. OXIDE SILICON e- ELECTRON TUNNELING THERMAL EMISSION Figure 49. Example of recovery mechanism of trapped charge by tunnel effect and thermal emission. According to [Oldh-86], [McWh-90]. III-62 Tunneling can be envisioned as a front that advances in time at a speed of 0.2 to 0.4 nm per decade of time. The distance that the front moves into the oxide at a given time t is given by [McWh-90]: (92) m=In( t) /2 where is the attempt to escape frequency is a tunneling parameter related to electron barrier height If the trap is farther than ~ 4 nm from the interface, it will be essentially inaccessible through tunneling during measurable times. As the spatial distribution of traps in the oxide is assumed to depend on the oxide fabrication process, the P.I.E. component due to tunneling can vastly differ from one process to another. One can therefore imagine a front of thermal neutralization similar to the front of tunneling neutralization. This thermal emission front can be written as: ( t  = k k / q In (AT2t) where is the difference in energy between trap and oxide valence band A is a constant which depends on the capture cross section These effects can be combined as indicated in fig. 49, according to [McWh-90]). As a consequence of these slow evolving post-irradiation processes, the simple data of the couple (value of a parameter, value of the dose at which it is obtained) is sometimes a poor indication of the actual response of a transistor. Other important parameters involved in the characterization and the response of a transistor are: the duration of the irradiation, the electric bias of the device during irradiation and after (or more generally the history of dose rates and biases), the record of the ambient temperature, etc. Thus, one must specify what sort of procedure has been used to perform the irradiation and obtain the data. The choice of the (presumably) standard procedure itself is determined by the context for which the data will be used (space, military, High Energy Physics, etc.). Standards have been 