Sustained Sub-60 mV/decade Switching via the Negative Capacitance Effect in MoS₂ Transistors

Area of Science:

• Semiconductor physics
• Materials science
• Nanoelectronics

Background:

• Negative capacitance (NC) in ferroelectric materials enables transistors to overcome the Boltzmann tyranny, achieving subthreshold swing (SS) below 60 mV/dec.
• Si-based NC field-effect transistors (NC-FETs) have shown this effect, but adapting it to 2D materials is crucial for device scaling.

Purpose of the Study:

• To demonstrate sustained sub-60 mV/dec switching in a 2D material-based FET using negative capacitance.
• To explore the potential of 2D materials for voltage- and size-scalable transistors.

Main Methods:

• Incorporation of hafnium zirconium oxide (HfZrO2 or HZO) ferroelectric into the gate stack of a molybdenum disulfide (MoS2) 2D FET.
• Fabrication and characterization of metal-ferroelectric-metal capacitors.
• Transfer of MoS2 onto the gate stack for characterization with standard and NC gate configurations.

Main Results:

• Achieved sustained sub-60 mV/dec switching, with a minimum SS of 6.07 mV/dec and an average of 8.03 mV/dec over four orders of magnitude in drain current.
• The 2D NC-FET showed a two-order-of-magnitude reduction in SS compared to a standard 2D FET.
• Realized a maximum internal voltage gain of approximately 28× with a ~12 nm HZO layer.
• Observed correlations between threshold voltage shifts and overlap capacitance, as well as HZO and HfO2 thicknesses.

Conclusions:

• The integration of HZO ferroelectrics into MoS2 2D-FETs enables remarkable low-voltage switching performance.
• The demonstrated 2D NC-FETs exhibit significant potential for creating transistors that are scalable in both size and operating voltage.
• Further investigation into unique dependencies can optimize NC-FET performance for future nanoelectronic applications.