Absolute Pressure Sensors
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Transcript of Absolute Pressure Sensors
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Absolute Pressure SensorsAbsolute Pressure Sensors
Z. Celik-Butler, D. Butler and M. Chitteboyina
Nanotechnology Research and Teaching Facility University of Texas at Arlington
http://www.uta.edu/engineering/nano/
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Absolute Pressure Sensor Model in CoventorWare
Cavity
Flexible superstrate
Flexible substrate
Sealed Pressure SensorWheatstone Bridge
Configuration
Bond Pads
Stress, Strain and Displacement simulations for the pressure sensor
is currently on-going
0.14cm x 0.14cm
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Clean silicon wafer
Fabrication Process Flow for the Absolute Pressure Sensor
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40 µm flexible polyimide substrate
Fabrication Process Flow for the Absolute Pressure Sensor
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Insulation layer 0.5 µm
Fabrication Process Flow for the Absolute Pressure Sensor
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Thick polyimide sacrificial layer 2.5 µm
Fabrication Process Flow for the Absolute Pressure Sensor
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Thin polyimide sacrificial layer 0.5 µm
Fabrication Process Flow for the Absolute Pressure Sensor
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Membrane layer 1µm
Etch holes
Fabrication Process Flow for the Absolute Pressure Sensor
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Piezoresistors 0.5 µm
Fabrication Process Flow for the Absolute Pressure Sensor
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Aluminum metallization 0.5 µm
Fabrication Process Flow for the Absolute Pressure Sensor
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Encapsulant layer 0.5 µm
Bond pads
Etch holes
Fabrication Process Flow for the Absolute Pressure Sensor
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Release both the sacrificial layers
Release both the sacrificial layers
Cavity
cross-section
Fabrication Process Flow for the Absolute Pressure Sensor
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Deposit final sealing layer 0.6 µm
Bond padscross-section
Cavity
Fabrication Process Flow for the Absolute Pressure Sensor
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Bond pads
Spin coat 40 µm flexible polyimide superstrate
Fabrication Process Flow for the Absolute Pressure Sensor
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Absolute Pressure Sensor ResultsSensor A (0.0 – 2.0 psi)
DISPLACEMENT PLOTSTRAIN YY PLOT STRAIN XX PLOTMISES STRESS PLOT
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STRAIN YY PLOT STRAIN XX PLOT
Absolute Pressure Sensor DesignSensor H (14.0 – 16.0 psi)
DISPLACEMENT PLOTMISES STRESS PLOT
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Absolute Pressure Sensor Fabrication Steps
STEP 1 On a clean wafer spin-coat ~ 40 µm flexible polyimide as the substrate layer followed by 600 nm passivation layer
STEP 2 Spin coat thick polyimide and cure
STEP 3
STEP 4
NEXT STEPS Deposit ~ 500 nm thick aluminum as the metallization layer Ash the sacrificial layer using oxygen plasma to suspend the membrane Deposit 0.5 µm encapsulation layer followed by 0.5 µm as the final sealing layer Etch the silicon wafer from the back side to get access to the bond pads and characterize the absolute pressure sensors
Piezoresistors ~ 25 nm
Passivation layer ~ 600 nm
membrane layer ~ 0.1 µm
Thick Sacrificial layer ~ 7 µm
Spin coat thin polyimide and cure
Deposit 0.1 µm membrane layer STEP 5 Deposit ~ 25 nm piezoresistor layer
Thin Sacrificial layer ~ 0.5 µm
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Absolute Pressure Sensor Fabrication Steps
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Absolute Pressure Sensor Characterization
1 2 3 4Vout Vin Vout Vin
R1
R2 R3
R4
Vin Vout
R1
R3R2 R4
The electrical circuit is complete with two active piezoresistors (R1 and R3) and two passive piezoresistors (R2 and R4) in a Wheatstone bridge configuration
The current-voltage characteristics is plotted and the true resistances are found Pressure is applied on top of the membrane and the change in output voltage vs. input voltage is plotted