Suppression Of Ambipolar Behavior Research Articles

Ant Lion Optimizer for Suppression of Ambipolar Conduction in Schottky Barrier Carbon Nanotube Field Effect Transistors

A mathematical model for the effect of oxide thickness on ambient conduction is provided in the Schottky Barrier Carbon Nanotubes (CNTs) Field Effect Transistor (SB-CNTFET). To develop them as the future of IC (integrated circuit) technology, the suppression of ambipolar behaviour in SB-CNTFET is imperative. The ambipolar nature of SB-CNTFET contributes to a high amount of leakage current. tox ≈ 49.91nm uses a dielectric of gate oxide with a thickness to inhibit the ambipolar behaviour. In an SB-CNTFET, the conductance is regulated by the electrical field at the source/drain contacts and the band bending length at the contacts is determined by tox. Therefore, the prime parameter tox that affects the Schottky barrier width and the subthreshold area. The suppression of ambipolar property is presented. The SB-CNTFET is produced using high-K dielectrics such as Zirconium dioxide. This work discusses the suppression of ambipolar activity in SB-CNTFETs without reducing the Ion current using an appropriate dielectric with optimum thickness.

Suppression of Ambipolar Behavior and Simultaneous Improvement in RF Performance of Gate-Overlap Tunnel Field Effect Transistor (GOTFET) Devices

This paper investigates a method to suppress the ambipolar current Iamb effectively, enhance the device performance with higher on current Ion, lower off current Ioff, lower inverse subthreshold slope SS and simultaneously improve the RF performance. Starting with a conventional double-gate TFET structure, the device optimization reported in this work has led to the gradual improvement in device performance in terms of higher Ion, lower Ioff, higher Ion/Ioff ratio and lower SS. The RF parameters of the optimized GOTFET, such as the mutual transconductance gm, gate-to-drain CGD, and gate-to-source CGS capacitances and unity-gain cut-off frequency fT are analyzed. We have optimized the tunnel FET device using the industry-standard $\text {synopsys}^{{\circledR }}$ TCAD tools by studying the impact of various device parameters and dimensions on performance. We demonstrated that at high negative voltages, the proposed nGOTFET would completely suppress the ambipolar behavior of the device without deteriorating the device performance. We have compared the ambipolar current Iamb, Ioff, Ion, SS with 45 nm technology MOSFET and the TFETs reported earlier in literature. For the first time, we have proposed a GOTFET which completely suppresses the ambipolar current at high negative biases, without compromising the high Ion (1.04 mA/μ m) and low Ioff (0.27 pA/μ m) and low SS (32 mV/dec) at room temperature.

Structural Modification of Doped Tunnel Field Effect Transistor for Enhanced Conduction Current and Lower Subthreshold Swing

The material solubility in the source region and abrupt source/channel junction profile are the major concern which is responsible for the improvement of the electrical characteristics of conventional physical doped tunnel field effect transistor (PD-TFET). For this, an additional negatively polarised electrode is mounted in P+ (source) – N (channel) – N+ (drain) structure over the source region to overcome material solubility. This improves the electrical characteristics of the device. Along with this, we have implanted a low workfunction metal layer (ML) in the oxide layer under the gate electrode for creating more abruptness at the junction to improve the subthreshold swing (SS) of the device. Thus, the proposed concept improves the DC/RF performance of the doped TFET device. Further to this, the optimization of metal layer workfunction and misalignment of metal layer in TFET have been performed to get optimum device characteristics. In addition to this, for the suppression of ambipolar behaviour, gate electrode is shorted from the drain side. Due to short length of gate electrode tunneling barrier width at the drain/channel junction increases, hence the tunneling probability decreases which reduces the ambipolar current to parasitic current. Shortening of gate electrode also improves the RF performance.

Approach to suppress the ambipolar current conduction and improve radiofrequency performance in polarity control electrically doped hetero TFET

In this work, a distinctive approach for the suppression of ambipolar behaviour of novel polarity control electrically doped hetero tunnel field effect transistor (TFET) has been reported. For this purpose, a wider band gap material, gallium arsenide phosphide has been employed at drain/channel regions. However, narrow band-gap material, silicon has been used in the source region. This combination of materials leads to a huge reduction in the ambipolar current and significant improvement in ON-state current due to the reduction in the electric field at the drain/channel interface and improvement in tunnelling rate at the source/channel interface, respectively. The proposed device also reduces the drain to source capacitance due to the presence of potential barrier width which leads to improvement in the radiofrequency performance. Therefore, the proposed device is very useful for ultralow power circuit applications. Moreover, polarity gates (PG1 and PG2) have been considered for the formation of n+ (drain) and p+ (source) regions. Hence, the proposed structure avoids ion implantation, random doping fluctuation, and high thermal budget unlike in the case of conventional TFETs, as the latter is physically doped. All the simulations have been performed using ATLAS software.

A novel approach for the improvement of electrostatic behaviour of physically doped TFET using plasma formation and shortening of gate electrode with hetero-gate dielectric

This article presents a new device configuration to enhance current drivability and suppress negative conduction (ambipolar conduction) with improved RF characteristics of physically doped TFET. Here, we used a new approach to get excellent electrical characteristics of hetero-dielectric short gate source electrode TFET (HD-SG SE-TFET) by depositing a metal electrode of 5.93 eV work function over the heavily doped source (P+) region. Deposition of metal electrode induces the plasma (thin layer) of holes under the Si/HfO\(_{2}\) interface due to work function difference of metal and semiconductor. Plasma layer of holes is advantageous to increase abruptness as well as decrease the tunneling barrier at source/channel junction for attaining higher tunneling rate of charge carriers (i.e., electrons), which turns into 86.66 times higher ON-state current compared with the conventional physically doped TFET (C-TFET). Along with metal electrode deposition, gate electrode is under-lapped for inducing asymmetrical concentration of charge carriers in the channel region, which is helpful for widening the tunneling barrier width at the drain/channel interface. Consequently, HD-SG SE-TFET shows suppression of ambipolar behavior with reduction in gate-to-drain capacitance which is beneficial for improvement in RF performance. Furthermore, the effectiveness of hetero-gate dielectric concept has been used for improving the RF performance. Furthermore, reliability of C-TFET and proposed structures has been confirmed in term of linearity.

A novel gate and drain engineered charge plasma tunnel field-effect transistor for low sub-threshold swing and ambipolar nature

In this paper, we focus on the improvement of figures of merit for charge plasma based tunnel field-effect transistor (TFET) in terms of ON-state current, threshold voltage, sub-threshold swing, ambipolar nature, and gate to drain capacitance which provides better channel controlling of the device with improved high frequency response at ultra-low supply voltages. Regarding this, we simultaneously employ work function engineering on the drain and gate electrode of the charge plasma TFET. The use of gate work function engineering modulates the barrier on the source/channel interface leads to improvement in the ON-state current, threshold voltage, and sub-threshold swing. Apart from this, for the first time use of work function engineering on the drain electrode increases the tunneling barrier for the flow of holes on the drain/channel interface, it results into suppression of ambipolar behavior. The lowering of gate to drain capacitance therefore enhanced high frequency parameters. Whereas, the presence of dual work functionality at the gate electrode and over the drain region improves the overall performance of the charge plasma based TFET.

Defect-induced Fermi level pinning and suppression of ambipolar behaviour in graphene

We report on systematic study of electronic transport behaviour of low-biased, disordered graphene nanowires. We reveal the emergence of unipolar transport as the defect concentration increases beyond 0.3% where an almost insulating behaviour is observed for n-type conduction whilst a metallic behaviour is observed for p-type conduction. The conductance shows a plateau that extends through the entire side above the Dirac point (n-branch) where the conductivity coincides with the minimum conductivity at the Dirac point. Raman spectroscopy and X-ray photoemission spectroscopy were used to probe the nature of the defects created by helium ion irradiation and revealed the presence of oxygen–carbon bonds as well as sp3 configurations on the irradiated samples from C KLL Auger spectrum. The observed behaviour is attributed to oxygen groups created after the sputtering of carbon atoms by incident helium ions. These groups act as charge traps, pinning the Fermi level to the Dirac point.