A. Pantellini

Buffer Traps in Fe-Doped AlGaN/GaN HEMTs: Investigation of the Physical Properties Based on Pulsed and Transient Measurements

This paper presents an extensive investigation of the properties of the trap with activation energy equal to 0.6 eV, which has been demonstrated to be responsible for current collapse (CC) in AlGaN/GaN HEMTs. The study was carried out on AlGaN/GaN HEMTs with increasing concentration of iron doping in the buffer. Based on pulsed characterization and drain current transient measurements, we demonstrate that for the samples under investigation: 1) increasing concentrations of Fe-doping in the buffer may induce a strong CC, which is related to the existence of a trap level located 0.63 eV below the conduction band energy and 2) this trap is physically located in the buffer layer, and is not related to the iron atoms but-more likely-to an intrinsic defect whose concentration depends on buffer doping. Moreover, we demonstrate that this level can be filled both under OFF-state conditions (by gate-leakage current) and under ON-state operation (when hot electrons can be injected to the buffer): for these reasons, it can significantly affect the switching properties of AlGaN/GaN HEMTs.

Hot-Electron Degradation of AlGaN/GaN High-Electron Mobility Transistors During RF Operation: Correlation With GaN Buffer Design

Comprehensive RF stress-test campaign has been performed over AlGaN/GaN high-electron mobility transistor employing different GaN buffer designs, including unintentional doping, carbon doping and iron doping. No signature of gate-edge degradation has been found, and good correlation emerges between the buffer composition, subthreshold leakage current, and permanent degradation of the RF performance. The degradation mechanism, more pronounced in devices with parasitic buffer conductivity, involves the generation of additional deep trap states, the worsening of the dynamic current collapse, and the subsequent degradation of RF output power.

Role of buffer doping and pre-existing trap states in the current collapse and degradation of AlGaN/GaN HEMTs

The aim of this work is to quantitatively investigate the influence of buffer doping on the current collapse of AlGaN/GaN HEMTs, and to analyze the contribution of trap states to the increase in current collapse detected after reverse-bias stress. The study was carried out on GaN-based HEMTs with increasing levels of iron doping in the buffer, which were submitted to drain current transient measurements and reverse-bias stress. Results demonstrate that the use of Fe-doping may significantly impact on current collapse; moreover, we demonstrate that the increase in current collapse detected after reverse-bias stress is not due to the generation of new types of defect, but to the increase in the signal of the defects which were already present before stress.

Field plate related reliability improvements in GaN-on-Si HEMTs

Abstract State of the art GaN on Silicon HEMTs fabricated with and without a field-plate structure have been tested by means of DC and RF reliability tests. The introduction of the field-plate structure greatly improves device reliability both during DC as well as RF testing. Results are thus suggesting that reliability in NOFP and FP devices is mainly limited by the high electric fields within the device structure causing an increase in traps concentration.

Influence of fluorine-based dry etching on electrical parameters of AlGaN/GaN-on-Si High Electron Mobility Transistors

The Fluorine-based dry etching process is extensively employed in the fabrication of GaN-based High Electron Mobility Transistors. This research activity aims to the identification of the SF6ICP etching process effects on the performances of depletion-mode AlGaN/GaN-on-Si HEMTs. By means of reverse-bias step-stress and time-resolved constant-stress, it has been observed (i) a short-term instability under low reverse bias conditions of both threshold voltage and gate leakage current, likely related to the permanent modification of electrical configuration of the Fluorine ions implanted within the epitaxial structure during the etching process; and (ii) that the introduction of the annealing phase mitigates the described instability.

Impact of field-plate geometry on the reliability of GaN-on-SiC HEMTs

Abstract GaN on SiC HEMTs fabricated with different gate-connected field plate structures have been tested by means of RF reliability tests. The increase in field-plate length yielded an improvement of both the dynamic and the reliability performance during RF testing. Results are thus suggesting that reliability in field-plate devices can be improved by a proper design of the field-plate geometry.

GaN-on-Silicon Evaluation for High-Power MMIC Applications

Today microwave market has identified GaN-HEMT technology as a strategic enabling technology for next generation MMICs to be implemented in high performance RF sub-assemblies such as T/R Modules, Solid State Power Transmitters, Compact Receivers, High Speed Communications. To allow commercial market entry of GaN technology, a tradeoff between high RF performance and low cost is mandatory and a possible solution is represented by GaN-on-Silicon substrate. In this scenario the evaluation of FETs RF performance and losses of passive components are demanding to understand the feasibility of GaN MMIC on Si. Following such approach, in SELEX Sistemi Integrati a 4 inches GaN-on-Si wafer containing discrete active devices and passive components has been fabricated with the 50μm Si thickness. RF FETs performance demonstrates an output power of 4W/mm @ 3GHz, while passive components characterization exhibits similar behavior of GaN SiC passive elements up to C Band.

Evaluation of FET performance and restrictions by low-frequency measurements

In this paper a characterization technique for the evaluation of transistor performance and restrictions is presented, based on a simple and low-cost measurement system. Experimental examples, carried out on a 0.5 × 1000 μm2GaN HEMT, are reported. The validity of the proposed approach is demonstrated by comparing the results with the ones obtained by means of commonly adopted measurement setups.

Ultra wide band power amplifier using GaN on Si HEMT device

This contribution describes the design of an ultra wide band hybrid power amplifier for applications in the frequency range from 1 GHz to 6 GHz. The amplifier is designed with a GaN-on-Si HEMT device provided by SELEX-SI, in a single ended configuration and using the source/load-pull and Scattering parameters measured data. The amplifier has been designed using a CAD oriented broad band matching approach for both input and output networks. From 1 GHz to 6 GHz, the expected output power at 3dB of gain compression is around 41 dBm.

Wide bandgap technology: The right solution for Space and Defense market

The procurement of critical solid state electronic components has always been strategic for companies operating in the Defense and Space market. To-day the situation is even more stringent because of the increasing importance of Gallium Nitride device. An “ideal” Foundry is a sources that can satisfy all the basic requirements for the development and production of competitive edge RF products, avoiding ITAR restriction, and ensuring a right tradeoff between cost and performance.