A Steep-Slope Transistor Combining Phase-Change and Band-to-Band-Tunneling to Achieve a sub-Unity Body Factor (original) (raw)
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A subthermionic tunnel field-effect transistor with an atomically thin channel
The fast growth of information technology has been sustained by continuous scaling down of the silicon-based metal-oxide fieldeffect transistor. However, such technology faces two major challenges to further scaling. First, the device electrostatics (the ability of the transistor's gate electrode to control its channel potential) are degraded when the channel length is decreased, using conventional bulk materials such as silicon as the channel. Recently, two-dimensional semiconducting materials 1-7 have emerged as promising candidates to replace silicon, as they can maintain excellent device electrostatics even at much reduced channel lengths. The second, more severe, challenge is that the supply voltage can no longer be scaled down by the same factor as the transistor dimensions because of the fundamental thermionic limitation of the steepness of turn-on characteristics, or subthreshold swing 8,9 . To enable scaling to continue without a power penalty, a different transistor mechanism is required to obtain subthermionic subthreshold swing, such as band-to-band tunnelling 10-16 . Here we demonstrate band-to-band tunnel field-effect transistors (tunnel-FETs), based on a two-dimensional semiconductor, that exhibit steep turn-on; subthreshold swing is a minimum of 3.9 millivolts per decade and an average of 31.1 millivolts per decade for four decades of drain current at room temperature. By using highly doped germanium as the source and atomically thin molybdenum disulfide as the channel, a vertical heterostructure is built with excellent electrostatics, a strain-free heterointerface, a low tunnelling barrier, and a large tunnelling area. Our atomically thin and layered semiconducting-channel tunnel-FET (ATLAS-TFET) is the only planar architecture tunnel-FET to achieve subthermionic subthreshold swing over four decades of drain current, as recommended in ref. 17, and is also the only tunnel-FET (in any architecture) to achieve this at a low power-supply voltage of 0.1 volts. Our device is at present the thinnest-channel subthermionic transistor, and has the potential to open up new avenues for ultra-dense and low-power integrated circuits, as well as for ultra-sensitive biosensors and gas sensors 18-21 .
Applied Physics Letters, 2011
This letter proposes a hybrid abrupt switch principle and a corresponding device architecture that combines quantum mechanical band-to-band and barrier tunneling mechanisms. The device overcomes the intrinsically low on-current (ION) of conventional tunnel field-effect transistors (TFETs) and the 60 mV/dec subthreshold swing limitation of metal-oxide-semiconductor FETs at room temperature. The device principle and characteristics are studied through two-dimensional numerical simulations. The predicted performance of such hybrid TFET architecture, implementing an ultrathin (0.5 nm) tunneling dielectric between metal source and silicon channel are: average SS values as low as 43 mV/dec, ION~49.3 μA/μm, and ION/IOFF~107.
Nanowire Tunnel Field Effect Transistors at High Temperature
Journal of Integrated Circuits and Systems, 2013
The aim of this work is to study how the performance of nanowire tunnel field effect transistors (TFETs) is influenced by temperature variation. First of all, simulated energy band diagrams were presented to justify its fundamental working principle and this analysis was compared to experimental data obtained for temperature ranging from 300 to 420 K. This methodology was performed for different nanowire diameters and bias conditions, leading to a deep investigation of parameters such as the ratio of on-state and off-state current (ION/IOFF) and the subthreshold slope (S). Three different transport mechanisms (band-to-band tunneling, Shockley-Read-Hall generation/recombination and trap-assisted tunneling) were highlighted to explain the temperature influence on the drain current. As the final step, subthreshold slope values for each configuration were compared to the room temperature. Therefore, it was observed that larger nanowire diameters and lower temperatures tended to increase...
Subthreshold-swing physics of tunnel field-effect transistors
AIP Advances, 2014
Band-to-band tunnel field-effect-transistors (TFETs) are considered a possible replacement for the conventional metal-oxide-semiconductor field-effect transistors due to their ability to achieve subthreshold swing (SS) below 60 mV/decade. This letter reports a comprehensive study of the SS of TFETs by examining the effects of electrostatics and material parameters of TFETs on their SS through a physics based analytical model. Based on the analysis, an intrinsic SS degradation effect in TFETs is uncovered. Meanwhile, it is also shown that designing a strong onset condition, quantified by an introduced concept - “onset strength”, for TFETs can effectively overcome this degradation at the onset stage, and thereby achieve ultra-sharp switching characteristics. The uncovered physics provides theoretical support to recent experimental results, and forward looking insight into more advanced TFET design.
IEEE Electron Device Letters, 2011
We propose a Heterojunction Vertical Tunneling FET and show using self-consistent ballistic quantum transport simulations that it can provide very steep subthreshold swings and high ON current, thereby improving the scalability of Tunnel FETs for high performance. The turn-on in pocket region of the device is dictated by modulation of heterojunction barrier height. The steepness of turn-on is increased because of simultaneous onset of tunneling in the pocket and the region underneath and also due to contribution to current by vertical tunneling in the pocket. These factors can be engineered by tuning heterojunction band offsets.
Tunneling field-effect transistor with a strained Si channel and a Si0.5Ge0.5 source
2011
We report on n-channel tunneling field-effect transistors (TFET) with a tensile strained Si channel and a compressively strained Si0.5Ge0.5 source. The device shows good performance with an average subthreshold swing S of 80mV/dec over a drain current range of more than 3 orders of magnitude. We observed that an applied back-gate bias increases the on-current by a factor of 1.6, and improves the off-current and the subthreshold swing (S). Low temperature measurements show a slightly temperature dependent S, characteristic for a tunneling dominated device.
A Tunnel FET for VDDV_{DD}VDD Scaling Below 0.6 V With a CMOS-Comparable Performance
IEEE Transactions on Electron Devices, 2011
We propose a modified structure of tunnel fieldeffect transistor (TFET), called the sandwich tunnel barrier FET (STBFET). STBFET has a large tunneling cross-sectional area with a tunneling distance of ∼2 nm. An orientation-dependent nonlocal band-to-band tunneling (BTBT) model was employed to investigate the device characteristics. The feasibility of the STBFET realization using a complementary metal-oxidesemiconductor-compatible process flow has been shown using advanced process calibration with Monte Carlo implantation. STBFET gives a high I ON , exceeding 1 mA/µm at I OFF of 0.1 pA/µm with a subthreshold swing below 40 mV/dec. The device also shows better static and dynamic performances for sub-1-V operations. STBFET shows a very good drain current saturation, which is investigated using an ab initio physics-based BTBT model. Furthermore, the simulated I ON improvement is validated through analytical calculations. We have also investigated the physical root cause of the large voltage overshoot of TFET inverters. The previously reported impact of Miller capacitance is shown to be of lower importance; the space-charge buildup and its relaxation at the channel drain junction are shown to be the dominant effect of large voltage overshoot of TFETs. The STBFET are shown to have negligible voltage overshoots compared with conventional TFETs. Index Terms-Band-to-band tunneling (BTBT), depletion region, epitaxial channel region, high-k spacer, inverter circuits, Miller capacitance, sandwich tunnel barrier, space charge and relaxation, tunneling field-effect transistor (TFET), voltage overshoot.
Ultrathin body InAs tunneling field-effect transistors on Si substrates
Applied Physics Letters, 2011
An ultrathin body InAs tunneling field-effect transistor on Si substrate is demonstrated by using an epitaxial layer transfer technique. A postgrowth, zinc surface doping approach is used for the formation of a p + source contact which minimizes lattice damage to the ultrathin body InAs compared to ion implantation. The transistor exhibits gated negative differential resistance behavior under forward bias, confirming the tunneling operation of the device. In this device architecture, the ON current is dominated by vertical band-to-band tunneling and is thereby less sensitive to the junction abruptness. The work presents a device and materials platform for exploring III-V tunnel transistors.