High Bandwidth CMOS Magnetic Sensors Based on the Miniaturized Circular Vertical Hall Device

Hall-effect devices make up by far the largest part of all magnetic sensors on the market today. The main reason is compatibility of Hall devices with modern semiconductor technology. In particular, integrated Hall sensor micro-systems fabricated in low-cost complementary metal oxide technology (CMOS) have dominated the market of magnetic sensors over the last decade. Recently, a new Hall device – the circular vertical Hall device (CVHD) – joined the family of CMOS compatible Hall devices. The CVHD can be biased and Hall voltage retrieved from it such that its output is a sine wave signal. The amplitude of the sine wave signal contains the information on the magnitude of the magnetic field, while the phase of the sine wave signal carries the information on the direction of the magnetic field. This is why a CHVD can be thought of as the first Hall device measuring an in-plane magnetic induction vector. It is due to this feature that the CVHD was first used as a sensing device in magnetic angular sensors. These CVHDs had a large number of contacts leading to a high angular accuracy, but limiting bandwidth of the sensor. This thesis was devoted to exploring and pushing the limits of CVHDs and integrated magnetic sensors based on CVHDs. The first aim of the thesis was to study the limits of bandwidth increase while keeping satisfying accuracy of angular sensors based on the CVHD. In order to increase the angular sensor's bandwidth, we optimized the CVHD, the front end of the sensor comprising the device and interface electronics, and finally the system level topology. The CVHD was ultimately miniaturized to the device containing only eight contacts (8CVHD). The smaller the number of contacts, the faster is obtained the sine wave signal from the CVHD. A novel symmetric Hall voltage retrieval facilitated by the geometry and including all contacts was used. It led to the residual offset voltage comparable with devices having a much larger number of contacts. It was shown that the increase of the sensor's bandwidth is not only limited by the device but also by the interface electronics. This is particularly so because the sensor system relies on the spinning current method for offset reduction. In this case, the interface electronics includes spinning switches and a preamplifier. The spinning current method introduces voltage spikes that decrease accuracy when increasing bandwidth. The modeling of the horizontal Hall device and the interface electronics containing spinning switches and preamplifier was presented. The model was extended for the specific case of the sensors based on the 8CVHD. Three solutions to tackling the challenge of increasing the spinning frequency, or equivalently sensor's bandwidth, while maintaining accuracy were proposed and discussed. The first one is a novel solution relying on the high input capacitance of the preamplifier which together with the sensing switch on-resistance filters out the voltage spikes. The second solution