Ferroelectric nanostructures fabricated by focused-ion-beam milling in epitaxial BiFeO3 thin films

We studied a suitable route to fabricate ferroelectric islands by focused-ion-beam milling in bismuth ferrite epitaxial thin films. Piezoresponse force microscopy shows that the damage induced by the milling process is extended to 1 μm away from the edge of the focused-ion-beam patterned islands. After a combined vacuum and oxygen atmosphere annealing procedure, ferroelectricity is fully recovered in structures with sizes down to 500 nm, while for 250 nm islands the defects at the interfaces induce polarization direction pinning.     

AlN/Si衬底上ZnO薄膜的择优取向生长

当ZnO薄膜直接沉积在Si衬底上时,由于ZnO与Si的晶格失配度大,不易于获得高质量的ZnO薄膜.因此,选择合适的衬底材料沉积ZnO薄膜,对提高其质量非常重要.本文采用射频磁控溅射法,通过在Si(100)衬底上预沉积AlN作为ZnO薄膜生长的缓冲层,获得了择优取向的ZnO薄膜.我们还讨论了ZnO薄膜在AlN/Si衬底上的取向生长机理.     

Pulsed laser deposition of BiFeO3 thin films with large polarization on Pt(111)/Ti/SiO2/Si by controlling substrate temperature

Bismuth ferrite (BiFeO₃) thin films with large polarization were grown on Pt(111)/Ti/SiO₂/Si by optimizing the substrate temperatures (T _sub). The BiFeO₃ thin films were prepared by pulsed laser deposition and the effects of T _sub (T _sub = 853–913 K) on crystallization orientation, surface morphology and properties of the films were investigated. The microstructure and morphology of the films showed a strong dependence on T _sub. The film prepared at T _sub = 893 K had a relatively high degree of (111) preferential orientation and densely packed morphology. A large polarization with the maximum remanent polarization of 108 μC/cm² was obtained, which was due to the high degree of preferential orientation and the dense surface morphology at the optimum substrate temperature.     

Low-rate sputter-deposited Fe3Si thin films on Si substrates: structural and ferromagnetic properties

Fe3Si thin films were sputter-deposited on Si(001) substrates. Structural investigations show that Fe3Si was deposited poly-crystalline with a Si-containing layer at the Fe3Si/Si interface. The formation of the layer was attributed to the influence of low deposition rates used in this study on the grain nucleation in Fe3Si. This layer helps to stabilize the ferromagnetic properties of the subsequent annealed films at 350 degrees C with 5 Oe obtained for coercive field H(c), approximately 920 emu/cm3 for saturation magnetization M(s) and approximately 0.9M(s) for remnant magnetization M(r).     

Chemical deposition of Al2O3 thin films on Si substrates

Uniform Al₂O₃ films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 10¹¹ eV^− 1cm^− 2 for annealing temperature at 750 °C.     

Electrical properties of thin PbTe films on Si substrates

An attempt was made to reduce the carrier concentration in thin PbTe films on Si substrates by optimizing deposition conditions. A modified hot-wall method was used for reproducible growth ofp-type films with 5 × 10¹⁵ < p(77 K) < 5 × 10¹⁷ cm^-3 andn-type films with 3 × 10¹⁵ < n(77 K) < 5 × 10¹⁶ cm^-3. The IR irradiation was found to have a significant effect on the temperature variation of film resistance. The activation energy of the IR-sensitivity centers was determined to be 0.11 ± 0.005 eV at room temperature and 0.18 ± 0.005 eV between 150 and 180 K.     

Plasma oxidation of Al thin films on Si substrates

In this study, Al thin films deposited on silicon wafers by direct current magnetron sputtering were oxidized under radio frequency 13.56 MHz O₂ plasma at temperatures up to 550 °C. During oxidation, plasma powers as well as oxidation temperature and time were varied to investigate the oxidation behavior of the Al films. X-ray photoelectron spectroscopy and Auger electron spectroscopy results show that the apparent alumina could be observed after O₂ plasma treatment with powers above 200 W as well as at temperatures above 250 °C. However, no alumina increment could be discerned after individual either heat treatment at 550 °C or plasma treatment at room temperature. The thickness of alumina layers increased remarkably with plasma power and could reach about 60 nm when undergone 400 W O₂ plasma treatment at 550 °C for 2 h. Moreover, the thickness of alumina increased parabolically with time during plasma oxidation aided by thermal treatment. The deduced activation energy of such plasma oxidation was 19.1 ± 0.5 kJ/mol.     

Structural and dielectric properties of Ba0.7Sr0.3TiO3 thin films grown on thin Bi layer-coated Pt(111)/Ti/SiO2/Si substrates

In this work, the growth and study of dielectric properties of Ba_0.7Sr_0.3TiO₃ (BST) thin films grown on thin Bi layer coated Pt(111)/Ti/SiO₂/Si substrates, depending on thin Bi layer thickness is reported. The BST thin film (thickness 180 nm) grown on 10-nm-thick Bi layer exhibited more improved structural and dielectric properties than that grown on bare Pt(111)/Ti/SiO₂/Si substrate. The 10-nm-thick Bi layer in optimum configuration was effective for the grain growth of BST phase and suppressed the formation of the oxygen-deficient layer at the interface between the BST thin film and bottom electrode, which resulted in an increase in dielectric constant and a decrease in leakage current density of the Pt/BST thin film/Pt capacitor.     

Characteristics of PbTiO3 thin films on Pt/Ti/SiO2/Si by continuous cooling process

In order to introduce a new deposition process for ferroelectric thin film, the deposition temperature was continuously cooled down from 580°C to 400°C during the deposition which we call continuous cooling process (CCP). X-ray diffraction patterns showed that the PbTiO₃ thin films deposited by the CCP and at 480°C had polycrystallinity, but at substrate temperatures of 400°C and 580°C had poor crystallinity. Scanning electron microscopy of the CCP-deposited film surface showed larger granular-like micrograins than that of the film deposited at 480°C and smaller than that of the film at 580°C. While there was no other phase formation at the PbTiO₃-Pt interface in the CCP-deposited film, resulting in a sharp interface, there was severe interface reaction at the PbTiO₃-Pt and the Pt-Si in the film deposited at 580°C, resulting in an abrupt interface. Atomic force microscopy under ambient conditions showed smoother surface of the film by the CCP than that of the films at 580°C. Furthermore, the film by the CCP had higher packing density than that of the film at 480°C. Besides enhancement of the structural properties, the CCP deposition appeared to have improved the electrical properties such as dielectric constant, dissipation factor, leak current density and polarization. In the case of the film by the CCP, polarization-electrical field measurement showed the saturation polarization of 27 Ccm^–2, remanent of 14 Ccm^–2 and coercive of 150 kV. These results indicate that the CCP in metalorganic chemical vapour deposition has a possibility for fabrication of PbTiO₃ ferroelectric thin films.     

Multiferroic BiFeO3 thin films for multifunctional devices

We report the metalorganic chemical vapor deposition of crystalline BiFeO3 films on platinized silicon substrates using n-butylferrocene, triphenylbismuth and oxygen. Based on thermogravimetric analysis data, the suitability of these two precursors for depositing BiFeO3 is discussed. The deposited films were characterized for structure and morphology using X-ray diffraction and scanning electron microscopy. Composition analysis using X-ray photoelectron spectroscopy revealed that the films were stoichiometric BiFeO3. Electrostatic force microscopy indicated that the film had polarizable domains that showed no deterioration in polarization over time long after electric poling. The film showed a saturation magnetization of 10 +/- 1 emu/cm3 at room temperature.     

Tensile strain engineering of Si thin films using porous Si substrates

Highly tensile strained (up to 2.2%) thin monocrystalline silicon (mc-Si) films were fabricated by a simple and low-cost method based on the in-plane expansion of meso-porous silicon (PS) substrates upon low temperature oxidation. To control the film thickness below 100 nm, an original “two wafer” technique was employed during the porosification process. This method enables the fabrication of a 60 nm thick mc-Si films on 250 μm thick meso-porous silicon substrates over areas as large as 2 in. with a surface roughness and cleanliness comparable to that of standard Si wafers. Crack-free 60 nm thick Si films can be strained up to 1.2% by controlled low temperature oxidation of the PS substrate. Structural and strain analysis of the PS/mc-Si structures performed by transmission electron microscopy and micro-Raman scattering spectroscopy are reported.     

Growth of Bi1.5MgNb1.5O7 thin films on Pt/Ti/SiO2/Si substrates by RF magnetron sputtering

In this letter, bismuth magnesium niobate (Bi_1.5MgNb_1.5O₇, BMN) thin films were deposited on Pt/Ti/SiO₂/Si substrates by using radio-frequency magnetron sputtering at various substrate temperatures. Based on the phase compositions and microstructures of these samples, we discussed the nucleation and growth of the BMN thin films and how the substrate temperature influenced these processes. The thin film begins to crystallize at 450 °C, and the annealed films were all composed of the cubic pyrochlore phase with a strong (222)-preferred orientation. The film deposited at 450 °C exhibited a large dielectric constant of 173, and a tunability of 26.6 % was obtained at a max dc bias field of 0.8 MV/cm.     

Fabrication and optical properties of Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) thin films on Si substrates using the PLD method.

Epitaxial 0.67Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3)-0.33PbTiO(3) (PMN-PT) thin films with electro-optic effects were fabricated on (PMN-PT) thin films with electro-optic effects were fabricated on (La0(0.5)Sr0(0.5))CoO(3) (LSCO)/CeO(2)/YSZ-buffered Si(001) substrates using double-pulse excitation pulsed laser deposition (PLD) method with a mask placed between the target and the substrate. Epitaxial growth of PMN-PT thin films was undertaken using the two-step growth method of PMN-PT film. The PMN-PT seed layer was deposited at 500 degrees C on the LSCO/CeO(2)/YSZ/Si, which temperature was the same as that used for LSCO deposition. The PMN-PT thin films were deposited on the PMN-PT seed layer at 600 degrees C, which enables growth of high-crystallinity PMN-PT films with smooth surfaces. We obtained optimum fabrication conditions of PMNPT film with micrometer-order thickness. Resultant films showed high crystallinity with full width at half maximum (FWHM) = 0.73 deg and 1.6 mum thickness. Electro-optic properties and the refractive index value were measured at 633 nm wavelength using the prism coupling method. The obtained refractive index was 2.59. The electro-optic coefficients r(13) and r(33) were determined by applying the electrical field between a semitransparent, thin top electrode of Pt and a bottom LSCO electrode. The electro-optic coefficient was r(13) = 17 pm/V at transverse electric field (TE) mode and r(33) = 55 pm/V at transverse magnetic field (TM) mode.     

Temperature dependence of oriented growth of Pb[Yb(1/2)Nb(1/2)]O(3)-PbTiO(3) thin films deposited on LNO/Si substrates

(1-x)Pb[Yb(1/2)Nb(1/2)]O(3)-xPbTiO(3) (PYbN-PT, x=0.5)(001) oriented thin films were deposited onto LaNiO3 (LNO)/Si(001) substrates by sol-gel processing. The crystallographic texture of the films was controlled by the annealing temperature and heating rate. Highly (001) oriented LNO thin films were prepared by a simple metal organic decomposition technique, and the samples were annealed at 700 °C and 750 °C using a rapid thermal annealing process and furnace, respectively. X-ray diffraction analysis revealed that the films of PYbN-PT were highly (001) oriented along LNO/Si substrates. The degree of PYbN-PT orientation is dependent on the heating rate and annealing temperature. Annealing heating rate of 10 °C/s and high annealing temperature near 750 °C produce the greatest degree of (001) orientation, which gives rise to improved dielectric properties.     

Mo/Si and Mo/Be multilayer thin films on Zerodur substrates for extreme-ultraviolet lithography

Multilayer-coated Zerodur optics are expected to play a pivotal role in an extreme-ultraviolet (EUV) lithography tool. Zerodur is a multiphase, multicomponent material that is a much more complicated substrate than commonly used single-crystal Si or fused-silica substrates. We investigate the effect of Zerodur substrates on the performance of high-EUV reflectance Mo/Si and Mo/Be multilayer thin films. For Mo/Si the EUV reflectance had a nearly linear dependence on substrate roughness for roughness values of 0.06-0.36 nm rms, and the FWHM of the reflectance curves (spectral bandwidth) was essentially constant over this range. For Mo/Be the EUV reflectance was observed to decrease more steeply than Mo/Si for roughness values greater than approximately 0.2-0.3 nm. Little difference was observed in the EUV reflectivity of multilayer thin films deposited on different substrates as long as the substrate roughness values were similar.     

Preparation,microstructure and dielectric properties of Ba0.5Sr0.5TiO3 thin films grown on Pt/Ti/SiO2/Si substrates by pulsed laser deposition

Barium strontium titanate Ba_0.5Sr_0.5TiO₃ (BST) thin films have been deposited on Pt/Ti/SiO₂/Si substrates by a pulsed laser deposition method. The low-frequency dielectric responses of the BST films, grown at different substrate temperatures (T_s), were measured as functions of frequency in the frequency range from 1 kHz to 1 MHz. With increase of T_s, the grain size of BST thin films became larger and the crystallinity was greatly improved, and then the dielectric permittivity increased, while the dielectric dispersion rose drastically. The origin of the large dielectric relaxation is believed to result from the aggravation of oxygen diffusion at the BST/Pt interface for the BST thin films grown at comparatively higher temperatures. This concept could be further explained by considering the influence of post-annealing in oxygen ambient on the dielectric properties of BST thin films. Our results reveal that the dielectric properties are strongly dependent on the processing conditions and the microstructure of thin films.