Post on 13-Apr-2017
transcript
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
“According to Moor’s
Law, our device size
should be half in
every technological
generation.
Our Challenges
>>make the device smaller
>>i.e. smaller transistor
>>2-D materials like graphene
becoming researchers interest.
>>GFETs may be a solution.
Key Terms:◇ Self-Aligned Short Channel gFETs◇ BN-dielectric encapsulation◇ Edge contact◇ Virtual-Source transport model◇ Balastic Conductivity & mobility◇ Quantum Capacitance
Device Stucture1
SiO substrate
h-BN
Monolayer Graphene
Cr/Au
HfO
• h-BN dielectric Encasultion
• Ballistic Conduction in Graphene
• Short Channel about 65nm
Typical FETs
Self Aligned Short ChannelSelf Aligned model
• Effective Oxide Thickness >> 3.5nm• Channel Length >> 65nm
Electrical Characteristics2
I D (m
A/µ
m)
I D (m
A/µ
m)
VD (V)
VD (V)
• Non-Saturating Characteristics in Short Channel/Gate length.
• Ballistic Conduction/ transport.
Virtual Source Model3
Modelling Equations:
◇ = (+)
◇
◇
◇ dE
◇
Parameters:ID = drain current W = device widthQx0e and Qx0h = arial electron and hole densities
Vx0 = carrier injection velocityCQ = quantum capacitance
Analysis from VS model:
𝐿𝐺 𝐿𝐺(nm) (nm)
Vx0
( c
m/s
)
(/V
s )
• 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 9.3cm/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.
• /
• CQ prevents Ceq from being reduced below CQ.
𝐶𝑒𝑞
/𝐶𝑜𝑥
(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?