On-Chip Thermal Testing Using MOSFETs in Weak Inversion

This paper analyzes the feasibility of using metal-oxide-semiconductor field-effect transistors (MOSFETs) operating in weak inversion as temperature sensors for on-chip thermal testing applications. MOSFETs in weak inversion are theoretically analyzed so as to know how their sensitivity to temperature depends on both dimensions and bias current. Theoretical predictions are then compared with simulations and experimental data resulting from MOSFETs fabricated in a commercial 0.35-mu m CMOS technology. The MOSFETs are experimentally subjected to changes of temperature generated by either a heating chamber or an on-chip power dissipating device. The performance of MOSFETs in weak inversion is also compared with that in strong inversion and with that of parasitic bipolar junction transistors. In the context of on-chip thermal testing, MOSFETs in weak inversion offer advantages in terms of layout area, linearity, current consumption, and spread of the sensitivity to temperature due to process variations.