Noise In SiGe HBTs Research Articles

Random telegraph noise in SiGe HBTs: Reliability analysis close to SOA limit

In this paper, we present extensive random telegraph signal (RTS) noise characterization in SiGe heterojunction bipolar transistors. RTS noise, observed at the base, originates at the emitter periphery while at the collector side distinct RTS noise is observed at high-injection that originates from the traps in the shallow trench regions. Time constants extracted from RTS during aging tests allow understanding of trap dynamics and new defect formation within the device structure. This paper provides the first demonstration of RTS measurements during accelerated aging tests to study and understand generation of defects under bias stress in SiGe HBTs operating at the limit of their safe-operating area.

Graded Applications of NQS Theory for Modeling Correlated Noise in SiGe HBTs

In this paper, we develop a correlated noise model for bipolar transistors from an accurate nonquasi-static model. The proposed noise model includes the signal delay through base-collector space-charge region and is implemented using four extra nodes. We also present a simplified version of the same model that requires only two extra nodes. A further simplified version that uses only one extra node is found to be identical with a state-of-the-art correlated noise model. When compared with the device simulation data, our proposed models show improved accuracy compared with the existing state-of-the-art noise models.

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 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> = 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 Chynoweth's 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 (NF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> , R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> , and Gamma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OPT</sub> ), 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.

Frequency and bias-dependent modeling of correlated base and collector current RF noise in SiGe HBTs using quasi-static equivalent circuit

This paper presents modeling of correlated RF noise in the intrinsic base and collector currents of SiGe heterojunction bipolar transistors using quasi-static equivalent circuits. The noises are first extracted from measured noise parameters using standard noise circuit analysis. Using the extraction results, model equations are proposed to describe both the frequency and bias dependence of the correlated noise sources using a single set of model parameters. The model is demonstrated using noise data from both measurement and microscopic noise simulation. The model is shown to work at frequencies up to at least half of the peak f/sub T/ and at biasing currents below high injection f/sub T/ rolloff.

Scaling and technological limitations of 1/f noise and oscillator phase noise in SiGe HBTs

This paper examines the impact of SiGe HBT scaling on 1/f noise and phase noise of oscillators and frequency synthesizers. The increase of transistor speed with scaling is shown to significantly increase the sensitivity of oscillation frequency to 1/f noise and, thus, degrade close-in phase noise, but decrease the sensitivity of oscillation frequency to base current shot noise and base resistance thermal noises. The results show that corner offset frequency defined by the intersect of the 1/f3 and 1/f2 phase noise has little to do with the traditional 1/f corner frequency. The relative importance of individual noise sources in determining phase noise is examined as a function of technology scaling, device sizing, and oscillation frequency. The collector current shot noise and base resistance noise are shown to set the fundamental limits of phase noise reduction. A methodology to identify the maximum tolerable 1/f K factor is established and demonstrated for the HBTs used

On the scaling limits of low-frequency noise in SiGe HBTs

The low-frequency noise in high-speed transistors generally increases (degrades) as device technologies down-scale for higher performance. Interestingly, the latest generation of deep-submicron SiGe HBTs breaks this trend, and we find record-low noise corner frequencies of 220 Hz in SiGe HBTs with a peak f T of 210 GHz. An explanation for this behavior based on a reduction of the number of dominant noisy traps is offered, and microscopic 2-D simulations of noise are used to support this claim and explore the origins and scaling limits of low-frequency noise in advanced SiGe HBTs.

Investigation of Compact Models for RF Noise in SiGe HBTs by Hydrodynamic Device Simulation

A comprehensive investigation of the SPICE and unified compact noise models is performed by comparison with the more fundamental hierarchical hydrodynamic device model. It is shown that the rather simple SPICE and unified compact noise models yield good results for frequencies up to 10 GHz for state-of-the-art SiGe HBTs with a low base resistance. The base noise resistance, a key parameter of the compact noise models turns out to be independent of frequency and bias. It can be well estimated based on the sheet resistance of the intrinsic and extrinsic base or with the modified circle-fit method. The unified model, which in comparison to the SPICE model considers in addition the finite transit time of shot noise, is found to be somewhat more accurate than the SPICE model, especially at higher frequencies and collector currents. But this is achieved at the expense of a transit time parameter which cannot be determined without accurate and detailed noise measurements or physics-based numerical simulations.

Impact of geometrical scaling on low-frequency noise in SiGe HBTs

The influence of geometrical scaling on low-frequency noise in SiGe HBTs is presented. Small-size transistors show a strong variation in noise across many samples, whereas the noise in larger devices is more statistically reproducible. This size-dependent variation in noise can produce challenges for accurate compact modeling. This effect is investigated using reverse-bias emitter-base stress and calculations based on the superposition of generation/recombination noise.

Experimental verification and numerical application of the thermodynamic approach to high-frequency noise in SiGe HBTs

We present experimental and numerical results on high-frequency noise of Silicon-Germanium heterojunction bipolar transistors (SiGe HBTs) based on small-signal analysis. The minimum noise figure for an SiGe HBT is determined from s-parameter measurements. The approach is verified through comparison with a conventionally measured noise figure and can be used to extract the noise figure from device simulation. By using a two-dimensional device simulation code, we calculate the high-frequency noise figure from the simulated y-parameters. The simulation results are in good agreement with the measured minimum noise figure. We use the model to predict the effect of lateral downscaling on the minimum noise figure.