The impact of carrier trapping at the substrate/buried oxide interface on the LF noise characteristics of Fully Depleted
MOSFETs has been calculated. The channel LF noise analysis based on carrier number fluctuation approach has been
extended to include charge variations at the substrate/buried oxide interface. The impact of fluctuations of substrate/BOX
interfacial charge on the channel drain current has thereby been studied as a function of gate bias. The results suggest
that substrate doping concentration, buried oxide thickness and dielectric material have non-negligible effect on the
contribution of the substrate interface noise to the total device noise. To our knowledge, the contribution of this noise to
the total noise of a FD-SOI device has never been studied.
Drain current-gate voltage Id(Vg) characteristics and power spectral density of drain current fluctuations were obtained on SiGe channel pMOSFETs and on their Si homologues, for drain current intensities varied from deep subthreshold to strong inversion regions. Devices with 2.2nm thick SiO2 gates and channel lengths 50nmd(Vg) characteristics, served for calculating the power spectral density versus drain current functions. The latter required adjusting the interface trap density and a parameter αc, accounting for the effect of the interface charge fluctuations on the hole mobility fluctuations, significant at high levels of trap filling i.e. high drain current. We found that the power spectral density in the SiGe devices was up to 10 times lower than in the Si controls at sufficiently high drain currents. The simulation, accounting for the data, required a significant lowering of αc for the SiGe channel. That implies that the low frequency noise reduction in SiGe MOSFETs results from a weaker interaction of the SiGe holes with the interface charges. The sub-0.1μm channel devices show a similar noise lowering, in spite of the significant hole mobility degradation.
A review of recent results concerning the low frequency noise in modern CMOS devices is given. The approaches such as the carrier number and the Hooge mobility fluctuations used for the analysis of the noise sources are presented and illustrated through experimental data obtained on advanced CMOS generations. The application of low frequency noise measurements as a characterization tool for large area MOS devices is also discussed. The main physical characteristics of random telegraph signals (RTS) observed in small area MOS transistors are reviewed. The impact of scaling down on the low frequency noise and RTS fluctuations in CMOS silicon devices is also addressed. Experimental results obtained on 0.35-0.12 μm CMOS technologies are used to predict the trends for the noise in future CMOS technologies e.g. 0.1μm and beyond. The formulation of thermal noise underlying the low frequency 1/f or RTS fluctuations in MOSFETs is also recalled for completeness.
Today, electromigration-the transport of metal caused by electrical current-is one of the major reliability problem. It is well known, the grain boundary is the main diffusion path in polycrystalline lines, but do not exist in bamboo lines. The new metallizations using barrier and cap layers generate a new diffusion path at the metal interfaces. In this paper, wafer-level electromigration tests were performed on TiN/AlCu/TiN/Ti lines. The activation energy and the lifetime are extracted for three linewidths with bamboo (0.7 micrometers ) and non-bamboo structures (3 micrometers and 5 micrometers ). The values are ranged between 0.91 eV (0.7 micrometers wide line) highlighting the interfacial diffusion and 0.67 eV (3 micrometers wide line) revealing the grain boundary diffusion. The extrapolated lifetimes are calculated. The bamboo line shows a lifetime dramatically higher than the non-bamboo lines. Finally, the failure locations are determined. They are randomly distributed for the widest lines, but the failures are always located near the cathode end segment in the bamboo line. This failure location is explained by the relation between the main diffusion path and the ion flux divergence.
Conference Committee Involvement (1)
Noise and Fluctuations in Circuits, Devices, and Materials
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