Research Bits: Mar. 5

Anti-ambipolar transistor; switching van der Waals magnets; fast electron beam inspection.


Anti-ambipolar transistor

Materials scientists from the City University of Hong Kong propose using transistors made of mixed-dimensional nanowires and nanoflakes to create multivalued logic devices.

By combining GaAsSb nanowires and MoS2 nanoflakes, the team created a hetero-transistor with anti-ambipolar transfer characteristics, in which positive (holes) and negative (electron) charge carriers can both transport concurrently within the semiconducting channel, with the flipping of transconductance. The flipping of transconductance doubles the frequency in response to the input analog circuit signal, reducing the number of devices required compared to conventional frequency multiplier in CMOS technology.

“Our mixed-dimensional, anti-ambipolar transistors can implement multi-valued logic circuits and frequency multipliers simultaneously, making this the first of its kind in the field of anti-ambipolar transistor applications,” said Johnny Ho, associate vice-president and associate head in the department of materials science and engineering at CityU, in a statement. “Our findings show that mixed-dimensional anti-ambipolar devices enable chip circuit design with high information storage density and information processing capacity. The technology developed in this research represents a big step towards next-generation multifunctional integrated circuits and telecommunications technologies.” [1]

Switching van der Waals magnets

Researchers at MIT used pulses of electrical current to switch the magnetization direction of an atomically thin van der Waals magnet at room temperature. Such materials are typically only controllable at extremely cold temperatures.

“The heterostructure device we have developed requires an order of magnitude lower electrical current to switch the van der Waals magnet, compared to that required for bulk magnetic devices,” said Deblina Sarkar, assistant professor in the MIT Media Lab and Center for Neurobiological Engineering and head of the Nano-Cybernetic Biotrek Lab, in a release. “Our device is also more energy efficient than other van der Waals magnets that are unable to switch at room temperature.”

The device uses nanoscale flakes of iron gallium telluride underneath a six-nanometer layer of platinum. “Our next milestone is to achieve switching without the need for any external magnetic fields. Our aim is to enhance our technology and scale up to bring the versatility of van der Waals magnet to commercial applications,” Sarkar added. [2]

Fast electron beam inspection

Researchers at the University of Konstanz filmed the operations of extremely fast electronic circuitry in an electron microscope at a bandwidth of tens of terahertz. The ultrafast electron beam probe provides femtosecond, nanometer, and millivolt resolutions under normal operating conditions.

The team created femtosecond electron pulses in a transmission electron microscope, compressed them with infrared laser light to an 80-femtosecond duration, and synchronized them to the inner fields of a laser-triggered electronic transmission line with the help of a photoconductive switch. Then, using a pump-probe approach, the researchers were able to directly sense the local electromagnetic fields in their electronic devices as a function of space and time.

The researchers said that this femtosecond electron beam probe approach enables diagnostic resolutions to be in principle only limited by the de Broglie wavelength of the electrons in the microscope and the cycle period of the infrared laser light that is applied for the all-optical electron pulse compression. The researchers added that the concept could be integrated into existing electron-beam inspection devices. [3]


[1] Wei Wang, You Meng, Weijun Wang, Pengshan Xie, Quan Quan, Bowen Li, Zhengxun Lai, SenPo Yip, Dengji Li, Dong Chen, Yezhan Li, Di Yin, Yuxuan Zhang, Johnny C. Ho, Multifunctional anti-ambipolar electronics enabled by mixed-dimensional 1D GaAsSb/2D MoS2 heterotransistors, Device, Volume 2, Issue 1, 2024, 100184, ISSN 2666-9986,

[2] Kajale, S.N., Nguyen, T., Chao, C.A. et al. Current-induced switching of a van der Waals ferromagnet at room temperature. Nat Commun 15, 1485 (2024).

[3] Mattes, M., Volkov, M. & Baum, P. Femtosecond electron beam probe of ultrafast electronics. Nat Commun 15, 1743 (2024).

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