Issue link: https://resources.pcb.cadence.com/i/1480204
APPLICATION NOTE 5 Figure 5: Simulation results for Singe-Event Upset Total Dose Effects Ionizing radiation produces both transient photocurrents and permanent damage in semiconductor devices. The degree of this permanent damage is proportional to the total accumulated dose and results in a general degradation of device performance. For example, when MOS structures are exposed to ionizing radiation, they experience a net change in the charge associated with the Si-SiO2 interface. This change in charge has the following two components: (i) the charge stored in the oxide, and (ii) the charge stored in the hole-electron interface traps. The net result is to shift the threshold voltages of both p-channel and n-channel devices toward enhancement mode operation. In addition to this threshold voltage shift, increases in the surface state density produce decreases in surface mobility and a variation in the turn on characteristic of the MOS transistors. The decreased mobility is the result of increased diffusion carrier scattering at the silicon surface. The variation in turn-on characteristics is caused by the filling and emptying of the surface traps as the channel is formed. Essentially all investigations of the effects of total dose radiation (permanent damage) on semiconductor devices have been made in terms of changes in the device electrical parameters. Analyses on MOS technologies are generally performed as follows: 1. Model parameters are extracted from test devices at several total dose levels over the range of interest. You must be very careful not to project much outside the range for which experimental data is available, since slight process variations can radically affect the model parameter versus total dose relationship. 2. An analysis of the model parameters is then performed to determine what parameters are most affected by the total dose and then, relationships are developed to describe the shift in the model parameters as a function of total dose. The following example is given to show the technique. It is assumed that changes in the threshold voltage and mobility are the dominant total dose effects.