Accumulation Mode Field Effect Transistors Research Articles

Performance assessment of pocket tunnel FET and accumulation mode FET for detection of streptavidin protein

In this paper, Dielectrically Modulated (DM) pocket Tunnel Field Effect Transistor (TFET) and Accumulation Mode Field Effect Transistor (AMFET) biosensors are examined for the Sensitivity estimation of different thicknesses of biotarget (Streptavidin)/bioreceptor (Biotin)/silica binding protein (SBP or APTES) biomolecules with a fully filled and partially filled cavity. The sensitivity parameter is based on realistic process detection and is calculated as the ratio of biotarget to bioreceptor drain current for neutral and charged biomolecules. The effect on the sensitivity for a filled cavity is observed for: a) varying the thickness of streptavidin and Biotin for fixed SBP (APTES) thickness, b) varying the thickness of streptavidin and APTES for fixed biotin thickness, for both Pocket TFET and AMFET. The maximum sensitivity is observed in 4 nm thick streptavidin for the front gate voltage V fg: −3.8 V and V fg: −1.6 V for pocket TFET and AMFET, respectively.

Impact of temperature on a ferroelectric interfaced negative capacitance double gate junctionless accumulation mode field effect transistor-compact model

Ferroelectric interfaced negative capacitance field effect transistors are gaining popularity for low power applications; however, as temperature is a constant influencing factor, further study is required to comprehend how these devices are influenced. Through a proposed compact model, this paper analytically investigates the influence of temperature on a ferroelectric interfaced negative capacitance double gate junctionless accumulation mode field effect transistor. This device integrates the benefits of negative capacitance with the junctionless accumulation mode structure. An extensive comparison of the proposed device is made with the existing structure to evaluate the benefits offered by the ferroelectric layer at different temperatures. The Landau–Khalatnikov equation and Pao–Sah integral are employed to obtain the surface potential and drain current model with temperature variation. Various key parameters of the device have been analysed extensively by varying the temperature from 200 to 500 K. It has been found that internal voltage amplification declines as temperature rises, but the sub-threshold swing increases from 46 to 72 mV decade −1 with an increase in temperature. Additionally, with a progressive rise in temperature, the loss of gain and degradation of gate capacitance are observed.

High-k perovskite gate oxide for modulation beyond 1014 cm-2.

Scaling down of semiconductor devices requires high-k dielectric materials to continue lowering the operating voltage of field-effect transistors (FETs) and storing sufficient charge on a smaller area. Here, we investigate the dielectric properties of epitaxial BaHf0.6Ti0.4O3 (BHTO), an alloy of perovskite oxide barium hafnate (BaHfO3) and barium titanate (BaTiO3). We found the dielectric constant, the breakdown field, and the leakage current to be 150, 5.0 megavolts per centimeter (MV cm−1), and 10−4 amperes per square centimeter at 2 MV cm−1, respectively. The results suggest that two-dimensional (2D) carrier density of more than n2D = 1014 per square centimeter (cm−2) could be modulated by the BHTO gate oxide. We demonstrate an n-type accumulation mode FET and direct suppression of more than n2D = 1014 cm−2 via an n-type depletion-mode FET. We attribute the large dielectric constant, high breakdown field, and low leakage current of BHTO to the nanometer scale stoichiometric modulation of hafnium and titanium.

Is accumulation or inversion mode dielectric modulated FET better for label-free biosensing?: A comparative investigation

In this paper, we present a comprehensive assessment of dielectric modulated accumulation mode field-effect transistor (AMFET) architecture for label-free biosensing in comparison with inversion mode field-effect transistor (IMFET) architecture. The underlying physics of the AMFET and IMFET biosensors was explored by investigating variation in the conduction band and the electron concentration profile (e−CP) under both ON-state and OFF-state due to charged and neutral bio molecule immobilisation. Subsequently, essential sensitivity parameters are estimated for biosensing. It is observed that the variation in electron concentration profile has a huge impact on the drain current and threshold voltage. Sensitivity evaluation predicts AMFET to have improved ION/IOFF, OFF-current and threshold (VTH) shift. AMFET shows enhanced sensitivity to charged biomolecules over neutral bio molecules. From the investigations done, the AMFET has outperformed at lower bias and fails to predict optimum results at higher bias compared to IMFET. This leaves a choice to use the desired device as per the biasing availability for label-free detection of the biomolecules.

Design approach to improve the performance of JAMFETs

In this paper, the authors propose the use of electrostatic doping for n + drain region formation in Junctionless accumulation mode field effect transistors (JAMFET). This electrostatically doped drain (EDD) JAMFET employs an additional unbiased electrode (auxiliary electrode) of low workfunction on the intrinsic drain region. This technique effectively suppresses the tunneling leakage, thereby reducing I OFF by 6 orders. The tunneling of electrons from valence band of channel to conduction band of drain happens due to enhanced band bending in OFF-state (V GS = 0 V, V DS = 1 V). The presence of additional electrode in EDD-JAMFET increases the width of tunnel barrier formed at channel–drain junction in OFF-state improving the I ON/I OFF ratio by 6 orders. The gate length scaling demonstrates that leakage suppression of EDD-JAMFET is more effective with approximately 3 orders smaller I OFF even at gate length of 5 nm. The performance of graded channel device (GC-EDD-JAMFET) by electrostatic doping is also explored. Significant improvements are observed in terms of I ON/I OFF, subthreshold slope SS, DIBL and f T. Finally, the analogue parameters such as Transconductance generation factor G m/I D, Intrinsic gain A V, output conductance G D, and ‘G m/I D × f T’ performance metrics are investigated which show significant improvement at small bias current, making it suitable for ultra-low power applications.

Dielectric Modulated Biosensor Architecture: Tunneling or Accumulation Based Transistor?

In this paper, we present a feasibility assessment of tunneling and accumulation mode p-type transistor architectures for use as dielectric-modulated biosensors. The performance of devices is compared through the estimation of the change in electrical characteristics between Iris antigen (bioreceptor) and anti-Iris antigen (target biomolecule) for a partially filled cavity. While tunnel field-effect transistors (TFETs) achieve higher sensitivity when biomolecules are positioned at the source–channel junction, the sensitivity rapidly diminishes when biomolecules are located away from the tunneling junction and, thus, severely limits their utility. Although accumulation mode field-effect transistors (AMFETs) also exhibit location-dependent sensitivity degradation, they show higher sensitivity values in comparison to the TFET for biomolecule layer located away from the source–channel junction. Furthermore, the application of back bias (~1 V) significantly improves the sensitivity (>8) for 40% filled cavity of p-type AMFET biosensors for all locations in the dielectric cavity. As higher sensitivity values over a wider biomolecule location are desirable, an AMFET performs better in comparison to the TFET cavity-modulated biosensor. This paper presents a systematic analysis, highlighting the benefits and limitations of each device for biosensing applications. Results highlight new viewpoints and insights in the design of AMFET-based cavity-modulated biosensors.

Simulation Study of Single-Event Burnout in Power Trench ACCUFETs

This paper presents 2-D numerical simulation results of single-event burnout (SEB) in power trench accumulation mode field effect transistor (ACCUFET) for the first time. In this device, a p+ base region is used to deplete the n− base region to achieve a low leakage current density, and the blocking voltage is supported by the n− drift region. We find that the depth of the p+ base region determines both the leakage current density and SEB performance, as a result, there is a tradeoff relationship between the two characteristics. The 60 V hardened power ACCUFET shown in this paper could demonstrate much better SEB performance without sacrificing the current handling capability compared with the standard UMOSFET. The hardened structure mentioned in this paper indicates that an n buffer layer is added between the epitaxial layer and substrate layer based on a basic power device. As a result, the safe operating area (SOA) of the 60 V, 80 V and 100 V hardened ACCUFET discussed in this paper could reach the value of breakdown voltage when the buffer layer is over a certain value, that can realize safety operation throughout entire LET range.

Accumulation mode field-effect transistors for improved sensitivity in nanowire-based biosensors

In this work, nanowire field-effect transistors (NW-FETs) constructed from a top-down approach has been utilized for the detection of biomolecules. Here, we demonstrate that the sensitivity of NW-FET sensors can be greatly enhanced when the same dopant type is used for both channel region and source and drain. This type of FET, known as accumulation mode field-effect transistors (AM-FETs), functions under different operating principle compared with conventional inversion mode FETs. The improved sensitivity is attributed to the different conduction mechanism and current components of AM devices. The results have been verified through a direct comparison with a conventional FET.

Reduced electric field in junctionless transistors

The electric field perpendicular to the current flow is found to be significantly lower in junctionless transistors than in regular inversion-mode or accumulation-mode field-effect transistors. Since inversion channel mobility in metal-oxide-semionductor transistors is reduced by this electric field, the low field in junctionless transistor may give them an advantage in terms of current drive for nanometer-scale complementary metal-oxide semiconductor applications. This observation still applies when quantum confinement is present.

Insulated gate depletion mode and accumulation mode field effect transistors on InP fabricated by electron beam lithography

An electron‐beam‐lithography‐compatible process for the fabrication of depletion mode and accumulation mode insulated gate field effect transisitors on InP has been developed and is reported in detail. The exposure system uses an unmodified scanning electron microscope interfaced with a minicomputer. Transistor gate length dimensions for the completed devices range from several microns to submicron, and the smallest gate length for the depletion mode device measures 0.25 μm. Device operation is presented and discussed, and device performance is shown to compare well with long gate devices made by optical lithography.