Semiconductor Material Realizing CAAC-OS FET1)
with World's Lowest Off-State Current
What is a "Crystalline Oxide Semiconductor"?

SEL discovered a crystal structure with c-axis alignment in a direction perpendicular to the film surface and without alignment in the a-b plane (CAAC), in a crystalline oxide semiconductor thin film formed at temperatures lower than 450℃. This is a completely novel crystal structure that differs from single crystals, which do not have distortions, as well as from polycrystals, which have clear grain boundaries.

Feature of CAAC structure

IGZO Single Crystal Structure

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Off-state current comparison between SiFET and CAAC-OS FET

The most distinctive characteristic of an FET using a CAAC-OS active layer is the extremely low off-state current in the order of y2)A/μm (10-24 A/μm). One of its physical properties, a large on/off ratio of 18 or more orders of magnitude, can dramatically reduce power consumption of devices.

▲ Off-state current of CAAC-OS FET[1]

Miniaturized CAAC-OS FET and its cutoff frequency characteristics

SEL has succeeded in fabricating a miniaturized CAAC-OS FET with a gate length of 13 nm (a CAAC-OS island width of 26 nm) applicable to LSI and achieved a cutoff frequency of 60 GHz for the first time in the world.

▲ STEM Image of CAAC-OS FET Cross Section[1]

▲ Frequency Characteristics of CAAC-OS FET

In addition to the CAAC-OS, we have discovered a crystal structure called nc-OS®and expanded the use of crystalline oxide semiconductors in a wide range of applications including the LSI field and the display field. For more detailed information on the crystalline oxide semiconductors, please refer to the book "Physics and Technology of Crystalline Oxide Semiconductor CAAC-IGZO." We will continue to develop new devices in the future.

[1] Reprinted with permission from A. Suzuki, et al., ECS Trans, vol. 98, No. 7, p. 13-27 (2020) Copyright 2020, The Electrochemical Society

1)FET・・・・・Field Effect Transistor
2)y(yocto)・・・The smallest unit prefix in the International System of Units (SI).
3)STEM・・・・・Scanning Transmission Electron Microscope
4)H21・・・・・H-parameter matrix element, which is one of evaluation parameters of electronic circuits, relating to the amplification characteristics of electronic circuits.

*CAAC-OS, nc-OS are registered trademarks of Semiconductor Energy Laboratory Co., Ltd.
(Japanese trademark registration No. 5473535 and No. 5761553).