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Eliot Quataert - One of the best experts on this subject based on the ideXlab platform.
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suppressed heat conductivity in the intracluster medium implications for the magneto Thermal Instability
Monthly Notices of the Royal Astronomical Society, 2021Co-Authors: Eliot Quataert, Thomas Berlok, Martin E Pessah, Christoph PfrommerAbstract:In the outskirts of the intracluster medium (ICM) in galaxy clusters, the temperature decreases with radius. Due to the weakly collisional nature of the plasma, these regions are susceptible to the magneto-Thermal Instability (MTI), which can sustain turbulence and provide turbulent pressure support in the ICM. This Instability arises due to heat conduction directed along the magnetic field, with a heat conductivity which is normally assumed to be given by the Spitzer value. Recent numerical studies of the ion mirror and the electron whistler Instability using particle-in-cell codes have shown that microscale instabilities can lead to a reduced value for the heat conductivity in the ICM. This could in turn influence the efficiency with which the MTI drives turbulence. In this paper we investigate the influence of reduced heat transport on the nonlinear evolution of the MTI by employing a subgrid model that mimics the influence of the mirror Instability on the heat conductivity. We use this subgrid model to assess the effect of microscales on the large scale dynamics of the ICM. We find that the nonlinear saturation of the MTI is surprisingly robust. Over a factor of $\sim 10^3$ the Thermal-to-magnetic pressure ratio and collisionality we find at most modest changes to the saturation of the MTI with respect to reference simulations where heat transport is unsuppressed.
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Thermal Instability in the cgm of l galaxies testing precipitation models with the fire simulations
Monthly Notices of the Royal Astronomical Society, 2021Co-Authors: Clarke J Esmerian, Eliot Quataert, Andrey V Kravtsov, Zachary Hafen, Claude Andre Fauchergiguere, Jonathan Stern, Dusan Keres, Andrew WetzelAbstract:Author(s): Esmerian, Clarke J; Kravtsov, Andrey V; Hafen, Zachary; Faucher-Giguere, Claude-Andre; Quataert, Eliot; Stern, Jonathan; Keres, Dusan; Wetzel, Andrew | Abstract: ABSTRACT We examine the thermodynamic state and cooling of the low-z circumgalactic medium (CGM) in five FIRE-2 galaxy formation simulations of Milky Way-mass galaxies. We find that the CGM in these simulations is generally multiphase and dynamic, with a wide spectrum of largely non-linear density perturbations sourced by the accretion of gas from the intergalactic medium (IGM) and outflows from both the central and satellite galaxies. We investigate the origin of the multiphase structure of the CGM with a particle-tracking analysis and find that most of the low-entropy gas has cooled from the hot halo as a result of Thermal Instability triggered by these perturbations. The ratio of cooling to free-fall time-scales tcool/tff in the hot component of the CGM spans a wide range of ∼1−100 at a given radius but exhibits approximately constant median values of ∼5−20 at all radii 0.1Rvir l r l Rvir. These are similar to the ≈10−20 value typically adopted as the Thermal Instability threshold in ‘precipitation’ models of the ICM. Consequently, a one-dimensional model based on the assumption of a constant tcool/tff and hydrostatic equilibrium approximately reproduces the number density and entropy profiles of each simulation but only if it assumes the metallicity profile and temperature boundary condition taken directly from the simulation. We explicitly show that the tcool/tff value of a gas parcel in the hot component of the CGM does not predict its probability of subsequently accreting on to the central galaxy. This suggests that the value of tcool/tff is a poor predictor of Thermal stability in gaseous haloes in which large-amplitude density perturbations are prevalent.
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Thermal Instability of Halo Gas Heated by Streaming Cosmic Rays
arXiv: Astrophysics of Galaxies, 2019Co-Authors: Philipp Kempski, Eliot QuataertAbstract:Heating of virialized gas by streaming cosmic rays (CRs) may be energetically important in galaxy halos, groups and clusters. We present a linear Thermal stability analysis of plasmas heated by streaming CRs. We separately treat equilibria with and without background gradients, and with and without gravity. We include both CR streaming and diffusion along the magnetic-field direction. Thermal stability depends strongly on the ratio of CR pressure to gas pressure, which determines whether modes are isobaric or isochoric. Modes with $\mathbf{k \cdot B }\neq 0$ are strongly affected by CR diffusion. When the streaming time is shorter than the CR diffusion time, Thermally unstable modes (with $\mathbf{k \cdot B }\neq 0$) are waves propagating at a speed $\propto$ the Alfven speed. Halo gas in photoionization equilibrium is Thermally stable independent of CR pressure, while gas in collisional ionization equilibrium is unstable for physically realistic parameters. In gravitationally stratified plasmas, the oscillation frequency of Thermally overstable modes can be higher in the presence of CR streaming than the buoyancy/free-fall frequency. This may modify the critical $t_{\rm cool}/t_{\rm ff}$ at which multiphase gas is present. The criterion for convective Instability of a stratified, CR-heated medium can be written in the familiar Schwarzschild form $d s_{\rm eff} / d z < 0$, where $s_{\rm eff}$ is an effective entropy involving the gas and CR pressures. We discuss the implications of our results for the Thermal evolution and multiphase structure of galaxy halos, groups and clusters.
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Thermal Instability and the feedback regulation of hot haloes in clusters groups and galaxies
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Prateek Sharma, Eliot Quataert, Michael Mccourt, Ian J ParrishAbstract:We present global multidimensional numerical simulations of the plasma that pervades the dark matter haloes of clusters, groups and massive galaxies (the ‘intracluster medium’; ICM). Observations of clusters and groups imply that such haloes are roughly in global Thermal equilibrium, with heating balancing cooling when averaged over sufficiently long time- and length-scales; the ICM is, however, very likely to be locally Thermally unstable. Using simple observationally motivated heating prescriptions, we show that local Thermal Instability (TI) can produce a multiphase medium – with ∼ 104 K cold filaments condensing out of the hot ICM – only when the ratio of the TI time-scale in the hot plasma (tTI) to the free-fall time-scale (tff) satisfies tTI/tff≲ 10. This criterion quantitatively explains why cold gas and star formation are preferentially observed in low-entropy clusters and groups. In addition, the interplay among heating, cooling and TI reduces the net cooling rate and the mass accretion rate at small radii by factors of ∼ 100 relative to cooling-flow models. This dramatic reduction is in line with observations. The feedback efficiency required to prevent a cooling flow is ∼ 10−3 for clusters and decreases for lower mass haloes; supernova heating may be energetically sufficient to balance cooling in galactic haloes. We further argue that the ICM self-adjusts so that tTI/tff≳ 10 at all radii. When this criterion is not satisfied, cold filaments condense out of the hot phase and reduce the density of the ICM. These cold filaments can power the black hole and/or stellar feedback required for global Thermal balance, which drives tTI/tff≳ 10. In comparison to clusters, groups have central cores with lower densities and larger radii. This can account for the deviations from self-similarity in the X-ray luminosity–temperature () relation. The high-velocity clouds observed in the Galactic halo can be due to local TI producing multiphase gas close to the virial radius if the density of the hot plasma in the Galactic halo is >rsim 10−5 cm−3 at large radii.
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Thermal Instability in gravitationally stratified plasmas implications for multiphase structure in clusters and galaxy haloes
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Michael Mccourt, Prateek Sharma, Eliot Quataert, Ian J ParrishAbstract:We study the interplay among cooling, heating, conduction and magnetic fields in gravitationally stratified plasmas using simplified, plane-parallel numerical simulations. Since the physical heating mechanism remains uncertain in massive haloes such as groups or clusters, we adopt a simple, phenomenological prescription which enforces global Thermal equilibrium and prevents a cooling flow. The plasma remains susceptible to local Thermal Instability, however, and cooling drives an inward flow of material. For physically plausible heating mechanisms in clusters, the Thermal stability of the plasma is independent of its convective stability. We find that the ratio of the cooling time-scale to the dynamical time-scale tcool/tff controls the non-linear evolution and saturation of the Thermal Instability: when tcool/tff≲ 1, the plasma develops extended multiphase structure, whereas when tcool/tff≳ 1 it does not. (In a companion paper, we show that the criterion for Thermal Instability in a more realistic, spherical potential is somewhat less stringent, tcool/tff≲ 10.) When Thermal conduction is anisotropic with respect to the magnetic field, the criterion for multiphase gas is essentially independent of the Thermal conductivity of the plasma. Our criterion for local Thermal Instability to produce multiphase structure is an extension of the cold versus hot accretion modes in galaxy formation that applies at all radii in hot haloes, not just to the virial shock. We show that this criterion is consistent with data on multiphase gas in galaxy groups and clusters; in addition, when tcool/tff≳ 1, the net cooling rate to low temperatures and the mass flux to small radii are suppressed enough relative to models without heating to be qualitatively consistent with star formation rates and X-ray line emission in groups and clusters.
D L Kwong - One of the best experts on this subject based on the ideXlab platform.
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Thermal Instability of effective work function in metal high spl kappa stack and its material dependence
IEEE Electron Device Letters, 2004Co-Authors: Moon Sig Joo, Byung Jin Cho, N Balasubramanian, D L KwongAbstract:Thermal Instability of effective work function and its material dependence on metal/high-/spl kappa/ gate stacks is investigated. It is found that Thermal Instability of the effective work function of metal electrode on a gate dielectric is strongly dependent on the gate electrode and dielectric material. Thermal Instability of a metal gate is related to the presence of silicon at the interface, and the Fermi-level pinning position is dependent on the location of silicon at the interface. The silicon-metal or metal-silicon bond formation by Thermal anneal at the metal/dielectric interface induces the donor-like or acceptor-like interface states, causing a change of effective work function.
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fermi level pinning induced Thermal Instability in the effective work function of tan in tan sio sub 2 gate stack
IEEE Electron Device Letters, 2004Co-Authors: Haoyong Yu, D.s.h. Chan, Jinfeng Kang, M F Li, W D Wang, D L KwongAbstract:In this letter, we demonstrate for the first time that the Fermi-level pinning caused by the formation of Ta(N)-Si bonds at the TaN/SiO/sub 2/ interface is responsible for the Thermal Instability of the effective work function of TaN in TaN/SiO/sub 2/ devices after high temperature rapid Thermal annealing (RTA). Because of weak charge transfer between Hf and Ta(N) and hence negligible pinning effect at the TaN/HfO/sub 2/ interface, the effective work function of TaN is significantly more Thermally stable on HfO/sub 2/ than on SiO/sub 2/ dielectric during RTA. This finding provides a guideline for the work function tuning and the integration of metal gate with high-/spl kappa/ dielectric for advanced CMOS devices.
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Fermi pinning-induced Thermal Instability of metal-gate work functions
IEEE Electron Device Letters, 2004Co-Authors: H Y Yu, J.f. Kang, X.p. Wang, D.s.h. Chan, Ming-fu Li, D L KwongAbstract:The dependence of the metal-gate work function on the annealing temperature is experimentally studied. We observe increased Fermi-level pinning of the metal-gate work function with increased annealing temperature. This effect is more significant for SiO/sub 2/ than for HfO/sub 2/ gate dielectric. A metal-dielectric interface model that takes the role of extrinsic states into account is proposed to explain the work function Thermal Instability. This letter provides new understanding on work function control for metal-gate transistors and on metal-dielectric interfaces.
P Spirito - One of the best experts on this subject based on the ideXlab platform.
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electro Thermal Instability in multi cellular trench igbts in avalanche condition experiments and simulations
International Symposium on Power Semiconductor Devices and IC's, 2011Co-Authors: Michele Riccio, Giovanni Breglio, P Spirito, Andrea Irace, E Napoli, Yoshihito MizunoAbstract:This paper reports on the results of a study on electro-Thermal Instability induced in multi-cellular Trench-IGBTs in avalanche condition. Experimental measurements, made on T-IGBTs, show possible inhomogeneous current distribution under Unclamped Inductive Switching (UIS) confirmed by transient infrared thermography measurements. Together with this, an analytical modeling of avalanche behavior has been included in a compact electro-Thermal simulator to study the interaction between a large numbers of elementary cells of T-IGBTs forced in avalanche condition. Electro-Thermal simulations qualitatively replicate the possible inhomogeneous operation observed experimentally. Finally a possible theoretical interpretation of the Instability in avalanche condition for T-IGBT is given.
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analytical model for Thermal Instability of low voltage power mos and soa in pulse operation
International Symposium on Power Semiconductor Devices and IC's, 2002Co-Authors: P Spirito, Giovanni Breglio, Vincenzo Dalessandro, N RinaldiAbstract:Thermal Instability presented by some high current power MOS has been shown to limit significantly the SOA capability. In this paper, we present a new analytical model to explain this type of Instability in transient operation, based on an analytical formulation for both the positive temperature coefficient of the drain current and for the Thermal resistance. The model is capable of predicting the onset of Thermal Instability for a given device structure and layout, and can be used both to define the allowed SOA of the device and as a design guide to design more rugged devices.
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electro Thermal Instability in low voltage power mos experimental characterization
International Symposium on Power Semiconductor Devices and IC's, 1999Co-Authors: G Breglio, F Frisina, Angelo Magri, P SpiritoAbstract:In this paper, we present experimental results of dynamic Thermal mapping on a new class of low voltage high current power MOSFETs. The reported results underline that, as in the case of power BJTs, the hot-spot phenomenon also occurs in this class of devices. Moreover, we give a theoretical interpretation of this phenomenon and propose a novel approach to understand the causes that can determine the temperature instabilities in such MOS devices.
Prateek Sharma - One of the best experts on this subject based on the ideXlab platform.
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shatter or not role of temperature and metallicity in the evolution of Thermal Instability
Monthly Notices of the Royal Astronomical Society, 2021Co-Authors: Hitesh Kishore Das, Prakriti Pal Choudhury, Prateek SharmaAbstract:We test how metallicity variation (a background gradient and fluctuations) affects the physics of local Thermal Instability using analytical calculations and idealized, high-resolution 1D hydrodynamic simulations. Although the cooling function ($\Lambda[T,Z]$) and the cooling time ($t_{\rm cool}$) depend on gas temperature and metallicity, we find that the growth rate of Thermal Instability is explicitly dependent only on the derivative of the cooling function relative to temperature ($\partial \ln \Lambda/\partial \ln T$) and not on the metallicity derivative ($\partial \ln \Lambda/ \partial \ln Z$). For most of $10^4~{\rm K} \lesssim T \lesssim 10^7~{\rm K}$, both the isobaric and isochoric modes (occurring at scales smaller and larger than the sonic length covered in a cooling time [$c_s t_{\rm cool}$], respectively) grow linearly, and at higher temperatures ($\gtrsim 10^7~{\rm K}$) the isochoric modes are stable. We show that even the nonlinear evolution depends on whether the isochoric modes are linearly stable or unstable. For the stable isochoric modes, we observe the growth of small-scale isobaric modes but this is distinct from the nonlinear fragmentation of a dense cooling region. For unstable isochoric perturbations we do not observe large density perturbations at small scales. While very small clouds ($\sim {\rm min}[c_st_{\rm cool}]$) form in the transient state of nonlinear evolution of the stable isochoric Thermal Instability, most of them merge eventually.
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Thermal Instability and the feedback regulation of hot haloes in clusters groups and galaxies
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Prateek Sharma, Eliot Quataert, Michael Mccourt, Ian J ParrishAbstract:We present global multidimensional numerical simulations of the plasma that pervades the dark matter haloes of clusters, groups and massive galaxies (the ‘intracluster medium’; ICM). Observations of clusters and groups imply that such haloes are roughly in global Thermal equilibrium, with heating balancing cooling when averaged over sufficiently long time- and length-scales; the ICM is, however, very likely to be locally Thermally unstable. Using simple observationally motivated heating prescriptions, we show that local Thermal Instability (TI) can produce a multiphase medium – with ∼ 104 K cold filaments condensing out of the hot ICM – only when the ratio of the TI time-scale in the hot plasma (tTI) to the free-fall time-scale (tff) satisfies tTI/tff≲ 10. This criterion quantitatively explains why cold gas and star formation are preferentially observed in low-entropy clusters and groups. In addition, the interplay among heating, cooling and TI reduces the net cooling rate and the mass accretion rate at small radii by factors of ∼ 100 relative to cooling-flow models. This dramatic reduction is in line with observations. The feedback efficiency required to prevent a cooling flow is ∼ 10−3 for clusters and decreases for lower mass haloes; supernova heating may be energetically sufficient to balance cooling in galactic haloes. We further argue that the ICM self-adjusts so that tTI/tff≳ 10 at all radii. When this criterion is not satisfied, cold filaments condense out of the hot phase and reduce the density of the ICM. These cold filaments can power the black hole and/or stellar feedback required for global Thermal balance, which drives tTI/tff≳ 10. In comparison to clusters, groups have central cores with lower densities and larger radii. This can account for the deviations from self-similarity in the X-ray luminosity–temperature () relation. The high-velocity clouds observed in the Galactic halo can be due to local TI producing multiphase gas close to the virial radius if the density of the hot plasma in the Galactic halo is >rsim 10−5 cm−3 at large radii.
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Thermal Instability in gravitationally stratified plasmas implications for multiphase structure in clusters and galaxy haloes
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Michael Mccourt, Prateek Sharma, Eliot Quataert, Ian J ParrishAbstract:We study the interplay among cooling, heating, conduction and magnetic fields in gravitationally stratified plasmas using simplified, plane-parallel numerical simulations. Since the physical heating mechanism remains uncertain in massive haloes such as groups or clusters, we adopt a simple, phenomenological prescription which enforces global Thermal equilibrium and prevents a cooling flow. The plasma remains susceptible to local Thermal Instability, however, and cooling drives an inward flow of material. For physically plausible heating mechanisms in clusters, the Thermal stability of the plasma is independent of its convective stability. We find that the ratio of the cooling time-scale to the dynamical time-scale tcool/tff controls the non-linear evolution and saturation of the Thermal Instability: when tcool/tff≲ 1, the plasma develops extended multiphase structure, whereas when tcool/tff≳ 1 it does not. (In a companion paper, we show that the criterion for Thermal Instability in a more realistic, spherical potential is somewhat less stringent, tcool/tff≲ 10.) When Thermal conduction is anisotropic with respect to the magnetic field, the criterion for multiphase gas is essentially independent of the Thermal conductivity of the plasma. Our criterion for local Thermal Instability to produce multiphase structure is an extension of the cold versus hot accretion modes in galaxy formation that applies at all radii in hot haloes, not just to the virial shock. We show that this criterion is consistent with data on multiphase gas in galaxy groups and clusters; in addition, when tcool/tff≳ 1, the net cooling rate to low temperatures and the mass flux to small radii are suppressed enough relative to models without heating to be qualitatively consistent with star formation rates and X-ray line emission in groups and clusters.
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Thermal Instability the feedback regulation of hot halos in clusters groups and galaxies
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Prateek Sharma, Eliot Quataert, Michael Mccourt, Ian J ParrishAbstract:Observations of clusters and groups imply that such halos are roughly in global Thermal equilibrium, with heating balancing cooling when averaged over sufficiently long time- and length-scales; the ICM is, however, very likely to be locally Thermally unstable. Using simple observationally-motivated heating prescriptions, we show that local Thermal Instability (TI) can produce a multi-phase medium---with ~ 10000 K cold filaments condensing out of the hot ICM---only when the ratio of the TI timescale in the hot plasma (t_{TI}) to the free-fall timescale (t_{ff}) satisfies t_{TI}/t_{ff} ~ 10 at all radii. When this criterion is not satisfied, cold filaments condense out of the hot phase and reduce the density of the ICM. These cold filaments can power the black hole and/or stellar feedback required for global Thermal balance, which drives t_{TI}/t_{ff} >~ 10. In comparison to clusters, groups have central cores with lower densities and larger radii. This can account for the deviations from self-similarity in the X-ray luminosity-temperature (L_X-T_X) relation. The high-velocity clouds observed in the Galactic halo can also be due to local TI producing multi-phase gas close to the virial radius.
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Thermal Instability in gravitationally stratified plasmas implications for multi phase structure in clusters and galaxy halos
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Michael Mccourt, Prateek Sharma, Eliot Quataert, Ian J ParrishAbstract:We study the interplay among cooling, heating, conduction, and magnetic fields in gravitationally stratified plasmas using simplified, plane-parallel numerical simulations. Since the physical heating mechanism remains uncertain in massive halos such as groups or clusters, we adopt a simple, observationally-motivated prescription which enforces global Thermal equilibrium when averaged over large scales. The plasma remains susceptible to local Thermal Instability, however, and cooling drives an inward flow of material. In contrast to previous results, we argue that the Thermal stability of the plasma is independent of its convective stability. We find that the ratio of the cooling timescale to the dynamical timescale t_cool/t_ff controls the saturation of the Thermal Instability: when t_cool/t_ff 1 it does not. (In a companion paper, we show that the criterion for Thermal Instability in a spherical potential is somewhat less stringent, t_cool / t_ff 1, the net cooling rate to low temperatures and the mass flux to small radii are suppressed enough relative to models without heating to be qualitatively consistent with star formation rates and x-ray line emission in groups and clusters.
A Magri - One of the best experts on this subject based on the ideXlab platform.
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Thermal Instability of low voltage power mosfets
IEEE Transactions on Power Electronics, 2000Co-Authors: A Consoli, F Gennaro, A Testa, G Consentino, Ferruccio Frisina, R Letor, A MagriAbstract:This paper analyzes an anomalous failure mechanism detected on last generation low voltage power metal oxide semiconductor (MOS) devices at low drain current. Such a behavior, apparently due to a kind of second breakdown phenomenon, has been scarcely considered in literature, as well as in manufacturer data sheets, although extensive experimental tests show that it is a common feature of modern low voltage metal oxide semiconductor held effect transistor (MOSFET) devices. The paper starts by analyzing some failures, systematically observed on low voltage power MOSFET devices, inside the theoretical forward biased safe operating area. Such failures are then related to an unexpected Thermal Instability of the considered devices. Experimental tests have shown that in the considered devices the temperature coefficient is positive for a very wide drain current range, also including the maximum value. Such a feature causes hot spot phenomena in the devices, as confirmed by microscope inspection of the failed devices. Finally, it is theoretically demonstrated that the Thermal Instability is a side effect of the progressive die size and process scaling down. As a result, latest power MOSFETs, albeit more efficient and compact, are less robust than older devices at low drain currents, thus requiring specific circuit design techniques.
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Thermal Instability of low voltage power mosfets
Power Electronics Specialists Conference, 1999Co-Authors: A Consoli, F Gennaro, A Testa, G Consentino, Ferruccio Frisina, R Letor, A MagriAbstract:Anomalous failures which occurred inside the theoretical forward biased safe operating area of the latest generation low voltage power MOS devices are reported and analyzed. The paper outlines how some technology improvements, while increasing the current capability, can induce Thermal Instability phenomena at low drain currents. It is demonstrated that the Thermal Instability is a side effect of the progressive scaling down. In the latest devices in fact, due to the high current capability, the rated current is obtained with a gate voltage very close to the threshold voltage. This affects the Thermal stability of modern low voltage power MOS devices that, although more efficient and compact, are less robust-leading to more effective circuit design techniques.
