We present a new defect/fault tolerant ultra low power CMOS circuit exploiting low level redundancy. We show that wiring and transistors may be damaged while the functionality is still kept. We also demonstrate a new full adder based on the basic building block, capable of sub fJ Power-Delay-Product for supply voltages below 100 mV, in a 120 nm process. The Power-Delay-Product is reduced by about 50 % compared to the best previously published FA based on a 6 transistor reconfigurable subthreshold NOR-3, MAJ-3, NAND-3 circuit. Transistors are exploited as four terminal devices operating in subthreshold and DC characteristics for a threshold element is demonstrated by chip measurements.