Temperature Dependence Of Threshold Voltage Research Articles

Comparison of Temperature Dependent Carrier Transport in FinFET and Gate-All-Around Nanowire FET

The temperature dependent carrier transport characteristics of n-type gate-all-around nanowire field effect transistors (GAA NW-FET) on bulk silicon are experimentally compared to bulk fin field effect transistors (FinFET) over a wide range of temperatures (25–125 °C). A similar temperature dependence of threshold voltage (VTH) and subthreshold swing (SS) is observed for both devices. However, effective mobility (μeff) shows significant differences of temperature dependence between GAA NW-FET and FinFET at a high gate effective field. At weak Ninv (= 5 × 1012 cm2/V∙s), both GAA NW-FET and FinFET are mainly limited by phonon scattering in μeff. On the other hand, at strong Ninv (= 1.5 × 1013 cm2/V∙s), GAA NW-FET shows 10 times higher dμeff/dT and 1.6 times smaller mobility degradation coefficient (α) than FinFET. GAA NW-FET is less limited by surface roughness scattering, but FinFET is relatively more limited by surface roughness scattering in carrier transport.

Estimating Junction Temperature of SiC MOSFET Using Its Drain Current During Turn-On Transient

Silicon carbide metal–oxide–semiconductor field-effect transistor (SiC MOSFET) has become a promising device due to its excellent material properties. Junction temperature is an important parameter and a significant health index. In this article, drain current during turn-on transient is taken as the thermo-sensitive electrical parameter (TSEP) to monitor the junction temperature of SiC MOSFET. Based on the physical properties of wide bandgap semiconductor materials, the switching behaviors of SiC MOSFET and the variation of drain current with temperature were studied. The influence of temperature dependence of threshold voltage and carrier mobility on drain current is analyzed. It is proven that the drain current has a positive temperature coefficient during turn-on transient. Finally, the validity of the proposed method is verified by the theoretical analysis and experiments.

Voltage sweep direction-dependent metal-insulator transition in a single-crystalline VO2 nanobeam embedded in a insulating layer

We report the metal-insulator transition behavior of a single-crystalline VO2 nanobeam partially embedded in a insulating SiO2 layer in up-sweep (from low to high voltages) and down-sweep (from high to low bias voltages) directions of the applied voltage. Compared to the up-sweep voltage direction, the down-sweep voltage direction exhibited a more distinct jump in electrical resistance over a narrower temperature range upon heating. The temperature range at which an abrupt transition in the current-voltage characteristics occurred were relatively wider upon heating and cooling in the up-sweep direction. The threshold voltage on the up-sweep exponentially increased with decreasing temperature, indicating the possible collective motion of carriers, whereas the temperature dependence of threshold voltage on the down-sweep showed a linear relation, indicating Joule heating effects.

Investigation of temperature-dependent small-signal performances of TB SOI MOSFETs**Project supported by the National Natural Science Foundation of China (No. 61331006) and the National Defense Pre-Research Foundation of China (No. 9140A11040114DZ04152).

This paper investigated the temperature dependence of the cryogenic small-signal ac performances of multi-finger partially depleted (PD) silicon-on-insulator (SOI) metal oxide semiconductor field effect transistors (MOSFETs), with T-gate body contact (TB) structure. The measurement results show that the cut-off frequency increases from 78 GHz at 300 K to 120 GHz at 77 K and the maximum oscillation frequency increases from 54 GHz at 300 K to 80 GHz at 77 K, and these are mainly due to the effect of negative temperature dependence of threshold voltage and transconductance. By using a simple equivalent circuit model, the temperature-dependent small-signal parameters are discussed in detail. The understanding of cryogenic small-signal performance is beneficial to develop the PD SOI MOSFETs integrated circuits for ultra-low temperature applications.

Temperature-dependent electro-optical and elastic properties of carbon nanotube doped polar smectogen octylcyanobiphenyl

We present a detailed study of electro-optical and elastic properties of smectogen octylcyanobiphenyl (8CB) liquid crystal doped with well-dispersed multi-walled carbon nanotubes (MWCNTs). We report new experimental data for the temperature dependence of threshold voltage, dielectric anisotropy, splay elastic constant, and rotational viscosity of MWCNT doped 8CB samples. We have observed that the dielectric permittivity along the long molecular axis and the splay elastic constant decrease with increasing CNT content while the threshold voltage remains the same. Throughout nematic and smectic A phases, the incorporation of CNTs into 8CB has been observed to decrease the dielectric anisotropy, resulting in decreased orientational order. Through optical on and off response time measurements, we have documented that doping 8CB with CNTs results in slower optical relaxation and increased viscosity. Our experimental results directly evidence that CNT doping disturbs the orientational order in 8CB-CNT composites, as previously advocated based on calorimetric data.

Mechanisms of temperature dependence of threshold voltage in high-k/metal gate transistors with different TiN thicknesses

The change in temperature coefficient of the threshold voltage (=dVth/dT) for poly-Si/TiN/high-k gate insulator metal–oxide–semiconductor field-effect transistors (MOSFETs) was systematically investigated with respect to various TiN thicknesses for both n- and p-channel MOSFETs. With increasing TiN thickness, dVth/dT shifts towards negative values for both n- and p-MOSFETs. A mechanism that changes dVth/dT, depending on TiN thickness is proposed. The main origins are the work function of TiN (ΦTiN) and its temperature coefficient (dΦTiN/dT). These are revealed to change when decreasing the thickness of the TiN layer, because the crystallinity of the TiN layer is degraded for thinner films, which was confirmed by ultraviolet photoelectron spectroscopy (UPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD).

Temperature dependences of threshold voltage and drain-induced barrier lowering in 60 nm gate length MOS transistors

The temperature dependence of threshold voltage (VT) and drain-induced barrier lowering (DIBL) characteristics for MOS transistors fabricated with three different threshold voltage technologies are studied. We found that the technique employed to adjust the VT value make the devices to be not well-scaled for short-channel effects for ultra-short devices at low temperatures. For devices with a short gate length (L<90nm) and being fabricated using the low threshold voltage (low-VT) technology, both the temperature dependencies of threshold voltage and DIBL are different to the standard-VT and high-VT ones. Abnormally large values of DIBL were found for low VT-devices because of the significant encroachment of drain depletion region on the channel region. On the other hand, the high substrate doping in high-VT process makes the devices to have a larger junction depth than that used in the standard process. It causes a poorer DIBL for short-channel devices. Hence the best scaling or design of the devices at room temperature does not imply that they should also be good at low temperatures, especially for L=60nm fabricated using the low-VT process. Different device design and process optimization are required for devices to be operated at temperatures beyond the nominal range.

Design of a Sub-0.4 V Reference Circuit in 0.18μm CMOS Technology

This paper proposes a low power voltage reference generator in 0.18μm CMOS technology.The circuit presented here includes MOSFETs in sub threshold mode and uses the temperature dependence of threshold voltages and sub-threshold current of MOSFET to form a temperature-insensitive reference. An input supply voltage of 1.8 Volt is used for the circuit generating a total current of 1.33μA. By varying the device temperature over the range of-20°C to 100°C corresponding variation over the output voltage was found to lie in the range 397.8 to 400.2 mV. Thus a 0.6% variation in voltage over the considered range of temperature is obtained.

Understanding temperature dependence of threshold voltage in pentacene thin film transistors

Threshold voltage in the pentacene-based organic thin film transistors is found to be linearly increased with decreasing measuring temperature, indicating that the threshold voltage is dominated by the deep hole trapping in an approximately energy-independent trap distribution. The slope of threshold voltage vs temperature is greatly reduced at 200–210 K when temperature is decreased, corresponding to a reduction in the deep trap density. H2O confined in pentacene is considered as one of the sources of the deep hole traps, and the slope change in the temperature dependence of threshold voltage is attributed to the phase transition of supercooled H2O.

Study of the Electrophysical Properties of Composite Varistors Based on Zinc Oxide and Polymer (Polyaniline)

In this experimental work, current-voltage characteristics of composite varisrors prepared on the base of zinc oxide with different weight percentages of polyaniline and temperature dependence of the samples characteristics have been studied. The activation energy of donor levels as well as the existence of hysteresis loop has been investigated. The comparison of experimental results shows that by increasing the polymer percentage in the varistor structure as long as the nonlinear behavior is conserved, the threshold voltage increases. This comparison also indicates that increasing the polymer content in the varistor structure causes the temperature dependence of threshold voltage to decrease. It is also concluded that, by the increase of polymer content in the varistor structure, the activation energy of donor levels and the hysteresis value are increased.

Quantum mechanical effect in temperature dependence of threshold voltage of extremely thin SOI MOSFETs

This paper examines the temperature dependence of the threshold voltage ( V TH) of extremely thin fully depleted SOI MOSFETs with thickness under 10 nm over a wide range of temperatures (31–300 K). The calculated temperature dependence of V TH shift for devices with 10 or 6 nm thick SOI layers is compared to experimental results. Theory suggests that the energy quantization of electrons in the ultra-thin SOI layer strongly suppresses the temperature dependence of threshold voltage. This is partially supported by a comprehensive analysis of the experimental results.

Quantum mechanical effect in temperature dependence of threshold voltage of extremely thin SOI MOSFETs

This paper examines the temperature dependence of the threshold voltage ( V TH ) of extremely thin fully depleted SOI MOSFETs with thickness under 10 nm over a wide range of temperatures (31–300 K). The calculated temperature dependence of V TH shift for devices with 10 or 6 nm thick SOI layers is compared to experimental results. Theory suggests that the energy quantization of electrons in the ultra-thin SOI layer strongly suppresses the temperature dependence of threshold voltage. This is partially supported by a comprehensive analysis of the experimental results.

Temperature dependence of DTMOS transistor characteristics

The characteristics of SOI DTMOS transistors are measured at various temperatures and compared with those of partially depleted SOI MOSFETs. The temperature dependence of threshold voltage and subthreshold characteristics is investigated both theoretically and experimentally. DTMOS devices operating at elevated temperature are shown to have higher drive current and transconductance and a lower temperature dependence of threshold voltage and subthreshold characteristics than partially depleted SOI MOSFETs.

Relationship between channel mobility and interface state density in SiC metal–oxide–semiconductor field-effect transistor

Temperature dependence of threshold voltage in n-channel SiC metal–oxide–semiconductor field-effect transistors (MOSFETs) was studied. Linear relation was observed between the threshold voltage shift when the temperature varies from −150 to 150 °C and the number of the interface states present within the energy range of 0.2–0.4 eV from the conduction band edge energy Ec. This relationship revealed that the interface state profile near Ec in n-channel SiC MOSFETs can be represented by that in n-type SiC MOS capacitors. The relationship between the channel mobility and the interface state profile also suggested that the interface states within the energy range of 0.2–0.4 eV from Ec have little influence on the channel mobility.

A cause for highly improved channel mobility of 4H-SiC metal–oxide–semiconductor field-effect transistors on the (112̄0) face

4H-silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors fabricated on both (112̄0) and (0001) faces were characterized at various temperatures. From the temperature dependence of channel mobility, carrier transport in the inversion layer at the SiO2/4H-SiC(112̄0) interface was found to be affected by phonon scattering (μ0∼T−2.2), while that at the SiO2/4H-SiC(0001) interface was thermally activated (μ0∼T2.6) due to the decrease of Coulomb scattering by emission of electrons from acceptor-like interface states. From the temperature dependence of threshold voltage, the density of acceptor-like interface states near the conduction band edge seems to be low at the SiO2/4H-SiC(112̄0) interface, but quite high (&amp;gt;1013 cm−2 eV−1) at the SiO2/4H-SiC(0001) interface. The low density of acceptor-like interface states near the conduction band edge on the (112̄0) face should be the primary cause for the high inversion-channel mobility.

Physical and Electro-Optical Properties of New Nematic LC Mixtures for Highly Multiplexed TN-Displays

A set of new, blended nematic liquid crystal mixtures to improve the performance of highly multiplexed TN-displays are presented. The physical and electro-optical properties of new LC mixtures have been investigated, along with the frequency and temperature dependence of threshold voltage about newly developed liquid crystals. The multiplexable mixtures are completely miscible and can be blended, thus leading to new mixtures covering a wide range of threshold voltages 1.2 > V10 > 2.0 V, nematic-isotropic phase transition temperatures 60 > Tc > 100[ddot]C, and/or optical anisotropies 0.13>Δ n>0.18.

Temperature Dependence of Threshold Voltage of Metal-Semiconductor Field Effect Transistors in the Presence of an Uneven Distribution of Interface and Bulk States

The temperature dependence of threshold voltage of metal-semiconductor field effect transistors is studied considering a generalised interface state model and an uneven distribution of interface and bulk impurity states. The analysis predicts a sharp variation of threshold voltage with temperature which is in contrast to the conventionally known temperature dependence due to the band gap energy. The theoretical results are found in agreement with previous experimental findings.

Relationship between Molecular Structure and Temperature Dependence of Threshold Voltage in Fluorinated Liquid Crystals

We evaluate the temperature dependence of threshold voltage and physical constants (anisotropy of dielectric constants and elastic constants) by using fluorinated phenylbicyclohexane liquid crystal compounds. It is found that the positions of fluorine substituents influence the dielectric constant and its temperature dependence. A systematic relationship between the fluorine substituents and physical constants was obtained.

Temperature dependence of threshold voltage in thin-film SOI MOSFETs

A first-order model for the temperature dependence of threshold voltage in thin-film silicon-on-insulator (SOI) n-MOSFETs is described. The temperature dependence of the threshold voltage of thin-film SOI n-channel MOSFETs is analyzed. Threshold voltage variation with temperature is significantly smaller in thin-film (fully depleted) devices than in thick-film SOI and bulk devices. The threshold voltage is shown to be dependent on the depletion level of the device, i.e. whether it is fully depleted or not. There exists a critical temperature below which the device is fully depleted, and above which the device operates in the thick-film regime.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Temperature dependence of GaAs metal–semiconductor field effect transistor threshold voltage

We have investigated the temperature dependence of threshold voltage (Vth) of n-channel GaAs metal–semiconductor field effect transistors with different gate materials and structures. It is found that Vth increases by 0.3–0.4 V as temperature decreases from 350 to 80 K. The Vth versus temperature relationship is approximately linear. The amount of Vth shift is independent of channel length from 0.8 to 3 μm and it does not strongly depend on the gate material used. Similar Vth increases are observed for different channel doping methods, such as ion implantation and molecular-beam epitaxy growth. Different GaAs substrates only show a small effect on the Vth temperature dependence. Calculations show that Fermi-level shift and energy-gap expansion with decreasing temperature account for only a fraction of the observed change in Vth. Our measurements indicate that the extra Vth shift is not mainly due to deep-level traps within the channel. Results from C–V measurements on metal/GaAs diodes suggest that build-in voltage changes with temperature are principally responsible for the Vth shift.