Influence Of Ballistic Effects In Ultra-Small MOSFETs

1. Influence Of Ballistic Effects In Ultra-Small MOSFETs J. SAINT MARTIN, V. AUBRY-FORTUNA, A. BOURNEL, P. DOLLFUS, S. GALDIN, C. CHASSAT stmartin@ief.u-psud.fr INSTITUT D'ÉLECTRONIQUE FONDAMENTALE IEF, UMR CNRS 8622, Université Paris Sud, Centre scientifique d'Orsay - Bât. 220 F-91405 ORSAY cedex FRANCE

2. Contents • Introduction • Channel length and ballistic transport • Bias dependence on ballisticity • Ballisticity and long-channel effective mobility

3. Contents • Introduction • Channel length and ballistic transport • Bias dependence on ballisticity • Ballisticity and long-channel effective mobility

4. Transport in decanano MOSFET Front gate Scattering counting region y 0 Source Drain Back gate Entrance Exit Quasi-ballistic transport: electron mean free path is similar to Lch • Bint = % of ballistic electrons at the drain-end • Beff = Monte Carlo simulation

5. Contents • Introduction • Channel length and ballistic transport • Bias dependence on ballisticity • Ballisticity and long-channel effective mobility

6. LG Fm = 4.46 eV VDD = 0.7 V SiO2 Tox = 1.2 nm x 5×1019 cm-3 5×1019 cm-3 y TSi = 5 nm 0 Undoped Tox = 1.2 nm SiO2 Tspacer = 5 nm Lch Ts pacer = 5 nm Toverlap = 5 nm Toverlap = 5 nm Studied devices

7. Transition for Lch≈ 50 nm in undoped channels From quasi-stationary to quasi-ballistic

8. Bint strongly increases for Lch < 100 nm Ballisticity and channel length

9. Gap between Bint and Beff no more constant for Lch < 30 nm Ballisticity and current

10. Strong impact of Bint on Beff for Bint < 20 % Beff(Bint): quasi linear correlation for Bint > 20% Beff(Bint) in undoped channels Decreasing impact of Bint on Beff

11. Contents • Introduction • Channel length and ballistic transport • Bias dependence on ballisticity • Ballisticity and long-channel effective mobility

12. Bint decreases whenVGS increases Bint decreases when VDS increases Bint as a function of VDS for different VGS

13. sta or bal sta or bal bal ‘sta-bal’ ‘bal-sta’ ‘Sta-bal’ and ‘bal-sta’ architectures sta

14. Bint decrease is due to scatterings in the 2nd half of the channel Bint (VDS): ‘sta-bal’ vs. ‘bal-sta’ Higher phonon scattering rate > driving field

15. Contents • Introduction • Channel length and ballistic transport • Bias dependence on ballisticity • Ballisticity and long-channel effective mobility

16. Ion and Bint increase similarly eff saturation for x > 0.15 Studied strained SGMOS LG = 25 nm V. Aubry-Fortuna et al.,to be published • ‘x’ increase • Strain increase • mt population increase • eff enhancement SiO2 Tox = 0.7 nm 2×1020 cm-3 2×1020 cm-3 LG = 18 nm TSi = 10 nm Strained Si 1.2×1019 cm-3 1.2×1019 cm-3 Si1-xGex (P) Pseudo substrate

17. Bint more relevant than µeff to account for Ion (Bint(Ion) linear for Bint [ 15%, 30%]) Ion(Bint) vs. Ion(eff)

18. Conclusions • Connections between Bint and: • channel length • strain • bias • High quasi ballistic influence for Bint < ≈ 20 % • Bint more relevant than µeff to account for Ion Role of MOS architecture (cf. paper)