Pooran Chandra Joshi

Structural and electrical characteristics of rapid thermally processed ferroelectric Bi4Ti3O12 thin films prepared by metalorganic solution deposition technique

Polycrystalline Bi4Ti3O12 thin films having layered perovskite structure were fabricated by metalorganic solution deposition technique on both Pt‐coated Si and bare Si substrates at a temperature as low as 500 °C. The effects of post‐deposition rapid thermal annealing on the structural and electrical properties were analyzed. The electrical measurements were conducted on metal–ferroelectric–metal capacitors. The typical measured small signal dielectric constant and dissipation factor at 100 kHz were 184 and 0.018 and the remanent polarization and the coercive field were 4.4 μC/cm2 and 84 kV/cm, respectively. The films exhibited high resistivity in the range 108–1012 Ω cm for films annealed at temperatures of 500–700 °C for 10 s. The I–V characteristics were found to be Ohmic at low fields and space‐charge‐limited at high fields. A V3/2 dependence of the current was observed in the space‐charge region. This could be explained by assuming the mobility to be field dependent since in thin films the electric f...

Properties of SrBi2Ta2O9 ferroelectric thin films prepared by a modified metalorganic solution deposition technique

Polycrystalline SrBi2Ta2O9 thin films having a layered-perovskite structure were fabricated by a modified metalorganic solution deposition technique using room temperature processed alkoxidecarboxylate precursor solution. It was possible to obtain a complete perovskite phase at an annealing temperature of 650 °C and no pyrochlore phase was observed even up to 600 °C. In addition, the SrBi2Ta2O9 thin films annealed at 750 °C exhibited better structural, dielectric, and ferroelectric properties than those reported by previous techniques. The effects of postdeposition annealing on the structural, dielectric, and ferroelectric properties were analyzed. The electrical measurements were conducted on Pt/SrBi2Ta2O9/Pt capacitors. The typical measured small signal dielectric constant and dissipation factor at 100 kHz were 330 and 0.023 and the remanent polarization and the coercive field were 8.6 μC/cm2 and 23 kV/cm, respectively, for 0.25-μm-thick films annealed at 750 °C. The leakage current density was lower th...

Thin films of layered-structure (1−x)SrBi2Ta2O9−xBi3Ti(Ta1−yNby)O9 solid solution for ferroelectric random access memory devices

We report on the thin films of solid–solution material (1−x)SrBi2Ta2O9−xBi3Ti(Ta1−yNby)O9 fabricated by a modified metalorganic solution deposition technique for ferroelectric random access memory devices. Using the modified technique, it was possible to obtain the pyrochlore free crystalline thin films at an annealing temperature as low as 600 °C. The solid–solution of layered perovskite materials helped us to significantly improve the ferroelectric properties, higher Pr and higher Tc, compared to SrBi2Ta2O9; a leading candidate material for memory applications. For example, the films with 0.7 SrBi2Ta2O9–0.3Bi3TiTaO9 composition and annealed in the temperature range 650–750 °C exhibited 2Pr and Ec values in the range 12.4–27.8 μC/cm2 and 68–80 kV/cm, respectively. The leakage current density was lower than 10−8 A/cm2 at an applied electric field of 200 kV/cm. The films exhibited good fatigue characteristics under bipolar stressing.

HIGHLY ORIENTED FERROELECTRIC CABI2NB2O9 THIN FILMS DEPOSITED ON SI(100) BY PULSED LASER DEPOSITION

We report the successful deposition of highly c-axis oriented CaBi2Nb2O9 (CBN) thin films directly on p-type Si(100) substrates by pulsed laser deposition. The CBN thin films exhibited good structural, dielectric, and CBN/Si interface characteristics. The electrical measurements were conducted on CBN thin films in a metal–ferroelectric–semiconductor (MFS) capacitor configuration. The typical measured small signal dielectric constant and the dissipation factor at a frequency of 100 kHz were 80 and 0.051, respectively. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10−7A/cm2 at an applied electric field of 100 kV/cm. The capacitance–voltage measurements on MFS capacitors established good ferroelectric polarization switching characteristics.

Properties of Ba(Mg1/3Ta2/3)O3 thin films prepared by metalorganic solution deposition technique for microwave applications

We report on the properties of Ba(Mg1/3Ta2/3)O3 thin films prepared by the metalorganic solution deposition technique. Bulk Ba(Mg1/3Ta2/3)O3 ceramics have shown excellent dielectric properties at microwave frequencies; however, the high sintering temperature of bulk material is the major obstacle in their use as dielectric resonators to miniaturize microwave circuits. It was possible to obtain an ordered-perovskite phase of 0.3-μm-thick Ba(Mg1/3Ta2/3)O3 films with trigonal symmetry at an annealing temperature of 700 °C, which is much lower than the bulk sintering temperatures. The electrical measurements were conducted on Pt/Ba(Mg1/3Ta2/3)O3/Pt capacitors. The typical measured small signal dielectric constant and dissipation factor at 100 kHz were 22.2 and 0.009, respectively. The dielectric constant of thin films was comparable to the typical values (er∼23.5–25) reported for bulk ceramics. The temperature coefficient of capacitance was −145 ppm/°C in the measured temperature range of 25–125 °C. The leaka...

Structural and electrical properties of crystalline (1−x)Ta2O5–xAl2O3 thin films fabricated by metalorganic solution deposition technique

Polycrystalline (1−x)Ta2O5–xAl2O3 thin films were fabricated by metalorganic solution deposition technique on Pt-coated Si substrate at a temperature of 750 °C. Thin films with 0.9Ta2O5–0.1Al2O3 composition exhibited improved dielectric and insulating properties compared to Ta2O5 thin films. The measured small signal dielectric constant and dissipation factor at 100 kHz were 42.8 and 0.005, respectively. The temperature coefficient of capacitance was 20 ppm/°C in the measured temperature range of 25–125 °C. The leakage current density was lower than 6×10−8 A/cm2 up to an applied electric field of 1 MV/cm. A charge storage density of 18.9 fC/μm2 was obtained at an applied electric field of 0.5 MV/cm. The high dielectric constant, low dielectric loss, low leakage current density, and good temperature and bias stability suggest (1−x)Ta2O5–xAl2O3 thin films to be a suitable dielectric layer in integrated electronic devices in place of conventional dielectrics such as SiO2 or Si3N4.

Polarity-controlled visible/infrared electroluminescence in Si-nanocrystal/Si light-emitting devices

We report the demonstration of a room-temperature visible/infrared color-switchable light-emitting device comprising a Si nanocrystal-embedded silicon oxide thin film on a p-type Si substrate. The device emits band-edge infrared light from the silicon substrate when the substrate is positively (forward) biased with respect to the Si-nanocrystal film. Under reverse bias, visible emission from the Si-nanocrystal film is observed. Compared to the photoluminescence of the Si-nanocrystal film, the visible electroluminescence is broader and blueshifted to shorter wavelength, and is ascribed to impact ionization in the Si-nanocrystal/SiO2 film.

Microstructural and Electrical Characteristics of Rapid Thermally Processed (Ba1—xSrx)TiO3 Thin Films Prepared by Metalorganic Solution Deposition Technique

Barium strontium titanate thin films including barium titanate BaTiO3 and strontium titanate SrTiO3 end members were fabricated on Pt-coated silicon and bare silicon substrates by metalorganic solution deposition (MOSD) technique using acetate precursors. Polycrystalline (Ba 1-x Sr X )TiO 3 thin films were obtained by rapid thermal annealing at 700 °C for 60s. The films were characterized for electrical properties in terms of dielectric permitivity, dissipation factor, and dc leakage current characteristics. A peak in dielectric constant was observed for (Ba 0.6 Sr 0.4 )TiO3 composition at room temperature. The typical measured small signal dielectric constant and dissipation factor for 0.5 μm-thick (Ba 0.6 Sr 0.4 )TiO3 films at 100 kHz were 450 and 0.012, respectively. (Ba 0.6 Sr 0.4 )TiO3 thin films exhibited a high voltage dependent tunability of 47% at an applied electric field of 0.5 MV/cm. The interfacial properties of Au/(Ba 0.6 Sr 0.4 )Ti0 3 /Si structure were examined by high frequency C-V measurements. A charge storage density of 39.6 fC/μm 2 and leakage current density of less than 10 -8 A/cm 2 were obtained for (Ba 0.6 Sr 0.4 )TiO 3 thin films at an applied electric field of 100 kV/cm.

Characterization of Ba0.6Sr0.4TiO3 thin films with Mg additive fabricated by Metalorganic decomposition technique

Abstract We report for the first time Ba0.6Sr0.4TiO3 (BST 60/40) thin films with Mg additive fabricated by Metalorganic decomposition technique on platinum coated silicon substrates using acetate-alkoxide precursors.[1] The structural and electrical properties of the BST thin films were greatly changed by additions of Mg. The surface morphology of the films was smooth with a dense microstructure. The typical small signal dielectric constant and the loss factor for a 0.4 μm thick undoped BST films were 450 and 0.013, respectively, at an applied frequency of 100 kHz. The dielectric loss was significantly reduced by the Mg content. The tunability (ΔC/C0) was found to change from 20.7% to 5.8% as the Mg additive content was changed from 0 to 20 mol%. The films exhibited high resistivity of the order of 1012 Ω-cm even up to an applied electric field of 100 kV/cm.

Low-temperature processing of SiO2 thin films by HD-PECVD technique for gate dielectric applications

We report on the fabrication and characterization of SiO2 thin films by high-density plasma enhanced chemical vapor deposition (HD-PECVD) technique at a processing temperature lower than 400°C for gate dielectric applications in thin film transistor (TFT) devices. An inductively coupled plasma source was used to couple the rf power to the top electrode. The SiO2 thin films were fabricated on p-Si wafers using nitrogen, nitrous oxide, and silane precursors. The deposition process was optimized in terms of the effects of rf power, gas flow rates, and system pressure on deposition rate, chemical etch rate, optical properties, and electrical characteristics. The effects of the processing variables on the refractive index, Si-O bond formation, and impurity related bonds were analyzed. The electrical properties of the films were evaluated from the I-V and C-V characteristics of the MOS capacitors. The effects of the SiO2 film thickness on the electrical characteristics of MOS capacitors were also investigated in the range of 30-100 nm. The influence of the low temperature processed gate dielectric on the performance of 500 Å poly-Si TFTs was evaluated in terms of the transfer and gate leakage characteristics. The microstructural and electrical characteristics of the HD-PECVD deposited SiO2 thin films suggest their suitability for the low temperature integration of TFTs on glass or other low temperature substrates.