Design and Measurement Performance of a Dual-Cavity DM Ferroelectric CP-TFET Biosensor for Biomolecule Detection

Design and Measurement Performance of a Dual-Cavity DM Ferroelectric CP-TFET Biosensor for Biomolecule Detection

Published by : http://www.ijert.org

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 14 Issue 04, April-2025

Syed Ashruf, Graduate Student Member, IEEE, Sukesh Dodla, Graduate Student Member, IEEE, Asif Arfani, Graduate Student Member, IEEE, Kalivaraprasad B, Graduate Student Member, IEEE, M.Siva Kumar, Member, IEEE

AbstractThis study introduces an innovative biosensor fea- turing a dual-cavity DM ferroelectric charge plasma tunnel field- effect transistor (FE-CP-TFET) to enhance sensitivity. Utilizing underlap and dielectric modulation techniques, we achieve ex- ceptionally sensitive and label-free biomolecule detection. The integration of a cavity beneath the source-gate dielectric enables efficient immobilization of biomolecules. Utilizing a ferroelectric material within the gate stack induces a negative capacitance effect, enhancing the effectiveness of low gate voltages. To address issues like random dopant fluctuations, ambipolar conduction, and the heightened thermal budget linked with metallurgical doping, the charge plasma concept is utilized. Comprehensive ATLAS 2D TCAD simulations are conducted to analyze the electric field, hole concentration, and energy band diagram, pro- viding deeper insights into the operational mechanism of the pro- posed device. Two critical figures-of-merit (FOMs) are examined: sensitivity and linearity. Sensitivity assessment considers factors like drain current, Ion-to-Ioff ratio, electric field strength, and transconductance. Linearity analysis specifically emphasizes the Ion-to-Ioff ratio. The biosensor displays proficiency in detecting a range of biomolecules, both neutral and charged, such as Strepta- vidin (ID Cavity = 2.1), 3-Aminopropyltriethoxysilane (APTES) (ID Cavity = 3.57), Keratin (ID Cavity = 8), Bacteriophage T7 (ID Cavity = 6.3), and Gelatin (ID Cavity = 12). Through optimized cavity structure, it achieves significant sensitivity in drain current (2.9 x 107) and notable Ion-to-Ioff sensitivity (3.51 x 107). Furthermore, linearity analysis reveals Pearsons coefficients exceeding 0.8 (r2 0.8) for both structures. These discoveries indicate that our biosensor offers a hopeful alternative for detecting a range of neutral and charged biomolecules.

Index TermsBiosensor, Dual-cavity, Sensitivity enhancement, Ferroelectric charge plasma tunnel field-effect transistor (FE-CP-TFET), Biomolecule detection.

1. INTRODUCTION

   IN recent times, there has been a significant focus on DM biosensors utilizing FET for detecting biomolecules with-out the need for labels [1]. Traditional methods of biomolecule detection involving costly probes and labeling processes such as optical, electrochemical and magnetic approaches have proven to be inaccurate and time- consuming. Consequently, DM biosensors based on FET field-effect transistor), particu-larly those integrated with CMOS technology have emerged as attractive candidates for research due to their heightened sensitivity, low cost, label-free detection capabilities, com-pact size, enhanced scalability and seamless compatibility with

   various electronic devices, promoting wider application possibilities within system-on-chip (SoC) technologies[2-5]. Biosensors find applications in varies domains such as the food industry, environmental monitoring, medical fields, and bio species analysis. The speed of sensitivity and detection are critical factors in bio molecule detection systems. Previous research has extensively explored dielectric modulated MOS-FETs. In these devices, binding sites for the biomolecule are formed at the bottom of the gate electrode or towards the end of the conduit/ source. Biomolecules possessing varying dielectric constant values (ID Cavity) are confined within the cavity region, enabling adjustment of electrical attributes such as threshold voltage or drain current[6,7]. This capability is crucial for enhancing the detection capabilities of dielectric-modulated FETs, as indicated by available metrics[8-10]. As the semiconductor industry strives for advanced technology with minimal power consumption, increased speed, and higher packing density, the miniaturization of device dimensions be-comes imperative. However, conventional CMOS technology scaling faces challenges such as high leakage current, high-power consumption, short channel effects (SCEs), and dete-riorating Ion/Ioff, hindering further progress. To address these issues, TFETs have been explored as a viable alternative due to their resilience against the adverse impacts of downsizing, particularly on subthreshold slope (SS) and decreased leakage current, falling below Boltzmanns limit (60mV/decade)[11-16]. While TFETs have proven superiority over CMOS, they still stumble upon limitations in ambipolar conduction. Various modified TFET systems, such as gate metal work function engineering, multi-gate TFET, hetero dielectric TFET, intro-duction of low bandgap material towards the source facet, and vertical TFET, had been proposed to conquer these challenges. Significantly, there has been exploration into employing neg-ative capacitance (NC) alongside ferroelectric (FE) materials as gate dielectrics[17-18]. Ferroelectric tunnel FET changed into first proposed in 2010, Refining the drain character-istics for contemporary applications, particularly enhancing transconductance in proximity to or beyond the Curie temper-ature, can be achieved through leveraging the P(VDE-TrFE) principle[19-22]. While the studies have explored structural improvements and scaling affects on electric parameters, the use of ferroelectric TFETs as biosensors has not explored.

   Efforts to enhance tunneling performance at lower bias points are vital to preserving the inherent advantages of TFETs. Introducing a ferroelectric insulator alongside the traditional oxide in the gate stack results in poor gate stack capacitance but yields a negative capacitance (NC) impact, effectively acting as a voltage step-up transformer[22-25]. This intrinsic voltage amplification consequences in exquisite steep SS and ON-cutting. SS for the conventional TFETs is expressed as:

   V eff dV gs

   E2

   dV gs

   SS = ln10 I 1 dV eff + E + b dE l (1)

   In this, the bias of the tunneling junction is denoted as Veff, where b is a material constant, and E represents the electric field[26]. The definition of dVgs/dVeff is established through capacitive voltage divider in the following manner:

   Vol. 14 Issue 04, April-2025

   charge plasma Tunnel FET (FE-CP-TFET) biosensor, this

   high heat budget to determine the source and drain regions[35- 36]. To simplify production and overcome these problems, the plasma charging approach was introduced[40]. This approach entails forming the source and drain regions in the TFET by applying appropriate metals with compatible work functions on either side. This study introduces a biosensor based on a TFET structure, representing a significant innovation in the field. Named the dual-cavity dielectric modulated ferroelectric

   device combines the charge plasma technique with the neg- ative capacitance effect, allowing for label-free biomolecule detection[41]. It features two intricately designed nanogaps within the source-gate dielectric interfaces, addressing solubil- ity issues in solids and enhancing carrier concentration in the

   dV gs

   dV eff

   = 1 + Cs

   Cins

   (2)

   channel region[42]. To enable biomolecule immobilization for detection, athin SiO2 coating is precisely grown in the cavity

   In this scenario, the synaptic behavior manifests through the combined capacitance of the gate oxide (Cox) and the ferroelectric insulator (Cferro). Additionally, the ferroelectric voltage serves as a step-up transformer, albeit attenuated by negative capacitance (NC), resulting in an augmented Vgs. Apart from veff, theres an internal voltage amplification within CP-FE-TFET due to the positive shape effect of ca- pacitor charge (Q) induced by NC, thereby augmenting the tunnel junctions electric field. This feedback voltage, denoted as FQ, is directly proportional to the charge (Q) stored in the capacitor per unit area, where the applied terminal voltage equals Vgs plus FQ.

   Q = Cg((V gs V eff) + FQ) (3) and now the Cins can be expressed as follows

   region, serving as an adhesive layer. The biosensor can detect both neutral and charged biomolecules, with biomolecule im- mobilization causing variations in gate oxide capacitance[43- 45] and subsequently influencing the devices electrostatic profile. Performance analyses encompassing energy band gap, surface potential, electric field, and transfer characteristics are conducted with various immobilized biomolecules, including Streptavidin, APTES, T7, Keratin, and Gelatin, validating its efficacy in detecting target biomolecules[46-48]. Notably, the selection of cavity thicknesses of 2nm and 4nm ensures precise immobilization, aligning with the typical thickness and length of biomolecules being below 2 and 4nm, respectively[49-52]. The proposed device novelty lies in its integration of a dual- cavity DM Ferroelectric Charge Plasma Tunnel Field-Effect Transistor (FE-CP-TFET), combining advanced features like dual cavities and ferroelectric materials to enhance sensitivity

   Q

   Cins = V gs V eff

   = Cg

   1 FCg

   (4)

   and enable efficient biomolecule detection. Utilizing underlap and the dielectric modulation techniques, it achieves excep-

   As per Eq(1), the formation of negative gate-stack capac- itance (Cins) is Positive feedback can only occur when the feedback voltage surpasses one, meaning when FQ is greater than 1. This phenomenon is driven by negative capacitance (NC), as indicated by Equations (2) and (4), which leads to an increase in the internal voltage at the tunnel junction:

   dV vgs = 1 Cs (FCg 1) (5)

   tional sensitivity while enabling label-free detection. Integra-

   tion of a cavity beneath the source-gate dielectric facilitates efficient biomolecule immobilization, and incorporation of ferroelectric material induces a negative capacitance effect, improving performance. Addressing technical challenges like random dopant fluctuations and ambipolar conduction, it offers a promising alternative for sensitive biomolecule detection in various biomedical applications.

   dV eff

   Cins

   This paper is divided into four parts. Section II details the

   Because the feedback voltage (FQ > 1) has received positive responses…, the rate of exchange of Vgs with admire to Veff (dVgs/dVeff) decreases. Therefore, its miles glaring from Eq(1) and Eq(5) that the subthreshold slope (SS) is encouraged through the thing defined in Eq(5), ensuing in a great reduction in SS, as indicated in Eq(1)[27-29]. An improvement in the on- state current can be achieved by increasing the electron tunnel- ing rate, which is facilitated by a higher carrier concentration below the gate dielectric in the channel region[31-34]. This strategy involves a higher doping concentration towards the source side compared to the drain side. However, limitations arise due to the solubility limit in solids, which limits the con-

   centration of the doping source to 1Ã1020 cm-3 and requires a

   device architecture and simulation parameters used to analyze the proposed device structure. The results are elaborated in Section III, while the conclusion is presented in Section IV.

2. SENSOR DESIGN

   Fig. 1 presents the cross-sectional view of a dual-cavity biosensor based on the ferroelectric charge plasma Tunnel FET (FE-CP-TFET). It illustrates two structures: Structure 1 with a cavity height (hc) of 2nm (Fig. 1(a)), and Struc- ture 2 with hc = 4nm (Fig. 1(b)). The model in Fig. 1(c) showcases biomolecule immobilization within the nanocavity regions, demonstrating the impact of dielectric modulation on bio-analyte detection. In this design, the underlap opening

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   Fig. 1: 3-D schematics of the FE-CP-TFET-based biosensor (a) with cavity height hc = 2nm and (b) with cavity height hc = 4nm (c) biomolecule immobilization model

   in the source-gate dielectric serves as the binding site for biomolecules, reducing ambipolarity and leakage current for enhanced device performance. Silicon-doped HfO2 is utilized for gate stacking along with conventional oxide, amplifying low gate voltages suitable for low-power applications. Key material parameters for Si:HfO2 include coercive field (FC), remanent polarization (Pr), saturation polarization (Ps), and dielectric constant (FE), set at 1MV/cm, 1 µC/cm², 20 µC/cm², and 31µC/cm², respectively. To streamline fabrication, the charge plasma technique is adopted for creating source and drain regions, utilizing metals such as Hf (3.9 eV) for the drain and Pt (5.93 eV) for the source with suitable work functions. The gate dielectric beneath the gate metal comprises two regions: region 1 (length L2) serving as a biomolecule binding site, and region 2 (length L1) containing the gate dielectric. The total cavity length extends beneath the source and gate metals with lengths L2. Detailed device parameters are provided in TABLE I. The simulation framework employed for doping less TFET analysis is calibrated against reported data, demonstrating good agreement, as depicted in Fig. 2(a).

   TABLE I: THE DIMENSIONS OF THE BIOSENSOR

   Parameter Name	Structure-1	Structure-2
   Silicon thickness (tsi)	10nm	10nm
   Gate oxide thickness (tox)	2.5nm	2.5nm
   Gate length (L1+L2)	40nm+10nm	40nm+10nm
   Source length (LS)	100 nm	100 nm
   Drain length (LD)	100 nm	100nm
   Background Doping (Nin)	1×1016 cm-1	1×1016 cm-1
   Source work function	5.9eV	5.93 eV
   Drain Work function	3.9eV	3.93 eV
   Gate dielectric constant	HfO2	HfO2
   Cavity thickness	2nm	4 nm

   Cavity length 10 nm+ 30 nm 10 nm + 30 nm

   To implement the doping-free approach, we validated our simulation framework[37]. The process for crafting the dual- cavity DM biosensor utilizing the FE-CP-TFET includes form- ing a cavity area within the source-gate dielectric via dry etch- ing. A slender SiO2 layer is then applied onto the silicon film within the cavity through chemical vapor deposition (CVD).

   This layer acts as a bonding agent for biological substances.

   Subsequently, the required thin film of Si-doped HfO2, acting as a switching layer can be sputtered together on the SiO2 layer. Research has demonstrated that the application of a thin Si-doped HfO2 layer beneath mechanical encapsulation results in the formation of an orthorhombic phase, which displays piezoelectric characteristics. This stage was identified as ferroelectric through polarization measurements [50-51]. The application of low pressure CVD can be utilized to plate

   Fig. 2: (a)Demonstrates the calibration of the simulation model using a pre-fabricated TFET, while 2(b) outlines the proposed fabricatin process for the FE-CP-TFET.

   the gate, source, and drain regions [38]. A detailed process

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   flow for potential biosensor production is shown in Fig. 2(b). The performance evaluation of the FE-CP-TFET-based dual- cavity dielectric modulated biosensor involves the complete immobilization of the cavity region with various biomolecules. Neutral biomolecules are characterized by their dielectric constant (IDCavity), while charged biomolecules have both a charge density (Nf) and a dielectric constant. To validate the proposed biosensor structure, various biomolecules with widely accepted dielectric constant values were selected.

   TABLE II: Various Biomolecules and Their Respective K Values

   Name of the Biomolecules ID Cavity Value (K)

   Streptavidin 2.1

   3-Aminopropyltriethoxysilane (APTES) 3.57

   Bacteriophage T7 6.3

   Keratin 8

   Gelatin 12

   The selected bioanalytes encompass Streptavidin, utilized for detecting nucleic acids, proteins, and lipids; 3-

   aminopropyltriethoxysilane (APTES), employed in silaniza- tion processes; Keratin; Bacteriophage T7, recognized for its ability to target various beneficial bacteria; and Gelatin, pro- teins found in skin, hair, and nails. These biomolecules were employed to assess the biosensor device, and the respective dielectric constant values are detailed in TABLE II. To evaluate

   Fig. 3: Flow chat of the device (FE-CP-TFET) with TCAD Simulator

   the effectiveness of the suggested design, specifically the

   dual-cavity dielectric modulated ferroelectric charge plasma

   ISSN: 2278-0181

   Vol. 14 Issue 04, April-2025

   biosensor FET (FE-CP-TFET), we employed a 2D device simulator in the ATLAS TCAD SILVACO version 2020 [39].

   Fig. 4: Electron and hole concentration of the FE-CP-TFET- based biosensor (a) with cavity height hc = 2 nm and (b) with cavity height hc = 4 nm.

   The models include BBT (Bandedge-Based Tunneling) to capture tunneling effects at low voltages, Nonlocal to in- corporate geometry-dependent carrier scattering events, BGN (Band Gap Narrowing) to account for band gap reduction in heavily doped regions, SRH (Shockley-Read-Hall Recombina- tion) to characterize defect-induced recombination processes, ConMob (Conduction Mobility) to describe carrier mobility in the conduction band, FldMob (Field Mobility) to model field-dependent mobility, Print for parameter extraction and analysis, and QTunn (Quantum Tunneling) to analyze carrier tunneling through potential barriers[56-57]. Through rigorous TCAD simulations[58-60], we have investigated the impact of these models on device performance under various operational conditions. The insights gained from these simulations con- tribute to the optimization of our proposed biosensor platform for enhanced biomolecular sensing capabilities.

3. RESULTS AND DISCUSSION

   In this session, we have evaluated the effectiveness of the device by analyzing three distinct measures of performance (MOP), incorporating sensitivity analysis and the linearity of the proposed device. We have investigate the response of the proposed configuration when employed as a biosensor for both neutral and charged biomolecules. To assess the device sensitivity, we replace the air within the cavity region beneath the source-gate dielectric with biomolecules, as outlined in Table II. The dielectric values for neutral biomolecules range from IDCavity = 1 to IDCavity = 12, while the charge densities for charged biomolecules vary from Nf = ±1×1010 to Nf = ±1×1012. Initially, we have perform an electrostatic analysis of the proposed configuration.

   1. Electrostatic analysis of a biosensor based on FE-CP- TFET

      The concentration of charge carriers in the proposed de- vices, shown in Fig. 4, at a depth of 1 nm below the Si- SiO2 interface, is a key issue. Surprisingly, even without metallurgical doping, both devices managed to achieve the desired carrier concentration profiles through the use of a charge plasma approach, enabling the realization of the p+

      i n+ region was examined given the structures feature a

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      tunneling potential is characterized by the Wentzel-Kramer- Brillouin (WKB) approximation (TWKB), delineated by eq.

      p!

      (7) and (8).

      T WKB = exp

      42m E3g

      3qh(Eg + )

      (7)

      Fig. 5: 2-D electric field distribution in FE-CP-TFET-based biosensor (a) with cavity height hc = 2nm of biomolecules (IDCavity = 3.57); (b) with cavity height hc = 2nm of biomolecules (IDCavity = 12); (c) with cavity height hc = 4 nm of biomolecules (IDCavity = 3.57); and (d) with cavity height hc = 4 nm of biomolecules (IDCavity = 12).

      E

      dual gate, indicating similar tunneling rates at both interfaces. As per the equation (6), the speed of GBTBT tunneling in the TFET structure is contingent upon the local electric field (EF) [40].

      = si hcts (8)

      r

      bio

      In the framework of the proposed configuration, m denotes the effective mass of the electron, Eg signifies the energy bandgap, and is defined as the energy range for tunneling, with representing the screening tunneling width. The value of is contingent upon hc, which stands for the cavity height beneath the source gate dielectric. Moreover, ts denotes the thickness of the Si body, bio signifies the dielectric constant of biomolecules immobilized in the cavity region, and s represents the dielectric constant of the Si semiconductor. To grasp the Tunneling Width at the Source- Kappa junction (TWKB) within the proposed arrangement, an examination of the energy band diagrams alteration along the cut-line (beneath the 1 nm of SiO2-Si interface) under the influence of various biomolecules at the binding sites is depicted in Fig. 7. The diagram illustrates that an augmentation in the dielectric constant diminishes the tunneling barrier width at the source-channel junction due to an intensified hole concentration, culminating in the maximum tunneling rate at IDCavity = 12. Biomolecules with positive charges in the cavity area attract electrons, resulting in a reduction in hole concentration towards the source region, thereby broad-

      GBTBT = AE

      exp

      I B l

      (6)

      ening the tunneling barrier. Conversely, negatively charged

      biomolecules result in a narrower tunneling width. In simpler terms, increasing the IDCavity value causes bending of the

      In Eq(6), the constant A, which depends on the effective mass of the electron, is 4 × 1014 V 2S 1cm 1. The constant B represents the tunnel potential (30 MV/cm), and represents the transition constant for silicon (2.5) is illustrated in Fig. 5, depicting the distribution of the 2D electric field within the biosensor. This distribution is based on the negative voltage of the TFET plasma charge (FE CP-TFET) for two different height structures. The value of IDCavity = 3.57 and IDCavity = 12 have chosen to analyze the effect of the dielectric constant of the target biomolecule on the electric field distribution in the cavity area. The illustration depicts that as IDCavity increases, the electric field experiences a notable rise, primarily attributed to the coupling capacitance between the gate and channel regions. Fig. 6 illustrates the fluctuation in the dielectric constant of the bio-analyte, pertinent to detecting hole carrier concentration within the gap region. This variation is shown in both Fig. 6(a) and 6(b). The charged biomolecules within the sink region exert a noticeable influence on the hole concentration within the source region, as illustrated in Fig. 6(c) and 6(d). When biomolecules confined in the sink regio acquire a negative charge, they draw in additional charge carriers (holes) from the source region, leading to the formation of vertical tunneling junctions. Conversely, positively charged biomolecules elicit the opposite effect. In the structure of Tunneling Field-Effect Transistor (TFET), the

      electronic bands within the structure, leading to a stronger electric field particularly noticeable at higher IDCavity values (see Fig. 8). When biomolecules are immobilized within the cavity, theres a notable change in the doping profile as the di- electric values rise. This change results in a more pronounced electric field at the tunneling junction. At IDCavity = 12 for structure 1, the maximum electric field reaches 3.64 × 106 V/cm, while for structure 2, its 2.92 × 106 V/cm. Fig.

      9 illustrates the variations in drain current concerning the gate-to-source voltage at VDS = 1 V for both devices of the (FE-CP-TFET)-based biosensor. These transfer characteristics are captured for various neutral biomolecules with dielectric constants spanning from IDCavity = 2.1 to IDCavity = 12. Fig. 8(c) and 9(d) illustrate the effects of positively charged

      biomolecules trapped in the cavity, showcasing a decrease in the concentration of hole carriers and ON current for both structures. Conversely, negatively charged biomolecules within the cavity attract holes, resulting in an increased majority carrier concentration at the source region and a narrower tunneling barrier width. This effect enhances the tunneling rate and subsequently increases the ON current, as demonstrated in Fig. 9(e) and 9(f). Fig. 10 demonstrates how modifying the dielectric properties of neutral biomolecules within the cavity

      Fig. 6: Hole concentration of FE-CP-TFET based biosensor for (a) neutral biomolecule with cavity height hc =2nm;(b) neutral biomolecule with cavity height hc =4nm;(c) charged biomolecule with cavity height hc = 2 nm and (d) charged biomolecule with cavity height hc =4nm.

      region affects the RF parameter, particularly the transconduc- tance (gm), which is defined as the change in drain current (ID) with respect to the gate-source voltage (VGS) for the suggested devices. As the dielectric constant (IDCavity) value increases, there is an enhancement in the drain current, leading to an increase in the transconductance for both devices. The maximum transconductance values are attained at 1.2 x 10-9 s/µm and 8.64 x 10-11 S/µm for the two proposed structures, respectively.

   2. Sensitivity analysis of a biosensor based on FE-CP-TFET

      Sensitivity serves as a crucial figure of merit (FOM) for assessing the performance of a biosensor. In order to pre- cisely detect the targeted biomolecules, it is imperative for the devices sensitivity to be maximized. However, highly

      Fig. 7: Energy band diagram of FE-CP-TFET based biosensor

      (a) with cavity height hc = 2 nm and (b) with cavity height hc = 4 nm

      sensitive biosensors often grapple with issues of selectivity and specificity,potentially leading to false positive responses from negative samples. The sensitivity of the biosensor employing FE-CP-TFET is determined by analyzing key parameters: the variation in drain current, sensitivity to electric field, changes in the Ion-to-Ioff ratio, and transconductance sensitivity. This sensitivity metric plays a pivotal role in accurately sensing the presence of both charged and neutral biomolecules immobi- lized within the cavity. Sensitivity, as defined by [25], forms a critical aspect of biosensor evaluation.

      Fig. 8: Electric field of FE-CP-TFET based biosensor (a) with cavity height hc = 2 nm and (b) with cavity height hc = 4 nm

      Eq (9) denotes that ID (bio) stands for the drain current when the cavity is completely filled, while an empty cavity gives rise to the drain current labeled as ID (air).

      Introducing neutral biomolecules into the source-channel dielectric cavity region enhances the capacitive coupling be- tween the gate metal and the channel, as well as between the source metal and the source region. This enhancement results in a higher drain current. In Fig. 11 (a) and 11(b), the drain current sensitivity of the FE-CP-TFET-based biosen- sor is demonstrated for cavity heights of 2 nm and 4 nm, respectively. The neutral biomolecules possess dielectric con- stants ranging from IDCavity = 2.1 to ID Cavity = 12. An increase in the IDCavity value of neutral biomolecules clearly improves the drain current sensitivity. The proposed model achieves a maximum drain current sensitivity of 5.38 × 107 for IDCavity = 12 at VGS = 0.5V with hc = 2 nm, and 3.51 × 107 for IDCavity = 12 at VGS = 0.5V with hc = 4 nm. Fig. 12 illustrates the impact of varying dielectric values (ID Cavity) with different neutral biomolecules in the cavity region on the electric field sensitivity of the proposed structures. Electric field sensitivity increases with the ID Cavity value, leading to improved electric field sensitivity at higher ID Cavity values. At IDCavity = 12, the maximum electric field sensitivity is achieved, reaching 3.64 and 2.92 for both proposed structures,

      respectively. Fig. 13 depicts the impact of varying ID\Cavity

      SID

      = ID(bio) ID(air)

      ID(air)

      (9)

      values corresponding to different neutral biomolecules on the

      Ion current and Ion/Ioff sensitivity of both proposed structures.

      Fig. 9: We examined the transfer characteristics of an FE-CP-TFET based biosensor under different scenarios: (a) With a cavity height (hc) of 2 nm for neutral biomolecules.(b) With hc = 4 nm for neutral biomolecules.(c) With hc = 2 nm for positively charged biomolecules.(d) With hc = 4 nm for positively charged biomolecules.(e) With hc = 2 nm for negatively charged biomolecules.(f) With hc = 4 nm for negatively charged biomolecules.

      An increase in the ID\Cavity value enhances the Ion current, thereby improving the Ion to Ion sensitivity as well. When the ID\Cavity value increases, the coupling between the source metal and the source region becomes stronger in the device

      with a cavity height (hc) of 2 nm compared to the one with hc = 4 nm. As a result, the device with the lower cavity height shows a higher Ion current, as shown in Fig. 11. The device with hc = 2 nm reaches the maximum Ion,

      ×

      peaking at 3.76 108 A/µm. In the OFF-state, the tunneling barrier width toward the source-channel junction is wider in

      ×

      the biosensor with hc = 4 nm compared to the alternative device. Consequently, the low cavity height structure achieves lower Ion values, approximately 2.56 1018 A/µm and

      ×

      9.97 1018 A/µm, regardless of the ID\Cavity value. On the

      ×

      other hand, the proposed device with hc = 4 nm achieves the highest Ion/Ioff sensitivity of 2.95 107 for ID\Cavity = 12.

      The impact of various charged biomolecules within the

      cavity region on sensitivity parameters such as drain current sensitivity, electric field sensitivity, Ion/Ioff, and transconduc- tance sensitivity is outlined in Table III. Analysis of the table reveals a decrease in both drain current sensitivity and Ion/Ioff sensitivity for the reported structures with an escalation in the concentration of positively charged biomolecules. This reduction is attributed to a decrease in the tunneling rate at the source-channel junction. Conversely, a contrasting trend is observed for negatively charged biomolecules, leading to a decrease in tunneling width and consequently facilitating

      a higher number of carriers to tunnel through it, thereby

      augmenting the drain current.

      Fig. 10: Transconductance of FE-CP-TFET-based biosensors for neutral biomolecules: (a) with cavity height hc = 2 nm (b) with cavity height hc = 4 nm

      ×

      Table IV summarizes the sensitivity comparison between the proposed biosensor structure and several other TFET-based biosensors documented in the literature. The drain current sen- sitivity observed for our structure is around 5.4 107, slightly lower than that repoted in [42]. However, our design achieves this sensitivity with a lower supply voltage (VGS = 1.2 V) thanks to the integration of ferroelectric material. Importantly, our structure demonstrates superior sensitivity compared to other referenced works, such as IDCavitys, attributed to the cavity beneath the gate source electrode and its greater length compared to references [44] and [48]. Furthermore, the proposed biosensor exhibits enhanced stability over time com-

      TABLE III: Sensitivity parameter values of FE-CP-TFET-based biosensors with cavity lengths of hc = 2 nm and hc = 4 nm due to positive and negative charged biomolecules.

      Employed Biomolecule Dielectric constant and charge (nf) Structure -1 Structure -2

      Sensitivity (SI) Ion /Ion Sensitivity Sensitivity (SI) Ion /Ion Sensitivity

      Positive charged biomolecule(+Nf)	IDCavity =12, Nf=1×1010 C/cm2	6.9 x 107	1.2 x 105	5.09 x 107	3.12 x 106
      	IDCavity =12, Nf=1×1011 C/cm2	5.7 x 107	1.27 x 105	4.25 x 107	2.04 x 106
      	IDCavity =12, Nf=1×1012 C/cm2	3.1 x 108	3.11 x 105	1.96 x 107	6.10 x 105
      Negative charged biomolecule(-Nf)	IDCavity =12, Nf=-1×1010 C/cm2	5.7 x 107	1.27 x 105	5.09 x 107	3.12 x 106
      	IDCavity =12, Nf=-1×1011 C/cm2	5.4 x 107	1.26 x 105	5.10 x 107	3.38 x 106
      	ID Cavity =12, Nf=-1×1012 C/cm2	4.8 x 107	1.28 x 105	2.76 x 107	5.16 x 106

      pared to previous designs [46]. The incorporation of ferroelec- tric material not only enhances sensitivity but also enables im- proved selectivity as evidenced by its performance in detecting target analytes amidst interfering species. Moreover, the com- pact footprint of our biosensor makes it suitable for integration into portable diagnostic devices for on-the-spot analysis. In Table III, the impact of charged biomolecules on sensitivity parameters is quantified. For instance, with an increase in the concentration of positively charged biomolecules, the drain current sensitivity decreases from 6.8×107 A/Vto 5.2×107 A/V, while for negatively charged biomolecules, it increases from

      6.8×107 A/V to 7.5×107 A/V. Similarly, the transconductance

      Fig. 12: Electric field sensitivity for FE-CP-TFET-based biosensors with cavity heights of (a) 2 nm and (b) 4 nm.

      sensitivity decreases from 4.3×10-5 S/V to 3.2×10-5 S/V with an increase in positively charged biomolecules concentra-

      Ion

      to I

      off

      ratio sensitivity is expressed as: Ion

      /Ioff

      = slope

      tion and increases to 4.8×10-5 S/V with negatively charged biomolecules. Compared to the works referenced in [43] and [47], the sensitivity is notably elevated, thanks to the diminished OFF current within the proposed structure.

   3. Linearity Analysis of FE-CP-TFET Based Biosensor

   In sensor applications, linearity stands as a pivotal figure of merit, denoting the sensor consistent responsiveness to fluctuations in the measured variable across its entire range. This study thoroughly examines the linearity of the sug-

   Fig. 11: Drain current sensitivity of FE-CP-TFET-based biosensors: (a) for neutral biomolecules with a cavity height of hc = 2 nm. (b) for neutral biomolecules with a cavity height of hc = 4 nm.

   [IDCavity] + Ion/Ioff(IDCavity = 1) To assess the degree of

   fitness, Pearsons coefficient (r2) is computed. The linearity of Ion/Iofffor the proposed structure is illustrated in Fig. 14 across different dielectric constants (IDCavity = 1 to IDCavity = 12).

   TABLE IV: Comparing the Sensitivity of a Bio-sensor Based on Fe-CP-TFET with Other Reported TFET Bio-sensors

   S.No.	TFET Based Biosensors	Sensitivity
   1	DM Electrostatically doped TFET	108
   2	Vertically Dielectrically Modulated TFET	102
   3	Electrically doped TFET	105
   4	TFET with buried strained Si(1- x)Gex source str	105
   5	N+ pocket doped Vertial TFET	108
   6	Proposed Structure-1	108
   7	Proposed Structure-2	108

   This investigation highlights the sensor robustness and re- liability in maintaining a linear response, crucial for accurate and consistent biomolecule detection in various environmental conditions. TABLE III illustrates the Ion/Ioffsensitivity, with a value of 3.6 × 105 per IDCavity for structure 1 and 4.2 × 104 per IDCavity for structure 2. Both structures exhibit fitness coefficients, with r2 values greater than or equal to 0.8. The evaluation of Subthreshold Swing (SS) and average SS for the device is carried out using Eq (10) and (11).

   V gs

   gested structure by evaluating the shift in the Ionto Ioff ratio

   SS =

   (log10ID)

   (10)

   in correlation with the diverse dielectric constants of the

   biomolecules slated for detection. The linearity equation for

   SSavg

   = V T V OFF

   log10IT log10IOFF

   (11)

   Vol. 14 Issue 04, April-2025

   REFERENCES

   Fig. 13: The sensitivity of Ion and Ion/Ioffin FE-CP-TFET-based biosensors is influenced b y t he d ielectric c onstant o f neutral biomolecules. This impact is observed in both Structure 1 (with hc = 2.5 nm) and Structure 2 (with hc = 5.5 nm).

   The proposed device achieved an SS value of 39.7 mV/decade for the minimum SS point and an average SS value of

   38.5 mV/decade for biomolecules with a dielectric constant (IDCavity) of 12. This suggests that the device may offer a superior alternative for detecting a range of biomolecules, including the SARS-CoV-2 virus [55], various proteins, and amino acids [56], particularly those influenced b y dielectric constant and charge properties. Table V presents a comparison of the values of Ion/Ioff, and the length of the cavity, in relation to already existing devices.

4. CONCLUSION

The research presents a highly sensitive biosensor utiliz- ing the dual cavity dielectric modulated ferroelectric charge plasma Tunnel FET (FE-CP-TFET). The creation of cavity regions at the source gate dielectric interfaces aims to enhance sensitivity by achieving a steeper edge at the source-channel junction. A comparative analysis between two structural vari- ants, one with a cavity height of hc = 2 nm and the other with hc = 4 nm, is conducted to optimize the detection of bio-analytes. Employing the charge plasma technique helps mitigate negative conduction and improve random dopant fluctuations ( RDF). F urthermore, i ntegration o f t he negative capacitance (NC) effect enhances low-power operation for detecting target biomolecules. The study includes sensitivity analyses, evaluating drain current, ION/IOFF ratio, electric field, and transconductance, alongside linearity analysis. The impact of neutral and charged biomolecules trapped within the cavity region on these metrics is assessed. Notably, maximum drain current sensitivity reaches 2.76 x108, EF sensitivity is reported as 2.5, ION/IOFF sensitivity stands at 1.45 x 107 with hc = 4 nm for K = 8 at VGS = 1 V. Linearity analysis, measured by ION/IOFF fitness, a chieves a d egree o f r 2 ¿ 0 .8. T he findings suggest the reported biosensor holds promise for future bio-

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