Research Bits: September 11

Combining digital and analog; ballpoint pen for LEDs; battery for smart contact lenses.


Combining digital and analog

Researchers from École Polytechnique Fédérale de Lausanne (EPFL) propose integrating 2D semiconductors with ferroelectric materials for joint digital and analog information processing, which could improve energy efficiency and support new functionality.

The device uses a 2D negative-capacitance tungsten diselenide/tin diselenide tunnel FET (TFET), which consumes less energy when switching, along with ferroelectric silicon-doped hafnium oxide that provides the possibility to continuously process and store memory at the same time.

The researchers also explored creating switches similar to biological synapses for neuromorphic computing. “The research marks the first-ever co-integration of von Neumann logic circuits and neuromorphic functionalities, charting an exciting course toward the creation of innovative computing architectures characterized by exceptionally low power consumption and hitherto unexplored capabilities of building neuromorphic functions combined with digital information processing,” said Adrian Ionescu, professor at EPFL and head of Nanolab.

“Our endeavors represent a significant leap forward in the domain of electronics, having shattered previous performance benchmarks, and is exemplified by the outstanding capabilities of the negative-capacitance tungsten diselenide/tin diselenide TFET and the possibility to create synaptic neuron function within the same technology,” said Adrian Ionescu, professor at EPFL and head of Nanolab.

Kamaei, S., Liu, X., Saeidi, A. et al. Ferroelectric gating of two-dimensional semiconductors for the integration of steep-slope logic and neuromorphic devices. Nat Electron (2023).

Ballpoint pen for LEDs

Researchers from Washington University in St. Louis developed ink pens that allow individuals to handwrite flexible, stretchable optoelectronic devices like LEDs and photodetectors on everyday materials including paper, textiles, rubber, plastics, and 3D objects.

“Handwriting custom devices was a clear next step after the printer,” said Chuan Wang, associate professor of electrical & systems engineering at WUSL. “We had the inks already, so it was a natural transition to take the technology we had already developed and modify it to work in regular ballpoint pens where it could be cheap and accessible to all.”

The team said that a ballpoint pen, filled with specially designed inks made of conductive polymers, metal nanowires, and perovskite materials enable a wide spectrum of emission colors. By writing layer upon layer with these functional inks, much like using multicolored pens, a variety of functional devices including disposable electronics, such as smart packaging, and personalized wearables, such as biomedical sensors, could be created.

Junyi Zhao demonstrates using a simple ballpoint pen to write custom LEDs on paper (left). The same pens can be used to draw multicolored designs on aluminum foil (top right) and to create light up sketches (bottom right). (Credit: Wang lab / Washington University in St. Louis)

Adapting printable ink to a standard ballpoint pen that was feasible for handwriting on everyday materials required a few tweaks to control wettability and improve writability. Most importantly, they had to make sure the ink could be applied to porous and fibrous substrates, including paper and textiles, without running or mixing.

“The translation from printer to ballpoint pen might look simple, but it’s actually a bit trickier than just loading ink,” said Junyi Zhao, a doctoral candidate at WUSL. “Our ink is specially formulated, so the pens are universal, meaning they’ll work on almost all substrates. Each single layer of the device is designed to be intrinsically elastic so it will survive deformation and can be bent, stretched and twisted without impacting device performance. For example, LEDs drawn on a glove could tolerate deformations from repeated fist grasping and releasing, and LEDs drawn on a rubber balloon could survive inflation-deflation cycles over and over.”

Wang added, “One area we’re really excited about is medical applications. Handwritten light emitters and detectors allow more patient-specific flexibility in creating wearable biomedical sensors and bandages that could have photodetectors and infrared LEDs drawn onto them for measuring pulse oximetry or to speed wound healing.”

Zhao, J., Lo, LW., Yu, Z. et al. Handwriting of perovskite optoelectronic devices on diverse substrates. Nat. Photon. (2023).

Battery for smart contact lenses

Researchers from Nanyang Technological University Singapore developed a flexible battery as thin as a human cornea, which stores electricity when it is immersed in saline solution and could potentially be used to power smart contact lenses.

The battery is made of biocompatible materials and does not contain wires or toxic heavy metals. It has a glucose-based coating that reacts with the sodium and chloride ions in the saline solution surrounding it, while the water the battery contains serves as the wire or circuitry for electricity to be generated.

In tests, the team demonstrated that the battery could produce a current of 45 microamperes and a maximum power of 201 microwatts, which would be sufficient to power a smart contact lens. It could be charged and discharged up to 200 times.

The team suggests that the battery would be placed for at least eight hours in a solution that contains a high quantity of glucose, sodium, and potassium ions, to be charged while the user is asleep. The battery could also be powered by human tears, as they contain sodium and potassium ions, at a lower concentration. Testing the current battery with a simulated tear solution, the researchers showed that the battery’s life would be extended an additional hour for every twelve-hour wearing cycle it is used.

“Although wireless power transmission and supercapacitors supply high power, their integration presents a significant challenge due to the limited amount of space in the lens. By combining the battery and biofuel cell into a single component, the battery can charge itself without the need for additional space for wired or wireless components. Furthermore, the electrodes placed at the outer side of the contact lens ensures that the vision of the eye cannot be obstructed,” said Li Zongkang, a PhD student from NTU.

The researchers plan further research to improve the amount of electrical current their battery can discharge. They will also be working with several contact lenses companies to implement the technology.

Jeonghun Yun, Zongkang Li, Xinwen Miao, Xiaoya Li, Jae Yoon Lee, Wenting Zhao, Seok Woo Lee, A tear-based battery charged by biofuel for smart contact lenses, Nano Energy, Volume 110, 2023, 108344, ISSN 2211-2855,

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