Characterization of Random Process Variations Using Ultralow-Power, High-Sensitivity, Bias-Free Sub-Threshold Process Sensor

• Published in: IEEE transactions on circuits and systems. I, Regular papers Vol. 57; no. 8; pp. 1838 - 1847
• Main Authors: Meterelliyoz, M, Song, P, Stellari, F, Kulkarni, J P, Roy, K
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2010; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Arrays; Circuits; CMOS; CMOS technology; Devices; Fluctuations; Monitoring; MOS devices; Process variations; Random processes; random threshold voltage variations; sensor; Sensor phenomena and characterization; Sensors; sub-threshold operation; Testing; Threshold voltage; Transistors
• ISSN: 1549-8328; 1558-0806
• DOI: 10.1109/TCSI.2009.2037449

We propose a novel ultralow-power, high-sensitivity, bias-free sub-threshold process variation sensor for monitoring the random variations in the threshold voltage. The proposed sensor characterizes the threshold voltage mismatch between closely spaced, supposedly identical transistors using the exponential current-voltage relationship of sub-threshold operation. The sensitivity of the proposed sensor is 2.3× better than the previous sensor reported in the literature which utilizes above-threshold operation. To further improve the sensitivity of the proposed sensor, an amplifier stage working in the sub-threshold region is designed. This enables 4× additional increase in sensitivity. A test-chip containing an array of 128 PMOS and 128 NMOS devices has been fabricated in 65-nm bulk CMOS process technology. A total of 28 dies across the wafer have been fully characterized and the random threshold voltage variations are reported here.