Doping-Less Tunnel Field Effect Transistor Using Compact-Si-Drain, SiGe-Channel, and Ge-Source
Authors: Lee Byongseog , Kim Minwon , Kim Ji-Hun , Yoo Sang-Dong , Shim Tae-Hun , Hong Jin-Pyo , Park Jeagun 
Published: December 2020

Design rules of the conventional MOSFETs are continuously decreasing, along with the strong requirement of extremely low subthreshold swing level of more than 50 mV/dec at a sub-6-nm node1. As the MOSFET devices cannot meet the demands of key markets, such outstanding electrical features: low-power, high on/off ratio, low off-current, and high on-current, a quantum tunnel FET(TFET) have garnered considerable interest as a crucial alternative to overcome the above issues. However, The TFET has the disadvantages of introducing random dopants fluctuation(RDF) event initially caused by carrier diffusion in the channel region2. Thus, doping-less(DL)-TFET approach using a charge-plasma concept has become highly promising option for use in future TET research areas3,4. In this work, we address a novel device structure and practical fabrication procedure for the sub-10-nm TFET ensuring advanced am-bipolar and ON-state current behaviors on the basis of the well-known charge plasma concept.
We experimentally fabricated and analyzed the conventional DL TFET (see Fig. 1(a)). The roughness of the gate oxide and the interface was high. (see Fig. 1(b)) As a result, the DL TFET showed relatively high am-bipolar and low ON-state current characteristics, as shown in Fig. 1(c). The proposed device includes a 3-nm-thick compact-drain(CD) for the efficient suppression of am-bipolar current and hetero-material(HM) of Si(drain)-SiGe(channel)-Ge(source) for the improved ON-state current, where a particular Ge-condensation process developed in our previous work is adapted for the formation of HM. The CD-HM-DL TFET starts with a thin SOI wafer and fin-type structure to facilitate the fabrication process, as seen in Fig. 1(d) and (e). The TCAD simulation findings imply that a silicon band-gap is highly dependent on the drain thickness owing to a quantum size effect and the band-gap energy is found to be a 1.27 eV at about 3-nm-thick silicon. In addition, the am-bipolar current of the 3-nm-thick CD-DL TFET provides an extremely low current (more than 160 times), when compared with that of a conventional doping-less(DL) TFET with 10-nm-thick drain, as displayed in Fig. 1(f). The HM-DL TFET based on the Si(drain)-SiGe(channel)-Ge(source) configuration exhibited a tunnel path of 2.1 nm at a gate voltage 1.5 V, which is 44.7 % lower than the conventional DL-TFET. The ON-state current of the HM-DL-TFET is 4.8 times higher than that of the conventional DL-TFET, as seen Fig. 1(g). When the compact Si-drain, SiGe-channel and Ge- source were applied, in particular, am-bipolar and ON-state characteristics were improved, as evident in Fig. 1(h). The results indicate that the proposed CD-HM-DL TFET may establish a useful and simple route for advanced electrical performance, such as suppressed am-bipolar current and increased ON-state current, which is possibly essential to the realization of low power and high performance applications by using a relatively small number of few fabrication steps.

Figure caption

Fig. 1. The conventional DL TFET and proposed CD-HM-DL TFET configuration and electrical characteristics (a) DL TFET schematics, (b) TEM Cross-sectional image, (c) I-V curve of DL TFET, (d) CD-HM-DL TFET schematics, (e) The AA’-line cross-sectional view, (f) band-gap energy with Si-thickness and I-V comparison of DL TFET with 3-nm-thick CD TFET (g) I-V comparison of DL TFET with Si(drain)-SiGe(channel)-Ge(source) HM TFET and (h) I-V comparison of DL TFET with CD-HM-DL TFET

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Acknowledgment

* This research was supported by Brain Korea 21 PLUS Program in 2020, the MOTIE (Ministry of Trade, Industry & Energy 10069063) and KSRC (Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device.

Figure 1