Single Event Upset

A Single Event Upset ( SEU ) is a soft error ( German "soft" error), the in semiconductor devices during the passage of high-energy ionizing particles (eg, heavy ions, protons) can be caused. It manifests itself, for example as BitFlip ( change of state of a bit ) in memory blocks or registers, which can lead to a malfunction of the affected component. The classification as a soft error occurs because an SEU causes no permanent damage to the affected part. An example of a hard error is the Single Event Latch -up (SEL).

Occurrence

Since the magnetic field and the Earth's atmosphere have a shielding effect for high-energy particles, SEUs occur at sea level only relatively rare, the occurrence at smaller and smaller structures is common as with smaller feature sizes and higher clock frequency range lower energies to a SEU to provoke. They have a great importance in the field of aerospace. Aircraft and in particular satellites and space vehicles are subjected to an elevated ( particle ) radiation, which is why the corresponding electronics are concerned here to a greater extent.

Operation

If crossing a matter ionizing particle gives energy to the surrounding material, which is known as Linear Energy Transfer (LET). In the semiconductor leads to a change in the charge distribution and thus - in simplified terms - cause a "switching" of a pn junction. The energy from the one SEU may occur in a semiconductor device, is referred to as, the index for th threshold ( German: threshold, threshold ) is. As a unit (relative to Si of the MOS semiconductor devices ) is used usually MeV -cm ² / mg. Different semiconductor devices differ greatly in susceptibility to SEUs. Component having a of about 100 MeV -cm ² / mg, are often referred to as SEU immune, but this only means that a part has been tested up to this value, while no SEU has occurred.

Countermeasures

Since a SEU may cause a component failure of a complete system, various measures are taken to prevent the occurrence of SEUs, or minimize the negative effects. In English we speak of SEU Mitigation. Besides the use of semiconductor devices, which have, due to the manufacturing technology used in an increased tolerance to radiation, inter alia, the following methods are used:

• Shielding: A ionizing radiation shielding shell is attached to the component to be protected. This method is only suited to trap particles of relatively low energy. When high-energy particles is namely when it crosses the shield so-called secondary radiation. However, the main disadvantage is the additional weight of shielding.
• Error correction: Stored data will be backed up by appropriate proceedings against single or multi-bit errors ( eg RS encoding). In case of an SEU causes a change of the memory contents, can thus restore the correct data.
• Triple Modular Redundancy ( TMR short ): In this method a abzusicherndes module is replaced by three identical and a subsequent decision stage (English Voter ). The voter is always the output value on which the majority of the three modules provides. A module may be, for example, a flip-flop of an FPGA, however, a complete processor.