Leakage Current Density Increase Research Articles

Three-Dimensional Mechanistic Modeling of Time-Dependent Dielectric Breakdown in Polycrystalline Thin Films

Time-dependent dielectric breakdown (TDDB) is a crucial issue for the dielectric reliability. In this work, we present a full three-dimensional mechanistic model for calculation of the TDDB process in polycrystalline thin films. The model is based on the multiphonon trap-assisted tunneling theory and takes into account the intrinsic three-dimensional discreteness of traps at the dielectric grain boundaries. The leakage current density is calculated by solving coupled three-dimensional master equation and Poisson equation. The net phonon emission associated with each charge trapping and release event is treated as a local point heat source, which then enters the Fourier heat equation for three-dimensional temperature distribution calculation. The generated trap is determined by local temperature and electric field, which is subsequently included in the next round of calculation of electric and thermal properties. A positive feedback loop gradually leads to an increase of trap density, temperature, and leakage current density, and finally the dielectric breakdown. Our model can, to a good approximation, reproduce the experimental leakage current density-voltage characteristics and the Weibull distribution of time to breakdown at different dielectric thicknesses, stress voltages, and environmental temperatures. We find that in realistic devices, the three-dimensional trap-to-trap transport of electrons contributes a non-negligible part to the leakage current when the dielectric approaches breakdown. Our approach of three-dimensional mechanistic simulation is computationally efficient such that evolution of ${10}^{3}$ traps during the TDDB process can be easily performed on a standard desktop computer.

Effect of Annealing Temperature on the Structural, Optical, and Electrical Properties of Al-Doped ZrO2 Gate Dielectric Films Treated by the Sol–Gel Method

In this article, we report the preparation of Al-doped ZrO2 (AZO) thin films by the sol–gel method. The electrical properties, microstructure, and optical properties of AZO high-k gate dielectric films at different annealing temperatures were systematically investigated. XRD results confirm that the AZO film was amorphous at a temperature of 600 °C, and Al doping raises the crystallization temperature of ZrO2. AFM and FESEM show a smooth surface of AZO film without cracks. As the annealing temperature increased from 600 to 900 °C, all of the films had similar RMS roughness under 1 nm, the film thickness decreased accordingly, the bandgap value increased from 5.77 to 5.82 eV, the valence band shift (ΔEv) increased, and the conduction band shift (ΔEc) decreased. XPS analysis showed that silicates were formed at the AZO/Si interfacial layer. Electrical performance tests showed that high-temperature annealing can effectively improve the electrical properties, as shown by the increase in dielectric constant (k) and the decrease in flat-band voltage (ΔVfb). However, an increase in leakage current density with increasing annealing temperature was observed due to the decrease in ΔEc and the appearance of crystallization caused by the increase in annealing temperature.

High temperature (500 °C) operating limits of oxidized platinum group metal (PtOx, IrOx, PdOx, RuOx) Schottky contacts on β -Ga2O3

Very high temperature operation β-Ga2O3 Schottky contacts were fabricated on moderately doped 2¯01 β-Ga2O3 single crystal substrates using four different types of intentionally oxidized platinum group metal (PGM) Schottky contacts (SCs), i.e., PtOx, IrOx, PdOx, and RuOx (x ∼ 2.0, 2.2, 1.1, and 2.4, respectively) formed by reactive rf sputtering of plain-metal targets in an oxidizing plasma. All four types of oxidized PGM SCs showed rectification ratios (at ± 3 V) of more than 10 orders of magnitude up to 300 °C, with almost no measurable increase in reverse leakage current density (Jrev) from that at room temperature. From 350 to 500 °C, a measurable increase in Jrev was observed, which was consistent with the thermionic emission of charge carriers over the respective image force (IF) lowered Schottky barriers. Despite this increase, PtOx(IrOx)[PdOx]{RuOx} SCs showed large rectification ratios (at ± 3 V) of 6 × 106(8 × 106)[5 × 105]{2 × 104} and IF-corrected barrier heights of 2.10(2.10)[1.90]{1.60} ± 0.05 eV, respectively, while operating at 500 °C. The significantly lower 500 °C barrier height of the RuOx SCs was due to the thermal reduction of RuOx to Ru that occurred above 400 °C. In contrast, the Schottky barriers of IrOx, PtOx, and PdOx SCs were thermally stable while operating at 500 °C, indicating significant potential for their use in very high temperature rectifying devices.

57Fe Mossbauer and electrical studies of Mn doped YFeO3 prepared via sol-gel technique

Polycrystalline YFe1−xMnxO3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) samples are prepared via sol-gel method. Structural characterization of these samples is done by x-ray diffraction (XRD) technique and Raman spectroscopic method. Intense peaks in XRD graphs show that the sample is crystalline in nature and Reitveld refined XRD data shows that the samples are formed in single phase. Raman spectroscopic study confirms the structure and phase purity of the samples. Room temperature 57Fe Mossbauer studies confirm that Fe ion exists in ferric state. The hyperfine field (Bhf) values are found to decrease with increase in manganese (Mn) concentration. This decrease in Bhf value indicates the increase in antiferromagnetic nature of the samples, which arises due to the weakening of magnetic interactions between the Fe ions. From room temperature leakage current density (J-E) measurements, it is observed that leakage current density increases with increase in Mn doping. Scanning electron micrographs explain the reason of increase in leakage current density based on the micro structure of the samples. The samples are found to exhibit Ohmic conduction mechanism in entire electric field range.

Electrical properties of MgO/GaN metal-oxide-semiconductor structures

Electrical properties of metal-oxide semiconductor (MOS) capacitors were measured with MgO/Al2O3 gate dielectrics deposited by atomic layer deposition (ALD) on GaN. For an Al2O3 (1 nm)/MgO (20 nm) dielectric layer, a leakage current density of 0.25 mA/cm2 at 1 V was measured for the MOS capacitor. A peak capacitance of ~0.1 μF/cm2 was obtained from the C-V measurements with significant hysteresis observed. In addition, a 15-minute forming gas anneal at 450 °C resulted in an increased leakage current density of 1 A/cm2 at 1 V while also increasing the peak capacitance by approximately 30%. To improve the performance, an Al2O3 (20 nm)/MgO (20 nm) dielectric stack was deposited that exhibited a leakage current density of ~1 × 10−5 mA/cm2 at 1 V, which corresponds to ~4 orders of magnitude lower current density than that of the single layer dielectric. Additionally, a 3-layer Al2O3 (10 nm)/MgO (20 nm)/Al2O3 (10 nm) stack also shows a leakage current density reduction of ~4 orders of magnitude, and a reduced density of interface states while remaining a high-k dielectric. The density of interface states was estimated to be between 6.8 × 1011 eV−1 cm−2 and 1.5 × 1012 eV−1 cm−2 for the 3-layer stack using the photo-assisted C-V method.

Thermally stable and low trap density SiNx/AlON bi-layer structure for AlGaN/GaN MIS-HEMTs

We investigated a thermally stable and low trap density insulator for AlGaN/GaN metal–insulator–semiconductor (MIS) high-electron-mobility transistors (HEMTs). Current–voltage and capacitance–voltage measurements were performed before and after post deposition annealing (PDA) at 700 °C. A large increase in leakage current and high interface state density were observed after the PDA in the MIS structure with AlOx. The interface state density was reduced to one-third in the MIS structure with AlON, probably due to the reduced carbon impurity density at the AlOx/GaN HEMT interfaces. Meanwhile, the MIS structure with SiNx maintained high breakdown voltages of over 200 V, even after the PDA. By employing SiNx/AlON layers, we demonstrated low interface state density of 2.3 × 1013 cm−2 eV−1 at Ec − 0.31 eV and suppressed leakage current at −200 V. We believe that the thermally-stable bi-layer structure is a promising technology for diamond deposition to improve heat dissipation.

Structure and Electrical Properties of Na0.5Bi0.5TiO3 Epitaxial Films with (110) Orientation

Pt/Na0.5Bi0.5TiO3/La0.5Sr0.5CoO3 (Pt/NBT/LSCO) ferroelectric capacitors were fabricated on (110) SrTiO3 substrate. Both NBT and LSCO films were epitaxially grown on the (110) SrTiO3 substrate. It was found that the leakage current density of the Pt/NBT/LSCO capacitor is favorable to ohmic conduction behavior when the applied electric fields are lower than 60 kV/cm, and bulk-limited space charge-limited conduction takes place when the applied electric fields are higher than 60 kV/cm. The Pt/NBT/LSCO capacitor possesses good fatigue resistance and retention, as well as ferroelectric properties with Pr = 35 μC/cm2. The ferroelectric properties of the Pt/NBT/LSCO capacitor can be modulated by ultraviolet light. The effective polarization, ΔP, was reduced and the maximum polarization Pmax was increased for the Pt/NBT/LSCO capacitor when under ultraviolet light, which can be attributed to the increased leakage current density and non-reversible polarization P^ caused by the photo-generated carriers.

Investigation of electrical inhomogeneity in ZnO varistor ceramics based on electronic relaxations

Spatially non-uniform electrical performance in ZnO varistor ceramics, which restricts application for higher energy absorption capability, is investigated in terms of electronic relaxations corresponding to intrinsic point defects. Decreased breakdown field and nonlinear coefficient are observed from 135.5 V/mm and 53 in central area to 122.0 V/mm and 20 in peripheral area as well as significantly increased leakage current density from 3.4 μA/cm2 to 18.3 μA/cm2. From microstructure analysis, grain size distribution is found relatively homogeneous, suggesting that electrically non-uniform grain boundaries should be responsible for divergent electrical properties. Investigation via energy dispersive spectrometer (EDS) shows higher Zn/O ratio in peripheral area, indicating higher possibility of generating intrinsic point defects like zinc interstitials and oxygen vacancies. This is further verified via dielectric spectroscopy that the densities of zinc interstitials and oxygen vacancies are both larger in peripheral area than those in central area. Oxygen is easier to be removed from ZnO lattice and diffuse into atmosphere during high-temperature sintering process, resulting in larger amount of oxygen vacancies in peripheral area. Meanwhile, more zinc atoms are removed from lattice and form interstitials as a result of distortion of ZnO lattice in peripheral area. Increased donor density in peripheral area attributed by oxygen vacancies and zinc interstitials results in decreased Schottky barrier height. Non-uniform distribution of Schottky barrier height is the origin of overall electrical inhomogeneity.

Neutral beam and ICP etching of HKMG MOS capacitors: Observations and a plasma-induced damage model

In this study, TiN/HfO2/Si metal-oxide-semiconductor (MOS) capacitors were etched by a neutral beam etching technique under two contrasting conditions. The configurations of neutral beam etching technique were specially designed to demonstrate a “damage-free” condition or to approximate “reactive-ion-etching-like” conditions to verify the effect of plasma-induced damage on electrical characteristics of MOS capacitors. The results show that by neutral beam etching (NBE), the interface state density (Dit) and the oxide trapped charge (Qot) were lower than routine plasma etching. Furthermore, the decrease in capacitor size does not lead to an increase in leakage current density, indicating less plasma induced side-wall damage. We present a plasma-induced gate stack damage model which we demonstrate by using these two different etching configurations. These results show that NBE is effective in preventing plasma-induced damage at the high-k/Si interface and on the high-k oxide sidewall and thus improve the electrical performance of the gate structure.

Solution-processed HfGdO gate dielectric thin films for CMOS application: Effect of annealing temperature

Annealing temperature dependent microstructure, optical and electrical properties of sol-gel-deposited HfGdO high-k gate dielectric thin films on Si substrates are systematically investigated. X-ray spectroscopy (XPS) analyses have confirmed that the interfacial layer at HfGdO/Si interface is mainly silicate and the component increases with increasing the annealing temperature. Moreover, the band offsets for HfGdO/Si gate stack as a function of annealing temperature also have been determined. As a result, it can be noted that increase in valence band offset (ΔEv) and reduction in conduction band offset (ΔEc) have been detected. Electrical characterizations have indicated that higher annealing temperature effectively improves the electrical characteristics, such as the increased effective permittivity (k) and the decreased flat band voltage shift (ΔVfb). However, due to the reduced ΔEc and the appearance of crystallization, increased leakage current density has been observed with the increase in annealing temperature.

Effect of carrier liquid on electrorheological performance and stability of oxalate group-modified TiO2 suspensions

By using oxalate group-modified TiO2 nanoparticles as the dispersing phase, different kinds of silicone oil with various viscosities and terminal groups (hydroxyl, hydrogen, and methyl) were used as the dispersing media to prepare different electrorheological (ER) fluids. Their zero-field viscosity, yield stress under direct current electric fields, ER efficiency, shear stability, leakage current density, and sedimentation stability were tested to study the effect of carrier liquid on the properties of ER fluids. The results indicate that the zero-field viscosity, the yield stress, and the leakage current density increase with increasing viscosity of the silicone oils. The effects of the viscosity on the ER efficiency, the shear stability, and the sedimentation ratio depend on the competition between the viscous resistance and the aggregation of the particles. Among the three ER fluids prepared with silicone oil with different terminal groups, hydroxyl-terminated oil based sample has the highest zero-field viscosity, the highest field-induced yield stress and ER efficiency, the largest current density, and the best sedimentation stability.

Electrical properties of SiNx films with embedded CNTs for MEMS capacitive switches

The present paper aims to provide a better insight on the electrical properties of silicon nitride (SiNx) dielectric films with embedded carbon nanotubes (CNTs) that can be used in RF MEMS capacitive switches. The effect of the embedded CNTs on the leakage current density and on the discharging processes of the films has been probed with the aid of metal-insulator-metal (MIM) capacitors and it has been found that the presence of CNTs results in an increase of leakage current density as well as to an acceleration of the charge displacement through the bulk of the dielectric films. Finally, the charging and discharging processes have been investigated in MEMS capacitive switches and it has been found that the use of CNTs in SiNx films results in an enhancement of charging processes but it also accelerates the discharging process.

Relating Electronic and Geometric Structure of Atomic Layer Deposited BaTiO3 to its Electrical Properties.

Atomic layer deposition allows the fabrication of BaTiO3 (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO2 and SiO2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO’s bonding environment captured by the XANES spectra. The spectral weight shifts to lower energy with increasing Ti content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate–film interfaces reveal BTO’s homogeneous growth on RuO2 and its distorted growth on SiO2. This work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices.

Hysteresis in Lanthanide Zirconium Oxides Observed Using a Pulse CV Technique and including the Effect of High Temperature Annealing.

A powerful characterization technique, pulse capacitance-voltage (CV) technique, was used to investigate oxide traps before and after annealing for lanthanide zirconium oxide thin films deposited on n-type Si (111) substrates at 300 °C by liquid injection Atomic Layer Deposition (ALD). The results indicated that: (1) more traps were observed compared to the conventional capacitance-voltage characterization method in LaZrOx; (2) the time-dependent trapping/de-trapping was influenced by the edge time, width and peak-to-peak voltage of a gate voltage pulse. Post deposition annealing was performed at 700 °C, 800 °C and 900 °C in N2 ambient for 15 s to the samples with 200 ALD cycles. The effect of the high temperature annealing on oxide traps and leakage current were subsequently explored. It showed that more traps were generated after annealing with the trap density increasing from 1.41 × 1012 cm−2 for as-deposited sample to 4.55 × 1012 cm−2 for the 800 °C annealed one. In addition, the leakage current density increase from about 10−6 A/cm2 at Vg = +0.5 V for the as-deposited sample to 10−3 A/cm2 at Vg = +0.5 V for the 900 °C annealed one.

Abnormal variation of band gap in Zn doped Bi0.9La0.1FeO3 nanoparticles: Role of Fe-O-Fe bond angle and Fe-O bond anisotropy

Bi0.9La0.1FeO3 (BLFO) and Bi0.9La0.1Fe0.99Zn0.01O3 (BLFZO) nanoparticles were prepared via a sol-gel method. The oxygen vacancies and holes increase with Zn doping analyzed through X-ray photoelectron spectroscopy, which could contribute to the increase of leakage current density. However, with the increase of the defects (oxygen vacancies and holes), the band gap of BLFZO also is increased. To explain the abnormal phenomenon, the bandwidth of occupied and unoccupied bands was analyzed based on the structural symmetry driven by the Fe-O-Fe bond angle and Fe-O bond anisotropy.

Effects of rapid thermal annealing on interfacial and electrical properties of Gd-doped HfO2 high-k gate dielectrics

In this work, we systematically investigated the effects of rapid thermal annealing on the interfacial and electrical properties, as well as band offsets of sputtering-derived Gd-doped HfO2 film on Si substrate. The results indicate that annealing temperature has little effect on the interfacial properties of Gd-doped HfO2 thin films, and the main component of interfacial layer is silicate without any silicide. Moreover, heat treatment can effectively improve the C–V characteristics of the samples, such as the increase of effective permittivity, reduction in ΔVfb and no obvious frequency dispersion. However, the increase of annealing temperature leads to the increase of leakage current density of Al/Gd-doped HfO2/Si MOS capacitor due to the decrease of the conduction band offset (ΔEc) and further crystallization of the samples. These investigation results might provide the guidance for the performance optimization of high k gated dielectrics to meet the requirements of future complementary-metal-oxide-semiconductor (CMOS) devices.

Effect of thermal annealing on the structure and properties of plasma enhanced chemical vapor deposited SiCOH film

The development of high-performance integrated circuit chips and the shrinkage of feature sizes according to Moore’s law bring forward continuously the requirements for low dielectric constant (low-k) materials with various excellent properties in the back-end-of-the-line (BEOL) interconnect. Porous SiCOH films prepared by plasma enhanced chemical vapor deposition (PECVD) through a porogen approach are widely applied to industry and extensively studied. Thermal annealing is an important process for fabricating the porous low-k films, which has a great influence on film structure as well as properties. SiCOH films are deposited by PECVD using tetraethoxysilane and limonene as precursors, and annealed at 450 ℃ for 1.5 h under nitrogen atmosphere. The evolutions of film structure and properties during thermal annealing are revealed, and the reaction mechanism for structure change is also proposed. Fourier transform inferred spectroscopy and solid state nuclear magnetic resonance results show that the as-deposited film is an organic-inorganic hybrid film composed of various kinds of Si-O-Si, -CHx, Si-O-CH2CH3, etc. The organic component is removed almost completely during thermal annealing, making a porous film with a Si-O-Si inorganic skeleton. The skeleton is also rearranged at the same time. Deconvolution of the Si-O-Si absorption band of the FTIR spectrum reveals that the cage-like Si-O-Si occupies the major part for both as-deposited and annealed films, while the amount of silicon suboxide Si-O-Si decreases and that of network Si-O-Si increases during thermal annealing, making the film more robust. More C=C and Si-C are formed through chemical reactions between Si-H, -CHx and Si-O-CH2-CH3, and crosslinking is further enhanced. Nitrogen adsorption/desorption isothermal measurement reveals that a large number of micropores with diameter less than 2-3 nm are created during thermal annealing, which is consistent with the removal of organic groups and the existence of cage-like Si-O-Si. As a result, both the refractive index and dielectric constant decrease significantly from 1.476 (λ =630 nm) and 3.45 to 1.365 and 2.60, respectively. Because of the increase of C=C after annealing, extinction coefficient and leakage current density increase. Although there is a shrinkage of 14.7% in film thickness and a reduction of mechanical properties after annealing, the Young’s modulus is still larger than 4 GPa. Considering all kinds of properties, the obtained film appears to be a competitive candidate as inter layer dielectrics in the BEOL interconnect of integrated circuits.

Modification of energy band alignment and electric properties of Pt/Ba0.6Sr0.4TiO3/Pt thin-film ferroelectric varactors by Ag impurities at interfaces

We report on the effects of Ag impurities at interfaces of parallel-plate Pt/Ba0.6Sr0.4TiO3/Pt thin film ferroelectric varactors. Ag impurities occur at the interfaces due to diffusion of Ag from colloidal silver paint used to attach the varactor samples with their back side to the plate heated at 600–750 °C during deposition of Ba0.6Sr0.4TiO3. X-ray photoelectron spectroscopy and secondary ion mass spectrometry suggest that amount and distribution of Ag adsorbed at the interfaces depend strongly on the adsorbent surface layer. In particular, Ag preferentially accumulates on top of the Pt bottom electrode. The presence of Ag significantly reduces the barrier height between Pt and Ba0.6Sr0.4TiO3 leading to an increased leakage current density and, thus, to a severe degradation of the varactor performance.

Degradation of ferroelectric and weak ferromagnetic properties of BiFeO3 films due to the diffusion of silicon atoms

Crystalline BiFeO3 (BFO) films each with a crystal structure of a distorted rhombohedral perovskite are characterized by X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The diffusion of silicon atoms from the substrate into the BiFeO3 film is detected by Rutherford backscattering spectrometry (RBS). The element analysis is performed by energy dispersive X-ray spectroscopy (EDS). Simulation results of RBS spectrum show a visualized distribution of silicon. X-ray photoelectron spectroscopy (XPS) indicates that a portion of silica is formed in the diffusion process of silicon atoms. Ferroelectric and weak ferromagnetic properties of the BFO films are degraded due to the diffusion of silicon atoms. The saturation magnetization decreases from 6.11 down to 0.75 emu/g, and the leakage current density increases from 3.8 × 10−4 up to 7.1 × 10−4 A/cm−2.

Effect of Oxygen Plasma on Low Dielectric Constant HSQ (Hydrogensilsesquioxane) Films

The commercially available hydrogensilsesquioxane (HSQ) offers a low dielectric constant. In this paper, the impact of oxygen plasma treatment has been investigated on the low-k HSQ films. Fourier transform infrared (FTIR) spectroscopy was used to identify the network structure and cage structure of Si-O-Si bonds and other possible bonds after treatments. C-V and I-V measurements were used to determine the dielectric constant, the electronic resistivity and the breakdown electric field, respectively. The result indicates that oxygen plasma treatment will damage the HSQ films by removing the hydrogen content. Both dielectric constant and leakage current density increase significantly after oxygen plasma exposure. The dielectric constant and leakage current density can both be decreased by annealing at 350°C for 1.5 h in nitrogen ambient. The reason is that the open porous of the external films can be modified and density of thin film be increased. The rough surface can be smoothed.