Fixed- and variable-length ring oscillators for variability characterization in 45nm CMOS

Fixed- and variable-length ring oscillators (RO´s) are designed for characterization of circuit-topology induced variations and spatial correlations. A 930µm × 775µm test array is implemented in a low-power 45nm CMOS process. Measurements from the fixed-length RO´s quantify an increase in variability with transistor stack height in logic gates and added variability associated to the top transistor in the stack. In addition, Variable-length RO´s (VRO´s) are designed to measure spatial correlation with a single-gate resolution.