A Completely Digital On-Chip Circuit for Local-Random-Variability Measurement

This paper presents a completely on-chip digital circuit to measure local threshold-voltage variation using an array of identical devices under test (DUTs) stacked with a single reference device. This technique detects on-chip variation of single devices, rather than matched device pairs or SRAM cells. The variation in V_t of the DUTs is detected as variation in frequency, measured by on-chip counters, resulting in a simple digital measurement. The circuit is implemented in NMOS and PMOS versions. The standard deviation of local threshold variation measured on a chip-to-chip basis on a full wafer. The results indicate that the test-structure estimates local random mismatch in MOS current (and threshold voltage) with a small time and complexity, and thus enable technology optimization and yield improvement.