Summary of Terahertz Optical Transistors Beat Silicon
Purdue researchers developed a CMOS-compatible all-optical transistor using aluminum-doped zinc oxide (AZO) that can switch in roughly 300 femtoseconds (~4 THz), potentially over 1,000× faster than silicon transistors. The AZO-based nano-photonic devices are low-temperature BEOL-compatible, have tunable dielectric permittivity across telecom IR bands, and rely on recombination time rather than RC delay, enabling much faster switching with design trade-offs.
Parts used in the All-Optical Transistor:
- Aluminum-doped zinc oxide (AZO) material
- CMOS-compatible substrate for BEOL fabrication
- Nano-photonic transistor structures
- Infrared telecom-compatible optical components/materials
PORTLAND, Ore.–Purdue University researchers have demonstrated a CMOS-compatible all-optical transistor capable of 4THz speeds, potentially over a 1000 times faster than silicon transistors.
Nano-photonic transistors processed at low-temperatures can be fabricated atop complementary metal oxide semiconductors (CMOS) to boost switching time by ~5,000-times less than 300 femtoseconds (fs) or almost 4 terahertz (THz), according to researchers at Purdue University. The aluminum-doped zinc oxide (AZO) material from which these optical transistors are fabricated has a tunable dielectric permittivity compatible with all telecommunications infrared (IR) standards.
“The limiting time is ~300fs for a speed of ~4THz although it could be faster if you sacrifice some of the performance,” doctoral candidate Nathaniel Kinsey told EE Times. Kinsey is working with Purdue University (West Lafayette, Indiana) professors Alexandra Boltasseva, a EE, and Vladimir Shalaev, the scientific director of nano-photonics at Purdue’s Birck Nanotechnology Center.
“What is important,” Kinsey continued, “is that electrical transistors are limited by the RC delay time while the limiting mechanism for our ‘all optical transistor’ is recombination time. These are entirely different mechanisms and the latter could enable much more freedom in engineering performance and responses to reach faster switching speeds than the electrical counterpart.”
The transparent conducting oxides making up these photonic transistors are CMOS-compatible materials with low optical loss that can be processed at temperatures low enough for back-end-of-line (BEOL) fabrication. Their metal-like, versatile and tunable behavior makes them ideal for fabricating optical transistors atop CMOS chips, however in the past their slow electron-hole recombination time for emitting photons exceeded 100
For more detail:
Terahertz Optical Transistors Beat Silicon
- What material is used to fabricate the all-optical transistor?
The transistor is fabricated from aluminum-doped zinc oxide (AZO). - How fast can the all-optical transistor switch?
Its limiting switching time is about 300 femtoseconds, corresponding to roughly 4 THz. - Can the optical transistor be fabricated on CMOS?
Yes, the AZO devices are CMOS-compatible and can be processed at low temperatures for BEOL fabrication. - Why can the optical transistor be faster than electrical transistors?
Because its limiting mechanism is recombination time rather than the RC delay that limits electrical transistors. - Is the AZO material compatible with telecommunications wavelengths?
Yes, AZO has a tunable dielectric permittivity compatible with telecom infrared standards. - Do the transparent conducting oxides have low optical loss?
Yes, the transparent conducting oxides used have low optical loss suitable for photonic devices. - Could the optical transistor be made even faster?
The article states it could be faster if some performance is sacrificed. - Who reported this research?
Researchers at Purdue University including Nathaniel Kinsey, Alexandra Boltasseva, and Vladimir Shalaev.
