Question

Question 1:

(a) Describe the effects of the width and doping level of drain drift region of an IGBT on its performance?

(b) Discuss the effect of negative temperature coefficient of resistance and localized collector current in a power BJT that causes second breakdown?

Answer 1

(a)

Diagram of IGBT structure –

Drain drift region have lightly doped n^- region.

Width and doping level of drain drift region in IGBT performance having following effects –

1. It decides forward blocking voltage of IGBT device.
2. Due to conductivity modulation it does not affect state voltage drop of IGBT device.

(b)

Negative temperature coefficient of resistor in power BJT means if temperature increases then resistance decreases.

Due to high collector current in power BJT temperature of BJT increases, Due to increases of temperature, resistance decreases that cause more collector current to flow.

Due to continuous process of temperature increase then current increase, breakdown of BJT happen that breakdown is called secondary breakdown.