importance regarding the reliability of power semiconductors, its influence will be
examined inmore detailedbelow.
is a high-energy particle radiation from out of space. This so-called
radiation (in the real sense it is a particle shower instead of radiation) consistsmainly of
protons, electrons and ionized atoms. Causes of the cosmic radiation are, for example,
the solar wind, supernova explosions, pulsars, etc. It is estimated that approximately
1000 particles per second and square meter hit the outer earth's atmosphere. The
primary radiation releases a secondary by collisionwith particles in the atmosphere. The
ratio of the particles of primary and secondary may be up 1 to one million. However,
only a small part thereof will end upon the surfaceof the earth.
Cosmic particle radiation
The influence of cosmic radiation on power semiconductorswas discovered in the early
90's of last century. There were more inexplicable failures during the blocking phase of
components especially in high-voltage applications, which could not be explained by
known failure mechanisms. Affected were, and still are, all power semiconductors
ranging fromMOSFETs, diodes and IGBTs to thyristors.
Based on extensive tests, measurements and simulations it was found that the cause of
these failures had to be the particle radiation from space. It turned out that the failure
probability of a power semiconductor caused by cosmic radiation has the following
The higher above sea level the device is in operation, the higher the probability
The higher the junction temperature of the component in operation, the lower
the probability of a fault (as long as the temperature does not reach values
above the permittedmaximumoperating temperature).
The higher the voltage rating of the component and the smaller the actual
blocking voltage is in operation, the lower theprobability of failure.
Cosmic radiation was discovered in 1912 by the Austrian physicist Victor Franz Hess (1883 - 1964). Originally
cosmic radiation was called high-altitude radiation. However, after its true origin was known, that name lost its
meaning. Misleadingly, cosmic radiation is often still calledhigh-altitude radiation.