Radiation Plus Electronics is a Bad Combo. Enter a New Rad-Hard Manufacturing MethodJuly 13, 2020 by Jake Hertz
Space radiation can wreak havoc on electronic devices. While there are many ways to prevent damage, MIT's newly-developed manufacturing technique using rad-hard CMOS technology shows promise.
Earth's atmosphere protects us from high energy-ionizing radiation such as gamma rays and x-rays. Engineers who design terrestrial electronics (i.e anything that doesn’t go into space) can go on with their work mostly oblivious to the effects of ionizing radiation on their designs.
However, once we start considering harsh environments—like that of space or high altitudes on earth—radiation becomes a focal point in design.
Radiation in Space
Radiation, in its most basic sense, is a form of energy emitted in the form of rays, electromagnetic waves, and/or particles. Humans are exposed to many forms of benign radiation such as light and radio waves.
However, in the depths of space, outside of the protective cloaking of our atmosphere, exist many different kinds of radiation.
Radiation in space. Image used courtesy of NASA
According to NASA, space radiation comes in three flavors: particles trapped in the Earth’s magnetic field, particles shot into space during solar flares, and galactic cosmic rays. Galactic cosmic rays are high-energy protons and heavy ions from outside our solar system. All of these forms of radiation are ionizing.
Space Radiation and Electronics
Because these forms of ionizing radiation exist in space, but not on earth, space electronics have to be designed with special considerations.
According to a NASA report on the effects of radiation on electronic devices, the ionizing nature of space radiation can penetrate devices and generate a charge inside silicon-based electronics.
This build-up of charge can disrupt the crystalline nature of an electronic component and cause a complete change or failure of the operational characteristics of the device. The function is degraded and then fails as the electronic components receive more radiation exposure.
Depiction of how radiation interferes with electronic systems. Image used courtesy of NASA
The effect of cosmic rays on electronics can also change digital states, leading to bit-flip errors and erroneous data. This effect of radiation continues to worsen as electronics get smaller and become more susceptible to the effects of a low-energy interferer.
How to Handle Space Radiation
While there are ways of accounting for bit-flip errors caused by radiation, the options for dealing with the structural damage to electronics are limited.
Most engineers opt to use radiation-hardened (or rad-hard) components in their designs. This could mean enclosing electrical systems in radiation-hardened enclosures, designing chips with rad-hard techniques, or both.
According to Fa-Xin Yu et al., some rad-hard IC design techniques include insulating substrates, utilizing bipolar integrated circuits, using wide-band-gap substrates, and utilizing SRAM instead of DRAM.
MIT Develops New Rad-Hard Manufacturing Method
MIT’s Lincoln Lab has long been working on ways to manufacture rad-hard integrated circuits. Their technology, which they call fully depleted silicon-on-insulator (FDSOI) CMOS technology, is currently being fabricated down to 90 nanometers.
A fully-depleted silicon-on-insulator CMOS wafer. Image used courtesy of Nicole Fandel and MIT
After nearly two decades of the technology maturing under the sponsorship of DARPA, it has finally found itself ready for the industry.
This comes after many years of optimizing FDSOI technology for a range of conditions, including RF range, ultra low power, both cryogenic and high temperatures, and radiation settings.
In June, it was announced that the fabrication technology focused on radiation environments will be transferred from MIT's Lincoln Lab to microchip manufacturer SkyWater for industry use.
Craig Keast, the associate head of Lincoln Laboratory's Advanced Technology Division, boasts that once the technology is transferred, it will be “the most advanced radiation-hardened-by-process technology available to the radiation circuit design community in the country.”
Teaming Up with the Department of Defense
The lifespan of this technology is a great example of how academia and industry often work together for the benefit of technological advancement.
By bringing this technology to industry, SkyWater hopes to help the Department of Defense develop solutions for national security and defense. SkyWater also sees the potential application of this technology in non-defense-related fields such as commercial space operations and medical imaging applications.
And, of course, this news should open many doors to developing electronics for space exploration.