Current Onset Voltage Research Articles

Backward Diode Rectifying Behavior in AgCrO2/In2O3

A backward diode consisting of all nondegenerate and transparent semiconducting oxides (TSOs) offers promising opportunities for designing multifunctional electronic devices. In this letter, we report the backward diode rectifying behavior in the nondegenerate AgCrO2/In2O3 p-n heterojunction. Both AgCrO2 and In2O3 films are transparent. The decrease of grain boundary in the In2O3 film can improve the backward diode rectifying performance. The optimized AgCrO2/In2O3 heterojunction exhibits a very high reverse rectification ratio that exceeds 103 along with a small tunneling current onset voltage. The backward diode rectifying behavior originates from the electron band-to-band tunneling (BTBT) current in the reverse voltage region, which is induced by type-III band alignment. This study will pave the way for achieving transparent backward diodes by using all nondegenerate TSOs p-n heterojunctions.

Hierarchical Co3O4 decorated PPy nanocasting core-shell nanospheres as a high performance electrocatalysts for methanol oxidation

In recent times, much attention has been paid to explore economic and highly active precious metal free electrocatalysts for energy conversion and storage systems due to the expensiveness of Pt-based catalysts. Here we developed a mesoporous core-shell like nanospheres composed of a metallic cobalt oxide core wrapped with a polypyrrole nanoshell (PPy/Co3O4) for methanol electrooxidation. The performance of the core-shell PPy/Co3O4 nanospheres as anodic catalyst material was measured in 1 M KOH electrolyte and the results obtained demonstrated that the hybrid possesses high catalytic activity in terms of current density and onset voltage. The core-shell PPy/Co3O4 delivers an oxidation current density of ∼111 mA/cm2 at 0.5 V with superior stability long run stability. The observed electrocatalytic performance of the porous PPy/Co3O4 nanospheres is attributed to the integrative effects of both Co-species and layered carbon shell and presence of exceptionally numerous mesopores. Results show evidence that the earth abundant PPy/Co3O4 provide a potential electrode material for methanol electrooxidation with a satisfactory reaction activity.

Influence of work function variation of metal gates on fluctuation of sub-threshold drain current for fin field-effect transistors with undoped channels

Influence of work function variation (WFV) in metal gates (MGs) on fluctuation of sub-threshold drain current is investigated in detail by analyzing fluctuation of current–onset voltage (COV) for fin field-effect transistors (FinFETs) with polycrystalline TiN and amorphous TaSiN MGs. The polycrystalline TiN MG exhibits anomalously increased COV fluctuation of the nMOS FinFETs in comparison to the pMOS case, while the amorphous MG exhibits well suppressed COV fluctuation both for the n- and pMOS FinFETs. Through the discussion with regard to the WFV due to the polycrystalline TiN grains, it is concluded that the sub-dominant grains of TiN with lower work function (WF) in TiN form localized potential valleys in the channel of the nMOS FinFETs resulting in the anomalous leak current in the sub-threshold condition. In the pMOS FinFETs, in contrast, the lower WF grains in TiN form localized potential peaks for holes, which have less impact on the sub-threshold leakage.

Statistical Analysis of Subthreshold Swing in Fully Depleted Silicon-on-Thin-Buried-Oxide and Bulk Metal–Oxide–Semiconductor Field Effect Transistors

The variability of subthreshold swing (SS) in fully depleted (FD) silicon-on-thin-buried-oxide (SOTB) MOSFETs is statistically analyzed and compared with that of conventional bulk MOSFETs. It is newly found that SS variability is small enough in deep subthreshold region (small drain current Ids) while it increases as increasing Ids. The mechanisms of this behavior is intensively investigated and it is found that the increase in SS variability is caused by current-onset voltage (COV) variability that is due to random dopant fluctuation (RDF). Since SOTB FETs have small COV variability thanks to an intrinsic channel, SS variability is much smaller than bulk FETs, which is a great advantage of FD SOTB in terms of Ion/Ioff ratio.

Statistical Analysis of Current Onset Voltage (COV) Distribution of Scaled MOSFETs

Statistical Analysis of Current Onset Voltage (COV) Distribution of Scaled MOSFETs

Suppression of Within-Device Variability in Intrinsic Channel Tri-Gate Silicon Nanowire Metal–Oxide–Semiconductor Field-Effect Transistors

In this paper, the variabilities of threshold voltage (VTH), drain-induced barrier lowering (DIBL), and current onset voltage (COV) in intrinsic channel silicon nanowire metal–oxide–semiconductor field-effect transistors (MOSFETs) were evaluated and compared with those of conventional bulk and fully depleted (FD) silicon-on-insulator (SOI) MOSFETs. The random component of variability is extracted by a “within-device” variability method to exclude the systematic component. It is found that the within-device variabilities of DIBL and COV as well as VTH are extremely small in intrinsic channel nanowire MOSFETs owing to the non-intentionally doped channel and small gate workfunction variability. The intrinsic channel nanowire MOSFET is promising for a future scaled device structure in terms of not only the short channel effect suppression but also the variability suppression.

Gate Length and Gate Width Dependence of Drain Induced Barrier Lowering and Current-Onset Voltage Variability in Bulk and Fully Depleted Silicon-on-Insulator Metal Oxide Semiconductor Field Effect Transistors

This paper presents the statistical analysis of a newly found drain current variability component called “current-onset voltage” (COV) variability as well as drain induced barrier lowering (DIBL) variability in bulk and fully-depleted (FD) silicon-on-insulator (SOI) devices. Intensive variability measurement data show that gate length and gate width dependent COV variability and DIBL variability in bulk metal–oxide–semiconductor field effect transistors (MOSFETs) deviate from the straight line in the Pelgrom plot. On the other hand, COV variability and DIBL variability in FD SOI MOSFETs fall on the straight line. Their mechanisms are discussed based on three-dimensional (3D) device simulation considering random dopant fluctuation (RDF). It is found that the saturation of the COV and DIBL variability in smaller devices is caused by weaker averaging effect of channel potentials.

Gate Length and Gate Width Dependence of Drain Induced Barrier Lowering and Current-Onset Voltage Variability in Bulk and Fully Depleted Silicon-on-Insulator Metal Oxide Semiconductor Field Effect Transistors

This paper presents the statistical analysis of a newly found drain current variability component called “current-onset voltage” (COV) variability as well as drain induced barrier lowering (DIBL) variability in bulk and fully-depleted (FD) silicon-on-insulator (SOI) devices. Intensive variability measurement data show that gate length and gate width dependent COV variability and DIBL variability in bulk metal–oxide–semiconductor field effect transistors (MOSFETs) deviate from the straight line in the Pelgrom plot. On the other hand, COV variability and DIBL variability in FD SOI MOSFETs fall on the straight line. Their mechanisms are discussed based on three-dimensional (3D) device simulation considering random dopant fluctuation (RDF). It is found that the saturation of the COV and DIBL variability in smaller devices is caused by weaker averaging effect of channel potentials.

High-Temperature Properties of Drain Current Variability in Scaled Field-Effect Transistors Analyzed by Decomposition Method

The properties of drain current variability in field-effect transistors (FETs) at high temperature are experimentally investigated. It is found that the on-state drain current (ION) at high temperature has a strong correlation with ION at room temperature and that there is no anomalous ION change from room temperature to high temperature. It is also found that ION variability at high temperature is smaller than that at room temperature. The origin of the decrease in ION variability with increasing temperature is analyzed by the decomposition method developed in our previous work. It is clarified that the decrease in the current–onset voltage component plays a dominant role, especially in the saturation region. Moreover, it is also clarified that thermal excitation of carriers suppresses current–onset voltage variability, and ultimately the current–onset voltage component of ION variability with increasing temperature.

Effects of gate electrode work function on electrical characteristics of pentacene-based field-effect devices

This paper presents the effects of the work function of an indium tin oxide (ITO) gate electrode on the electrical characteristics of two pentacene-based field-effect devices—metal-insulator-semiconductor (MIS) capacitors and field-effect transistors (FETs). The ITO work function was varied by employing base and acid treatments. Flat-band voltage shifts of the MIS capacitors were found to result from the shift in the work function. The current onset and threshold voltage of the FETs were also found to be influenced by the work function. These results demonstrate the correlation of the flat-band conditions of pentacene-based field-effect devices with the gate electrode work function.

Relation between the built-in voltage in organic light-emitting diodes and the zero-field voltage as measured by electroabsorption

Change of title: On the determination of the built-in voltage in organic light-emitting diodes from electro-absorption measurements. For developing understanding of the current density onset voltage and injection barriers in organic light-emitting diodes (OLEDs), a precise determination of the built-in voltage, Vbi, is of crucial importance. Commonly, Vbi is assumed to be equal to the voltage V0,EA at which in an electroabsorption (EA) experiment the reflection of light at the OLED is found to become insensitive to a small voltage modulation. However, this assumption is shown to lead to significant errors for devices with well-injecting contacts. From an analysis of EA experiments for hole-only devices containing a polyfluorene-based copolymer, it is shown that V0,EA may be interpreted as an effective current density onset voltage, agreeing with the commonly accepted picture, but that for these devices Vbi is ~0.5 V larger than V0,EA. This is found to be consistent with predictions of V0,EA from model calculations of the electric field and light-absorption profiles in the semiconducting layer.

Development of a novel epitaxial-layer segmentation method for optoelectronic device fabrication

Describes the development of a new process for segmenting epitaxial-layer material and fabricating cleaved-cavity lasers. The technique, which involves growth substrate removal and use of a novel epitaxial-layer cleaving tool, is applicable to a variety of different materials and devices. IV-VI semiconductor epitaxial layers grown by molecular beam epitaxy on silicon [111] substrates with a water-soluble barium fluoride buffer layer were used. The layers were metallurgically bonded to the rectangular tips (500×1040 μm) of copper bars held together by a small vise apparatus, the substrate was removed by dissolving the barium fluoride buffer layer in water, and the copper bars were separated by releasing the vise assembly. Current versus voltage characterization of separated p-n junction IV-VI epilayer structures on the tips of the copper bars showed nonlinear behavior with a forward bias current onset voltage /spl sim/250 mV, a value consistent with the room temperature bandgaps of the IV-VI alloys used. These results demonstrate the utility of this technique for obtaining epitaxial-layer structures with typical cleaved-cavity in-plane laser dimensions.

Gate-length dependence of negative differential resistance in ridge-type InGaAs/InAlAs quantum wire field-effect transistor

We investigate the gate-length dependence of negative differential resistance (NDR) in a ridge-type InGaAs/InAlAs quantum wire field-effect transistor with a gate varying from 50 nm to 1 μm in length. The gate leakage current is detectable only with the onset of NDR and increases with larger gate bias. The NDR could be attributed to the real space transfer of channel carrier into the barrier layer by gate field-assisted tunneling. The NDR characteristics are dependent strongly on gate length. The improvement in NDR characteristic in terms of peak-to-valley current ratio and onset voltage (VNDR) is observed clearly with the reduction of gate length. The QWIR-FETs with shorter gate length show the NDR even at room temperature. The improvement in NDR characteristic is attributed to a velocity overshoot enhanced by the suppression of scattering probability.

Gate-Length Dependence of Negative Differential Resistance in InGaAs/InAlAs Quantum Well Field-Effect Transistor

We have investigated the gate-length dependence of negative differential resistance (NDR) in an InGaAs/InAlAs quantum well field-effect transistor (QW-FET) by varying the gate length from 50 nm to 0.8 µm. A pronounced N-shaped NDR is clearly observed in these QW-FETs. The gate leakage current is detectable only by the onset of NDR. We believe that the NDR should be attributed to the real space transfer of channel electrons into the barrier layer with low mobility underneath the gate by gate field-assisted tunneling (RSTT). Both peak-to-valley current ratio (PVR) and onset voltage (VNDR) are found to be strongly dependent on the gate length. The NDR characteristics in terms of PVR and VNDR are improved dramatically by reducing the gate length, and originate from the velocity overshoot due to the suppression of scattering probability.

Free Conducting Particles in a Coaxial Compressed-Gas-Insulated System

The effect of free conducting particles (FCPs) on the voltage-insulating performance of a short length of transmission line was quantitatively studied over the pressure range 0 to 300 psig for nitrogen and 0 to 125 psig for SF6. The FCPs were selected aluminum filings deliberately inserted into the concentric cylindrical (3"×10" dia.) electrode system. DC voltages of either polarity were produced by a Van de Graaff generator. The observed forms of interelectrode current included intermittent pulses or 'bursts', 'fireflies', steady corona, and sparks. Up to five-fold reductions in the current-onset voltage insulating strength resulted from the introduction of FCPs. For pressures up to 75 psig the sparking voltage in SF6 was 4 to 5 times higher than the sparking value in nitrogen. An electrostatic particle trap proved effective in reducing FCP-caused discharges. The dynamic equilibrium mechanism of 'fireflies' was studied in detail.