Laurent Brunel

Bio: Laurent Brunel is an academic researcher from University of Bordeaux. The author has contributed to research in topics: Transistor & Thermal resistance. The author has an hindex of 5, co-authored 8 publications receiving 72 citations.

Thermal Characterization Using Optical Methods of AlGaN/GaN HEMTs on SiC Substrate in RF Operating Conditions

Abstract: Performance and reliability of wide bandgap high-power amplifiers are correlated with their thermal behavior. Thermal model development and suitable temperature measurement systems are necessary to quantify the channel temperature of devices in real operating conditions. As a direct temperature measurement within a channel is most of the time not achievable, the common approach is to measure the device temperature at different locations close to the hotspot and then to use simulations to estimate the channel temperature. This paper describes a complete thermal characterization of AlGaN/gallium nitride (GaN) on silicon carbide high electron-mobility transistors (HEMTs) when devices are operating in dc bias, pulsed, and continuous wave. Infrared thermography, charge-coupled device-based thermoreflectance microscopy, and micro-Raman spectroscopy have been performed to extract the thermal resistance of the components. Results have been compared with simulations using a 3-D finite-element model to estimate the operating channel temperature. Measurements have shown that the RF-biased thermal resistance and the dc-biased thermal resistance of GaN HEMTs are similar.

Temperature measurements in RF operating conditions of AlGaN/GaN HEMTs using IR microscopy and Raman spectroscopy

Abstract: Performance and reliability of a high power amplifier are correlated with its thermal behavior. Thermal model development and suitable temperature measurement systems are necessary to quantify the channel temperature of devices in real operating conditions. In this paper, temperature measurements applying X-band RF dynamic signal are presented. Infrared microscopy and Raman spectroscopy performed on 8×125μm-wide with 0.25μm-long gates AlGaN/GaN on SiC based HEMTs will be discussed. Measurements will be compared with simulation results to extract the operating thermal resistance.

Electronic surface and dielectric interface states on GaN and AlGaN

Abstract: GaN and AlGaN have shown great potential in next-generation high-power electronic devices; however, they are plagued by a high density of interface states that affect device reliability and performance, resulting in large leakage current and current collapse. In this review, the authors summarize the current understanding of the gate leakage current and current collapse mechanisms, where awareness of the surface defects is the key to controlling and improving device performance. With this in mind, they present the current research on surface states on GaN and AlGaN and interface states on GaN and AlGaN-based heterostructures. Since GaN and AlGaN are polar materials, both are characterized by a large bound polarization charge on the order of 1013 charges/cm2 that requires compensation. The key is therefore to control the compensation charge such that the electronic states do not serve as electron traps or affect device performance and reliability. Band alignment modeling and measurement can help to determi...

A Review of Raman Thermography for Electronic and Opto-Electronic Device Measurement With Submicron Spatial and Nanosecond Temporal Resolution

Abstract: We review the Raman thermography technique, which has been developed to determine the temperature in and around the active area of semiconductor devices with submicron spatial and nanosecond temporal resolution. This is critical for the qualification of device technology, including for accelerated lifetime reliability testing and device design optimization. Its practical use is illustrated for GaN and GaAs-based high electron mobility transistors and opto-electronic devices. We also discuss how Raman thermography is used to validate device thermal models, as well as determining the thermal conductivity of materials relevant for electronic and opto-electronic devices.

Stability and Reliability of Lateral GaN Power Field-Effect Transistors

Abstract: GaN electronics constitutes a revolutionary technology with power handling capabilities that amply exceed those of Si and other semiconductors in many applications. RF, microwave, and millimeter-wave GaN-based power amplifiers are now deployed in commercial communications, radar, and sensing systems. GaN power transistors for electrical power management are also starting to reach the marketplace. From the dawn of this technology, inadequate transistor stability and reliability have represented stumbling blocks preventing widespread commercial use of GaN electronics. Intense research has been devoted to addressing these issues, and great progress has taken place recently. This article reviews some of the most interesting and significant stability and reliability issues that have plagued GaN power field-effect transistors for RF and power management applications.

Experimental Characterization of the Thermal Time Constants of GaN HEMTs Via Micro-Raman Thermometry

Abstract: Gallium nitride (GaN) high-electron mobility transistors (HEMTs) are a key technology for realizing next generation high-power RF amplifiers and high-efficiency power converters. However, elevated channel temperatures due to self-heating often severely limit their power handling capability. Although the steady-state thermal behavior of GaN HEMTs has been studied extensively, significantly fewer studies have considered their transient thermal response. In this paper, we report a methodology for measuring the transient temperature rise and thermal time constant spectrum of GaN HEMTs via time-resolved micro-Raman thermometry with a temporal resolution of 30 ns. We measured a broad spectrum of time constants from $\approx 130$ ns to $\approx 3.2$ ms that contribute to the temperature rise of an ungated GaN-on-SiC HEMT due to aggressive, multidimensional heat spreading in the die and die-attach. Our findings confirm previous theoretical analysis showing that one or two thermal time constants cannot adequately describe the transient temperature rise and that the temperature reaches steady-state at $\approx {16}L^{{2}}/\pi ^{{2}}\alpha $ , where $L$ and ${\alpha }$ are the thickness and thermal diffusivity of the substrate. This paper provides a practical methodology for validating transient thermal models of GaN HEMTs and for obtaining experimental values of the thermal resistances and capacitances for compact electrothermal modeling.

Humidity sensing properties of K0.5Na0.5NbO3 powder synthesized by metal organic decomposition

Abstract: K0.5Na0.5NbO3 (KNN) powder is synthesized via a metal-organic decomposition (MOD) method and characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and energy dispersive spectrometer (EDS). A humidity sensor, which is consisted of five pairs of Ag Pd interdigitated electrodes and an Al2O3 ceramic substrate, is fabricated by spin-coating the KNN powder on the substrate. The humidity sensing properties of the KNN humidity sensor are investigated at room temperature within the relative humidity (RH) range of 11–95%. The variations of the KNN humidity sensor impedance are about four orders of magnitude within the whole humidity range from 11% to 95% RH at the frequencies of 60 Hz and 100 Hz. The response time and recovery time of the KNN humidity sensor are all about 8 s and 18 s, and their maximum hystereses are all around 2% RH at 60 Hz and 100 Hz. Furthermore, at low RH and frequency conditions, the dielectric dissipation factor (DF) values of the KNN humidity sensor are small and hardly change, indicating that the KNN humidity sensor is of good insulating properties and reliability. The KNN powder is of broader potential applications for fabricating high performance humidity sensors.