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We demonstrate the polycrystalline-silicon (poly-Si) junctionless (JL) thin-film transistor (TFT) with a planar structure and an ultra-thin channel film thickness ~1.5-nm exhibiting subthreshold swing (S.S.) less than 60 mV/decade. The S.S. of the poly-Si JL-TFT shows abnormal drain-voltage dependence, which the higher drain voltage leads to the smaller S.S. The minimum S.S. (S.S.min) observed in this letter is about 30 mV/decade, which is a record low S.S.min. The sub-60-mV/decade S.S. of the poly-Si JL-TFT is attributed to the impact ionization effect resulting from the high lateral electric field at the drain side at OFF-state. It is different from the conventional inversion-mode transistor, whose pinch-off point is observed at ON-state rather than the OFF-state. The lateral electric field is also found to be increasing with decreasing the channel thickness, and as a consequence, the impact ionization effect is more pronounced when the channel thickness is thinner. This letter shows a new concept for JL transistors, which would be helpful for the development of poly-Si JL-TFTs and the applications of 3-D integrated circuit and non-volatile memory. [ABSTRACT FROM AUTHOR]

In this paper, low-temperature polycrystalline silicon (poly-Si) tunnel thin-film transistors (tunnel-TFTs) are demonstrated to show excellent short-channel effects immunity due to their special current transport mechanism: inter-band tunneling. The ammonia (NH 3 ) plasma surface treatment before the deposition of gate dielectric can significantly reduce the grain boundary trap state densities (N GB ) of poly-Si channel film and the interface trap state densities (N it ) at the gate-oxide/poly-Si interface. About 27% reduction of N GB by NH 3 plasma surface treatment can reduce the minimum drain current ~ 0.51 × and improve the subthreshold slope due to the suppression of trap-assisted tunneling, which dominates the current transport in the subthreshold operation region. In addition, about 37% reduction of N it by NH 3 plasma surface treatment can significantly enhance the on-state current ~ 2.86 × due to the increase of band bending of poly-Si channel potential, which can decrease the tunneling distance to increase the electron tunneling probability. Consequently, the performance improvement of poly-Si tunnel-TFTs by the NH 3 plasma surface treatment would be helpful for the development of system-on-panel and three-dimension integrated circuits. [ABSTRACT FROM AUTHOR]

In this brief, the tunnel FETs (TFETs) with a polycrystalline-Si (poly-Si) channel have been demonstrated, and the performance of the poly-Si TFET shows a significant improvement by the reduction of interface trap states ( N\mathrm {{it}} ) near the conduction band edge. The ON-state current ( I\mathrm{\scriptscriptstyle ON} ) conduction mechanism, band-to-band tunneling, of poly-Si TFETs is strongly affected by the band bending of poly-Si channel. The N2 plasma surface treatment before the gate dielectric deposition can produce a plasma-induced interfacial layer to reduce N\mathrm {it} obviously, which greatly enhances the surface potential modulation by the gate and improves the I\mathrm{\scriptscriptstyle ON} value of poly-Si TFETs \sim 3.7\times . The OFF-state current ( I_{\mathrm { {min}}} ) attributed to the trap-assisted tunneling (TAT) can also be reduced by a factor of \sim 40 %, because of the passivation of grain boundary trap ( N\mathrm {trap} ) of the poly-Si channel film. Consequently, the ON/OFF current ratio is enhanced from 9.42\times 10^{5} to 6.13\times 10^6 . In addition, the subthreshold swing, $I_{{\mathrm{\scriptscriptstyle ON}}}$ , and I_{\mathrm { {min}}} of poly-Si TFET exhibit superior short-channel effect immunity, which shows good feasibility for implementing high packing density of poly-Si thin-film transistors, such as 3-D nonvolatile memory and pixel driving device. [ABSTRACT FROM AUTHOR]

In this paper, NH3 plasma directly applied to the surface of poly-Si channel is studied for the development of high-performance low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) with HfO2 high- \kappa gate dielectric. The reduction of threshold voltage from 1.52 to 0.62 V, the decrease of subthreshold swing from 227 to 151 mV/decade, and the enhancement of field effect mobility \mu _{\mathrm {FE}} from 31 to 65 cm ^{\mathrm {\mathbf {2}}}$ /Vs are observed after NH3 plasma surface treatment. It can be attributed to the NH3 plasma surface treatment enabling defect passivation and plasma-induced interfacial layer (PIL) growth. To decouple the impacts of defect passivation and PIL growth, the device without PIL is also fabricated. This paper demonstrates the important impacts of NH3 plasma surface treatment on the improvement of electrical characteristics of LTPS-TFTs. [ABSTRACT FROM PUBLISHER]

In this paper, the opposite impacts of N2O plasma surface treatment on the n- and p-channel low-temperature poly-Si thin-film transistors (LTPS-TFTs) with HfO2 gate dielectric are investigated. Significant performance improvement of n-channel LTPS-TFT by N2O plasma surface treatment is observed, including threshold voltage reduction \Delta V\mathrm {\mathbf {TH}}\sim -0.57 V, 1.55× higher transconductance G\mathit {m} , and 1.82× higher driving current I{\rm{drv}} . However, p-channel LTPS-TFT shows serious performance degradation after N2O plasma surface treatment, including threshold voltage increase \Delta V\mathrm {\mathbf {TH}}~\sim -0.99 V, transconductance G\mathit {m} reduction, and driving current I\mathrm {\mathbf {drv}} degradation. The difference of the two mechanisms of N2O plasma surface treatment, namely, plasma induced interfacial layer (PIL) growth effect and trap passivation effect on poly-Si, is elaborated by a process of the PIL removal after the PIL growth. As a result, the trap passivation effect benefits both n- and p-channel LTPS-TFTs. The PIL growth effect shows the opposite impacts on the n- and p-channel LTPS-TFTs, that benefits n-channel LTPS-TFT and degrades p-channel LTPS-TFT seriously. Therefore, the negative impacts of N2O plasma surface treatment on the p-channel LTPS-TFTs can be eliminated by a PIL removal step in the process. These results would be critical for the applications of system-on-panel and 3-D integrated circuit. [ABSTRACT FROM PUBLISHER]

In this letter, the impact of crystallization method on the electrical characteristics of polycrystalline silicon (poly-Si) tunnel field-effect transistors (TFETs) is investigated. Different crystallization methods may result in different amounts of interface traps (Nit) and bulk traps (NGB). TFETs crystallized with solid-phase crystallization (SPC) and metal-induced lateral crystallization (MILC) were fabricated and compared. In comparison with the SPC TFETs, the MILC TFETs exhibit \sim 4.5\times higher ON-state current I_{\text {ON}} , subthreshold swing reduction \Delta \text{S}$ .S. \sim 202$ mV/decade, and larger \sim 7.2\times $ ON/OFF current ratio. According to the measurement of a monitor poly-Si thin-film transistor, replacing SPC with MILC results in a reduced and a reduced \text{N}_{\mathrm {\mathbf {GB}}}\sim 0.36 \times , respectively. It can enhance the gate-to-tunnel junction controllability. Consequently, lowering trap density favors reducing power consumption of TFETs and provides a promising solution for future low-power driving circuits in portable electronics. [ABSTRACT FROM PUBLISHER]