Power Semiconductor Devices.pdf

Power Semiconductor Devices
Robin Giese
Princeton University EE341
12/14/2000
Requirements for power devices
• Primarily on/off control of high-I/V vs.
amplification
– several 1000V, peak currents 3000A
– reverse breakdown voltage important for reliable OFF state
• effective switching
– low ON state drop voltage (I=V/R)
– high current density
– low driving current
• basic devices: (Power-) BJT, MOSFET
– BJT: requires high gate current for both ON and OFF
– MOSFET: somewhat more difficult to make
Topics covered
• Requirements
• Silicon Controlled Rectifier
• lighting control
• Insulated Gate Bipolar Transistor
• High power device challenges
• Manufacturing challenges
p-n-p-n diode
•3 states:
– reverse blocking
– forward blocking
– forward conducting
– device pops from forward blocking to forward conducting
state
– device recovers from conducting state to forward or
reverse blocking states after V is released
p-n-p-n diode: fwd blocking
• Separate diodes: forward, reverse, forward bias
• p-n diode: holes from p → n, e from n → p,
supplied from ohmic contacts
• p-n-p-n J1: hole from ohmic contact on p1 wants
to cross to n1, needs e to ‘exchange’ with n1 to
maintain space charge neutrality
• n1 has no ohmic contact, J2 in reverse bias, no e
can be supplied → no current
p-n-p-n diode in reverse blocking
• Separate diodes: reverse, forward, reverse bias
• J2 could conduct: holes from p2 to n1, etc.
• However, no supply of holes from n2 through
reverse-biased J3 → again, no current
p-n-p-n diode leakage
• Go back to forward bias: J1/J3 forward biased, J2
reverse-biased
• Recall: p1 is waiting for e e from n1 through
J1, but n1 has no e supply
• However: thermal EHP generation at J2 gives e to
n1, hole to p2 → small leakage current
• Sample applies to p-n-p-n in reverse bias
p-n-p-n forward conduction state
→ holes →
← E ←
→→
Vrv
•J2 in reverse bias
-> depletion region ext