Sylvain Laurent

Modeling of trap induced dispersion of large signal dynamic Characteristics of GaN HEMTs

We propose here a non-linear GaN HEMT model for CAD including a trapping effects description consistent with both small-signal and large-signal operating modes. It takes into account the dynamics of the traps and then allows to accurately model the modulated large signal characteristics that are encountered in telecommunication and radar signals. This model is elaborated through low-frequency S-parameter measurements complementary to more classical pulsed-IV characterizations. A 8×75μm AlInN/GaN HEMT model was designed and particularly validated in large-signal pulsed RF operation. It is also shown that thermal and trapping effects have opposite effects on the output conductance, thus opening the way for separate characterizations of the two effects.

On-Wafer Single-Pulse Thermal Load–Pull RF Characterization of Trapping Phenomena in AlGaN/GaN HEMTs

In this paper, a new characterization method, which allows the determination of the time constants of traps in AlGaN/GaN high electron-mobility transistors is proposed. The approach is based on the current transient method for assessing the time constants that are involved in real working conditions. To do that the dc filling pulses, which are classically used in this method, are replaced by RF filling pulses, which reproduce the real large-signal conditions. To investigate the impact of large-signal working conditions on the trapping phenomena, on-wafer single-pulse load-pull characterizations are carried out at different temperatures and for two different output load impedances: maximum of power-added efficiency and mismatched impedance. The results obtained show the deep impact of the load-line excursion on the current collapse of the detrapping drain current. A comparison between the single-pulse RF load-pull characterization and single-pulse dc measurement is finally presented.

Highlighting trapping phenomena in microwave GaN HEMTs by low-frequency S -parameters

This paper presents an original characterization method of trapping phenomena in gallium nitride high electron mobility transistors (GaN HEMTs). This method is based on the frequency dispersion of the output-admittance that is characterized by low-frequency S-parameter measurements. As microwave performances of GaN HEMTs are significantly affected by trapping effects, trap characterization is essential for this power technology. The proposed measurement setup and the trap characterization method allow us to determine the activation energy Ea and the capture cross-section σn of the identified traps. Three original characterizations are presented here to investigate the particular effects of bias, ageing, and light, respectively. These measurements are illustrated through different technologies such as AlGaN/GaN and InAlN/GaN HEMTs with non-intentionally doped or carbon doped GaN buffer layers. The extracted trap signatures are intended to provide an efficient feedback to the technology developments

A Microwave Modeling Oxymoron?: Low-Frequency Measurements for Microwave Device Modeling

For a number of decades, the modeling of microwave transistors relied on specific well-known characterization methods. Those methods include S-parameters measurement through vector network analyzers (VNAs) ranging from the lower end of the RF spectrum to the millimeter-wave (mm-wave) region and load pull measurements of transistors used for the design of power amplifiers (PAs). Later, the availability of more powerful computer-aided design (CAD) software enabled the need for models of active microwave devices, thus driving a huge amount of research activity on microwave transistor modeling. Simultaneously, new transistor technologies were invented, combining working concepts such as heterojunction bipolar transistors (HBTs), metal semiconductor field effect transistors (MESFETs) or high electron mobility transistors (HEMTs) and new materials such as gallium arsenide (GaAs), gallium nitride (GaN), indium phosphide (InP), and silicon germanium (SiGe), to cite only the main ones.

Non-linear electro-thermal AlGaN/GaN model including large-signal dynamic thermal-trapping effects

This paper presents a non-linear electro-thermal AlGaN/GaN model for CAD application with a new additive thermal-trap model to take into account the dynamic behavior of trap states and their associated temperature variation. The thermal-trap model is extracted through low-frequency small-signal CW S-parameter measurements and large-signal pulsed-RF measurements at different temperatures. This thermal-trap model allows accurately predicting the physical temperature activation of traps and also the thermal signature of traps. It is also demonstrated that extrapolation of trap model parameters by stretched multi-exponential function of drain current transient measurements during pulsed-RF excitations allows deeply improving the envelope simulations.

Trap characterization of AlGaN/GaN HEMTs through drain current measurements under pulsed-RF large-signal excitation

An advanced microwave characterization technique has been developed to determine the trapping and detrapping time constants due to wide Pulsed-RF large-signal excitation of AlGaN/GaN High-Electron Mobility Transistors (HEMTs). This approach is based on combined Continuous Waveform (CW) Time-Domain Load-Pull measurements and low frequency (LF) drain current transient measurements under one wide non-periodic Pulsed-RF excitation to investigate trapping phenomena. The trap capture and emission time constants are extracted by applying the current-transient method for different RF large-signal input power levels and for varying duration of pulse-width (PW) of the one pulse-RF excitation. The strong influence of the RF load-line excursion in the Drain current collapse after the RF stimulus is also demonstrated.

Characterization and nonlinear modeling of MASMOS® transistor in order to design power amplifiers for LTE applications

This paper reports on the first experimental characterizations and modeling process of a MASMOS® transistor with a classical model, largely used for the modeling of other transistors. From DC IV and S-parameters measurements a large signal model (LSM) has been carried out. The great interest of this model is to allow a simulation time reduced by a factor of 100 compared to foundry model, like BSIM3 model, in classical one-tone HB simulation and to perform multi-tones simulation which is not possible with the foundry model due to prohibitive simulation times. The LSM has been validated through extensive multi-tones and load pull measurements. A good agreement between LSM simulation results and measurements fully validates the proposed modeling methodology. This LSM will serve to design a power amplifier (PA) for LTE applications.

Characterization of Defects in AlGaN/GaN HEMTs Based on Nonlinear Microwave Current Transient Spectroscopy

This paper presents a new nonlinear microwave-based characterization methodology for the study of the deep levels proprieties in gallium nitride (GaN)-based high electron mobility transistors (HEMTs). Currently, it is unique measurement method allowing the extraction of time constants of HEMTs operating under large signal RF conditions. This method improves the conventional dc techniques, since it employs RF excitation during the filling condition to investigate the impact of “real-life” RF excitation on the trapping mechanisms. The experimental results demonstrate that, beyond the presence of Poole–Frenkel effect, the slow detrapping time constant is accelerated by the power dissipation of the trapping bias point. Moreover, it is possible to distinguish the impact of dc and RF conditions on the trapping phenomena. The temperature measurements allow identifying the 0.75-eV deep level, attributed to extended defects in GaN, when ionized under dc excitation. This deep level trap is probably located in the buffer layer and contributes to the RF trapping phenomenon.

Linearity characterization of RF circuits through an unequally spaced multi-tone signal

An Unequally Spaced Multi-Tone signal (USMT) is used for the assessment of nonlinear devices and circuits. The statistical properties of the signal are described. The setup measurements for such a signal are given either by using a Large Signal Network Analyzer (LSNA) or a Nonlinear Vector Network Analyzer (Keysight PNA NVNA with SA option). A USMT Load Pull (USMT-LP)set-up has been developed using a LSNA and it is shown how to extend this set-up to a NVNA receiver. The set-up is fully on-wafer calibrated at all the frequencies of interest. The USMT-LP set-up is configured to make measurements with USMT signals up to eight frequencies and allows measuring simultaneously the MT output power, gain, Power Added Efficiency (PAE), Carrier to Intermodulation (C/I) ratio or Noise Power Ratio (NPR) in order to derive the Error Vector Magnitude (EVM) induced by the device.

Drain current transient and low-frequency dispersion characterizations in AlGaN/GaN HEMTs

This paper presents a detailed trap investigation based on combined pulsed I/V measurements, drain current transient (DCT) measurements and low-frequency dispersion measurements of transconductance (LF Y21) and output conductance (LF Y22). DCT characterization is carried out over a 7-decade time scale. LF Y21 and Y22 measurements are carried out over the frequency range from 100 Hz to 1 GHz. These combined measurements were performed at several temperatures for AlGaN/GaN high electron mobility transistors under class AB bias condition and allowed the extraction of the activation energy (Ea) and the capture cross section (σc) of the identified traps. Extensive measurements of these characteristics as a function of device bias are reported in this work to understand the dynamic trap behavior. This paper demonstrated a correlation between LF small-signal (LF Y21 and Y22) and large-signal voltage steps (DCT) results. These measurements allow identifying the same 0.64 eV deep level, attributed to a native defect of GaN, possibly located in the buffer layer.