Dual Coil Micro-SpeakerDual Coil Micro-Speaker
EMCR870 MEMS Fabrication EMCR870 MEMS Fabrication February 26 2007February 26 2007
Chris NassarChris Nassar
DesignDesign•Two aluminum 38 turn square coils acting in parallel.
•Large low Resistance poly silicon return path
•4440µm X 4000 µm Diaphragm
MAGNET
Resistance CalculationsResistance Calculations
53419076*028.*SquaresRR sCoil
NSides
SIDESNSquares1
9
2
*)1(*9 SIDESSIDES
SIDES
NNNSquares
•Using this formula, the number of squares in the original design was 20256.
•The inner 10 coils (1180 squares) were removed yielding a total of 19076 squares.
• Using a sheet resistance of .028/sq for Al, the resistance of one coil is found to be 534.
•The sheet resistance of the poly was 98/sq. The poly return path can be approximated to be slightly over a quarter of a square.
• A poly resistance of 30 will be used in all further calculations.
25498 polyR
Simple Circuit TheorySimple Circuit TheoryC R 1 C R 2
1
2
C 1
1
2
C 1
R _ P O L Y
V 1V
POLYRCR
VI
_2
CR
VI
2
•The thevenin resistance of the complete circuit shown above is 290 using the values calculated on the previous page.
Measured ResistanceMeasured ResistanceAverage Resistance
0
200
400
600
800
1000
1200
1 2 3 4 5 6 7 8 9 10 11 12
Wafer Die
Res
ista
nce
(O
hm
s)
Metal1
Metal2
Metal 1: Average = 604, Stdev = 124
Metal 2: Average = 879, Stdev = 114
Theoretical DisplacementTheoretical Displacement
Current(A) Pressure PSI Displacement (µm)0.002 0.00475 0.02
0.01 0.0237 0.10.02 0.04756 0.2
0.025 0.0594 0.270.03 0.071344 0.330.04 0.095 0.430.06 0.14 0.640.08 0.19 0.870.1 0.2378 1
0.12 0.2853 1.30.14 0.33 1.50.16 0.38 1.70.2 0.41 1.87
u0 1.25664E-06Height,z (m) 5.00E-03Bm (T) 0.5
2 24 4
2 23 3
1 13 1 249.98 1
1 116
P R P Ry
E E
E = Young’s Modulus, = Poisson’s Ratio for Aluminum =0.35
*The second equation corrects all units assuming that pressure is mmHg, radius and diaphragm is m, Young’s Modulus is dynes/cm2, and the calculated displacement found is m.
Circular diaphragm displacement
Force on one coil
Current(A) Pressure PSI Displacement (µm)0.002 0.00475 0.020.01 0.0237 0.10.02 0.04756 0.2
0.025 0.0594 0.270.03 0.071344 0.330.04 0.095 0.430.06 0.14 0.640.08 0.19 0.870.1 0.2378 1
0.12 0.2853 1.30.14 0.33 1.50.16 0.38 1.70.2 0.41 1.87
Audio Amplifier CircuitAudio Amplifier Circuit
+3
-2
V+7
V-4
OUT6
U1
LM741
+3
-2
V+7
V-4
OUT6
U2
LM741
VDD
GND
R1
10k
R2
10k
GND
VDD
VDD
GND
C1
1uR3
1M
R4
100kR5
10k
AUDIO IN
GND
M1
GND
1
2
C1
1
2
C2
CR1 CR2
HIGH VOLTAGE SUPPLY•DC bias point must put the diaphragm on the edge of deflection and keep the power MOSFET in saturation.
•The signal must be centered around the DC bias point.
•It must provide some amplification
Audio Amplifier CircuitAudio Amplifier CircuitApproximate
Voltage/Current Levels used
•VDD ≈ 6V
•Vgate ≈ 3V
•Id ≈ .2A
•Vhigh voltage supply ≈ 70V
Test SetupTest Setup
ResultsResultsMicro-Speaker in actionMicro-Speaker in action
Micro-Speaker
Queen’s original
Frequency AnalysisFrequency Analysis
Micro-Speaker after noise removal and amplification
Queen’s original
Frequency AnalysisFrequency Analysis
Looking AheadLooking AheadAnalysis of Frequency ResponseAnalysis of Frequency Response
Is the poor quality due to the electronics or Is the poor quality due to the electronics or the membrane?the membrane?
Low voltage versionLow voltage version Integrated ElectronicsIntegrated Electronics