Tunneling Field-Effect Transistors (TFETs) With Subthreshold Swing (SS) Less Than 60 mV/dec
TL;DR: In this paper, a 70-nm n-channel tunneling field effect transistor (TFET) with sub-threshold swing (SS) of 52.8 mV/dec at room temperature was demonstrated.
Abstract: We have demonstrated a 70-nm n-channel tunneling field-effect transistor (TFET) which has a subthreshold swing (SS) of 52.8 mV/dec at room temperature. It is the first experimental result that shows a sub-60-mV/dec SS in the silicon-based TFETs. Based on simulation results, the gate oxide and silicon-on-insulator layer thicknesses were scaled down to 2 and 70 nm, respectively. However, the ON/ OFF current ratio of the TFET was still lower than that of the MOSFET. In order to increase the on current further, the following approaches can be considered: reduction of effective gate oxide thickness, increase in the steepness of the gradient of the source to channel doping profile, and utilization of a lower bandgap channel material
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25 Oct 2010
TL;DR: This review introduces and summarizes progress in the development of the tunnel field- effect transistors (TFETs) including its origin, current experimental and theoretical performance relative to the metal-oxide-semiconductor field-effect transistor (MOSFET), basic current-transport theory, design tradeoffs, and fundamental challenges.
Abstract: Steep subthreshold swing transistors based on interband tunneling are examined toward extending the performance of electronics systems. In particular, this review introduces and summarizes progress in the development of the tunnel field-effect transistors (TFETs) including its origin, current experimental and theoretical performance relative to the metal-oxide-semiconductor field-effect transistor (MOSFET), basic current-transport theory, design tradeoffs, and fundamental challenges. The promise of the TFET is in its ability to provide higher drive current than the MOSFET as supply voltages approach 0.1 V.
1,389 citations
Cites background from "Tunneling Field-Effect Transistors ..."
...The demonstrated TFETs of Fig. 1 show that, with the exception of the Choi [ 36 ], the measured sub-60-mV/ decade swings occur at channel currents in the pA/� m range well below a typical transistor threshold voltage....
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...At this writing, less than 60-mV/decade subthreshold swings have been reported in only a few TFETs based on carbon nanotubes (CNT) [6], [35], Si [ 36 ]–[39], Ge [40], and p þ Ge=n þ Si [41] channels....
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TL;DR: This work experimentally demonstrate interlayer band-to-band tunneling in vertical MoS2/WSe2 van der Waals (vdW) heterostructures using a dual-gate device architecture with important implications toward the design of atomically thin tunnel transistors.
Abstract: Two-dimensional layered semiconductors present a promising material platform for band-to-band-tunneling devices given their homogeneous band edge steepness due to their atomically flat thickness. Here, we experimentally demonstrate interlayer band-to-band tunneling in vertical MoS2/WSe2 van der Waals (vdW) heterostructures using a dual-gate device architecture. The electric potential and carrier concentration of MoS2 and WSe2 layers are independently controlled by the two symmetric gates. The same device can be gate modulated to behave as either an Esaki diode with negative differential resistance, a backward diode with large reverse bias tunneling current, or a forward rectifying diode with low reverse bias current. Notably, a high gate coupling efficiency of ∼80% is obtained for tuning the interlayer band alignments, arising from weak electrostatic screening by the atomically thin layers. This work presents an advance in the fundamental understanding of the interlayer coupling and electron tunneling in ...
556 citations
TL;DR: In this article, a detailed study of the doping-less tunnel field effect transistor (TFET) on a thin intrinsic silicon film using charge plasma concept was performed using calibrated simulations.
Abstract: Using calibrated simulations, we report a detailed study of the doping-less tunnel field effect transistor (TFET) on a thin intrinsic silicon film using charge plasma concept. Without the need for any doping, the source and drain regions are formed using the charge plasma concept by choosing appropriate work functions for the source and drain metal electrodes. Our results show that the performance of the doping-less TFET is similar to that of a corresponding doped TFET. The doping-less TFET is expected to be free from problems associated with random dopant fluctuations. Furthermore, fabrication of doping-less TFET does not require a high-temperature doping/annealing processes and therefore cuts down the thermal budget, opening up possibilities for fabricating TFETs on single crystal silicon-on-glass substrates formed by wafer scale epitaxial transfer.
433 citations
Cites background from "Tunneling Field-Effect Transistors ..."
...I. INTRODUCTION TUNNEL field-effect transistors (TFET) are attractingattention because of their low subthreshold swing and low OFF-state leakage current [1]–[8]....
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TL;DR: In this article, the authors theoretically calculate the parameters A and B of Kane's direct and indirect BTBT models at different tunneling directions for Si, Ge and unstrained Si1-xGex.
Abstract: Germanium is a widely used material for tunnel FETs because of its small band gap and compatibility with silicon. Typically, only the indirect band gap of Ge at 0.66 eV is considered. However, direct band-to-band tunneling (BTBT) in Ge should be included in tunnel FET modeling and simulations since the energy difference between the Ge conduction band edges at the L and Γ valleys is only 0.14 eV at room temperature. In this paper, we theoretically calculate the parameters A and B of Kane's direct and indirect BTBT models at different tunneling directions ([100], [110], and [111]) for Si, Ge and unstrained Si1-xGex. We highlight how the direct BTBT component becomes more important as the Ge mole fraction increases. The calculation of the band-to-band generation rate in the uniform electric field limit reveals that direct tunneling always dominates over indirect tunneling in Ge. The impact of the direct transition in Ge on the performance of two realistic tunnel field-effect transistor configurations is illustrated with TCAD simulations. The influence of field-induced quantum confinement is included in the analysis based on a back-of-the-envelope calculation.
373 citations
Cites background from "Tunneling Field-Effect Transistors ..."
...source is based on band-to-band tunneling (BTBT) [1]–[7]....
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TL;DR: The tunnel field effect transistor (TFET) is considered a future transistor option due to its steep-slope prospects and the resulting advantages in operating at low supply voltage as mentioned in this paper.
Abstract: The tunnel field-effect transistor (TFET) is considered a future transistor option due to its steep-slope prospects and the resulting advantages in operating at low supply voltage ( $\mathrm{V}_{\rm DD}$ ). In this paper, using atomistic quantum models that are in agreement with experimental TFET devices, we are reviewing TFETs prospects at $\mathrm{L}_{\rm G}= 13$ nm node together with the main challenges and benefits of its implementation. Significant power savings at iso-performance to CMOS are shown for GaSb/InAs TFET, but only for performance targets which use lower than conventional $\mathrm{V}_{\rm DD}$ . Also, P-TFET current-drive is between $1\times $ to $0.5\times $ of N-TFET, depending on choice of $\mathrm{I}_{\rm OFF}$ and $\mathrm{V}_{\rm DD}$ . There are many challenges to realizing TFETs in products, such as the requirement of high quality III–V materials and oxides with very thin body dimensions, and the TFET’s layout density and reliability issues due to its source/drain asymmetry. Yet, extremely parallelizable products, such as graphics cores, show the prospect of longer battery life at a cost of some chip area.
357 citations
Cites background from "Tunneling Field-Effect Transistors ..."
...But due to the availability of high-quality material together with years of know-how, Si and Si/Ge TFETs have been studied the most, with [2] showing the first of many devices with SS < 60mV/dec....
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References
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TL;DR: How the structure of the nanotube is the key enabler of this particular one-dimensional tunneling effect is discussed, which is controlled here by the valence and conduction band edges in a bandpass-filter-like arrangement.
Abstract: A detailed study on the mechanism of band-to-band tunneling in carbon nanotube field-effect transistors (CNFETs) is presented. Through a dual-gated CNFET structure tunneling currents from the valence into the conduction band and vice versa can be enabled or disabled by changing the gate potential. Different from a conventional device where the Fermi distribution ultimately limits the gate voltage range for switching the device on or off, current flow is controlled here by the valence and conduction band edges in a bandpass-filter-like arrangement. We discuss how the structure of the nanotube is the key enabler of this particular one-dimensional tunneling effect.
846 citations
"Tunneling Field-Effect Transistors ..." refers background in this paper
...In this letter, tox and tSOI are reduced to 2 and 70 nm, respectively, for sub-60-mV/dec SS....
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TL;DR: In this paper, the subthreshold swing of field effect interband tunnel transistors is not limited to 60 mV/dec as in the MOSFET, but instead is shown to be sub-60 mv/dec.
Abstract: A formula is derived, which shows that the subthreshold swing of field-effect interband tunnel transistors is not limited to 60 mV/dec as in the MOSFET. This formula is consistent with two recent reports of interband tunnel transistors, which show lower than 60-mV/dec subthreshold swings and provides two simple design principles for configuring these transistors. One of these principles suggests placing the gate adjacent to the tunnel junction. Modeling of this configuration verifies that sub-60-mV/dec swing is possible.
555 citations
"Tunneling Field-Effect Transistors ..." refers background in this paper
...In this letter, tox and tSOI are reduced to 2 and 70 nm, respectively, for sub-60-mV/dec SS....
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TL;DR: In this paper, the complementary Si-based tunneling transistors are investigated in detail, and it is found that the band-to-band tunneling current is controlled by the gate-tosource voltage.
Abstract: The metal oxide semiconductor field effect transistor (MOSFET) is scaling to a “tunneling epoch”, in which multiple leakage current induced by different tunneling effects exist. The complementary Si-based tunneling transistors are presented in this paper. The working principle of this device is investigated in detail. It is found that the band-to-band tunneling current is be controlled by the gate-to-source voltage. Due to the reverse biased p-i-n diode structure, an ultra-low leakage current is achieved. The sub-threshold swing of TFET is not limited by kt/q, which is the physical limit of the MOSFET. Using the CMOS compatible processes, the complementary TFETs (CTFET) are fabricated on one wafer. From a circuit point of view, the compatibility between TFET and MOSFET enables the transfer of CMOS circuits to CTFET circuits.
428 citations
08 Dec 2002
TL;DR: The I-MOS as discussed by the authors uses modulation of the breakdown voltage of a gated p-i-n structure in order to switch from the OFF to the ON state and vice versa.
Abstract: One of the "fundamental" problems in the continued scaling of MOSFETs is the 60 mV/decade room temperature limit in subthreshold slope. In this paper, we report initial studies on a new kind of transistor, the I-MOS. The I-MOS uses modulation of the breakdown voltage of a gated p-i-n structure in order to switch from the OFF to the ON state and vice versa. Since impact-ionization is an abrupt function of the electric field (or the carrier energy), simulations show that the device has a subthreshold slope much lower than kT/q. Simulations also show that it is indeed possible to make complementary circuits with switching speeds comparable to or exceeding CMOS. Experimental results on a silicon based prototype verify the basic concept and show very steep subthreshold slopes with high speed turn-on and turn-off. Lower bandgap materials are also being investigated to reduce the value of the breakdown voltage and permit lower voltage operation.
367 citations
259 citations
"Tunneling Field-Effect Transistors ..." refers background in this paper
...However, because the TFET uses the band-toband tunneling instead of thermionic emission, its ON current is expected to be lower than that of the MOSFET, for the same channel material....
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