Introduction

Semiconductor technology advancement has led to the miniaturization and integration of transistors into sub-10 nm nodes and it’s scaling down gradually1, targeting higher performance and energy-efficient designs2. However, as transistor dimensions shrink, the short-channel effects (SCEs) and standby current show prominent effects on device performance and reliability concerns in radiation-prone environments3,4. To address these challenges, multi-gate field-effect transistors outperform conventional planar MOSFETs5 with enhanced electrostatic control and improved scalability. Among these, 3D vertical channel FinFET have gained attention with the gate wraps around the channel6, significantly suppressing SCEs and providing a high ION/IOFF ratio7,8,9,10. Vertical channel in FinFET not only improves the gate control but also the overall conducting length of device resulting in the faster switching. FinFET-based processors and memory technologies have been widely adopted in modern integrated circuits (ICs) for applications in satellites, high-altitude flights, and military/aerospace electronics, ultra-low power applications11,12,13. At low transistor technology, material engineering techniques were explored to overcome the effect of SCE’s, use of high-k dielectric gate stacks and ferroelectric materials. High-k dielectrics (HfO2) with an SiO2 interfacial layer help neutralize trap charges and maintain electrostatic integrity14 while negative capacitance FinFET (NC-FinFET) utilizing ferroelectric oxides like PZT (Lead Zirconate Titanate) exhibit improved stability at different process corners. Literature shows that logic switching is improved with low power consumption with ferroelectric material due to spontaneous reversible polarization in PZT(Pb(ZryTi1−y)O3)15. PZT(Pb(ZryTi1−y)O3) is a mixer of Zr and T with added flexibility and tetragonal and rhombohedral ferroelectric phases that show excellent ferroelectric properties and nonvolatile retention. Ferroelectric material shows a negative capacitance effect that steps up voltage, resulting in subthreshold slope under limit at low technology node16.

The subthreshold slope (SS) is calculated as

$$SS=\frac{\partial {V}_{gs}}{\partial {\text{log}}_{10}{I}_{d}}=60x{10}^{-3}\left(1+\frac{{C}_{D}}{{C}_{ox}}\right)$$
(1)

Here, CD and Cox are dielectric and oxide capacitance, respectively. Internal capacitance is responsible for SS variation that can be varied by the addition of ferroelectric or negative capacitance material that leads to changes in switching performance of the transistor17. The value of SS < 60 mV/V is suitable for good switching characteristics and low power consumption.

Process, voltage and temperature variations are usually checked to analyse the transistor performances meeting the desired value based on specific applications. Since the environment also exposes electronic components to high levels of ionizing radiation, which can severely impact device performance and overall lifespan. One of the critical radiation-induced phenomena is total ionizing dose (TID) degradation, where radiation-generated charges accumulate at the Si/SiO2 interface, leading to threshold voltage (Vth) shift, increased leakage current (IOFF), SS degradation and reduced transconductance (gm)18. Ferroelectric layer (PZT) in MOSFET not only improves the performance but makes the device immune to high radiation effects. Recent advancements in transistor technologies have extended their applications beyond digital logic, enabling their use in high sensitivity biosensing19, analog amplification and integrated photonic platforms20. Moreover, studies on ferroelectric and nanoscale device variants, such as steep-slope NC-FETs and photonic-coupled FETs demonstrate their potential for multifunctional circuits21. These developments further emphasize the relevance of our proposed PZT-based NC-FinFET in radiation-hardened electronics and multifunctional device architectures22,23,24,25,26.

In this work, a new NC-FinFET is designed and simulated to obtain improved switching performance for low power and low voltage conditions. Also, the proposed NC-FinFET with PZT (ferroelectric) is investigated for TID effects and compared existing FinFET with oxides SiO2 and HfO2 respectively. The impact of TID radiation (up to 2000 krad ionising dose) on device performance metrics including threshold voltage shift (ΔVth), SS and Ion/Ioff ratio are analysed27. The proposed NC-FinFET design exploit the negative capacitance properties of ferroelectric material (PZT) to obtain an optimal solution for achieving radiation-hardened electronics. This work presents a comprehensive analysis of radiation-induced degradation in NC-FinFET performance highlighting the potential of negative capacitance technology to overcome TID effects. Device reliability is critical in nanoscale FinFET, where aging mechanisms such as bias temperature instability (BTI) and hot carrier effects (HCE) can severely degrade performance. Aging typically results in threshold voltage (Vth) shifts due to interface trap generation, while HCE leads to mobility degradation and transconductance loss. Recent studies have shown that NC-FETs with ferroelectric oxides exhibit enhanced immunity to these effects due to the negative capacitance (NC) effect which reduces the effective electric field across the gate dielectric and mitigates carrier injection damage28,29.

The findings contribute to the development of next-generation radiation-hardened ICs that ensures long-term stability and reliability in space and defence applications along with ultra-low power high speed processor applications30,31.

Device architecture & simulation models

The design of an n-type NC-FinFET with linear gate work function modulation and PZT as the gate oxide is proposed. Figure 1a shows a 3D schematic of the NC-FinFET, while Table 1 provides detailed specifications of the device region material and dimensions. The proposed design considers a channel length (Lg) of 30 nm, fin width (WFIN) of 10 nm, and fin height (HFIN) of 70 nm. Additionally, the depth of the buried oxide (BOX) layer below the fin is set at 30 nm and the substrate depth is 20 nm. The BOX layer additionally suppresses the leakage through bulk silicon region. The source and drain n-type regions are doped with pentavalent impurity atoms concentration of 2 × 1018 cm−3, while the p-type channel and substrate are lightly doped with trivalent impurity atoms at 1 × 1016 cm−3. The gate metal work function is linearly modulated from 4.2 eV to 4.6 eV with a step size of 0.1. These structural and material choices are optimized for enhanced electrostatic control and improved device performance in nanoscale FinFET architectures.

Fig. 1
figure 1

(a) 3D structure of NC-FinFET, (b) 2D view of NC-FinFET.

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Table 1 Showing dimensions and material used.
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The 2D structure of NC-FinFET with a PZT oxide layer is depicted in Fig. 1b, showing the device geometry and dielectric and oxide material stack under the gate. The materials used in Proposed NC-FinFET include Silicon (Si) for the channel, source/drain, Platinum (Pt) for the gate, PZT for the ferroelectric oxide, SiO2 for the buried oxide (BOX) and Aluminium (Al) for contacts. PZT layer between the gate and the silicon channel enables negative capacitance effects that enhance electrostatic control and reduce subthreshold slope (SS) resulting in to improved switching efficiency. The vertical fin architecture further suppresses short-channel effects (SCEs) which ensures a better Ion/Ioff ratio and overall device stability. These structural enhancements make NC-FinFET for ultra-low-power, radiation-hardened circuits and high-performance electronic applications.

For the NC-FinFET design on TCAD, multiple models based on device physics are included, specifically the drift–diffusion model level 1 (DDML1), high mobility models, Lombardi mobility, Fermi statistics, Shockley–Read–Hall (SRH) recombination, Band model, Auger recombination, Esurface model and trap physics32. The 3D simulated structure of the NC-FinFET is the integration of these models. The advanced TID model is employed to analyze the total ionizing dose (TID) effects on the device. The TID (total ionizing dose) effect induced trap charges in the BOX layer33,34,35. Most of the trap charges are positive in nature resulting in an increase of standby current and Vth shift along the negative axis. The linear gate work function variation reduces the standby current and increases the Vth36. This work compares TID effects on the proposed NC-FinFET and other conventional FinFET with SiO2 and HfO2 gate oxides (Lg = 30 nm).

Results analysis

In this section, simulation results are demonstrated for different FinFET architectures in pre and post radiation conditions with different values of TID.

Impact of ionizing radiation on Electrostatic behaviour

Cogenda TCAD’s tool is used to analyse the electrostatic behaviour and 3D visualization of transistors electrostatic behaviour. In this, a cut line across the channel region is made to visualise the thermal image of transistor that provides valuable facts of about the device’s electrostatic behaviour.

Potential distribution in NC-FinFET with a PZT oxide layer at 100 krad before radiation-induced charge trapping was analysed to evaluate the device’s pre-radiation electrostatic behaviour that is conserved as a reference for higher radiation values. Figure 2a shows the potential variation across the device, ranging from − 4.989 V to − 4.000 V which indicates a well-balanced and stable electrostatic environment. Before exposure to high radiation doses, the Si/PZT interface and gate stack exhibit uniform potential contours, ensuring stable threshold voltage (Vth), minimal subthreshold leakage (Ioff) and controlled channel potential. The ferroelectric properties of PZT further contribute to enhanced charge control, which prevents excessive field stress and improves device reliability in radiation-prone environments.

Fig. 2
figure 2

(a) potential at 100krad for PZT (before radiation), (b) potential at 2000krad for PZT (after radiation).

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Figure 2b illustrates 2000 krad TID (high radiation) impact on radiation-induced charge trapping in transistor channel potential distributions. In high radiation, the Si/PZT interface exhibits increased charge trapping and potential distortions resulting in the variation in the device’s threshold voltage (Vth) and subthreshold characteristics. Compared to the pre-radiation (low TID) at 100 krad, the potential distribution is less uniform, indicating the presence of interface traps and radiation-induced oxide charge accumulation. This work contributes to increased subthreshold leakage (Ioff) and potential degradation in Ion/Ioff performance.

Potential distribution of FinFET architecture with SiO2/HfO2 is compared with NC-FinFET at a 2000 krad dose rate as depicted in Fig. 3, which shows the depth of the potential well and charge confinement behaviour across the channel.

Fig. 3
figure 3

Potential distribution along fin of NC-FinFET.

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PZT-based NC-FinFET exhibits the deepest potential well (~ − 4.8 V) with flat nature under the channel, demonstrating superior electrostatic control and charge stabilization. HfO2-based FinFET shows moderate potential well depth, balancing radiation resilience and performance. Conventional FinFET with SiO2 has the shallowest well (~ − 4.6 V), indicating weaker charge confinement and higher radiation-induced threshold voltage shifts.

Electric field distribution in NC-FinFET with a PZT oxide layer before radiation effects at 100 krad TID is analyzed to establish the baseline electrostatic behavior. Figure 4a shows the electric field intensity across the device with a maximum value of ~ 1.589 × 106 V/cm, which is getting concentrated at the Si/PZT and PZT/gate interfaces. Before radiation-induced charge trapping occurs, the electric field remains uniform and ensures stable threshold voltage (Vth), minimal subthreshold leakage and controlled channel potential. The SiO2 interface acts as an insulator, maintaining electrostatic integrity across the gate stack.

Fig. 4
figure 4

(a) electric field at 100krad for PZT, (b) electric field at 2000krad for PZT.

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Figure 4b shows the effect of 2000 krad TID on the NC-FinFET electrostatics performance. Electric field (1.604 × 106 V/cm) lines are concentrated near the Si/PZT and PZT/gate interfaces as well as in the bulk channel region. The enhanced electric field in the gate stack and channel regions results from radiation-induced charge trapping, which modifies the potential distribution and threshold voltage (Vth). High field regions at the drain end can contribute to hot carrier effects resulting device performance degradation. Moreover, increased electric field stress in the gate oxide raises concerns about gate leakage currents, resulting in degraded Ion/Ioff ratio and overall device reliability.

Figure 5 presents the graphical illustration of electric field variations of NC-FinFET at a 2000 krad dose rate across channel comparison other FinFETs with HfO2 and SiO2. PZT-based NC-FinFET exhibits the highest electric field peaks (~ 7.5 × 105 V/cm), showing strong gate control and negative capacitance effect, resulting in enhanced electrostatic stability. FinFET shows a moderate field distribution with HfO2 showing a radiation resistance behaviour, while FinFET with SiO2 shows the lowest field intensity (~ 4.5 × 105 V/cm), indicating weaker electrostatic confinement and higher susceptibility to radiation-induced degradation.

Fig. 5
figure 5

Electric Field.

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Radiation effect on transistor performance

Vog⁺ represents positively charged oxygen vacancies in the gate oxide region of PZT material. When a FinFET undergoes total ionizing dose (TID) radiation exposure, high-energy photons break the oxygen bonds in the oxide layer leading to oxygen vacancies (Vog). Some of these vacancies become positively charged (Vog⁺) by capturing holes or losing electrons. VodH⁺ is positively charged hydrogen-related oxygen defects in the oxide layer. In radiation-prone environments, hydrogen atoms (H⁺) combine with oxygen vacancies (Vod), forming positively charged defect states (VodH⁺)37,38,39. In Proposed NC-FinFET structures, the formation of Vog⁺ and VodH⁺ under total ionizing dose (TID) radiation significantly influences device performance. The impact of TID on NC(PZT) based NC-FinFET is compared with conventional FinFET and FinFET with HfO2. Table 2 presents a comparative performance parameter shift in different types of FinFET, modelled with SiO2, HfO2 and PZT as dielectric materials on similar device dimensions.

Table 2 TID impact on performance parameters of different FinFET.
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Figure 6a is analysed to understand the impact of radiation on charge trapping. Vog + is charge distribution in NC-FinFET with a PZT oxide layer under a TID of 200 krad. The simulation reveals a high concentration of positive charges near the Si/PZT and PZT/gate interfaces with charge densities ranging from 2.40 × 1014 cm−3 to 1.588 × 1017 cm−3. The observed charge accumulation modifies the electrostatic potential leading to possible threshold voltage shifts and variations in subthreshold characteristics40. Ferroelectric properties of PZT help to mitigate excessive charge trapping, resulting in better stability than conventional HfO2/SiO2-based FinFET. 2000 krad TID was analysed to evaluate radiation-induced charge trapping. As shown in Fig. 6b a significant increase in oxide trap density is observed with charge values ranging from 3.32 × 1014 cm−3 to 7.235 × 1017 cm−3 compared to lower radiation doses (200 krad). In Fig. 6b the charge accumulation is more pronounced, particularly at the Si/PZT interface and PZT/gate interface. This leads to a greater threshold voltage shift (Vth) increased subthreshold leakage (Ioff) and a higher density of interface traps, resulting in degradation of the subthreshold slope (SS)41. Distribution of radiation-induced hydrogen vacancy charge (VodH +) in NC-FinFET with a PZT oxide layer at 200 krad TID was analysed to understand its impact on charge trapping and device degradation. Figure 7a shows the charge accumulation profile with higher concentrations (~ 5081 cm−3) observed near the Si/PZT interface. TID value of 1600 krad was analysed to assess its impact on charge trapping, threshold voltage shifts and device degradation. Figure 7b shows the charge distribution with higher concentrations (~ 4949 cm−3) localized at the Si/PZT interface42.

Fig. 6
figure 6

(a) PZT Vog + at 200krad, (b) PZT Vog + at 2000krad.

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Fig. 7
figure 7

(a) PZT vodH + at 200krad, (b) PZT vodH + at 1600krad.

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Ionizing radiation effect on gate capacitance

Figure 8 presents the results, showing capacitance–voltage (CGS-V) characteristics for SiO2, HfO2 and PZT under a 400 krad and the impact of different gate oxides on capacitance retention. PZT exhibits the highest capacitance values, confirming the negative capacitance effect that enhances gate control and improves switching performance. HfO2 shows moderate capacitance, benefiting from its high-k dielectric properties, while SiO2-based FinFET shows the lowest capacitance making it more susceptible to radiation-induced threshold voltage shifts and electrostatic degradation.

Fig. 8
figure 8

Capacitance–voltage (CGS-V) characteristics of NC-FinFET.

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Ionizing radiation effect on transfer characteristic

Figure 9 shows transfer characteristics of FinFET with HfO2 at different radiations. The devices are undergone to high radiation in On-state (VG = VDD and VS = VD = 0) or worst-case bias condition. Under 2000 krad dose, the high gate work function method reduces Ioff as illustrated in Table 3. In the radiation environment, the low gate work function increases the energy barrier at the source side due to its low electron mobility32.

Fig. 9
figure 9

Drain current at different TID.

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Table 3 Comparative Pre and Post Radiation effect on performance.
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Figure 10a presents the results, Id-Vgs characteristics for SiO2, HfO2 and PZT-based NC-FinFET structures before radiation. SiO2 exhibits the highest drive current (Id) but with increased leakage (Ioff) whereas HfO2 shows a reduction in leakage due to the high-k dielectric effect. PZT-based NC-FinFET shows highest electrostatic control, reduced subthreshold leakage and a steep subthreshold slope (SS) making it ideal for low-power applications.

Fig. 10
figure 10

(a) Drain current at different dielectric before radiation, (b) Drain current at different dielectric after radiation.

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After radiation, Fig. 10b shows that FinFET with HfO2 exhibits a noticeable threshold voltage shift, which is consistent with prior studies reporting radiation-induced charge trapping and interface state generation in high-k HfO2 dielectrics while PZT-based NC-FinFET show superior radiation resilience with minimal Vth shift and reduced leakage current. The ferroelectric PZT layer effectively mitigates charge trapping effects, stabilizing the subthreshold behaviour and Ion/Ioff ratio. PZT are more resistant to radiation induced degradation makes them suitable for space and high-radiation applications43,44.

Pre and post radiation Ids versus Vgs curve for all three devices (SiO2, HfO2, PZT) are analysed and compared, it is notice from the plot for the dose rate ranging from 0 to 2000krad that Ioff for the lower doses are less affected in all three devices with values 10−14 A/µm ,10−15 A/µm and 10−16 A/µm respectively. Whereas for the higher doses, Ioff shows 2-decade difference. But no degradation is observed in Ion performance in conventional and proposed devices, showing similar pre & post-radiation value up to 10−6 A/µm33. A comparative pre and post radiation effects are shown in Fig. 11 for different FinFET. Also, pre and post radiation effect is separately demonstrated for NC-FinFET in Fig. 12.

Fig. 11
figure 11

Pre & Post radiation drain current for different dielectric.

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Fig. 12
figure 12

Pre & Post radiation drain current NC-FinFET with PZT.

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Ionizing radiation effect on transconductance (g m )

Transconductance parameter of proposed NC-FinFET is analysed comparing with the other FinFET with HfO2 and SiO2 before radiation exposure. Figure 13 presents the results before radiation exposure. SiO₂ based FinFET show the highest peak gm, indicating superior carrier transport in a pre-radiation environment. However, NC-FinFET exhibits a more stable transconductance profile than conventional FinFET and provides a balance between gate control and leakage suppression offering improved radiation tolerance.

Fig. 13
figure 13

Transconductance of NC-FinFET before radiation.

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Transconductance (gm) with gate voltage (Vgs) characteristics for SiO₂, HfO₂ and PZT were analysed to evaluat2e radiation-induced variations in carrier transport and gate control efficiency. Figure 14 presents the results, transconductance response after a 2000 krad dose. After radiation exposure, all three devices exhibit degradation in peak (gm) due to charge trapping and interface defects. However, NC-FinFET exhibits the most stable transconductance profile, confirming the role of negative capacitance in improving carrier mobility. The Conventional FinFET with HfO2 shows moderate improvement over SiO2 but is inferior to the NC-FinFET transconductance.

Fig. 14
figure 14

Transconductance of NC-FinFET at 2000 krad dose rate.

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Ionising radiation impact on subthreshold swing

Subthreshold swing is the key parameters that tells the behaviour of the device in subthreshold region or transistor in OFF state. Decreasing SS indicates improved switching behaviour due to radiation-induced trap-assisted electrostatic stabilization in NC-FinFET. (PZT) as shown in Fig. 15. Figure 16 shows Ion/Ioff ratio under radiation exposure for different FinFET architectures.

Fig. 15
figure 15

Subthreshold Swing variation under radiation exposure.

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Fig. 16
figure 16

Ion/Ioff Ratio under radiation exposure.

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Threshold Voltage (V th ) Shift

Radiation induced the accumulation of trap charge at Si/SiO2 and oxides shifting the Vth of transistor. These trap charges lead to subthreshold degradation, resulting in reduced gate control and device’s electrostatic integrity. For FinFET with SiO2, Vth decreases but remains constant for HfO2. For NC-FinFET with PZT, Vth increases as dose rate changes from 0 to 2000 krads. At the higher radiation of 2000 krad dose, SiO2 shows 0.02875%, PZT shows 0.005629%. These changes in the Vth are mainly due to the material variations. Figure 17 depicts a radiation effect on threshold voltage shift under extreme dose rate conditions45,46,47.

Fig. 17
figure 17

Threshold Voltage of Pre & Post Radiation.

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Although the threshold voltage (Vth) shift observed under TID (Fig. 17) appears numerically small (0.0056% for PZT and 0.02875% for SiO2), its impact is significant in nanoscale FinFET operation. Even millivolt-scale shifts in Vth can exponentially increase off-state leakage (Ioff) and degrade noise margins in radiation-hardened circuits. The minimal shift in the PZT compared to SiO2 and HfO2 devices highlights its superior immunity to radiation-induced interface trap formation and fixed oxide charge accumulation. This further shows the Ion/Ioff ratio (~ 101⁰) and improved SS (39.9 mV/dec) post-irradiation.

Comparative performance analysis

This section compares different performance parameters under extreme radiation conditions of different FinFET architectures. The radiation up to 2000 krad has a nominal impact on the proposed NC-FinFET as shown in Table 3. Also, the proposed NC-FinFET demonstrated higher switching ratio and lowest value of subthreshold slope in pre radiation condition. FinFET with HfO2 (High-K) is very close to the performance of NC-FinFET with PZT due to similar properties of HfO2 to the negative capacitance or ferroelectric material. FinFET with SiO2 is showing the lowest performance in terms of switching current ratio and transconductance along with an inferior subthreshold slope compared to the NC-FinFET and FinFET with HfO2.

NC behaviour in PZT originates from its intrinsic ferroelectric polarization, which enhances gate control by countering depolarization effects. Although explicit hysteresis loops are not presented here due to simulation constraints, prior studies have shown stable polarization in ultra-thin PZT layers (2–3 nm) used in NC-FETs, achieving steep slopes without hysteresis through capacitance-matching conditions. This aligns with our simulation results, where sub-60 mV/dec SS was obtained consistently without bi-stability, indicating stabilized NC operation48,49.

Regarding reliability, ferroelectric stacks have been experimentally verified to maintain > 90% polarization retention under high radiation fluences with PZT showing superior defect tolerance compared to HfO2-based ferroelectric20. Under TID, ferroelectric domains mitigate trapped charge accumulation by self-compensating internal fields, resulting in minimal Vth shift (0.0056%) and stable SS (39.9 mV/dec) in our study. This shows that PZT not only facilitates NC behaviour but also retains robust electrostatic stability under combined ferroelectric and radiation stress conditions, validating its suitability for radiation-hardened NC-FinFET.

Conclusion

This study provides an in-depth analysis of the total ionizing dose (TID) effects on conventional FinFET and the proposed negative capacitance FinFET architecture with PZT and compares the performance. The proposed NC-FinFET shows a high value of switching current ratio of ~ 1010 with very low off-state current of ~ 10−16 A/um and high transconductance efficiency up to 3.87 V−1. The design shows key performance SS, Ion/Ioff, Vth and gm variations under ionising radiation exposure up to 2000 krad. Findings indicate that the NC-FinFET exhibits superior radiation resilience compared to the conventional FinFET with SiO2 and HfO2. The addition of the ferroelectric PZT oxide enhances charge stability, reduces subthreshold leakage and overcomes radiation-induced variations. Moreover, the negative capacitance effect in NC-FinFET significantly improves electrostatic control, resulting in a stable Ion/Ioff ratio even under high radiation exposure. Furthermore, work function modulation in NC-FinFET helps in maintaining a stable charge distribution results in reduced radiation induced defects. The electric field and potential analysis highlight the capability of NC-FinFET to suppress short-channel effects and improve device reliability in radiation-prone environments (1.604 × 106 V/cm) and (− 4.989 V to − 4.000 V) respectively. Overall, the study confirms that NC-FinFET with ferroelectric PZT oxide are highly suitable for radiation-hardened applications, including space electronics, defence systems and ultra-low-power circuits. Future work can focus on further optimizing the material engineering of negative capacitance layers to enhance long-term radiation stability and exploring multi-gate architectures to improve overall device performance.