Shankar Dutta

Improved electrical properties of PbZrTiO3/BiFeO3 multilayers with ZnO buffer layer

In this study, the effect of ZnO buffer layer on the electrical properties of PbZrTiO3/BiFeO3 (PZT/BFO) multilayers has been reported. For this, PZT/BFO multilayers were spin-coated with and without ZnO buffer layer on platinized silicon wafers. X-ray diffraction results of both the films showed polycrystalline phase pure perovskite structure. Both the films show a dense and homogeneous grain structure. The electric properties of the films were measured. The ZnO buffered multilayer thin film showed ∼3 times improvement in remnant polarization compared to the multilayer thin film with no buffer. The buffered samples were found to have higher dielectric constant (1000 at 100 Hz) compared to that of sample (580 at 100 Hz)) with no buffer. Dielectric constants of both the films were found to be ∼30% tunable at 5 V. The buffered film also showed low leakage current density and higher dielectric breakdown compared to the multilayer thin film without buffer.

Growth and electrical properties of spin coated ultrathin ZrO2 films on silicon

Ultrathin (<50 nm) zirconium oxide (ZrO2) films are being intensively studied as high-k dielectrics for future metal-oxide-semiconductor (MOS) technology. In this paper, ultrathin ZrO2 films are deposited on silicon substrates by spin on deposition technique and annealed at 700 °C for different duration. The phase formation and morphological study have been performed by x-ray diffraction and scanning electron microscopy, respectively. Electrical properties of the films are investigated. The threshold voltages of the MOS structure were found to vary from −1.5 V to −2.5 V as the annealing time increases. The dielectric constants of the films are found to be 7.2–7.67 at 1 KHz. Leakage current of the films is found to increase with the annealing time. The dielectric breakdown field of the film is found to be 6.29–8.15 MV/cm.

Estimation of residual stress in Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayers deposited on silicon

Thin multilayer films possess residual stress components which vary from microscopic to macroscopic scale. In this study, Pb(Zr0.52Ti0.48)O3/BiFeO3 (PZT-BFO) multilayer thin film is deposited via chemical solution deposition technique on silicon substrate. The microscopic and macroscopic residual stress components of the multilayer films are investigated. The average microscopic residual stress is estimated to be 791.15 MPa (tensile) by using x-ray diffraction technique; on the other hand, the average macroscopic stress is found to be 774.23 MPa (tensile) by using wafer curvature measurement technique. As the thermally grown SiO2 layer possesses compressive stress, the combined residual stress of the PZT-BFO multilayer and SiO2 will almost cancel each other. This is reasonably encouraging for integration of the multilayer in MEMS structures.

Electrical properties of ultrathin titanium dioxide films on silicon

Ultrathin (<50 nm) titanium dioxide (TiO2) films are being widely investigated as high-k dielectrics for future metal oxide semiconductor (MOS) technology. In this paper, ultrathin TiO2 films (∼20 nm) were deposited on silicon substrates by sputtering technique and subsequently annealed at 800 °C in oxygen environment for different durations (15–60 min). The annealed films were polycrystalline in nature with rutile phase. The value of dielectric constant was found to be 32–60 at 1 kHz measurement frequency. Threshold voltages of the MOS structures were found to vary from −0.1 to −0.5 V with the duration of annealing. Leakage current density (1 × 10−2–1 × 10−8 A/cm2 at 1 V) and dielectric breakdown fields (8.15–9.8 MV/cm) were observed to improve with annealing time.

Effect of Ni substitution on the optical properties of BiFeO3 thin films

This paper reports about single phase Ni-substituted (0–20 at%) BiFeO3(BFO) thin films for future optoelectronic device applications. The effect of Ni substitution on the microstructure, ferroelectric and optical properties of spin-coated BFO thin films were investigated. The x-ray diffractionpeaks corresponding to the (012) and (110) planes were found to be gradually shifted towards the lower diffraction angle side with the increasing Ni substitution in BFO films. The strain values in the corresponding planes were found to be increasing sharply upto the 10 at%. The Ni substituted BFO films were found to have larger grain sizes compared to that of the pristine BFO film. The remnant polarization enhanced with the Ni substitutions and the 20 at% Ni substituted BFO films showed a 3.5 times higher remnant polarization than the pristine BFO films. The optical band gaps were found to be increasing from 2.85 to 3.18 eV with the increase in Ni substitution upto 5 at%. Raman and infra-red absorption data confirmed that the Ni substitution at Fe sites induces structural distortion at both Fe sites and Bi sites in BFO films. Due to the structural distortion, ferroelectric and optical properties of BFO films were significantly modified.

Electrical properties of spin coated ultrathin titanium oxide films on GaAs

In recent years, ultrathin (<50 nm) metal oxide films have been being extensively studied as high-k dielectrics for future metal oxide semiconductor (MOS) technology. This paper discusses deposition of ultrathin TiO2 films (~10 nm) on GaAs substrates (one sulfur-passivated, another unpassivated) by spin coating technique. The sulfur passivation is done to reduce the surface states of GaAs substrate. After annealing at 400 °C in a nitrogen environment, the TiO2 films are found to be polycrystalline in nature with rutile phase. The TiO2 films exhibit consistent grain size of 10–20 nm with thickness around 10–12 nm. Dielectric constants of the films are found to be 65.4 and 47.1 corresponding to S-passivated and unpassivated substrates, respectively. Corresponding threshold voltages of the MOS structures are measured to be −0.1 V to −0.3 V for the S-passivated and unpassivated samples, respectively. The S-passivated TiO2 film showed improved (lower) leakage current density (5.3 × 10−4 A cm−2 at 3 V) compared to the unpassivated film (1.8 × 10−3 A/cm2 at 3 V). Dielectric breakdown-field of the TiO2 films on S-passivated and unpassivated GaAs samples are found to be 8.4 MV cm−1 and 7.2 MV cm−1 respectively.

Growth and morphological evolution of c-axis oriented AlN films on Si (100) substrates by DC sputtering technique

Aluminum nitride (AlN) films were grown on Si substrates by dc magnetron sputtering in plasma containing a mixture of argon and nitrogen, using a pure aluminum target. In this paper, we studied the growth of AlN films on Si(100) substrates under varying gas ratio (N2 to Ar gas ratio) by DC reactive magnetron sputtering at moderate deposition temperature (400°C-600°C). Phase formation and orientation of the thin films were determined by Grazing Incidence X-Ray Diffraction (GIXRD). Surface morphology of the deposited thin films was investigated by Scanning Electron Microscope. Film orientations were studied by varying the gas ratio and deposition temperature to obtain (002) oriented film. The highest Texture coefficient along (002) direction (γ=3.2) is obtained for optimized growth condition at Argon to Nitrogen gas ratio 10:10 and substrate temperature 550°C. This oriented film can be used in MEMS based devices.Aluminum nitride (AlN) films were grown on Si substrates by dc magnetron sputtering in plasma containing a mixture of argon and nitrogen, using a pure aluminum target. In this paper, we studied the growth of AlN films on Si(100) substrates under varying gas ratio (N2 to Ar gas ratio) by DC reactive magnetron sputtering at moderate deposition temperature (400°C-600°C). Phase formation and orientation of the thin films were determined by Grazing Incidence X-Ray Diffraction (GIXRD). Surface morphology of the deposited thin films was investigated by Scanning Electron Microscope. Film orientations were studied by varying the gas ratio and deposition temperature to obtain (002) oriented film. The highest Texture coefficient along (002) direction (γ=3.2) is obtained for optimized growth condition at Argon to Nitrogen gas ratio 10:10 and substrate temperature 550°C. This oriented film can be used in MEMS based devices.

Effect of residual stress on modal patterns of MEMS vibratory gyroscope

Deep boron diffusion often induces residual stress in bulk micromachined MEMS structures, which may affect the MEMS devices operation. In this study, we studied the modal patterns of MEMS vibratory gyroscope under the residual stress (100 – 1000 MPa). Modal patterns and modal frequencies of the gyro are found to be dependent on the residual stress values. Without any residual stress, the modal frequencies drive and sense modeswere found to be 20.06 kHz and 20.36 kHz respectively. In presence of 450 MPa residual stress, the modal frequencies of the drive and sense modes were changed to 42.75 kHz and 43.07 kHz respectively.

Optical properties of spin coated Co0.6Zn0.4Mn0.3Fe1.7O4 thin films deposited on silicon and platinum coated silicon substrates

ABSTRACT This work presents optical properties of Zn and Mn co-doped CFO (Co0.6Zn0.4Mn0.3Fe1.7O4) films deposited on Si and Pt coated Si substrates by spin coating technique. X-ray diffraction pattern of the films exhibited spinel cubic structure with polycrystalline phase. Optical characteristics of the CZFMO films are studied using photoluminscence and UV-visible spectroscopy. With the rise in annealing temperature, quenching in PL emission was observed for films grown on silicon; whereas a marginal enhancement in emission was observed for films deposited on the Pt / Si substrate. Optical band gap of the films are found to vary between 2.3 – 2.7 eV range.

Improved design for microplasma generation using planar interdigitated terminal (IDT) structure for explosive fuse applications

This paper discusses about improved design for microplasma generation using a planar interdigitated terminal (IDT) structure. The IDT structure is fabricated by Au electroplating (5 µm) using a single mask process on quartz wafer. The gap between the subsequent IDT fingers is kept at 30 µm. The IDT structure showed microplasma generation at 570–580 V bias in atmospheric condition.