Soft Error Rate
Soft error rate (SER) is the rate at which a device or system encounters or is predicted to encounter soft errors. It is typically expressed as either number of failures-in-time (FIT), or mean time between failures (MTBF). The unit adopted for quantifying failures in time is called FIT, equivalent to 1 error per billion hours of device operation. MTBF is usually given in years of device operation. To put it in perspective, 1 year MTBF is equal to approximately 114,077 FIT (approximately ).
While many electronic systems have an MTBF that exceeds the expected lifetime of the circuit, the SER may still be unacceptable to the manufacturer or customer. For instance, many failures per million circuits due to soft errors can be expected in the field if the system does not have adequate soft error protection. The failure of even a few products in the field, particularly if catastrophic, can tarnish the reputation of the product and company that designed it. Also, in safety- or cost-critical applications where the cost of system failure far outweighs the cost of the system itself, a 1% chance of soft error failure per lifetime may be too high to be acceptable to the customer. Therefore, it is advantageous to design for low SER when manufacturing a system in high-volume or requiring extremely high reliability.
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