Wireless, Single Chip, High Temperature Monitoring of Power Semiconductors

Abstract: Because failures in power electronics can cause production stops and unnecessary damage to interconnected equipment, monitoring schemes that are able to predict such failures provide various economic and safety benefits. The primary motivation for this thesis is that such monitoring schemes can increase the reliability of energy production plants. Power semiconductors are crucial components in power electronics, and monitoring their temperatures yields information that can be used to predict incipient failures.This thesis presents a system concept for wireless, single-chip, high-temperature monitoring of power semiconductors. A wireless single-chip solution is both cost effective and easy to integrate with existing power semiconductor modules. However, the concept presents two major challenges: the implementation of wireless power and communication, and the low-power design of the temperature sensors. Thus, the feasibility of using on-chip coils to provide communication with and obtain power from an external reader coil is assessed, and a low-power, high-temperature bandgap temperature sensor is developed. The sensor is capable of operating in the high-temperature range, allowing it to be useful for detecting incipient faults, particularly solder faults, at up to 230 °C. This is achieved by compensating for leakage currents that arise in hot reverse-biased p-n junctions, which become significant at these high temperatures.A single-chip, on-chip coil solution provides the combined advantages of galvanic isolation from the power device and simplicity of integration in existing modules. However, as the use of a wireless design with a small on-chip coil will limit the amount of available power, it incurs the disadvantage of requiring a low-power design for the sensor. Initial experiments have been performed on a prototype on-chip coil to assess the feasibility of this concept and provide insight into the challenges of on-chip coil design.In this thesis, focus is placed on the challenge of how to handle large leakage currents in low-power integrated silicon circuits. At high temperatures, these leakage currents can approach or even surpass the level of the circuit's quiescent current. Earlier work on leakage current compensation techniques is examined, compared to and combined with a compensation technique designed to compensate for collector-base leakage in the main bipolar pair of a Brokaw bandgap reference. Experiments show that fully analogue sensors operating at up to 228 °C with an accuracy of 10 °C that consume only 8.2 µW are feasible. If a higher accuracy, such as 3 °C, is required, then a temperature range of up to 200 °C can be achieved with a power consumption of 2.3 µW.It is likely that the high temperature range and low power consumption of the sensors presented in this thesis, in combination with on-chip coils, will make them suitable for use in solder fault prediction in power semiconductor modules.