Excess noise in AlGaAs/GaAs heterojunction bipolar transistors andassociated TLM test structures

Noise measurements both on transmission line model (TLM) test structures and on associated HBT's are presented. Contact noise is proved to be negligible in the TLM's related to the base structure of transistors. A Hooge parameter for p⁺⁺ doped GaAs is extracted. Activation energies are calculated from results versus temperature. Considering the TLM related to the structure of the emitter, it is shown that the g-r levels observed originate from the AlGaAs layer. Noise measurements on HBT's also exhibit excess noise. A value of the cutoff frequency between the equivalent input current white noise and the 1/f component is given. The base current dependencies associated with different measurement configurations suggest the 1/f noise to come from the base or the emitter-base junction. The g-r components are studied as a function of temperature. Activation energies are deduced. Finally a comparison of the TLM and HBT noise results is presented. The presence of the complex DX center and of g-r levels in the base region are proposed as possible origins for the g-r noise in HBT's     

Une nouvelle définition des volumes libres dans les liquides non associés: application à la détermination des diamètres moléculaires

Résumé Une étude systématique des volumes libres extrapolés à fluidité nulle a été menée sur une vingtaine de liquides. Une nouvelle équation est proposée pour ce volume libre limite, noté «V.L.L.» et nous la comparons à celle déduite des calculs de l'Hydrodynamique classique; elle permet de déterminer les valeurs de diamètres moléculaires; ces dernières sont en bon accord avec celles obtenues de la viscosité des gaz, de la diffusion Raman ou Rayleigh. En outre, et aux erreurs expérimentales près, les valeurs des diamètres moléculaires sont données pour 10 dérivés du benzène, valeurs qui ne se trouvent pas, à notre connaissance, dans la littérature, exception faite du benzène pur.

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Summary A systematic study of free volumes extrapolated at zero fluidity is executed for 20 liquids. A new equation for this Limit Free Volume (V.L.L.) is proposed and compared with the theoretically calculated free volume; values of molecular diameters are determined and found to be in good agreement with values obtained from gas viscosity, Raman and Rayleigh scattering, respectively. Moreover, within experimental error, values of molecular diameters are found for 10 benzene derivatives which are not, at our knowledge, available in the literature, except for pure benzene.

Avec 1 figure et 3 tableaux     

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

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.     

Low frequency noise in p/sup +/-GaAs resistors

The noise behaviour of p/sup +/-GaAs transmission line models (TLMs) associated with the technology of heterojunction bipolar transistors is presented. Devices of different lengths all exhibit excess noise composed of 1/f and generation-recombination noise. Noise spectra are studied as a function of different bias and different sample lengths. Contact noise is shown to be negligible. Values of the Hooge parameter alpha are extracted.<>