Jean-Guy Tartarin

On the effects of hot carriers on the RF characteristics of Si/SiGe heterojunction bipolar transistors

This work for the first time experimentally investigates the hot carrier effects on the RF characteristics (up to 30 GHz) of Si/SiGe heterojunction bipolar transistors (HBTs). Reverse base-emitter voltage stresses were applied at room temperature on BiCMOS compatible, sub-micron transistors. The main observed degradation is a decrease of S/sub 21/. It was found that this degradation is minimized (maximized) when biasing at constant collector (base) current. These results may be valuable indications also for degradations induced by ionizing radiations.

High-frequency noise in heterojunction bipolar transistors

Abstract Noise parameter modelling of heterojunction bipolar transistors at microwave frequencies, based on the hybrid- π equivalent circuit is proposed in this letter. The results indicate that correlated shot noise sources are needed to describe the noise behaviour of the intrinsic transistor and that the correlation coefficient is frequency dependent. This model can be easily implemented in commercial CAD software provided that the small-signal equivalent circuit including parasitic elements has been previously determined.

Hot carrier effects in Si-SiGe HBTs

Life tests were performed at room temperature on Si-SiGe HBTs by reverse biasing the base-emitter junction under open collector conditions. The effects on the DC, the low-frequency noise, and the microwave characteristics were investigated both by the analysis of experimental data and by simulations and analytical models. The stress-induced surface damage close to the emitter perimeter was identified to be the degradation mechanism mainly responsible for the variations observed, in all the investigated parameters.

Assessing Zener-Diode-Structure Reliability From Zener Diodes' Low-Frequency Noise

An electrical-stress test has been conducted on 98 Zener conventional reference diode structures, and it has been observed that 45% of these devices failed after 3000 h. However, this high failure ratio can be reduced to below 25%, or less, provided that an appropriate low-frequency-noise (LFN) characterization is initially performed and that all the devices exhibiting a larger LFN are subtracted from the lot subjected to electrical-stress test. Further results obtained after a 4500-h electrical-stress test conducted on a reduced number of diodes fully validate this finding.

Reliability investigation in SiGe HBT's

This paper addresses some reliability properties of SiGe HBTs. We first verified that no major problems were related to the SiGe layer through DC life tests. In the second step, we investigated the hot carrier influence on the DC, noise and microwave properties of these devices. We found that some degradation was occurring at the extrinsic base region in the vicinity of the emitter associated with some surface recombination. These assumptions have been described by physical simulations and confirmed by low frequency noise characterization. Finally, it has been demonstrated that microwave properties are affected by the mechanism and we propose a bias method that results in its minimization.

Low frequency noise behavior in GaN HEMT’s on silicon substrate

In this paper, we report low frequency noise (LFN) data obtained on passivated AlGaN/GaN HEMT’s grown by MBE on a silicon substrate. In order to localize the LFN sources, we have measured all the extrinsic gate and drain current noise generators and their coherence versus bias in the linear regime. We have found that the gate noise sources result from leakage phenomena at gate-source and gate-drain regions. Drain noise sources are mostly located in the active channel below the gate and they feature an equivalent Hooge coefficient of about 10-3. Secondly, in order to build a LFN model that fits the requirements of a CAD simulator, we have measured the LFN sources for numerous bias points in the saturation region and therefore we have studied the bias dependence of the different noise sources under normal operating conditions. Results show that the gate terminal noise current impacts heavily the overall LFN of the transistor contrary to others III-V HEMTs, and that specific bias conditions are needed in order to reduce the LFN.

Low Frequency Noise Of AlGaN/GaN HEMT Grown On Al2O3 , Si And SiC Substrates

Newly developed GaN technology offers great potential for military and space, as well as some high volume applications. The devices are grown on different substrates (sapphire, silicon and silicon carbide), involving differences on the performances, price, and technological complexity. The design of a fully integrated transceiver in such a technology necessitates great noise performances for the linear (low noise amplifiers, LNA) and non-linear (voltage controlled oscillator, VCO) applications. The low noise figure already published on this technology up to X-band, associated to the capability to handle high power levels avoid the integration of a limiter stage that deteriorates the overall noise figure in conventional architectures. The low frequency noise performances are useful both for the technology assessment (maturitys indicator) and for the non-linear circuit design (conversion to phase noise around the carrier). This paper presents the noise performances of AlGaN/GaN HEMT grown on SiC substrate. Low frequency noise contributors in the ohmic and saturated regime are discussed. Residual phase noise characterization at 10 GHz correlates the results about the noise sources involved, and linear high frequency noise figure measurements are also presented, targeting respectively VCO and LNA applicationsThe use of wide bandgap materials for broadcast telecommunication and defense systems allow high power, high efficiency and high integration levels of active devices thanks to their microwave electrical performances. GaN based devices have also demonstrated great potential for high frequency linear low noise applications. However, low frequency noise (LFN) performances characteristics are still under progress as they are related to the material quality and process control. As a consequence, the LFN sources identification and modeling in AlGaN/GaN devices have a twofold stake: on one hand it contributes to the process improvement by the identification of the main noise sources, and on the other hand the nonlinear noisy model can be used for CAD of non linear circuits such as low phase noise oscillators. This study focuses on the confrontation of High Electron Mobility Transistors (HEMT) featuring 0.15x2x50μm2 gate dimension grown by MOCVD on sapphire (Al2O3), silicon (Si) and silicon carbide (SiC) substrates. Each substrate has got its own advantages and drawbacks in terms of cost, wafer size, thermal conductivity and lattice mismatch. This paper deals with the noise mechanisms relative to the use of several substrates: for that purpose, low frequency noise measurements have been performed under different biasing conditions for each substrate. The contributions of the different noise sources (1/f, generation-recombination centers (GR),...) are discussed for each substrate and related to each technological process.

A cost-effective technique for extending the low-frequency range of a microwave noise parameter test set

The operating frequency range of an on-wafer noise parameter test set based on the multiple-impedance technique has been extended in the low-microwave frequency range (down to the L-band). A simple technique, using a phase shifter cascaded with the microwave tuner, allows different reflection coefficients of the load impedance to be obtained at the device input. These coefficients are well distributed over the Smith chart in the entire frequency range. As an example, noise parameters of a passive device have been measured between 1 and 8 GHz, and a good agreement between measured and calculated values is observed. This technique has also been used to measure the noise parameters of different heterojunction bipolar transistors. A minimum noise figure of 1 dB was obtained at 1 GHz on a GaAlAs/GaAs HBT which is in agreement with expected results.

Gate defects analysis in AlGaN/GaN devices by mean of accurate extraction of the Schottky Barrier Height, electrical modelling, T-CAD simulations and TEM imaging

This paper proposes an investigation focused on the Schottky diode related electrical behaviors on GaN high frequency technologies. As the Schottky diode represents the electrical input terminal (the command) of High Electron Mobility Transistors (HEMTs), this study also correlates with some first order degradation in the active channel (current IDS). Non-invasive methods and related models have been used to determine the accurate Schottky Barrier Height (SBH) of the diode in terms of mean value and dispersion; this approach is convenient to evidence different failure mechanisms on virgin and stressed devices that can be correlated with DC or transient electrical parameters. It is shown that according to given temperature windows and IGS ranges, linear relationships can be extracted between the mean SBH and the inhomogeneities of the SBH that appear in forward-biased diode mode. This original approach permits to determine an increase or a decrease of the global SBH after a stress period. Electrical behaviors issued from the proposed non-destructive technique and from electrical modelling of the diode at different temperatures are found to be consistent with Transmission Electron Microscope (TEM) investigations. T-CAD models have also been used and tuned to account for the impact of interface fixed charge density changes on the electrical signatures of the HEMTs.

Robust GaN Electronics for Highly Reliable BF and RF Analog Systems in Aerospace Applications

The reliability and robustness of electronic subsystems dedicated to control and communications in the aerospace sector is more than ever one of the key points for safety and security, essentially during landing operations. As aircraft manufacturers have to diversify their mean of communication systems control (Full-Duplex and System), the reliability can be improved both by setting redundant remote networks, and also by using matched technologies for increased performances and robustness: the wide band-gap Gallium Nitride technology (GaN) newly developed fits perfectly to the requirements of systems such as Microwave Landing System (MLS) or Distance Measuring Equipments (DME) used during the final landing approach. Actually, GaN technology takes advantage of a natural immunity to electromagnetic perturbations, and is suitable for circuit design in the RF frequency band (up to 5 GHz for aircraft applications). The GaN based circuits are able to improve transceivers efficiency (and so the radio-link budget) thanks to their low noise figure (receiver) and high output power (transmitter), reducing digital bit error rate during the code demodulation. This point is crucial while electronic runs in an urban environment. Moreover, the next electronic systems developed for composite aircraft will be more exposed to high electric field and CEM problems in circuits. Furthermore, this GaN integrated technology allows a reduction of volume for transmitters subsystems , and is easy to setup (aircraft maintenance): the risk of immobilisation during the aircraft exploitation will be reduced and his maintainability will be easier. Finally, this technology is also perfectly suited for ground navigation control systems such as radar. This work presents the challenge for civil and military future avionic systems by making use of GaN based technologies.