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MoS2 RF Transistor
Suki Zhang
02/15/17
Motivation for MoS2 RF Transistor
• MoS2 is a semiconductor, transition-metal dichalcogenide (TMD) materials [3]
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Bandgap, direct 1.8eV, indirect 1.3eV for SL
good mechanical strength
high mobility (> 80cm2/Vs)
high on/off ratio (> 108)
good current saturation, on state current density 300 uA/um
40uS/um transconductance
Voltage gain >30 Av= gm/gds
GHz RF performance
• Self-consistent ballistic quantum transport simulations, cutoff frequencies well
above 100 GHz , with channel lengths of Lg ∼ 15 nm, operating in the ballistic
limit [2]
• Large-area MoS2 can be prepared using either liquid-phase exfoliation or CVD
growth.
[2] Yoon, Y.; Ganapathi, K.; Salahuddin, S. How Good Can Monolayer MoS2 Transistors Be? Nano Lett. 2011, 11, 3768−3773.
[3] A. Sanne et al., “Radio frequency transistors and circuits based on CVD MoS2 ,” Nano Lett., vol. 15, no. 8, pp. 5039–5045, Aug. 2015
• fT: cutoff frequency, unity current gain
Intrinsic
[6]
Extrinsic
[5]
• fmax: maximum frequency of oscillation, unity power gain
[5]
[5 ]D. Krasnozhon, D. Lembke, C. Nyffeler, Y. Leblebici, and A. Kis, “MoS2Transistors Operating at Gigahertz Frequencies,” Nano
Letters, vol. 14, no. 10, pp. 5905–5911, Aug. 2014.
[6] Z. Dong and J. Guo, “Assessment of 2-D Transition Metal Dichalcogenide FETs at Sub-5-nm Gate Length Scale,” IEEE
Transactions on Electron Devices, vol. 64, no. 2, pp. 622–628, 2017.
• Thickness dependent
• SL, fT 6.7 Ghz, fmax 5.3 Ghz [3]
• ML, , fT 42 Ghz, fmax 50 Ghz [4]
• Channel length dependent
[1]
• Rigid substrate and flexible substrate with strain
[1]Cheng, R.; Jian, S.; Chen, Y.; Weiss, N.; Cheng, H. C.; Wu, H.; Huang, Y.; Duan, X. Nat. Commun. 2014, 5, 5143
[3] A. Sanne et al., “Radio frequency transistors and circuits based on CVD MoS2 ,” Nano Lett., vol. 15, no. 8,
pp. 5039–5045, Aug. 2015
[4] R. Cheng et al., “Few-layer molybdenum disulfide transistors and circuits for high-speed flexible
electronics,” Nature Commun., vol. 5, Oct. 2014, Art. no. 5143.
2015
[5]
[1]
fT 6.7 Ghz
fmax 5.3 Ghz
[1]Cheng, R.; Jian, S.; Chen, Y.; Weiss, N.; Cheng, H. C.; Wu, H.; Huang, Y.; Duan, X. Nat. Commun. 2014, 5, 5143
[5 ]D. Krasnozhon, D. Lembke, C. Nyffeler, Y. Leblebici, and A. Kis, “MoS2Transistors Operating at Gigahertz Frequencies,” Nano Letters, vol. 14, no. 10, pp. 5905–5911, Aug. 2014.
• Exfoliated few layer
MoS2
• fT 42 Ghz
• fmax 50 Ghz
• Higher than Single
layer
μfe=gm*L/(W*Cg*Vds)
[5]
[5 ]D. Krasnozhon, D. Lembke, C. Nyffeler, Y. Leblebici, and A. Kis, “MoS2Transistors
Operating at Gigahertz Frequencies,” Nano Letters, vol. 14, no. 10, pp. 5905–5911,
Aug. 2014.
Flexible MoS2 RF
Transistors with
Strain CVD monolayer MoS
2016
2
• Bandgap increased with
compressive strain, contact
resistance increased, lower FT
• Comparable FT with rigid
substrate
[5 ]D. Krasnozhon, D. Lembke, C. Nyffeler, Y.
Leblebici, and A. Kis, “MoS2Transistors
Operating at Gigahertz Frequencies,” Nano
Letters, vol. 14, no. 10, pp. 5905–5911, Aug.
2014.
[5]
MoS2 Vs. Graphene
RF Transistors
• The highest cutoff frequency (fT) achieved in MoS2 is much
lower than that in graphene
• Much lower carrier mobility
• Much higher contact resistance
[7]K. D. Holland et al., "Impact of contact resistance on the fT
and fmax of Graphene vs. MoS2 transistors," IEEE Transactions
on Nanotechnology, pp. 1–1, 2016.
Overall
• Mos2 with bandgap enable integrating digital and analog circuit in a
single chip
• It is capable to make highly flexible electronics
• High cut off frequency (fT) and High maximum frequency of oscillation
(fmax)
• Improve carrier mobility
• Shorter channel length
• Reduce contact resistance
• Graphene between MoS2 and metal
• Doping contacts
• Use high K ALD dielectrics