1. MoS2 RF Transistor
Suki Zhang
02/15/17

2. Motivation for MoS2 RF Transistor
MoS2 is a semiconductor, transition-metal dichalcogenide (TMD) materials [3]
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

3. fT: cutoff frequency, unity current gain
fmax: maximum frequency of oscillation, unity power gain
Intrinsic
[6]
Extrinsic
[5]
[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
[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.

4. Channel length dependent
Thickness dependent
SL, fT 6.7 Ghz, fmax 5.3 Ghz [3]
ML, , fT 42 Ghz, fmax 50 Ghz [4]
Channel length dependent
Rigid substrate and flexible substrate with strain
[1]
[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

5. 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

6. 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

7. Flexible MoS2 RF Transistors with Strain
2016
CVD monolayer MoS2
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
[5]

8. 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.

9. 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