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

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

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

Transport in decanano MOSFET B int = % of ballistic electrons at the drain-end B eff = EntranceExit y 0 Scattering counting region SourceDrain Front gate Back gate Monte Carlo simulation Quasi-ballistic transport: electron mean free path is similar to L ch

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

Studied devices  m = 4.46 eV V DD = 0.7 V T ox = 1.2 nm T Si = 5 nm L ch LGLG T ox = 1.2 nm T spacer = 5 nm SiO 2 Undoped 5×10 19 cm -3 T overlap = 5 nm y x 0

From quasi-stationary to quasi-ballistic Transition for L ch ≈ 50 nm in undoped channels

Ballisticity and channel length B int strongly increases for L ch < 100 nm

Ballisticity and current Gap between B int and B eff no more constant for L ch < 30 nm

B eff (B int ) in undoped channels Strong impact of B int on B eff for B int < 20 % Decreasing impact of B int on B eff B eff (B int ): quasi linear correlation for B int > 20%

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

B int as a function of V DS for different V GS B int decreases when V DS increases B int decreases when V GS increases

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

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

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

Studied strained SGMOS 1.2×10 19 cm -3 T ox = 0.7 nm T Si = 10 nm L G = 25 nm SiO 2 Strained Si 1.2×10 19 cm -3 2×10 20 cm -3 2×10 20 cm -3 Si 1-x Ge x (P) Pseudo substrate L G = 18 nm V. Aubry-Fortuna et al.,to be published ‘x’ increase  Strain increase  m t population increase   eff enhancement  eff saturation for x > 0.15 I on and B int increase similarly

I on (B int ) vs. I on (  eff ) B int more relevant than µ eff to account for I on (B int (I on ) linear for B int  [ 15%, 30%])

Conclusions  Connections between B int and: channel length strain bias  High quasi ballistic influence for B int < ≈ 20 %  B int more relevant than µ eff to account for I on Role of MOS architecture (cf. paper)