Ba0.6,Sr0.4)TiO3, thin films have been deposited on (100)-orientated MgO substrates by metal-organic decomposition process. The annealing step has been performed for samples on which the amorphous layers have different thicknesses. The influence of the annealing condition on the BST60 thin films was investigated. Tunability and dielectric loss were found to be improved when the annealing is performed for amorphous layers of smaller thickness. UV-Photoyield Spectroscopy (UV-PYS) has been used in order to explain these improvements. It was revealed that, a decrease in the thickness of the amorphous layer that will be annealed will cause a reduction in the concentration of the oxygen vacancies in the film and, with it, an improvement in tuning behavior of the BST thin films.
Integrated Ferroelectrics, 2006
Polycrystalline Ba(Ti0.85Sn0.15)O3 (BTS15) thin films have been prepared on Pt/Ti/SiO2/Si wafers ... more Polycrystalline Ba(Ti0.85Sn0.15)O3 (BTS15) thin films have been prepared on Pt/Ti/SiO2/Si wafers by Metal-Organic Decomposition (MOD) process. Spin-coating was performed in N2 atmosphere using different gas flow rates from 0 to 5 l/min while keeping the other fabrication steps the same. The influence of N2 gas during the spin-coating was investigated. Investigations using XRD and AFM revealed that nitrogen gas flow plays an important role in obtaining films with a good crystallinity and a good grain size/RMS roughness ratio. Also, XPS and UV-PYS investigations revealed that, for the samples obtained when using 4 l/min N2 flow during spinning, the concentration of oxygen vacancies has the smallest value among the investigated samples. The BTS samples with nitrogen flow rate of 4 l/min have the highest polarization and the smallest leakage current among the investigated samples. Changes in electrical properties were explained considering the fact that the grain size and the roughness of the sample are affected by the different nitrogen flow rate and that the oxygen vacancy concentration is also influenced by the N2 gas flow. Temperature Coefficient of Dielectric constant (TCD), a parameter of infrared sensitivity, becomes more than 1%/K for a large temperature range when the N2 flow rate was 4 l/min, making this film suitable for infrared sensing applications.
Integrated Ferroelectrics, 2004
Ba(Ti1—xSnx)O3 (BTS) ferroelectric thin films have been prepared by metal-organic decomposition m... more Ba(Ti1—xSnx)O3 (BTS) ferroelectric thin films have been prepared by metal-organic decomposition method whose final annealing temperature was optimized to 700°C for dielectric bolometer. High temperature coefficient of dielectric constant (TCD) of 1–3%/K and low dielectric loss of 0.04 have been obtained in x = 0.15 and 0.17. Field-induced pyroelectricity of the BTS film was calculated to be an excellent value
Journal of the American Ceramic Society, May 3, 2011
Aerosol deposition method was used as an alternative deposition technique in crystalline electrol... more Aerosol deposition method was used as an alternative deposition technique in crystalline electrolyte deposition process. Crystalline Li1.3Al0.3Ti1.7(PO4)3 thick layers were successfully deposited on stainless‐steel substrates and X‐ray diffractometry, scanning electron microscopy, transmission electron microscopy, and AC impedance techniques were used to characterize these films. The density of the deposited films was between 83% and 86% of the theoretical density and Vickers hardness was calculated to have values between 260 and 280 Hv. Bulk and total conductivities were 3.62 × 10−3 and 1.12 × 10−6 S/cm, respectively, and DC conductivity was <10−10 S/cm for a wide range of film thicknesses. Improvement in total conductivity of the Li1.3Al0.3Ti1.7(PO4)3 samples is still needed to make these films more suitable for all‐solid‐state Li‐ion batteries.
Journal of Applied Physics, Mar 15, 2009
The effect of thermal treatment on physical properties of (Ba0.6,Sr0.4)TiO3 (BST60) ferroelectric... more The effect of thermal treatment on physical properties of (Ba0.6,Sr0.4)TiO3 (BST60) ferroelectric thick films deposited by aerosol deposition (AD) technique has been investigated by x-ray photoelectron spectroscopy (XPS) and complex impedance spectroscopy (CIS) to explain the leakage current behavior of the films. The leakage current increases when the thermal treatment temperature was increased. By XPS analysis it was found that the films are not formed entirely of BST60 phase. Carbonates of Ba or/and Sr and TiO2 coexist with the BST phase, and it is believed to play an important role in the properties of the AD-deposited BST60 thick films. CIS analysis revealed that the grain boundary region becomes less resistive with the increase in thermal treatment temperature. Also, it has been observed after comparing the electric modulus of green and thermally treated samples that the activation energy for electron-hole formation becomes smaller with the increase in thermal treatment temperature above 600 °C. Decrease in resistivity at the grain boundary regions and activation energy is believed to be caused by the diffusion from the highly conductive isolated areas present in the grain boundary toward the entire grain boundary area with increase in thermal treatment temperature.
センサ・マイクロマシンと応用システムシンポジウム講演概要集, 2003
Sensors and Materials, 2004
Ferroelectric Ba(Ti Sn )O (BTS ) thin film is newly prepared on the Pt/Ti/SiO /Si substrate by me... more Ferroelectric Ba(Ti Sn )O (BTS ) thin film is newly prepared on the Pt/Ti/SiO /Si substrate by metal-organic decomposition. The firing condition is determined by thermogravi- metric and differential thermal analysis. The BTS thin film with a flat surface and uniform thickness is obtained by spin coating in N atmosphere that avoids moisture. The BTS film has a per- ovskite phase and a preferential (110) texture. It is also found that the crystalline structure is cubic at 24 C with a lattice constant of 4.01 , and a grain size of about 30 nm was estimated by Scherrer equation and SEM image. From - hysteresis loop at 20 C, the polarization at and the electric field at are found to be 1.07 C/cm and 24.0 kV/cm, respectively. It is observed that the dielectric constant decreases monotonously from about 830 to 630 with increasing temperature ranging from 20 Ct o 50 C. Fi- nally, it is found that the BTS thin film shows a sufficient ferro- electricity and is an attractive material for funct...
IEEE MTT-S International Microwave Symposium Digest, 2005.
We have newly designed and fabricated both Ba x Sr 1-x TiO 3 (BST) ferroelectric thin film tunabl... more We have newly designed and fabricated both Ba x Sr 1-x TiO 3 (BST) ferroelectric thin film tunable phase shifter and pseudomorphic HEMT MMIC digital 360-degree phase shifter. A low loss BST thin film was obtained on MgO substrate by preparation of initial layer by pulsed laser deposition (PLD) and following metal-organic-decomposition (MOD) method. For the interdigital capacitors with finger spacing of 10 μm, dielectric loss was found to be as low as 0.002 to 0.004 when applied surface electric field was from m40 to ±40 kV/cm at measuring frequency of 1 MHz, where tunability was about 12%. Moreover, it increases up to about 40% in a Pt/BST/Pt stacked capacitor structure when the applied electric field was from m170 to ±170 kV/cm at the same frequency. When applying dc bias voltage of 0 to 60 V to the electrodes of the CPW pattern (width:60 μm, gap:10 μm, length:2.5 mm), a differential phase shift of 18 degree was obtained at 20 GHz with insertion loss of about -2 dB for Au/Cr interconnection. A 3-stage LC-ladder-type phase shifter with variable capacitors of BST film was designed to have a differential phase shift of about 40 degrees at 20 GHz. A fabricated phase shifter shows successfully the shift of 40 degree at 20GHz with bias of 60 V. The HEMT MMIC also shows a digital 360-degree phase shift with 11.25 degree interval, thus the BST phase shifter can be usable for phase adjustment of the MMIC. Finally it is found that the new BST film process is very promising for realizing a micro and millimeter-wave tunable device.
MRS Proceedings, 2004
ABSTRACTBarium Strontium Titanate (BST) thin films have been deposited on (100)-oriented MgO subs... more ABSTRACTBarium Strontium Titanate (BST) thin films have been deposited on (100)-oriented MgO substrate by combining preparation of initial layer by Pulsed Laser Deposition and main layer by Metal-Organic-Decomposition method. Films with an initial layer of 20, 30 and 40 nm thickness and final thickness of 400, 650 and 800 nm have been obtained. Physical and dielectric properties of the BST thin films have been characterized from the viewpoint of frequency-agile micro and millimeter wave circuit applications. The results reveal that Ba0.6Sr0.4TiO3 thin films have a good crystallinity with characteristic orientation that is affected by the deposition conditions of the initial layer. Interdigital capacitor with a gap of 10 μm has been characterized and the dielectric loss and tunability are as low as 0.002 to 0.004 and 12%, respectively, at frequency of 1 MHz for the applied voltage from -/+40V to +/-40V. At microwave frequencies, classical coplanar waveguide lines formed on BST/(100)M...
2008 17th IEEE International Symposium on the Applications of Ferroelectrics, 2008
ABSTRACT The aerosol deposition (AD) technique is unique among today??s film growing technologies... more ABSTRACT The aerosol deposition (AD) technique is unique among today??s film growing technologies because ceramic thick films can be fabricated at room temperature. Thick (Ba0.6,Sr0.4)TiO3 films have been fabricated on Si/SiO2/Ti/Pt substrates by AD method. As-deposited films and films postannealed at different temperatures have been investigated by SEM, XRD, XPS, UV-PYS and impedance spectroscopy. UV-PYS measurements showed that Fermi level is found closer to the valence band when postannealing temperature has been increased, suggesting that the films are acting more strongly like a p-type semiconductor as postannealing temperature increases. Leakage currents have been found to increase with increase in postannealing temperature and it is believed that this effect is caused by increase in the conductance of grain boundary as revealed by impedance spectroscopy measurements. A secondary phase is observed in XRD patterns of the samples annealed at temperatures of 7000C or above. The decrease in grain boundary resistance observed by impedance spectroscopy measurements with increase of annealing temperature is explained by a reduced potential barrier at the grain-grain boundary interface by annealing.
Key Engineering Materials, 2009
(Ba0.6,Sr0.4)TiO3 thick films have been fabricated on various substrates and their physical and e... more (Ba0.6,Sr0.4)TiO3 thick films have been fabricated on various substrates and their physical and electrical properties were analyzed. The effect of primary powder condition on the quality of the BST fabricated films using aerosol deposition technique has been investigated keeping in mind results shown in the literature for BST films fabricated with classical deposition techniques. Presence of carbonates and TiO2 has been demonstrated by XPS analysis and the leakage current behavior has linked to the presence of TiO2 at the grain boundaries. The films showed good insulating properties, with small leakage densities being on the order of 10-6 A/cm2 for an applied electric field of 150 kV/cm.
Journal of the American Ceramic Society, 2011
ABSTRACT
Journal of Applied Physics, 2009
ABSTRACT
Japanese Journal of Applied Physics, 2010
(Ba0.6,Sr0.4)TiO3 (BST60) thick films were fabricated on Cu substrates by aerosol deposition (AD)... more (Ba0.6,Sr0.4)TiO3 (BST60) thick films were fabricated on Cu substrates by aerosol deposition (AD) method. The quality of the raw powder was checked and optimized to increase the dielectric constant of the fabricated films without the need of a post-film-formation annealing procedure. The carbonate phase has been observed in the raw powder and it was successfully reduced by thermally treating the powder at 900 °C. The AD-fabricated films obtained from the 900 °C thermally-treated powder show a dielectric constant of 200, which is much higher than that of the AD-fabricated films obtained from the raw powders. The leakage currents in the films fabricated from 900 °C thermally-treated powders stay below 10-7 A/cm2 when the applied electric field is less than 500 kV/cm, being at least one order of magnitude smaller than the leakage values in the AD-fabricated films obtained from the raw powder. The above results indicate that thermally treating the powder at 900 °C is a satisfactory method of improving the electrical properties of the AD-fabricated BST60 thick films.
Japanese Journal of Applied Physics, 2008
ABSTRACT
Integrated Ferroelectrics, 2005
ABSTRACT
Integrated Ferroelectrics, 2006
Barium strontium titanate, (Ba0.6,Sr0.4)TiO3, thin films have been deposited on (100)-orientated ... more Barium strontium titanate, (Ba0.6,Sr0.4)TiO3, thin films have been deposited on (100)-orientated MgO substrates by metal-organic decomposition process. The annealing step has been performed for samples on which the amorphous layers have different thicknesses. The influence of the annealing condition on the BST60 thin films was investigated. Tunability and dielectric loss were found to be improved when the annealing is performed for amorphous layers of smaller thickness. UV-Photoyield Spectroscopy (UV-PYS) has been used in order to explain these improvements. It was revealed that, a decrease in the thickness of the amorphous layer that will be annealed will cause a reduction in the concentration of the oxygen vacancies in the film and, with it, an improvement in tuning behavior of the BST thin films.
Integrated Ferroelectrics, 2006
Polycrystalline Ba(Ti0.85Sn0.15)O3 (BTS15) thin films have been prepared on Pt/Ti/SiO2/Si wafers ... more Polycrystalline Ba(Ti0.85Sn0.15)O3 (BTS15) thin films have been prepared on Pt/Ti/SiO2/Si wafers by Metal-Organic Decomposition (MOD) process. Spin-coating was performed in N2 atmosphere using different gas flow rates from 0 to 5 l/min while keeping the other fabrication steps the same. The influence of N2 gas during the spin-coating was investigated. Investigations using XRD and AFM revealed that nitrogen gas flow plays an important role in obtaining films with a good crystallinity and a good grain size/RMS roughness ratio. Also, XPS and UV-PYS investigations revealed that, for the samples obtained when using 4 l/min N2 flow during spinning, the concentration of oxygen vacancies has the smallest value among the investigated samples. The BTS samples with nitrogen flow rate of 4 l/min have the highest polarization and the smallest leakage current among the investigated samples. Changes in electrical properties were explained considering the fact that the grain size and the roughness of the sample are affected by the different nitrogen flow rate and that the oxygen vacancy concentration is also influenced by the N2 gas flow. Temperature Coefficient of Dielectric constant (TCD), a parameter of infrared sensitivity, becomes more than 1%/K for a large temperature range when the N2 flow rate was 4 l/min, making this film suitable for infrared sensing applications.
Integrated Ferroelectrics, 2004
Ba(Ti1—xSnx)O3 (BTS) ferroelectric thin films have been prepared by metal-organic decomposition m... more Ba(Ti1—xSnx)O3 (BTS) ferroelectric thin films have been prepared by metal-organic decomposition method whose final annealing temperature was optimized to 700°C for dielectric bolometer. High temperature coefficient of dielectric constant (TCD) of 1–3%/K and low dielectric loss of 0.04 have been obtained in x = 0.15 and 0.17. Field-induced pyroelectricity of the BTS film was calculated to be an excellent value