A group of researchers from Purdue University have experimentally demonstrated how to harness a property called negative capacitance to reduce power consumption in MOSFETs.
The negative capacitance arises in ferroelectric materials. When a voltage pulse is applied, the voltage across the ferroelectric capacitor is found to decrease with time in exactly the opposite direction to which voltage for a regular capacitor should change.
The researchers used an extremely thin layer of the semiconductor molybdenum disulfide to make a channel adjacent to the MOSFET gate. Then they used a ferroelectric material called hafnium zirconium oxide to create a negative capacitor.
Hafnium oxide is now widely used as the dielectric in the gates of modern transistors. The new design replaces the hafnium oxide with hafnium zirconium oxide. “The overarching goal is to make more efficient transistors that consume less power, especially for power-constrained applications such as mobile phones, distributed sensors, and emerging components for the internet of things,” said Peide Ye, Purdue’s Richard J. and Mary Jo Schwartz Professor of Electrical and Computer Engineering.
Findings are detailed in a research paper published on Dec. 18 in the journal Nature Nanotechnology.
MOSFET switching normally requires a minimum of 60 mV for every tenfold increase in current, a requirement called the thermionic limit. However, transistors that harness negative capacitance might break this fundamental limit, switching at far lower voltages and resulting in less power consumption.
New findings demonstrate the ferroelectric material and negative capacitance in the gate results in good switching in both the on and off states. The negative capacitance was created with a process called atomic layer deposition, which is commonly used in industry, making the approach potentially practical for manufacturing.
The research is ongoing, and future work will explore whether the devices switch on and off fast enough to be practical for ultra-high speed commercial applications.
“However, even without ultrafast switching, the device could still have a transformative impact in a broad range of devices that may operate at lower frequency and must operate with low power levels,” Ye said.
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