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?