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

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-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.

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 Homework: Read and study Chapter 4 Power Device pp.183-203 “Modern Semiconductor Device Physics”