3D Transistors

By Karanvir Singh

10105EN065

• Introduction to 3D transistors• Need for 3D transistors • Operation• Comparison with 2D transistors• Advantages • Applications • Conclusion • References

CONTENTS

Introduction3D 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.

Moore’s Law

Silicon-only planar transistors are fast approaching their scaling limit.

Short channel effects limiting scaling into sub nanometer regime.

Oxide thickness cannot be scaled down further, problems of tunneling.

Need to keep Silicon technology as the base technology while innovating future devices; cost is an important factor.

Performance and power dissipation need to be improved. Smaller is faster !!

Need for 3D transistors

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

Short-Channel EffectShort-Channel Effect

a. DIBL (Drain Induced Barrier Lowering) effect shifts the characteristics to the left when VD is increased.b. S increases when the channel length is decreased.

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 channel.

Tri-gate transistor

Operation

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 drive currents.

Transistor characteristics

Planar MOSFET

2 D Planar transistor

Steeper sub-threshold slope that reduces leakage current.

Better switching operation.

3D Transistor

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

transistors can operate at lower voltage with good performance, reducing active power by >50%

Transistor Gate Delays

Advantages 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. Off current) Higher drive current for a given transistor

footprint implies better performance More compact hence enabling higher transistor

density which translates to smaller overall microelectronics.

The primary challenges to integrating non planar tri-gate devices into conventional semiconductor manufacturing processes include: Fabrication of a thin silicon "fin" tens of

nanometers wide Fabrication of matched gates on multiple sides of

the fin

Integration challenges

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 power-efficient 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.

Conclusion

[1] Isabelle Ferain, Cynthia A. Colinge & Jean-Pierre Colinge, “Multigate transistors as the future of classical metal-oxide semiconductor field effects transistors”. [2] Aniket A. Breed/ Dr. Marc Cahay, “Design and Evolution of modern SOI fully-depleted MOSFETs”.[3] Jack Kavalieros, Brian Doyle, “ Tri-Gate Transistor Architecture with High-k Gate Dielectrics, Metal Gates”.[4] Viranjay M. Srivastava, Setu P. Singh, ”Analysis and Design of Tri-Gate MOSFET with High Dielectrics Gate”. [5] http://en.wikipedia.org/wiki/Multigate_device[6] http://www.intel.com/content/www/us/en/energy/intel-22nm-3-d-tri-gate-transistor-technology.html 

References

Thank you