Effects of Shadows on Photocurrent Compensated Integrated Circuits

Simple calculations show that high-z components such as wires, capacitors, and solder bonds can easily cast shadows with edges only 25 ¿m wide when illuminated with a low energy (E < 60 keV) x-ray beam. If one of these shadows falls between a photocurrent compensating diode-transistor pair, the mismatch in dose can drastically reduce the transient hardness of the integrated circuit. Results of pulsed x-ray tests on the Texas Instruments RSN 54L 71 R-S flip-flop and RSN 54L 00 quad two input nand gate showed that the upset threshold of a given state of the flip-flop was lowered by as much as a factor of 29 and the nand gate by a factor of 5.7.