Tunnel Field Effect Transistor (TFET) is a gated reverse biased p-i-n structure characterized by band-to-band tunneling for current conduction, unlike MOSFETs which use thermionic emission. Key features of TFET include very low off current, low on current, high ion/ioff ratio, and subthreshold swing not limited to 60 mV/decade. The tunneling current is notably sensitive to the effective mass of charge carriers and other parameters such as the energy bandgap.

1. Introduction
to Tunnel
Field Effect
Transistor
- Gadarapulla Rasheed
28-06-2024 1

2. Introduction to Tunnel FET
• Tunnel FET is a gated reverse biased P-I-N structure.
• Basic structure of TFET consists of source, channel and drain. Unlike
MOSFETs, the doping of the drain and the source are of opposite types in
a TFET.
• The current conduction mechanism of TFET is Band-to-Band Tunneling
(BTBT) whereas in a MOSFET, it is due to the thermionic emission of the
carrier over the potential barrier.
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VD > 0 V VS= 0
VGS > 0
VD < 0 V VS= 0
VGS < 0

3. The Concept of Tunneling
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Source: The Tunneling Transistor, by Alan Seabaugh (IEEE Spectrum, Oct 2013)

4. Energy Band Diagram of n-TFET
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5. Subthreshold Swing (SS)
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Transfer char. of MOSFET and Tunnel FET
[Ionescu A.M et al., Nature, 2011]
In a MOSFET,
SS = 1 +
𝐶𝑑
𝐶𝑜𝑥
ln(10)
𝑘𝑇
𝑞
SS ≈ 60 mV/decade @ 300 K
Subthreshold Swing (SS)=
𝑑𝑉𝐺𝑆
𝑑𝑙𝑜𝑔10𝐼𝐷
Subthreshold Slope =
1
𝑆𝑢𝑏𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑 𝑆𝑤𝑖𝑛𝑔
due to Boltzmann distribution of charge carriers.

6. Features of Tunnel FET
 Very low OFF current (IOFF)
 Low ON current (ION)
 High ION/IOFF ratio
 Band-to-band tunnelling
 SS is not limited to 60mV/decade
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𝐼𝐷 ∝ exp −
4 2m∗𝐸𝑔
∗
3
2
3 𝑒 ℏ 𝐸𝑔
∗
+ ΔΦ
𝜀Si
𝜀ox
𝑡ox𝑡Si ΔΦ


















E
e
3
2
3
*
g
E
*
2m
4
exp
BTBT
T

Where,
m∗
- effective mass of charge
𝐸𝑔
∗
- effective energy bandgap
εsi, εox - permittivity of Si and oxide
tSi, tox- thickness of Si and oxide
ΔФ – Energy overlap window
E - Electric Field
Tunneling probability,
• Tunneling current is most sensitive to the effective
masses because the tunneling probability depends
exponentially on them.

7. 28-06-2024 7
Thank You