Stanford’s Technology for Flexible Electronics with Molybdenum Disulfide

Stanford’s Technology for Flexible Electronics with Molybdenum Disulfide

At present, wearable flexible electronics are difficult to manufacture, but Stanford University researchers stated they have made breakthroughs, which use the molybdenum disulfide (MoS₂). Ultrathin flexible computer circuits have been an engineering goal for many years, but technically hindered the degree of miniaturization necessary to achieve high performance.

Recently, researchers at Stanford University have invented a manufacturing technique that can yield flexible, atomically thin transistors with a length of fewer than 100 nanometers. these transistors are several times shorter than before. The researchers detailly present the technique in a paper published in Nature Electronics.

With this progress, said the researchers, ‘flexible electronics’ will be closer to reality. Flexible electronic devices are expected to be bendable and shapeable, and are worn or implanted in the human body to perform various health-related tasks. More importantly, the Internet of Things refers to almost every device in our lives is interconnected with flexible electronic devices, and should also benefit from flexible electronic technology.

So far, the engineering challenge is that the flexible materials of wearable flexible electronic products would simply melt and decompose during the production process.

According to Eric Pop, a professor of electronic engineering at the University, and Alwin Daus, a postdoctoral scholar in Pop‘s Lab, who developed the technology, a solution is a step-by-step approach, starting with a non-flexible base substrate, that is, on a piece of solid silicon coated with glass. On the board, a layer of atomic-level two-dimensional semiconductor molybdenum disulfide film is formed, overlaid with small nano-patterned gold electrodes.

Due to this step is performed on a traditional silicon substrate, the nano-scale transistor sizes can be patterned with existing advanced patterning techniques, achieving a resolution that is impossible on a flexible plastic substrate.

The layering technique called chemical vapor deposition grows only one atomic MoS₂ film at a time. The resulting film is only three atoms thick, but it needs to reach 850 degrees Celsius to function.

In contrast, the flexible substrate made of polyimide loses its shape long ago at around 360 degrees Celsius and completely decomposes at higher temperatures.

The researchers firstly draw patterns on the hard silicon and form the critical components, and then cool it to apply flexible materials without damage. By immersing in deionized water, the entire device stack is peeled off and completely transferred to the flexible polyimide.

After several additional manufacturing steps, the result is that the performance of flexible transistors is several times higher than that of any product previously produced with atomically thin semiconductors.

The researchers said that although the entire circuit can be built and then transferred to a flexible material, some complications in the subsequent layers make these additional steps easier after transfer.

Finally, the entire structure is only 5 microns thick, including flexible polyimide, which is about ten times thinner than human hair.

Although the Stanford’s technological achievement of producing nanoscale transistors on flexible materials with molybdenum disulfide is remarkable, the researchers also describe their flexible electronics as "high-performance" devices, which in the context means they can handle high currents. At the same time, it works at low voltage, which is required for low power consumption.

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