Wireless High-Temperature Monitoring of Power Semiconductors : A Single-Chip Approach

Abstract: Because failures in power electronic equipment 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 electronic equipment, and monitoring their temperatures yields information that can be used to predict emerging 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. To address these challenges, the feasibility of using on-chip coils to provide communication with and to obtain power from an external reader coil is demonstrated, and a low-power, high-temperature bandgap temperature sensor is developed.For the challenge of generating geometries of on-chip coils with high power transfer efficiencies, a gradient ascent algorithm is used to generate geometries that provide high power transfer efficiency at the frequency of interest. A theory is developed, focused on the relation between optimised coil geometries and the load requirements of an application. A cutoff-point is discovered, beyond which power delivered to the load does not increase even if the load is made lighter. Electromagnetic simulations for an on-chip coil model are presented, which show that this load-limit lies around 10 kΩ for one 350 nM process. The model is verified with measurements on manufactured devices.To generate coils which operate within a desired frequency band in which sufficient radiated energy is permitted, a methodology for tuning on-chip coils with on-chip fuses is presented. The decision to use fuses for tuning instead of transistors for this application is due a transistor's requirement of a DC supply for bias. For wireless single-chip systems, no such DC supply is available at system start-up. The methodology presented addresses the challenge of achieving high Q~factors for capacitor-fuse series connections despite the fact the fuse resistance of on-chip fuses is finite in their blown state and non-zero in their active state.A single-chip, on-chip coil solution comes with advantages such as galvanic isolation from the power device and simplicity of integration in existing modules. However, because 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 temperature sensor. Therefore, a design is presented of a temperature sensor consuming power in the microwatt range in the high-temperature region where it is useful for detecting incipient faults, particularly solder faults. This is achieved by compensating for leakage currents that arise in hot reverse-biased p-n junctions, which become significant at these temperatures.At high temperatures, these leakage currents can approach or even surpass the level of a 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 at least 230 °C for a sensitivity of 2 mV/°C are feasible at a power consumption around 10 µW. Such sensors would yield a resolution of 2 °C if an 8-bit analogue-to-digital converter is employed. However, the transmission of data to the transmitter coil remains future work. Furthermore, a discussion is held to address design of unimplemented system components which are needed in order to implement a complete single-chip temperature measurement system. Points discussed include high-temperature analogue-to-digital conversion, clock generation and wireless communication.