Area-efficient reconfigurable-array-based oscillator for standard cell characterisation

Today's multi-million digital integrated circuit design highly depends on the quality of the standard cell library. In this study, an all-digital reconfigurable-array-based test structure is presented to test the quality (i.e. functionality and performance) of all types of logic gates in the standard cell library using the reconfigurable array of gate delay measurement cell. The gate delay is estimated using the least squares method with measured reconfigurable ring oscillator's (RO) period/frequency. As the least squares method averages out the random noise in the measured RO period, measured gate delay is estimated accurately. The reconfigurable-array structure can easily isolate a faulty standard cell from a non-faulty standard cell. The test structure is area efficient with a saving of 1.6× and 2× area compared with the normal RO-based delay measurement in 180 nm and 65 nm technology node, respectively. A subset of standard cells is tested using this reconfigurable-array structure. A test chip has been fabricated in an industrial 180 nm technology node to study the feasibility of the approach. The measured results from 20 chips are reported to show the amount of within-die and die-to-die variation.