1. Lecture 10 Power Device (1)
Introduction
Power Rectifiers
Schottky-Barrier Rectifier
Junction-Barrier-Controlled Schottky (JBS) Rectifier
Trench-MOS-Barrier Schottky (TMBS) Rectifier
p-i-n Rectifier
Merged p-i-n/Schottky Rectifier
Power MOSFET

2. 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

3. Metal-Semiconductor (Schottky) contact
A=120 A/cm2-K2 for free electron

4. A* is Richardson constant

5. Image-Force Lowering, Schottky effect or Schottky-barrier lowering

6. Power Rectifiers Schottky-barrier rectifier for low operating voltage (<100V); New improvement using junction-barrier-controlled 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.

7. 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.

8. 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

9. 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

10. Trade-off btw JR and VF

11. The ultimate limiting factor : Power dissipation in the rectifier

12. 2. Junction-Barrier-Controlled Schottky (JBS) Rectifier

13. 3. Trench-MOS-Barrier Schottky Rectifier

15. p-i-n Rectifier
Charge neutrality in the n-drift region

16. 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

17. 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.

18. 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.

19. Homework: Read and study Chapter 4 Power Device pp
Homework: Read and study Chapter 4 Power Device pp “Modern Semiconductor Device Physics”