CMOS Failures

Question 1

What are the main causes of failures in CMOS systems?

Answer 1

Extrinsic	causes
• Manufacturing defects
• Variations
Intrinsic causes
• Aging of transistors and metal wires
• Wear‐out 
Environmental causes
• Ionizing	/particleradiation
• Electromagnetic fields and noise
• Temperature and mechanical stress

Question 2

Explain NBTI.

Answer 2

Negative Bias Temperature Influence
Positive charges build up at the silicon channel interface
Triggered when vin = 0 and high temperatures.
Partial recovery when vin = vdd.

Question 3

Explain HCI Hot Carrier Injection.

Answer 3

High energy holes or electrons may penetrate and damage the oxide.
Caused if high electric fields between drain and source exists.
Occurs only during saturation.
Causes reduction in max operating frequency.

Question 4

Time Dependent Dielectric Breakdown (TDDB).

Answer 4

Oxide is damaged by injected charge.

Hard failure when a permanent conducting path is formed in the oxide.

Question 5

What does Thermal cycling may cause.

Answer 5

Mechanical distress due to fatigue.
Power on/off … Load variation.

Relevant at interfaces between different materials (on die, packing …)

Question 6

Explain the terms :
SET
SEU
SEL
SEGR

Answer 6

SET Single event transient
SEU Single Event Upset (change of state of a mem cel due to a SET)

SEL Latch-up

SEGR : High energy particle damages the gate permanently.