A cmos capacitive pressure sensor chip for finger
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Transcript of A cmos capacitive pressure sensor chip for finger
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
A CMOS CAPACITIVE PRESSURE SENSOR CHIP FOR FINGER PRINT
DETECTION
OutlineWhy CMOS Capacitive pressure SensorConceptDevice FabricationArchitectureExperimentConclusion
Why CMOS capacitive pressure 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
Concept
Detect Different pressure induced by ridges and valleys of finger printBecause of difference in the contact area on the surface ,capacitance also varies.
Device fabrication
Architecture
Circular Membrane radios is 20 µm and four support beams on the sides are 8 μm long and2 μm wide. The total size of a sensing pixel by inclusion of the surrounding anchor area is 65×65 μm2
Architecture
Constant Current Source is 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
ArchitectureArchitecture of Sensor array and the in-pixel capacitive sensing circuit
Schematics of Current Source
Constant Current Source
Experiment
Simulated and measured force-displacement curves.
Measured output waveforms from different sensing membranes before pressure was applied
Capacitance change vs applied pressure
Measured value and Simulated values are close to each other
Measured capacitance changes of 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
ConclusionCapacitive Pressure Sensor array is presented
for finger print detectionSensor 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
Question ?