Structural and electrical properties of radio frequency magnetron sputtered tantalum oxide films: Influence of post-deposition annealing

The as-deposited and annealed radio frequency reactive magnetron sputtered tantalum oxide (Ta₂O₅) films were characterized by studying the chemical binding configuration, structural and electrical properties. X-ray photoelectron spectroscopy and X-ray diffraction analysis of the films elucidate that the film annealed at 673 K was stoichiometric with orthorhombic β-phase Ta₂O₅. The dielectric constant values of the tantalum oxide capacitors with the sandwich structure of Al/Ta₂O₅/Si were in the range from 14 to 26 depending on the post-deposition annealing temperature. The leakage current density was <20 nA cm^?2 at the gate bias voltage of 0.04 MV/cm for the annealed films. The electrical conduction mechanism observed in the films was Poole–Frenkel.     

Effect of high-temperature annealing on lanthanum aluminate thin films grown by ALD on Si(1 0 0)

Amorphous lanthanum aluminate thin films were deposited by atomic layer deposition on Si(1 0 0) using La(ⁱPrCp)₃, Al(CH₃)₃ and O₃ species. The effects of post-deposition rapid thermal annealing on the physical and electrical properties of the films were investigated. High-temperature annealing at 900 °C in N₂ atmosphere leads to the formation of amorphous La-aluminosilicate due to Si diffusion from the substrate. The annealed oxide exhibits a uniform composition through the film thickness, a large band gap of 7.0 ± 0.1 eV, and relatively high dielectric constant (κ) of 18 ± 1.     

Structural,chemical, and electrical properties of Y2O3 thin films grown by atomic layer deposition with an (iPrCp)2Y(iPr-amd) precursor

Y₂O₃ thin films were grown by atomic layer deposition (ALD) through a heteroleptic liquid (iPrCp)₂Y(iPr-amd) precursor at 350 °C. The structural and chemical properties of both as-deposited and annealed Y₂O₃ films at 500 °C and 700 °C are analyzed by atomic force microscopy for variation in surface roughness, X-ray diffraction for crystalline structure, and X-ray photoelectron spectroscopy for chemical states. The as-deposited Y₂O₃ film shows the same crystalline orientation along the plane (222), a stoichiometric state, and minimal hydroxylate formation up to 700 °C. Being the dielectric layer in the metal-oxide-semiconductor capacitor, the as-deposited ALD-Y₂O₃ films with liquid (iPrCp)₂Y(iPr-amd) precursor without any post-deposition annealing show the much lower leakage density than ALD-Y₂O₃ with solid Y(MeCp)₃.     

Thermal annealing effect on zinc nitride thin films deposited by reactive rf-magnetron sputtering process

Zinc nitride films were deposited by reactive radio-frequency magnetron sputtering using a zinc target in a nitrogen and argon plasma. The deposited films were annealed in either air or O₂ at 300 °C to investigate the annealing effect on the microstructure, optical properties, and electronic characteristics of zinc nitride films. It was found that the annealing process decreased the crystallinity of zinc nitride films. It was also found that the optical band gap decreased from 1.33 eV to 1.14 eV after annealing. The analysis of film composition suggested that the concentration of oxygen increased slightly after annealing. Although the conduction type of both as-deposited and annealed films were n-type, the annealed films exhibited a higher resistivity, lower carrier concentration and lower mobility than the as-deposited films. Also, it was found that the as-deposited films did not exhibit any photoconducting behavior whereas the annealed films exhibited a pronounced photoconducting behavior.     

Characterization of TiAl alloy films for potential application in MEMS bimorph actuators

In this letter, we demonstrate the feasibility of applying TiAl alloy film for the fabrication of bimorph actuators. The TiAl alloy films were prepared by thermal annealing at 400°C of Ti/Al multilayers, which were deposited by DC magnetron sputtering from Ti and Al targets. The microstructure and surface morphology of TiAl alloy films were analyzed by X-ray diffraction and scanning electron microscopy, which showed that TiAl alloy film is formed in the mixed phases of TiAl₃ and Ti₃₆Al₆₄, depending on the deposition conditions. The resistivity of TiAl film is about 9 μΩ cm, and the stress is about 200 MPa. Our nano-indentation measurements showed that the Young's modulus and hardness of TiAl alloy films are 175 and 6.5 GPa, respectively, which are larger than that of Al and comparable to Si. We have successfully fabricated the bimorph actuators based on the TiAl alloy films and our test cantilevers up to 500 μm long showed very straight with tip bending as small as ±5 μm, indicating negligible stress gradient in TiAl film. Our preliminary testing results indicated that TiAl alloy film has potential application for bimorph actuators.     

Defect modification in ZnInSnO transistor with solution-processed Al2O3 dielectric by annealing

The properties of solution-processed Al₂O₃ thin films annealed at different temperatures were thoroughly studied through thermogravimetry–differential thermal analysis, UV–vis-NIR spectrophotometer measurements, scanning electron microscopy, X-ray diffraction, atomic force microscopy and a series of electrical measurements. The solution-processed ZnInSnO thin films transistors (TFTs) with the prepared Al₂O₃ dielectric were annealed at different temperatures. The TFTs annealed at 600 °C have displayed excellent electrical performance such as the field-effect mobility of 116.9 cm² V⁻¹ s⁻¹ and a subthreshold slope of 93.3 mV/dec. The performance of TFT device could be controlled by adjusting the annealing temperature. The results of two-dimensional device simulations demonstrate that the improvement of device performance are closely related with the reduction of interface defects between channel and dielectric and subgap density of stats (DOS) in the channel layer.     

Structural and optoelectronic properties of nanostructured TiO2 thin films with annealing

About 480 nm thick titanium oxide (TiO₂) thin films have been deposited by electron beam evaporation followed by annealing in air at 300–600 °C with a step of 100 °C for a period of 2 h. Optical, electrical and structural properties are studied as a function of annealing temperature. All the films are crystalline (having tetragonal anatase structure) with small amount of amorphous phase. Crystallinity of the films improves with annealing at elevated temperatures. XRD and FESEM results suggest that the films are composed of nanoparticles of 25–35 nm. Raman analysis and optical measurements suggest quantum confinement effects since Raman peaks of the as-deposited films are blue-shifted as compared to those for bulk TiO₂ Optical band gap energy of the as-deposited TiO₂ film is 3.24 eV, which decreases to about 3.09 eV after annealing at 600 °C. Refractive index of the as-deposited TiO₂ film is 2.26, which increases to about 2.32 after annealing at 600 °C. However the films annealed at 500 °C present peculiar behavior as their band gap increases to the highest value of 3.27 eV whereas refractive index, RMS roughness and dc-resistance illustrate a drop as compared to all other films. Illumination to sunlight decreases the dc-resistance of the as-deposited and annealed films as compared to dark measurements possibly due to charge carrier enhancement by photon absorption.     

Thermal conductivity of AlN thin films deposited by RF magnetron sputtering

Aluminum nitride (AlN) film, which is being investigated as a possible passivation layer in inkjet printheads, was deposited on a Si (1 0 0) substrate at 400 °C by radio frequency (RF) magnetron sputtering using an AlN ceramic target. Dependence on various reactive gas compositions (Ar, Ar:H₂, Ar:N₂) during sputtering was investigated to determine thermal conductivity. The crystallinity, grain size, and Al–N bonding changes by the gas compositions were examined and are discussed in relation to thermal conductivity. Using an Ar and 4% H₂, the deposited AlN films were crystalline with larger grains. Using a higher nitrogen concentration of 10%, a near amorphous phase, finer morphology, and an enhanced Al–N bonding ratio were achieved. A high thermal conductivity of 134 W/mk, which is nine times higher than that of the conventional Si₃N₄ passivation film, was obtained with a 10% N₂ reactive gas mixture. A high Al–N bonding ratio in AlN film is considered the most important factor for higher thermal conductivity.     

Effects of thermal annealing on the morphology of the AlxGa(1−x)N films

Effects of thermal annealing on the morphology of the Al_xGa_(1−x)N films with two different high Al-contents (x=0.43 and 0.52) have been investigated by atomic force microscopy (AFM). The annealing treatments were performed in a nitrogen (N₂) gas ambient as short-time (4 min) and long-time (30 min). Firstly, the films were annealed as short-time in the range of 800–950 °C in steps of 50–100 °C. The surface root-mean-square (rms) roughness of the films reduced with increasing temperature at short-time annealing (up to 900 °C), while their surface morphologies were not changed. At the same time, the degradation appeared on the surface of the film with lower Al-content after 950 °C. Secondly, the Al_0.43Ga_0.57N film was annealed as long-time in the range of 1000–1200 °C in steps of 50 °C. The surface morphology and rms roughness of the film with increasing temperature up to 1150 °C did not significantly change. Above those temperatures, the surface morphology changed from step-flow to grain-like and the rms roughness significantly increased.     

Effect of thermal annealing on structural and optical properties of titanyl phthalocyanine thin films

Thin films of titanyl phthalocyanine (TiOPc) have been deposited on both fused quartz and glass substrates by the thermal evaporation technique. The structural and optical properties of the as-deposited and annealed films have been reported. The structural features of the as-deposited and annealed films have been studied by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and Fourier-transform infrared (FT-IR) technique. The optical constants (refractive index, n, and absorption index, k) of the films have been presented for the first time in the wavelength range 200–2500 nm by using spectrophotometric measurements at nearly normal incidence. The band gaps of the as-deposited film at 1.48 eV and 2.5 eV corresponding to Q-band and B or Soret band were red-shifted to 1.15 eV and 2.19 eV, respectively, when the film annealed at 433 K.     

Investigation of Zr–N thin films for use as diffusion barrier in Cu metallization

Zr–N thin films as a barrier in Cu/Si contact were investigated. The Cu/Zr–N/Si specimens were prepared and annealed at temperatures up to 700 °C in N₂ ambient for an hour. Characterization of phase composition and crystallite structure of the barriers was performed by XRD, the film morphology was examined using atomic force microscopy (AFM), and the composition profiles of the as-deposited and annealed samples of Cu/Zr–N/Si were identified by Auger electron spectroscopy (AES). It is evident that the Zr–N film structure is very sensitive to the deposition conditions. Cu/Zr–N/Si contact systems showed better thermal stability so that the Cu₃Si phase could not be detected. It is indicated from the comparison analysis results that the Zr–N film showed better thermal stability with increasing N₂ flow ratio and/or negative substrate bias.     

Deposition of aluminum oxide-doped zinc oxide transparent nano-films on glass substrates for electrostatic discharge applications

Aluminum oxide-doped zinc oxide (ZnO:Al₂O₃) transparent thin films were deposited by DC magnetron sputtering on glass substrates; film thickness can be correlated with deposition time. The effect of ZnO:Al₂O₃ film thickness on electrical properties, ultraviolet (UV) transmission, surface morphology and structure, solvent resistance, and scratch hardness was investigated. The surface roughness and crystallite size of deposited films increased from 0.75 to 2.22 nm and from 14 to 57 nm, respectively, as the film thickness was increased from 18 to 112 nm. In contrast, the percent UV transmission (% T) of ZnO:Al₂O₃ deposited glass plates at a wavelength of 365 nm increased when the film thickness was decreased. The electrical properties of nano-film deposited glass plates such as electrical resistance, tribo-charge voltage, and decay time were in the range of electrostatic discharge (ESD) specifications. The ZnO:Al₂O₃ nano-film deposited glass substrate possessed good acetone and iso-propanol resistance as well as high scratch hardness. This work opens up the possibility of using the ZnO:Al₂O₃ transparent ultra-thin film on glass substrate in ESD applications based on their excellent properties in terms of the relatively thin and adjustable ZnO:Al₂O₃ film thickness needed.     

Effect of thermal annealing on physical properties of vacuum evaporated In2S3 buffer layer for eco-friendly photovoltaic applications

The present communication reports the effect of thermal annealing on the physical properties of In₂S₃ thin films for eco-friendly buffer layer photovoltaic applications. The thin films of thickness 150 nm were deposited on glass and indium tin oxide (ITO) coated glass substrates employing thermal vacuum evaporation technique followed by post-deposition thermal annealing in air atmosphere within a low temperature range 150–450 °C. These as-deposited and annealed films were subjected to the X-ray diffraction (XRD), UV–vis spectrophotometer, current–voltage tests and scanning electron microscopy (SEM) for structural, optical, electrical and surface morphological analysis respectively. The compositional analysis of as-deposited film is also carried out using energy dispersive spectroscopy (EDS). The XRD patterns reveal that the as-deposited and annealed films (≤300 °C) have amorphous nature while films annealed at 450 °C show tetragonal phase of β-In₂S₃ with preferred orientation (109) and polycrystalline in nature. The crystallographic parameters like lattice constant, inter-planner spacing, grain size, internal strain, dislocation density and number of crystallites per unit area are calculated for thermally annealed (450 °C) thin films. The optical band gap was found in the range 2.84–3.04 eV and observed to increase with annealing temperature. The current–voltage characteristics show that the as-deposited and annealed films exhibit linear ohmic behavior. The SEM studies show that the as-deposited and annealed films are uniform, homogeneous and free from crystal defects and voids. The grains in the thin films are similar in size and densely packed and observed to increase with thermal annealing. The experimental results reveal that the thermal annealing play significant role in the structural, optical, electrical and morphological properties of deposited In₂S₃ thin films and may be used as cadmium-free eco-friendly buffer layer for thin films solar cells applications.     

Microstructure evolution of amorphous silicon thin films upon annealing studied by positron annihilation

Amorphous silicon (a-Si) thin films were prepared on glass substrates by plasma enhanced chemical vapor deposition (PECVD). Influence of annealing temperature on the microstructure, surface morphology, and defects evolution of the films were studied by X-ray diffraction (XRD), atomic force microscope (AFM) and positron annihilation Doppler broadening spectroscopy (DBS) based on a slow positron beam, respectively. The S parameter of the as-deposited a-Si thin film is high, indicative of amorphous state of Si film with many defects. The a-Si gradually grows into polycrystalline silicon with increasing temperature to 650 °C. For the films annealed below ~450 °C, positron diffusion lengths are rather small because most positrons are trapped in the defects of the a-Si films and annihilated there. With further rising the temperature to 600 °C, the diffusion length of positrons increases significantly due to the removal of vacancy-type defects upon annealing at a high temperature. The results indicate that the coalescence of small vacancy-type defects in a-Si thin film and the crystallization of a-Si occur around 450 °C and 650 °C, respectively.     

The correlation of γ-irradiation,particle size and their effects on physical properties of AgInSe2 nanostructure thin films

In this work the effect of γ-irradiation on the optical and electrical properties of near stoichiometric AgInSe₂ nanostructure thin films have been characterized. The XRD pattern of ingot AgInSe₂ powder prepared by solid state reaction showed tetragonal polycrystalline single-phase structure. The thin films of thickness 75 nm were prepared by inert gas condensation (IGC) technique at using constant Ar flow and substrate temperature of 300 K.Thin films were exposed to annealing process at 473 K for 2 h in vacuum of 10⁻² Torr. The amorphous and tetragonal nanocrystalline structures were detected for as-deposited and annealed films respectively by grazing incident in-plane X-ray diffraction (GIIXD) technique. The structure and average particle size of annealed irradiated films by different γ-doses from 0 to 4 Mrad were determined using high resolution transmission electron microscope (HRTEM). Optical transmission, reflection and absorption spectra were studied for both annealed unirradiated and irradiated films. Two optical transitions for each annealed unirradiated and film exposed to γ-irradiation doses from 0 to 4 Mrad were observed. The evaluated E_g1 due to 1^st transition have decreased from 1.52 to 1.44 eV and E_g2 due to 2^nd transition have decreased from 2.83 to 2.30 eV as the particle size increased from 7.3 to 9.5 nm by raising the irradiation dose up to 1 Mrad. The behavior of d.c. electrical conductivity with temperature that measured under vacuum was examined for all films under investigation. The evaluated activation energies due to irradiation doses are ranging from 0.58 to 0.68 eV.     

Investigation of Si/SiGe/Si heterostructure implanted by H ion and annealed in vacuum and dry O2 ambient

The 20-nm-thick Si cap layer/74-nm-thick Si_0.72Ge_0.28 epilayer/Si heterostructures implanted by 25 keV H⁺ ion to a dose of 1×10¹⁶ cm⁻² were annealed in ultra-high vacuum ambient and dry O₂ ambient at the temperature of 800 °C for 30 min, respectively. Rutherford backscattering/ion channeling (RBS/C), Raman spectra, high-resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) were used to characterize the structural characteristics of the Si_0.72Ge_0.28 layer. Investigations by RBS/C demonstrated that the crystal quality of the Si/Si_0.72Ge_0.28/Si heterostructure sample implanted by 25 keV H⁺ in conjunction with subsequent annealing in dry O₂ ambient is superior to that of identical sample annealing in ultra-high vacuum ambient. The less strain relaxation of SiGe layer of the Si/Si_0.72Ge_0.28/Si heterostructures implanted by H ion and annealed in dry O₂ ambient at the temperature of 800 °C for 30 min could be doublechecked by Raman spectra as well as HRXRD, which was compared with that in an identical sample annealed in ultra-high vacuum ambient for identical thermal budget. In addition, the SiGe layer of the H-implanted Si/SiGe/Si heterostructural sample annealed in dry O₂ ambient accompanied by better crystal quality and less strain relaxation made its surface morphology superior to that of the sample annealed in ultra-high vacuum ambient at the temperature of 800 °C for 30 min, which was also verified by AFM images.     

MEMS based low cost piezoresistive microcantilever force sensor and sensor module

In the present work, we report fabrication and characterization of a low-cost MEMS based piezoresistive micro-force sensor with SU-8 tip using laboratory made silicon-on-insulator (SOI) substrate. To prepare SOI wafer, silicon film (0.8 µm thick) was deposited on an oxidized silicon wafer using RF magnetron sputtering technique. The films were deposited in argon (Ar) ambient without external substrate heating. The material characteristics of the sputtered deposited silicon film and silicon film annealed at different temperatures (400–1050 °C) were studied using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The residual stress of the films was measured as a function of annealing temperature. The stress of the as-deposited films was observed to be compressive and annealing the film above 1050 °C resulted in a tensile stress. The stress of the film decreased gradually with increase in annealing temperature. The fabricated cantilevers were 130 μm in length, 40 μm wide and 1.0 μm thick. A series of force–displacement curves were obtained using fabricated microcantilever with commercial AFM setup and the data were analyzed to get the spring constant and the sensitivity of the fabricated microcantilever. The measured spring constant and sensitivity of the sensor was 0.1488 N/m and 2.7 mV/N. The microcantilever force sensor was integrated with an electronic module that detects the change in resistance of the sensor with respect to the applied force and displays it on the computer screen.     

Effects of oxygen concentration on the properties of Al-doped ZnO transparent conductive films deposited by pulsed DC magnetron sputtering

The effect of oxygen concentration on the properties of Al-doped ZnO (AZO) transparent conductive films has been investigated on the films deposited by pulsed DC magnetron sputtering using a cylindrical ZnO target containing 2 wt% Al. AZO films were deposited at 230 °C to the thickness of about 1000 nm and the oxygen concentration was controlled by varying the O₂/Ar supply ratio from 0 to 0.167. With the increasing O₂/Ar ratio, crystallinity of the AZO films deteriorated while the film surface became smooth. Accompanying this, electrical properties also deteriorated significantly. When the O₂/Ar ratios were 0 and 0.033, the AZO films showed metallic conduction behavior with the electrical resistivity in the mid 10^?4 Ω cm range. However, when the ratios were 0.100 and 0.167, the films showed poor electrical conduction behavior similar to semiconductors as deduced from the transmittance behavior. Spectroscopic analysis showed that such deteriorating properties are due to the formation of condensed oxide group through the reaction between excess oxygen and dopant aluminum.     

Optical and electrical properties of nickel oxide thin films synthesized by sol–gel spin coating

Nickel oxide thin films were prepared by the sol–gel technique combined with spin coating onto glass substrates. The as-deposited films were pre-heated at 275 °C for 15 min and then annealed in air at different temperatures. The effects of the annealing temperature on the structural and optical properties of the films are studied. The results show that 600 °C is the optimum annealing temperature for preparation of NiO films with p-type conductivity and high optical transparency. Then, by using these optimized deposition parameters, NiO thin films of various thicknesses were deposited at the same experimental conditions and annealed under different atmospheres. Surface morphology of the films was investigated by atomic force microscopy. The surface morphology of the films varies with the annealing atmosphere. Optical transmission was studied by UV–vis spectrophotometer. The transmittance of films decreased as the thickness of films increased. The electrical resistivity, obtained by four-point probe measurements, was improved when NiO layers were annealed in N₂ atmosphere at 600 °C.     

Study of sensitivity and selectivity of α-Fe2O3 thin films for different toxic gases and alcohols

This paper presents a detailed study on the sensitivity and selectivity of α-Fe₂O₃ thin films produced by deposition of Fe and post-deposition annealed at two temperatures of 600 °C and 800 °C with flow of oxygen for application as a sensor for toxic gases including CO, H₂S, NH₃ and NO₂ and alcohols such as C₃H₇OH, CH₃OH, and C₂H₅OH. The crystallographic structure of the samples was studied by X-ray diffraction (XRD) method while an atomic force microscope (AFM) was employed for surface morphology investigation. The electrical response of the films was measured while they were exposed to various toxic gases and alcohols in the temperature range of 50–300 °C. The sample annealed at higher temperature showed higher response for different gases and alcohols tested in this work which can be due to the higher resistance of this sample. Results also indicated that the α-Fe₂O₃ thin films show higher selectivity to NO₂ gas relative to the other gases and alcohols while the best sensitivity is obtained at 200 °C. The α-Fe₂O₃ thin film post-deposition annealed at 800 °C also showed a good stability and reproducibility and a detection limit of 10 ppm for NO₂ gas at the operating temperature of 200 °C.