Reduced Leakage Current Density Research Articles

Improved dielectric tunability of PZT/BST multilayer thin films on Ti substrates

PbZr0.2Ti0.8O3/Ba0.6Sr0.4TiO3 (PZT/BST) multilayer thin films on LaNiO3 buffered Ti substrates were fabricated by sol-gel method. Results show that there are tetragonal PZT phase and cubic BST phase in the phase structure of PZT/BST films. These films with small grain size also exhibit enhanced dielectric temperature stability and reduced leakage current density. Dielectric anomaly is found for such PZT/BST multilayers: the maximum of dielectric constant and tunability respectively reaches 501 and 41.1% (400 kV/cm) when the thickness content of BST films is 50%. The corresponding temperature coefficient of permittivity (TCP) is only 2.7 × 10−4/°C. Furthermore, dielectric constant and tunability of such PZT/BST thin films are calculated by phenomenological theory. The experimental data of dielectric constant and tunability are both in between the calculated results of without and complete electrostatic coupling, indicating that dielectric anomaly is caused by electrostatic coupling and part coupling takes place in the fabricated films.

Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films

Abstract Lead free Bi 0.5 (Na 0.8 K 0.2 ) 0.5 TiO 3 thin films doped with BiFeO 3 (abbreviated as BNKT-xBFO) (x = 0, 0.02, 0.04, 0.08, 0.10) were deposited on Pt(111)/Ti/SiO 2 /Si substrates by sol-gel/spin coating technique and the effects of BiFeO 3 content on the crystal structure and electrical properties were investigated in detail. The results showed that all the BNKT-xBFO thin films exhibited a single perovskite phase structure and high-dense surface. Reduced leakage current density, enhanced dielectric and ferroelectric properties were achieved at the optimal composition of BNKT-0.10BFO thin films, with a leakage current density, dielectric constant, dielectric loss and maximum polarization of −4 A/cm 3 , ~ 978 , ~ 0.028 and ~ 74.13 μC/cm 2 at room temperature, respectively. Moreover, the BNKT-0.10BFO thin films possessed superior energy storage properties due to their slim P-E loops and large maximum polarization, with an energy storage density of 22.12 J/cm 3 and an energy conversion efficiency of 60.85% under a relatively low electric field of 1200 kV/cm. Furthermore, the first half period of the BNKT-0.10BFO thin film capacitor was about 0.15 μs, during which most charges and energy were released. The large recoverable energy density and the fast discharge process indicated the potential application of the BNKT-0.10BFO thin films in electrostatic capacitors and embedded devices.

Effect of microwave annealing on electrical characteristics of TiN/Al/TiN/HfO2/Si MOS capacitors

In this letter, microwave annealing over a wide range of power (300–2700 W) in nitrogen ambient was performed on TiN/Al/TiN/HfO2/Si metal-oxide-semiconductor capacitors. Capacitors with rapid thermal annealing at 500 °C were also fabricated for comparison at the same wafer temperature measured during microwave annealing at 2700 W. For microwave annealed capacitors, key parameters such as equivalent oxide thickness, interface state density, oxide trapped charge, leakage current density, and breakdown voltage were all improved with increasing microwave annealing power. For the capacitor with rapid thermal annealing at 500 °C, diffusion of Al into TiN and growth of the interfacial oxide layer are detected, leading to the shift in flat-band voltage and increase in equivalent oxide thickness, respectively. The results further indicate that it is more effective to remove the charged traps by microwave annealing than by rapid thermal annealing, and the reduction in leakage current density after microwave annealing corresponds to the reduction in charge traps based on a trap-assisted tunneling model. With no trade-off relationship between the electrical characteristics and no undesired effect such as diffusion of species, microwave annealing demonstrates great potential for the post-metallization annealing process for the high-k/metal gate structure.

The effect of ozone concentration during atomic layer deposition on the properties of ZrO2 films for capacitor applications

In this study, we report the effect of process conditions on the crystallinity and energy band structure of atomic layer deposition (ALD) ZrO2 films deposited, using tris(dimethylamino) cyclopentadienyl zirconium as a precursor and ozone as a reactant. ZrO2 films exhibited systematic changes in phase and energy band gap as a function of the ozone concentration. The crystal phase was transformed from the monoclinic phase to a tetragonal phase in the presence of higher ozone concentrations. In addition, spectroscopic ellipsometry measurements showed that the optical band gap and oxygen vacancy defects decreased with increasing ozone concentration. The valence band maximum also shifted closer to the Fermi energy level with increasing ozone concentration. The change in electronic structure driven by a high concentration of ozone led to reduced leakage current density and a high dielectric constant in the ZrO2-based metal-insulator-metal capacitors. These improvements were not observed for depositions performed using conventional ZrO2 ALD with oxygen and water reactants.

Effect of UV/ozone plasma treatment on sol–gel-derived HfO2 thin films

This study reports on the fabrication and characterization of sol–gel-derived HfO2 thin films on indium tin oxide (ITO) substrates. The films were dried in air and ultraviolet (UV)/ozone plasma environments and finally annealed at various temperatures ranging from 300 to 500°C. Crystallization of the films was observed to occur even at low annealing temperature of 300°C. Scanning electron microscopy results indicate that the films dried in the air environment were not uniform, and the grains were observed to be separated from each other. In contrast, the UV/ozone plasma-treated thin films exhibited smooth and uniform surfaces. The reduction of leakage current density of more than 3 orders of magnitude was observed with the UV/ozone plasma treated films. High transmittance of nearly 99% was observed for the films dried in both the air and UV/ozone plasma environments. Nanoindentation results of the air-dried films revealed pop-in events in the load–displacement curve at specific depths of 12.74 and 19.68nm; in contrast, smooth and regular curves without any discontinuities along either the loading or unloading sections were observed for the UV/ozone plasma-treated films. The obtained results demonstrated that UV/ozone plasma-treatment is proved to be a promising technique in improving the quality of HfO2 on ITO substrates.

The 10% Gd and Ti co-doped BiFeO3: A promising multiferroic material

In this investigation, undoped BiFeO3, Gd doped Bi0.9Gd0.1FeO3, and Gd-Ti co-doped Bi0.9Gd0.1Fe1-xTixO3 (x = 0.10, 0.20) materials were synthesized to report their multiferroic properties. The structural analysis and phase identification of these multiferroic ceramics were performed using Rietveld refinement. The Rietveld analysis has confirmed the high phase purity of the 10% Gd-Ti co-doped Bi0.9Gd0.1Fe0.9Ti0.1O3 sample compared to that of other compositions under investigation. The major phase of this particular composition is of rhombohedral R3c type structure (wt% >99%) with negligible amount of impurity phases. In terms of characterization, we address magnetic properties of this co-doped ceramic system by applying substantially higher magnetic fields than that applied in previously reported investigations. The dependence of temperature and maximum applied magnetic fields on their magnetization behavior have also been investigated. Additionally, the leakage current density has been measured to explore its effect on the ferroelectric properties of this multiferroic system. The outcome of this investigation suggests that the substitution of 10% Gd and Ti in place of Bi and Fe, respectively, in BiFeO3 significantly enhances its multiferroic properties. The improved properties of this specific composition is associated with homogeneous reduced grain size, significant suppression of impurity phases and reduction in leakage current density which is further asserted by polarization vs. electric field hysteresis loop measurements.

Performance and Reliability of TiO2/ZrO2/TiO2(TZT) and AlO-Doped TZT MIM Capacitors

Metal-insulator-metal capacitors for dynamic random access memory applications have been realized using TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (TZT) and AlO-doped TZT [TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /AlO/ ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (TZAZT) and TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /AlO/ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /AlO/ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (TZAZAZT)] dielectric stacks. High-capacitance densities of 46.6 fF/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (for TZT stacks), 46.2 fF/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (for TZAZT stacks), and 46.8 fF/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (for TZAZAZT stacks) have been achieved. Low leakage current densities of about 4.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> , 5.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> , and 9.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (at -1 V) have been obtained for TZT, TZAZT, and TZAZAZT stacks, respectively. We analyze the leakage current mechanisms at different electric field regimes, and compute the trap levels. The effects of constant voltage stress on the device characteristics were studied, and excellent device reliability was demonstrated. The electrical characteristics of the devices were correlated with the structural analysis through X-ray diffraction measurements and the surface chemical states analysis through X-ray photoelectron spectroscopy measurements. The doped-dielectric stacks (AlO-doped TZT: TZAZT and TZAZAZT) help to reduce leakage current density and improve reliability, without substantial reduction in capacitance density, compared with their undoped counterparts (TZT).

The Electrical and Enhanced Magnetic Properties of (Ce, Co) Doped BiFeO3 Particles Synthesized Via Sol-Gel Method

Bi1-xCexFe1-yCoyO3 (BCFCO, x = 0, 0.05, 0.1, 0.15; y = 0, 0.05, 0.1, 0.15) particles were synthesized by a sol-gel method to enhance the electrical and magnetic properties of BiFeO3. The structure and morphology properties of Bi1-xCexFe1-yCoyO3 particles were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM). XRD patterns show that the BCFCO particles are main single-phase perovskite structure with R3c space group. The enhancement of room-temperature ferromagnetism was obtained in the BCFCO particles. Obvious hysteresis loops of BCFCO were observed, which indicate ferromagnetic order. BCFCO particles exhibit reduction in leakage current density.

Improved dielectric properties of CaCu3Ti4O12 films with a CaTiO3 interlayer on Pt/TiO2/SiO2/Si substrates prepared by pulsed laser deposition

We report the greatly improved dielectric properties of CaCu3Ti4O12 (CCTO) films with a 60 nm-thick CaTiO3 (CTO) interlayer on Pt/TiO2/SiO2/Si substrates. Both CCTO films and CTO interlayers were prepared by pulsed laser deposition (PLD). With increasing the thickness of CCTO from 200 nm to 1.3 μm, the dielectric constants (e r ) at 10 kHz in both CCTO single-layered and CCTO/CTO double-layered films increased from ∼260 to ∼6000 and from ∼630 to ∼3700, respectively. Compared with CCTO single-layered films, CCTO/CTO double-layered films irrespective of CCTO film thickness exhibited a remarkable decrease in their dielectric losses (tanδ) (<0.1 at the frequency region of 1 - 100 kHz) and highly reduced leakage current density at room temperature. The reduced leakage currents in CCTO/CTO double-layered films are attributable to relatively higher trap ionization energies in the Poole-Frenkel conduction model.

Improved electrical transport properties in high quality nanocrystalline silicon carbide (nc-SiC) thin films for microelectronic applications

High quality nanocrystalline silicon carbide (nc-SiC) thin films sputtered deposited on Pt/Ti/SiO2/Si substrate were investigated for its crystallinity dependent dielectric properties (εr-f, εr-E) and J–E characteristics. The gain in intensity of highly oriented (105) X-ray reflection evident the improvement in crystallinity of nc-SiC thin films with increase in deposition temperature. An observable enhancement in dielectric properties and reduction in leakage current density (J) with increase in crystallinity was ascribed to enhanced dipole density and reduced micropipe density respectively. A minimum J∼10−9A/cm2 at 0kV/cm was observed with increase in the crystallinity of SiC thin films. The conduction mechanism in all nc-SiC thin films endures a transition from low field dominating ohmic conduction to interface limited Schottky emission prevailing at high field (E>60kV/cm).

Structural, morphological and multiferroic properties of the hydrothermally grown gadolinium (Gd) and manganese (Mn) doped sub-micron bismuth ferrites

Pure BiFeO3 and Gd, Mn doped BiFeO3 particles were synthesized with a hydrothermal method in a reaction solution containing a mineralizer of KOH. The products were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectroscopy, physical property measurement system and ferroelectric test system. Rietveld refinement and Raman spectra results reflect that the Gd, Mn doped samples undergo compositional-driven phase transition from rhombohedral to orthorhombic. Selected area electron diffraction and high-resolution transmission electron microscopy confirm the single-crystalline nature of our as-prepared samples. Compared with the linear magnetization-magnetic field relation in pure BiFeO3 particles, a clear hysteresis M–H loop can be observed in the Bi0.9Gd0.1FeO3 sample, which is ascribed to distorted spin cycloid and the magnetically active characteristic of Gd3+. Enhanced ferroelectric properties and reduced leakage current density were obtained in BiFe0.9Mn0.1O3 and Bi0.9Gd0.1Fe0.9Mn0.1O3. The leakage current density of the BiFe0.9Mn0.1O3 and Bi0.9Gd0.1Fe0.9Mn0.1O3 was reduced by two orders of magnitude as compared to that of pure BiFeO3.

Effects of LaNiO3 seeding layers on the crystal structure and electrical properties in 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 thin films

In this work, the high-quality 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 (hereafter abbreviated as BNT–BT) lead-free piezoelectric thin films were synthesized by introducing LaNiO3 (hereafter abbreviated as LNO) seeding layers. The effects of LNO seeding layers on the crystal structure and electrical properties were systematically investigated. The X-ray diffraction patterns indicate that highly (100)-oriented BNT–BT films were prepared through utilizing LNO seeding layers. The maximum piezoelectric coefficient d33⁎ of ~100pm/V, remanent polarization 2Pr of ~18μC/cm2 and dielectric constant ɛr ~410 have been obtained in the highly (100)-oriented BNT–BT films. The observed tremendous enhancement of piezoresponse, ferroelectric and dielectric properties in LNO-seeded films can be attributed to the better crystallization quality, higher degree of (100)-preferred orientation and reduced leakage current density. These findings demonstrate that LNO-seeded BNT–BT thin films integrating with silicon substrates may provide a wide range of applications in high-performance MEMS devices.

Origin of enhanced multiferroic properties in Dy and Co co-doped BiFeO3 ceramics

Structural, magnetic and ferroelectric properties of polycrystalline BiFeO3, Bi0.9Dy0.1FeO3, BiFe0.97Co0.03O3 and Bi0.9Dy0.1Fe0.97Co0.03O3, which were prepared by solid-state method, have been investigated. The X-ray diffraction (XRD) patterns reveal that all the samples are in single phase and show rhombohedrally distorted perovskite structure with R3c space group. Both XRD and Raman-scattering studies show that Dy and Co co-doped sample has a compressive lattice distortion induced by co-substitution of Dy and Co ions at the A and the B sites, respectively. Dy and Co co-doping favors weak ferromagnetism ordering with evident magnetic hysteresis loop and enhances magnetization values at room temperature. Ferroelectric hysteresis loop for Dy and Co co-doped sample shows the nearly saturated polarization at 40 kV/cm and large remnant polarization. Dy dopant is prominent in the reduced leakage current density, while Co dopant is remarkable in the improved remnant magnetization in Bi0.9Dy0.1Fe0.97Co0.03O3 ceramic. By using a simple model, it was found that the anharmonicity of canted spiral cycloidal spin structure was responsible for the weak ferromagnetism of pure BiFeO3, and the enhanced magnetization in Co-doped sample was attributed to the transition from the incommensurate cycloidal spiral spin structure towards the G-type canted collinear antiferromagnetic structure.

Improved ferroelectric and leakage current properties of Er-doped BiFeO3 thin films derived from structural transformation

Multiferroic pure and Er-doped BiFeO3 thin films were prepared using a sol–gel technique. The effect of Er-doped concentration on the crystal structure and on the ferroelectric and leakage current properties of BiFeO3 films were studied in detail. The study showed the enhanced ferroelectric polarization and reduced leakage current density that occurred after doping Er. Such improved ferroelectric and leakage properties are attributed to ferroelectric distortion and to the change of leakage current conduction mechanisms derived from the structural transformation that occurred after doping Er. The rhombohedral structure of pure BiFeO3 transforms to the coexistence of tetragonal and orthorhombic symmetry structure as Er-doped concentration x increased gradually to 0.15, then to the orthorhombic structure when x = 0.20. The present work provides an easy method to decrease the leakage current and improve the ferroelectric properties of BiFeO3 films.

Smooth cubic commensurate oxides on gallium nitride

Smooth, commensurate alloys of ⟨111⟩-oriented Mg0.52Ca0.48O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.

Extremely stable organic photovoltaic incorporated with WOxdoped PEDOT:PSS anode buffer layer

The state of interfaces between organic semiconductors and/or metals in organic devices severely impacts their performance and stability. The commonly used organic semiconductor PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)) is hygroscopic in nature and can therefore be easily damaged if exposed to air and/or light illumination. In this study, we doped PEDOT:PSS with WOx nanocrystallites and found that organic photovoltaics (OPVs) with the WOx doped PEDOT:PSS degrade only by 5%, while OPVs with undoped PEDOT:PSS retain only 23% of their initial power conversion efficiency (PCE) after storing for 5000 h in air. Also, doping PEDOT:PSS with WOx enhances the initial PCE by ∼13%, owing to reduced leakage current density and better Ohmic contact between the PEDOT:PSS and the anode.

The effects of La substitution on ferroelectric domain structure and multiferroic properties of epitaxially grown BiFeO3 thin films

We report the influence of La substitution in epitaxial BiFeO3 thin films prepared by pulsed layer deposition on a Nb-doped SrTiO3 substrate, focusing on ferroelectric domain structure, leakage current, and multiferroic properties. Enhanced ferroelectric remanent polarization and reduced leakage current density were established via La substitution in the BiFeO3 film. Based on leakage conduction mechanism and piezoelectric force microscopy studies, this is indicative of reduced trap densities and increased domain energy. Besides that, the ferromagnetic properties were improved by the La doping as well. The possible mechanisms for the enhancement of electrical and multiferroic characteristics are extensively discussed.

High permittivity cerium oxide thin films on AlGaN/GaN heterostructures

Cerium oxide (CeO2) thin films have been grown by metal-organic chemical vapor deposition on AlGaN/GaN heterostructures and their insulating properties as gate dielectric layer have been explored. The deposited thin films have been found to be textured on the GaN based heterostructures and exhibited a permittivity of 26. This high permittivity value and large band gap are certainly advantageous with respect to other reported materials for the metal insulator semiconductor high electron mobility transistor application. The reduced leakage current density clearly suggests that these CeO2 films are very promising as gate dielectric for AlGaN/GaN transistors low power consumption technology.

Performance and Reliability of ${\rm Gd}_{2}{\rm O}_{3}$ and Stacked ${\rm Gd}_{2}{\rm O}_{3}\hbox{-}{\rm Eu}_{2}{\rm O}_{3}$ Metal-Insulator-Metal Capacitors

Gd2O3-based metal-insulator-metal capacitors have been characterized with single layer (Gd2O3) and bilayer (Gd2O3/Eu2O3 and Eu2O3/Gd2O3) stacks for analog and DRAM applications. Although single layer Gd2O3 capacitors provide highest capacitance density (15 fF/μm2), they suffer from high leakage current density, poor capacitance density-voltage linearity, and reliability. The stacked dielectrics help to reduce leakage current density (1.2×10-5 A/cm2 and 2.7 × 10-5 A/cm2 for Gd2O3/Eu2O3 and Eu2O3/Gd2O3, respectively, at -1 V), improve quadratic voltage coefficient of capacitance (331 ppm/V2 and 374 ppm/V2 for Gd2O3/Eu2O3 and Eu2O3/Gd2O3, respectively, at 1 MHz), and improve reliability, with a marginal reduction in capacitance density. This is attributed to lower trap heights as determined from Poole-Frenkel conduction mechanism, and lower defect density as determined from electrode polarization model.

Improvement in electrical characteristics of HfO2 gate dielectrics treated by remote NH3 plasma

We report the structural and electrical characteristics of hafnium oxide (HfO2) gate dielectrics treated by remote NH3 plasma under various radio-frequency (RF) powers at a low temperature. Significant increase of effective dielectric constant (keff), decrease of capacitance equivalent thickness (CET), reduction in leakage current density, and suppression of the interfacial layer thickness were observed with the increase of the RF power in the remote NH3 plasma treatment. The effects of hydrogen passivation and depassivation on the HfO2/Si interface due to the remote NH3 plasma treatment were also observed by the variation of photoluminescence (PL) intensity, indicating that the PL measurement is applicable to probe the interfacial properties. An ultrathin interfacial layer (∼0.3nm), a high keff, (20.9), a low leakage current density (9×10−6A/cm2), and a low CET (1.9nm) in the nitrided HfO2 film were achieved, demonstrating that the nitridation process using remote NH3 plasma under a high RF power at a low temperature is a promising way to improve in electrical properties of high-K gate dielectrics.