Characterization of Inverse Temperature Dependence in logic circuits

As the supply voltage (V_DD) approaches the device threshold voltage (V_T), the elevated temperature results in increased device current. This phenomenon is generally known as Inverse Temperature Dependence (ITD). In this paper, we propose a test structure with a built-in poly-resistor-based heater to characterize ITD in digital circuits. Our measurements from a 130nm test-chip show that the Zero-Temperature-Coefficient (ZTC) point varies by circuit type, and further fluctuates due to process variation. A more accurate ITD-sensitive thermal sensor is thus needed for better temperature tracking.