Ferroelectric and leakage current characteristics of (Pb0.72La0.28)Ti0.93O3 thin films prepared by a sol-gel process

(Pb_1 − xLa_x)Ti_1 − x/4O₃(x = 28 mol%, denoted as PLT) thin films were grown on Pt/Ti/SiO₂/Si substrates by using a sol-gel process. The Pt/PLT/Pt film capacitor showed well-saturated hysteresis loops at an applied electric field of 500 kV/cm with spontaneous polarization (P_s), remanent polarization (P_r) and coercive electric field (E_c) values of 9.23 μC/cm², 0.53 μC/cm² and 19.7 kV/cm, respectively. At 100 kHz, the dielectric constant and dissipation factor of the film were 748 and 0.026, respectively. The leakage current density is lower than 1.0 × 10⁻⁷ A/cm²over the electric field range of 0 to 200 kV/cm. And the Pt/PLT interface exist a Schottky emission characteristics.     

Studies on dielectric relaxation and defect generation for reliability assessments in ultrathin high-k gate dielectrics on Ge

In this work, we present the results of dielectric relaxation and defect generation kinetics towards reliability assessments for Zr-based high-k gate dielectrics on p-Ge (1 0 0). Zirconium tetratert butoxide (ZTB) was used as an organometallic source for the deposition of ultra thin (∼14 nm) ZrO₂ films on p-Ge (1 0 0) substrates. It is observed that the presence of an ultra thin lossy GeO_x interfacial layer between the deposited high-k film and the substrate, results in frequency dependent capacitance-voltage (C-V) characteristics and a high interface state density (∼10¹² cm⁻² eV⁻¹). Use of nitrogen engineering to convert the lossy GeO_x interfacial layer to its oxynitride is found to improve the electrical properties. Magnetic resonance studies have been performed to study the chemical nature of electrically active defects responsible for trapping and reliability concerns in high-k/Ge systems. The effect of transient response and dielectric relaxation in nitridation processes has been investigated under high voltage pulse stressing. The stress-induced trap charge density and its spatial distribution are reported. Charge trapping/detrapping of stacked layers under dynamic current stresses was studied under different fluences (−10 mA cm⁻² to −50 mA cm⁻²). Charge trapping characteristics of MIS structures (Al/ZrO₂/GeO_x/Ge and Al/ZrO₂/GeO_xN_y/Ge) have been investigated by applying pulsed unipolar (peak value - 10 V) stress having 50% duty-cycle square voltage wave (1 Hz-10 kHz) to the gate electrode.     

Highly (1 0 0)-oriented Pb(Zr0.20Ti0.80)O3/(Pb1−xLax)Ti1−x/4O3 multilayered thin films prepared by RF magnetron sputtering

The Pb(Zr_0.20Ti_0.80)O₃/(Pb_1−xLa_x)Ti_1−x/4O₃ (x = 0, 0.10, 0.15, 0.20) (PZT/PLT_x) multilayered thin films were in situ deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering technique with a PbO_x buffer layer. With this method, all PZT/PLT_x multilayered thin films possess highly (1 0 0) orientation. The PbO_x buffer layer leads to the (1 0 0) orientation of the multilayered thin films. The effect of the La content in PLT_x layers on the dielectric and ferroelectric properties of the PZT multilayered thin films was systematically investigated. The enhanced dielectric and ferroelectric properties are observed in the PZT/PLT_x (x = 0.15) multilayered thin films. The dielectric constant reaches maximum value of 365 at 1 KHz for x = 0.15 with a low loss tangent of 0.0301. Along with enhanced dielectric properties, the multilayered thin films also exhibit large remnant polarization value of 2P_r = 76.5 μC/cm², and low coercive field of 2E_c = 238 KV/cm.     

Thin titanium oxide films deposited by e-beam evaporation with additional rapid thermal oxidation and annealing for ISFET applications

Titanium oxide (TiO₂) has been extensively applied in the medical area due to its proved biocompatibility with human cells [1]. This work presents the characterization of titanium oxide thin films as a potential dielectric to be applied in ion sensitive field-effect transistors. The films were obtained by rapid thermal oxidation and annealing (at 300, 600, 960 and 1200 °C) of thin titanium films of different thicknesses (5 nm, 10 nm and 20 nm) deposited by e-beam evaporation on silicon wafers. These films were analyzed as-deposited and after annealing in forming gas for 25 min by Ellipsometry, Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy (RAMAN), Atomic Force Microscopy (AFM), Rutherford Backscattering Spectroscopy (RBS) and Ti-K edge X-ray Absorption Near Edge Structure (XANES). Thin film thickness, roughness, surface grain sizes, refractive indexes and oxygen concentration depend on the oxidation and annealing temperature. Structural characterization showed mainly presence of the crystalline rutile phase, however, other oxides such Ti₂O₃, an interfacial SiO₂ layer between the dielectric and the substrate and the anatase crystalline phase of TiO₂ films were also identified. Electrical characteristics were obtained by means of I-V and C-V measured curves of Al/Si/TiO_x/Al capacitors. These curves showed that the films had high dielectric constants between 12 and 33, interface charge density of about 10¹⁰/cm² and leakage current density between 1 and 10⁻⁴ A/cm². Field-effect transistors were fabricated in order to analyze I_D x V_DS and log I_D × Bias curves. Early voltage value of −1629 V, R_OUT value of 215 MΩ and slope of 100 mV/dec were determined for the 20 nm TiO_x film thermally treated at 960 °C.     

Properties of ALD HfTaxOy high-k layers deposited on chemical silicon oxide

HfTa_xO_y high-k dielectric layers with different compositions were deposited using ALD on 1 nm SiO₂ generated by ozone based cleaning of 200 mm Si(1 0 0) surface. Physical characterization of blanket layers and C-V mapping demonstrates that the ALD layers have excellent uniformity and controllable compositions. The layers with a composition of HfTaO_5.5 remain amorphous after annealing at 900 °C. The C-V measurements of MOS capacitors show no hysteresis, negligible frequency dispersion and interfacial state density smaller than 3 × 10¹¹ (cm⁻² eV⁻¹). k-value of the amorphous layers varies in the range from 20 to 25, depending on layer composition. The flat band voltage does not shift with the increase of EOT, implying that the effect of fixed charge densities in the layers is negligible. The I-V measurements show a leakage reduction comparable to that of the ALD HfO₂ layers.     

Physical properties in thin films of iron oxides

We have grown hematite (α-Fe₂O₃) thin films on stainless steel substrates and magnetite (Fe₃O₄) thin films on (0 0 1)-Si single crystal substrates by a RF magnetron sputtering process. α-Fe₂O₃ thin films were grown in an Ar atmosphere at substrate temperatures around , and Fe₃O₄ thin films in an Ar/O₂ reactive atmosphere at substrate temperatures around . Conversion electron Mössbauer (CEM) spectra of α-Fe₂O₃ thin films exhibit values for hyperfine parameter characteristic of the hematite stoichiometric phase in the weak ferromagnetic state [R.E. Vandenberghe, in: Mössbauer Spectroscopy and Applications in Geology, University Gent, Belgium, 1990. [1]]. Furthermore, the relative line intensity ratio suggests that the magnetization vector of the polycrystalline film is aligned preferentially parallel to the surface. The CEM spectra of Fe₃O₄ thin films show the presence of only the stoichiometric phase, and the values for the hyperfine fields and isomer shifts of the A and B sites are consistent with bulk Fe₃O₄[1]. The X-ray diffraction (XRD) pattern of the polycrystalline thin films also corresponds to α-Fe₂O₃ and Fe₃O₄ [JCPDS, X-ray diffraction data cards, 2001. [2]]. The samples were also analyzed by atomic force microscopy (AFM) and they reveal a grain morphology common for polycrystalline films. We found an average grain size of 211 nm and surface roughness of 45 nm in α-Fe₂O₃ films and an average grain size of 148 nm and surface roughness of 1.2 nm in Fe₃O₄ films.     

Improvement on low-temperature deposited HfO2 film and interfacial layer by high-pressure oxygen treatment

In this study, high-pressure oxygen (O₂ and O₂ + UV light) technologies were employed to effectively improve the properties of low-temperature-deposited metal oxide dielectric films and interfacial layer. In this work, 13 nm HfO₂ thin films were deposited by sputtering method at room temperature. Then, the oxygen treatments with a high-pressure of 1500 psi at 150 °C were performed to replace the conventional high temperature annealing. According to the XPS analyses, integration area of the absorption peaks of O-Hf and O-Hf-Si bonding energies apparently raise and the quantity of oxygen in deposited thin films also increases from XPS measurement. In addition, the leakage current density of standard HfO₂ film after O₂ and O₂ + UV light treatments can be improved from 3.12 × 10⁻⁶ A/cm² to 6.27 × 10⁻⁷ and 1.3 × 10⁻⁸ A/cm² at |Vg| = 3 V. The proposed low-temperature and high pressure O₂ or O₂ + UV light treatment for improving high-k dielectric films is applicable for the future flexible electronics.     

Influence of the deposition parameters on the growth of SiGe nanocrystals embedded in Al2O3 matrix

Si_1−xGe_x nanocrystals (NCs), embedded in Al₂O₃ matrix, were fabricated on Si (100) substrates by RF-magnetron sputtering technique with following annealing procedure at 800 °C, in nitrogen atmosphere. The presence of Si_1−xGe_x NCs was confirmed by grazing incidence X-ray diffraction (GIXRD), grazing incidence small angle X-ray scattering (GISAXS) and Raman spectroscopy. The influence of the growth conditions on the structural properties and composition of Si_1−xGe_x NCs inside the alumina matrix was analyzed. Optimal conditions to grow Si_1−xGe_x (x∼ 0.8) NCs sized between 3 and 4 nm in Al₂O₃ matrix were established.     

Rare earth-based high-k materials for non-volatile memory applications

A study of a La-based high-k oxide to be employed as active dielectric in future scaled memory devices is presented. The focus will be held on La_xZr_1−xO_2−δ (x = 0.25) compound. In order to allow the integration of this material, its chemical interaction with an Al₂O₃ cap layer has been studied. Moreover, the electrical characteristics of these materials have been evaluated integrating them in capacitor structures. The rare earth-based ternary oxide is demonstrated to be a promising candidate for future non-volatile memory devices based on charge trapping structure.     

Effect of a silicon nitride buffer layer on the electrical properties of tantalum pentoxide films

Ta₂O₅ films with a buffer layer of silicon nitride of various thicknesses were deposited on Si substrate by reactive sputtering and submitted to annealing at 700 °C in nitrogen atmosphere. The microstructure and the electrical properties of thin films were studied. It was found that with a buffer layer of silicon nitride the electrical properties of Si_xN_y/Ta₂O₅ film can be improved than Ta₂O₅ film. When the thickness of the buffer layer was 3 nm, the Si_xN_y/Ta₂O₅ film has the highest dielectric constant of 27.4 and the lowest leakage current density of 4.61 × 10⁻⁵ A/cm² (at −1 V). For the Si_xN_y (3 nm)/Ta₂O₅ film, the conduction mechanism of leakage current was also analyzed and showed four types of conduction mechanisms at different applied voltages.     

Fully strained Si0.75Ge0.25 epitaxial films with HfSiO gate dielectrics for high mobility channel metal-oxide semiconductor devices

The authors report on fully strained Si_0.75Ge_0.25 metal-oxide-semiconductor capacitors with HfSiO₂ high-k gate dielectric and TaN metal gate fabricated on Si substrates. Fully strained Si_0.75Ge_0.25 films are directly grown on Si substrates below the critical thickness. HfSiO₂ high-k gate dielectrics exhibit an equivalent oxide thickness of 13-18 Å with a permittivity of 17.7 and gate leakage current density lower than SiO₂ gate oxides by >100×. Interfacial oxide of the HfSiO₂/Si_0.75Ge_0.25 stack consists primarily of SiO₂ with a small amount of Ge and Hf. High performance SiGe field effect transistors are highly manufacturable with excellent electrical characteristics afforded by the fully strained HfSiO₂/SiGe gate stack.     

HfAlOx high-k gate dielectric on SiGe: Interfacial reaction, energy-band alignment, and charge trapping properties

Ultra thin HfAlO_x high-k gate dielectric has been deposited directly on Si_1−xGe_x by RF sputter deposition. The interfacial chemical structure and energy-band discontinuities were studied by using X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (TOF-SIMS) and electrical measurements. It is found that the sputtered deposited HfAlO_x gate dielectric on SiGe exhibits excellent electrical properties with low interface state density, hysteresis voltage, and frequency dispersion. The effective valence and conduction band offsets between HfAlO_x (E_g = 6.2 eV) and Si_1−xGe_x (E_g = 1.04 eV) were found to be 3.11 eV and 2.05 eV, respectively. In addition, the charge trapping properties of HfAlO_x/SiGe gate stacks were characterized by constant voltage stressing (CVS).     

Occurrence of ferroelectricity in epitaxial BiMnO3 thin films

In this paper, we report evidence of ferroelectricity in perovskite manganite (BiMnO₃) thin films synthesized via r.f. magnetron sputtering method on a single-crystal (1 0 0)-oriented SrTiO₃:Nb 0.1% and Pt/TiO₂/SiO₂/Si substrates. X-ray diffraction measurements were used to analyse the crystal structure of the thin films, revealing epitaxial growth for BiMnO₃ films with their (1 1 1) and (2 2 2) planes parallel to the (0 0 1) and (0 0 2) planes of the SrTiO₃ substrate. AFM measurements were performed to investigate surface morphology; quantitative values of roughness and grain size are in the range between 300 and 500 nm. Ferroelectric characterization was conducted at low temperatures and at 300 K. Hysteresis loops (polarization vs. voltage) were obtained, showing saturation polarizations of , and at 105, 122, and 300 K. Resistance vs. temperature measurements were performed, which indicated this to be very robust insulating material.     

Fabrication and characterization of Zr-rich Zr-aluminate films for high-κ gate dielectric applications

Two kinds of Zr-rich Zr-aluminate films for high-κ gate dielectric applications with the nominal composition of (ZrO₂)_0.8(Al₂O₃)_0.2 and (ZrO₂)_0.9(Al₂O₃)_0.1, were deposited on n-type silicon wafer by pulsed laser deposition (PLD) technique at different deposition conditions. X-ray diffraction (XRD) reveals that the (ZrO₂)_0.8(Al₂O₃)_0.2 film could remain amorphous after being rapid thermal annealed (RTA) at the temperature above 800 °C, while the other one displays some crystalline peaks at 700 °C. The energy gap calculated from optical transmittance spectrum of (ZrO₂)_0.8(Al₂O₃)_0.2 film on quartz is about 6.0 eV. Sputtering depth profile of X-ray photoelectron spectroscopy and Auger electron spectroscopy indicate that a Zr-Si-O interfacial layer was formed at the near surface of the silicon substrate. The dielectric constant of the (ZrO₂)_0.8(Al₂ O₃)_0.2 film has been determined to be 22.1 by measuring a Pt/(ZrO₂)_0.8(Al₂ O₃)_0.2/Pt MIM structure. An EOT of 1.76 nm with a leakage current density of 51.5 mA/cm² at 1 V gate voltage for the film deposited in N₂ were obtained. Two different pre-treatments of Si substrates prior to depositions were also carried out and compared. The results indicate that a surface-nitrided Si substrate can lead to a lower leakage current density. The amorphous Zr-rich Zr-aluminate films fabricated by PLD have promising structure and dielectric properties required for a candidate material for high-κ gate dielectric applications.     

The structural and electrical properties of the SrTa2O6/In0.53Ga0.47As/InP system

The structural and electrical properties of SrTa₂O₆(SrTaO)/n-In_0.53GaAs_0.47(InGaAs)/InP structures where the SrTaO was grown by atomic vapor deposition, were investigated. Transmission electron microscopy revealed a uniform, amorphous SrTaO film having an atomically flat interface with the InGaAs substrate with a SrTaO film thickness of 11.2 nm. The amorphous SrTaO films (11.2 nm) exhibit a dielectric constant of ∼20, and a breakdown field of >8 MV/cm. A capacitance equivalent thickness of ∼1 nm is obtained for a SrTaO thickness of 3.4 nm, demonstrating the scaling potential of the SrTaO/InGaAs MOS system. Thinner SrTaO films (3.4 nm) exhibited increased non-uniformity in thickness. From the capacitance-voltage response of the SrTaO (3.4 nm)/n-InGaAs/InP structure, prior to any post deposition annealing, a peak interface state density of ∼2.3 × 10¹³ cm⁻² eV⁻¹ is obtained located at ∼0.28 eV (±0.05 eV) above the valence band energy (E_v) and the integrated interface state density in range E_v + 0.2 to E_v + 0.7 eV is 6.8 × 10¹² cm⁻². The peak energy position (0.28 ± 0.05 eV) and the energy distribution of the interface states are similar to other high-k layers on InGaAs, such as Al₂O₃ and LaAlO₃, providing further evidence that the interface defects in the high-k/InGaAs system are intrinsic defects related to the InGaAs surface.     

Fabrication and electrical characteristics of ultrathin (HfO2)x(SiO2)1−x films by surface sol-gel method and reaction-anneal treatment

Hafnium oxide (HfO₂) films were deposited on Si substrates with a pre-grown oxide layer using hafnium chloride (HfCl₄) source by surface sol-gel process, then ultrathin (HfO₂)_x(SiO₂)_1−x films were fabricated due to the reaction of SiO₂ layer with HfO₂ under the appropriate reaction-anneal treatment. The observation of high-resolution transmission electron microscopy indicates that the ultrathin films show amorphous nature. X-ray photoelectron spectroscopy analyses reveal that surface sol-gel derived ultrathin films are Hf-Si-O alloy instead of HfO₂ and pre-grown SiO₂ layer, and the composition was Hf_0.52Si_0.48O₂ under 500 °C reaction-anneal. The lowest equivalent oxide thickness (EOT) value of 0.9 nm of film annealed at 500 °C has been obtained with small flatband voltage of −0.31 V. The experimental results indicate that a simple and feasible solution route to fabricate (HfO₂)_x(SiO₂)_1−x composite films has been developed by means of combination of surface sol-gel and reaction-anneal treatment.     

A novel thermally-stable zirconium amidinate ALD precursor for ZrO2 thin films

ZrO₂ thin films were deposited by the atomic layer deposition process on Si substrates using tetrakis(N,N′-dimethylacetamidinate) zirconium (Zr-AMD) as a Zr precursor and H₂O as an oxidizing agent. Tetrakis (ethylmethylamino) zirconium (TEMA-Zr) was also evaluated for a comparative study. Physical properties of ALD-derived ZrO₂ thin films were studied using ellipsometry, grazing incidence XRD (GI-XRD), high resolution TEM (HRTEM), and atomic force microscopy (AFM). The ZrO₂ deposited using Zr-AMD showed a better thermal stability at high substrate temperature (>300 °C) compared to that using TEMA-Zr. GI-XRD analysis reveals that after 700 °C anneal both ZrO₂ films enter tetragonal phase. The electrical properties of N₂-annealed ZrO₂ film using Zr-AMD exhibit an EOT of 1.2 nm with leakage current density as low as 2 × 10⁻³ A/cm² (@V_fb−1 V). The new Zr amidinate is a promising ALD precursor for high-k dielectric applications.     

High-mobility pentacene thin-film transistor by using LaxTa(1−x)Oy as gate dielectric

Pentacene organic thin-film transistors (OTFTs) using La_xTa_(1−x)O_y as gate dielectric with different La contents (x = 0.227, 0.562, 0.764, 0.883) have been fabricated and compared with those using Ta oxide or La oxide. The OTFT with La_0.764Ta_0.236O_y can achieve a carrier mobility of 1.21 cm² V⁻¹s⁻¹s, which is about 40 times and two times higher than those of the devices using Ta oxide and La oxide, respectively. As supported by XPS, AFM and noise measurement, the reasons lie in that La incorporation can suppress the formation of oxygen vacancies in Ta oxide, and Ta content can alleviate the hygroscopicity of La oxide, resulting in more passivated and smoother dielectric surface and thus larger pentacene grains, which lead to higher carrier mobility.     

Characterization of CMOS sub-65 nm metallic contact by laser scattering: Thermal stability of Ni(Si1−xGex)

Very efficient in particles detection, light scattering also offers fast non-invasive full-mapping wafer surface state. This sensitivity was used in the case of germano-silicide process development. As a matter of fact, we report on haze measurement performances, compared to the usual methods used to investigate thermal stability of Ni(Si_1−xGe_x), such as sheet resistance (SR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). We observed defectivity related to thermal agglomeration and Ge-segregation of Ni(Si_1−xGe_x) on strain Si_1−xGe_x (x ? 30%) by haze measurement (like SEM observations) earlier than SR measurement. Moreover, we noticed that a high Ge content affects at lower temperature the stability of Ni(Si_1−xGe_x) with a segregation phenomena.     

Electrodepositing ZnxMnyOz alloys from zinc oxide to manganese oxide

Electrodeposition has emerged as a practical and simple method to synthesise semiconductor materials under different forms, thin films or nanostructured layers. This work reports on the cathodic electrodeposition of ZnMnO thin layers using both zinc and manganese chlorides as precursors. The composition of thin films can be varied from binary zinc oxide to manganese oxide varying the Mn/(Mn+Zn) ratio between 0 and 1. The composition of Zn_xMn_yO_z films was obtained by energy dispersive spectroscopy. Zn_1−xMn_xO films with Mn/Zn ratio less than 10% exhibit a crystalline wurtzite structure typical of ZnO fully oriented in the (0 0 2) direction. Higher Mn content leads to deformation of the ZnO lattice and the wurtzite structure is no longer maintained. X-ray photoelectron spectroscopy points out that Mn₃O₄ tends to be deposited when a high Mn/Zn ratio is used in the starting solution. Magnetic measurements on films with Mn/(Zn+Mn) ratio near 1 reveal magnetic characteristics similar to Mn₃O₄ compounds. The transmission spectra of Zn_xMn_yO_z show the typical absorption edge of crystalline ZnO while the wurtzite structure is maintained and it shifts to higher wavelengths when Mn content increases.