Transcript Power FET Structure DMOS and VMOS

Power FET Structure
DMOS and VMOS
Abstract
Power MOSFETS are designed to handle significant power levels. It’s
main advantages are its high commutation speed and good efficient
at low levels. Power MOSFETS have different structures than lateral
MOSFETS by having a vertical structure rather than a planar
structure. The DMOS and VMOS both exhibit a vertical structure that
will be discussed.
By: John Fox, Jake French
4/25/14
Outline
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DMOS
o What is is?
o Where is it used?
DMOS Structure
VMOS
o What is is?
o Where is it used?
VMOS Structure
DMOS
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Double diffused metal oxide semiconductor
Most Power MOSFETs are made using this technology
Used in switching applications with high voltage and
high frequency behavior
Typically used in:
Automobile control electronics
Inkjet printheads
Power supplies
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DMOS Structure
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The DMOS device incorporates a double diffusion
process
The p-substrate region and the n+ source contact are
diffused through a common window defined by the edge
of the gate
The p-substrate region is diffused deeper than the n+
source
The surface channel length is defined as the lateral
diffusion distance between the p-substrate and the n+
source
DMOS Structure
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Electrons enter the source terminal and flow laterally
through the inversion layer under the gate to the n-drift
region
The electrons then flow vertically through the n-drift
region to the drain terminal
The conventional current direction is from the drain to
the source
DMOS Structure
Cross-section of a double-diffused MOS (DMOS)
transistor
Semiconductor Physics and
Devices Textbook by Donald
A. Neamen
DMOS Structure
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Most important characteristics are the breakdown
voltage and on-resistance
The increase in resistance with temperature provides
stability for the power MOSFET
DMOS is similar to a BJT, they share high-voltage and
high-frequency characteristics
DMOS Structure
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A lightly doped drift region between the drain contact
and the channel region helps ensure a very high
breakdown voltage
The n-drift region must be moderately doped so that the
drain breakdown voltage is sufficiently large
The thickness of the n-drift region should be as thin as
possible to minimize drain resistance
VMOS
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V-groove MOSFET - a power MOSFET in which the
channel region is formed along a v-shape d groove
formed in the surface of the semiconductor
This MOSFET gets its name from the “V” shape groove
that is formed after the p-substrate diffusion is
performed over the entire surface followed by the n+
source diffusion
VMOS
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VMOS power devices are used in medium voltage
power supply switching applications and medium power
RF amplifiers
Typically used in:
Hi-fi audio power amplifiers
Broadband high-frequency amplifiers
Switching power amplifiers which convert AC power
sources in DC at arbitrary voltages
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VMOS
Cross-section of a Vertical channel MOS (VMOS)
transistor
Semiconductor Physics and
Devices Textbook by Donald
A. Neamen
VMOS Structure
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The V-groove is easily fabricated by anisotropically
etching a (100) silicon surface using a concentrated
KOH solution.
V shaped gate region increases the cross-sectional
area of the source-drain path.
This reduces the on resistance of the device allowing it
to handle high voltages
VMOS Structure
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The gate consists of a metallised area over the V
groove and this controls the current flow in the P region.
As the gate is fabricated in this way it means that the
device retains the exceptionally high input resistance
typical of the MOS family of devices.
VMOS Structure
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Current flows horizontally between the source and
drain, controlled by the potential on the gate.
As the current only flows through a relatively small area,
resistance values can be high reducing the efficiency of
the device.
One of the main drawbacks of the VMOS power device
is that the structure is more complicated than a
traditional FET and this makes it slightly more
expensive.
Summary
Power MOSFETS differ from lateral MOSFETS with the
vertical structure of the DMOS and the VMOS. These are
used in a variety of applications that desire high switching
speeds and a variety of voltage levels. The doping and
channel lengths contribute to the characteristics of each
of these MOSFETS.
References
Poole, Ian. "VMOS Field Effect Transistor." :: Radio-Electronics.Com. N.p.,
n.d. Web. 22 Apr. 2014.
"V-Groove MOS (VMOS)." Electronic Circuits and DiagramElectronics
Projects and Design RSS. N.p., 4 Aug. 2010. Web. 22 Apr. 2014.
"Double-Diffused MOS (DMOS)." Electronic Circuits and DiagramElectronics
Projects and Design RSS. N.p., 28 July 2010. Web. 22 Apr. 2014.
"Double-diffused MOS (DMOS) Technology | JEDEC." Dictionary Entries.
N.p., n.d. Web. 22 Apr. 2014.
Van Zeghbroeck, Bart. "Chapter 7: MOS Field-Effect-Transistors." Power
MOSFETs. N.p., 2011. Web. 22 Apr. 2014.
Neamen, Donald A. "15.5 Power MOSFETs." Semiconductor Physics and
Devices: Basic Principles. New York, NY: McGraw-Hill, 2012. N. pag. Print.
Key Points
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A power MOSFET has a vertical configuration and an
interdigitated gate-source surface structure
DMOS uses a double diffusion process
Most important characteristics are the breakdown
voltage and the on-resistance.
V shaped gate increases the cross-sectional area of the
source-drain path.
The main advantages are the high commutation speed
and its good effiency at low voltages.