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The Hall Effect sensors are one of the most commonly used sensing technologies today. They are employed in many applications for direct magnetic field sensing and serve a multitude of low power applications within automotive and industrial electronics as current sensors, for contactless switching, position detection and in electronic compasses. In order to select Hall cells with high performance, good models that would accurately predict their characteristic parameters are undoubtedly necessary. Firstly, by setting up the actual research framework and giving details about the basic considerations regarding Hall Effect devices, the thesis domain is presented. A brief overview of the state-of-the-art in Hall Effect sensors development and applications on the market is included with emphasis on the offset levels achieved. The Hall voltage theoretical background and its rapid evaluation were provided. For six different types of Hall plates, three-dimensional representations were obtained for the inverse of the geometrical correction factor G. Various formulae for Hall mobility evaluation were provided, with a discussion on the relative error obtained in its calculation. Focusing on the analysis at device level, an attentive investigation of the geometrical correction factor as well as its maximization was proposed. In order to obtain maximum sensitivity for Hall cells integrated in the same process, a geometry that would provide a high geometrical correction factor it is advised to be chosen. The close connection between the general aspects and their associated details, regarding the twelve (designed and integrated) Hall cells, was presented. In premiere, three of them have been designed and proposed by the author. The reason behind the specific Hall cells geometries is announced and some designed layouts are given. To test the integrated cells, both an AC and DC automated measurements setup was used. This allows reliable and fast obtention of the desired experimental results. The Hall cells were tested for their input voltage-current characteristics at room temperature, resistance, resistance variation with the temperature, Hall voltage, dissipated power, etc. The absolute sensitivity versus the biasing current was also measured for all the integrated cells. The offset measurements results were just briefly presented, as there is another chapter entirely devoted to its detailed assessment. Parameters extraction was performed on specific tested Hall cells and the Hall cells linearity was also analyzed. A complex physical computing code, for predicting and assessing Hall cells performance with the aid of three dimensional simulations was developed and perfected. The influence of shape, dimensions, n-well concentration, contacts dimension and positioning with respect to the active region on the sensors performance were all aspects covered within this work. To this purpose, different constitutional devices including cross-like cells such as such as basic, L and XL and other shapes as the borderless and optimum have been modeled and subsequently tested for Hall voltage, absolute, current-related and voltage-related sensitivities. An analysis of the induced offset by a geometrical asymmetry has been performed on different cross-like Hall Effect sensors. In reverse reaction, any mix of various theoretical considerations can be validated now by three dimensional standard simulations. An optimum shape has been integrated which offers a good tradeoff between high sensitivity and low offset. The best device polarization scheme within each device has also been investigated. Selecting the best Hall sensor is closely related to the performance aimed to be achieved, may it be the highest sensitivity, the lowest offset or good power consumption. Further, without repeating ourselves, we can say that the proposed circuit model (implemented and repeatedly tested here) contains both geometrical and physical parameters and is able to predict the Hall voltage, sensitivity and their temperature drift. The temperature effects on Hall cells behavior has been carefully addressed and thoroughly analyzed, by implementation of Hall scattering factor and carrier concentration temperature dependence, including freeze-out effect for the latter. The full set of analytical equations governing this behavior has been implemented in VERILOG-A. Temperature dependence of Hall cells current-related sensitivity both by a full set of analytical equations and temperature coefficients has been investigated. In this way, the quadratic behavior of current-related sensitivity was proven. Moreover, the simulations performed for the integrated Hall cells and the results obtained are in a good agreement with the theory. In the actual conditions, after a specific calibration, the model developed by author will also be used for Hall Effect sensors offset prediction. As we already know, the offset and its drift are some of the most important figures of merit in the Hall cells performance assessment. The first objective of the present work was to develop Hall cells which will be able to provide magnetic equivalent offset at room temperature lower than ±30 μT and offset drifts with the temperature less that ±0.3 μT/ C. To measure the Hall cells offset, automated measurements setups were used to test the single, two and four phase residual offset, etc. Both AC and DC measurements were performed. Therefore, we have identified by intensive measurements the cell having the best performance in terms of offset at room temperature and offset temperature drift. An important section is devoted to the quadratic dependence of the residual offset with the biasing current. First and second order coefficient were extracted by curve fitting. To analyze and assess the offset voltage, the homogeneous models for Hall cells behavior investigation, previously presented, were transformed in non-homogeneous models. In this particular case, the non-homogeneous FEM model is built out of a homogeneous region in the middle (repetition of the elementary cell) plus different cells on the borders used to emulate the offset. These latter cells have their internal parameters changed. Various simulations were performed in circuit environment for offset analysis of particular Hall cells. The original non-homogeneous FEM model employing the first type of cell conducted by the author was used to predict misalignment offset for different asymmetries scenarios, as well as the offset temperature drift. |
