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