Electrical properties of Bi3.15Nd0.85Ti2.8-xZr0.2MnxO12 thin films with different Mn content synthesized by chemical solution deposition (CSD)

Bi_3.15Nd_0.85Ti_2.8-xZr_0.2Mn_xO₁₂ (BNTZM) thin films with various Mn content (x = 0, 0.005, 0.01, 0.03, and 0.05) have been prepared on Pt/Ti/SiO₂/Si (100) substrates by a chemical solution deposition (CSD) technique. The crystal structures of BNTZM thin film have been analyzed by X-ray diffraction (XRD). The dependence of Mn contents on the ferroelectric, dielectric properties, and leakage current of these BNTZM films have been thoroughly investigated. The XRD analysis demonstrated that all the BNTZM thin films were of typical bismuth-layer-structured ferroelectrics (BLSF) polycrystalline structure and exhibited a highly preferred (117) orientation. Among these BNTZM films, the BNTZM thin film with Mn content equal to 0.01 exhibits the maximum remnant polarization (2P_r) of 48μC/cm² and a low coercive field (2E_c) of 177 kV/cm. In addition, the BNTZM thin film with x = 0.01 (Mn) showed a fatigue-free behavior up to 1 × 10¹⁰ read/write cycles.     

Microstructure and dielectric properties of La2O3 films prepared by ion beam assistant electron-beam evaporation

Ultrathin La₂O₃ gate dielectric films were prepared on Si substrate by ion assistant electron-beam evaporation. The growth processing, interfacial structure and electrical properties were investigated by various techniques. From XRD results, we found that the La₂O₃ films maintained the amorphous state up to a high annealing temperature of 900 °C for 5 min. From XPS results, we also discovered that the La atoms of the La₂O₃ films did not react with silicon substrate to form any La-compound at the interfacial layer. However, a SiO₂ interfacial layer was formed by the diffusion of O atoms of the La₂O₃ films to the silicon substrate. From the atomic force microscopy image, we disclosed that the surface of the amorphous La₂O₃ film was very flat. Moreover, the La₂O₃ film showed a dielectric constant of 15.5 at 1 MHz, and the leakage current density of the La₂O₃ film was 7.56 × 10⁻⁶ A/cm² at a gate bias voltage of 1 V.     

Effect of film thickness on the breakdown temperature of atomic layer deposited ultrathin HfO2 and Al2O3 diffusion barriers in copper metallization

We investigate the effect of thickness of HfO₂ and Al₂O₃ barrier films on the breakdown temperature of Cu/barrier film/Si structures. The HfO₂ and Al₂O₃ films are deposited using tetrakis-diethylamino hafnium and tris-diethylamino aluminum, respectively, as the metal precursors and ozone as the oxidizer at 250 °C. Interactions between the layers of Cu/barrier film (1 or 2 nm-thick)/Si structures due to high-temperature annealing in N₂ are probed using sheet resistance measurements. The crystallinity of the multilayer structure and the possible formation of any anneal-induced reaction products are investigated with X-ray diffraction (XRD). The formation of Cu-silicide phase(s) due to diffusion of Cu atoms through the barrier layer indicates the failure of the corresponding diffusion barrier. The surface morphology of Cu is examined using scanning electron microscopy (SEM) and elemental mapping is done with energy dispersive X-ray spectroscopy (EDS). Our results show that both 1 and 2 nm-thick HfO₂ and Al₂O₃ barrier films are capable of restricting the diffusion of Cu at high annealing temperatures; therefore, they could be used as effective diffusion barriers between Cu and Si.     

Microstructural,optical and electrical properties of GeO2 thin films prepared by sol‐gel method

GeO₂ thin films were prepared by sol‐gel method on ITO/Glass substrate. The electrical and optical properties and the microstructures of these films were investigated with special emphasis on the effects of an annealing treatment in ambient air. The films were annealed at various temperatures from 500 °C to 700 °C. Structural analysis through X‐ray diffraction (XRD) and atomic force microscope (AFM) showed that surface structure and morphological characteristics were sensitive to the treatment conditions. The optical transmittance spectra of the GeO₂/ITO/Glass were measured using a UV‐visible spectrophotometer. All films exhibited GeO₂ (101) orientation perpendicular to the substrate surface where the grain size increased with increasing annealing temperature. The optical transmittance spectroscopy further revealed high transparency (over 70 %) in the wave range 400 – 800 nm of the visible region. At an annealing temperature level of 700 °C, the GeO₂ films were found to possess a leakage current density of 1.31×10^‐6A/cm² at an electrical field of 20 kV/cm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Poole‐Frenkel electrical conduction in europium oxide films deposited on Si(100)

Thin Eu₂O₃ films were prepared on Si (P) substrates to form MOS devices. The oxide crystal structure was determined by X‐ray diffraction (XRD). The electrical transport properties of the devices with amorphous and crystalline Eu oxide were investigated. The current‐voltage and current‐temperature characteristics suggest a Poole‐Frenkel (PF) type mechanism of carrier transport through the device when the applied field is more than 105 V/cm. A deviation from PF leakage current course was found and attributed to the current carrier trapping. We have also observed that, the dielectric spectra of MOS structure are different when the insulator is an amorphous or crystalline thin film. From which we calculate the relaxation time (τ) of the interface (insulator/semiconductor) dipoles. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and characterization of ZnO-TiO2 films obtained by sol-gel method

The sol-gel route has been applied to obtain ZnO-TiO₂ thin films. For comparison, pure TiO₂ and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400-750 °C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400 °C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn₂TiO₄, anatase TiO₂ and amorphous fraction. The XRD analysis presumes that Zn₂TiO₄ becomes a favored phase at the highest annealing temperature of 750 °C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO-TiO₂ films have been compared with those of single component films (ZnO and TiO₂). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature.     

Effects of tantalum doping on microstructure and ferroelectric properties of Bi4Ti3O12 thin films prepared by a sol–gel method

Tantalum-substituted Bi₄Ti₃O₁₂ (Bi₄Ti_3-x/5Ta_x/5O₁₂, BTTO) thin films were fabricated on Pt(111)/Ti/SiO₂/Si(100) substrates by sol–gel technology. The effects of various processing parameters, including Ta content (x=0～0.08) and annealing temperature (500～800 °C), on the growth and properties of thin films were investigated. X-ray diffraction analysis shows that the BTTO thin films have a bismuth-layered perovskite structure with preferred (117) orientation. With the increase of Ta content, the grain size of film decreased slightly, and highly (117)-oriented BTTO films were obtained in the composition of x=0.06. Ta doping on the B-site of Bi₄Ti₃O₁₂ could induce the distortion of oxygen octahedral and decrease the oxygen vacancy concentration by a compensating effect. The highly (117)-oriented BTTO thin films with x=0.06 exhibits the maximum remanent polarization (2P_r) of 50 μC/cm² and a low coercive field (2E_c) of 104 kV/cm, fatigue free characteristics up to ≧ 10⁸ switching cycles.     

Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–In<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films on sapphire substrates: Synthesis and ultraviolet photoconductivity

The structure and electrical and optical properties of β-Ga₂O₃–In₂O₃ thin films on sapphire substrates with different orientations have been investigated. The samples have been prepared by annealing of gallium–indium metallic films on sapphire substrates in air at different gallium-to-indium ratios in the initial mixture. The photoconductivity of these structures in the solar-blind ultraviolet spectral region has been examined.     

Effects of oxide buffer layers on the microstructure and electrical properties of PLZST 2/87/10/3 antiferroelectric thin films

In the present work, the effects of oxide buffer layers, such as ZrO₂, CeO₂ and TiO₂, on the microstructure and electrical properties of (Pb_0.97La_0.02)(Zr_0.87Sn_0.10Ti_0.03)O₃ (PLZST 2/87/10/3) antiferroelectric (AFE) thin films were investigated systematically. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) pictures illustrated that the crystalline orientation and surface microstructure of PLZST 2/87/10/3 AFE thin films had a close relation with these oxide buffer layers. As a result, the final electrical properties of AFE films were tuned by these buffer layers. Electrical measurements result showed that the dielectric properties, polarization characteristic and current–field curves of AFE thin films could be tailored by selecting a proper oxide buffer layer.     

Effect of Thermal Annealing on Structural Properties,Morphologies and Electrical Properties of TiO2 Thin Films Grown by MOCVD

TiO₂ thin films, were deposited on Si(100) and Si(111) substrates by metalorganic chemical vapor deposition at 500 °C, and have been annealed for 2 min, 30 min and 10 hours at the temperature from 600 °C to 900 °C, in oxygen and air flow, respectively. XRD and atomic force microscopy characterized the structural properties and surface morphologies of the films. As‐deposited films show anatase polycrystalline structure with a surface morphology of regular rectangled grains with distinct boundaries. Rutile phase formed for films annealed above 600 °C, and pure rutile polycrystalline films with (110) orientation can be obtained after annealing under adequate conditions. Rutile annealed films exhibit a surface morphology of equiaxed grains without distinct boundaries. The effects of substrate orientation, annealing time and atmosphere on the structure and surface morphology of films have also been studied. Capacitance‐Voltage measurements have been performed for films deposited on Si(100) before and after annealing. The dielectric properties of TiO₂ films were greatly improved by thermal annealing above 600 °C in oxygen.     

Effect of annealing on the structural,electrical and optical properties of nanostructured TiO2 thin films

Nanostructured titanium dioxide thin films were prepared using reactive pulsed laser ablation technique. Effects of annealing on the structural, morphological, electrical and optical properties are discussed. The structural, electrical and optical properties of TiO₂ films are found to be sensitive to annealing temperature and are described with GIXRD, SEM, AFM, UV‐Visible spectroscopy and electrical studies. X‐ray diffraction studies showed that the as‐deposited films were amorphous and at first changed to anatase and then to rutile phase with increase of annealing temperature. Optical constants of these films were derived from the transmission spectra and the refractive index dispersion of the films, subjected to annealing at different temperatures, is discussed in terms of the single oscillator‐Wemple and Didomenico model. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and properties of (Pb0.90La0.10)TiO3 thick films prepared by RF magnetron sputtering with a PbO buffer layer

The (Pb_0.90La_0.10)TiO₃ [PLT] thick films (3.0 μm) with a PbO buffer layer were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering method. The PLT thick films comprise five periodicities, the layer thicknesses of (Pb_0.90La_0.10)TiO₃ and PbO in one periodicity are fixed. The PbO buffer layer improves the phase purity and electrical properties of the PLT thick films. The microstructure and electrical properties of the PLT thick films with a PbO buffer layer were studied. The PLT thick films with a PbO buffer layer possess good electrical properties with the remnant polarization (P_r=2.40 μC cm⁻²), coercive field (E_c=18.2 kV cm⁻¹), dielectric constant (ε_r=139) and dielectric loss (tan δ=0.0206) at 1 kHz, and pyroelectric coefficient (9.20×10⁻⁹ C cm⁻² K⁻¹). The result shows the PLT thick film with a PbO buffer layer is a good candidate for pyroelectric detector.     

Enhancement of ferroelectricity in the compositionally graded (Pb,Sr)TiO3 thin films derived by a sol–gel process

The compositionally graded Pb_1−xSr_xTiO₃ (PST) films with a fine compositional gradient from Pb_0.6Sr_0.4TiO₃ to Pb_0.3Sr_0.7TiO₃ were fabricated on LNO-buffered Pt/Ti/SiO₂/Si substrates by a sol–gel deposition method. The graded films crystallized into a pure perovskite structure and exhibited highly (1 0 0) preferred orientation after post-deposition annealing. Dielectric and ferroelectric properties were investigated as a function of temperature, frequency and direct current bias field. Dielectric constant peaks, common to a ferroelectric transition, were not observed in the temperature range of 25–250 °C within which the dielectric constant showed weak temperature dependence. This compositionally graded thin film can result in a dielectric constant more than double and a remanent polarization at least two and a half times larger than conventional PST thin films.     

Stability and formation of pyrochlore phase in doped Sr0.8Bi2.3Ta2O9 thin films

Ferroelectric thin films of bismuth-containing layered perovskite Sr_0.8Bi_2.3Ta_2−xM_xO₉ (SBTM), where M is V, Ti, W, and Zr, have been prepared on Pt/Ti/SiO₂/Si substrates using the metal-organic decomposition method. The effect of the incorporated B-site cations on pyrochlore phase formation and microstructure evolution of SBTM films was investigated. The pyrochlore phase formation has been identified due to out-diffusion of titanium from underneath platinum layer to participate in the reaction with the films. Furthermore, the formation of pyrochlore phase in the SBTM films has been observed strongly dependent on the characteristics of incorporated M cation. The substitution of both W and V for Ta leads to the formation of pyrochlore phase at lower annealing temperature (750–800 °C). On the other hand, the addition of Zr can retard the formation of pyrochlore phase from 850 to 900 °C. A model based on the binding energy of octahedral structure is used to elucidate the formation and stability of the pyrochlore phase present in the SBT film.     

MOCVD growth of GaN on Si(1 1 1) substrates using an ALD-grown Al2O3 interlayer

GaN thin films have been grown on Si(1 1 1) substrates using an atomic layer deposition (ALD)-grown Al₂O₃ interlayer. This thin Al₂O₃ layer reduces strain in the subsequent GaN layer, leading to lower defect densities and improved material quality compared to GaN thin films grown by the same process on bare Si. XRD ω-scans showed a full width at half maximum (FWHM) of 549 arcsec for GaN grown on bare Si and a FWHM as low as 378 arcsec for GaN grown on Si using the ALD-grown Al₂O₃ interlayer. Raman spectroscopy was used to study the strain in these films in more detail, with the shift of the E₂(high) mode showing a clear dependence of strain on Al₂O₃ interlayer thickness. This dependence of strain on Al₂O₃ thickness was also observed via the redshift of the near bandedge emission in room temperature photoluminescence (RT-PL) spectroscopy. The reduction in strain results in a significant reduction in both crack density and screw dislocation density compared to similar films grown on bare Si. Screw dislocation density of the films grown on Al₂O₃/Si substrates approaches that of typical GaN layers on sapphire. This work shows great promise for the use of oxide interlayers for growth of GaN-based LEDs on Si.     

Effect of temperature on dielectric properties of SnO2/Sb2O3 mixed thin films

Thin films of various thicknesses in the MIM structure have been prepared from the powder of SnO₂/Sb₂O₃ mixed sample by the thermal evaporation technique in a vacuum of 10⁻⁵ Torr. Dielectric properties of SnO₂/Sb₂O₃ mixed thin films have been studied with temperature starting from LNT to RT and above RT and frequency ranging from 100 Hz to 16 kHz. The activation energy for the migration of charge carriers in SnO₂/Sb₂O₃ mixed thin films has been calculated and it is found to be 0.23 eV. The results thus obtained on dielectric properties of SnO₂/Sb₂O₃ mixed thin films are presented and discussed.     

High-quality silicon/insulator heteroepitaxial structures formed by molecular beam epitaxy using Al2O3 and Si

Heteroepitaxial growth of γ-Al₂O₃ films on a Si substrate and the growth of Si films on the γ-Al₂O₃/Si structures by molecular beam epitaxy have been investigated. It has been found from AFM and RHEED observations that, γ-Al₂O₃ films with an atomically smooth surface with an RMS values of ∼3 Å and high crystalline quality can be grown on Si (1 1 1) substrates at substrate temperatures of 650–750°C. Al₂O₃ films grown at higher temperatures above 800°C, did not show good surface morphology due to etching of a Si surface by N₂O gas in the initial growth stage. It has also been found that it is possible to grow high-quality Si layers by the predeposition of Al layer followed by thermal treatment prior to the Si molecular beam epitaxy. Cross-sectional TEM observations have shown that the epitaxial Si had significantly improved crystalline quality and surface morphology when the Al predeposition layer thickness was 10 Å and the thermal treatment temperature was 900°C. The resulting improved crystalline quality of Si films grown on Al₂O₃ is believed to be due to the Al₂O₃ surface modification.     

Structural and electrical properties of Germanium-doped Sb70Te30 eutectic thin films

Ge-doped Sb₇₀Te₃₀ eutectic films show high potential for high transfer rate recording and non-volatile memory applications. Their potential applications are based on the difference in optical and electrical properties between the crystalline and amorphous phases. However, the structure and crystallization mechanism of such films is not yet well understood.The aim of this work is to study the amorphous-to-crystalline phase transformation mechanism in eutectic thin films of pure Sb₇₀Te₃₀ and doped with 2, 5 and 10 at% of Ge. Results of isokinetics and isothermal annealing were carried out using various techniques: four-probe electrical, optical reflectance and X-ray measurements.The results of optical and electrical measurements of Ge doped Sb₇₀Te₃₀ eutectic films showed that the addition of Ge increases both, the crystallization temperature and the effective activation energy of crystallization and that the mechanism of crystallization does not depend on Ge contents.In amorphous films, Ge acts as impurity center and does not affect the optical band gap value, but decreases the pre-exponential factor in the thermally activated conductivity. In crystalline films, Ge is probably incorporated into the Sb₇₀Te₃₀ structure and Ge vacancy are responsible for p-type metallic conduction, which increases with increasing the Ge content.     

Dielectric properties of Zr-Sn-Ti-O thin films prepared by pulsed laser deposition

Zr_0.26Sn_0.23Ti_0.51O₂ (ZSTO) films with a dielectric constant of about 40 have been prepared directly on silicon substrates by pulsed laser deposition at 600 °C. TEM observation showed that the as-deposited films are amorphous. Differential thermal analysis showed that the ZSTO films crystallize at about 620 °C. Capacitance-voltage (C-V) characteristics of metal-oxide-semiconductor (MOS) composed of Pt/ZSTO/Si prepared at different deposition temperature have been measured. The EOT of the MOS structures with the same ZSTO physical thickness increased slightly when the deposition temperature increased. The EOT is about 4.2 nm for the 40 nm ZSTO deposited at 600 °C. The leakage current characteristics of ZSTO films for the as deposited, post-annealed in oxygen ambient and post-annealed in nitrogen ambient by rapid thermal annealing have been studied comparatively. The films post-annealed in nitrogen ambient have the lowest leakage current and the as-deposited films have the largest leakage current characteristics. It is proposed that amorphous Zr-Sn-Ti oxide stabilized at 600 °C is a potential dielectric material for dynamic random access memory and high k dielectric gate applications.     

Characterisation of ALCVD Al2O3-ZrO2 nanolaminates, link between electrical and structural properties

Al₂O₃ and ZrO₂ mixtures for gate dielectrics have been investigated as replacements for silicon dioxide aiming to reduce the gate leakage current and reliability in future CMOS devices. Al₂O₃ and ZrO₂ films were deposited by atomic layer chemical vapor deposition (ALCVD) on HF dipped silicon wafers. The growth behavior has been characterized structurally and electrically. ALCVD growth of ZrO₂ on a hydrogen terminated silicon surface yields films with deteriorated electrical properties due to the uncontrolled formation of interfacial oxide while decent interfaces are obtained in the case of Al₂O₃. Another concern with respect to reliability aspects is the relatively low crystallization temperature of amorphous high-k materials deposited by ALCVD. In order to maintain the amorphous structure at high temperatures needed for dopant activation in the source drain regions of CMOS devices, binary Al/Zr compounds and laminated stacks of thin Al₂O₃ and ZrO₂ films were deposited. X-ray diffraction and transmission electron microscope analysis show that the crystallization temperature can be increased dramatically by using a mixed oxide approach. Electrical characterization shows orders of leakage current reduction at 1.1-1.7 nm of equivalent oxide thickness. The permittivity of the deposited films is determined by combining quantum mechanically corrected capacitance voltage measurements with structural analysis by transmission electron microscope, X-ray reflectivity, Rutherford backscattering, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy. The k-values are discussed with respect to formation of interfacial oxide and possible silicate formation.