MOSFET temperature sensors for on-chip thermal testing

• A MOSFET can be used as a sensor to measure on-chip thermal variations caused by the power dissipated by other embedded circuits.
• In the context of on-chip thermal testing, temperature sensors based on MOSFET have advantages versus those based on BJT.
• The main advantages are in terms of compatibility to process, layout area and sensitivity to thermal variations.
• Theoretical models, simulations, and experimental data resulting from a 0.35 μm CMOS technology prove the previous ideas.

This paper analyses theoretically and experimentally the temperature dependence of metal–oxide–semiconductor field-effect transistors (MOSFET) with the aim of using them as a temperature sensor in on-chip thermal testing applications. The proposed analysis provides rules for the selection of the dimensions and the bias current of the MOSFET in order to have a high sensitivity to on-chip thermal variations generated by the circuit under test (CUT). These theoretical predictions are then contrasted with simulations and experimental data resulting from MOSFETs fabricated in a commercial 0.35 μm CMOS technology. Simulations and experimental results with MOSFETs are also compared with those obtained using a parasitic bipolar junction transistor (BJT). Such a comparison shows that MOSFET-based temperature sensors offer, in the context of on-chip thermal testing, the following advantages: fully compatible with the fabrication process, less area required around the CUT, and more sensitive to on-chip thermal variations caused by the CUT.