Satellites orbiting the earth are subjected to very harsh environmental conditions. Consider this one aspect: They need ways to adjust their orbits. This is done with small rocket thrusters controlled by small motors or actuators. In turn, these are controlled by electronic circuitry. Both the circuitry and the motors must survive in the harsh environment of space. This means it is very hot when in sunlit areas and very cold in the dark. NASA has published some useful background info on motors for such applications. See this document for background info.
Over the past several decades, interest in high reliability (high-rel) motors has further increased. This is due to the need to optimize the amount of space used on orbiting platforms: more functionality must be integrated on the same module. This in turn has led to the implementation of more functionality done at the integrated circuit level. More companies are adding high-rel and radiation hardened (RH) devices to their portfolios, such as the devices that my company produces.
The testing process and the qualification procedure are essential to ensure the zero failure condition on such an important type of application. In particular, the aerospace applications require a high reliability and robustness to radiation, because of the open space environment is a hard ambient due to the ionizing radiation.
So what is the best way to test and to qualify the robustness of a product for aerospace applications?
There are many standards under which parts can be rad-hard certified. For example, in the US, the RHA certification is issued by the DLA (Defense Logistics Agency). In Europe, the referring agency for the certification of the robustness to the radiation of the electronic integrated devices is the ESA (European Space Agency).
The sources of the radiations present in the open space are mainly four:
- heavy ions
- γ (gamma) rays
These radiation sources can modify the electric configuration of the atoms of the material exposed to the radiation. Hence these four sources may alter the ICs and generate a failure in the circuitry contained on the modules.
The sources (1) and (2), besides being high energy particles, are also subatomic particles that make up the structure of the atom. These parts have a conventionally assigned negative and positive electrical charge, respectively. This is not the case of source (3) — it's not a particle, but instead an atom having a different number of protons than electrons. This atom can be charged both positively (number of protons > number of electrons) or negatively (number of protons < number of electrons) by subtracting or adding electrons to the electron cloud which surrounds the nucleus of the atom.
It’s very interesting to observe that the sources (1) through (3) are electric sources due to the structure of the atom whilst source (4) is generated from a mutation of an atomic structure. As an example of the generation of radiation — γ rays — there is an isotope of cobalt (cobalt-60) which doesn't have a stable atomic structure. There are nuclear transitions occurring in its nucleus the result of which produces γ rays. These are high energy photons (~100 keV). These are generated when cobalt-60 decays to nickel-60. A beta particle (free electron) is also produced.
Either the γ ray or the beta particle can cause problems. In the next part of this blog, we'll peer into the silicon structure. We'll see how those problems manifest inside the IC.