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Journal ArticleDOI

Fully coupled thermoelectromechanical analysis of GaN high electron mobility transistor degradation

05 Apr 2012-Journal of Applied Physics (American Institute of Physics)-Vol. 111, Iss: 7, pp 074504
TL;DR: In this article, a fully coupled multi-dimensional continuum model of the thermoelectromechanics of GaN HEMTs is presented and discussed, and the possibilities of crack propagation and fracture of the AlGaN are also analyzed.
Abstract: A fully coupled multi-dimensional continuum model of the thermoelectromechanics of GaN HEMTs is presented and discussed. The governing equations are those of linear thermoelectroelasticity, diffusion-drift transport theory, and heat conduction, with full coupling assumed, i.e., all mechanical, electrical, and thermal variables are solved for simultaneously. Apart from the known strains induced by epitaxy, plane-strain conditions are assumed, so that two-dimensional simulation suffices. Important aspects of the model are that it incorporates “actual” device geometries and that it captures field/stress concentrations that often occur near material discontinuities and especially at corners. The latter are shown to be especially important with regards to understanding the mechanisms of both electrical and mechanical degradation in GaN HEMTs. Various possible contributors to degradation are discussed, including electron injection, the inverse piezoelectric effect, thermal stress, SiN intrinsic stress, and device geometry. The possibilities of crack propagation and fracture of the AlGaN are also analyzed.
Citations
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Journal ArticleDOI
TL;DR: In this article, a comprehensive review of AlGaN/GaN high electron mobility transistor failure physics and reliability is presented, focusing on mechanisms affecting the gate-drain edge, where maximum electric field and peak temperatures are reached.
Abstract: This paper presents a comprehensive review of AlGaN/GaN high electron mobility transistor failure physics and reliability, focusing on mechanisms affecting the gate-drain edge, where maximum electric field and peak temperatures are reached. Physical effects at the origin of device degradation (inverse piezoelectric effect, time-dependent trap formation and percolative conductive paths formation, and electrochemical AlGaN and GaN degradation) are discussed on the basis of literature data and unpublished results. Thermally activated mechanisms involving metal-metal and metal-semiconductor interdiffusion at the gate Schottky junction are also discussed.

127 citations


Cites methods from "Fully coupled thermoelectromechanic..."

  • ...[63], [64] have analyzed stress-related failure in GaN HEMTs using a fully-coupled, multidimensional electroelastic 2-D simulator....

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Journal ArticleDOI
TL;DR: In this paper, coupled electro-thermo-mechanical simulation and Raman thermometry were used to analyze the evolution of mechanical stress in AlGaN/GaN high electron mobility transistors (HEMTs).
Abstract: Coupled electro-thermo-mechanical simulation and Raman thermometry were utilized to analyze the evolution of mechanical stress in AlGaN/GaN high electron mobility transistors (HEMTs). This combined analysis was correlated with electrical step stress tests to determine the influence of mechanical stress on the degradation of actual devices under diverse bias conditions. It was found that the total stress as opposed to one dominant stress component correlated the best with the degradation of the HEMT devices. These results suggest that minimizing the total stress as opposed to the inverse piezoelectric stress in the device is necessary in order to avoid device degradation which can be accomplished through various growth methods.

55 citations

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E2 (high), A1 longitudinal optical (LO), and E 2 (low) optical phonon frequencies in wurtzite GaN.
Abstract: As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result in elevated device temperatures, degraded performance, and shorter lifetimes. Although micro-Raman spectroscopy has become one of the most popular techniques for measuring localized temperature rise in GaN HEMTs for reliability assessment, decoupling the effects of temperature, mechanical stress, and electric field on the optical phonon frequencies measured by micro-Raman spectroscopy is challenging. In this work, we demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E2 (high), A1 longitudinal optical (LO), and E2 (low) optical phonon frequencies in wurtzite GaN. We also validate experimentally that the pinched OFF state as the unpowered reference accurately measures the temperature rise by removing the effect of the vertical electric field on the Raman spectrum and that the vertical electric field is approximately the same whether the channel is open or closed. Our experimental results are in good quantitative agreement with a 3D electro-thermo-mechanical model of the HEMT we tested and indicate that the GaN buffer acts as a semi-insulating, p-type material due to the presence of deep acceptors in the lower half of the bandgap. This implementation of micro-Raman spectroscopy offers an exciting opportunity to simultaneously probe thermal, mechanical, and electrical phenomena in semiconductor devices under bias, providing unique insight into the complex physics that describes device behavior and reliability. Although GaN HEMTs have been specifically used in this study to demonstrate its viability, this technique is applicable to any solid-state material with a suitable Raman response and will likely enable new measurement capabilities in a wide variety of scientific and engineering applications.

48 citations

Proceedings ArticleDOI
14 Apr 2013
TL;DR: In this article, a comprehensive on-state reliability evaluation on depletionmode (VTH~-4V) AlGaN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors (MIS-HEMTs) with a bi-layer dielectric (in-situ Si3N4/Al2O3) was performed at 200°C.
Abstract: This paper reports on a comprehensive on-state reliability evaluation on depletion-mode (VTH~-4V) AlGaN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors (MIS-HEMTs) with a bi-layer dielectric (in-situ Si3N4/Al2O3). We have studied the strength and the lifetime of the dielectric to breakdown by means of a Time Dependent Dielectric Breakdown (TDDB) experiment performed at 200°C and the trapping effects induced by applying a positive gate voltage stress. Additionally, for the first time, we have studied the effect of the on-state stress as a function of the drain voltage. The results show that 1) Based on a Time Dependent Dielectric Breakdown (TDDB) evaluation, an applied gate voltage stress of +6V for the lifetime of 20 years can be extrapolated at 200°C. 2) By fitting with a power law, applying +1V gate voltage for 20 years leads to a threshold voltage shift of 0.2V. This guarantees a good reliability margin when these devices are used in cascode switching circuit applications. 3) A new mechanism of high junction temperature thermal de-trapping was observed during a high drain bias stress.

46 citations


Cites background from "Fully coupled thermoelectromechanic..."

  • ...Therefore, since the highest junction temperature is located at the gate edge [17][18], we suggest that the partial recovery of the VTH at a high drain voltage is attributed to the thermal de-trapping phenomenon that we observed at high temperature ambient [16]....

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Journal ArticleDOI
TL;DR: In this article, the authors used a substrate replacement process in which a thick diamond substrate is grown by chemical vapor deposition following removal of the original Si substrate, and measured average and maximum temperatures in the gate-drain access region were 176 °C and 205 °C, respectively.
Abstract: Record DC power has been demonstrated in AlGaN/GaN high electron mobility transistors fabricated using a substrate replacement process in which a thick diamond substrate is grown by chemical vapor deposition following removal of the original Si substrate. Crucial to the process is a ~30 nm thick SiN interlayer that has been optimized for thermal resistance. The reductions obtained in self-heating have been quantified by transient thermoreflectance imaging and interpreted using 3D numerical simulation. With a DC power dissipation level of 56 W/mm, the measured average and maximum temperatures in the gate-drain access region were 176 °C and 205 °C, respectively.

46 citations


Cites methods from "Fully coupled thermoelectromechanic..."

  • ...The steady-state thermal resistance of sample GaNDi-2 was verified by 2D electrothermal simulation performed using Comsol ® [18], where model details have been described elsewhere [19]....

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References
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Journal ArticleDOI
TL;DR: In this article, the authors investigated the effect of surface scratches on the mechanical strength of solids, and some general conclusions were reached which appear to have a direct bearing on the problem of rupture, from an engineering standpoint, and also on the larger question of the nature of intermolecular cohesion.
Abstract: In the course of an investigation of the effect of surface scratches on the mechanical strength of solids, some general conclusions were reached which appear to have a direct bearing on the problem of rupture, from an engineering standpoint, and also on the larger question of the nature of intermolecular cohesion. The original object of the work, which was carried out at the Royal Aircraft Estab­lishment, was the discovery of the effect of surface treatment—such as, for instance, filing, grinding or polishing—on the strength of metallic machine parts subjected to alternating or repeated loads. In the case of steel, and some other metals in common use, the results of fatigue tests indicated that the range of alternating stress which could be permanently sustained by the material was smaller than the range within which it was sensibly elastic, after being subjected to a great number of reversals. Hence it was inferred that the safe range of loading of a part, having a scratched or grooved surface of a given type, should be capable of estimation with the help of one of the two hypotheses of rupture commonly used for solids which are elastic to fracture. According to these hypotheses rupture may be expected if (a) the maximum tensile stress, ( b ) the maximum extension, exceeds a certain critical value. Moreover, as the behaviour of the materials under consideration, within the safe range of alternating stress, shows very little departure from Hooke’s law, it was thought that the necessary stress and strain calculations could be performed by means of the mathematical theory of elasticity.

10,162 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the role of spontaneous and piezoelectric polarization on the carrier confinement at GaN/AlGaN and AlGaN/GaN interfaces.
Abstract: Carrier concentration profiles of two-dimensional electron gases are investigated in wurtzite, Ga-face AlxGa1−xN/GaN/AlxGa1−xN and N-face GaN/AlxGa1−xN/GaN heterostructures used for the fabrication of field effect transistors. Analysis of the measured electron distributions in heterostructures with AlGaN barrier layers of different Al concentrations (0.15

2,581 citations

Journal ArticleDOI
TL;DR: In this paper, a combination of high resolution x-ray diffraction, atomic force microscopy, Hall effect, and capacitance-voltage profiling measurements is used to calculate the polarization induced sheet charge bound at the AlGaN/GaN interfaces.
Abstract: Two dimensional electron gases in Al x Ga 12x N/GaN based heterostructures, suitable for high electron mobility transistors, are induced by strong polarization effects. The sheet carrier concentration and the confinement of the two dimensional electron gases located close to the AlGaN/GaN interface are sensitive to a large number of different physical properties such as polarity, alloy composition, strain, thickness, and doping of the AlGaN barrier. We have investigated these physical properties for undoped and silicon doped transistor structures by a combination of high resolution x-ray diffraction, atomic force microscopy, Hall effect, and capacitance‐voltage profiling measurements. The polarization induced sheet charge bound at the AlGaN/GaN interfaces was calculated from different sets of piezoelectric constants available in the literature. The sheet carrier concentration induced by polarization charges was determined

1,439 citations

Journal ArticleDOI
TL;DR: In this article, the dc small-signal and microwave power output characteristics of AlGaN/GaN HEMTs are presented, and it is demonstrated that gate lag is related to surface trapping and drain current collapse is associated with the properties of the GaN buffer layer.
Abstract: The dc small-signal, and microwave power output characteristics of AlGaN/GaN HEMTs are presented. A maximum drain current greater than 1 A/mm and a gate-drain breakdown voltage over 80 V have been attained. For a 0.4 /spl mu/m gate length, an f/sub T/ of 30 GHz and an f/sub max/ of 70 GHz have been demonstrated. Trapping effects, attributed to surface and buffer layers, and their relationship to microwave power performance are discussed. It is demonstrated that gate lag is related to surface trapping and drain current collapse is associated with the properties of the GaN buffer layer. Through a reduction of these trapping effects, a CW power density of 3.3 W/mm and a pulsed power density of 6.7 W/mm have been achieved at 3.8 GHz.

617 citations

Journal ArticleDOI
TL;DR: In this article, a more complete data set of n-and p-channel MOSFET piezoresistance and strain-altered gate tunneling is presented along with new insight into the physical mechanisms responsible for hole mobility enhancement.
Abstract: This paper reviews the history of strained-silicon and the adoption of uniaxial-process-induced strain in nearly all high-performance 90-, 65-, and 45-nm logic technologies to date. A more complete data set of n- and p-channel MOSFET piezoresistance and strain-altered gate tunneling is presented along with new insight into the physical mechanisms responsible for hole mobility enhancement. Strained-Si hole mobility data are analyzed using six band k/spl middot/p calculations for stresses of technological importance: uniaxial longitudinal compressive and biaxial stress on [001] and [110] wafers. The calculations and experimental data show that low in-plane and large out-of-plane conductivity effective masses and a high density of states in the top band are all important for large hole mobility enhancement. This work suggests longitudinal compressive stress on [001] or [110] wafers and channel direction offers the most favorable band structure for holes. The maximum Si inversion-layer hole mobility enhancement is estimated to be /spl sim/ 4 times higher for uniaxial stress on (100) wafer and /spl sim/ 2 times higher for biaxial stress on (100) wafer and for uniaxial stress on a [110] wafer.

568 citations