A new water-based switch is thousands of times faster than current semiconductors

Water becomes conductive within one trillionth of a second.

Researchers have developed a water-based switch that becomes conductive thousands of times faster than current state-of-art semiconductor-based switches. Such switches are used in computers, smartphones, and wireless communications.

Essentially, a short but powerful laser pulse converts the water into a conductive state within less than a trillionth of a second (10-12 seconds), during which time it behaves almost like a metal.

What are transistors?

Transistors are a crucial component in electronic devices because they can control the flow of electricity through a circuit, effectively acting as a switch. When a transistor is turned on or "saturated," it allows current to flow through it, and when it is turned off or "cut off," it does not allow current to flow.

The speed of a transistor is determined by how quickly it can switch between its conductive and non-conductive states. This is known as the transistor's switching speed or switching frequency.

The faster a transistor can switch, the faster a computer system can perform tasks.

Modern computers use a variety of techniques to increase the switching speed of transistors, including the use of advanced semiconductor materials. However, they are still "limited in their speed," explains Dr. Claudius Hoberg, author of the study, Faculty of Chemistry and Biochemistry at Ruhr-University Bochum.

Now, researchers at Ruhr University Bochum, Germany, have developed a new concept for switches with unprecedented speed.

Ultra-fast water-based switches with terahertz frequencies

To create the switch, researchers used a highly concentrated sodium iodide dissolved water- in simpler terms, salty water. And sprayed this salty water from a custom-made nozzle as a thin sheet only a few microns thick.

"Think of it like squeezing a gardening hose to make the jet of water broad and flat, only on a much smaller scale," explains Hoberg.

Next, the water jet was excited with a short but powerful laser pulse at 400 nanometers (nm). This bumps electrons out of the dissolved salts, increasing the conductivity of water. Since the laser pulse is so fast, the water becomes conductive and behaves almost like a metal.

All of this happens in less than one trillionth of a second, which translates to potential computer speeds in the terahertz (THz) range, making this water-based switch faster than the fastest semiconductor switching speed currently known. "A speed of 10-12 seconds was observed in the terahertz range," says Hoberg.

A second laser reads back the state of the water.

Faster computing

Researchers hope the findings will lead to new research avenues and water-based technologies.

Terahertz devices could someday enable much faster computing, and water-based technology could offer a more environmentally friendly alternative to rare-earth metals. However, this is just a concept at the moment.

There are still many challenges before the technology can be practically implemented in electronic systems.

The research is published in the journal APL Photonics.


Ultra-fast switches are essential devices for basic research and technological development. Here, we demonstrate that aqueous solutions of sodium iodide can be used for this purpose. When pumped with an intense optical pulse at 400 nm, these water-based liquids display large and fast responses in the terahertz range, around 1 THz. In a 9M NaI solution at a temperature comprised between 10 and 50 °C, the relative variation of the terahertz peak transmission drops by 20% at the pump–probe overlap and recovers with a fast time constant of ∼70 fs. As the optical properties of the liquid vary on a timescale shorter than the terahertz cycle, it is possible to tailor the shape of the transmitted terahertz fields. In this way, we demonstrate the frequency upshifting of terahertz radiation from about 1 to 3 THz and beyond with an efficiency of 4%.

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