Circuit design methodologies

Extensive alpha particle sensitivity studies were performed on a second-generation 64K DRAM. To better understand the observed data a model was developed relating the electrical signal margins of the device to the alpha soft-error-rate (S.E.R.). In order to achieve a satisfactory fit to the data the model had to include several subtle matrix interactions previously considered to be "second-order-effects". Simple calculations of the cell\´s stored-charge were inadequate in explaining our observations. Several of these effects were found to have dramatic impact on the resulting S.E.R., often producing changes of an order-of-magnitude or more. These effects will be reviewed in this paper. An appreciation of the significance of these matrix interactions is important if a memory chip designer is to achieve the maximum potential alpha immunity in his new circuit. By applying the modeling techniques described in this paper to a new design, improvements can be made in the electrical signal margins which result in substantial improvement in the alpha S.E.R.