Improvements of Cmos Hall Microsystems and Application for Absolute Angular Position Measurements

The compatibility of some Hall sensors with CMOS electronics allows the co-integration of sensors and electronics on the same chip to obtain a low costmicrosystem. In addition to a careful sensor design, the relationships betweenthe system components, i.e. sensors and electronics, allow us to improvesubstantially the behavior of the microsystem. The first objective of this thesis isto create a toolbox to construct very accurate CMOS Hall microsystems; eachso-called tool solves a limitation of Hall sensors. We also built for angularmeasurements a 2-dimensional Hall microsystem, i.e. a microsystem with twoorthogonal axes of sensitivity. This microsystem is based on vertical Hallsensors placed orthogonally. CMOS Hall sensors suffer from several non-idealities, such as low sensitivity,sensitivity drift, offset and non-linearities. What's more, a 2-dimensional sensorsuffers from sensitivity mismatch between the Xand Y-sensors and non-orthogonality between the measurement axes. Sensitivity drift and offset are themost challenging problems for which new tools are necessary. The first tool is calibration coils for the self-calibration of Hall microsystems.These coils are in-situ iising the metallization layers of the technology. Weobtain a coi1 efficiency of 290mTfA and 230mTfA for respectively miniaturizedHall plates and miniaturized CMOS vertical Hall sensors. Note that miniaturizedsensors are obligatory for efficient coils. Using external laboratory voltage andcurrent references, we obtain an outstanding thermal drift of less than30ppd0C. We also propose a calibration scheme, called geometrical reference,which is independent of the electric references; the sensitivity is in that case afunction of only the sensor and the coi1 geometry. The second tool is an efficient reduction of the Hall sensor offset using thespinning current technique. We analyze the sources of residual offset of Ourmicrosystem to find the major sources of residual offset: the electronic circuitand the sensor itself. We develop a feedback scheme for the spinning currentmethod to reduce drastically the residual offset by one order of magnitude to a1.2mV standard deviation from the output. Miniaturized sensors aredegenerated, because they suffer from non-linearities; that's why a four phasesspinning ciment is required. We also multiplex the electronics for the X and Yaxis of the angular sensor in order to guarantee the matching of the amplificationchain and to reduce the electronics surface. CMOS Hall Microsystemsand Angular Position Measurements1