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M. Fadlallah 1,3 , G. Ghibaudo 1 , J. Jomaah 1 and G. Guégan 2

LAM. ULIS’03. M.FADLALLAH et al. Influence of ultra-thin gate oxide on the electric performance and low frequency noise of sub -0.1µm NMOSFETs. Influence of ultra-thin gate oxide on the electric performance and low frequency noise of sub -0.1µm NMOSFETs.

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M. Fadlallah 1,3 , G. Ghibaudo 1 , J. Jomaah 1 and G. Guégan 2

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  1. LAM ULIS’03 M.FADLALLAH et al. Influence of ultra-thin gate oxide on the electric performance and low frequency noise of sub -0.1µm NMOSFETs Influence of ultra-thin gate oxide on the electric performance and low frequency noise of sub -0.1µm NMOSFETs M. Fadlallah1,3, G. Ghibaudo1, J. Jomaah1 and G. Guégan2 1)IMEP/LPCS, ENSERG, BP 257, 38016 Grenoble, France 2) CEA/LETI, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France 3) LAM UFR Sciences, Moulin de la Housse, BP 1039, 51687 Reims cedex 2

  2. LAM ULIS’03 M.FADLALLAH et al. Influence of ultra-thin gate oxide on the electric performance and low frequency noise of sub -0.1µm NMOSFETs OUTLINE • Introduction • Static performance • Short Channel effect • Extraction method parameter • Low frequency noise • 1/f low frequency noise • Ohmic mode • Saturation mode • Influence of the gate current • Conclusion

  3. LAM ULIS’03 M.FADLALLAH et al. Influence of ultra-thin gate oxide on the electric performance and low frequency noise of sub -0.1µm NMOSFETs INTRODUCTION • OBJECTIVE : Ultimate CMOS devices (channel lenght<50nm & oxide thickness below 1nm) • Many problems related to the channel length shortening and ultra-thin gate oxide • 1/f noise reinforced with channel length reduction and ultra-thin oxide • High gate current

  4. STATIC PERFORMANCE Typical Id & gm vs Vg transfer characteristics

  5. -2 1,6.10 L(µm)= 0.075 -2 1,4.10 0.1 1/2 -2 1,2.10 0.175 0.25 -2 1.10 - (AV) 0.5 1 -3 8.10 Y function -3 6.10 VD=0.05V W=10µm -3 4.10 -3 2.10 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Vg (V) STATIC PERFORMANCE • Extraction of the main static MOSFET parameter using Y function The Y function is independent of : Mobility attenuation factor Series resistance of drain and source Extraction of Vt and Gm using the linear part of Y

  6. STATIC PERFORMANCE • Charge sharing effect : we can not neglect the part of charge controlled by the drain and source junction with respect to the gate • Reduction of the threshold voltage at small gate length Variation of the threshold voltage

  7. STATIC PERFORMANCE • Drain Induced Barrier Lowering (DIBL) For a MOSFET with short channel => Important penetration of electric field from the drain towards source The barrier potential at source reduces due to the influence of drain bias

  8. STATIC PERFORMANCE • DIBL EFFECT Variations of DIBL coeficient DIBL=dLog(Id)/dVd

  9. LOW FREQUENCY NOISE • 1/f noise : Two principle models • Carrier number fluctuations (Mc Whorter) • Hole trapping • Flat band voltage spectral density • Correlated mobility fluctuations : tunnelling constant (0.1nm) Nt : slow oxide trap density (/eV/cm3) : Vs/C SVFB : flat band voltage spectral density

  10. LOW FREQUENCY NOISE • 1/f noise : Two principle models • Mobility fluctuations (HOOGE) • Empiric (h=10-3-10-7) depend of the quality of devices • N : total carrier number

  11. LOW FREQUENCY NOISE • 1/f noise due to carrier number fluctuations • Oxide trap density Nt=1.1017-5.1017 /eVcm3 Variations of the normalized drain current noise SId/Id2 (symbols) and corresponding (gm/Id2) (solid line) with drain current Id

  12. LOW FREQUENCY NOISE • Variation of Svg1/2(V/Hz1/2) with gate voltage drive (Vg-Vt) for extraction of coulomb scattering coefficient 

  13. LOW FREQUENCY NOISE • 1/f noise : Saturation mode • The Good correlation between SId/Id2 (symbols) & (gm/Id)2 confirms that the sources of 1/f noise of these devices are the carrier number fluctuations due to electron trapping in the oxide • Nt values extracted in saturation confirm those obtained in the linear regime

  14. 1.10 1.10 0 0 - - 1 1 1.10 1.10 VD=0.05V W=10µm VD=0.05V W=10µm VD=0.05V W=10µm - - 2 2 1.10 1.10 0.055 0.055 0.055 1.10 1.10 - - 3 3 - - 4 4 1.10 1.10 L(µm) = L(µm) = L(µm) = - - 5 5 1.10 1.10 0.5 0.5 0.5 0.5 0.5 0.5 - - 6 6 1.10 1.10 Id (A) Id (A) Id (A) 0.25 0.25 0.25 - - 7 7 1.10 1.10 0.175 0.175 0.175 - - 8 8 1.10 1.10 0.15 0.15 0.15 1.10 1.10 - - 9 9 0.1 0.1 0.1 1.10 1.10 - - 10 10 gate gate gate curent (A) curent (A) curent (A) 0.065 0.065 0.065 - - 11 11 1.10 1.10 0.055 0.055 0.055 - - 12 12 1.10 1.10 NMOS NMOS NMOS t t t =1.2nm =1.2nm =1.2nm ox ox ox 1.10 1.10 - - 13 13 1.10 1.10 - - 14 14 - - 0.5 0.5 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 Vg Vg Vg (V) (V) (V) INFLUENCE OF THE GATE CURRENT • the impact of the gate current relatively high proved to be critical for advanced devices • the ultra-thin gate oxide is not harmful for the functionality of devices in static terms and 1/f noise

  15. CONCLUSIONS • Output transfer characteristics • 1/f noise in linear and saturation modes • the source of 1/f noise is always due to the carrier number with correlated mobility fluctuations • The slow oxide trap density deduced in linear and saturation modes is a good indication of the quality of ultra-thin dielectric • the ultra-thin gate oxide is not harmful for the functionality of devices in static terms and noise

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