OPTICAL-DETECTION OF MULTIBIT LOGIC SIGNALS AT INTERNAL NODES IN A FLIP-CHIP MOUNTED SILICON STATIC RANDOM-ACCESS MEMORY INTEGRATED-CIRCUIT

We report the first optical measurements of multiple bit-pattern logic signals at internal nodes in a flip-chip mounted silicon static random-access memory integrated circuit. This probing system measures signals by interferometrically detecting the electrically induced charge-density modulation within devices and parasitic pn junctions. The optical measurements, made on an output driver circuit, compared well with those on an external high-speed oscilloscope. Measurements made at internal points generally compared well with circuit simulations. However, the bit-sense circuit measurements suggested internal logic-level problems in the circuit design.