**5. Impact of heavy-ion track parameters on the transistor transient response**

In this section we study in detail the impact of several ion track parameters as well as the influence of the ion-strike location along the channel on the bipolar amplification of the three devices considered in this work. We change one parameter at a time in order to decorrelate the effects induced on the transient current and bipolar gain.

### **5.1. Ion track characteristic time**

We begin with the characteristic time of the Gaussian time dependence of the ion track, s\_hi. This parameter has a large influence on the transient current. For all previous simulations we used s\_hi=2 ps since, as stated before, a very good agreement was found in a previous work between simulations and experimental data. To illustrate the impact of s\_hi on the transient current and bipolar gain, we performed additional simulations with s\_hi=0.5 ps. In these simulations the ion strikes in the middle of the channel and all other simulation parameters are unchanged (the same as those defined in section 2.2). Figure 7 shows the current transients obtained with s\_hi=2 ps and s\_hi=0.5 ps in JL-DGFET. As expected, the "prompt" component of the drain current transient is much narrower for s\_hi=0.5 ps that for s\_hi=2 ps. However, the transient tail is the same in both cases, which is normal, since the transient tail is essentially governed by the floating-body effects and the recombination mechanisms taking place in the device and does not depend on the time parameters of the ion track.

1

dle of the channel between the source and drain contacts.

the effects induced on the transient current and bipolar gain.

device and does not depend on the time parameters of the ion track.

**5.1. Ion track characteristic time**

0.1 1 10 100

JL-DGFET IM-DGFET FDSOI

LET (MeV/(mg/cm2))

**Figure 6.** Bipolar gain versus the ion-strike LET in JL-DGFET, IM-DGFET and FDSOI. The ion strikes vertically in the mid‐

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

**5. Impact of heavy-ion track parameters on the transistor transient response**

In this section we study in detail the impact of several ion track parameters as well as the influence of the ion-strike location along the channel on the bipolar amplification of the three devices considered in this work. We change one parameter at a time in order to decorrelate

We begin with the characteristic time of the Gaussian time dependence of the ion track, s\_hi. This parameter has a large influence on the transient current. For all previous simulations we used s\_hi=2 ps since, as stated before, a very good agreement was found in a previous work between simulations and experimental data. To illustrate the impact of s\_hi on the transient current and bipolar gain, we performed additional simulations with s\_hi=0.5 ps. In these simulations the ion strikes in the middle of the channel and all other simulation parameters are unchanged (the same as those defined in section 2.2). Figure 7 shows the current transients obtained with s\_hi=2 ps and s\_hi=0.5 ps in JL-DGFET. As expected, the "prompt" component of the drain current transient is much narrower for s\_hi=0.5 ps that for s\_hi=2 ps. However, the transient tail is the same in both cases, which is normal, since the transient tail is essentially governed by the floating-body effects and the recombination mechanisms taking place in the

other particular locations, along the x axis, between the source and drain contacts.

10

Bipolar amplification

236 Computational and Numerical Simulations

**Figure 7.** Drain current transients in JL-DGFET for two characteristic times of the Gaussian time dependence of the ion track. LET=1 MeV/(mg/cm2), VG=0 V and VD=0.75 V.

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 of FDSOI.

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

### **5.2. Ion track radius**

We have also analyzed the impact of the ion track radius on the JL-DGET transient response. For the previous analysis a very narrow (20 nm) was considered in order to facilitate the comparison with experimental and simulation results in [35] and [44]. In the following, we show simulation results performed with a larger characteristic radius r=70 nm and we compare them with results obtained at r=20 nm. The purpose of this study is to determine if the value of the ion track radius changes the conclusions regarding the increased single-event suscept‐ ibly of JL-DGFET compared to IM-DGFET. Our simulation results show that for both JL-DGFET and IM-DGFET, the current peak is higher when considering a narrow radius, mainly because more charge is deposited in the channel region of the device than in the source/drain region. This is confirmed by the collected charge which decreases when the ion track radius increases. The bipolar gain calculated for all devices considering r=70 nm is plotted in Fig. 9; results obtained for r=20 nm are also reported. Figure 9 shows that when the track radius increases the bipolar gain is only slightly modified for IM-DGFET. For JL-DGFET the bipolar gain at low LET is lower for r=70 nm than for r=20 nm, probably due to the lower deposited charge. However, at high LET the bipolar gain for r=70 nm is very similar to that obtained for r=20 nm. In spite of these variations of the collected charge and bipolar gain when the ion track radius increases, the previous trends and conclusions concerning the JL-DGFET transient response to heavy ion radiation are not changed. In the case of a larger radius the bipolar gain changes for all devices, but the bipolar amplification of JL-DGFET is still higher than that of IM-DGFET (for all LET values). These results are consistent with simulation data obtained in [39]. Compared to FDSOI, the bipolar amplification of JL-DGFET is weaker for LET values less than 1 MeV/(mg/cm2 ), and becomes slightly higher for LET>1 MeV/(mg/cm2 ).

**5.3. Ion strike location between source and drain contacts**

Ion strike location

for the ion strike considered in this work are also indicated.

(mg/cm2

Until now we have considered that the ion hits the device in the middle of the channel. In this part we are changing the location of the ion strike along the channel (x-axis) in order to study the impact of this position on the radiation sensitivity of JL-DGFET compared to that of IM-DGFET and FDSOI. In the following, the track radius is 20 nm, s\_hi=2 ps and all other parameters are those defined in section 2.2. Several locations of ion strike are considered between the source contact (x=0) and the drain contact (x=60 nm), as shown in Fig. 10.

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

The 3-D profile of the heavy-ion charge density in the entire silicon film (the same for all three devices) is shown in this figure for an ion strike in x=10 nm. For this particular location, as shown in Fig. 10, the ion track is not entirely contained on the silicon film. This is also the case for other locations, which requires a specific calculation of the deposited charge. For each location, the current transient is simulated and the collected charge is extracted from this

0 10 20 25 30 35 40 45 50 55 60

**Figure 10.** D profiles of the heavy-ion charge density in the silicon film of JL-DGFET for an ion strike at x=10 nm and LET=2 MeV/(mg/cm2). The values of the heavy-ion charge density are in cm-3. For a better view of the film, gate mate‐ rial, spacers and isolation oxide are not shown. The position of the ion strike is indicated by the arrow. Other positions

For simulations considering the ion strike in the middle of the channel (x=30 nm), we saw that JL-DGFET always shows a higher bipolar gain than IM-DGFET (for all LET values). In addition, the bipolar gain of JL-DGFET is also higher than that of FDSOI for intermediate and high LET. The purpose of this section is to verify whether these conclusions also apply to other locations of the ion strike along the channel. The collected charge as a function of the x location is shown in Fig. 11 for both very low and very high LET values. The deposited charge, calculated for each x location and each LET, is also reported in this figure to facilitate the comparison. The deposited charge is maximum in the middle of the channel and decreases towards the sides of the silicon film, because a smaller part of ion track is contained in the active region when the ion strike position moves towards the source or drain contacts. At very low LET=0.2 MeV/

) and for all x locations, the lowest collected charge is obtained for IM-DGFET and the

x (nm)

http://dx.doi.org/10.5772/57048

239

transient. Finally, the bipolar gain is calculated at a given LET for each x value.

**Figure 9.** Bipolar amplification versus the ion-strike LET in JL-DGFET, IM-DGFET and FDSOI for two radii of the ion track. VG=0 V and VD=0.75 V.

### **5.3. Ion strike location between source and drain contacts**

**5.2. Ion track radius**

238 Computational and Numerical Simulations

than 1 MeV/(mg/cm2

track. VG=0 V and VD=0.75 V.

0

5

10

Bipolar amplification

15

We have also analyzed the impact of the ion track radius on the JL-DGET transient response. For the previous analysis a very narrow (20 nm) was considered in order to facilitate the comparison with experimental and simulation results in [35] and [44]. In the following, we show simulation results performed with a larger characteristic radius r=70 nm and we compare them with results obtained at r=20 nm. The purpose of this study is to determine if the value of the ion track radius changes the conclusions regarding the increased single-event suscept‐ ibly of JL-DGFET compared to IM-DGFET. Our simulation results show that for both JL-DGFET and IM-DGFET, the current peak is higher when considering a narrow radius, mainly because more charge is deposited in the channel region of the device than in the source/drain region. This is confirmed by the collected charge which decreases when the ion track radius increases. The bipolar gain calculated for all devices considering r=70 nm is plotted in Fig. 9; results obtained for r=20 nm are also reported. Figure 9 shows that when the track radius increases the bipolar gain is only slightly modified for IM-DGFET. For JL-DGFET the bipolar gain at low LET is lower for r=70 nm than for r=20 nm, probably due to the lower deposited charge. However, at high LET the bipolar gain for r=70 nm is very similar to that obtained for r=20 nm. In spite of these variations of the collected charge and bipolar gain when the ion track radius increases, the previous trends and conclusions concerning the JL-DGFET transient response to heavy ion radiation are not changed. In the case of a larger radius the bipolar gain changes for all devices, but the bipolar amplification of JL-DGFET is still higher than that of IM-DGFET (for all LET values). These results are consistent with simulation data obtained in [39]. Compared to FDSOI, the bipolar amplification of JL-DGFET is weaker for LET values less

), and becomes slightly higher for LET>1 MeV/(mg/cm2

JL-DGFET, r=20 nm JL-DGFET, r=70 nm IM-DGFET, r=20 nm IM-DGFET, r=70 nm FDSOI, r=20 nm FDSOI, r=70 nm

0.1 1 10 100

LET (MeV/(mg/cm2))

**Figure 9.** Bipolar amplification versus the ion-strike LET in JL-DGFET, IM-DGFET and FDSOI for two radii of the ion

).

Until now we have considered that the ion hits the device in the middle of the channel. In this part we are changing the location of the ion strike along the channel (x-axis) in order to study the impact of this position on the radiation sensitivity of JL-DGFET compared to that of IM-DGFET and FDSOI. In the following, the track radius is 20 nm, s\_hi=2 ps and all other parameters are those defined in section 2.2. Several locations of ion strike are considered between the source contact (x=0) and the drain contact (x=60 nm), as shown in Fig. 10.

The 3-D profile of the heavy-ion charge density in the entire silicon film (the same for all three devices) is shown in this figure for an ion strike in x=10 nm. For this particular location, as shown in Fig. 10, the ion track is not entirely contained on the silicon film. This is also the case for other locations, which requires a specific calculation of the deposited charge. For each location, the current transient is simulated and the collected charge is extracted from this transient. Finally, the bipolar gain is calculated at a given LET for each x value.

**Figure 10.** D profiles of the heavy-ion charge density in the silicon film of JL-DGFET for an ion strike at x=10 nm and LET=2 MeV/(mg/cm2). The values of the heavy-ion charge density are in cm-3. For a better view of the film, gate mate‐ rial, spacers and isolation oxide are not shown. The position of the ion strike is indicated by the arrow. Other positions for the ion strike considered in this work are also indicated.

For simulations considering the ion strike in the middle of the channel (x=30 nm), we saw that JL-DGFET always shows a higher bipolar gain than IM-DGFET (for all LET values). In addition, the bipolar gain of JL-DGFET is also higher than that of FDSOI for intermediate and high LET. The purpose of this section is to verify whether these conclusions also apply to other locations of the ion strike along the channel. The collected charge as a function of the x location is shown in Fig. 11 for both very low and very high LET values. The deposited charge, calculated for each x location and each LET, is also reported in this figure to facilitate the comparison. The deposited charge is maximum in the middle of the channel and decreases towards the sides of the silicon film, because a smaller part of ion track is contained in the active region when the ion strike position moves towards the source or drain contacts. At very low LET=0.2 MeV/ (mg/cm2 ) and for all x locations, the lowest collected charge is obtained for IM-DGFET and the

lowest.

0

5

10

Bipolar amplification

MeV/(mg/cm2) and (b) LET=30 MeV/(mg/cm2).

0 10 20 30 40 50 60

LET=0.2 MeV/(mg/cm2)

JL-DGFET IM-DGFET FDSOI

x (nm)

highest collected charge for FDSOI (Fig. 11(a)). This result shows that the trend obtained for x=30 nm is confirmed for all other locations. For all devices, the collected charge has a bellshaped profile with a maximum around the middle of the channel (where the deposited charge is the highest) and two minima at the source and drain contacts (where the deposited charge is the lowest). The collected charge is always higher than the deposited charge for all x locations, which indicates a strong bipolar amplification. The behavior is quite different for LET=80 MeV/(mg/cm2 ), as shown in Fig. 11(b). For ion strikes located between the source contact and the middle of the channel, the collected charge is higher for JL-DGFET than that of FDSOI and IM-DGFET. It is also interesting to note that for x locations situated between the source contact (x=0) and the middle of the channel, the collected charge is lower than the deposited charge. This indicates that the bipolar amplification is very low and there is a strong recombination of the deposited charge in the device. Beyond x=30 nm, the collected charge for JL-DGFET decreases and becomes lower than that of IM-DGFET and FDSOI. These results show that for a high LET, the trends obtained for ion strikes in the middle of the channel are no longer valid for ion strikes located in the vicinity of the drain region, beyond x=30 nm. In addition, these results show, for the first time, that JL-DGFET is able to collect a smaller amount of charge than IM-DGFET for these specific values of x location and LET. 11(a)). This result shows that the trend obtained for x=30 nm is confirmed for all other locations. For all devices, the collected charge has a bell-shaped profile with a maximum around the middle of the channel (where the deposited charge is the highest) and two minima at the source and drain contacts (where the deposited charge is the lowest). The collected charge is always higher than the deposited charge for all x locations, which indicates a strong bipolar amplification. The behavior is quite different for LET=80 MeV/(mg/cm2), as shown in Fig. 11(b). For ion strikes located between the source contact and the middle of the channel, the collected charge is higher for JL-DGFET than that of FDSOI and IM-DGFET. It is also interesting to note that for x locations situated between the source contact (x=0) and the middle of the channel, the collected charge is lower than the deposited charge. This indicates that the bipolar amplification is very low and there is a strong recombination of the deposited charge in the device. Beyond x=30 nm, the collected charge for JL-DGFET decreases and becomes lower than that of IM-DGFET and FDSOI. These results show that for a high LET, the trends obtained for ion strikes in the middle of the channel are no longer valid for ion strikes located in the vicinity of the drain region, beyond x=30 nm. In addition, these results show, for the first time, that JL-DGFET is able to collect a smaller amount of charge than IM-DGFET for these specific values of x location and LET.

beyond 40 nm. The trend changes for LET values above 20 MeV/(mg/cm2

comparison. (a) LET=0.2 MeV/(mg/cm2) and (b) LET=80 MeV/(mg/cm2).

LET=0.2 MeV/(mg/cm2)

0 10 20 30 40 50 60

Deposited charge (Qdep)

x (nm)

LET=0.2 MeV/(mg/cm2)

MeV/(mg/cm2

0

0.05

Collected charge (fC)

0.1

0.15

JL-DGFET IM-DGFET FDSOI

lowest.

0

LET=80 MeV/(mg/cm2).

5

10

Bipolar amplification

DGFET becomes the lowest.

JL-DGFET IM-DGFET FDSOI

MeV/(mg/cm2) and (b) LET=30 MeV/(mg/cm2).

0

0.5

1

Bipolar amplification

1.5

2

(a) LET=0.2 MeV/(mg/cm2) and (b) LET=30 MeV/(mg/cm2).

0 10 20 30 40 50 60

x (nm)

visualized in Fig. 12(b) which shows the bipolar amplification for LET=30 MeV/(mg/cm2

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

Finally, Fig. 13 shows the bipolar amplification as a function of x location for LET=80

in terms of radiation resistance, for x location beyond about 30 nm, the bipolar gain of JL-

). Although for x less than 30 nm IM-DGFET remains the most interesting device

0

(a) (b)

2

4

Collected charge (fC)

6

8

0

(a) (b)

0 10 20 30 40 50 60

LET=80 MeV/(mg/cm2)

x (nm)

**Figure 13.** Bipolar amplification as a function of the x position of the ion strike in JL-DGFET, IM-DGFET and FDSOI for

**Figure 12.** Bipolar amplification as a function of the x position of the ion strike in JL-DGFET, IM-DGFET and FDSOI for

JL-DGFET IM-DGFET FDSOI

0.5

1

1.5

Bipolar amplification

2

2.5

11(a)). This result shows that the trend obtained for x=30 nm is confirmed for all other locations. For all devices, the collected charge has a bell-shaped profile with a maximum around the middle of the channel (where the deposited charge is the highest) and two minima at the source and drain contacts (where the deposited charge is the lowest). The collected charge is always higher than the deposited charge for all x locations, which indicates a strong bipolar amplification. The behavior is quite different for LET=80 MeV/(mg/cm2), as shown in Fig. 11(b). For ion strikes located between the source contact and the middle of the channel, the collected charge is higher for JL-DGFET than that of FDSOI and IM-DGFET. It is also interesting to note that for x locations situated between the source contact (x=0) and the middle of the channel, the collected charge is lower than the deposited charge. This indicates that the bipolar amplification is very low and there is a strong recombination of the deposited charge in the device. Beyond x=30 nm, the collected charge for JL-DGFET decreases and becomes lower than that of IM-DGFET and FDSOI. These results show that for a high LET, the trends obtained for ion strikes in the middle of the channel are no longer valid for ion strikes located in the vicinity of the drain region, beyond x=30 nm. In addition, these results show, for the first time, that JL-DGFET is able to collect a smaller amount of charge than IM-DGFET for these specific values of x location and LET.

Figure 11.Collected charge as function of the x location in IM-DGFET, JL-DGFET and FDSOI. The deposited charge is also plotted for

JL-DGFET IM-DGFET FDSOI

0 10 20 30 40 50 60

x (nm)

LET=80 MeV/(mg/cm2)

Deposited charge (Qdep)

To confirm these new findings and highlight the range of LET for which these observations are valid, we calculated the bipolar gain as a function of x for different LET values. Figure 12(a) shows, as expected, that at LET=0.2 MeV/(mg/cm2) the bipolar gain of FDSOI is the highest and the gain of JL-DGFET is situated between that of FDSOI and IM-DGFET. JL-DGFET is therefore more resistant to radiations than FDSOI, but IM-DGFET remains the most interesting device for low LET. This trend continues when LET increases until LET values around 0.5 MeV/(mg/cm2). For LET values between 0.5 MeV/(mg/cm2) and 20 MeV/(mg/cm2) (approximately), JL-DGFET shows the highest bipolar gain for all x locations, IM-DGFET always having the lowest gain. The bipolar gain of JL-DGFET is slightly higher than that of FDSOI for x locations beyond 40 nm. The trend changes for LET values above 20 MeV/(mg/cm2). This can be visualized in Fig. 12(b) which shows the bipolar amplification for LET=30 MeV/(mg/cm2). Finally, Fig. 13 shows the bipolar amplification as a function of x location for LET=80 MeV/(mg/cm2). Although for x less than 30 nm IM-DGFET remains the most interesting device in terms of radiation resistance, for x location beyond about 30 nm, the bipolar gain of JL-DGFET becomes the

Figure 12.Bipolar amplification as a function of the x position of the ion strike in JL-DGFET, IM-DGFET and FDSOI for (a) LET=0.2

JL-DGFET IM-DGFET FDSOI

0 10 20 30 40 50 60

LET=30 MeV/(mg/cm2)

x (nm)

). This can be

http://dx.doi.org/10.5772/57048

).

241

Figure 11.Collected charge as function of the x location in IM-DGFET, JL-DGFET and FDSOI. The deposited charge is also plotted for comparison. (a) LET=0.2 MeV/(mg/cm2) and (b) LET=80 MeV/(mg/cm2). **Figure 11.** Collected charge as function of the x location in IM-DGFET, JL-DGFET and FDSOI. The deposited charge is also plotted for comparison. (a) LET=0.2 MeV/(mg/cm2) and (b) LET=80 MeV/(mg/cm2).

To confirm these new findings and highlight the range of LET for which these observations are valid, we calculated the bipolar gain as a function of x for different LET values. Figure 12(a) shows, as expected, that at LET=0.2 MeV/(mg/cm2) the bipolar gain of FDSOI is the highest and the gain of JL-DGFET is situated between that of FDSOI and IM-DGFET. JL-DGFET is therefore more resistant to radiations than FDSOI, but IM-DGFET remains the most interesting device for low LET. This trend continues when LET increases until LET values around 0.5 MeV/(mg/cm2). For LET values between 0.5 MeV/(mg/cm2) and 20 MeV/(mg/cm2) (approximately), JL-DGFET shows the highest bipolar gain for all x locations, IM-DGFET always having the lowest gain. The bipolar gain of JL-DGFET is slightly higher than that of FDSOI for x locations beyond 40 nm. The trend changes for LET values above 20 MeV/(mg/cm2). This can be visualized in Fig. 12(b) which shows the bipolar amplification for LET=30 MeV/(mg/cm2). Finally, Fig. 13 shows the bipolar amplification as a function of x location for LET=80 MeV/(mg/cm2). Although for x less than 30 nm IM-DGFET remains the most interesting device in terms of radiation resistance, for x location beyond about 30 nm, the bipolar gain of JL-DGFET becomes the To confirm these new findings and highlight the range of LET for which these observations are valid, we calculated the bipolar gain as a function of x for different LET values. Figure 12(a) shows, as expected, that at LET=0.2 MeV/(mg/cm2 ) the bipolar gain of FDSOI is the highest and the gain of JL-DGFET is situated between that of FDSOI and IM-DGFET. JL-DGFET is therefore more resistant to radiations than FDSOI, but IM-DGFET remains the most interesting device for low LET. This trend continues when LET increases until LET values around 0.5 MeV/ (mg/cm2 ). For LET values between 0.5 MeV/(mg/cm2 ) and 20 MeV/(mg/cm2 ) (approximately), JL-DGFET shows the highest bipolar gain for all x locations, IM-DGFET always having the lowest gain. The bipolar gain of JL-DGFET is slightly higher than that of FDSOI for x locations

0

(a) (b)

0.5

1

1.5

Bipolar amplification

2

2.5

Figure 12.Bipolar amplification as a function of the x position of the ion strike in JL-DGFET, IM-DGFET and FDSOI for (a) LET=0.2

JL-DGFET IM-DGFET FDSOI

0 10 20 30 40 50 60

LET=30 MeV/(mg/cm2)

x (nm)

0

(a) (b)

2

4

Collected charge (fC)

6

8

comparison. (a) LET=0.2 MeV/(mg/cm2) and (b) LET=80 MeV/(mg/cm2).

LET=0.2 MeV/(mg/cm2)

0 10 20 30 40 50 60

Deposited charge (Qdep)

x (nm)

lowest.

0

0.05

Collected charge (fC)

0.1

0.15

JL-DGFET IM-DGFET FDSOI

11(a)). This result shows that the trend obtained for x=30 nm is confirmed for all other locations. For all devices, the collected charge has a bell-shaped profile with a maximum around the middle of the channel (where the deposited charge is the highest) and two minima at the source and drain contacts (where the deposited charge is the lowest). The collected charge is always higher than the deposited charge for all x locations, which indicates a strong bipolar amplification. The behavior is quite different for LET=80 MeV/(mg/cm2), as shown in Fig. 11(b). For ion strikes located between the source contact and the middle of the channel, the collected charge is higher for JL-DGFET than that of FDSOI and IM-DGFET. It is also interesting to note that for x locations situated between the source contact (x=0) and the middle of the channel, the collected charge is lower than the deposited charge. This indicates that the bipolar amplification is very low and there is a strong recombination of the deposited charge in the device. Beyond x=30 nm, the collected charge for JL-DGFET decreases and becomes lower than that of IM-DGFET and FDSOI. These results show that for a high LET, the trends obtained for ion strikes in the middle of the channel are no longer valid for ion strikes located in the vicinity of the drain region, beyond x=30 nm. In addition, these results show, for the first time, that JL-DGFET is able to collect a smaller amount of charge than IM-DGFET for these specific values of x location and LET.

Figure 11.Collected charge as function of the x location in IM-DGFET, JL-DGFET and FDSOI. The deposited charge is also plotted for

JL-DGFET IM-DGFET FDSOI

0 10 20 30 40 50 60

x (nm)

LET=80 MeV/(mg/cm2)

Deposited charge (Qdep)

the bipolar gain of FDSOI is the highest and the gain of JL-DGFET is situated between that of FDSOI and IM-DGFET.

device in terms of radiation resistance, for x location beyond about 30 nm, the bipolar gain of JL-DGFET becomes the

beyond 40 nm. The trend changes for LET values above 20 MeV/(mg/cm2 ). This can be visualized in Fig. 12(b) which shows the bipolar amplification for LET=30 MeV/(mg/cm2 ). Finally, Fig. 13 shows the bipolar amplification as a function of x location for LET=80 MeV/(mg/cm2 ). Although for x less than 30 nm IM-DGFET remains the most interesting device in terms of radiation resistance, for x location beyond about 30 nm, the bipolar gain of JL-DGFET becomes the lowest. JL-DGFET is therefore more resistant to radiations than FDSOI, but IM-DGFET remains the most interesting device for low LET. This trend continues when LET increases until LET values around 0.5 MeV/(mg/cm2). For LET values between 0.5 MeV/(mg/cm2) and 20 MeV/(mg/cm2) (approximately), JL-DGFET shows the highest bipolar gain for all x locations, IM-DGFET always having the lowest gain. The bipolar gain of JL-DGFET is slightly higher than that of FDSOI for x locations beyond 40 nm. The trend changes for LET values above 20 MeV/(mg/cm2). This can be visualized in Fig. 12(b) which shows the bipolar amplification for LET=30 MeV/(mg/cm2). Finally, Fig. 13 shows the bipolar amplification as a function of x location for LET=80 MeV/(mg/cm2). Although for x less than 30 nm IM-DGFET remains the most interesting

highest collected charge for FDSOI (Fig. 11(a)). This result shows that the trend obtained for x=30 nm is confirmed for all other locations. For all devices, the collected charge has a bellshaped profile with a maximum around the middle of the channel (where the deposited charge is the highest) and two minima at the source and drain contacts (where the deposited charge is the lowest). The collected charge is always higher than the deposited charge for all x locations, which indicates a strong bipolar amplification. The behavior is quite different for

contact and the middle of the channel, the collected charge is higher for JL-DGFET than that of FDSOI and IM-DGFET. It is also interesting to note that for x locations situated between the source contact (x=0) and the middle of the channel, the collected charge is lower than the deposited charge. This indicates that the bipolar amplification is very low and there is a strong recombination of the deposited charge in the device. Beyond x=30 nm, the collected charge for JL-DGFET decreases and becomes lower than that of IM-DGFET and FDSOI. These results show that for a high LET, the trends obtained for ion strikes in the middle of the channel are no longer valid for ion strikes located in the vicinity of the drain region, beyond x=30 nm. In addition, these results show, for the first time, that JL-DGFET is able to collect a smaller amount

of charge than IM-DGFET for these specific values of x location and LET.

LET=0.2 MeV/(mg/cm2)

comparison. (a) LET=0.2 MeV/(mg/cm2) and (b) LET=80 MeV/(mg/cm2).

also plotted for comparison. (a) LET=0.2 MeV/(mg/cm2) and (b) LET=80 MeV/(mg/cm2).

0 10 20 30 40 50 60

Deposited charge (Qdep)

x (nm)

12(a) shows, as expected, that at LET=0.2 MeV/(mg/cm2

). For LET values between 0.5 MeV/(mg/cm2

LET=0.2 MeV/(mg/cm2)

), as shown in Fig. 11(b). For ion strikes located between the source

11(a)). This result shows that the trend obtained for x=30 nm is confirmed for all other locations. For all devices, the collected charge has a bell-shaped profile with a maximum around the middle of the channel (where the deposited charge is the highest) and two minima at the source and drain contacts (where the deposited charge is the lowest). The collected charge is always higher than the deposited charge for all x locations, which indicates a strong bipolar amplification. The behavior is quite different for LET=80 MeV/(mg/cm2), as shown in Fig. 11(b). For ion strikes located between the source contact and the middle of the channel, the collected charge is higher for JL-DGFET than that of FDSOI and IM-DGFET. It is also interesting to note that for x locations situated between the source contact (x=0) and the middle of the channel, the collected charge is lower than the deposited charge. This indicates that the bipolar amplification is very low and there is a strong recombination of the deposited charge in the device. Beyond x=30 nm, the collected charge for JL-DGFET decreases and becomes lower than that of IM-DGFET and FDSOI. These results show that for a high LET, the trends obtained for ion strikes in the middle of the channel are no longer valid for ion strikes located in the vicinity of the drain region, beyond x=30 nm. In addition, these results show, for the first time, that JL-DGFET is able to collect a smaller amount of charge than IM-DGFET for these specific values of x location and LET.

Figure 11.Collected charge as function of the x location in IM-DGFET, JL-DGFET and FDSOI. The deposited charge is also plotted for

JL-DGFET IM-DGFET FDSOI

0 10 20 30 40 50 60

x (nm)

) the bipolar gain of FDSOI is the highest

) (approximately),

LET=80 MeV/(mg/cm2)

Deposited charge (Qdep)

0

(a) (b)

**Figure 11.** Collected charge as function of the x location in IM-DGFET, JL-DGFET and FDSOI. The deposited charge is

To confirm these new findings and highlight the range of LET for which these observations are valid, we calculated the bipolar gain as a function of x for different LET values. Figure

and the gain of JL-DGFET is situated between that of FDSOI and IM-DGFET. JL-DGFET is therefore more resistant to radiations than FDSOI, but IM-DGFET remains the most interesting device for low LET. This trend continues when LET increases until LET values around 0.5 MeV/

JL-DGFET shows the highest bipolar gain for all x locations, IM-DGFET always having the lowest gain. The bipolar gain of JL-DGFET is slightly higher than that of FDSOI for x locations

2

4

Collected charge (fC)

6

8

To confirm these new findings and highlight the range of LET for which these observations are valid, we calculated the bipolar gain as a function of x for different LET values. Figure 12(a) shows, as expected, that at LET=0.2 MeV/(mg/cm2) the bipolar gain of FDSOI is the highest and the gain of JL-DGFET is situated between that of FDSOI and IM-DGFET. JL-DGFET is therefore more resistant to radiations than FDSOI, but IM-DGFET remains the most interesting device for low LET. This trend continues when LET increases until LET values around 0.5 MeV/(mg/cm2). For LET values between 0.5 MeV/(mg/cm2) and 20 MeV/(mg/cm2) (approximately), JL-DGFET shows the highest bipolar gain for all x locations, IM-DGFET always having the lowest gain. The bipolar gain of JL-DGFET is slightly higher than that of FDSOI for x locations beyond 40 nm. The trend changes for LET values above 20 MeV/(mg/cm2). This can be visualized in Fig. 12(b) which shows the bipolar amplification for LET=30 MeV/(mg/cm2). Finally, Fig. 13 shows the bipolar amplification as a function of x location for LET=80 MeV/(mg/cm2). Although for x less than 30 nm IM-DGFET remains the most interesting device in terms of radiation resistance, for x location beyond about 30 nm, the bipolar gain of JL-DGFET becomes the

) and 20 MeV/(mg/cm2

Figure 12.Bipolar amplification as a function of the x position of the ion strike in JL-DGFET, IM-DGFET and FDSOI for (a) LET=0.2

JL-DGFET IM-DGFET FDSOI

0 10 20 30 40 50 60

LET=30 MeV/(mg/cm2)

x (nm)

0

(a) (b)

0.5

1

1.5

Bipolar amplification

2

2.5

LET=80 MeV/(mg/cm2

240 Computational and Numerical Simulations

lowest.

(mg/cm2

0

0.05

Collected charge (fC)

0.1

0.15

JL-DGFET IM-DGFET FDSOI

0

5

10

Bipolar amplification

MeV/(mg/cm2) and (b) LET=30 MeV/(mg/cm2).

0 10 20 30 40 50 60

JL-DGFET IM-DGFET FDSOI

x (nm)

Figure 12.Bipolar amplification as a function of the x position of the ion strike in JL-DGFET, IM-DGFET and FDSOI for (a) LET=0.2 MeV/(mg/cm2) and (b) LET=30 MeV/(mg/cm2). **Figure 12.** Bipolar amplification as a function of the x position of the ion strike in JL-DGFET, IM-DGFET and FDSOI for (a) LET=0.2 MeV/(mg/cm2) and (b) LET=30 MeV/(mg/cm2).

**Figure 13.** Bipolar amplification as a function of the x position of the ion strike in JL-DGFET, IM-DGFET and FDSOI for LET=80 MeV/(mg/cm2).

We summarize these results in Table 1, indicating for each range of values the device having the lowest bipolar gain:

concerning JL-DGFET, which shows lower bipolar amplification than IM-DGFET and FDSOI

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

JL-DGFET IM-DGFET FDSOI

FD SOI 50 nm [35] FD SOI 80 nm [35] Experimental [35]

10 30 50 70 90

LET (MeV/(mg/cm2))

**Figure 14.** Bipolar amplification vs. LET in JL-DGFET, IM-DGFET and FDSOI for an ion strike at x=50 nm and comparison

For JL-DGFET, we also investigated the impact of channel doping level on the drain current transient and bipolar amplification. Three channel doping levels have been considered in simulation: 1×1019, 2×1019 and 3×1019 cm-3. In JL-DGFET the channel thickness has to be sufficiently small in order to be able to fully deplete the channel of carriers and to turn the device off [29]. The higher the channel doping level, the smaller the film thickness needs to be. This condition is satisfied for all the doping levels and the film thickness considered here. All devices have been calibrated to fill the ITRS Low-Power requirements for the technology node corresponding to the year 2015 [5]. In order to facilitate the comparison, the gate work-function

When the channel doping increase, the floating body effects are enhanced and the drain current transient is longer, as shown in Fig. 15. Both the collected charge (Fig. 16) and bipolar ampli‐ fication (Fig. 17) increase with the channel doping. Impact ionization is also larger for higher doping levels, which additionally contribute to enhance the bipolar amplification. Very high values of the bipolar gain are found for a channel doping of 3×1019 cm-3, but these values are reduced when a larger ion track radius is considered in simulation. Finally, at very high LET

**6. Impact of film doping level on the JL-DGFET transient response**

has been finely tuned to obtain the same off-state current (IOFF) for all devices.

the electric field collapses and the bipolar gain decreases below 2.5 for all devices.

).

http://dx.doi.org/10.5772/57048

243

for ion strikes near the drain and ion LET values higher than 20 MeV/(mg/cm2

0

with experimental and simulated data obtained in [35] for FD SOI MOSFET.

2

4

Bipolar amplification

6

x=50 nm


In addition, compared to FDSOI, JL-DGFET is also more resistant to radiation for LET<0.5 MeV/(mg/cm2 ) and all x locations. These results show that there are LET ranges and specific ion-strike locations for which JL-DGFET can be more interesting in terms of radiation hardness than more conventional inversion-mode devices such as FDSOI and IM-DGFET.


**Table 1.** Simulation results summary indicating the device characterized by the lowest bipolar gain as function of the ion strike location and LET values.

Finally, we compared our results with experimental and simulation results published in Ref. [35]; the purpose is to validate a part of our previous results showing that JL-DGFET could have a lower radiation sensitivity than inversion-mode devices such as IM-DGFET and FDSOI for ion strikes near the drain and ion LET values higher than 20 MeV/(mg/cm2 ). In [35] we investigated the transient response of inversion-mode FD single-gate SOI MOSFET designed with 80 and 50 nm gate length, 11 nm-thick silicon film and intrinsic channel. In that work we found an excellent agreement between experimental bipolar gain values (measured by heavy ions experiments) and simulated bipolar gain obtained with 3-D numerical simulation. The results were also consistent with experimental data obtained by pulsed laser irradiation performed on 80 nm gate length FD SOI MOSFETs fabricated with the same technology [44]. In [35] the ion strikes in a location situated in the drain region, location equivalent to x=50 nm in the present work. For this reason, we plot in Fig. 14, the bipolar gain for JL-DGFET, IM-DGFET and FDSOI for a ion strike at x=50 nm and ion LET values between 10 and 100 MeV/(mg/cm2 ). The experimental and simulation data from [35] are also reported in Fig. 14. This figure indicates that the bipolar gain in JL-DGFET is lower than the experimental and simulated bipolar gain in FD SOI 80 nm and FD SOI 50 nm. The comparison is not easy because the silicon film thickness and the channel length are not the same in JL-DGFET and FD SOI devices measured in [35]. However, these experimental data confirm our simulation results concerning JL-DGFET, which shows lower bipolar amplification than IM-DGFET and FDSOI for ion strikes near the drain and ion LET values higher than 20 MeV/(mg/cm2 ).

We summarize these results in Table 1, indicating for each range of values the device having

**a.** for ion strike locations in the first part of the channel (between the source contact and the middle of the channel) IM-DGFET has the lowest bipolar amplification for all LET values.

In addition, compared to FDSOI, JL-DGFET is also more resistant to radiation for LET<0.5

ion-strike locations for which JL-DGFET can be more interesting in terms of radiation hardness

**Table 1.** Simulation results summary indicating the device characterized by the lowest bipolar gain as function of the

Finally, we compared our results with experimental and simulation results published in Ref. [35]; the purpose is to validate a part of our previous results showing that JL-DGFET could have a lower radiation sensitivity than inversion-mode devices such as IM-DGFET and FDSOI

investigated the transient response of inversion-mode FD single-gate SOI MOSFET designed with 80 and 50 nm gate length, 11 nm-thick silicon film and intrinsic channel. In that work we found an excellent agreement between experimental bipolar gain values (measured by heavy ions experiments) and simulated bipolar gain obtained with 3-D numerical simulation. The results were also consistent with experimental data obtained by pulsed laser irradiation performed on 80 nm gate length FD SOI MOSFETs fabricated with the same technology [44]. In [35] the ion strikes in a location situated in the drain region, location equivalent to x=50 nm in the present work. For this reason, we plot in Fig. 14, the bipolar gain for JL-DGFET, IM-DGFET and FDSOI for a ion strike at x=50 nm and ion LET values between 10 and 100

This figure indicates that the bipolar gain in JL-DGFET is lower than the experimental and simulated bipolar gain in FD SOI 80 nm and FD SOI 50 nm. The comparison is not easy because the silicon film thickness and the channel length are not the same in JL-DGFET and FD SOI devices measured in [35]. However, these experimental data confirm our simulation results

). The experimental and simulation data from [35] are also reported in Fig. 14.

for ion strikes near the drain and ion LET values higher than 20 MeV/(mg/cm2

**Ion strike location x LET values Lowest bipolar gain**

than more conventional inversion-mode devices such as FDSOI and IM-DGFET.

), the bipolar gain of IM-DGFET is always the smallest.

) and all x locations. These results show that there are LET ranges and specific

), JL-DGFET has the lowest bipolar gain; the JL-DGFET becomes

All LET values IM-DGFET

). In [35] we

< 20 MeV/(mg/cm2) IM-DGFET > 20 MeV/(mg/cm2) JL-DGFET

the lowest bipolar gain:

242 Computational and Numerical Simulations

**•** for LET<20 MeV/(mg/cm2

**•** for LET>20 MeV/(mg/cm2

Between source contact and middle of the channel

Beyond the middle of the channel

ion strike location and LET values.

MeV/(mg/cm2

MeV/(mg/cm2

**b.** for x locations beyond the middle of the channel:

more resistant to radiation than IM-DGFET and FDSOI.

**Figure 14.** Bipolar amplification vs. LET in JL-DGFET, IM-DGFET and FDSOI for an ion strike at x=50 nm and comparison with experimental and simulated data obtained in [35] for FD SOI MOSFET.
