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# Vlassis Petoussis Sensorcomm 2009

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### Vlassis Petoussis Sensorcomm 2009

1. 1. Novel Dynamic Technique Reducing the Offset Voltage in a New Hall Effect Sensor Vlassis N. Petoussis University of Thessaly. Department of Electrical & Computer Engineering.
2. 2. The Main Goals We present a model and numerical analysis of a new Hall effect sensor which using a novel offset reduction method. We calculate the function which governs the changes in the electric field inside the new Hall effect sensor in presence of magnetic field. Control in MatLab environment the equipotential lines and monitor the changes when biasing conditions are change. The combination of his pioneering form and the elaborate sequence of using the dynamic spinning current technique.
3. 3. Spinning Current vs Offset Voltage The offset of the Hall plate is the voltage that is measured when no magnetic field is applied. The following equation represents the theoretical situation, when an offset is added : V = ISB + V H offset Figure. 1. An eight contact spinning-current Hall plate with spinning- the possible bias current directions To reduce the offset, which is time variant, spinning current Hall plates was developed Fig1.[1]. For our theoretical approach [2]-[3]-[4] in the development of the new Hall effect sensor in this present work, we use for a model (cell like device) the split-current model. We estimate the magnetic field resolution and the appropriate boundary conditions to explain the electric field and potential inside the sensor Fig.2 Figure 2: The split-current Hall effect device. split- device
4. 4. Boundary conditions In our split-current model we use Dirichlet (D) and Neumann (N) boundary conditions as we can see in Fig. 3a. We use Dirichlet boundary conditions in contacts with positive or zero potential and Neumann boundary conditions elsewhere, especially in regions which the sensor communicates with the natural environment. With this way the current density in x direction we need to be a zero, and in y direction to be a non zero. (a) (b) Figure. 3. The boundary conditions for a split-current element Hall effect device. a) Graphic representation of a simple model in split- even phase, with D and N presented the boundary conditions. Dirichlet boundary conditions in contacts with positive or zero potential and phase, Neumann boundary conditions elsewhere. b) The area of the received Hall voltage tacked in four places of the sensor. We can see that the received margins of the field in our model is well separated each other (black trapezoid areas). (black
5. 5. Basic equations For an p-type and n-type semiconductor we can write respectively: ∂Φ µpB ∂Φ µn B = −c ( B ) = c( B) ∂x 1 + ( µ p B) 2 ∂x 1 + ( µ n B) 2 These equations give us the dependence of the electric field inside the sensor in presence of magnetic field. Furthermore these relations allow us to simulate the changes of the equipotential lines in MatLab environment solving this PDE equations for different values of magnetic induction B One of the most important problems in our analysis and simulations was the determination of the drift mobilities. To solve this problem we decide to use the following empirical expressions [5] 1265 cm2 µn = (65.0 + 16 −3 0.72 ) 1 + [ NT /(8.5x10 cm )] Vs 447.3 cm 2 µ p = (46.7 + ) 1 + [ N T /(6.3x1016 cm −3 )]0.72 Vs
6. 6. The New Hall Effect Sensor Device Wheel Hall Sensor (WHS) In University of Thessaly we designed and we are ready to develop a novel Hall sensor device which uses elaborate spinning current technique [6]. The novel Hall device that we call “Wheel Hall Senor (WHS)” is presented in Figures 4a and 4b. The current enters the device, as presented in the aforementioned Figures, in two phases namely the even phase (PHASE-P) and the odd phase (PHASE-N). (a) (b) Figure. 4. The novel Hall device that we call “Wheel Hall Senor” or WHS. (a) The even phase (PHASE-P) (b) the odd phase (a) (PHASE- (PHASE-N). (PHASE-
7. 7. The offset reduction method To reduce the offset, the new Hall effect sensor uses spinning-current technique in the symmetrical Hall plate. In the offset reduction sequence the direction of the bias current is splited right and left and the corresponding output voltage is measured on the contacts in 450 to the current direction in each phase. When sixteen outside and sixteen inside contacts are used, the bias current is switched 450 for each measurement, the voltage contacts are switched outside to inside respectively (Fig. 5). For each phase of the bias current, four output (VH+ and VH-) and input (VH- and VH+) voltages are measured in a rotating clock wise. Finally for each turn in PHASE-P and PHASE-N, totally sixteen Hall voltages are measured. Each harmonic biasing current in each phase produces an offset voltage witch totally in turns gives us the offset cancellation. So offset caused from current IAD in phase P cancel the offset caused from current ICD in phase N and IAD in phase N cancel the offset caused from current IAF in phase P. Finally the one offset in one phase cancel the other in next phase. (a) (b) Figure. 5. The even phases (a) and the odd phases (b). With I we denote the current bias in 450 direction in each measurement and VH+ and VH- denoted the two Hall Voltage references in each phase (for n-type material). n-
8. 8. Field Simulations in MatLab To complete our analysis we present simulations of the device structure in to control our theoretical approach that we already developed. The theory to control the electric field of the device when it is exposed in perpendicular external magnetic field. In a Matlab environment we solved the Laplace equation inside the device and calculate and simulate the electric field and the equpotential lines inclination in the WHS in a presence of magnetic induction, the results represented in figures 6a and 6b. (a) (b) Fig. 6. The novel Hall device that we call “Wheel Hall Senor” or WHS. (a) The electric field and the equpotential lines in the even (a) phase (PHASE-P) for B non zero, (b) The electric field and the equpotential lines in the odd phase PHASE-N) for B non zero. (PHASE- PHASE- zero.
9. 9. CONCLUSIONS In this presentation we define the method and some of our theoretical simulations in MatLab environment for a new Hall effect sensor which is uses a novel tehqnique to reduce the offset voltage. We already to develop this novel Hall sensor (Wheel Hall Sensor) in CADANCE simulators to take Hall voltage measurements in a semi real conditions. After this we already to publish the results in future papers. ACKNOWLEDGMENTS I would like to thank Pr. Dr. Manolis Vavalis for the useful advices and helpful discussions. Furthermore I would like to thank the Electrical Engineering & Computer Engineering Department of the University of Thessaly for the technical support and fulfillment of this project. REFERENCES [1] Munter P.J.A, A low offset spinning current Hall plate. Sensors and Actuators, A21-A23 (1990) 743-746 Actuators, A21- 743- [2] Sandra Bellekom, Lina Sarro. International Conference on Solid-State Sensors and Actuators, Chicago, Bellekom, Sarro. Solid- June 16-19, 1997 p.233-p236. 16- p.233- [3] Vlassis N. Petousis, Panos Dimitropoulos. Galvanomagnetic Effects : “Sensors Depending on Hall Petousis, Dimitropoulos. Effect” “Journal of Engineering Science and Technology Review” Vol.2.Lecture Note pp.1-7. Vol.2.Lecture pp.1- [4] R.S. Popovic, Hall Effect Devices, Adam Hilger, Bristol, 1991. Popovic, Hilger, [5] A. W. Vinal and N. A. Masnari, “Response to commenton Magnetic transistor behavior explained of Masnari, emmiter injection, not carrier deflaction,” IEEE Electron Device Lett., vol. EDL-3, pp. 396-397, 1982. deflaction,” Lett., EDL- 396- [6] Vlassis N. Petoussis , P.Dimitropoulos , George Stamoulis, A Novel Hall Effect Sensor Using Elaborate P.Dimitropoulos Stamoulis, Offset Cancellation Method, Sensors & Transducers Journal, Vol. 100, Issue 1, January 2009, pp. 85-91. 85-