lock-in thermography

**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.