Substrate Fed I2L Ionizing Radiation Upset Mechanism

The limiting dose rate upset mechanism of substrate fed I2L is caused by NPN secondary collector photocurrents generated as a result of primary photocurrent flows in the intrinsic and extrinsic base. The upset level is related to process parameters, device geometry and chip bias current level. Calculated vs measured upset levels on test vehicle are in good agreement over large bias and upset ranges. To improve the upset level the width of collectors must be minimized to reduce intrinsic base resistance and extrinsic base resistance can be reduced through introducing a P+ extrinsic base diffusion and placing the base contact at the center of the device. As the major photocurrents flow through the devices in the same manner as current supplied by the external injector bias supply, an electrical screen for dose rate hardness is possible.