The thermal effect on the output conductance in AlGaN/GaN HEMT's

Bellakhdar, A.; Telia, A.; Semra, L.; Soltani, A.

doi:10.1109/icm.2012.6471365

Cited by 6 publications

(7 citation statements)

References 7 publications

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“…For higher currents, the g m curves diverge significantly for different supply voltages, with g m decreasing for increasing supply voltages, reaching peak g m earlier and at lower values. This decrease in g m can be attributed to self-heating of the transistor and the associated effects on the channel [34]. For higher drain currents, g m drops at approximately the same rate for all supply voltages.…”

Section: On the Origin Of Small-signal Gain Variationmentioning

confidence: 86%

Analysis of Gain Variation With Changing Supply Voltages in GaN HEMTs for Envelope Tracking Power Amplifiers

Alt

Hirshy

Jiang

et al. 2019

IEEE Trans. Microwave Theory Techn.

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Envelope tracking (ET) is a promising power amplifier (PA) architecture for current and future communications systems, that uses dynamic modulation of the supply voltage to provide high efficiency and potentially very wide bandwidth over a large dynamic range of output power. The dynamic nature of the supply voltage can lead to a problematic variation in transistor gain however, particularly in GaN HEMTs. This paper describes and analyses this behaviour and the detrimental effect it can have on ET PAs. Contributing factors and origins of gain variation are described in detail along with how, for the first time, meaningful comparisons can be made between different devices. Using these guidelines, gain variation is shown to be a widespread issue effecting most GaN HEMTs presented in literature. To allow an analysis of the intrinsic device behaviour, an extended transistor model is developed that takes the effect of gate and source field plates into account. This model is refined using measurement data and used to demonstrate the fact that the parasitic gate-drain capacitance (C GD ) is the main contributor to the small-signal gain variation; a significant part of the overall gain variation. Based on this knowledge, possible strategies to reduce gain variation at the transistor technology level are proposed, allowing the optimisation of GaN HEMTs specifically for ET PAs. One identified strategy involves reducing the length of the gate field plate, and is shown to be a viable approach to reduce the gain variation in GaN HEMTs, albeit at an increased RF/dc dispersion.

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Section: On the Origin Of Small-signal Gain Variationmentioning

confidence: 86%

Analysis of Gain Variation With Changing Supply Voltages in GaN HEMTs for Envelope Tracking Power Amplifiers

Alt

Hirshy

Jiang

et al. 2019

IEEE Trans. Microwave Theory Techn.

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“…The lower transconductance, at higher temperature, results in lower switching speed and consequently lower di/dt. The lower transconductance is caused by a reduction of device electron mobility with increasing temperature [17].…”

Section: A Temperature Dependence Of Peak Current Gradient DI S /Dt| Maxmentioning

confidence: 99%

Overtemperature Protection Circuit for GaN Devices Using a di/dt Sensor

Hedayati

Wang

Dymond

et al. 2021

IEEE Trans. Power Electron.

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Power semiconductor devices have maximum junction temperature limits, but it is not straightforward to sense or infer temperature inside sealed devices in running converters. One method is to observe electrical behavior that is known to be temperature dependent. For example, in some gallium nitride (GaN) power semiconductor devices, the maximum slope of the device current at turn-ON has been shown to reduce as the junction temperature increases. This article demonstrates the first noncontact overtemperature protection circuit for GaN power devices that exploits this effect and overcomes the complication that this inverse proportionality is affected by load current. A variant of a previously reported magnetic field "Infinity Sensor," named after its figure-ofeight topology and high bandwidth (>200 MHz), measures di/dt. Using the sensor signal as the only input, a detection circuit finds peak di/dt, and a high-speed integrator derives instantaneous load current. The reference voltage for the decision-making part of the circuit is automatically adjusted as a function of load current, in order to counteract the dependence of di/dt on load current. Experimental results on a 400 V, 2 kW buck converter show the protection circuit successfully activating within ±5°C of a preprogrammed junction temperature setting, independently of load current, for settings of 100, 120, and 140°C. Index Terms-Gallium Nitride (GaN), indirect temperature sensing, overtemperature protection, temperature-sensitive electrical parameters (TSEPs), turn-ON di/dt, wideband gap. I. INTRODUCTIONP ROTECTION circuits are typically necessary to make a power converter robust, increase functionality, and achieve sufficient reliability [1]-[3]. In particular, the control scheme of the converter should be capable of protecting the switches against overtemperature. A general practice in the industry is to place temperature sensing chips on the board, as close as possible to the switching devices, or, in systems using modules, the modules will often include a thermistor attached to the substrate.

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“…Here i=n for electrons and p for holes, respectively, N is the doping concentration, and To=300 K. The parameters µmax,i , µmin,i , Ng,i , γi, αi and βi are taken from [32] see Table 4.…”

Section: Current-voltage Characteristicsmentioning

confidence: 99%

“…Parameter values for low-field electron mobility[32] The drain conductance is an important microwave parameter that determines the maximum voltage gain delivered by the device. The drain conductance of the HEMT is evaluated as[24]:…”

mentioning

confidence: 99%

An analytical model for the current voltage characteristics of GaN-capped AlGaN/GaN and AlInN/GaN HEMTs including thermal and self-heating effects

Bellakhdar¹,

Telia²,

Coutaz³

2020

IJECE

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We present an analytical model for the I-V characteristics of AlGaN/GaN and AlInN/GaN high electron mobility transistors (HEMT). Our study focuses on the influence of a GaN capping layer, and of thermal and self-heating effects. Spontaneous and piezoelectric polarizations at Al (Ga,In)N/GaN and GaN/Al(Ga,In)N interfaces have been incorporated in the analysis. Our model permits to fit several published data. Our results indicate that the GaN cap layer reduces the sheet density of the two-dimensional electron gas (2DEG), leading to a decrease of the drain current, and that n+-doped GaN cap layer provides a higher sheet density than undoped one. In n+GaN/AlInN/GaN HEMTs, the sheet carrier concentration is higher than in n+GaN/AlGaN/GaN HEMTs, due to the higher spontaneous polarization charge and conduction band discontinuity at the substrate/barrier layer interface.

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The thermal effect on the output conductance in AlGaN/GaN HEMT's

Cited by 6 publications

References 7 publications

Analysis of Gain Variation With Changing Supply Voltages in GaN HEMTs for Envelope Tracking Power Amplifiers

Analysis of Gain Variation With Changing Supply Voltages in GaN HEMTs for Envelope Tracking Power Amplifiers

Overtemperature Protection Circuit for GaN Devices Using a di/dt Sensor

An analytical model for the current voltage characteristics of GaN-capped AlGaN/GaN and AlInN/GaN HEMTs including thermal and self-heating effects

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