Main Leakage Mechanism Research Articles

Ultrawide bandgap vertical β-(AlxGa1−x)2O3 Schottky barrier diodes on free-standing β-Ga2O3 substrates

Ultrawide bandgap β-(AlxGa1−x)2O3 vertical Schottky barrier diodes on (010) β-Ga2O3 substrates are demonstrated. The β-(AlxGa1−x)2O3 epilayer has an Al composition of 21% and a nominal Si doping of 2 × 1017 cm−3 grown by molecular beam epitaxy. Pt/Ti/Au has been employed as the top Schottky contact, whereas Ti/Au has been utilized as the bottom Ohmic contact. The fabricated devices show excellent rectification with a high on/off ratio of ∼109, a turn-on voltage of 1.5 V, and an on-resistance of 3.4 mΩ cm2. Temperature-dependent forward current-voltage characteristics show effective Schottky barrier height varied from 0.91 to 1.18 eV while the ideality factor from 1.8 to 1.1 with increasing temperatures, which is ascribed to the inhomogeneity of the metal/semiconductor interface. The Schottky barrier height was considered a Gaussian distribution of potential, where the extracted mean barrier height and a standard deviation at zero bias were 1.81 and 0.18 eV, respectively. A comprehensive analysis of the device leakage was performed to identify possible leakage mechanisms by studying temperature-dependent reverse current-voltage characteristics. At reverse bias, due to the large Schottky barrier height, the contributions from thermionic emission and thermionic field emission are negligible. By fitting reverse leakage currents at different temperatures, it was identified that Poole–Frenkel emission and trap-assisted tunneling are the main leakage mechanisms at high- and low-temperature regimes, respectively. Electrons can tunnel through the Schottky barrier assisted by traps at low temperatures, while they can escape these traps at high temperatures and be transported under high electric fields. This work can serve as an important reference for the future development of ultrawide bandgap β-(AlxGa1−x)2O3 power electronics, RF electronics, and ultraviolet photonics.

Impact of dislocation density on the ferroelectric properties of ScAlN grown by molecular beam epitaxy

We report on the effect of dislocation density on the ferroelectric properties of single-crystalline ScAlN thin films grown by molecular beam epitaxy. Wurtzite phase and atomically smooth ScAlN films have been grown on bulk GaN, GaN on sapphire, and GaN on Si substrates with dislocation densities ranging from ∼107 to 1010 cm−2. Despite the significant difference in dislocation density, ferroelectricity is observed in all three samples. The presence of high densities of dislocations, however, results in enhanced asymmetric P–E loops and overestimated remnant polarization values. Further measurements show that the leakage current and breakdown strength can be improved with decreasing dislocation density. Detailed studies suggest that trapping/detrapping assisted transport is the main leakage mechanism in epitaxial ferroelectric ScAlN films. This work sheds light on the essential material quality considerations for tuning the ferroelectric property of ScAlN toward integration with mainstream semiconductor platforms, e.g., Si, and paves the way for next-generation electronics, optoelectronics, and piezoelectronics.

Structure and electrical properties of Zn‐doped BiFeO3 films

AbstractBiFe1−xZnxO3 (x = 0, 0.5, 1, 1.5, 2 mol%) (BFZO) films were prepared on ITO/glass substrates by a sol‐gel method. The effects of different Zn contents on the structures and electrical properties of the BFZO films were investigated. From X‐ray diffraction (XRD), microstructure and X‐ray spectroscopy (XPS) results, the BFZO films with a Zn content of 1 mol% showed a better crystal structure and grain development, and the Fe2+ and oxygen vacancy concentrations in this sample were the lowest among all the evaluated BFZO films. The P‐E hysteresis loop indicated that the BFZO films with 1 mol% Zn had the highest remanent polarization (2Pr), which was 82.4 μC/cm2, along with a coercive field (2Ec) of 887 kV/cm at the tested electric field of 857 kV/cm. The BFZO film with 1 mol% Zn had the lowest leakage current density, which was 3.54 × 10−7 A/cm2 at the tested electric field of 200 kV/cm. Both at high and low electric fields, the space charge‐limited current (SCLC) conduction mechanism was the main leakage mechanism. When the test frequency was 105 Hz, the dielectric constant was 133, and the dissipation factor was 0.015.

Leakage Current Conduction Mechanism of Au-Pt-Ti/ HfO2-Al2O3/n-InAlAs Metal-Oxide-Semiconductor Capacitor under Reverse-Biased Condition

Au-Pt-Ti/high-k/n-InAlAs metal-oxide-semiconductor (MOS) capacitors with HfO2-Al2O3 laminated dielectric were fabricated. We found that a Schottky emission leakage mechanism dominates the low bias conditions and Fowler–Nordheim tunneling became the main leakage mechanism at high fields with reverse biased condition. The sample with HfO2 (4 m)/Al2O3 (8 nm) laminated dielectric shows a high barrier height ϕB of 1.66 eV at 30 °C which was extracted from the Schottky emission mechanism, and this can be explained by fewer In–O and As–O states on the interface, as detected by the X-ray photoelectron spectroscopy test. These effects result in HfO2 (4 m)/Al2O3 (8 nm)/n-InAlAs MOS-capacitors presenting a low leakage current density of below 1.8 × 10−7 A/cm2 from −3 to 0 V at 30 °C. It is demonstrated that the HfO2/Al2O3 laminated dielectric with a thicker Al2O3 film of 8 nm is an optimized design to be the high-k dielectric used in Au-Pt-Ti/HfO2-Al2O3/InAlAs MOS capacitor applications.

Trap-assisted tunneling current of ultrathin InAlN/GaN HEMTs on Si (1 1 1) substrate

In this paper, the reverse gate leakage current mechanism of ultrathin InAlN/GaN high-electron mobility transistors on Si (1 1 1) substrate which treated with and without surface treatment process is systematically investigated. Current-voltage (I-V) measurement in temperature range from 273 K to 473 K and capacitance-voltage (C-V) measurement under 300 K are used to analyze the main leakage mechanism. For the whole reverse bias region (−30 V to 0 V), the best reasonable fitting calculation results correspond to the experimental values is based on trap-assisted tunneling (TAT) current mechanism, which indicates the dominant reverse leakage current of the ultrathin InAlN/GaN HEMTs device is derived from TAT current. N2 plasma surface treatment method is proposed to optimize the interface of the Schottky contact, which is an important way to reduce the reverse leakage current examined by the extracted values of trap energy levels (φt) and thermal activation energy (Ea) as well as XPS results. Further, for high reverse bias condition, electric field saturation across the barrier layer is not sufficient to support the slow rise trend of the TAT current, a modified electric field model was proposed to accurately explain this phenomenon.

Sub-Thermal Subthreshold Characteristics in Top–Down InGaAs/InAs Heterojunction Vertical Nanowire Tunnel FETs

This letter demonstrates top-down InGaAs/InAs heterojunction vertical nanowire tunnel FETs with sub-thermal subthreshold characteristics over two orders of magnitude of current. A minimal subthreshold swing of 53 mV/decade at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> = 0.3 V has been obtained at room temperature. An I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> (defined as the highest current level where the subthreshold characteristics exhibit a transition from sub- to super-60 mV/decade behavior) of 4.3 nA/μm has been achieved at V s = 0.3 V. Compared with an earlier device generation, much reduced temperature dependence of the subthreshold characteristics is observed in this letter. The major difference between the two device generations is the drastically reduced interface trap density, evidenced by the improvement in the subthreshold swing of InGaAs vertical nanowire MOSFETs fabricated at the same time. This result suggests oxide-semiconductor interface trap-assisted tunnelling the main leakage mechanism in III-V TFETs fabricated by our process. The improvement in the interface quality has been enabled by improved gate oxide deposition and post-deposition treatment.

Predicting Gas Leakage in the Rotary Engine—Part I: Apex and Corner Seals

The Wankel rotary engine offers a greater power density than piston engines, but higher fuel consumption and higher hydrocarbon emissions, in large part due to poor gas sealing. This paper presents a modeling approach to evaluate the gas leakage of apex and corner seals in rotary engines. The apex seal is modeled as a deformable beam and its dynamics is coupled with the gas flows around the seal. It is shown that the main leakage mechanisms are: (1) corner seal clearance leakage, (2) leakage around the apex seal through the spark plug cavities, and (3) flank leakage at high speed. The side piece corner orifice and the trailing spark plug cavity also contribute to leakage, but to a lesser extent. Leakage through the seal–housing interface is negligible as the apex seal can conform to the distorted shape of the rotor housing.

Predicting Gas Leakage in the Rotary Engine—Part II: Side Seals and Summary

The Wankel rotary engine offers a greater power density than piston engines, but higher fuel consumption and hydrocarbon emissions, in large part due to poor gas sealing. This paper presents a model for the deformable dynamics of the side seal, which completes a set of modeling tools for the comprehensive assessment of the gas leakage mechanisms in the rotary engine. It is shown that the main leakage mechanisms for the side seals are: (1) opening of the inner flank due to the contact with the trailing corner seal, (2) flow through the gap with the leading corner seal, (3) simultaneous opening of both inner and outer flanks due to body force at high speed, and (4) running face leakage due to nonconformability at high speed. The leakage mechanisms are qualitatively validated at low speed with observed oil patterns on the rotor from laser-induced fluorescence (LIF) experiments. Finally, the predicted total leakage area for all the gas seals ranges from 1.5 mm2/chamber at low speeds to 2 mm2/chamber at high speeds, which is in agreement with the previous experimental studies, and the three gas seal types (side seals, apex seals, and corner seals) each accounts for about 1/3 of the total leakage, with minor variation as a function of speed.

Analysis of Intrinsic Retention Characteristics for 2x-Nm NAND Flash Memory Using TCAD Simulation

The retention characteristic of memory devices is an important issue as the size of the chip is scaled down continuously. However, it is hard to retain the reliable retention characteristic at smaller size of chip since the interference and leakage problems are induced by scaling down the chip. This paper suggests the main leakage mechanisms of 2x-nm flash memory at the pre-cycling situation by comparing the measurement Vth data with TCAD simulation to analyze this problem. Based on the results, we identify the failure mechanisms and factors which affect degradation of intrinsic retention characteristics.

Leakage Current Mechanisms in Epitaxial Gd[sub 2]O[sub 3] High-k Gate Dielectrics

We report on leakage current mechanisms in epitaxial gadolinium oxide (Gd(2)O(3)) high-k gate dielectrics suitable for low standby power logic applications. The investigated p-type metal-oxide-semi con doctor capacitors are gated with complementary-metal-oxide-semiconductor-compatible fully silicided nickel silicide electrodes. The Gd(2)O(3) thickness is 5.9 nm corresponding to a capacitance equivalent oxide thickness of 1.8 nm. Poole-Frenkel conduction is identified as the main leakage mechanism with the high-frequency permittivity describing the dielectric response on the carriers. A trap level of Phi(T) = 1.2 eV is extracted. The resulting band diagram strongly suggests hole conduction to be dominant over electron conduction.

Temperature-Dependent Characteristics of Cylindrical Gate-All-Around Twin Silicon Nanowire MOSFETs (TSNWFETs)

The characteristics of cylindrical gate-all-around twin silicon nanowire field-effect transistors with a radius of 5 nm have been measured in temperatures <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T </i> ranging from 4 to 300 K. The dependence of the off-current suggests that thermal generation in the channel is the main leakage mechanism. The dependence of the subthreshold swing exhibits no body effects but shows degradations due to slight differences in the threshold voltages and in the body effect constants of the twin nanowires. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T </i> dependence of the peak normalized transconductance g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> /V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> gives a clue of 1-D phonon scattering and suggests that surface roughness scattering at the nanowire wall is dominant at low values.

Ionic and electronic defects in a‐BaTiO3 thin films studied by transient and steady state conductivity measurements

AbstractConduction mechanisms in BaTiO3 films deposited at low temperatures on Cu‐electrodes have been investigated in transient and steady regimes as a function of temperatures and electric field. This work aims to identify possible defects which govern the leakage current. Electrical measurements reveal that Space Charge Limited Current (SCLC) constitutes the main leakage mechanism in both the transient and the steady regimes. Based on the theory of SCLC, two types of defects can be detected. At higher temperatures, oxygen vacancies constitute the main defects which migrate across the film to generate an ionic leakage current. Diffusion of these defects is thermally activated with an activation energy around 1 eV. Moreover, at lower temperatures the J ‐E measurements reveals the presence of a discrete set of shallow traps at 0.45 eV below the conduction band with an effective density of 4 × 1022 m–3. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

High-quality ultrathin chemical-vapor-deposited Ta 2O 5 capacitors prepared by high-density plasma annealing

Highly reliable ultrathin low-pressure chemical-vapor-deposited (LPCVD) tantalum pentoxide (Ta 2O 5) capacitors were fabricated by using high-density plasma (HDP) annealing in N 2O at 400 °C after film deposition. It was found that HDP annealing in N 2O could significantly reduce the leakage current of Ta 2O 5 capacitors so as to produce better time-dependent dielectric breakdown characteristics than either conventional oxygen-plasma annealing or high-density plasma annealing in O 2. It was also found that HDP annealing in N 2O will not significantly increase the thickness of interface layer between Ta 2O 5 and the underlying silicon bottom electrode. Therefore, highly reliable ultrathin Ta 2O 5 capacitors can be fabricated by using HDP annealing in N 2O. The leakage current mechanism was also investigated. It was found that Poole–Frenkel emission and Fowler Nordheim (FN) tunneling was the main leakage mechanism in low and high electric field, respectively, as for the deposited Ta 2O 5 films. For the N 2O HDP-annealed Ta 2O 5 films, it was found that, the main leakage mechanism was Schottky emission in low electric field and Poole–Frenkel emission in high electric field.

Thickness dependence of leakage current behavior in epitaxial (Ba,Sr)TiO3 film capacitors

Thickness dependence of leakage current behavior in Pt/(Ba,Sr)TiO3/Pt film capacitors was investigated by fabricating epitaxial (Ba,Sr)TiO3 thin films having different thicknesses of 55–225 nm but with an identical interface state on Pt(001)/MgO(001) substrates by a radio-frequency magnetron sputtering technique. In the 55-nm-thick film, the Schottky emission is found to be a main leakage mechanism over a wide electric field range. In sharp contrast, instead of the Schottky emission, the Fowler–Nordheim tunneling dominates particularly in the thicker films (⩾90 nm) at high electric fields. According to the energy band model proposed to explain these results, the major leakage conduction mechanism is likely to be associated with overlapping of the depletion layers formed at the top and bottom interfaces.

Leakage current modeling of test structures for characterization of dark current in CMOS image sensors

In this paper, we present an extensive study of leakage current mechanisms in diodes to model the dark current of various pixel architectures for active pixel CMOS image sensors. Dedicated test structures made in 0.35-/spl mu/m CMOS have been investigated to determine the various contributions to the leakage current. Three pixel variants with different photodiodes-n/sup +//pwell, n/sup +//nwell/p-substrate and p/sup +//nwell/p-substrate-are described. We found that the main part of the total dark current comes from the depletion of the photodiode edge at the surface. Furthermore, the source of the reset transistor contributes significantly to the total leakage current of a pixel. From the investigation of reverse current-voltage (I-V) characteristics, temperature dependencies of leakage current, and device simulations we found that for a wide depletion, such as n-well/p-well, thermal Shockley-Read-Hall generation is the main leakage mechanism, while for a junction with higher dopant concentrations, such as n/sup +//p-well or p/sup +//n-well, tunneling and impact ionization are the dominant mechanisms.