Formation of Ge nanocrystals and evolution of the oxide matrix in as-deposited and annealed LPCVD SiGeO films

SiGeO films were deposited by LPCVD using Si₂H₆, GeH₄ and O₂ as reactive gases and furnace annealed to segregate the possible excess of Si and Ge in the form of nanocrystals embedded in an oxide matrix. For low GeH₄:Si₂H₆ flow ratios and deposition temperatures of 450 ^°C or lower, the deposited film consists of a SiO₂ matrix incorporating Ge. No Ge oxides and no nanocrystals are detected. After annealing of the samples with SiO₂ matrices at temperatures of 600 ^°C or higher, quasi-spherical isolated Ge nanocrystals with diameters ranging from 4.5 to 9 nm and homogeneously distributed throughout the whole film thickness are formed. In the samples deposited with low GeH₄:Si₂H₆ flow ratios, the original SiO₂ matrix holds its composition.     

Controllable off-plane deflection of cantilevers for multiple scanning proximity probe arrays

The presented work reports the fabrication of 4×32 arrays of fully addressable proximity probes, which are initially and controllably off-plane deflected (bent). Such a deflection is required for the simultaneous approach and scanning of all cantilevers. It is realized by deposition of the silicon cantilevers with Si₃N₄ film inducing tensile stress. ANSYS simulations are used to calculate the off-plane deflection for different thickness of the cantilever and the Si₃N₄ layer and compared with experimentally obtained values. Cantilever arrays with set bending up to 50 μm, employing LPCVD silicon nitride film with a tensile stress of 750 MPa are fabricated.     

Low-voltage-drive and high output current ZnO thin-film transistors with sputtering SiO2 as gate insulator

Low-voltage-drive ZnO thin-film transistors (TFTs) with room-temperature radio frequency magnetron sputtering SiO₂ as the gate insulator were fabricated successfully on the glass substrate. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 4.2 V, a field effect mobility of 11.2 cm²/V s, an on/off ratio of 3.1 × 10⁶ and a subthreshold swing of 0.61 V/dec. The drain current can reach to 1 mA while the gate voltage is only of 12 V and drain voltage of 8 V. The C–V characteristics of a MOS capacitor with the structure of ITO/SiO₂/ZnO/Al was investigated. The carrier concentration N_D in the ZnO active layer was determined, the calculated N_D is 1.81 × 10¹⁶ cm⁻³, which is the typical value of undoped ZnO film used as the channel layer for ZnO-TFT devices. The experiment results show that SiO₂ film is a promising insulator for the low voltage and high drive capability oxide TFTs.     

Effect of Si in reactively sputtered Ti-Si-N films on structure and diffusion barrier performance

34 Si₂₃N₄₃ (b3) and Ti₃₅Si₁₃N₅₂ (c3), are synthesized by reactively sputtering a Ti₅Si₃ or a Ti₃Si target, respectively. The silicon-lean film (c3) has a columnar structure closely resembling that of TiN. As a diffusion barrier between a shallow Si n⁺p junction diode and a Cu overlayer, this material is effective up to 700 °C for 30 min annealing in vacuum, a performance similar to that for TiN. The silicon-rich (b3) film contains nanocrystals of TiN, randomly oriented and embedded in an amorphous matrix. A film of (b3) maintains the stability of the same diode structure up to 850 °C for 30 min in vacuum. This film (b3) is clearly superior to TiN or to (c3). Similar experiments performed with Al instead of Cu overlayers highlight the importance of the thermodynamic stability of a barrier layer and demonstrate convincingly that for stable barriers the microstructure is a parameter that directly determines the barrier performance. Received: 18 November 1996/Accepted: 22 January 1997     

Structural and electrical properties of fluorine-doped zinc tin oxide thin films prepared by radio-frequency magnetron sputtering

Transparent and conductive thin films of fluorine doped zinc tin oxide (FZTO) were deposited on glass substrates by radio-frequency (RF) magnetron sputtering using a 30 wt% ZnO with 70 wt% SnO₂ ceramic targets. The F-doping was carried out by introducing a mixed gas of pure Ar, CF₄, and O₂ forming gas into the sputtering chamber while sputtering ZTO target. The effect of annealing temperature on the structural, electrical and optical performances of FZTO thin films has been studied. FZTO thin film annealed at 600 °C shows the decrease in resistivity 5.47 × 10⁻³ Ω cm, carrier concentration ∼10¹⁹ cm⁻³, mobility ∼20 cm² V⁻¹ s⁻¹ and an increase in optical band gap from 3.41 to 3.60 eV with increasing the annealing temperatures which is well explained by Burstein–Moss effect. The optical transmittance of FZTO films was higher than 80% in all specimens. Work function (ϕ) of the FZTO films increase from 3.80 eV to 4.10 eV through annealing and are largely dependent on the amounts of incorporated F. FZTO is a possible potential transparent conducting oxide (TCO) alternative for application in optoelectronics.     

Towards a thin films electrochromic device using NASICON electrolyte

The optimisation of the morphology of WO₃ thin films allowed a more efficient electrochromic colouring using Na⁺ ions than H⁺ ones. Therefore, sodium superionic conductor (Na₃Zr₂Si₂PO₁₂, NASICON) films may be used as electrolyte in inorganic electrochromic devices. In this paper, the structure, chemical composition, morphology and electrochromic properties of WO₃, ZnO:Al and Na₃Zr₂Si₂PO₁₂ thin films were studied to develop a novel type of electrochromic device. WO₃, ZnO:Al and Na₃Zr₂Si₂PO₁₂ thin films were deposited using reactive magnetron sputtering of tungsten, zinc and aluminium and Zr–Si and Na₃PO₄ targets, respectively. For transparent conductive oxide coatings, a correlation was established between the deposition parametres and the film’s structure, transmittance and electrical resistivity. Classical sputtering methods were not suitable for the deposition of NASICON films on large surface with homogenous composition. On the other hand, the use of high-frequency pulsed direct current generators allowed the deposition of amorphous films that crystallised after thermal annealing upon 700 °C in the Na₃Zr₂Si₂PO₁₂ structure. Amorphous films exhibited ionic conductivity close to 2 × 10⁻³ S cm⁻¹. Finally, preliminary results related to the electrochromic performance of NASICON, WO₃ and indium tin oxide devices were given. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, France, Sept. 9–15, 2007.     

Room-temperature ferromagnetism in N+-implanted ZnO:Mn thin films

Mn–N co-doped ZnO films with wurtzite structure were fabricated by RF magnetron sputtering together with the ion-implantation technique. Then a post-annealing at 650 °C for 10 min in a N₂ atmosphere was performed to activate the implanted N⁺ ions and recover the crystal quality, and a p-type ZnO:Mn–N film with a hole concentration of about 2.1×10¹⁶ cm^?3 was obtained. It is found that the Mn mono-doped ZnO film only exhibits paramagnetic behavior, while after N⁺-implantation, it shows ferromagnetism at 300 K, and the magnetization of the ZnO:Mn–N films can be further enhanced by thermal annealing due to the activation of the N acceptors. Our experimental results confirm that the codoping N acceptors are favorable for ferromagnetic ordering of Mn²⁺ ions in ZnO, which is consistent with the recent theoretical calculations.     

Structural and photoluminescence properties of silicon nanocrystals embedded in SiC matrix prepared by magnetron sputtering

Si nanocrystals (NCs) embedded in an SiC matrix were prepared by the deposition of Si-rich Si_1?xC_x/SiC nanomultilayer films using magnetron sputtering, subsequently followed by thermal annealing in the range of 800～1200 °C. As the annealing temperature increases to 1000 °C, Si NCs begin to form and SiC NCs also start to emerge at the annealing temperature of 1200 °C. With the increase of annealing temperature, two photoluminescence (PL) peaks have an obvious redshift. The intensity of the low-energy PL peak around 669～742 nm gradually lowers, however the intensity of high-energy PL peak around 601～632 nm enhances. The low-energy PL peak might attribute to dangling bonds in amorphous Si (a-Si) sublayers, and the redshift of this peak might be related to the passivation of Si dangling bonds. Whereas the origin of the high-energy PL peak may be the emergence of Si NCs, the redshift of this peak correlates with the change in the size of Si NCs.     

Fluoride-doped MWCNT/Si3N4 composite with improved mechanical and structural properties

The addition of carbon nanotubes (CNT) in ceramic composites has stimulated a substantial interest due to their high mechanical, thermal and electrical properties. This approach used fluoride additives (AlF₃ and MgF₂) to prepare multi-walled carbon nanotubes/silicon nitride (MWCNT/Si₃N₄) composite densified at 1700 °C for 1 h by hot press (HP) sintering. The microstructural analyses of MWCNT/Si₃N₄ composites indicate that the fluoride additives have substantially improved densification and the transformation of α-Si₃N₄ to β-Si₃N₄. As observed, the mechanical properties, i.e. flexural strength, fracture toughness, Young's modulus and hardness of MWCNT/Si₃N₄ composites are improved with an increasing concentration of MWCNT. These results attributed to the highly dense composites, strong interfacial interaction and the pull-out mechanism of MWCNT and β-Si₃N₄. The maximum values of fracture toughness flexural strength, Young's modulus, and hardness were 12.76 ± 1.15 MPa.m^0.5, 883 ±46 MPa, 260 ±9 GPa, and 26.4 ± 1.3 GPa, respectively. The improved mechanical properties also ascribed to the synergistic strengthening and toughening influence of MWCNT and β-Si₃N₄.     

Characterization of photonic nanojets in dielectric microdisks

The direct imaging of photonic nanojets in different dielectric microdisks illuminated by a laser source is reported. The SiO₂ and Si₃N₄ microdisks are of height 650 nm with diameters ranging from 3 μm to 8 μm. The finite-difference time-domain calculation is used to execute the numerical simulation for the photonic nanojets in the dielectric microdisks. The photonic nanojet measurements are performed with a scanning optical microscope system. The photonic nanojets with high intensity spots and low divergence are observed in the dielectric microdisks illuminated from the side with laser source of wavelengths 405 nm, 532 nm and 671 nm. The experimental results of key parameters are compared to the simulations and in agreement with theoretical results. Our studies show that photonic nanojets can be efficiently created by a dielectric microdisk and straightforwardly applied to nano-photonics circuit.     

Structure and electrical characterization of amorphous ErSiO films deposited by rf magnetron sputtering on Si (001)

Amorphous ErSiO films have been fabricated on p-type Si (001) substrates using rf magnetron sputtering technique. X-ray diffraction, high-resolution transmission electron microscopy, and atomic force microscopy were employed to investigate the samples. It is found that ErSiO film exhibits a flat surface, a sharp interface and superior electrical properties after post-deposition annealing in O₂ ambience for 30 min at 450°C. The effective dielectric constant of the film is measured to be 14.2, and the effective oxide thickness reaches 1.9 nm, with a low leakage current density of 1.1×10⁻⁴ A/cm² at an electric field of 1 MV cm⁻¹ after annealing at 450°C. The obtained characteristics make the amorphous ErSiO films a promising substitute for SiO₂ as a high-k gate dielectric.     

Crystallisation kinetics of amorphous Si–C–N ceramics: Dependence on nitrogen partial pressure

The crystallisation kinetics of amorphous precursor-derived ceramics of composition Si₂₆C₄₁N₃₃ is investigated as a function of temperature and nitrogen partial pressure using X-ray diffractometry. Isothermal annealing at a pressure of 1 bar leads to simultaneous crystallisation of Si₃N₄ and SiC, while only crystalline SiC is formed with annealing at a reduced pressure of 1 mbar. Rate constants of crystallisation are determined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) formalism. For temperatures below 1700°C, crystallisation rates are significantly higher for annealing at 1 mbar compared to 1 bar. For an explanation of the results, a model is proposed, which is based on diffusion-controlled nucleation and growth of crystalline Si₃N₄ and SiC in an amorphous matrix combined with thermal decomposition of Si₃N₄ at high temperatures.     

Reactive Ion Beams Sputtering of Vanadium Oxides Films for Uncooled Microbolometer

Vanadium oxides thin films for uncooled bolometric detectors have been fabricated on Si₃N₄-film-coated Si substrates by low temperature reactive ion beam sputtering in a controlled oxygen atmosphere. The typical growth temperature is kept at 200°C during sputtering, which is compatible with the post-CMOS technology. The as-deposited film exhibits sheet resistance and temperature coefficient resistant of 32 k and –0.025 K^–1 at room temperature, respectively.     

The microstructures and the electrical and optical properties of ZnO:N films prepared by thermal oxidation of Zn3N2 precursor

Samples of p-type ZnO:N films were prepared on glass substrates by thermal oxidation of Zn₃N₂ precursor, which was produced by reactive magnetron sputtering with a metallic zinc target in Ar/N₂ working gas. The microstructures and the electrical and optical properties of the samples were systematically investigated as a function of the annealing temperature. The results indicate that the annealing temperature has strong effects on the conductivity and photoluminescence (PL) properties of the obtained ZnO:N films. With an annealing temperature of 500 ^°C in oxygen flux, ZnO:N samples show the best p-type characteristics. The doping mechanism and the doping efficiency are briefly discussed based on the experimental results.     

Effect of poly silicon thickness on the formation of Ni-FUSI gate by using atomic layer deposited nickel film

The effect of poly-Si thickness on silicidation of Ni film was investigated by using X-ray diffraction, auger electron spectroscopy, cross-sectional scanning transmission electron microscopy, resistivity, I–V, and C–V measurements. The poly-Si films with various thickness of 30–200 nm were deposited by LPCVD on thermally grown 50 nm thick SiO₂, followed by deposition of Ni film right after removing the native oxide. The Ni film was prepared by using atomic layer deposition with a N²-hydroxyhexafluoroisopropyl-N¹ (Bis-Ni) precursor. Rapid thermal process was then applied for a formation of fully silicide (FUSI) gate at temperature of 500 °C in N₂ ambient during 30 s. The resultant phase of Ni-silicide was strongly dependent on the thickness of poly-Si layer, continuously changing its phase from Ni-rich (Ni₃Si₂) to Si-rich (NiSi₂) with increasing the thickness of the poly-Si layer, which is believed to be responsible for the observed flat band voltage shift, ΔV_FB, in C–V curves.     

Surface structure of γ-Fe2O3(111)

The surface structure of γ-Fe₂O₃(111) has been investigated with a range of surface techniques. Two different surface structures were discovered depending upon surface preparation techniques. Sputtering followed by annealing in vacuum produced a reduced surface characterised by a (2 × 2) LEED pattern, whereas sputtering followed by annealing in 1 × 10^? 6 mbar oxygen produced a surface characterised by a (√3 × √3)-R30° LEED pattern. The latter appears to be a very low conductivity surface, whereas the former has the band gap expected for maghemite (~ 2.0 eV). We propose that the reduced surface is a magnetite-like layer, whereas the oxidised surface is an Fe₂O₃-like layer.     

Growth of AlN nanostructures by a rapid thermal process

Aluminum nitride nanorods were grown during rapid thermal annealing of multi-layered Al₂S₃ /BaS thin films. Depending on the thickness ratio between the BaS and Al₂S₃ layers, nanowires or straight nanorods were obtained. Typical dimensions for the nanorods were a diameter in the range of 50-100 nm and a length of 2-5 μm. The nanostructures are formed upon annealing at a relatively low temperature of 900 ^°C when aluminum evaporates from the thin film, but remains trapped between the thin film surface and the Si wafer, which is used as a support during the annealing. The nitrogen is provided by N₂ gas flushed through the annealing chamber. High-resolution transmission electron microscopy showed crystalline, wurtzite-structured AlN nanorods. The growth mechanism in terms of thin film composition, annealing parameters and the role of catalysts is discussed.     

The impact of ultra thin silicon nitride buffer layer on GaN growth on Si (1 1 1) by RF-MBE

Ultra thin films of pure silicon nitride were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma with a high content of nitrogen atoms. The effect of annealing of silicon nitride surface was investigated with core-level photoelectron spectroscopy. The Si 2p photoelectron spectra reveals a characteristic series of components for the Si species, not only in stoichiometric Si₃N₄ (Si⁴⁺) but also in the intermediate nitridation states with one (Si¹⁺) or three (Si³⁺) nitrogen nearest neighbors. The Si 2p core-level shifts for the Si¹⁺, Si³⁺, and Si⁴⁺ components are determined to be 0.64, 2.20, and 3.05 eV, respectively. In annealed sample it has been observed that the Si⁴⁺ component in the Si 2p spectra is significantly improved, which clearly indicates the crystalline nature of silicon nitride. The high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and photoluminescence (PL) studies showed a significant improvement of the crystalline qualities and enhancement of the optical properties of GaN grown on the stoichiometric Si₃N₄ by molecular beam epitaxy (MBE).     

Characterization of magnesium oxide gate insulators grown using RF sputtering for ZnO thin-film transistors

A ZnO thin-film transistor (TFT) with an MgO insulator was fabricated on a silicon (100) substrate using a radiofrequency magnetron sputtering system. The MgO insulator was deposited using the same deposition system; the total pressure during the deposition process was maintained at 5 mTorr, and the oxygen percentage of O₂/(Ar + O₂) was set at 30%, 50%, or 70%. The process temperature was maintained at below 300 °C. The dielectric constant of the MgO thin layer was approximately 11.35 with an oxygen percentage of 70%. This ZnO TFT displayed enhanced transistor properties, with a field-effect mobility of 0.0235 cm² V⁻¹ s⁻¹, an I_ON/I_OFF ratio of ∼10⁵, and an SS value of 1.18 V decade⁻¹; these properties were superior to those measured for the MgO insulators synthesized using oxygen percentages of 30% and 50%.     

Size-dependent luminescence in Y2Si2O7 nanoparticles doped with Ce3+ ions

Powders and thin films of nanocrystalline yttrium disilicate (Y₂Si₂O₇) doped with Ce³⁺ have been prepared by a sol–gel method. Structure and morphology of the synthesised samples have been determined and spectroscopic properties compared. The triclinic α-Y₂Si₂O₇ form (space group P 1-) for the powders annealed between 1000°C and 1200°C has been found. A total conversion into a thortveitite-type monoclinic β-Y₂Si₂O₇ polymorph after annealing of powder samples at 1400°C (space group C2/m) has been observed. In the case of films even at 1300°C the basically pure triclinic α-Y₂Si₂O₇ phase was observed with luminescent spectroscopy. The influence of grain size, controlled by thermal treatment, on the structure and luminescence properties of the fabricated materials are presented and discussed.