Transient stress characterization of AlGaN/GaN HEMTs due to electrical and thermal effects
TL;DR: Finite element simulation results of the transient stress response of an AlGaN/GaN high electron mobility transistor (HEMT) suggest transient failure mechanisms may differ from those previously studied under DC operation due to large amount of cyclic loading of a device around the gate structure.
About: This article is published in Microelectronics Reliability.The article was published on 2015-12-01 and is currently open access. It has received 34 citations till now. The article focuses on the topics: Stress (mechanics) & High-electron-mobility transistor.
Citations
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TL;DR: In this article, gate resistance thermometry (GRT) was used to determine the channel temperature of AlGaN/GaN high electron-mobility transistors under various bias conditions.
Abstract: In this paper, gate resistance thermometry (GRT) was used to determine the channel temperature of AlGaN/GaN high electron-mobility transistors. Raman thermometry has been used to verify GRT by comparing the channel temperatures measured by both techniques under various bias conditions. To further validate this technique, a thermal finite-element model has been developed to model the heat dissipation throughout the devices. Comparisons show that the GRT method averages the temperature over the gate width, yielding a slightly lower peak temperature than Raman thermography. Overall, this method provides a fast and simple technique to determine the average temperature under both steady-state and pulsed bias conditions.
40 citations
Cites background from "Transient stress characterization o..."
...Joule heating mostly occurring in the depletion region and requires the need for electrothermal simulations [16]....
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TL;DR: In this paper, the authors studied the self-heating mechanism and its impact on electrical performance of short gate length GaN high electron mobility transistors (HEMTs) based on electrothermal TCAD simulations.
Abstract: In this paper, we study the self-heating mechanism and its impact on electrical performance of short gate length GaN high electron mobility transistors (HEMTs) based on electrothermal TCAD simulations. We propose an equivalent channel temperature to quantify the current degradation due to self-heating and also resolve the discrepancies between temperature measurements through electrical methods and thermal methods in the literature. We then explain the equivalent channel temperature’s behavior using the temperature- and field-dependent electron transport theory for short gate length HEMTs. The implications and guidelines to the various aspects of device design are also discussed.
39 citations
Cites background from "Transient stress characterization o..."
...Therefore, both the top surface and the two sidewalls are assumed adiabatic [28]....
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TL;DR: In this article, the authors used transient thermoreflectance imaging (TTI) to measure the temperature rise of the passivated gate metal measured by TTI and the averaged gate temperature monitored by gate resistance thermometry (GRT).
Abstract: The development of steady-state thermal characterization techniques for AlGaN/GaN high-electron mobility transistors (HEMTs) has been used to measure the device’s peak temperature under DC conditions. Despite these methods enabling the accurate quantification of the device’s effective thermal resistance and power density dependence, transient thermometry techniques are necessary to understand the nanoscale thermal transport within the active GaN layer where the highly localized joule heating occurs. One technique that has shown the ability to achieve this is transient thermoreflectance imaging (TTI). The accuracy of TTI is based on using the correct thermoreflectance coefficient. In the past, alternative techniques have been used to adjust the thermoreflectance coefficient to match the correct temperature rise in the device. This paper provides a new method to accurately determine the thermoreflectance coefficient of a given surface and is validated via an electrical method: gate resistance thermometry (GRT). Close agreement is shown between the temperature rise of the passivated gate metal measured by TTI and the averaged gate temperature monitored by GRT. Overall, TTI can now be used to thermally map GaN HEMTs under pulsed conditions providing simultaneously a submicrosecond temporal resolution and a submicrometer spatial resolution.
38 citations
Additional excerpts
...transiently powered GaN HEMTs is complex [13]....
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01 Jan 2011
TL;DR: In this article, a physics-based finite element model of operation of an AlGaN/GaN HEMT with device geometry inputs taken from transmission electron microscope cross sections and calibrated by comparison with measured electrical data comprising standard field-effect transistor metrics and less well-known model parameters is presented.
Abstract: : We present a physics-based finite-element model of operation of an AlGaN/GaN HEMT with device geometry inputs taken from transmission electron microscope cross sections and calibrated by comparison with measured electrical data comprising standard field-effect transistor metrics and less well-known model parameters. A variety of electrical outputs from the model are compared to experiment, and the level of agreement is reported.
17 citations
21 Mar 2021
TL;DR: In this paper, the surge-energy robustness of a 650-V rated cascode GaN HEMT in the unclamped inductive clamping (UIS) test was investigated.
Abstract: Surge energy robustness of power devices is highly desired in many power applications such as automotive powertrains and power grids. While Si and SiC power MOSFETs withstand surge energy through avalanching, GaN high-electron-mobility transistors (HEMTs) have no avalanche capability. Recent studies have revealed that the p-gate GaN HEMT withstands surge energy through capacitive charging and fails when the peak capacitive voltage reaches its breakdown voltage (BV). This work, for the first time, studies the surge-energy robustness of a 650-V rated cascode GaN HEMT in the unclamped inductive clamping (UIS) test. The cascode GaN HEMT was found to withstand the surge energy via capacitive charging but accompanied by the Si MOSFET avalanching. Two failure modes were observed, both occurring in the GaN HEMT. The first mode is featured by a short between the HEMT gate and drain (cascode source and drain), while the second mode is featured by a short between the HEMT source and drain. Statistical results of multiple devices tested under different load inductance show that the second failure mode predominates. Additionally, the device failure voltage in mode I is statistically higher than that in mode II. Failure analysis of both modes is presented, and the physical explanations of the two modes and their competitions are proposed. These results provide important new insights into the robustness of cascode GaN HEMTs.
16 citations
References
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TL;DR: In this paper, the thermal expansion and thermal expansion anisotropy of alpha-SiC polytype of hexagonal (6H) polytype over the 20-1000 C range were determined using X-ray diffraction.
Abstract: X-ray diffraction is presently used to determine the thermal expansion of the hexagonal (6H) polytype of alpha-SiC over the 20-1000 C range. The principal (alpha-11 and alpha-33) axial coefficients of thermal expansion can be expressed by second-order polynomials; the former is noted to be larger than the latter over the entire temperature range, while the thermal expansion anisotropy increases continuously with increasing temperature. The thermal expansion and thermal expansion anisotropy obtained are compared with previously published results for the (6H) polytype, and discussed with respect to the structure.
88 citations
TL;DR: In this paper, the authors studied a temperature increase and a heat transfer into a substrate in a pulsed operation of 0.5 length and 150 /spl mu/m gate width AlGaN/GaN HEMTs grown on silicon.
Abstract: We studied a temperature increase and a heat transfer into a substrate in a pulsed operation of 0.5 length and 150 /spl mu/m gate width AlGaN/GaN HEMTs grown on silicon. A new transient electrical characterization method is described. In combination with an optical transient interferometric mapping technique and two-dimensional thermal modeling, these methods determine the device thermal resistance to be /spl sim/70 K/W after 400 ns from the start of a pulse. We also localized the high-electron mobility transistor heat source experimentally and we extracted a thermal boundary resistance at the silicon-nitride interface of about /spl sim/7/spl times/10/sup -8/ m/sup 2/K/W. Thermal coupling at this interface may substantially influence the device thermal resistance.
76 citations
"Transient stress characterization o..." refers background in this paper
...Of those that have studied the transient response of AlGaN/GaN HEMTs, their focus was primarily on either electrical or thermal performance [12, 22, 23]....
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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.
75 citations
"Transient stress characterization o..." refers background in this paper
...numerical multi-physics coupled simulations [6, 18-20] and experimentally during DC electrical testing [4, 21], few have studied the transient stress development even though these devices have numerous applications in the RF regime....
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TL;DR: In this paper, micro-Raman spectroscopy was used to measure temperature and stress in state-of-the-art AlGaN/GaN HEMTs.
Abstract: In this paper, we utilize micro-Raman spectroscopy to measure temperature and stress in state-of-the-art AlGaN/GaN HEMTs. A rigorous discussion on the physical accuracy, precision, and precautions for diverse Raman thermometry methods is developed. Thermometry techniques utilizing shifts in a single Raman Stokes peak position underpredict the channel temperature due to induction of operational thermoelastic stress in operating devices. Utilizing the change in phonon linewidth by employing a proper reference condition gives true temperature results. Making use of frequency shifts in both the E2(high) and A1(LO) phonon modes offers accurate and time-efficient means to determine the state of temperature and thermal stress in operating AlGaN/GaN HEMTs presuming that linear relations between phonon frequencies and temperature/stress are well determined. Useful applications of this method such as monitoring stress in GaN wafers between fabrication steps and Raman thermography on AlGaN/GaN HEMTs are demonstrated.
74 citations
"Transient stress characterization o..." refers methods in this paper
...The material properties for the electro-thermal model including temperature dependent thermal conductivities, heat capacities, and temperature- and mole-fractiondependent semiconductor band gaps have been taken from [20] and [29]....
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...For this work, material properties were chosen from literature based upon values that have been previously verified through numerical simulations and experimental results [6, 29]....
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...A thermal boundary resistance is applied at the GaN/SiC interface to account for the thermal resistance of the AlN nucleation layer [6, 29]....
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...A fixed mechanical boundary condition was placed on the bottom of the package and an x-direction fixed mechanical boundary condition was placed along the symmetry line, which is consistent with [29], and all other surfaces are unrestrained....
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TL;DR: In this article, the optical phonon modes of GaN nucleation layers with the thickness of 7 and 45nm, grown on sapphire (0001) substrates by metal organic chemical vapor deposition at low temperatures (500-600°C).
Abstract: Using Raman spectroscopy, we have studied the optical phonon modes of GaN nucleation layers with the thicknesses of 7 and 45nm, grown on sapphire (0001) substrates by metal organic chemical vapor deposition at low temperatures (500–600°C). These layers consisted of mixed hexagonal and cubic phases. The Raman results from mixed phases were compared with those from pure hexagonal layers which were grown at higher temperatures over 1000°C. The E2H and A1(LO) phonon modes are observed at 548 and 733cm−1 for 45nm thick nucleation layer, while the silent low-frequency B1 mode which is forbidden in good quality hexagonal GaN is observed at 314cm−1. The presence of the strong hexagonal modes for GaN nucleation layers of 45nm thick confirms the crystalline nature of the GaN nucleation layer and dominant hexagonal phase in this mixed cubic-hexagonal nucleation layer. The observed frequencies are shifted with respect to the corresponding A1 and E2 phonon modes in hexagonal GaN. The decrease in mode frequency implies the presence of in-plane tensile strain in these GaN nucleation layers of 45nm thick. The Raman scattering spectra taken from different positions on the sample show similar spectral features, indicating that the GaN nucleation layers of 45nm thick are homogeneous in micron scale.
65 citations
"Transient stress characterization o..." refers background in this paper
...In addition, residual stresses exist due to fabrication processes [6, 12-15]....
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