Laurent Brunel

Analysis of Schottky Gate degradation evolution in AlGaN/GaN HEMTs during HTRB stress

GaN based technologies are promising in terms of electrical performances for power and high frequencies applications and their reliability assessment remains a burning issue. Thus, a good understanding of their degradation mechanisms is required to warranty their reliability. In this paper, an electrical parasitic effect has been observed on the gate-source diode forward characteristics of a set of devices under HTRB stress carried out at 175 °C up to 4000 h. This parasitic effect has been attributed to lateral surface conduction and correlated with EL signature under diode forward biasing conditions but not under transistor pinch-off biasing conditions. Then, physical analyses have pointed out the formation and growing over time of pits and cracks at the gate edge on the drain side

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

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.

Influence of gate leakage current on AlGaN/GaN HEMTs evidenced by low frequency noise and pulsed electrical measurements

The study of the pulsed drain current or noise characteristics in AlGaN/GaN HEMTs is the key of knowledge for designing the power amplifiers, the low noise amplifiers and the oscillators or mixers, but it is well accepted today that this study is not fully accomplished without pointing on the effect of the gate leakage current; It is obvious that the transistors leakage current may disturb its operation at high power and high frequency. Leakage currents studies are also an area of great importance in optimization of safe operating area and reliability of HEMTs. Therefore, room temperature pulsed I-V and low frequency noise measurements of gate and drain currents of AlGaN/GaN HEMTs have been investigated under different bias conditions on two devices showing identical drain current and different gate current levels. The results show a correlation between two non-destructive measurement techniques applied on devices under test.

Evidence of relationship between mechanical stress and leakage current in AlGaN/GaN transistor after storage test

In this paper, leakage current signatures in AlGaN HEMT are studied after storage at 300 °C. Electrical characterization of the gate to source diode as a function of the temperature has been performed on HEMT with two different gate pad topologies, but it has not allowed identifying significant difference in the electron transport mechanisms. In forward and low reverse bias, the preeminent conduction mechanism can be attributed to thermionic field emission (TFE). By localized FIB cuts, Optical Beam Induced Resistance Change (OBIRCh) analysis was used to localize current path. Results tend to indicate that mechanical stresses in the gate structure strongly influences the leakage current of the transistor. The OBIRCh analysis technique, widely used in silicon technology, appears to be a very efficient tool to localize leakage paths, in particular for HEMT topology with source terminated field plate.

Schottky gate of AlGaN/GaN HEMTs: Investigation with DC and low frequency noise measurements after 7000 hours HTOL test

This paper reports on AlGaN/GaN high electron mobility transistors (HEMTs) that have been aged by high temperature operating life test (HTOL) during 7000 hours. DC characterization of some aged devices revealed an electrical parasitic effect named “Belly-Shape” that is detected on the gate-source and gate-drain diodes forward current-voltage characteristics. The belly-shape effect is characterized by higher gate current compared to the one of the virgin device for VGs/d below 1.2V. Low frequency gate current noise measurements have been performed at 300K and VDS=0V to analyze the physical origin of this parasitic effect. The relative LF gate current noise is higher for aged than for virgin devices. For Vgs/d <; 1.2V, devices without the parasitic effect exhibit 1/f noise which is proportional to the square of IG, while the devices with the parasitic effect exhibit visible Lorentzian noise that is that is nonrepeatable even when measured with the same bias conditions as well as the belly shape effect in the dc characteristics. On the contrary, all devices present 1/f noise for Vgs/d >1.2V where the gate current is governed by diode series resistance.