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Properties of Self-Aligned Short-Channel Graphene FETs

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Abidur Rahman
Abidur Rahman
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Properties of Self-Aligned Short-Channel Graphene Field-Effect Transistors Based on Boron-Nitride- Dielectric Encapsulation and Edge Contacts Source: IEEE Transactions on Electron Devices (Volume: 62, Issue: 12) Presented By- Kazi Mohammad Abidur Rahman
“
Key Terms: ◇ Self-Aligned Short Channel gFETs ◇BN-dielectric encapsulation ◇ Edge contact ◇ Virtual-Source transport model ◇ Balastic Conductivity & mobility ◇ Quantum Capacitance
Device Stucture1
SiO2 substrate h-BN Monolayer Graphene Cr/Au HfO2 • h-BN dielectric Encasultion • Ballistic Conduction in Graphene • Short Channel about 65nm
Typical FETs Self Aligned Short Channel Self Aligned model • Effective Oxide Thickness >> 3.5nm • Channel Length >> 65nm
Electrical Characteristics2
ID(mA/µm) ID(mA/µm) VD (V) VD (V) • Non-Saturating Characteristics in Short Channel/Gate length. • Ballistic Conduction/ transport.
Virtual Source Model3
Modelling Equations: ◇ 𝐼 𝐷 𝑊 = (𝑄 𝑥0𝑒+𝑄 𝑥ℎ0)𝑣 𝑥𝑜 𝐹𝑠𝑎𝑡 ◇ 𝐹𝑠𝑎𝑡 = 𝑉 𝐷𝑆 ′ 𝑉𝑠𝑎𝑡 (1+( 𝑉′ 𝐷𝑆 𝑉𝑠𝑎𝑡)1 𝛽) 𝛽 ◇ 𝑉𝑠𝑎𝑡 = 𝐿 𝐺 𝑣 𝑥0 𝜇 ◇ 𝑄 𝑥0𝑒(ℎ) = 0 ∞ 8𝜋 𝐸 (ℎ𝑣)2 + 1 1+𝑒 (𝐸+𝐸 𝑐𝑠(𝑑)) 𝑘 𝐵×𝑇dE ◇ 𝐶 𝑄 ≈ 𝐶 𝑄𝑖 1 + ( 𝐸 𝑐 𝑘 𝐵×𝑇×ln(4) )2 Parameters: ID = drain current W = device width Qx0e and Qx0h = arial electron and hole densities Vx0 = carrier injection velocity CQ = quantum capacitance
Analysis from VS model: 𝐿 𝐺 𝐿 𝐺(nm) (nm) Vx0(107 cm/s) 𝜇(103 𝑐𝑚2 /Vs) • Carrier injection velocity decreases & mobility increases with increase in gate length. • Ballistic conduction nature decreases with increase in LG
Some Experimental Outcomes ◇Channel Length(LG) down to 67nm. ◇Highest ballistic velocity and effective mobility achieved were 9.3× 107 cm/s and 13700cm2/Vs.>> highest in any gFET.
Quantum Capacitance • An important consideration for low-density-of-states systems e.g. 2-D materials. • Acts in series with Electrostatic Capacitance. • 𝐶𝑒𝑞 = 𝐶 𝑜𝑥 𝐶 𝑄/ 𝐶 𝑜𝑥 + 𝐶 𝑄 • CQ prevents Ceq from being reduced below CQ. 𝐶𝑒𝑞𝐶𝑜𝑥 𝑡 𝑜𝑥 −1 (nm-1)
Effects of Quantum Capacitance ◇Degrades trans-conductance (gm) and output conductance (gds) characteristics. ◇Achieved gm=600µS/µm & gds =300µS/µm. ◇Substantially worse than Si CMOS.
Conclusion ◇Ballistic Short-Channel h-BN encapsulated GFETs with EOT<3.5nm exhibits highest achieved mobility and carrier velocity. ◇Though shows some limitations due to some fundamental limitations of graphene. ◇GFETs can be solution for future nanodevices.
Thanks! Any questions?

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Properties of Self-Aligned Short-Channel Graphene FETs

  • 1. Properties of Self-Aligned Short-Channel Graphene Field-Effect Transistors Based on Boron-Nitride- Dielectric Encapsulation and Edge Contacts Source: IEEE Transactions on Electron Devices (Volume: 62, Issue: 12) Presented By- Kazi Mohammad Abidur Rahman
  • 2. “
  • 3.
  • 4. Key Terms: ◇ Self-Aligned Short Channel gFETs ◇BN-dielectric encapsulation ◇ Edge contact ◇ Virtual-Source transport model ◇ Balastic Conductivity & mobility ◇ Quantum Capacitance
  • 6. SiO2 substrate h-BN Monolayer Graphene Cr/Au HfO2 • h-BN dielectric Encasultion • Ballistic Conduction in Graphene • Short Channel about 65nm
  • 7. Typical FETs Self Aligned Short Channel Self Aligned model • Effective Oxide Thickness >> 3.5nm • Channel Length >> 65nm
  • 9. ID(mA/µm) ID(mA/µm) VD (V) VD (V) • Non-Saturating Characteristics in Short Channel/Gate length. • Ballistic Conduction/ transport.
  • 11. Modelling Equations: ◇ 𝐼 𝐷 𝑊 = (𝑄 𝑥0𝑒+𝑄 𝑥ℎ0)𝑣 𝑥𝑜 𝐹𝑠𝑎𝑡 ◇ 𝐹𝑠𝑎𝑡 = 𝑉 𝐷𝑆 ′ 𝑉𝑠𝑎𝑡 (1+( 𝑉′ 𝐷𝑆 𝑉𝑠𝑎𝑡)1 𝛽) 𝛽 ◇ 𝑉𝑠𝑎𝑡 = 𝐿 𝐺 𝑣 𝑥0 𝜇 ◇ 𝑄 𝑥0𝑒(ℎ) = 0 ∞ 8𝜋 𝐸 (ℎ𝑣)2 + 1 1+𝑒 (𝐸+𝐸 𝑐𝑠(𝑑)) 𝑘 𝐵×𝑇dE ◇ 𝐶 𝑄 ≈ 𝐶 𝑄𝑖 1 + ( 𝐸 𝑐 𝑘 𝐵×𝑇×ln(4) )2 Parameters: ID = drain current W = device width Qx0e and Qx0h = arial electron and hole densities Vx0 = carrier injection velocity CQ = quantum capacitance
  • 12. Analysis from VS model: 𝐿 𝐺 𝐿 𝐺(nm) (nm) Vx0(107 cm/s) 𝜇(103 𝑐𝑚2 /Vs) • Carrier injection velocity decreases & mobility increases with increase in gate length. • Ballistic conduction nature decreases with increase in LG
  • 13. Some Experimental Outcomes ◇Channel Length(LG) down to 67nm. ◇Highest ballistic velocity and effective mobility achieved were 9.3× 107 cm/s and 13700cm2/Vs.>> highest in any gFET.
  • 14. Quantum Capacitance • An important consideration for low-density-of-states systems e.g. 2-D materials. • Acts in series with Electrostatic Capacitance. • 𝐶𝑒𝑞 = 𝐶 𝑜𝑥 𝐶 𝑄/ 𝐶 𝑜𝑥 + 𝐶 𝑄 • CQ prevents Ceq from being reduced below CQ. 𝐶𝑒𝑞𝐶𝑜𝑥 𝑡 𝑜𝑥 −1 (nm-1)
  • 15. Effects of Quantum Capacitance ◇Degrades trans-conductance (gm) and output conductance (gds) characteristics. ◇Achieved gm=600µS/µm & gds =300µS/µm. ◇Substantially worse than Si CMOS.
  • 16. Conclusion ◇Ballistic Short-Channel h-BN encapsulated GFETs with EOT<3.5nm exhibits highest achieved mobility and carrier velocity. ◇Though shows some limitations due to some fundamental limitations of graphene. ◇GFETs can be solution for future nanodevices.