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. © 2009 IEEE.