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Dual Coil Micro-Speaker EMCR870 MEMS Fabrication February 26 2007 Chris Nassar Chris Nassar

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Design Two aluminum 38 turn square coils acting in parallel. Large low Resistance poly silicon return path 4440µm X 4000 µm Diaphragm MAGNET

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Resistance Calculations 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.

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Simple Circuit Theory The thevenin resistance of the complete circuit shown above is 290 using the values calculated on the previous page.

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Measured Resistance Metal 1: Average = 604 , Stdev = 124 Metal 2: Average = 879 , Stdev = 114

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Theoretical Displacement 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

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Audio Amplifier Circuit 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

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Audio Amplifier Circuit Approximate Voltage/Current Levels used V DD ≈ 6V V gate ≈ 3V I d ≈.2A V high voltage supply ≈ 70V

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Test Setup

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Results Micro-Speaker in action

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Micro-Speaker Queen’s original Frequency Analysis

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Micro-Speaker after noise removal and amplification Queen’s original Frequency Analysis

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Looking Ahead Analysis of Frequency Response Analysis of Frequency Response Is the poor quality due to the electronics or the membrane? Is the poor quality due to the electronics or the membrane? Low voltage version Low voltage version Integrated Electronics Integrated Electronics

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