**4. Transient operation**

The 3-D distributions of the carrier density simulated before and after the ion strike are shown in Fig. 3 for JL-DGFET, IM-DGFET and FDSOI. The 2-D profile of the electrostatic in a crosssection (plane x-z in Fig. 1) corresponding to the middle of the channel is plotted in Fig. 4.

**Figure 3.** D profiles of electron density in JL-DGFET, IM-DGFET and FDSOI before the ion strike, at t=10 ps (maximum charge generation) and at t=100 ps. The values of the electron density are in cm-3. For a better view of the film, gate material, spacers and isolation oxide are not shown. The ion strike LET is 0.1 MeV/(mg/cm2), VG=0 V, VD=0.75 V.

As shown in Fig. 3, the density profiles are strongly affected by the ion strike in the three devices. As expected, the charge density on the y axis is symmetrical with respect to the middle of the film in double-gate devices and it is asymmetrical in FDSOI. At maximum deposited charge (t=10 ps), the electron density sharply increases compared to the steady state; after t=10 ps, the electron density decreases with time due to charge transport and carrier recombination mechanisms.

The ion strike not only disturbs the charge density, but also the electrostatic potential (Fig. 4) and induces a transient current which can be visualized at the drain contact. Simulated drain current transients due to the ion strike are reported in Fig. 5 for LET=0.1 MeV/(mg/cm2 ). The "prompt" components of the current transients are almost identical for the three devices; on the contrary, the transient tails, representing the slow discharge component (due to floatingbody effects and carrier recombination mechanisms) are very different. FDSOI shows the longest transient tail indicating the presence of stronger floating-body effects than in doublegate devices. This is confirmed by the bipolar amplification which is plotted as a function of the ion-strike LET in Fig. 6. For LET=0.1 MeV/(mg/cm2 ), the bipolar gain is higher in FDSOI than in JL-DGFET and IM-DGFET. IM-DGFET shows the lowest bipolar gain owing to its double-gate configuration and its intrinsic channel. In spite of its double-gate structure, JL-DGFET has a higher bipolar gain than IM-DGFET essentially because the highly-doped silicon film enhances the floating-body effects; however, at low LET values the bipolar amplification of JL-DGFET is lower than that of single-gate FDSOI.

Drain current (A)

LET=0.1 MeV/(mg/cm2), VG=0 V and VD=0.75 V.

LET=0.1 MeV/(mg/cm2).

10-10

10-9

10-8

10-7

10-6

Before

t=100ps

ion strike t=10ps

Investigation of Sensitivity to Heavy-Ion Irradiation of Junctionless Double-Gate MOSFETs by 3-D Numerical Simulation

t=10ns t=100ns

**Figure 4.** D profiles of the electrostatic potential (in V) within the JL-DGFET structure at different times before and after the ion strike. For a better view of the silicon film, the gate material, spacers and isolation oxide are not shown.

t=1ns

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235

Time (s)

**Figure 5.** Drain current transients in JL-DGFET, IM-DGFET and FDSOI. All the transistors are biased in the off-state.

10-13 10-12 10-11 10-9 10-8 10-7 10-10 10-6

LET=0.1 MeV/(mg/cm2)

JL-DGFET IM-DGFET FDSOI

Investigation of Sensitivity to Heavy-Ion Irradiation of Junctionless Double-Gate MOSFETs by 3-D Numerical Simulation http://dx.doi.org/10.5772/57048 235

**4. Transient operation**

234 Computational and Numerical Simulations

JL-DGFET

IM-DGFET

FDSOI

mechanisms.

The 3-D distributions of the carrier density simulated before and after the ion strike are shown in Fig. 3 for JL-DGFET, IM-DGFET and FDSOI. The 2-D profile of the electrostatic in a crosssection (plane x-z in Fig. 1) corresponding to the middle of the channel is plotted in Fig. 4.

**Figure 3.** D profiles of electron density in JL-DGFET, IM-DGFET and FDSOI before the ion strike, at t=10 ps (maximum charge generation) and at t=100 ps. The values of the electron density are in cm-3. For a better view of the film, gate material, spacers and isolation oxide are not shown. The ion strike LET is 0.1 MeV/(mg/cm2), VG=0 V, VD=0.75 V.

As shown in Fig. 3, the density profiles are strongly affected by the ion strike in the three devices. As expected, the charge density on the y axis is symmetrical with respect to the middle of the film in double-gate devices and it is asymmetrical in FDSOI. At maximum deposited charge (t=10 ps), the electron density sharply increases compared to the steady state; after t=10 ps, the electron density decreases with time due to charge transport and carrier recombination

The ion strike not only disturbs the charge density, but also the electrostatic potential (Fig. 4) and induces a transient current which can be visualized at the drain contact. Simulated drain current transients due to the ion strike are reported in Fig. 5 for LET=0.1 MeV/(mg/cm2

"prompt" components of the current transients are almost identical for the three devices; on the contrary, the transient tails, representing the slow discharge component (due to floatingbody effects and carrier recombination mechanisms) are very different. FDSOI shows the longest transient tail indicating the presence of stronger floating-body effects than in doublegate devices. This is confirmed by the bipolar amplification which is plotted as a function of

than in JL-DGFET and IM-DGFET. IM-DGFET shows the lowest bipolar gain owing to its double-gate configuration and its intrinsic channel. In spite of its double-gate structure, JL-DGFET has a higher bipolar gain than IM-DGFET essentially because the highly-doped silicon film enhances the floating-body effects; however, at low LET values the bipolar amplification

the ion-strike LET in Fig. 6. For LET=0.1 MeV/(mg/cm2

of JL-DGFET is lower than that of single-gate FDSOI.

). The

), the bipolar gain is higher in FDSOI

Before ion strike t=10ps t=100ps

**Figure 4.** D profiles of the electrostatic potential (in V) within the JL-DGFET structure at different times before and after the ion strike. For a better view of the silicon film, the gate material, spacers and isolation oxide are not shown. LET=0.1 MeV/(mg/cm2), VG=0 V and VD=0.75 V.

**Figure 5.** Drain current transients in JL-DGFET, IM-DGFET and FDSOI. All the transistors are biased in the off-state. LET=0.1 MeV/(mg/cm2).

Drain current (A)

track. LET=1 MeV/(mg/cm2), VG=0 V and VD=0.75 V.

0

of the Gaussian time dependence of the ion track.

5

10

Bipolar amplification

15

of FDSOI.

10-10

10-9

10-8

10-7

10-6

10-5

10-4

JL-DGFET

Time (s)

**Figure 7.** Drain current transients in JL-DGFET for two characteristic times of the Gaussian time dependence of the ion

Investigation of Sensitivity to Heavy-Ion Irradiation of Junctionless Double-Gate MOSFETs by 3-D Numerical Simulation

Unlike the transient current, bipolar amplification is only slightly influenced by the value of s\_hi. Figure 8 shows that the gain bipolar in JL-DGFET is always higher than that of IM-DGFET (for all LET values). Compared to FDSOI, JL-DGFET is more interesting for very low LET (lower than 0.5 MeV/(mg/cm2)) where FDSOI has a stronger bipolar gain. However, for intermediate and high LET, the bipolar gain of JL-DGFET becomes slightly higher than that

0.1 1 10 100

JL-DGFET, s\_hi=2 ps JL-DGFET, s\_hi=0.5 ps IM-DGFET, s\_hi=2 ps IM-DGFET, s\_hi=0.5 ps FDSOI, s\_hi=2 ps FDSOI, s\_hi=0.5 ps

LET (MeV/(mg/cm2))

**Figure 8.** Bipolar amplification versus the ion-strike LET in JL-DGFET, IM-DGFET and FDSOI for two characteristic times

10-13 10-12 10-11 10-9 10-8 10-7 10-10 10-6

s\_hi=2 ps s\_hi=0.5 ps

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237

**Figure 6.** Bipolar gain versus the ion-strike LET in JL-DGFET, IM-DGFET and FDSOI. The ion strikes vertically in the mid‐ dle of the channel between the source and drain contacts.

We recall here that in simulations presented in Fig. 6 the ion strikes the devices in the middle of the channel. We will see in section 5 that, for particular LET values, the bipolar amplification of JL-DGFET may be lower than that of IM-DGFET and FDSOI if the ion strikes the channel in other particular locations, along the x axis, between the source and drain contacts.
