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A cmos capacitive pressure sensor chip for finger
This document summarizes a research paper on developing a CMOS capacitive pressure sensor chip for fingerprint detection. The chip uses differences in capacitance induced by the ridges and valleys of fingerprints to detect fingerprint patterns. It has an array of circular membranes that change capacitance with applied pressure. An external ADC converts the sensor's output signals into a fingerprint image showing the detected ridges and valleys. Experimental results demonstrated the sensor array's ability to successfully detect fingerprint patterns and was relatively insensitive to temperature variations.
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A cmos capacitive pressure sensor chip for finger
- 1. A CMOS CAPACITIVEPRESSURE SENSOR CHIP FOR FINGER PRINT DETECTION Yung-Shih Hsiung and Michael S-C Lu Department of Electrical engineering and Institute of Nano engineering & Micro System NTHU Reporter-Vivek Hegde Course Lectured By- Dr.Cheng-Hsien Liu
- 2. Outline Why CMOS Capacitivepressure Sensor Concept Device Fabrication Architecture Experiment Conclusion
- 3. Why CMOS capacitivepressure sensor? Biometric uses whorl ,loop and arc patterns of finger print Ridge. In optical-Photographed image is stored for subsequent identification Piezoresitive uses wheat stone bridge and sensors are more sensitive to temperature
- 4. Concept Detect Different pressureinduced by ridges and valleys of finger print Because of difference in the contact area on the surface ,capacitance also varies.
- 5.
- 6. Architecture Circular Membrane radios is 20 µm and four support beams on the sides are 8 μ m long and 2 μ m wide. The total size of a sensing pixel by inclusion of the surrounding anchor area is 65×65 μ m2
- 7. Architecture Constant Current Sourceis used to Charge Sensing Capacitor Capacitor potential is Periodically reset by transistor Switch. 8x32 Signals are Sequentially measured through shared buffer via Decoder Control. O/P Signal is processed by External 14-Bit A/D Converter Capacitance Change with respect to the uniform pressure applied to the membrane
- 8. Architecture Architecture of Sensorarray and the Schematics of Current Source in-pixel capacitive sensing circuit Constant Current Source
- 9. Experiment Simulated and measured force- displacement curves.
- 10. Measured output waveformsfrom different sensing membranes before pressure was applied
- 11. Capacitance change vsapplied pressure Measured value and Simulated values are close to each other
- 12. Measured capacitance changesof the array by: (a) applying a pressure on the right side of the chip;(b) pressing part of the finger tip on the chip. Shows successful detection of ridges and valleys
- 13. Conclusion Capacitive Pressure Sensorarray is presented for finger print detection Sensor development take advantage of multiple metal layer and fast electronics provided by the sub micro meter CMOS process Post CMOS fabrication can be conducted at the chip level Is almost insensitive to temperature variations
- 14.