Extreme transistor scaling with 2D materials
As a 2D material, MoS2 can be grown in stable form with nearly atomic thickness and atomic precision. The researchers synthesized the material down to a monolayer, only 0.6nm thick and then fabricated devices with scaled contact and channel length, as small as 13nm and 30nm respectively.
Using these very scaled dimensions, combined with scaled gate oxide thickness and high K dielectric, the researchers were able to achieve some of the best device performances so far. Most importantly, these transistors enable a comprehensive study of fundamental device properties and calibration of TCAD models. The calibrated TCAD model is used to propose a realistic path for performance improvement.
(SS) with thinner HfO2.
Theoretical studies recommend 2D materials as the perfect channel material for extreme transistor scaling as only little short channel effects are expected compared to the current Si-based devices. Hints of this potential have already been published with one-of-a-kind transistors built on natural flakes of 2D materials.
For the first time, imec has tested these theoretical findings through a comprehensive set of 2D-materials-based transistor data. The devices with the smallest footprint have a channel length of 30nm with a contact pitch under 50nm.
ON current as high as 250µA/µm has been demonstrated with a 50nm SiO2 gate dielectric. Here, an ON current of about 100 µA/µm and an excellent SSmin of 80mV/dec (for VD =50mV) have been demonstrated with 4nm HfO2 in a back-gated configuration.
with contact length 13nm and channel length 29nm
Transfer characteristics have improved sub-threshold swing
(SS) with thinner HfO2.
What’s more, device performance is not impacted by contact length scaling, confirming that carriers are injected from the edge of the contact metal directly into the channel, in line with TCAD simulations. The work confirms that TCAD models capture large parts of device physics and guide experimental validation and mapping the application space. Part of the paper that is presented at IEDM is dedicated to setting the path for device optimization for reaching Si-like performance targets.
“Although still an order of magnitude away from Si transistors, we have brought our MOSFET devices into a realm where they show promising performance for future logic and memory applications”, explains Iuliana Radu, director of Exploratory and Quantum Computing imec. “To bridge this order of magnitude, we have identified a path of systematic improvements such as a further reduction of the gate oxide thickness, the implementation of a double-gated architecture, and further reduction of channel and interface defects. We are transferring this insight to our 300mm-wafer platform for transistors with 2D materials, which was announced at last year’s IEDM.”
imec – www.imec-int.com
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