Secure IC with Countermeasure to Unpowered Physical Attack using On-chip Photodiode and Charge Pump

Abstract

An unpowered invasive or semi-invasive physical attack on a chip can be a severe threat to the secure data stored in the target chip. This paper presents a secure circuit that can detect unpowered attacks and destroy internal secure data using an on-chip photodiode and charge pump under an unpowered condition. If the chip is under a physical attack including decapsulation, the chip will be exposed to the incident light. The proposed circuit detects the light and converts this light into an electrical signal, which then activates the self-destroying circuit without need for power supply. The self-destroying mechanism uses a gate voltage which is higher than the gate-oxide breakdown voltage that can destroy the transistor of the chip. An on-chip photodiode is used for light sensing. As the harvested voltage from the photodiode is not enough to cause gate-oxide breakdown of the transistor, a charge pump is used to generate the high gate voltage. The charge pump is fabricated using a standard 0.18 mu m complementary metal-oxide-semiconductor (CMOS) process with an area of 0.12 mm(2). The charge pump output increases to 7 V with a supply voltage of 0.7 V.