Mindaugas Ramonas

Systematic Compact Modeling of Correlated Noise in Bipolar Transistors

A systematic method for the integration of correlated shot-noise sources into compact models (CMs) is presented, which significantly improves the accuracy of predicted high-frequency noise in transistors. The developed method relies on a system theory approach, and hence, is not limited to specific CM or device type. In this paper, the method is applied to the CM HICUM, which serves a vehicle for verification purposes. The method and its implementation were verified for SiGe heterojunction bipolar transistors based on measured data for frequencies up to 50 GHz, as well as on device simulation data up to 500 GHz, obtained from simulations of both hydrodynamic and a Boltzmann transport model.

Impact Ionization Noise in SiGe HBTs: Comparison of Device and Compact Modeling With Experimental Results

The noise behavior resulting from impact ionization (II) was investigated at room temperature for silicon-germanium (SiGe) heterojunction bipolar transistors with box Ge profile (true HBTs), featuring a maximum transit frequency of fT = 80 GHz. Noise parameters (NPs) were measured over a wide range of collector-emitter voltages. Modeling was performed using a generalized hydrodynamic (HD) device simulation with a local temperature approach for avalanche generation, drift- diffusion (DD) simulation with a local field model, and the compact model (CM) HICUM/L2 with a conventional local field Chynoweths law for avalanche generation. Local temperature model parameters were calibrated by matching the avalanche multiplication factor (M) to results obtained from full-band Monte Carlo (MC) simulations. The spectral density of II current noise, obtained from the CM, is in fair agreement with the HD model. Verification of NPs (NFmin, Rn, and GammaOPT), obtained with compact and HD model, against experimental values proved that the weak avalanche model is accurate enough to capture II noise in investigated SiGe HBTs.

Noise modeling of advanced technology high speed SiGe HBTs

Noise parameters of SiGe HBTs fabricated in different technologies were measured in the 1–26 GHz frequency range. The standard dc, ac characteristics and noise parameters were compared to the compact model HICUM. Very good agreement was obtained for all technologies. The noise parameters were simulated with a new systematic noise correlation model, implemented and realized in HICUM via Verilog-A. The model was verified up to 500 GHz against TCAD simulations and Boltzman Transport equation solution method. The compact realization of the new noise correlation model is applicable to all SPICE-like circuit simulators.

Microwave Noise In Biased AlGaN/GaN And AlGaN/AlN/GaN Channels

Noise temperature is measured at 10 GHz at room temperature for biased AlGaN/GaN and AlGaN/AlN/GaN two‐dimensional channels. Interpretation of the experimental results, through Monte Carlo simulation, takes into account interaction of hot electrons with phonons. The calculated longitudinal noise temperature exceeds the transverse one, but the resultant anisotropy of noise becomes substantially weaker when accumulation of nonequilibrium (hot) optical phonons is taken into account. The considered intense interaction of hot electrons with hot phonons and weak coupling with the thermal bath shifts the hot‐electron‐hot‐phonon subsystem closer to the equilibrium at the elevated temperature as compared with the hot‐electron subsystem interacting with the equilibrium phonons.

Microscopic modeling of high frequency noise in SiGe HBTs

The SIMS doping profile of SiGe heterojunction bipolar transistor is calibrated for best agreement of the hydrodynamic model results with the experiment. DC and small-signal data is used for the calibration. The terminal current noise calculations are performed using both hydrodynamic and drift-diffusion models with the calibrated doping profile. The calculation results are compared with the experimental values. Overall good agreement for the minimum noise figure, the noise resistance, and the optimum reflection coefficient is obtained. The difference between the hydrodynamic and drift-diffusion model results is analyzed using spectral intensities of the base and collector current fluctuations.

Spherical harmonics solver for coupled hot-electron — Hot-phonon system

In polar semiconductors with intensive electron-optical-phonon interaction excess energy of non-equilibrium (hot) electrons, supplied by the external electric field, is transferred to longitudinal optical (LO) phonons. LO phonons are displaced from equilibrium with the thermal bath, and hot-phonon effects take place. The kinetics of such a non-equilibrium electron/optical-phonon system is described by two coupled nonlinear Boltzmann-type equations for the non-equilibrium electron and LO phonon distribution functions. Here, to our knowledge for the first time, we present a spherical harmonics expansion (SHE) method for the coupled system for electrons and LO phonons. The nonlinear system of coupled equations is solved with a Gummel type iterative scheme and the Newton-Raphson method. Simulation results are verified against a Monte Carlo model and good agreement is obtained. Hot phonon effects increase the mean energy of electrons and decrease the drift velocity.

Microscopic modeling of impact-ionization noise in SiGe heterojunction bipolar transistors

Terminal current noise calculations are performed for a SiGe heterojunction bipolar transistor in a wide range of collector-emitter bias conditions. The generalized hydrodynamic (HD) model with a local temperature approach for avalanche generation is used. The parameters of the local temperature model are calibrated by matching the avalanche multiplication factor to results obtained by full-band Monte Carlo simulations. The noise figure calculation results are compared with experimental values and overall good agreement is obtained. The hydrodynamic and a drift-diffusion (DD) model are used to investigate terminal current noise due to impact-ionization. The behavior of the current noise spectral intensity is found to be different for the two models. The Fano factor of the collector current fluctuations is well described by the avalanche multiplication factor in the case of the DD model, whereas the HD model evidences no correlation between the Fano factor and the avalanche multiplication factor. The collector terminal electron transfer functions are used to discuss the difference.

Langevin-Boltzmann approach for fluctuations in a hot-electron-hot-phonon system

A deterministic model for fluctuations in a non-equilibrium bulk electron-phonon system based on the Boltzmann-Langevin equation is used to investigate the influence of nonequilibrium (hot) phonons on electron small signal and noise properties of undoped bulk GaN at room temperature. The discretization of the kinetic equations for the coupled electron-phonon system and stabilization of the Newton-Raphson scheme is discussed. The hot-phonon effect enhances the electron noise temperature and reduces the small signal mobility at a low frequency. The hot-phonon contribution are important above the frequency defined by the hot-phonon lifetime.

Investigation of SiGe Heterojunction Bipolar Transistor over an Extreme Temperature Range

Dc, high frequency (hf) characteristics and noise of SiGe HBTs were investigated in a wide ambient temperature (T) range from 4 K to 423 K. SiGe HBTs with low emitter concentration (LEC) and trapezoidal Ge base doping were found good candidates for cryogenic applications. Both hydrodynamic (HD) device simulation and compact model (CM) HICUM show good agreement with experimental data in the temperature range of 300 K–423 K. The collector current did not show any leakage related to electric field assisted tunneling via traps in the base. Rapid decrease of transit frequency (fT) with T is explained in terms of the carrier delay distribution. Noise figure (NFmin) analysis reveals that the main noise contributors are related to collector current fluctuations (shot‐like noise) and thermal noise in the base at high T. Base current fluctuations related noise becomes of importance only at high injection. Simulated diffusion noise distribution shows that collector terminal electronic noise originates at the emitter‐base (BE) junction but not in base‐collector (BC) junction area.Dc, high frequency (hf) characteristics and noise of SiGe HBTs were investigated in a wide ambient temperature (T) range from 4 K to 423 K. SiGe HBTs with low emitter concentration (LEC) and trapezoidal Ge base doping were found good candidates for cryogenic applications. Both hydrodynamic (HD) device simulation and compact model (CM) HICUM show good agreement with experimental data in the temperature range of 300 K–423 K. The collector current did not show any leakage related to electric field assisted tunneling via traps in the base. Rapid decrease of transit frequency (fT) with T is explained in terms of the carrier delay distribution. Noise figure (NFmin) analysis reveals that the main noise contributors are related to collector current fluctuations (shot‐like noise) and thermal noise in the base at high T. Base current fluctuations related noise becomes of importance only at high injection. Simulated diffusion noise distribution shows that collector terminal electronic noise originates at the emitter...

Microscopic modeling of fluctuations in polar semiconductors with high density electron gas

Numerical methods for microscopic modeling of electronic fluctuations are considered. A deterministic Boltzmann-Langevin method for simulation of the long-lasting correlations is proposed for a coupled hot-electron-hot-phonon gas in a polar semiconductor. The effects of the nonequilibrium phonons and the Pauli exclusion principle on spectra of the hot-electron noise temperature are demonstrated.