Decrease In Threshold Voltage Research Articles

Electrical Properties and Reliability of AlGaN/GaN High Electron Mobility Transistor under RF Overdrive Stress at High Temperature.

We have investigated the electrical properties and reliability of AlGaN/GaN high electron mobility transistors (HEMT) under high-temperature RF overdrive stress. The experimental results show that the drain current and transconductance of the device decrease at 25 °C and 55 °C but do not change significantly at 85 °C before and after the stress. The decline rate of the saturation drain current, the degradation amplitude of transconductance, and the drift amplitude of threshold voltage decrease with the increase in temperature. The results of pulse I-V and low-frequency noise tests show that the current collapse is inhibited, and the trap density is reduced at higher temperatures. The Electroluminescence (EL) test shows that the luminescence characteristics of the device after RF overdrive stress are more scattered and weaker. We believe that the degradation at lower temperatures is mainly due to the influence of the hot electron effect (HEE), while the change in electrical properties at higher temperatures is due to the weakening of HEE and the improvement of the Schottky interface.

Functionalized Phenanthrene Imide‐Based Polymers for n‐Type Organic Thin‐Film Transistors

AbstractHigh‐performing n‐type polymers are crucial for the advance of organic electronics field, however strong electron‐deficient building blocks with optimized physicochemical properties for constructing them are still limited. The imide‐functionalized polycyclic aromatic hydrocarbons (PAHs) with extended π‐conjugated framework, high electron deficiency and good solubility serve as promising candidates for developing high‐performance n‐type polymers. Among the PAHs, phenanthrene (PhA) features a well‐delocalized aromatic π‐system with multiple modifiable active sites . However, the PhA‐based imides are seldom studied, mainly attributed to the synthetic challenge. Herein, we report two functionalized PhAs, CPOI and CPCNI, by simultaneously incorporating imide with carbonyl or dicyanomethylene onto PhA. Notably, the dicyanomethylene‐modified CPCNI exhibits a well stabilized LUMO energy level (−3.84 eV), attributed to the synergetic inductive effect from imide and cyano groups. Subsequently, based on CPOI and CPCNI, two polymers PCPOI‐Tz and PCPCNI‐Tz were developed. Applied to organic thin‐film transistors, owing to the strong electron‐deficiency of CPCNI, polymer PCPCNI‐Tz shows an improved electron mobility and largely decreased threshold voltage compared with PCPOI‐Tz. This work affords two structurally novel electron‐deficient building blocks and highlights the effectiveness of dual functionalization of PhAs with strong electron‐withdrawing groups for devising n‐type polymers.

Functionalized Phenanthrene Imide-Based Polymers for n-Type Organic Thin-Film Transistors.

High-performing n-type polymers are crucial for the advance of organic electronics field, however strong electron-deficient building blocks with optimized physicochemical properties for constructing them are still limited. The imide-functionalized polycyclic aromatic hydrocarbons (PAHs) with extended π-conjugated framework, high electron deficiency and good solubility serve as promising candidates for developing high-performance n-type polymers. Among the PAHs, phenanthrene (PhA) features a well-delocalized aromatic π-system with multiple modifiable active sites . However, the PhA-based imides are seldom studied, mainly attributed to the synthetic challenge. Herein, we report two functionalized PhAs, CPOI and CPCNI, by simultaneously incorporating imide with carbonyl or dicyanomethylene onto PhA. Notably, the dicyanomethylene-modified CPCNI exhibits a well stabilized LUMO energy level (-3.84 eV), attributed to the synergetic inductive effect from imide and cyano groups. Subsequently, based on CPOI and CPCNI, two polymers PCPOI-Tz and PCPCNI-Tz were developed. Applied to organic thin-film transistors, owing to the strong electron-deficiency of CPCNI, polymer PCPCNI-Tz shows an improved electron mobility and largely decreased threshold voltage compared with PCPOI-Tz. This work affords two structurally novel electron-deficient building blocks and highlights the effectiveness of dual functionalization of PhAs with strong electron-withdrawing groups for devising n-type polymers.

Designing and performance analysis of 7 T CNTFET based novel SRAM cell for IoT application

The selection of the title includes designing of SRAM cell using CNTFET because CNTFET overcomes all the issues coming from CMOS technology beyond the 10nm technology node. With the reduction in channel length, the threshold voltage required for CMOS-based technology increases, and the corresponding off-state current decreases. This can prove to be a significant advancement for the semiconductor industry. With the evolution of the new generation of the technology era, especially beyond 10 nm, CMOS is not able to fulfil all the required conditions, as beyond 10 nm technology node, threshold voltage decreases, and consequently off-state current and leakage power increase. This is the reason that CNTFET can be considered a prominent replacement of CMOS transistor for the designing of SRAM cells with the technology node beyond 10 nm. This designed SRAM cell is applicable for IoT applications because IoT uses a microcontroller and the SRAM cell is used as a data memory in the microcontroller. A Data memory always requires high speed, ultra-low power dissipation, and high stability from the cell. Thus, to fulfil this requirement, performance analysis to identify the problem statement of conventional cells and then to improve their performance based on the findings is essential. This is the reason that the 7 T CNTFET-based SRAM novel cell is introduced, and its performance is going to be further improved so that the designed novel cell becomes compatible with IoT applications. Leakage power and stability factor are the main performance parameters to improve of SRAM cells.

Impact of porous nanoparticles on the electro-optical and dielectric parameters of nematic liquid crystals for display applications: Cost effective approach

In this study, several vital electro-optical and dielectric properties of nematic liquid crystal (NLC) dispersed with porous carbon nanoparticles (PCNP) with three different concentrations were measured. NLCs are birefringent materials. Increased birefringence was observed for NLC-PCNP composites. Dielectric study was also performed for NLC dispersed with PCNPs. Dielectric anisotropy was found to be increased for PCNP dispersed NLC system. Contrast ratio was also measured for NLC dispersed with PCNP, and it is found to be enhanced. Decreased threshold voltage was observed after dispersing PCNP into NLC. High birefringence reduces the cell gap so this work may be applicable in the making of flat panel displays (FPDs).

Graphene oxide and reduced graphene oxide in the anisotropic media of nematic liquid crystals 4’-pentyl-4-cyano-biphenyl

ABSTRACTGraphene oxide is hydrophilic due to its oxygen functionality, making it easy to disperse in liquid crystalline media. The nanocomposites of graphene oxide and reduced graphene oxide have been prepared in a nematic liquid crystal. Results reveal rising transition temperatures, enthalpies, and order parameters for graphene oxide dispersed nanocomposites. UV-Vis spectroscopy results show an increase of the optical band gap for graphene oxide whereas decrease for reduced graphene oxide dispersed system. Impedance spectroscopy is used for the determination of various parameters such as permittivity, dielectric anisotropy, conductivity, relaxation frequency and activation energy. Results show that the dielectric anisotropy is increased for graphene oxide dispersed nanocomposite, however, reduced graphene oxide dispersed system demonstrates the opposite property. Relaxation frequency has increased for graphene oxide dispersed system while unchanged for reduced graphene oxide dispersed system. Conductivity of reduced graphene oxide dispersed nanocomposite has increased by three orders of magnitude but for graphene oxide dispersed system, it has decreased as compared to that of the pure sample. We observed decrease in threshold voltage, elastic constant, and rotational viscosity for both GO/rGO dispersed systems. The outcome for the graphene oxide dispersed nanocomposite looks to be more effective due to the system’s enhanced molecular polarisability.

Investigation of hetero gate oxide hetero stacked triple metal vertical tunnel FET with variable interface trap charges and temperature

The performance of the hetero gate oxide hetero stacked triple metal vertical tunnel FET (HGO-HS-TMG V-TFET) in both dc and analog/RF is examined in this work. GaSb (a low bandgap material) and Si are layered in the source area. The reliability of the device is also examined by analyzing the consequence of interface trap charges (ITC) like donor (positive ITC) and acceptor (negative ITC) at diverse temperature values on DC, analog/RF and linearity performance of the device by dint of Silvaco ATLAS. Simulation shows Shockley-Read-Hall (SRH) phenomena predominate at reduced gate voltage, causing IOFF deterioration that, at high temperatures, results in ION/IOFF degradation. Whereas the band-to-band tunneling (BTBT) phenomenon—which is weakly influenced by temperature changes—is common at high gate voltages. As a result, IOFF degrades at elevated temperatures about a magnitude of 102, going from 10−19 A (200 K) to 10−17 A (400 K). Additionally, at elevated temperature values, it becomes apparent that the cut-off frequency (fT) increases and the threshold voltage (Vth) decreases, which leads to an improvement in device performance. Moreover, ITC alters flat band voltage and gate control, which impacts the device's performance. Device performance is improved when ITC is positive, while it is decreased when ITC is negative.

Single event transient of SOI FinFET with total ionizing dose irradiation

Total ionizing dose (TID) irradiation impacts the device leakage currents or threshold voltage, which affects the single event transient (SET) vulnerability of electronics under radiation environment. SET response of SOI FinFET at 14 nm technology node after TID exposure is carried out at different dose level. Results show that the drain current peak presents a slight fluctuant with total dose, while the collected charge and the bipolar amplification coefficient first decrease with total dose and then increase. The potential reason is also discussed from competing mechanisms associated with decreasing threshold voltage from TID irradiation and increasing the drain diffuse current from the potential of the channel.

Enhancement in Performance and Reliability of Transparent IGZO Thin-Film Transistors by ITO/Ti Stacked Source/Drain Contacts

Enhancement in performance and reliability of transparent IGZO thin-film transistor (TFT) was achieved by adopting a laminated structure with a thin ITO layer and an ultrathin Ti layer as the source/drain (S/D) contacts. Compared with the transparent TFT with pure ITO S/D contacts, the transparent TFT with the ITO/Ti S/D contacts showed three times of enhancement in field-effect mobility from 4.75 to 12.10 cm2/Vs, two times of enhancement in on/off current ratio from 7.0 × 107 to 1.54 × 108, three times of reduction in contact resistance from 15.74 to 4.64 kΩ, and a decrease in threshold voltage from 3.11 V to 2.80 V. The TFT with the ITO/Ti S/D contacts also maintained an extremely low leakage current at zero gate bias (for the device with channel width/channel length of 40 μm/5 μm, the leakage current was ∼1 × 10−13 A). In addition, the TFT with the ITO/Ti S/D contacts showed a hump-free transfer curve and a smaller shift in threshold voltage under negative bias illumination stress. The enhancement in performance and reliability makes the transparent TFT with the ITO/Ti S/D contacts very promising in transparent display applications.

Impact Analysis of Off-State Avalanche-Breakdown Stress on 650 V-Class Superjunction MOSFET

In this work, the reliability degradation of a 650 V-class superjunction (SJ) MOSFET under continuous violent OFF-state avalanche-breakdown stress is studied. Decreased threshold voltage and increasing saturation current have been observed which are attributed to the injection of hot holes below the trench bottom into the gate oxide layer. High-energy electrons and holes are generated under OFF-state avalanche stress leading to accelerated and violent collision ionization. The body diode suffers from severe avalanche breakdown leading to heat generation by collision ionization. In addition, the injection of hot holes is further enhanced with the assistance of the electrical field at the bottom of the gate. These phenomena are further analyzed by experimental characterizations and theoretical simulation using TCAD tools. Our comprehensive study on the reliability degradation behaviors of SJ devices under OFF-state avalanche-breakdown stress can be instructive in future device optimization and failure analysis.

Structure and electronic properties of thin Ge2Sb2Te5 films produced by DC ion-plasma spattering

The optical properties of Ge2Sb2Te5 thin films were studied as a function of thickness. An increase in optical band gap with decreasing film thickness has been observed. The current– voltage characteristics measured in Ge2Sb2Te5 thin films in the current mode are studied. A decrease in switching time and threshold voltage with decreasing film thickness is established.

AlN/AlGaN/AlN quantum well channel HEMTs

We present a compositional dependence study of electrical characteristics of AlxGa1−xN quantum well channel-based AlN/AlGaN/AlN high electron mobility transistors (HEMTs) with x=0.25,0.44, and 0.58. This ultra-wide bandgap heterostructure is a candidate for next-generation radio frequency and power electronics. The use of selectively regrown n-type GaN Ohmic contacts results in contact resistance that increases as the Al content of the channel increases. The DC HEMT device characteristics reveal that the maximum drain current densities progressively reduce from 280 to 30 to 1.7 mA/mm for x=0.25,0.44, and 0.58, respectively. This is accompanied by a simultaneous decrease (in magnitude) in threshold voltage from −5.2 to −4.9 to −2.4 V for the three HEMTs. This systematic experimental study of the effects of Al composition x on the transistor characteristics provides valuable insights for engineering AlGaN channel HEMTs on AlN for extreme electronics at high voltages and high temperatures.

Effect of oxygen plasma on ITO surface and OLED physical properties

In this study, we treated the surface of indium tin oxide (ITO) with oxygen plasma. In doing so, ITO thin films were exposed to oxygen plasma. This treatment was performed with plasma oxygen at 4, 6, and 8 min. The ITOs were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and ultraviolet-visible (UV–vis) spectroscopy. These characterizations showed that the structure and transparency were only slightly changed by the treatment. However, the plasma treatment improved the surface morphology and changed the thickness and electrical properties of the ITOs. The surface roughness of the ITOs was reduced from 2.34 to 0.899 nm by the treatment. With an 8-min plasma treatment, the strength of the sheet without ITO treatment increased from 12.61 to 13.97 Ω/□.The organic light-emitting diodes (OLEDs) with glass/ITO/PEDOT:PSS/Alq3/Al structure were fabricated. Characterization of the OLEDs showed a decrease in threshold voltage (from 5.7 to 3.53 v), a decrease in resistance, and an increase in irradiance intensity due to plasma treatment.

Morphological, dielectric, electro-optic and photoluminescence properties of titanium oxide nanoparticles enriched polymer stabilized cholesteric liquid crystal composites

Herein, TiO2 nanoparticles (NPs) dispersed polymer stabilized cholesteric liquid crystal (PSCLC) composites are prepared and studied. Effect of TiO2 NPs doping in varying concentration into PSCLC, on the phases, molecular states, dielectric, electro-optic and photoluminescence properties are investigated in studied samples. The morphological studies reveal that the TiO2 NPs are responsible to switch the orientation of liquid crystal molecules into homeotropic state at a lower voltage. The permittivity reduced from 9.62 to 7.75 at an optimum doping amount (0.5 wt%) of TiO2 NPs. At this concentration, an improvement in dielectric anisotropy was found. A decrease in threshold voltage from 3.2 V to 1.4 V was observed. Further, the saturation voltage also decreases from 10.5 V to 7.5 V at 0.5 wt% doped TiO2 NPs. The photoluminescence intensity increase with TiO2 NPs concentration however emission wavelength does not change. This work may provide a facile approach to fabricate the low energy consumption based electro-optical devices with the affordable and eco-friendly nature of TiO2 NPs.

Adaptif eşik temelli az karmaşık QRS algılama algoritması

In this study, a QRS detection algorithm with a low processing load based on time-domain thresholding is proposed. The ECG signal is filtered only with a low pass filter to reduce the computational load. After the filtering, derivation and squaring are also performed. In the Thresholding stage, a linear decreasing threshold voltage method using addition operation instead of multiplication is proposed. Simulations on MIT-BIT Arrhythmia Database have yielded 99.2925% sensitivity (% Se) and 99.6759% positive predictivity (+ P). The proposed algorithm is compared with two similar algorithms in terms of both performance and processing load. It is shown that the proposed algorithm is better than its counterparts, especially in terms of processing load. However, it is observed that it gave worse results in terms of Sensitivity (% Se).

SWITCHING EFFECT IN COMPOUNDS InGaSe2 AND InGaTe2

The presented work presents the results of studying the current-voltage characteristics of ternary compounds of the type, crystallizing in the tetragonal syngony, at various temperatures in a static mode. It was found that the compounds InGaSe2, InGaTe2 have switching properties with memory. With increasing temperature, the threshold voltage decreases and the most pronounced S-shaped characteristics are observed at low temperatures. It is shown that an obligatory condition for the appearance of negative resistance in the investigated phases is the existence of an additional mechanism of increase in the conductivity of the base region that accompanies injection. During injection, physical processes occur that lead either to an increase in the penetration depth of injected carriers, or to an additional increase in their concentration at each point, or to an increase in the proportion of injected carriers in the total p-n junction current. It was found that at low voltages across the diode, the base resistance is high and almost all of the applied voltage drops across it. As the voltage increases, the concentration of injected carriers in the base increases and its resistance decreases. Therefore, as the current increases, the total voltage increases. The current is a monotonic function of the applied voltage. This leads to a decrease in the share of the voltage drop at the base, which leads to amplification and a new redistribution of voltage between the base and the p-n junction. This is the positive feedback necessary for the appearance of negative resistance. Thus, in ternary semiconductors of the type, the obligatory conditions for the appearance of negative resistance are the existence of an additional mechanism of an increase in the conductivity of the base region that accompanies injection.

Degradation Behavior and Mechanism of SiC Power MOSFETs Under Repetitive Transmission Line Pulse Stress

The electrostatic discharge robustness of silicon carbide (SiC) power metal–oxide–semiconductor field-effect transistors (MOSFETs) are investigated by the transmission line pulse (TLP) method. The degradation behavior of key electrical parameters of the device under repetitive TLP stress is investigated. A decrease in threshold voltage, an increase in gate leakage current, and the degradation of gate capacitance parameters are observed compared with the prestress values. Low-frequency noise (LFN) test results show that after multiple TLP stress cycles, the typical leakage current noise of the device increases by approximately one order of magnitude compared to prestress, which means that the trap density extracted based on the McWhorter model increases by one order of magnitude after 1000 TLP stress pulses. Furthermore, sources of defects in the gate oxide dielectric of the devices after stresses are analyzed. The physical mechanism of the changes of SiC MOSFETs characteristics could be attributed to the hole trapping by oxygen vacancy defects and single carbon interstitial in the oxide layer after TLP stresses, which induces an electrostatic effect and results in the changes in the electrical properties of the devices. The results may be useful in the design and application of SiC power MOSFETs.

LCINDEP: a novel technique for leakage reduction in FinFET based circuits

Due to the continuous downsizing of metal oxide semi-conductor field effect transistor devices, power dissipation is one of the vital issues for the integrated circuit design. As a result of voltage scaling at lower technology nodes, threshold voltage decreases which results in increase in leakage current, hence leads to increase in leakage power dissipation. In this paper, a novel low leakage technique called LCINDEP (leakage control input DEPendent) is proposed for nano-scaled circuits. The device characteristics and hence overall performance gets affected due to increased power dissipation. Proposed LCINDEP technique is extensively demonstrated for low power operation and reliability analysis. Various short gate (SG) fin type field effect transistor (FinFET) logic circuits are simulated using LCINDEP technique and comparative analysis is performed with the already available leakage reduction techniques. The proposed LCINDEP technique provides reduced leakage power by 89.71% and 91.92% in LCINDEP SG FinFET NAND and NOR gates respectively with respect to the conventional SG FinFET NAND and NOR gates. Besides this benchmark circuits like ring oscillator and ISCAS-85 C17 show decrease in power dissipation by 24.75% and 35.5% respectively with LCINDEP technique in respect to the conventional FinFET circuits. Reliability analysis in terms of process voltage and temperature variations is performed using Monte Carlo Approach for 5000 samples, which also depicts that proposed LCINDEP technique is more reliable than the available low power techniques. The normalized standard deviations (σ/µ)% is improved by 54.68% and 43.93% for power delay product metric in the proposed technique compared to the conventional one for SG FinFET NAND and NOR gates respectively. All the simulations are performed at 16 nm technology node for FinFET logic devices using predictive technology model multigate based on BSIM-CMG on HSPICE tool.

A quantum dot crossbar with sublinear scaling of interconnects at cryogenic temperature

We demonstrate a 36 × 36 gate electrode crossbar that supports 648 narrow-channel field effect transistors (FET) for gate-defined quantum dots, with a quadratic increase in quantum dot count upon a linear increase in control lines. The crossbar is fabricated on an industrial 28Si-MOS stack and shows 100% FET yield at cryogenic temperature. We observe a decreasing threshold voltage for wider channel devices and obtain a normal distribution of pinch-off voltages for nominally identical tunnel barriers probed over 1296 gate crossings. Macroscopically across the crossbar, we measure an average pinch-off of 1.17 V with a standard deviation of 46.8 mV, while local differences within each unit cell indicate a standard deviation of 23.1 mV. These disorder potential landscape variations translate to 1.2 and 0.6 times the measured quantum dot charging energy, respectively. Such metrics provide means for material and device optimization and serve as guidelines in the design of large-scale architectures for fault-tolerant semiconductor-based quantum computing.

Investigation of total ionizing dose effects in 4H–SiC power MOSFET under gamma ray radiation

In this work, the gamma ray radiation-induced total ionizing dose (TID) effects in SiC power MOSFETs are investigated. The transistor characteristics, such as transfer curve, output curve, drain-source ON-state resistance and terminal capacitance, are characterized to quantify the radiation tolerance. The threshold voltage is found to be sensitive to radiation and decreases with radiation dose increasing. An increased drive current and decreased drain-source ON-state resistance are resulted due to the decreased threshold voltage. The increased gate input capacitance exists after radiation. Verified in Sentaurus TCAD 2D simulation, the radiation-induced trap charge and interface states at SiO2/SiC interface are found to dominate the degradation of electrical behaviors in SiC power MOSFET.