MoS2 RF Transistor Suki Zhang 02/15/17

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

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. 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.

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. 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 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. 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