Download Lecture 11 Power Device (1) - Purdue College of Engineering

Lecture 10 Power Device (1)
• Introduction
• Power Rectifiers
1. Schottky-Barrier Rectifier
2. Junction-Barrier-Controlled Schottky
(JBS) Rectifier
3. Trench-MOS-Barrier Schottky (TMBS)
Rectifier
4. p-i-n Rectifier
5. Merged p-i-n/Schottky Rectifier
• Power MOSFET
Introduction on Power
Semiconductor Devices
1950s Power bipolar transistor and thyristor
1970s Power MOSFETs
• insignificant steady-state input current
• possible to integrate its control circuit, leading to
large reduction in the size and complexity of the
power electronic systems
• Higher switching speed of the MOSFET allowed
major improvements in the performance of power
electronic systems.
• Better < 200 V
1980s MOS-bipolar structures –Insulated-gate bipolar
transistor (IGBT) possible 4.5 kV
1990s SiC power devices and also GaN power devices
Metal-Semiconductor (Schottky)
contact
A=120 A/cm2-K2 for free electron
A* is Richardson constant
Image-Force Lowering, Schottky
effect or Schottky-barrier lowering
Power Rectifiers
Schottky-barrier rectifier for low
operating voltage (<100V); New
improvement using junction-barriercontrolled Schottky (JBS) rectifier or
trench-MOS-barrier Schottky (TMBS)
rectifier
For high opertaing voltage (>200V),
the p-i-n rectifier has been the device
of choice.
1. Schottky-Barrier Rectifier
The series resistance per unit area
=the specific on-resistance
If a reverse breakdown voltage of 50V
The drift has a Ron,sp=1x10-4 Ohm–cm2
A voltage drop of only 10 mV across this
region at a current density of 100A/cm2.
VF: on-state voltage drop
ФB: Schottky-barrier height
JF: on-state current density
For Schottky Barrier of 0.8 V, VF: 0.5 V >> JF: 100A/cm2
At small reverse-bias, the leakage current of the Schottky diode is
given by the saturation current of the contact. However, in the case of
the high voltages that power devices must support, Schottky-barrier
lowering must be accounted for.
The optimization of the characteristics
Of the Schottky power rectifier requires
A trade off between
Forward voltage drop and
Reverse leakage current
Trade-off btw JR and VF
The ultimate limiting factor : Power dissipation in the rectifier
2. Junction-Barrier-Controlled
Schottky (JBS) Rectifier
3. Trench-MOS-Barrier Schottky
Rectifier
p-i-n Rectifier
Charge neutrality in the n-drift region
Current density increases; na increases; conductivity increases;
Resistivity decreases; voltage drop is constant
This is important for maitaining a low on-state voltage drop even at
High operating current densities in p-i-n rectifiers
Continuity equation:
Final solution:
A major limitation to the performance of p-i-n rectifiers at high frequencies is
the power loss during switching from the on-state to the off-state.
--Reverse recovery
Smaller trr can be obtained by reducing
τHL the high-level lifetime by introducing
Recombination centers into the i region.
Merged p-i-n/Schottky (MPS)
Rectifier
Increase high-level lifetime, produces an increase in the on-state voltage drop,
Resulting in a tradeoff between on-state losses and switching losses.
Homework:
Read and study
Chapter 4
Power Device pp.183-203
“Modern Semiconductor Device
Physics”