Chemical vapour deposition of epitaxial Ni-Zn ferrite films by thermal decomposition of acetylacetonato complexes

Epitaxial (Ni, Zn)Fe₂O₄ films were prepared on (100) MgO single crystal substrate by lowpressure chemical vapour deposition using a thermal decomposition of acetylacetonatocomplexes, Ni(acac)₂, Zn(acac)₂ and Fe(acac)₃. These complexes were evaporated at 157, 79 and 146° C, respectively, and transported with nitrogen carrier gas (flow rate 100 ml min⁻¹) to the deposition furnace. Polycrystalline and epitaxial films were grown at 500 to 600 and 600 to 650° C, respectively, under a pressure of 12 torr. The epitaxial film of Ni_1−xZn_xFe₂O₄ (x⋍0.4) treated at 600° C for 60 min, showed the saturation magnetization of 67 e.m.u. g⁻¹ and the coercive force of 20 to 30 Oe.     

C-axis-oriented Bi3.25La0.75Ti3O12 ferroelectric thin film fabricated by chemical solution deposition

C-axis-oriented Bi_3.25La_0.75Ti₃O₁₂ (BLT) ferroelectric thin films were successfully prepared by chemical solution deposition. According to X-ray diffraction, it is found that the orientation degree increases with the increase of sintering temperature, and at the same time the grain morphology changes from equiaxed to plate-like. Due to the dense morphology and [Bi₂O₂]²⁺ layer of c-preferred orientation of BLT film sintered at 650 °C, it exhibits the lowest leakage current density at room temperature. Additionally, a linear relation between V^0.5 and log(J / T²) is found, suggesting the behavior of leakage current of BLT films obeys the Schottky emission model. P–E loops show that the c-axis-oriented BLT ferroelectric film exhibits low polarization and small coercive field.     

Conductivity threshold and kinetics of the phase transition in Fe2O3-Fe3O4 thin films made by chemical vapour deposition

Iron oxide films were made by chemical vapour deposition and annealing post-treatment. Optical and d.c. electrical measurements probed the Fe₂O₃ Fe₃O₄ transition. It could be understood as a thermally activated process, with an activation energy equal to the band-gap of Fe₂O₃. A.c. electrical data gave evidence against the transition being percolative.     

Chemical vapour deposition of nitrogen-doped titanium dioxide thin films

Nitrogen-doped titanium dioxide is often considered as a promising nanomaterial for photocatalytic applications. Here we report the first results of a study of APCVD of N-doped TiO2 thin films prepared with the use of ammonia as a source of nitrogen and titanium tetraisopropoxide (TTIP) as a source of Ti and O atoms. The obtained films were analyzed with X-ray diffraction, infrared spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, UV-Vis spectroscopy, and ellipsometry. It was found that the film growth rate in the TTIP-NH3-Ar reaction system varied insignificantly with substrate temperature in the range of 450,..., 750 degrees C and did not exceed 4.4 nm/min. Yellow and orange layers with nitrogen content of about 7.6% were formed at the deposition temperature higher than 600 degrees C. The results of the structure analysis of the deposited films showed that addition of ammonia led to stabilization of the amorphous phase in the films. The effect of ammonia on optical and photocatalytic properties was also considered.     

Oxygen surface exchange kinetics measurement by simultaneous optical transmission relaxation and impedance spectroscopy: Sr(Ti,Fe)O3-x thin film case study

We compare approaches to measure oxygen surface exchange kinetics, by simultaneous optical transmission relaxation (OTR) and AC-impedance spectroscopy (AC-IS), on the same mixed conducting SrTi_0.65Fe_0.35O_3-x film. Surface exchange coefficients were evaluated as a function of oxygen activity in the film, controlled by gas partial pressure and/or DC bias applied across the ionically conducting yttria-stabilized zirconia substrate. Changes in measured light transmission through the film over time (relaxations) resulted from optical absorption changes in the film corresponding to changes in its oxygen and oxidized Fe (~Fe⁴⁺) concentrations; such relaxation profiles were successfully described by the equation for surface exchange-limited kinetics appropriate for the film geometry. The k_chem values obtained by OTR were significantly lower than the AC-IS derived k_chem values and k_q values multiplied by the thermodynamic factor (bulk or thin film), suggesting a possible enhancement in k by the metal current collectors (Pt, Au). Long-term degradation in k_chem and k_q values obtained by AC-IS was also attributed to deterioration of the porous Pt current collector, while no significant degradation was observed in the optically derived k_chem values. The results suggest that, while the current collector might influence measurements by AC-IS, the OTR method offers a continuous, in situ, and contact-free method to measure oxygen exchange kinetics at the native surfaces of thin films.     

Physical properties of (La,Sr)Ti(O,N)3 thin films grown by pulsed laser deposition

Thin films of La_xSr_1−xTiO_3+x/2 (x = 0, 0.25, 0.5, 0.75, 1) were grown by laser ablation on two different kinds of substrates (SrTiO₃ (STO) and MgO) and were subsequently ammonolysed to yield the corresponding oxynitrides La_xSr_1−xTi(O,N)₃. For both substrates all films were found to grow epitaxially to the (1 0 0) direction of the cubic perovskite structure, except for x = 0.5 that grew parallel to the (1 1 0) direction. For some of the films TiN was detected as impurity phase. Scanning electron microscopy revealed that the films are dense and homogeneous with thicknesses around 350 nm. Atomic force microscopy showed that the surface roughness of the films varied between 4.2 and 14.1 nm. The employed substrate had a strong influence on the electrical properties. Films grown on STO exhibited a metallic behaviour, in contrast to the films grown on MgO, which were insulating.     

Characterization of Pb(Zr,Ti)O3 thin films obtained by MOD

Pb(Zr, Ti)O₃ thin films were deposited by dip-coating on polycrystalline alumina substrates by using an MOD method. The thickness and homogeneity of the films were measured as a function of dip rates and solution concentration. Heating and cooling schedules determined the main structure of the crystallized films. Rheology measurements and Fourier transform-infrared spectra were carried out to obtain a better knowledge of the solution features. A microstructural development study and some ferroelectric measurements were also carried out.     

Optical properties of pb(Zr,Ti)O(3) films prepared by aerosol deposition

The optical properties and related band structure of ferroelectric lead zirconate titanate [PZT, Pb(Zr0(0.6)Ti0(0.4))O(3)] films prepared on glass substrates at room temperature by aerosol deposition were investigated. The reflectance and transmittance of the PZT films were measured in the wavelength range from UV to nearinfrared. The measured optical spectra were analyzed using dielectric function models that describe optical transitions in the band gap region. Optical absorption of the as-deposited PZT films was found to be larger than that of the annealed PZT films in the near-infrared wavelength range. The analyzed results indicated that post-deposition annealing increased the band gap energy of the PZT films, corresponding to a decrease in optical absorption.     

Preparation of Pb(Zr0.52Ti484848)O3 thin films on silicon-on-insulator substrates by excimer laser deposition combined with rapid thermal annealing

In this paper we report the fabrication of ferroelectric Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films on Si-on-Insulator (SOI) substrates with and without an electrode by pulsed excimer laser deposition combined with rapid thermal annealing. Based on the structural and interfacial characteristics analysis by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM) and automatic spreading resistance measurement (ASR), the film structure and orientation were revealed to be dependent on the annealing time and annealing temperature as well as deposition temperature. From RBS spectra and XTEM observation it is shown that the PZT thin films did not interact with the top silicon layers of SOI and that the composition of the film was similar to the target. The ASR measurements showed that the electrical properties of PZT/SOI as well as PZT/Pt/SOI were abrupt, and that the electrical properties of the SOI substrates were still good after the PZT growth.     

Structural and dielectric properties of La substituted polycrystalline Ca(Ti0.5Fe0.5)O3

Polycrystalline Ca_1?x La _x (Ti_0.5Fe_0.5)O₃ were prepared by the standard solid state reaction technique. Pellet shaped samples prepared from each composition were sintered at 1573 K for 5 h. The X-ray diffraction analysis indicated the formation of a single-phase orthorhombic structure. The lattice parameters as well as densities increased but the average grain sizes decreased with the increase of La content. The dielectric measurements were carried out at room temperature as a function of frequency and composition. The experimental results revealed that dielectric constant (?′) decreased but dielectric loss (tan δ) and ac electrical conductivity (σ _ac ) increased as frequency increased. The composition dependence of ?′ and tan δ indicated that they decreased with the increase of La content. The σ _ac was derived from the dielectric measurements and it is concluded that the conduction in the present samples is due to mixed polarons hopping.     

(111)-Oriented Pb(Zr0.52Ti0.48)O3 thin film on Pt(111)/Si substrate using CoFe2O4 nano-seed layer by pulsed laser deposition

Perovskite Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin film with perfect (111)-orientation was achieved on CoFe₂O₄ seeded-Pt(111)/Ti/SiO₂/Si substrate by pulsed laser deposition technique using target with limited excess Pb. Pyrochlore phase formation was suppressed on Pt by CoFe₂O₄ nano-seed layer (~7 nm), and perovskite PZT was achieved at temperature as low as 550 °C. CoFe₂O₄ seed layer that has perfect (111)-orientation acts as a promoter for perfectly (111)-orientated growth of PZT. PZT film grown at 600 °C has higher degree of crystalline orientation, lower surface roughness, and compacted microstructure in comparison to the film grown at 550 °C. The PZT film has a nano-size grain-feature structure with grain size of about 40–60 nm. Perovskite formation was also confirmed by ferroelectric measurement. The ferroelectric properties of PZT film grown at 600 °C is higher than that grown at 550 °C which could be attributed to the enhancement of the crystalline orientation, crystallinity, and microstructure of the film.     

A highly sensitive Pb(Zr,Ti)O3 thin film ultrasonic micro-sensor with a grooved diaphragm

A highly sensitive piezoelectric ultrasonic micro-sensor with a grooved multilayer membrane was developed by a Si-based MEMS technique. The groove was located at one-quarter of the distance away from the edge of the membrane and opened into piezoelectric layer. The piezoelectric layer Pb(Zr,Ti)O(3) (PZT) was 2.2 microm thick and was prepared by a sol-gel method. The prepared PZT film was pure perovskite and showed a highly (100) textured structure. The sensitivity of the fabricated piezoelectric ultrasonic sensor without the groove structure was 100 microV/Pa. In comparison, the sensitivity of the ultrasonic sensor with the groove structure was about 500 microV/Pa, which is 5 times that without the groove structure. The diaphragm having grooves showed a corrugate-like structure that was formed by residual stress. The high sensitivity of the membrane with the grooved diaphragm is considered to relate to the corrugate-like structure.     

Chemical vapour deposition (CVD) of borophosphosilicate glass films

Chemical vapour deposition (CVD) has become the standard method for the fabrication of microelectronic devices for use in the semiconductor industry. In this investigation, it has been used to grow films of silicon dioxide (SiO₂) and borophosphosilicate glass (BPSG) at both atmospheric and low pressures under various conditions. The growth behaviour of SiO₂ and BPSG films has been investigated as a function of the O₂/SiH₄ ratio. Both processes give a similar trend, with the growth rates of BPSG being somewhat higher than SiO₂. The variation in the growth rate with O₂/SiH₄ ratio has been explained in terms of relative transport and kinetic reaction rates. The effects of temperature on the deposition rate have also been studied and the activation energy calculated showed two distinct regions corresponding to mass transport control and kinetic control regimes. Both BPSG and SiO₂ have been annealed under various furnacing conditions. It has been shown that the addition of boron and phosphorous results in much lower reflow temperatures and times. This has a significant bearing on the performance characteristics of devices. Initial results from rapid thermal annealing (RTA) work are also presented, and RTA is shown to be a viable annealing process.     

Crystal morphology of ternary compound (Cr,Fe)5Si3 obtained by in situ chemical vapour deposition

Ternary compound crystals of (Cr, Fe)₅Si₃ were obtained on a quartz substrate by the in situ CVD process using in situ reaction of the stainless steel 410 powder, Si₂Cl₆ and hydrogen, and its crystal morphology was examined in some detail. Crystals with various interesting morphologies, such as spiral, conical, rose-like, seaweed-like, globefish-like, etc., were obtained. The most commonly observed growth habits of the crystals were spiral, conical and seaweed-like crystals.     

Sharp boron doping within thin SiGe layer by rapid thermal chemical vapour deposition

Abstract

Boron δ doping of Si and SiGe has been investigated using rapid thermal chemical vapour deposition from the SiH₄–GeH₄?H₂ system with B₂H₆ as the B source gas. By incorporation of B into the growing Si film, B peaks with an exponential decay length of 1·7 nm/ decade were prepared. The B peak concentration was found to be dependent on Ge concentration, doping time, and doping temperature. An explanation of the results obtained is proposed based on a transitional behaviour between equilibrium and kinetic control of the process. If the B δ doping is carried out by interrupting the epitaxy, the process is controlled by the surface adsorption equilibrium. Hence B δ layers of about one monolayer thickness were prepared in Si and SiGe with an exponential decay length of 1·4 nm/decade at a temperature of 350°C.

MST/3293     

Characterization of sol-gel Pb(Zr0.53Ti0.47O3) in thin film bulk acoustic resonators

The behavior of {f111g}-textured Pb(Zr(0.53Ti0.47O3) (PZT) deposited by the sol-gel technique in thin film bulk acoustic resonators (TFBAR's) was investigated at a resonance frequency of about 1 GHz. The resonators were fabricated on Si wafers using deep silicon etching to create a membrane structure and using platinum as top and bottom electrodes. The best response of the resonators was observed at a bias voltage of -15 kV/cm with values of about 10% for the coupling constant and about 50 for the quality factor. This voltage corresponds to optimal values of piezoelectric constant d33 and dielectric constant measured as a function of the electric field. The influence of a bias voltage on the resonance frequency, antiresonance frequency, and coupling constant were observed. Both the resonance and antiresonance frequency show a hysteretic change with applied bias. This effect can be used to shift the whole band of a filter by applying a voltage. The TFBAR structure also allowed us to extract values for materials parameters of the PZT film. Dielectric, piezoelectric, and elastic properties of the f111g-textured PZT film are reported and compared to direct measurements and to literature values.     

Intrinsic microcrystalline silicon prepared by hot-wire chemical vapour deposition for thin film solar cells

Microcrystalline silicon (μc-Si:H) prepared by hot-wire chemical vapour deposition (HWCVD) at low substrate temperature T_S and low deposition pressure exhibits excellent material quality and performance in solar cells. Prepared at T_S below 250 °C, μc-Si:H has very low spin densities, low optical absorption below the band gap, high photosensitivities, high hydrogen content and a compact structure, as evidenced by the low oxygen content and the weak 2100 cm⁻¹ IR absorption mode. Similar to PECVD material, solar cells prepared with HWCVD i-layers show increasing open circuit voltages V_oc with increasing silane concentration. The best performance is achieved near the transition to amorphous growth, and such solar cells exhibit very high V_oc up to 600 mV. The structural analysis by Raman spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM) shows considerable amorphous volume fractions in the cells with high V_oc. Raman spectra show a continuously increasing amorphous peak with increasing V_oc. Crystalline fractions X_C ranging from 50% for the highest V_oc to 95% for the lowest V_oc were obtained by XRD. XRD-measurements with different incident beam angles, TEM images and electron diffraction patterns indicate a homogeneous distribution of the amorphous material across the i-layer. Nearly no light induced degradation was observed in the cell with the highest X_C, but solar cells with high amorphous volume fractions exhibit up to 10% degradation of the cell efficiency.     

Fabrication of nanocrystalline silicon carbide thin film by helicon wave plasma enhanced chemical vapour deposition

Nanocrystalline cubic silicon carbide thin films have been fabricated by helicon wave plasma enhanced chemical vapour deposition on Si substrates using the mixture of SiH₄, CH₄, and H₂ at a low substrate temperature of 300 °C. The infrared absorption spectroscopy analyses and microstructural characteristics of the samples deposited at various magnetic fields indicate that the high plasma intensity in helicon wave mode is a key factor to the success of growing nanocrystalline silicon carbide thin films at a relative low substrate temperature. Transmission electron microscopy measurements reveal that the films consist of silicon carbide nanoparticles with an average grain size of several nanometers, and the light emission measurements show a strong blue photoluminescence at room temperature, which is considered to be caused by the quantum confine effect of small size silicon carbide nanoparticles.