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High-temperature semiconductors -- mission to Venus

  1. May 23, 2015 #1
    I was motivated to research this by discovering plans for a Venus rover: Windsurfing on a Wicked World | NASA That planet has the problem of a surface temperature of about 450 C and pressure around 92 bar. Its atmosphere is mostly CO2 with a few percent N2 and much less of various other gases.

    To date, the champion survivor on that planet is Venera 13 at 127 minutes. Toleration of Venus surface temperature will be necessary for doing better than that. On the mechanical side, that is not much a problem. That temperature is rather mild by some industrial standards, and I easily found several lubricants that can work in much higher temperatures. For electricity storage, sodium–sulfur batteries run at 300 - 350 C, so a 450-C battery may be feasible. Ferromagnetic materials are likely not a problem. They lose their ferromagnetism at above their Curie temperatures, but some common ferromagnetic materials have Curie temperatures well above Venus's surface temperature.

    The big weak spot is semiconductor components, and that's what I'm asking about. Design of high-temperature electronics is not very advanced, as far as I can tell (High-Temperature Electronics at Analog Devices, Extreme-Temperature Electronics (Tutorial - Part 1)). Some commercially-available components are rated for temperatures of 200 C or even 300 C, but they look like rather simple ones. There are various things that one can do to improve temperature tolerance, like trench isolation and silicon-on-insulator. Looking at alternative materials, silicon carbide goes up to over 600 C, though only simple components have been demonstrated with it, as far as I've been able to find out.

    Fun fact: a favorite way of torture-testing electronic components is to run them at high temperatures. That makes them fail much faster.

    Is anyone here familiar with the state of the art in such components?
     
    Last edited: May 23, 2015
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  3. May 23, 2015 #2

    Hesch

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    As stated in the link, diamond is the superior material, though very expensive.

    But have you thought of simply cooling the "electronic box"? I don't think that thermal isolation is a solution since the electronic circuits will produce heat.
     
  4. May 23, 2015 #3

    mfb

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    Discrete components don't look so hard (there are commercial SiC devices), but I guess such a probe should have some computer inside, and I am not aware of integrated circuits on SiC-basis.

    Cooling sounds like the easiest option.
     
  5. May 23, 2015 #4
    One can do chemical-vapor-deposition diamond films. Is that very expensive?
    Except that the whole purpose of high-temperature semiconductors is to get away from having to cool them. Doing so requires extra apparatus and it is impractical in some environments, like deep oil wells and Venus's surface. For an oil well, it would have to fit into a borehole, a further constraint, though Venus's surface does not impose that constraint. Venus's surface does impose another constraint: inaccessibility for repairs.
     
  6. May 23, 2015 #5
    Diamond is likely the "best" material because it has a very high thermal conductivity (~5 times that of copper). Thermal conductivity is less useful when the background heat is high. It may not be the best choice for this application.

    Keeping power use low is critical. That means simple controls with less computational power onboard the craft.

    Vacuum tubes still work for power amplification. They could be used for communications or in other places where power is needed. They could be kept outside a cooled electronics compartment.
     
  7. May 23, 2015 #6
    I've done some research and here's what I found:

    Silicon Carbide Logic Circuits Work at Blistering Temperatures - IEEE Spectrum
    Silicon carbide is good because it has a larger band gap between valence and conduction electrons than silicon does. That means that it takes more heat to kick electrons up into the conduction band, making it too easy for currents to flow. But it's rather difficult to make good insulating layers for CMOS transistors, now often used in IC's, so the Case Western team is using JFET's instead.

    Philip Neudeck has a team at NASA working on this problem, and they've gotten chips that can run for thousands of hours around 500 °C. Their first chips had only 10 transistors on a chip, and they are planning on designs with over 300 transistors.

    Having working transistors does not mean the end of the problems to be overcome. Connecting the transistors in the chip, packaging the chip, and connecting the chip to other components.

    High Temperature Silicon Carbide CMOS Integrated Circuits - rsl_semi_published_hiten2011.pdf -- including working on the insulator layers in the transistors.

    Future high temperature applications for SiC integrated circuits - Zetterling - 2012 - physica status solidi (c) - Wiley Online Library -- also mentions lower on-resistance and possibly being radiation-hardened.
     
  8. May 23, 2015 #7

    marcusl

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    JFET's have much higher power draw and dissipation than CMOS so I expect that to be a significant issue.
     
  9. May 23, 2015 #8

    Svein

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    I seem to remember that Honeywell has a high-temperature process. We did something with them back in 2003 and I remember that they had no standard circuit, they just processed circuits designed in VHDL.
     
  10. May 23, 2015 #9

    Hesch

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    What about using the good old radio tubes. You can save a lot of energy on Venus, not using so much power to keep them heated up.
     
  11. May 23, 2015 #10

    rbelli1

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    I wonder if and how small a tube integrated circuit could be made with modern MEMS processes.

    BoB
     
  12. May 23, 2015 #11
    Glenn Research Center at Lewis Field Development of High Temperature Silicon Carbide (SiC) Electronics for Intelligent Engine Systems -- for jet engines.

    Seems to be proposing:
    High-temperature radio equipment and photovoltaic cells -- what a Venus rover will need. This presentation also mentions SiC capacitive pressure sensors.

    Stability goals:
    For testing in a jet engine on the ground: >1000 hr
    For most aviation and space applications: >100,000 hr

    Also mentions tests of high-temperature-tolerant chip packaging.

    High Temperature SiC Electronics: Update and Outlook
    It covers much of the ground of the previous one, but with additional numbers. Like these temperature upper limits:

    Ordinary silicon chips: 150 C
    Silicon-on-insulator chips: 300 C
    SOI only for low-power applications; SiC better for high-power ones

    The authors concede that JFET's are limited by their high power consumption, about 1 milliwatt per gate -- can't get very many of them onto a chip.

    But SiC JFET's can function all the way down to -125 C. Good for space travel.

    Also some stuff on multilevel interconnects -- integrated-circuit internal "wires".

    Plans: 4-bit A/D and D/A converters, 2*2 static RAM, op amp, ring oscillator, binary AM radio transmitter
     
  13. May 24, 2015 #12

    mfb

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    Time to dig out the old 8-bit CPU designs? ;)

    The potential applications on Earth help, that gives a good reason to spend a significant amount of money on research.
     
  14. May 24, 2015 #13

    Svein

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    Some of which are:
    • Instrumentation of very deep bore holes
    • Instrumentation of semi-active volcanoes
     
  15. May 24, 2015 #14
    I didn't notice whether the temperature of 500ºC was the oven or the junction temperature. Junction temperature seems more likely. Given that jFETs are relative power hogs, 500ºC will severely limit the power available in a passively cooled system with an ambient temperature of 462ºC. And since 462ºC is the mean temperature, the probe will likely need to shut down during temperature spikes. Or perhaps we can limit the probe to the icy wastes of Venus where the temperature plummets to 380ºC. (On a mountaintop.)

    Plus there's the need to protect against hot acid. While such protective coatings exist, most of them seem to be poor thermal conductors. Perhaps graphene will work though. Does anyone know how resistant graphene is to acid?
     
  16. May 24, 2015 #15
    Venus's surface likely does not vary much in temperature, to within altitude variation. It has pretty much the same temperature in daytime and nighttime, for instance. Venus has a rather long day-night cycle: about 116.75 Earth days. So it's almost 59 Earth days of daytime and 59 Earth days of nighttime.

    Atmosphere of Venus - Wikipedia, The Environment of Venus

    The highest mountains on Venus are the Maxwell Montes at about 10 km, higher than Mt. Everest. The temperature declines to about 385 C and the pressure to about 47 bar. That's all that one gets for landing on top of Venus's highest mountains.

    Venus's sulfuric acid is in its clouds. So it's mainly a problem of one wants to go ballooning there. It decomposes at about 300 C to sulfur trioxide and water, and sulfur trioxide decomposes in turn to sulfur dioxide and oxygen. So on the surface, it's SO2 that one has to worry about. Hot concentrated sulfuric acid can react with carbon (Sulfuric acid - Wikipedia), so it may be able to corrode graphene. There are at least some materials that resist sulfuric acid, however, as ought to be evident from the continued structural integrity of lead-acid batteries and laborarory glassware.
     
  17. May 24, 2015 #16
    Many embedded systems still use 8-bit chips, so one can use some of those designs. Their main value is their low power consumption -- they don't have as many transistors as 32-bit ones do. That's also why many embedded systems still use 16-bit chips.
     
  18. May 24, 2015 #17

    marcusl

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    That's a relief. We can build our space vehicle out of lead and just strap 6 or 10 rockets together to hoist it into space :wideeyed:
     
  19. May 24, 2015 #18
    That is not necessary. Construction of Lead Acid Battery | Electrical4u
    Ebonite is a kind of hard rubber.

    Venus's sulfuric acid is only a problem at cloud altitudes, and the temperature there is around Earth temperatures. So coating everything with plastic ought to work. There's even a commercial product that does that: http://www.neptuneresearch.com/product/acid-coat/ [Broken]
     
    Last edited by a moderator: May 7, 2017
  20. May 24, 2015 #19
    Yet plastic is a poor thermal conductor. Thus coating the probe with plastic will limit thermal dissipation.

    Perhaps we could place the probe in a shell that breaks open after passing through the acid? The inside could have some antacid to handle any residuals.
     
  21. May 24, 2015 #20

    Baluncore

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    Initially it would be better to use redundant serial processors, with only 1bit each. That will be lower power and more fault tolerant, but they only run at the speed of dark. Speed is not important when you are stuck on the surface of Venus because you do not have to run MS Windows. Serial processsors, such as the PDP-8/S were used in the early days of computing for mobile applications in the oil industry. The CPU of the PDP-8/S, had only about 519 logic gates.
     
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