Research Bits: Nov. 28

Switchable photodetector and neuromorphic vision sensor; MEMS accelerometers; amorphous silicon carbide.


Switchable photodetector and neuromorphic vision sensor

Researchers from the Institute of Metal Research at the Chinese Academy of Sciences built a device that can be switched between being a photodetector and neuromorphic vision sensor by adjusting the operating voltage. The trench-bridged GaN/Ga2O3/GaN heterojunction array device exhibits volatile and non-volatile photocurrents at low and high voltages, respectively, by manipulating the ionization and de-ionization processes of oxygen vacancies in Ga2O3.

When operating as a photodetector at low voltage, the device demonstrates a fast photoresponse speed and a high responsivity, enabling complex functionalities such as optically controlled logic circuits, photonic imaging, and optical communication. As a neuromorphic vision sensor at high voltage, the device can simulate neuron/synaptic functions, including paired pulse facilitation, transition from short-term to long-term plasticity, learning-experience behavior, and image memory. [1]

MEMS accelerometers

Researchers from Binghamton University and Northeastern University found an improved design for MEMS accelerometers by investigating a manufacturing mistake. “We made a MEMS accelerometer that was initially flat with four springs on the side,” said Shahrzad “Sherry” Towfighian, a professor in the College of Engineering and Department of Mechanical Engineering at Binghamton. “You can think of it like a suspended plate, and if you put the base on something that is moving, one will have relative motion with respect to other one. The top plate also will impact the bottom plate, and that friction converts to charges on surfaces because of contact and separation, so we have made these accelerometers self-powered.”

However, when manufacturing the MEMS, one batch came out dome-shaped and with two broken springs. In testing the mis-manufactured MEMS, they found them to be more resilient. “They could resist up to 70G [70 times normal gravity on Earth] without any sign of breakage, and they gave us the largest output voltage. With a higher signal-to-noise ratio, the accelerometer is more sensitive and has better detection,” said Towfighian. “We will design all later devices based on this dome shape that gives us larger range of motion and more resilience so that more robust devices can be created.” [2]

Amorphous silicon carbide

Researchers at Delft University of Technology developed a new material with mechanical properties crucial for vibration isolation on a microchip. Called amorphous silicon carbide (a-SiC), it could be used to create ultra-sensitive nanomechanical sensors and solar cells, among other potential applications. It has a tensile strength of 10 GigaPascal, ten times greater than Kevlar. Additionally, it can be produced at wafer scales. [3]


[1] Feng, S., Li, J., Feng, L., Liu, Z., Wang, J., Cui, C., Zhou, O., Deng, L., Xu, H., Leng, B., Chen, X.-Q., Jiang, X., Liu, B., Zhang, X., Dual-Mode Conversion of Photodetector and Neuromorphic Vision Sensor via Bias Voltage Regulation on a Single Device. Adv. Mater. 2023, 2308090.

[2] Mousavi, M., Alzgool, M., Davaji, B., Towfighian, S., High Signal-to-Noise Ratio Event-Driven MEMS Motion Sensing. Small 2023, 2304591.

[3] Xu, M., Shin, D., Sberna, P. M., van der Kolk, R., Cupertino, A., Bessa, M. A., Norte, R. A., High-Strength Amorphous Silicon Carbide for Nanomechanics. Adv. Mater. 2023, 2306513.

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