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Spectrometer on a Chip

Spectrometer on a Chip. Seth Robert Bank Jeffrey Scott Kline ECE 345 Project 14 T.A. Ben Floering 5/3/99. Introduction. Spectroscopy is one of the best methods for determining chemical makeup Spectrometers Have application in many areas e.g. analyzing drinking water for lead

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Spectrometer on a Chip

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  1. Spectrometer on a Chip Seth Robert Bank Jeffrey Scott Kline ECE 345 Project 14 T.A. Ben Floering 5/3/99

  2. Introduction • Spectroscopy is one of the best methods for determining chemical makeup • Spectrometers • Have application in many areas • e.g. analyzing drinking water for lead • Are large and typically not portable

  3. Objective • Design and build a spectrometer using • Prism for refraction • Silicon based p-i-n photodetectors for detection • External logic for display of the spectrum

  4. Spectrometer Incident light o 60 o 60 prism air silicon 1 2 3 4 5 p-i-n photodetectors

  5. Block Diagram of Design Optics Design/Layout of Photodetectors Fabrication of Photodetectors External Circuit Final Product

  6. Design/Layout ofPhotodetectors • Linear array of p-i-n photodiodes • Continuous intrinsic region design made possible by • blocking wells • linear array geometry • Resolution limited by the lithography

  7. Photodetector Layout n p i-region p n n p p n n p p n n p p n n p Vcc

  8. Fabrication ofPhotodetectors • Masks • Designed with CAD program • Printed on 5080 dpi laser printer • Simulated on DIFCAD Software • Processing done in ECE 344 Lab

  9. External Circuit free p i n Vcc + - Vcc

  10. Optics • Assume collimated light source • Snell’s Law dictates specific beam location • non-linear relationship between beam wavelength and beam location • Fresnel Equations for power at multiple interfaces

  11. Integration ToFinal Product • Align prism to detectors via microscope • Aperture placement/alignment done with use of test beam

  12. Problems and Challenges • Lithography Problems • Masks • Kasper Mask Aligner • Aluminum lift off • Impossible to isolate devices and bias each detector seperately

  13. Functional Tests • Measurement of optical generation current and reverse leakage current • Laser light source • External circuit functionality check

  14. Results

  15. Results Current Predicted (A) Measured (A) I0 0.676 0.4489 Iopto 0.6141 0.7809

  16. Recommendations • Commercially viable with modifications • Use transmission grating for dispersion • Higher quality mask set • e-beam • Optics • Collimating optics • Employ commercial products in alignment • Calibration capabilities • Can any light source • Integrate external circuit

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