**3. Basic mechanisms of single-event effects on microelectronic devices**

In this section, we briefly summarize the physical mechanisms related to the production of SEE in microelectronic devices by a charged particle. This general scheme can be applied to all particles able to directly deposit an electrical charge along their track (heavy ions, alphaparticles, low energy protons and low energy muons). As we already mentioned for neutrons, the ionization is indirect since neutron is a neutral particle but it can induce charged particles (recoil atoms or secondary particle) by nuclear reaction with the atoms of the target material. The following scenario can thus be applied separately to all secondary charged particles produced by the neutron.

Considering a single charged particle, the passage of this particle through a portion of a microelectronic circuit consists in three main successive steps: (1) the charge deposition by the energetic particle striking the sensitive region, (2) the transport of the released charge into the device and (3) the charge collection in the sensitive region of the device. Figure 3 schematically shows these successive steps in the case of the passage of the energetic charged particle through a reverse-biased n+/p junction. In the following we succinctly describe these different mechanisms, for a detailed presentation we invite the reader to consult references [5][16-19].

**Figure 3.** Charge generation, transport and collections phases in a reverse-biased junction and the resultant current pulse caused by the passage of an energetic charged particle. After Baumann [5]. © 2005 Institute of Electrical and Electronics Engineers Inc., reproduced with permission.

*Charge deposition (or generation):* When the particle strikes the device, an electrical charge along the particle track can be deposited by direct ionization of the target material. This direct ionization is mainly produced by inelastic interactions and transmits a large amount of energy to the electrons of the struck atoms. These electrons produce a cascade of secondary electrons which thermalize and create electron-hole pairs along the particle path [Figure 3(a)]. In a semiconductor or insulator, a large amount of the deposited energy is thus converted into electron-hole pairs, the remaining energy being converted into heat and a very small quantity in atoms displacement. It was experimentally shown that the energy necessary for the creation of an electron-hole pair depends on the material bandgap. In a Silicon substrate, one electron-hole pair is produced for every 3.6 eV of energy lost by the particle.

314 Numerical Simulation – From Theory to Industry

0.68 MeV/(mg/cm²), as summarized in Table 1.

charged particles produced by the neutron.

consult references [5][16-19].

in silicon vary from 19 to 46 µm and their initial Linear Energy Transfer (LET) from 0.47 to

In this section, we briefly summarize the physical mechanisms related to the production of SEE in microelectronic devices by a charged particle. This general scheme can be applied to all particles able to directly deposit an electrical charge along their track (heavy ions, alphaparticles, low energy protons and low energy muons). As we already mentioned for neutrons, the ionization is indirect since neutron is a neutral particle but it can induce charged particles (recoil atoms or secondary particle) by nuclear reaction with the atoms of the target material. The following scenario can thus be applied separately to all secondary

Considering a single charged particle, the passage of this particle through a portion of a microelectronic circuit consists in three main successive steps: (1) the charge deposition by the energetic particle striking the sensitive region, (2) the transport of the released charge into the device and (3) the charge collection in the sensitive region of the device. Figure 3 schematically shows these successive steps in the case of the passage of the energetic charged particle through a reverse-biased n+/p junction. In the following we succinctly describe these different mechanisms, for a detailed presentation we invite the reader to

**Figure 3.** Charge generation, transport and collections phases in a reverse-biased junction and the resultant current pulse caused by the passage of an energetic charged particle. After Baumann [5]. ©

*Charge deposition (or generation):* When the particle strikes the device, an electrical charge along the particle track can be deposited by direct ionization of the target material. This direct ionization is mainly produced by inelastic interactions and transmits a large amount of energy to the electrons of the struck atoms. These electrons produce a cascade of secondary electrons which thermalize and create electron-hole pairs along the particle path [Figure 3(a)]. In a semiconductor or insulator, a large amount of the deposited energy is thus

2005 Institute of Electrical and Electronics Engineers Inc., reproduced with permission.

**3. Basic mechanisms of single-event effects on microelectronic devices** 

As already mentioned, neutrons of the terrestrial environment do not interact directly with target material since they do not ionize the matter on their passage. However, the products resulting from a nuclear reaction can deposit energy along their traces, in the same manner as that of direct ionization. Since the creation of the column of electron-hole pairs of these secondary particles is similar to that of ions, the same models and concepts can be used.

*Charge transport*: When a charge column is created in the semiconductor by an ionizing particle, the released carriers are quickly transported and collected by elementary structures (e.g. p-n junctions). The transport of charge relies on two main mechanisms [Figures 3(b) and 3(c)]: the charge drift in regions with an electric field and the charge diffusion in neutral zones. The deposited charges can also recombine with other mobile carriers existing in the lattice.

*Charge collection*: The charges transported in the device induce a parasitic current transient [Figure 3(d)], which could induce disturbances in the device and associated circuits. The devices most sensitive to ionizing particle strikes are generally devices containing reverselybiased p-n junctions, because the strong electric field existing in the depletion region of the p-n junction allows a very efficient collection of the deposited charge. The effects of ionizing radiation are different according to the intensity of the current transient, as well as the number of impacted circuit nodes. If the current is sufficiently important, it can induce a permanent damage on gate insulators (gate rupture, SEGR) or the latch-up (SEL) of the device. In usual low power circuits, the transient current may generally induce only an eventual change of the logical state (cell upset).
