Hall Effect Sensors ROCHESTER INSTITUTE OF TECHNOLOGY MICROELECTRONIC ENGINEERING

Transcription

1 ROCHESTER INSTITUTE OF TECHNOLOGY MICROELECTRONIC ENGINEERING Hall Effect Sensors Dr. Lynn Fuller, Corey Shay, Michell Graciani Melo Espitia Webpage: Electrical and 82 Lomb Memorial Drive Rochester, NY Tel (585) Fax (585) Department webpage: Hall_Effect_Sensors.ppt Page 1

2 ADOBE PRESENTER This PowerPoint module has been published using Adobe Presenter. Please click on the Notes tab in the left panel to read the instructors comments for each slide. Manually advance the slide by clicking on the play arrow or pressing the page down key. Page 2

3 OUTLINE Tutorial Earths Magnetic Field Magnets Introduction Theory Example Calculations Van Der Pauw s Measurements Commercial Devices Applications Testing References Homework Page 3

4 TUTORIAL Magnetic Field Lines Lines used to visualize the magnetic flux, not physical lines but just a visualization tool. N S Weber - The S.I. unit for magnetic flux, F. It is the amount of magnetic flux which, when linked at a uniform rate with a single-turn electric circuit during an interval of 1 second, will induce in this circuit an electromotive force of 1 volt. Maxwell The C.G.S. unit for magnetic flux Page 4

5 TUTORIAL Gauss - Unit of magnetic induction, B (flux density), lines of magnetic flux per square centimeter in the C.G.S. system of measurement. Equivalent to lines per square inch in the English system, and Webers per square meter or Tesla in the S.I. system. Tesla - Unit for magnetic induction, B (flux density), lines of magnetic flux per square meter in the M.K.S. system of measurement. One Tesla equals 10,000 Gauss. Magnetic Field Intensity, H units of Amperes/meter in M.K.S. system and units of Oersteds in C.G.S. system. In vacuum B and H are equal. Reluctance - R = L/µ S Permeability - µ = µo µr Relative permeability - µr = see table for different materials Permeability of free space - µo = 0.4 p (G cm/a) = 4pE-7 (Tm/A) Page 5

6 TUTORIAL LORENTZ FORCE EQUATION F = qe + q ( v x B ) Lorentz force on a charged particle Example 1: + v Example 2: vy v B w/m2 + vx + Page 6

7 TUTORIAL The magnitude of the Earth's magnetic field ranges from 25 to 65 µt (or 25,000 to 65,000 nt) (or 0.25 to 0.65 G). It can be thought of as the magnetic field of a bar magnet at the center of the earth tilted at an angle of 11 degrees with respect to the rotational axis Magnetic field sensor in my cell phone. Sensor Kinetics Compass App uses magnetic field and GPS data Page 7

8 MAGNETIC FIELD INTENSITY IN NANO TESLA Page 8

9 LINES OF EQUAL DECLINATION If you are standing at the four corners in the US the magnetic field sensor would read 12 E of true north. In NY the magnetic field sensor would read 12 W of true north. Page 9

10 KJ Magnetics Page 10

11 THE HALL EFFECT The Hall effect was discovered in 1879 by Edwin H Hall. The Hall voltage (V H ) is created across a conductor, transverse to the current flow (I) and perpendicular to a magnetic field (B). The Hall coefficient is defined as the ratio of the Hall voltage to the product of Current and magnetic field. The Hall coefficient is a function of the carrier type (+ or -), charge (q=1.6e-19), and carrier concentration (n). V H = - I B q n t - V H + L B t I w Page 11

12 HALL VOLTAGE To maximize the Hall voltage (V H ) we want I and B large and n and t small. V H = - I B q n t Example: find V H for a square metal rod 1mm x 1mm in crossection. Let I= 100 ma and B = earths magnetic field ~50uT, n=1e28m -3 V H = -I B / (q n t) = - 0.1(50uT) /(1.6e-19 (1e28m -3 ) 0.001m) e-12 = pv (not realistic to measure) Example: find V H for a lightly doped diffused structure 1um thick. Let I = 100 ma and B = earths magnetic field ~50uT, n = 1e16cm -3 = 1e22m -3 V H = -I B / (q n t) = - 0.1(50uT) /(1.6E-19(1e22m -3 )1e-6m) e-3V = mv (possible to measure) Page 12

13 HALL COEFFICIENT The Hall coefficient (R H ) is defined as the ratio of Hall Voltatge (V H ) to I and B. R H is a ratio of Voltage perpendicular to current and magnetic field so it is not a resistance but can be used to compare different materials or structures. A large Hall coefficient is good for sensors. It has units of m 3 /coulomb, m 3 /Ampere- second, cm 3 /coulomb or ohm-cm/gauss. (or other variations) R H = -V H t I B R H = - 1 q n Material R H (10-12 ohm cm/g) Ag -0.8 Al -0.4 Au E16 cm-3-1,000,000 Page 13

14 EXAMPLE CALCULATION OF HALL COEFFICIENT R H = - 1 q n Example: find R H for a metal (Al) with n=2e29m -3 in units of m 3 /coulomb or ohm-cm/gauss With one free electron per atom in its metallic state, the electron density of copper can be calculated from its bulk density and its atomic mass E-12 m 3 /Coulomb and divide by 100 to get 0.31E-12 ohm cm/g Example: find R H for a n-type silicon with n=1e16cm -3 =1e21m E-4 m 3 /Coulomb and divide by 100 to get 6.25E-6 ohm cm/g a million times larger number than for Aluminum (ohm cm/g) Page 14

15 LAYOUT OF VAN DER PAUW S NWELL PWELL N+ P+ Page 15

16 PHOTO OF N-WELL VAN DER PAUW oxide aluminum p-substrate n-well Page 16

17 VAN DER PAUW TEST RESULTS N-Well Van Der Pauw Measured Rhos=888 ohm/sq Calculated Rhos=1/(q u dose) dose=9.5e12 cm-2 Rhos= ~1000 ohms Page 17

18 MAGNET PLACEMENT ON PROBE CARD B F i silicon magnet well Page 18

19 Hall Voltage VH Hall Effect Sensors MEASURED VH VERSUS I no magnet magnet top up magnet top down ma Current I (ma) Page 19

20 ANALYSIS OF DATA Calculate VH for no magnet at 1 ma, VH = ~ 4uV (earth s 60uT field) Measured VH is ~46 mv Conclusion is there is an offset of ~46mV With the magnet we have ~36mV and the difference is ~-10mV Calculate B of the magnet ~0.152 Tesla = 1520 Gauss Compare to data sheet value of 2952 Gauss at the surface of magnet. Placement of magnet is few mm away from the magnet surface. With the magnet flipped we have ~56mV and the difference is ~+10mV also giving ~0.152Tesla = 1520 Gauss but opposite sign. Page 20

21 ANALYSIS OF DATA Offset voltage Equipotential lines are perpendicular to the electric field lines. Voltage should be zero for no magnetic field (we found 46mV) Poor geometry choice Shows proof of concept Mechanical stress in packaged devices has been attributed to uv offsets in commercial sensors. +V H GND I V -V H Page 21

22 BETTER DESIGN Hall Voltage Contacts Current Contact L W t n-silicon p-silicon Current Contact This type of design should result in lower offset voltage. Page 22

23 HONEYWELL SS49 SENSOR Hall Effect Position Sensor Typical Supply voltage 5V DC Offset voltage 2.0 V Sensitivity 0.9 mv/g Dimensions 1.5mmx2mmx3mm Page 23

24 ALLEGRO A1326 HALL EFFECT SENSOR Typical Supply voltage 5V DC Offset voltage 2.5 V Sensitivity 2.5 mv/g Dimensions 1.5x2x3mm Page 24

25 AK8975/B ELECTRONIC COMPASS Page 25

26 Contactless switches Proximity sensors Electronic Compass Position Control Speed Control Anti-lock brake Ignition timing Measuring of I or B APPLICATIONS Fluke-i410 AC/DC Clamp On Current Probe Page 26

27 TESTING STATIC MAGNETIC FIELDS BASICS Number of turns, N Current, I (A) I Magneto motive force (mmf, Vm) = NI Cross sectional area (S) = Area Reluctance (R) = L/µ S N Permeability (µ) = µo µr Relative permeability (µr) = see table below Permeability of free space, = µo = 0.4 p (G cm/a) = 4pE-7 (Tm/A) MPL is mean path length L G is length of small air gap Flux Density B = F S Flux F = N I R MPL Reluctance for Toroid MPL L R = + G µoµr S µos L G Toroid Flux Density for Toroid B = 0.4 p µ R N I MPL + µ R L G Page 27

28 TESTING EXAMPLE CALCULATIONS Example (see circuit shown on the previous page) Given: Vin=10V, N=20 Turns, Lg=2mm Wurth Elektronik Toroidal Ferrite Core OD=29.5mm, I=19.0mm, L=7.7mm, µr=800 Find the Flux Density B in the gap MPL=p(OD-ID) 2 /4 = 86.6mm B = 0.4 p µ R N I MPL + µ R L G 0.4 p B = B = 11.9 Gauss Material µr Relative Permeability Metglas 1,000,000 Ferrite (Ni-Zn) Steel 100 Nickel Aluminum 1.00 Air 1.00 Vacuum 1 Permeability (µ) = µo µr Relative permeability (µr) = see table Permeability of free space, = µo = 0.4 p (Gcm/A) = 4pE-7 (Tm/A) Page 28

29 MACHINING THE TOROID Toroid and Diamond Cutting Tool Page 29

30 CIRCUIT TO GIVE KNOWN FLUX DENSITY Vin +V V +V 2N3904 2N3906 -V I N MPL L G Vin V H V H Sensor If R=100 W then I=10Vin ma R I = Vin/R B = 0.4 p µ R N I MPL + µ R L G Page 30

31 VOLTAGE TO CURRENT CIRCUIT DETAILS 741Op Amp +10 V +10 V Vin 2N < Flux < 30 Gauss p-p -10 V Input: +/- 10 V Supply Vin at 1Khz 0<Vin<1V p-p 0<I<100mA p-p R3 & R4 current limiting 33 Ohms 33 Ohms 2N V I Alegro A1326: 5 V Supply 10mA Bias Sensitivity ~2.5mV/G 10 Ohms Page 31

32 PROTO BOARD OF MAGNET FIELD GENERATOR Vin Vout Allegro A1326 V to I circuit Ferrite toroid with 60 turns of wire to produce a magnetic field. Centered in the gap of the toroid is the commercial hall effect sensor. Page 32

33 MEASURED SENSOR OUTPUT AND TOROID CURRENT The measured output voltage from the sensor is displayed in yellow. Vpp shown at the bottom is 92 mv. The current is shown using a current probe and displayed by the green sign wave. The 150mVp-p is equal to 100mA p-p Page 33

34 COREY SHAY TESTING HALL SENSORS Picture Here of RIT set up Vin and Vout from Oscilloscope Page 34

35 CALCULATED TOROID GAP FIELD STRENGTH Permeability of Free Space (µo): 0.4π Relative Permeability for Toroid (µr): 800 Number of turns: 60 Current: A p-p Mean Path Length (MPL): 7.85 cm Gap Length (Lg): 0.3 cm B = (0.4π(800)(60*0.156))/(7.85+(800*0.3))= 38.5 Gauss p-p Page 35

36 DISCUSSION OF RESULTS The toroid magnetic field strength can be calculated from the flux density equation. As shown on the previous page the calculated flux density is 38.5 Gauss. The Alegro sensor has a sensitivity of ~2.5 mv/gauss. This then gives the estimated Hall voltage of around 96mV. The measured Hall voltage was around 92mV; which is roughly a 4% error. We can conclude that this method of generating a known magnetic field to evaluate and calibrate Hall effect sensors is reasonable. Page 36

37 RIT HALL SENSOR MADE WITH PMOS PROCESS Hall Sensor and other devices on PMOS Chip Hall Sensor PMOS Chip Packaged Sensor Page 37

38 CALCULATED HALL VOLTAGE FOR RIT PMOS SENSOR NEAR 2952 GAUSS MAGNET Sensor Current (A) Hall Voltage (mv) Vh=-IB/qnt Vh=(-0.01*0.2952)/(1.6E-19*2E15*10000) = 0.92mV Note: 10,000 Gauss =1 Tesla 10,000 is used to convert cm 2 to meters 2 in the dose. Page 38

39 MEASURED HALL VOLTAGE FOR RIT PMOS SENSOR With a current input of 0.03 amps No Magnet Hall Voltage (V) South-Polarity Hall Voltage (V) North-Polarity Hall Voltage (V) Hall Voltage (V) / Page 39

40 CONCLUSION FOR RIT PMOS HALL SENSOR The sensor near a magnet (of B=~ 2952 Gauss) responded as expected. The offset voltage for sensor current of 0.03A is Volts. The sensitivity is 1.12E-3 mv/gauss. The toroid did not produce a strong enough field to see any change in the RIT PMOS sensor output voltage. At 32 Gauss with a doping dose of 2E15 cm -2, the expected Hall Voltage is approximately 30µV. (difficult to measure) To increase the sensitivity of the sensor, the dose could be decreased. If the dose is decreased to 2E12; the corresponding Hall Voltage would be 30mV, which is something that could be measured. In addition minimizing the Vout contact cut size (redesign) should reduce the output off-set voltage. Page 40

41 REFERENCES 1. Glossary of magnet terminology. 1 May 2013, 2. Hall Effect. Wikipedia: The Free Encyclopedia. Wikimedia Foundation, Inc., 3 May Web. 3. Device Electronics for Integrated Circuits, Richard S. Muller, Theodore I. Kamins, Mansun Chan, John Wiley & Sons.,3 rd Ed., Micromachined Transducers, Gregory T. A. Kovacs, McGraw Hill, Page 41

42 HOMEWORK HALL EFFECT SENSORS 1. Using the data on the following page, calculate the magnetic field strength created by the large magnet. 2. Look up the data sheet for the magnetic field sensor that you have in your phone. 3. Calculate the expected sensor output voltage for the following conditions: Honeywell SS49 sensor, sensor supply voltage = 5 volts, Toroid of 50 Turns, I=200mA p-p. Page 42

43 Hall Voltage VH Hall Effect Sensors MEASURED VH VERSUS I no magnet magnet top up magnet top down ma Current I (ma) Page 43