Rpp Method
This CREME96/HUP module calculates the single-event-effect (SEE) rate due to direct ionization using the Rectangular Parallelpiped (RPP) model, in which the bit sensitive volume is assumed to have this shape. In order to apply this method, you must specify the sensitive volume dimensions (x,y,z) in microns.
The "z" dimension is generally the smallest RPP dimension. Specifically, z is defined as the thickness of the device along the beam during normally-incident irradiation in accelerator SEE cross-section measurements. SEE rate calculations can be particularly sensitive to the value of "z", since "z" provides the distance scale in converting from effective LET to deposited charge. In some cases, RPP dimensions can be obtained from the chip designers and manufacturers. The RPP dimensions can also be determined from careful analysis of accelerator ground-test data, provided that the chip's SEE response has been measured over a sufficiently broad range of angles and effective LET values. See [PETERSEN1993], [CONNELL1995] - Ed Smith has recently developed a simplified version of HICUP, implemented in EXCEL, which simultaneously determines RPP dimensions and Weibull cross-section parameters from accelerator data. Contact edwardsmith@cox.net for further details. If no other information on RPP dimensions is available, the following rules of thumb may provide reasonable estimates:
"Typical charge collection depths are 0.5 microns for SOS and SOI, and 2 microns for CMOS/epi. As technology develops SOI may approach 0.1 microns. For current technology it runs from 0.2 to 0.5 microns. One micron has ordinarily been used for CMOS or bipolar devices; however this appears to be overly conservative. It may be more appropriate to use a value like four microns. For bulk, a general rule would be to use the distance between the top of the depletion region and where the lightly doped epi transitions to a heavily depleted substrate. If the sensitive volume is a well, use ½ of the distance between the bottom of the (sensitive volume) depletion region and the top of the well depletion region."
The CREME96 HUP routine, which calculates SEUs due to direct ionization, allows for inclusion of funnels. To do so, simply enter the funnel length (which must be specified in microns) in the appropriate input field. By default, the funnel length is set to zero, which suppresses funnels. For further information on the RPP method, see [PETERSEN1992] Document Actions |