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Current Saturation in Few-layer MoS2 FET
| Content Provider | Semantic Scholar |
|---|---|
| Author | Hsu, Allen Shi, Yumeng Palacios, Tom'as |
| Copyright Year | 2012 |
| Abstract | The discovery of graphene in 2004 has sparked great interest in 2-dimensional (2D) materials for their use in the next generation of electronic devices.[1] Although graphene exhibits some remarkable and really unique electrical properties that may help overcome some of the main limitations in analog electronics,[2][3] its lack of bandgap has limited its use for digital applications. On the other hand, molybdenum disulphide (MoS2), another two-dimensional material with a band gap of 1.8 eV in single layer and 1.2 eV in bulk, has recently been used in field effect transistors with excellent gate modulation and current pinch-off.[4][5][6] Monolayer MoS2 is composed of one layer of molybdenum atoms sandwiched between two layers of sulphur atoms for a total thickness of 0.65 Å. Mobility around 300 cm 2 /V.s and an on-off current ratio exceeding 10 7 have been experimentally demonstrated while a large gm (4.4 mS/μm) and excellent short channel behavior (drain induced barrier lowering ~10 mV/V and subthreshold swing ~60 mV/decade with gate length of 15nm) have been predicted. Its potential to reduce short channel effect in highly scaled devices thanks to its excellent electrostatic confinement, together with its high thermal stability, chemical inertness and mechanical properties makes MoS2 transistors excellent candidates for low power mixed-signal electronics. In this paper, we show MoS2 FETs with current saturation, for the first time. The saturation behaviour is extremely important for building both digital and analog circuits. This property is lacking in most graphene FETs due to its zero bandgap and is also not observed in the MoS2 FETs reported in the literature so far. Few-layer MoS2 flakes are first obtained from bulk crystals using adhesive-tape-based micromechanical exfoliation onto degenerately-doped Si substrates covered with 285nm thick SiO2. The sample was then annealed at 300C for 6 hours in forming gas (20 sccm H2 and 600 s ccm Ar) to flatten the flakes and remove the tape residues. The number of layers in the MoS2 flake is then confirmed by optical microscopy, Raman spectrum and Atomic Force Microscopy (AFM). The exfoliated MoS2 flakes we investigate always have 1 layer to 6 layers with thickness of 0.7 to 4nm. Figure 1(a) shows the optical micrograph of a typical few-layer MoS2 flake. The Raman spectrum (Inset of Figure 1 (a)) was measured at room temperature using a 532 nm laser. Two peaks at 384 and 405 cm -1 are attributed to the in-plane E 1 2g and out-of-plane A1g vibration of MoS2 respectively.[7] The AFM image (Figure 1(b)) demonstrates that the current sample has very clean and flat surface. This flake contains 5 layers of MoS2, with a total thickness of 3.5 nm, as shown in the step image in the inset of figure 1(b). The metal contacts are defined using electron beam (e-beam) lithography, followed by deposition of 3 nm titanium / 50 nm gold metal stacks using e-beam evaporation. Figure 1(c) shows an optical micrograph of two parallel FET devices fabricated on the flake in Figure 1(a). They have a gate length of 2 m and gate width of 3.5 m. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.phantomsnet.net/Graphene_Conf/2012/Abstracts/2012_Yu_Lili_liliyu@mit.edu_Graphen%202012%20abstract-Lili%20Yu%20MIT.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
