It is ironic that the same magnetic field that freed 12th-century explorers to navigate the world's oceans with the aid of a compass is making it more challenging for our technologically advanced civilization to explore and exploit the use of near-earth space. The earth is under constant bombardment from ionizing particles of solar, interstellar and galactic origin, and many of these particles become trapped in the earth's magnetic field. These trapped particles-mostly electrons and protons-form the Van Allen Belts, regions of potentially intense ionizing radiation.
Ionizing radiation degrades nearly all of the integrated circuits (ICs) used in commercial electronics. A desktop PC would survive only about 18 days if it were placed in an equatorial orbit 2,000 km above the earth. In general, the more complex the electronic device, the more sensitive it is to ionizing radiation.
The total-dose degradation of electronics can be viewed in relatively simple terms by considering the charge generated and ultimately trapped within the isolation oxides (SiO2) of ICs as a result of radiation exposure. Ionizing radiation produces electron-hole pairs with the electrons rapidly swept from the oxide. This leaves behind a net positive charge trapped in the insulator that is responsible for nearly all the total-dose degradation seen in CMOS ICs.
In addition to the total-dose degradation discussed above, ICs can suffer single-event effects such as single-event upset, single-event latch-up, and single-event burnout. Static random-access memory (SRAM)-based field-programmable gate arrays (FPGAs) can also suffer from single-event reprogramming. A storage cell that contains a binary one, for example, can be flipped to a binary zero; similarly, a storage cell that contains a binary zero can be switched to a binary one.
The deposited charge can lead to a significant current pulse capable of changing the state of a typical six-transistor latch cell.
To meet the electronics needs of satellite-system manufacturers, a small subgroup of IC companies has developed methods of hardening their electronics against the effects of both total-dose degradation due to long-term exposure of electrons and protons and single-event effects due to heavy ion strikes.
Among the alternatives finding their way into commercial space applications are hardening components built on commercial process lines and shielding screened commercial components. Each approach has its advantages. Shielding screened commercial components allows for the largest selection of components for space systems. The major drawback to this approach is that the limited intrinsic hardness of the components restricts the orbits where they can fly.
A new method for dramatically increasing the intrinsic radiation hardness of electronics built on a commercial line introduced last year by UTMC Microelectronic Systems uses a self-contained process module-a series of contiguous additional processing steps-for hardening the component. The process improvements are combined with UTMC's single-event-upset-hard and single-event latch-up-immune design libraries to produce ICs ideally suited for surviving the natural space environment.
The ability to find cost-effective solutions may be the key to successfully exploiting near-earth space, just as the invention of the compass freed early explorers to roam the earth.