silicon carbide pressure sensors for venus …
TRANSCRIPT
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SILICON CARBIDE PRESSURE SENSORS FOR
VENUS ENVIRONMENT
R. S. Okojie1, D. Lukco2, R. D. Meredith1, L. M. Nakley1, and K. Phillips3
1NASA Glenn Research Center, Cleveland, OH 44135;
[email protected], (216)433-65222Vantage Partners, LLC, NASA Glenn Research Center, Cleveland OH,
3Sierra Lobo Corporation, NASA Glenn Research Center, Cleveland OH.
Primary Sponsor: NASA Transformational Tools and Technologies Project of the
ARMD
Task Support: Long Life In-Situ Solar System Explorer (LLISSE) of SMD
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Interest in Venus has been stimulated by the ongoing debate about
Earth’s planetary evolution, particularly in regards to its climate, and
NASA has proposed a flagship mission to Venus to be launched in the
near future. Quantifying how the Venus evolution ran its course will
greatly aid researchers trying to model Earth’s climate dynamics.
Motivation
ObjectiveTo determine the long-term robustness and survivability of semi-
encapsulated piezoresistive silicon carbide pressure sensors in a simulated
Venus atmosphere where pressure ~90 bar, temperature ~ 465 ⁰C, and
aggressive reactive chemistry (SO2, COS, etc). This is with the goal of
infusion into future Venus science missions
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Legacy SiC Pressure Sensors for Aero-Engine Applications
Demonstrated at 800 ⁰C!
3
NASA SiC Pressure Sensors
0
15
30
45
0 50 100 150 200
Net
Ou
tpu
t (m
V)
Applied pressure (psi)
Room 300 ºC 500 ºC 700 ºC 800 ºC
Sensor 273Excitation Voltage = 10V
800 oC Pressure Sensor Demonstrated!Sensor get better with increase in temperature!
Net Output vs. Static Pressure
Approved for public release; distribution unlimited.
Alireza Behbahani and Kenneth Semega, “Sensing challenges for controls and PHM in the hostile operating conditions
of modern turbine engine.” AFRL-RZ-WP-TP-2008-2184
Leverage the superior attributes of
piezoresistive SiC based pressure
sensors at higher temperature:
-Batch fabrication
-Higher gauge factor
-Portability
Tech Leapfrog
Technology Enabling Space
Infusion into Venus missions require material and structural considerations to
survive the chemistry and high pressure
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Simulated Venus Atmospheric Conditions
Temperature: 460 ⁰C +/- 10 ⁰C
Pressure: 1356 psia +/- 20 psia
Chemistry: “Venus atmosphere” 96.5% CO2, 3.5% N2, 180 ppm SO2, 12 ppm
CO, 51 ppm COS, 2 ppm H2S, 0.5 ppm HCl, 2.5 ppb HF
Range: SO2 concentration range 100-200 ppm
Glenn Extreme Environment Rig (GEER)
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Contact wire
Sealing Glass
Reference Cavity
SiC Pressure Sensor
TC
go
es i
n he
re
AlN
Plug-In Type SiC Absolute Pressure Sensor
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Plug-In Type SiC Pressure Sensor Extension for Insertion into GEER
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Start Up Vessel leak checked to 1400 psia at ambient temperature with high purity nitrogen.
Next, the vessel will be purged of residual air and nitrogen by performing three
pressure/vacuum cycles. The vessel will be left under vacuum after the last purge
cycle in preparation for the specialty gas fill.
Constituents of Venus atmosphere will be delivered to the vessel at ambient
temperature starting with the vessel at negative pressure. The fill process will begin
with CO2 which will continue to flow continuously as the remaining specialty gas are
filled. Specialty gases will be filled in the following order:
Inlet valve closed to isolate the gas mixture within the vessel. Vessel temperature
set point set to 456 C and the heaters will increase at 7 C/hr until the set point is
reached.
Shutdown Upon completion of test, the vessel temperature set point will be reduced to 150 C. During
cool down, the gas mixture will remain inside the vessel. Once the average gas
temperature reaches 150 C, the mixture will be vented and the vessel will be thoroughly
purged with dry nitrogen. The heaters will maintain an average internal temperature of 150
C during venting and purging. Once the purge is complete, the heaters will be turned off
allowing the vessel to cool to ambient temperature. A small amount of nitrogen will be left
inside the vessel during the final cool down to maintain positive pressure inside the vessel.
GEER Test Conditions
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Room Temperature SiC Pressure Response in GEER Chamber(Purge and Vent Steps at room temp)
Sensitivity~0.21 µV/psi
0.44
0.442
0.444
0.446
0.448
0.45
0.452
0 5 10 15 20 25
Ou
tpu
t (V
)
Hours
~1346 psi
14 psi
Nitrogen Venting
Vin=10 VGain=10
0.44
0.442
0.444
0.446
0.448
0.45
0.452
0 2 4 6 8 10 12 14 16 18 20 22
Ou
tpu
t (V
)
Hours
1327 psi 1346 psi
Pressure ramped to 1346 psi and held steady @room (some changes)
Vin=10 VGain=10
0.44
0.442
0.444
0.446
0.448
0.45
0.452
0 1 2 3 4
Ou
tpu
t (V
)
Hours
376 psi
1327 psi
Nitrogen purge. Temperature held relatively steady @ room
Vin=10 VGain=10
Pressure ramp-up Ramp and Dwell Ramp down
1327 psia1327 psia
14 psia
Vin=10 V
Gain=10 Vin=10 V
Gain=10
Vin=10 V
Gain=10
1346 psia ~1346 psia14 psi
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SiC Pressure Sensor Response during GEER Chamber
2.24
2.245
2.25
2.255
2.26
2.265
2.27
0 5 10 15 20 25
Ou
tpu
t (V
)
Hours
Vin=10 VGain=50
Leak check: Pressure Ramp up from 14 psi to 1345 psi @ room
14 psi
1360 psi hold and dwell
2.4 psi
14 psia
2.4 psia
1360 psia hold and dwell
Leak check: Pressure ramp up from 14 psi to 1360 psi @ room
Vin=10 V
Gain=10
Vin=10 V
Gain=50
?
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• Sensor reliably operational for 12 earth days
• Sensor survived 60 earth days (Test duration)
-170
-120
-70
-20
30
80
130
0 100 200 300 400 500 600 700 800 900
Ou
tpu
t (m
V)
Hours
Vin=10 VGain=1
6.7 psi16.9 C
1345 psi451 CReference point
732 psi, 150 C, all gases in;Temperature ramp up to Venus condition
Operational Life of Sensor A
N2 Purge/Temp Ramp Up
Venus condition: 460 C, 1336-1346 psi (SO2 boosting)
SiC Pressure Sensor Operational Life in GEER
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Post GEER Chamber Analysis
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Post GEER Chamber Analysis
Sensor glass seal
AlN Header
Crystal growth on two adjacent Au wire
AlN back glass seal
Au wire with no crystal growth
Before AfterSensor diaphragm
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• Sealing Glass and sensor remained intact
• AlN header intact
• No loss of reference cavity
Sensor diaphragm
Post GEER Chamber Analysis
Sensor Top View
Glass seal
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Two reaction paths:
1. TiCuSil braze material between ceramic tube and stainless steel tube
• Cu and Ag sulfide crystals grow outward and eventually over the
Au wires terminals.
• Touching of the crystal between wires would result in shunt
resistance.
2. Au-plated Ni wire in individual ceramic tube holes
• Ni diffuses out of Au plating and reacts with SO2 to form nickel
sulfide.
• Continued consumption of the Ni will result in gradual increase
in resistance and sensor output
Key Observations
Inside Chamber Outside Chamber
TiCuSil brazeCeramic tube with Au plated Ni wires SS tube
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Devices Materials Outcome
Electronics Packaging Pb PbS
Al2O3 No reaction
Insulation CaO CaSO3, CaSO4
SiC Electronics Pt PtS; fibers when present as thin film
Pt (in the presence of Au) PtS spheres
Au No reaction, but mobile
Ir No reaction, but mobile
SiC No reaction
SiO2 No reaction
Feedthrough Materials Cu Cu2S crystals
Ni NiS crystals
CuBe Cu2S crystals; Cl found on surface
SiC Pressure Sensor Kovar (Ni-Co-Fe) NiS, FexOy
AlN No reaction
Ag-Cu Braze segregation into Cu2S and Ag; Ag mobile
GEER Components Inconel 625 (Ni-Cr-Mo-Fe) NiS, CrxOy
304 SS Mirror finish, low corrosion rate
Al foil/Mg dopedMgO on surface, MgF inner layer,
Al bulk no reaction
Table 4 Tested Materials with Corresponding Outcomes
Lukco, D. et al, Earth and Space Science, doi.org/10.1029/2017EA000355
Materials Tested in Simulated Venus Atmosphere
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Sensor room temperature test shows good linear response to pressure
Sensor stable and reliably operational for ~12 earth days
Sensor physical structure survived 60 earth days of testing
Primary failure mechanism : Gradual NiS formation on Au-plated Ni
wire resulted in changes in wire resistance
Long term reliable operation beyond 12 days is in the works
Plan to integrate with temperature sensor and electronics in progress
Open to collaboration for infusion into any Venus science mission
architecture
Summary, Conclusion, and Future Plans
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Thank You!
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