Introduction to 3D transistors
Need for 3D transistors
Comparison with 2D transistors
3D transistors employ a single gate stacked on top
of two vertical gates allowing for essentially three
times the surface area for electrons to travel, without
increasing the size of the gate.
The Gate is the terminal that drives the transistor on
and off, and acts like a capacitance where charge is
stored making the channel conductive. When the
gate is charged, it creates an inversion layer between
the Source and the Drain,
where electrons can flow.
The number of transistors on an integrated circuit
doubles approximately every two years which is
achieved by scaling down the transistor size.
Silicon-only planar transistors are fast approaching their
Short channel effects limiting scaling into sub nanometer
Oxide thickness cannot be scaled down further, problems
Need to keep Silicon technology as the base technology
while innovating future devices; cost is an important
Performance and power dissipation need to be improved.
Smaller is faster !!
Planar MOSFET Scaling (Short-Channel Effect)
Lg = 0.35 m, Tox = 8 nm
Lg = 0.18 m, Tox = 4.5 nm
Lg = 0.10 m, Tox = 2.5 nm
Lg = 0.07 m, Tox = 1.9 nm
a. DIBL (Drain Induced Barrier Lowering) effect
shifts the characteristics to the left when VD is
b. S increases when the channel length is
3D or Tri-Gate transistors form conducting channels
on three sides of a vertical fin structure, providing
“fully depleted” operation and tighter control on the
The additional control enables as much transistor
current flowing as possible when the transistor is in
the 'on' state (for performance), and as close to zero
as possible when it is in the 'off' state (to minimize
power), and enables the transistor to switch very
quickly between the two states (again, for
performance) due to improved sub-threshold slope
and increased inversion layer area provides higher
The steeper sub-threshold slope can also be used to target a
lower threshold voltage, allowing transistors to operate at lower
voltage to reduce power and/or improve switching speed.
2D vs. 3D transistor
22 nm 3D Tri-Gate
operate at lower
voltage with good
power by >50%
Dramatic performance gain at low operating
voltage, better than Bulk Planar transistor
37% performance increase at low voltage
>50% power reduction at constant performance
Improved switching characteristics (On current vs.
Higher drive current for a given transistor footprint
implies better performance
More compact hence enabling higher transistor
density which translates to smaller overall
The primary challenges to integrating non planar trigate devices into conventional semiconductor
manufacturing processes include:
Fabrication of a thin silicon "fin" tens of
Fabrication of matched gates on multiple sides of
The new chip technology, called tri-gate transistors,
replaces flat, two-dimensional streams of transistors
with a 3D structure.
The technology will allow manufacturers to create
transistors that are faster, smaller and more powerefficient which will be used in the next generation of
desktops, laptops and mobile chips.
Tri-Gate transistors are an important innovation
needed to continue Moore’s Law.
 Isabelle Ferain, Cynthia A. Colinge & Jean-Pierre Colinge,
“Multigate transistors as the future of classical metal-oxide
semiconductor field effects transistors”.
 Aniket A. Breed/ Dr. Marc Cahay, “Design and Evolution of
modern SOI fully-depleted MOSFETs”.
 Jack Kavalieros, Brian Doyle, “ Tri-Gate Transistor
Architecture with High-k Gate Dielectrics, Metal Gates”.
 Viranjay M. Srivastava, Setu P. Singh, ”Analysis and Design
of Tri-Gate MOSFET with High Dielectrics Gate”.