Introduction to MOSFET.

1. MOSFET
BY – DHWANI SAMETRIYA

2. OUTLINE
• Introduction to Electronics
• MOSFET
• SPICE Model for MOSFET
• CMOS Technology Scaling
• FinFET
• References

3. INTRODUCTION
TO
ELECTRONICS

4. ELECTRONICS
• In early 19th century, Electronics was treated separately from
electrical branch and “ electron” was identified and measurement
of its electric charge took place.
• Then, vacuum tubes and conducting wires were used in order to
achieve amplification of radio signals but they were expensive,
bulky and heat up when performing at higher operating range.

5. INTRODUCTION OF TRANSISTOR
• In 1947, Bell Laboratory invented a series of new devices known as
Transistor with remarkable potential for expanding the utility of
electronic equipment.
• Transistors are made up of crystalline solid materials known as
Semiconductors which have electrical properties that can be varied over
extremely wide range by addition of minuscule properties of other
elements.
• Electrons (-Ve Charge) and Holes (+Ve Charge) carries valuable properties
in semiconductors which can be exploited in many electronics devices.
• Si and Ge are primary material used in Semiconductors but today III-V
(group of elements in periodic table) semiconductors are also used.

7. CONT..
• In order to achieve a compact, lightweight, cost effective and with less
power dissipation, concept of Integrated circuit was introduced by Texas
Instruments.
• Millions of transistors can be integrated on a single Si substrate (Si Chip)
can be known as Integrated Circuit (IC).
IC Technology Transistor Count
SSI < 100
MSI 101 – 1000
LSI 1001 – 10,000
VLSI > 100,000
ULSI > 100,000,000

8. MOSFET

9. COMPARISON OF BJT AND MOSFET

10. MOSFET
• Metal Oxide Semiconductor Field Effect
Transistor (MOSFET) is fundamental
building block for CMOS and Digital
circuits.
• Compare to BJT, MOSFET has less Silicon
area, less fabrication processing steps and
small physical geometry can help to
enhance overall performance of Large
scale ICs.
• MOSFET can work as a switch which can be
controlled by Voltage applied at Gate (G)
terminal.

11. MOSFET SYMBOLS

12. STRUCTURE OF MOSFET

13. THRESHOLD OF MOSFET
• Value of VG for which
transistor is Turned ON
will be known as “
Threshold Voltage “.
• Threshold voltage can
be adjusted with
implementation of
dopants into channel
area during fabrication.

14. MOSFET I/V CHARACTERISTICS

15. Saturation Region
Over dry Voltage
Linear Region

16. SECOND ORDER EFFECTS
• Body Effect

17. • Channel Length Modulation

18. SPICE MODEL
FOR MOSFET

19. SPICE
• The simulation program with an integrated circuit emphasis (SPICE) is a
software tool for the simulation of circuits.
• Extension of SPICE Files are: *.cir, *.sp, or *.spi
• SPICE has built-in models for the semiconductor devices, and the user
needs to specify only the pertinent model parameter values.
PMOS and NMOS in LTSPICE Software

20. TYPES OF ANALYSIS
Type Analysis
DC Analysis
dc operating point of the circuit with
inductors shorted and capacitors opened.
AC Small-Signal Analysis
ac output variables as a function of
frequency.
Transient Analysis
transient output variables as a function of
time over a user-specified time interval
Pole-Zero Analysis
the poles and/or zeroes in the small-signal
ac transfer function.
Small-Signal Distortion Analysis
steady-state harmonic and intermodulation
products for small input signal magnitudes.
Noise Analysis
device-generated noise for the given circuit
& noise contributions of each device (and
each noise generator within the device) to
the output port voltage.

21. MOSFET LAYOUT

23. CMOS
TECHNOLOGY
SCALING

24. SCALING
• MOS technology scaling has been a primary driver of the
electronics industry and has provided a path toward both denser
and faster integration.

25. TYPES OF SCALING
1) Constant Field Scaling
2) Constant Voltage Scaling
3) General Scaling

26. CONT.
1) Constant Field Scaling/Full Scaling
all the dimensions of MOS device scaled down by same factor S.
Keeping all electric field patterns constant avoid breakdown and
other secondary effects
Primary Scaling Factors Scalded by
Tox, L, W, Xj (all in linear dimension) 1/K
Na , Nd (doping concentration) αK
VDD (Supply Voltage) α/K

27. CONT.
1) Constant Voltage Scaling
Supply voltage scaling is not feasible option in terms of
compatibility with earlier chips voltage. Thus, Supply voltage is
kept constant while scaling all other MOS device parameters.
Primary Scaling Factors Scalded by
Tox, L, W, Xj (all in linear dimension) 1/K
Na , Nd (doping concentration) K2
VDD (Supply Voltage) 1

28. CONT.
1) General Scaling
Voltage scaling makes difficult to turn off device which in turn
increase rate of leakage current. Thus a more general scaling model
needed which scales device dimensions and voltage proportionally
with α and K scaling factors respectively.
Primary Scaling Factors Scalded by
Tox, L, W, Xj (all in linear dimension) 1/K
Na , Nd (doping concentration) αK
VDD (Supply Voltage) α/K

29. we will compare experimental results of 3 different nm technologies that
are :
1. 90nm.
2. 65nm.
3. 45nm.

30. 90 NM & 65 NM CMOS TECHNOLOGY
• As the gate oxide was scaled the gate leakage increased; this increase in gate
leakage was insignificant until the 90nm technology node.
• At the 90nm and 65nm nodes, the scaling of the gate oxide slowed as a
result of the power limitations from the increase in gate leakage.

31. NEED OF 45 NM CMOS TECHNOLOGY
• In order to overcome the limitation in 90 nm and 65 nm CMOS technologies,
a gate dielectric with a higher dielectric constant (high-k) has been
introduced in 45 nm CMOS technology.
• This enabled a >25x gate leakage reduction while scaling the Tox by 0.7x.
• The effective gate length required for 45 nm technology is 25nm.
• The high-k +metal gate transistors exhibit excellent short channel
characteristics due to the combination of Tox scaling.
• MOS performance is improved by using the high - k+metal gate as well as by
the enhancements to the embedded SiGe processing.

33. FINFET

34. CHALLENGES OF MOSFET
• drastic increase in the sub threshold leakage current in nm regime due to
aggressive scaling.
• Loss of gate control on channel due to Narrow channel length results
inability to turn off device.
• The use of thinner gate oxides and high-k dielectric materials helps alleviate
this problem by increasing the gate-channel capacitance.
• All these challenges raise a need to introduced an alternative for MOSFETS
and FinFET comes into picture.

35. FINFET
• the transistor channel is a thin
vertical fin with the gate fully
“wrapped” around the channel
formed between the source and the
drain.
• The gate of the FinFET can be
thought of as a “multiple” gate
surrounding the thin channel. Such a
multiple gate can fully deplete the
channel of carriers resulting in much
better electrostatic control of the
channel and thus better electrical
characteristics.

38. THE GEOMETRIC KEY PARAMETERS OF
FINFETS
• Lg – Length of the gate,
• h – Height of the FIN,
• tox – Thickness of gate oxide,
• tox-top - Oxide thickness of top gate and fin,
• Tsi- Thickness of the fin
• Channel Doping

39. ADVANTAGES OF FINFET
• Very good electrostatic control of the channel.
• Greatly reduced short channel effects.
• High integration density, 3D, vertical channel orientation delivers more
performance per linear “w” than planar.
• Smaller variability, especially variability resulting from random dopant
fluctuation primarily due to doping-free or low doping channels.

40. REFERENCES

41. REFERENCES
1) http://www.intel.com/content/www/us/en/silicon-innovations/intel-22nm-technology.html
2) http://www.hindawi.com/journals/aelc/2014/365689/
3) http://www.eecs.berkeley.edu/~tking/presentations/KingLiu_2012VLSI-Tshortcourse
4) S. Jim Hawkinson, “Analysis and Performance Comparison of CMOS and FinFET for VLSI
Applications”, International Journal of Emerging Technology and Advanced Engineering, Volume 3,
Issue 2, February 2013.
5) Adel S. Sedra, Kenneth Carless Smith, “Microelectronic Circuits”, ISBN 0-19-514252-7, Oxford
University Press NY, 2004.
6) Sung-mo (steve) kang and Yusuf Leblebigi, “CMOS Digital Integrated Circuits”, ISBN 0-07-246053-9,
McGrow-Hill Publication, 2003.
7) Robert Boylestad and Louis Nashelsky, “ELECTRONIC DEVICES AND CIRCUIT THEORY”, ISBN:
9780133757347, Prentice Hall International editions, 1996.