F. Pascal

Noise correlation measurements in bipolar transistors. I. Theoretical expressions and extracted current spectral densities

Low-frequency noise measurements are performed on classical Si bipolar transistors and on AlGaAs/GaAs heterojunction bipolar transistors (HBTs) mounted in a common-emitter configuration. Expressions for the spectral densities are derived taking into account a correlation between base and collector noise sources ib and ic. Values of emitter series resistances and of the base ideality factor are determined from these noise measurements. Then the spectral densities related to ib and ic as well as the cross-spectrum are extracted. In the case of classical Si transistors, the excess noise is attributed to the current noise source ib. The effect of the base series resistance is shown on the white noise. For the HBTs, the white noise is not reached. The excess noise is attributed to the correlated current noise sources ib and ic. From the analysis of the current spectral densities with base current the increase of correlation with bias is revealed. The extracted current spectral densities provide the foundation ...

Low-frequency noise behavior of polysilicon emitter bipolar junction transistors: a review

For many analog integrated circuit applications, the polysilicon emitter bipolar junction transistor (PE-BJT) is still the preferred choice because of its higher operational frequency and lower noise performance characteristics compared to MOS transistors of similar active areas and at similar biasing currents. In this paper, we begin by motivating the reader with reasons why bipolar transistors are still of great interest for analog integrated circuits. This motivation includes a comparison between BJT and the MOSFET using a simple small-signal equivalent circuit to derive important parameters that can be used to compare these two technologies. An extensive review of the popular theories used to explain low frequency noise results is presented. However, in almost all instances, these theories have not been fully tested. The effects of different processing technologies and conditions on the noise performance of PE-BJTs is reviewed and a summary of some of the key technological steps and device parameters and their effects on noise is discussed. The effects of temperature and emitter geometries scaling is reviewed. It is shown that dispersion of the low frequency noise in ultra-small geometries is a serious issue since the rate of increase of the noise dispersion is faster than the noise itself as the emitter geometry is scaled to smaller values. Finally, some ideas for future research on PE-BJTs, some of which are also applicable to SiGe heteorjunction bipolar transistors and MOSFETs, are presented after the conclusions.

Comparison of low frequency noise and high frequency performances of double and simple polysilicon Bi-CMOS BJT

Abstract The issue of this paper concerns 0.35 μm Bi-CMOS double polysilicon bipolar transistors and 0.5 μm Bi-CMOS simple polysilicon bipolar transistors. Low-frequency noise measurements are performed. Noise spectral densities are analysed versus bias and geometry. From these noise measurements, base and emitter series resistances are extracted. A comparison of both technologies is done. Though double polysilicon transistors have a more complex structure than the simple polysilicon ones, they exhibit similar or even better performances. Indeed, DC characteristics and noise levels are equivalent for both technologies. Double polysilicon transistors exhibit a reduction of the base resistance and a significant improvement of the transition frequency f T is obtained.

Noise correlation measurements in bipolar transistors. II. Correlation between base and collector currents

Low-frequency noise measurements were performed on heterojunction bipolar transistors (HBTs) and presented in part I of this article. These measurements revealed a partial correlation between base and collector noise current sources. With the help of the current spectral densities determined in part I, the coherence function is calculated and studied versus bias in this second part. Important values of the coherence function are obtained at the highest bias. Then the spectral densities Sc and Snc associated to the correlated and uncorrelated parts of the collector current noise source are extracted and analysed. All spectra exhibit excess noise. A difference in shape is clearly observed because of an important generation-recombination component occurring around 1 kHz on the correlated part only. To compare the behavior of different transistors a normalized coupling coefficient is introduced. The correlation is seen to increase with the scaling-down of devices. The investigation of the coupling coefficient...

Impact of carbon concentration on 1∕f noise and random telegraph signal noise in SiGe:C heterojunction bipolar transistors

The influence of carbon concentration on the low-frequency noise (LF noise) of Si∕SiGe:C∕Si heterojunction bipolar transistors (HBTs) is investigated. When carbon is incorporated into these HBTs, representative noise spectra of the input current spectral density SIB show significant generation-recombination (GR) components. On the other hand, for transistors without carbon incorporation, no GR components were observed. When only 1∕f noise component is observed, the 1∕f noise level is found to be independent of the carbon concentration and the associated figure of merit of the normalized noise magnitude KB has a very good value of ∼4×10−10μm2. In order to relate the 1∕f noise and the high-frequency performance of the transistor, we studied and modeled the figure of merit defined as the ratio fc∕fT (fc is the low-frequency corner frequency and fT the unity current-gain frequency). Then we performed a detailed analysis of the GR components associated with the presence of the carbon. We found that the observe...

Characterization of polysilicon bipolar transistors by low-frequency noise and correlation noise measurements

Low-frequency noise measurements are performed in order to characterize quasi-self-aligned polysilicon bipolar transistors. After a theoretical analysis we present a study of the influence of the base source resistance on the correlation between the input and the output noise sources of the transistors. We observe that a partial correlation between the input and the output voltage noise sources appears and varies with the source resistance, the bias and the emitter size of the transistors. As a consequence we demonstrate the influence of the fluctuations of the collector current. Taking into account these results, we propose different extraction methods for the emitter and base series resistances. To confirm and extend these measurements, high-frequency results are also presented.

Analysis of 1/f noise current sources in InP/InGaAs heterojunction bipolar transistors

The 1/f noise of double InP/InGaAs heterojunction bipolar transistors is measured and analyzed. Standard mesa transistors, transistors with an air-bridge-connected base and hexagonal shaped transistors conceived for digital circuits are studied. These differences in the technology will have an influence on the origin of the noise sources. Regarding noise analysis, the base and collector internal current noise sources ib and ic are assumed to be correlated for all devices. This is highlighted by the voltage noise correlation function between the input and the output of the devices presenting an unusual behavior versus bias and geometry. The collector current noise source is divided into a correlated and uncorrelated part with base current. These parts give rise to spectral densities Sc and Snc. They are shown to have distinct origins for the different types of transistor geometry.

Influence of geometry and passivation on noise in GaInP/GaAs heterojunction bipolar transistors

First order and low-frequency noise measurements are performed on GaInP/GaAs heterojunction bipolar transistors. The base current is decomposed into different components. Passivated transistors exhibit higher gain values, hence the passivation layer limits recombinations on the extrinsic device. Noise is measured in the 1 Hz–100 kHz frequency range on common-emitter-mounted transistors. The 1/f component is analyzed. The emitter series resistances are extracted. The proximity of the base contact on the smaller devices lead to a higher noise level due to enhanced recombinations. Extrinsic and intrinsic phenomena are put forward with the help of noise analysis versus base current and collector current density. An attempt is made to locate the 1/f noise sources. Unlike first order measurements, noise characterization shows that the passivation layer can be at the origin of recombination-type phenomena.

Impact of Technological Parameters on the Low Frequency Noise of Advanced Heterojunction Bipolar Transistors

Usually, the 1/f noise sources in heterojunction bipolar transistors (HBTs) are located in the intrinsic emitter‐base (E‐B) volume, either in the E‐B junction space charge region or at the polycrystalline‐silicon/monocrystalline‐silicon interface in the neutral emitter layer. In this paper, to probe more accurately the location of the noise sources responsible for the 1/f noise, investigations on different HBTs fabricated with different technological parameters are undertaken. First, we have shown that carbon content has a negligible influence on 1/f noise level, but for high carbon content significant generation‐recombination (G‐R) noise components appear. Second, by studying influence of the emitter‐base junction depth, we have shown that the 1/f noise sources are located at the polycrystalline‐silicon/monocrystalline‐silicon interface. Using statistical estimators, we have studied and modelled the dispersion of the 1/f noise. It was found that the dispersion in the noise level increases as the inverse ...

Dc and low frequency noise analysis of hot-carrier induced degradation of low complexity 0.13 μm CMOS bipolar transistors

The dc and the low frequency noise in Si bipolar junction transistors (BJTs) of a 0.13 μm CMOS technology are presented in this paper. In particular, the influence of a superficial base doping (SBD) layer is investigated in devices before and after hot-carrier stress induced degradation. A classical increase in the perimeter non-ideal (generation/recombination) base current is observed on stressed transistors. Prestress 1/f noise analysis shows that both surface and perimeter contribution are present. Their relative importance is dependent on presence or not of the SBD and of the geometry. After stress, a very significant increase in the 1/f noise level is measured. It is associated to the creation of a large number of traps at the emitter perimeter.