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mos2 analog electronics

mos2 analog electronics

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mos2 analog electronics

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  1. MoS2 Analog Electronics

  2. Analysis of the paper “Analog two-dimensional semiconductor electronics” • Overview • Objective • MoS2 growth • Device architecture and device fab • Electrical verification • OPAMP fabrication • Transistor model • OPAMP performance • OPAMP circuits • Fully 2D platform (sensor and electronics)

  3. Objective • Sensors based on 2-D materials (such as our NG micro-sensors) still have to be interfaced with external components supplied by traditional silicon-based devices. • A fully 2D platform (sensor and electronics) is highly attractive because it will allow sensors and electronic to be as close as possible.

  4. MoS2 growth • MoS2 was grown on c-plane sapphire • Precursors: • Sulfur powder • MoO3 powder • Temperature 700 C • Time 10 minutes • Grain size of the order of 10 µm (measured with polarization resolved optical second harmonic generation)

  5. Device architecture • The devices consisted of bottom gated n-channel FETs.

  6. Device fab • The bottom gate electrodes are defined by the first metal layer (Ti/Au, 2/25 nm). • Al2O3 was then deposited as dielectric (30 nm using ALD) • Vias were etched using 30% KOH • Next, the MoS2 film was lift off spinning a polystyrene (PS) film and immersing it in KOH. It was then rinsed in DI water and transferred onto the target substrate in a glove-box. The PS was then dissolved in toluene. • The last step was etching in Ar/SF6 to define the actual transistor channel and the deposition of the source and drain contacts.

  7. Electrical measurement of a single MoS2 transistor • The single transistors show: • Small hysteresis • On/off ratios exceeding 8 orders of magnitude • Mobilities peaking around 10 cm-2V-1s-1 • Subthreshold swing of 130 mV dec-1 • Vth of around 3.2 V

  8. OPAMP (schematic) • Three stage design with 12 transistors • Atot=AIAIIIAIV • The amplifier was designed for Atot= 43 dB • The bias current is supplied using Wilson current mirror (M5,M6,M8)

  9. OPAMP (practical implementation)

  10. Transistor model • Since a complete model for back-gated 2D semiconductor FETS is not available, they fitted their experimental results with a Enz-Krummenacher-Vittoz (EKV) model both in subthreshold and inversion. • A statistic block was introduced to take in account Vth (from measurements) and mobility (from Montecarlo simulations) variability • Using the inversion model (all transistors operates in inversion) they obtained a nominal Atot=39.5±10.3 dB.

  11. Transistor model

  12. Transistor model

  13. Transistor model

  14. OPAMP performance • The OPAMP was measured with a bias current IB=5-10 µA and VDD/Vss=±10V showing: • Gain of 33 dB • Large swing of almost 15 V • CM rejection ratio of 50 dB • Rolling off at 5 kHz and fT=0.3 MHz • However, the phase margin is not above 60

  15. Analog electronic circuits

  16. 2D sensors plus 2D electronics • To demonstrate the possibility to fabricate a fully 2D platform they fabricated and opto-electronic circuit. • Both the photodetector and the amplifier for signal preconditioning were made from the same MoS2 film

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