Lock-In Thermography (LIT) is a non-destructive failure analysis technique that detects minuscule heat signatures from defects — by applying a periodic (AC) bias to the device and using a lock-in amplifier with an infrared camera to extract the tiny thermal signal from background noise.

What Is Lock-In Thermography?

• Principle: A defect (short, leakage path) dissipates power locally. This creates a tiny temperature rise ($mu K$ to $mK$).
• Lock-In: The bias is modulated at frequency $f$. The IR camera signal is demodulated at $f$, rejecting all noise at other frequencies.
• Sensitivity: Can detect temperature differences as small as 10-100 $mu K$.

Why It Matters

• Gate Oxide Shorts: Pinpoints the exact location of a leakage path on the die.
• Non-Destructive: Can be performed through the backside of the silicon (no decapsulation needed for thin die).
• Speed: Quickly identifies the defect region before targeted cross-sectioning.

Lock-In Thermography is thermal fingerprinting for defects — finding hot spots invisible to the naked eye by amplifying the faintest heat signatures.