Soft error generation

Low alpha particle emission materials are available enabling the encapsulation of 64 and 256K dynamic RAMs without the fear of soft error generation due to alpha particle emissions from the moulding compound. 

With the increase in packing density of dynamic RAMs, soft errors caused by alpha particles are becoming an increasingly important cause of device malfunctioning. (For further information on soft errors see Section 10.3.) Alpha particles are emitted from uranium and thorium isotopes residual in most packaging materials and thin films of polyimides deposited upon a chip surface have been successfully evaluated as alpha particle barriers. Polyimides can be made pure enough to contain no detectable amounts of uranium or thorium and a 40 xm thick film may reduce the soft error generation rate by up to 1000 times. A typical example of a commercially available polyimide alpha particle barrier is DuPont s Pyralin PIH 61454. 

As the denuded zone concept relies essentially on a two layer system other applications seem to be possible, which heavily depend on material with layered differences in lifetime (diffusion length). One of the areas is in the field of --particle sensitivity. 06 -particles emitted from the device package or from the environment create electron-hole pairs, which may lead to soft errors in memories. This can be suppressed if the carriers generated recombine at the oxygen precipitates rather than being able to diffuse to the memory cells. 

There is an increasing amount of li t sensitive opto-devioes that need UV-VIS protection. Alpha particle radiation is caused by a very low level of uranium and cosmic radiation present as background radiation in the device package and the atmosphere, respectively, and which could generate a temporary soft error in operating dynamic random access memory (DRAM), such as the 64 K, 256 K, 1 and 4 Megabits DRAM devices. This type of alpha particle radiation has become a major concern, especially in high density memory devices. 

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