Reduced Leakage Current Density Research Articles

Electrical properties in lanthanides substituted (Bi0.9 A 0.1)(Fe0.975Co0.025)O3−δ (A = La, Eu, Gd) thin films

Multiferroic BFO and (Bi0.9A0.1)(Fe0.975Co0.025)O3−δ (A = La, Eu, Gd) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. The thin films were annealed at 550 °C for 30 min by using a conventional annealing process under a nitrogen atmosphere. Reduced leakage current density and improved ferroelectric properties were observed in the co-doped thin films compared to the BFO thin film. The enhanced properties observed in the co-doped thin films could be considered as being the result of the suppression of oxygen vacancies and of the modified microstructure.

Electrical properties of chemical solution deposited (Bi0.9RE0.1)(Fe0.975Cu0.025)O3−δ (RE=Ho and Tb) thin films

Pure BiFeO3 (BFO) and (Bi0.9RE0.1)(Fe0.975Cu0.025)O3−δ (RE=Ho and Tb, denoted by BHFCu and BTFCu) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. The BHFCu and BTFCu thin films showed improved electrical and ferroelectric properties compared to pure BFO thin film. Among them, the BTFCu thin film exhibited large remnant polarization (2Pr), low coercive field (2Ec) and reduced leakage current density, which are 89.15C/cm2 and 345kV/cm at 1000kV/cm and 5.38×10−5A/cm2 at 100kV/cm, respectively.

Surfactant assisted growth of MgO films on GaN

Thin epitaxial films of 〈111〉 oriented MgO on [0001]-oriented GaN were grown by molecular beam epitaxy and pulsed laser deposition using the assistance of a vapor phase surfactant. In both cases, surfactant incorporation enabled layer-by-layer growth and a smooth terminal surface by stabilizing the {111} rocksalt facet. 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. These data verify numerous predictions regarding the role of H-termination in regulating the habit of rocksalt crystals.

Impact of ultrathin Al2O3 interlayer on thermal stability and leakage current properties of TiO2/Al2O3 stacking dielectrics

Ultrathin TiO2/Al2O3 stacking structures were fabricated using an atomic layer deposition technique. The effect of the ultrathin Al2O3 interlayer on interfacial thermal stability and leakage current properties were studied. After thermal annealing of the TiO2/Al2O3/TiO2/Al2O3/Si structure at 700 °C for 60 s, the Al2O3 double layers remained amorphous, although the layers of TiO2 were crystallized. The amorphous Al2O3 divided the grain boundaries which would otherwise serve as diffusion paths for atoms and as leakage current channels from the TiO2 layers. As a result, atomic diffusion and surface roughness were suppressed, and the leakage current value was reduced by about a 1.5 order of magnitude compared with TiO2/Al2O3/Si. The improved interfacial stability as well as the reduced leakage current density indicates the present stacking structure has potential application in future high-performance microelectronics.

Response to “Comment on ‘Open-circuit voltage dependency on hole-extraction layers in planar heterojunction organic solar cells’” [Appl. Phys. Lett. 100, 266101 (2012)

Yow-Jon Lin 1 had commented that our explanation on Voc relationship as a function of leakage current density in our paper 2 is not completely accurate. In this paper, we have not fully described the tendency of Voc increase in relation to reduction of leakage current density. Seeing inset of Fig. 3 at a glance gives the feeling that there is some tendency of Voc increase with reduction of leakage current density. But, we believe that this is not accurate analysis. Inset of Fig. 3 shows that only two or three data points are closer to the slope. A large deviation on the Voc relationship had existed with leakage current density values using our hole extraction layers; and this was our research motivation. Then, we investigated what could be the other parameters showing such tendency. It can be seen in the inset of Fig. 3, TAPC and NPB have high leakage levels as 10 4 mA/cm 2 range, their devices have high Voc values upto 1.1V. As a comparison 2-TNATA has a bit lower leakage level than TAPC and NPB, however, its Voc is about 0.95V. Therefore, these data could not explain the exact relationship between Voc and leakage current levels. Then, it was difficult to say as results showed somewhat deviation from a real diode. So, we analyzed more sensitive parameters to explain Voc variation. Mobility values and HOMO levels of hole extraction layers were revealed as such parameters to explain more accurately about the variation of Voc values rather than leakage current in our devices. Hence, in our paper, we said about the little tendency of VOC increase with reduction of leakage current density. There may have a little contributions to Voc by leakage current levels, our experimental results showed that leakage current cannot be a significant factor to determine the Voc values in our devices. The other parameters such as mobility values and HOMO levels should be given important consideration in determining the Voc of the devices. 1 Y.-J. Lin, Appl. Phys. Lett. 100, 266101 (2012). 2 C. Kulshreshtha, J. W. Choi, J. Kim, W. S. Jeon, M. C. Suh, Y. Park, and J. H. Kwon, Appl. Phys. Lett. 99, 023308 (2011).

Enhancement of ferroelectricity in gadolinium (Gd) and transition metal (Ni, Co, Cr) Co-doped BiFeO3 thin films via a chemical solution deposition technique

The BiFeO3 (BFO) and the gadolinium and transition metal ions co-doped (Bi0.9Gd0.1)(Fe0.975TM0.025)O3-δ (TM = Ni, Co and Cr, BGFNi, BGFCo and BGFCr) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. Compared to the pure BFO, improved electrical and ferroelectric properties were observed in the co-doped (Bi0.9Gd0.1)(Fe0.975TM0.025)O3-δ thin films. Among the thin films, the BGFCr thin film exhibited large remnant polarization (2Pr), low coercive field (2Ec), and reduced leakage current density, which are 136 μC/cm2, 1360 kV/cm at 1470 kV/cm, and 5.14 × 10-6 A/cm2 at 100 kV/cm, respectively.

Atomic Layer Deposition and Characterization of Amorphous ErxTi1-xOy Dielectric Ultra-Thin Films

Er1-xTixOy dielectric thin films were deposited on Si(100) substrates by atomic layer deposition (ALD) using tris(methylcyclopentadienyl)erbium [(CpMe)3Er] and tetrakis(diethylamino)titanium [TDEAT] as metal precursors, and O3 as oxidant. The deposition temperature dependence of both Er2O3 and TiO2 film growths showed the overlapping ALD window of 175–250°C. Compositional tunability of Er1-xTixOy films was obtained through deposition process control. Carbon and nitrogen impurities in as-deposited films were found to be below X-ray photoelectron spectroscopy detection level. Glancing incidence X-ray diffraction and phase-shifting interferometry results showed that ErxTi1-xOy films with ALD cycle ratios (Er2O3/TiO2) of 1:8 or higher have a good thermal stability and remain amorphous with unchanged surface roughness after post-deposition rapid thermal processing (RTP) at 700°C in O2. Electrical measurements showed that optimized amorphous Er1-xTixOy films after RTP exhibited a dielectric constant of ∼36, a hysteresis voltage of less than 10 mV, and a leakage current density of 10−8 A/cm2 at −1 MV/cm; such properties compare favorably with the properties of other reported amorphous titanium-based ternary dielectrics on Si. The sizable reduction of leakage current density of Er1-xTixOy found in our study suggests that amorphous Er1-xTixOy thin films are promising future dielectrics in Si integrated circuit technology.

Ultraviolet assisted processing: A unique approach to mitigate oxygen vacancies and attain low loss highly tunable Ba0.60Sr0.40TiO3 thin films

Isothermal (700 °C) ultraviolet annealing (UVA) processing of crystallized Ba0.60Sr0.40TiO3 (BST) thin films for exposure times up to 225 min films has been studied. The BST films, grown on PtSi wafers via the metalorganic solution deposition (MOSD) technique, were crystallized via conventional furnace annealing (CFA) prior to UVA treatment, and the effects of UV annealing time on the structural, dielectric, and insulation properties were evaluated. The experimental results demonstrated significantly improved structural, dielectric, and insulation properties for the UVA films. Specifically, lattice parameter contraction (toward that of bulk BST60/40) and a 20% reduction in loss were observed for the UVA treated films with respect to the CFA/control film. Leakage current characteristics were found to be the most sensitive characterization technique to access material property modification as a result of UVA exposure time. Specifically, the 225 min UVA exposure time resulted in a three-order of magnitude reduction in leakage current density compared to the CFA film, and the lowest value observed was 1.06 × 10−7 A/cm2 at E = 300 kV/cm. The useable tunability (tunability value at the maximum acceptable leakage current, 500 pA) was found to be elevated by a factor of two with respect to that of the CFA/control BST film (52.31%/UVA film vs. 18.5%/control film). It is suggested that the improved material properties are due to the mitigation of unwanted oxygen vacancies within the film after UV-annealing. A mechanistic model is presented and discussed.

Oxygen-enhanced wet thermal oxidation of GaAs

An oxygen-enhanced wet thermal oxidation process is used to grow smooth, uniform, insulating native oxides of GaAs. At 420 °C, a maximum linear growth rate of 4.8 nm/min is observed for oxidation in water vapor with 2000 ppm O2 added relative to the N2 carrier gas, with growth ceasing by 7000 ppm. Films as thick as 800 nm with surface roughness as low as 0.2 nm are demonstrated. In fabricated metal-oxide-semiconductor capacitors, a 412 nm thick native oxide film exhibits a factor of ∼2700 reduction in leakage current density at 1 V relative to a direct metal (Au:Ti) to GaAs contact.

Effects of post-oxidation annealing temperature on ZrO 2 thin film deposited on 4H-SiC substrate

ZrO 2 thin film has been formed on n-type 4H-SiC substrate using a combination of metal sputtering (∼25 nm thick) and thermal oxidation (15 min at 500 °C) processes. Effects of post-oxidation annealing temperature (600–900 °C) on the physical and electrical properties of the thin film have been investigated. High resolution transmission electron microscopy attached with energy dispersive X-ray has been used to examine cross-sectional morphology and to study element chemical distribution of the investigated region. Selected area diffraction analysis has been employed to examine crystallinity of the samples. Metal-oxide-semiconductor capacitors have been fabricated to examine leakage current through the oxide using current–voltage measurement. Oxide-semiconductor interface-trap density has been extracted using capacitance–voltage measurement. The annealing process reduced leakage current density as low as one order of magnitude. However, breakdown voltage of the oxide has been reduced. Dielectric constant extracted from this work ranges from 22 to 80, depending on the annealing temperature.

Structural and Electrical Analysis of Thin Interface Control Layers of MgO or Al2O3 Deposited by Atomic Layer Deposition and Incorporated at the High-k/III-V Interface of MO2/InxGa1-xAs (M = Hf|Zr, x = 0|0.53) Gate Stacks

Control of the high-k/III-V interface by deposition of thin (~1-2 nm) interface control layers (ICLs) of Al2O3 or MgO, as part of an overall bi-layer structure with a high-k metal oxide MO2 (M = Hf|Zr), is explored. An Al2O3 or MgO ICL is deposited on unpassivated InxGa1-xAs (x = 0|0.53) substrates prior to MO2 gate oxide deposition, forming a Pd/high-k/ICL/III-V gate stack. The aim of a bi-layer structure is to enable continued device scaling using a high-k MO2 oxide while improving the high-k/III-V interface quality and interfacial band structure, with an Al2O3 or MgO ICL. Metal-oxide-semiconductor capacitor (MOSCAP) devices with an Al2O3 ICL on p-GaAs display significantly reduced leakage current density, and reduced frequency dispersion of accumulation capacitance when compared to a no-ICL device, indicating an improved high-k/III-V band structure and interface quality, respectively. Further studies on ZrO2/Al2O3/In0.53Ga0.47As devices find a reduced defect response with a post-metal forming gas anneal.

A Novel Investigation on Using Strain in Barriers of 1.3 μm AlGaInAs-InP Uncooled Multiple Quantum Well Lasers

In this study we investigate strain effect in barriers of 1.3 μm AlGaInAs-InP uncooled multiple quantum well lasers. Single effective mass and Kohn–Luttinger Hamiltonian equations have been solved to obtain quantum states and envelope wave functions in the structure. In the case of unstrained barriers, our simulations results have good agreement with a real device fabricated and presented in one of the references. Our main work is proposal of 0.2% compressive strain in the structure Barriers that causes significant reduction in Leakage current density and Auger current density characteristics in 85 °C. 20% improvement in mode gain-current density characteristic is also obtained in 85°C.

Design considerations to improve high temperature characteristics of 1.3 μm AlGaInAs-InP uncooled multiple quantum well lasers: Strain in barriers

Uncooled multiple quantum well lasers have great attraction because of their lower power dissipation and smaller size than traditional semiconductor lasers. In this study we will investigate the strain effect in barriers of 1.3 μm AlGaInAs-InP uncooled multiple quantum well lasers. We simulate a laser structure using a band-to-band transition approach. Single effective mass theory has been used for conduction band and Kohn–Luttinger Hamiltonian has been solved for valance band to obtain quantum states and envelope wave functions in the structure. In the case of unstrained barriers, the results have good agreement with a real device fabricated and presented in one of the references. Our main work is proposal of 0.2% compressive strain in the structure Barriers that cause 20% improvement in mode gain–current density characteristic. Significant reduction in leakage current density and Auger current density characteristics is also obtained at 85 °C. Optical gain–photon energy spectrum is increased more than 3% proportional to unstrained barriers.

Twinning rotation and ferroelectric behavior of epitaxial BiFeO3 (001) thin film

A twinning rotation structure is revealed by reciprocal space mappings obtained from synchrotron X-ray diffraction for the epitaxial BiFeO3 thin film that was grown on (001) SrTiO3 substrate. The lattice strain is not fully relaxed at a film thickness of 720 nm. The structure is indexed as a monoclinic with lattice parameters a=5.610(1) Å, b=5.529(1) Å, c=4.031(1) Å, and β=89.34(1)°. The twinning rotation leads to an enhanced remanent polarization (2Pr=164 μC/cm2, 2Ec=510 kV/cm) and greatly reduced leakage current density of 1.2×10−6 A/cm2 at 100 kV/cm.

Low-voltage organic thin-film transistors with hydrophobic hafnium oxynitride film as gate insulator

An excellent gate dielectric of amorphous HfON (a-HfON) can be fabricated by flashing a Hf metal layer prior to a-HfON deposition. Nitrogen incorporation in the HfON film can reduce leakage current density from 8 × 10 −7 to 10 −7 A/cm 2. And surface roughness of a-HfON is reduced by the flash Hf metal layer from 1.9 to 1.2 nm. With the flash Hf metal layer, field effect mobility (0.17 cm 2/V s), threshold voltage (−0.3 V), subthreshold swing (−0.209 V/decade), and on/off current ratio (3.2 × 10 3) can be achieved for organic thin-film transistors with a-HfON gate dielectric.

Ferroelectric Properties of Cr-Doped BiFeO3 Films Crystallized below 500 °C

Cr-doped BiFeO3 (BFCO) thin films were formed on Pt/Ti/SiO2/Si(100) substrates by chemical solution deposition, in which the nominal Fe/Cr ion ratio was changed from 100/0 to 40/60. The spin-coated, dried, and prefired films were finally crystallized in air, nitrogen, and oxygen flow mainly at temperatures below 500 °C. X-ray diffraction analysis revealed that polycrystalline grains of BiFeO3 (BFO) were formed in the films with ratios smaller than 80/20 after crystallization at 450 °C. It was also found from cross-sectional energy dispersive X-ray spectroscopy-scanning transmission electron microscopy (EDX–STEM) that Fe and Cr atoms mainly existed in different crystallites. On the basis of these results, a growth model in which the low-temperature crystallization of BFO is triggered by Bi7CrO12.5 crystallites is proposed. The leakage current density and remanent polarization (Pr) in BFCO films increased with increasing Fe ratio, and a large Pr of 60 µC/cm2 was obtained in a 450 °C-crystallized BFCO film with the 80/20 ratio measured at 1.6 MV/cm and 10 kHz. In the 500 °C-crystallized BFCO films with a Cr doping ratio of more than 50 at. %, a Pr close to the initial value was obtained even after 108 switching cycles owing to the reduced leakage current density.

Growth and Material Characterization of Hafnium Titanates Deposited by Atomic Layer Deposition

Hafnium titanate (HTO) films were deposited within a large Hf–Ti compositional range by atomic layer deposition using precursors. The Hf content of the layers is well controlled by the precursor pulse ratio, as indicated by Rutherford backscattering. The saturation conditions of ternary HTOs are different compared to those of the binary oxides. First-principles simulation confirmed the enhancement of the Hf precursor reactivity in the presence of Ti–OH. Growth curves of HTOs showed a good linearity with the number of reaction cycles. A linear correlation between density, quantified by X-ray reflectometry, and composition was observed. X-ray diffraction indicated that the as-deposited films are amorphous up to , depending on the ratio. The orthorhombic diffraction lines in the samples (30–64% Hf) annealed at were observed. For a Hf content higher than 82%, a monoclinic -like structure was reported. The dielectric constant and leakage current depend on the Ti content, the film crystallinity, and the anneal atmosphere. The postdeposition anneal in is found to have a drastic effect in leakage current density reduction and could be a key for further improvements of HTO electrical properties.

Reduced Electrical Defects and Improved Reliability of Atomic-Layer-Deposited HfO2 Dielectric Films by In Situ NH3 Injection

The improvements in the reliability of thin films afforded by in situ injection during their atomic layer depositions were studied. The injection increased nitrogen content and reduced the residual carbon in the film, which resulted in the reduced leakage current density and improved reliabilities. A smaller flatband voltage shift, higher breakdown field, and the suppressed degradation of interface traps by constant voltage stress were obtained due to the solid interfacial layer formation, decreased carbon content, and reduction of electrical defects by oxygen vacancies. The solid interfacial layer improved the thermal stability of the films. Detailed analysis of the current-voltage characteristics revealed the electrical conduction behavior and nature of defects.

The effect of KrF laser annealing within an ultrashort time on metal-alumina-nitride-oxide-silicon-type flash memory devices

The effect of laser annealing (LA) within an ultrashort time on metal-alumina-nitride-oxide-silicon-type flash memory device is investigated. Conventional high-temperature annealing leads to the degrading quality of high-k blocking oxide due to the long annealing time. On the contrary, an optimized LA at an energy of 500 mJ/cm2 can effectively improve the blocking efficiency due to the reduction in leakage current density. Using the results of x-ray photoemission spectroscopy and high-resolution cross-sectional transmission electron microscopy, this improvement was attributed to the minimized decomposition of the Al2O3 layer and the interfacial layer growth between Al2O3 and Si3N4.

Electrically stable low voltage operating ZnO thin film transistors with low leakage current Ni-doped Ba0.6Sr0.4TiO3 gate insulator

We report on the fabrication of low-voltage ZnO thin-film transistors using 1% Ni-doped Ba0.6Sr0.4TiO3 as the gate insulator. The Ni-doped BST, deposited by RF magnetron sputtering at room temperature, significantly reduced leakage current density to less than 6 × 10−9 A/cm, as compared to a current density of 5 × 10−4 A/cm for undoped BST films at 0.5 MV/cm. The ZnO thin-film transistor with the Ni-doped BST gate insulator exhibited a very low operating voltage of 4 V. The field-effect mobility, the current on/off ratio and subthreshold swing were 2.2 cm2 V/s, 1.2 × 106, and 0.21 V/dec respectively.