CMOS-Process Compatible Embedded Sensors for Power Electronics Devices

In this thesis, sensors are described whose fabrication processes are compatible with standard CMOS silicon processes. These sensors are then able to be integrated onto conventional silicon power devices with ease. The sensors are intended to form part of a larger control system for performance monitoring and protection of the power devices they’re integrated with and, because the power devices and sensors are intimately coupled, the control and monitoring can be very closely associated to the individual power devices being supervised. Two types of sensor are investigated in this work 1) Temperature sensors, which utilise the temperature-dependency of existing structures within the power semiconductor device to determine the on-chip temperature and 2) Magnetic sensors which are intended to be fabricated adjacent to current-carrying conductors on the power device and act as current-sensors by detecting the intensity of the magnetic field generated by the device current. The investigation into temperature sensors focusses mainly on their usefulness in characterising the thermal structure of the power device and creating thermal models which represent this structure. A full electro-thermal model for the device could then be constructed by combining the isothermal electrical device model with the derived thermal model. This work also investigates the thermal behaviour of individual structural elements within the device construction by direct comparison of similarly constructed devices and isolating the thermal effects of structural differences. A similar technique is employed to investigate the thermal effects of environmental conditions. A full description of the measurement system required, and the techniques employed, to perform this investigation is given in Chapter 3 and the experimental analysis is given in Chapter 4. Two variations of magnetic sensor are investigated. The first is a split-drain LD MagFET which is characterised for relative current sensitivity and found to be comparable with the highest reported for this type of sensor. This sensor is described and characterised in Chapter 5. The second is a novel 4-terminal magnetic sensor, whose relative current sensitivity is found to be several orders of magnitude higher than that of the highest reported split-drain MagFET. This device, together with an analysis of degradation due to imperfect processing, is characterised in Chapter 6