The long-awaited future of developing electronic components that can be worn on the skin or on clothing has so far proven too elusive, but researchers from Stanford University claim that they have succeeded in bringing about a breakthrough in this field
![Description of the transfer process for a two-dimensional semiconductor together with nanoprinted contacts (left) and a photo of a transparent, flexible substrate with the structure transferred to it (right) [Courtesy: Victoria Chen/Alwin Daus/Pop Lab]](https://www.hayadan.org.il/images/content3/2021/07/2D-Semiconductor-With-Nanopatterned-Contacts-Manufacturing-1536x8741-1.jpg)
[Translation by Dr. Moshe Nachmani]
Computer printed circuits, which are extremely thin and flexible, have been an engineering goal for many years, but technical bumps have prevented them from reaching the level of miniaturization required to achieve high performance. Now, researchers from Stanford University have succeeded in inventing a manufacturing method that allows the acceptance of flexible transistors, one-atom thick and less than a hundred nanometers long - many times smaller than any transistor developed so far. The method is detailed in an article published a long time ago in the prestigious scientific journal Nature Electronics.
In light of the progress made by the Stanford researchers, they claim that the field called "flextronics" is now closer than ever to reality. Flexible electronic components guarantee the production of bendable computer circuits, for structural design and operation while maintaining efficient energy requirements, components that can be worn on the body and even implanted inside the body to perform a myriad of health-related tasks. Moreover, the rising field of the "Internet of Things", where almost every device in our daily lives will be integrated and interfaced with flexible electronic components, should also benefit from such electronic components.
Two-dimensional semiconductors
Among the most suitable materials for the development of flexible electronic components, XNUMXD semiconductors have shown good performance thanks to their mechanical and electronic properties, even at the nanoscale, properties that make them better candidates than organic or conventional silicon-based materials. The engineering challenge until now has been that the production of such extremely thin devices requires the use of a process that requires too much heat for the plastic substrate - these flexible materials will simply melt and break down during production. The solution, the researchers explain, lies in carrying out this process in stages, starting with a basic substrate that is not flexible at all. On top of a solid slab of glass-coated silicon, the researchers created a thin, atomically thick layer based on a two-dimensional semiconductor of molybdenum disulfide (MoS2) covered with nanometric gold electrodes with a defined structural pattern. In view of the fact that this step is carried out on a normal silicon substrate, the nanometer dimensions of the transistor can be designed with the help of advanced design methods, while obtaining a separation capacity that is not otherwise possible on a flexible plastic substrate. The layer production method, known as "Chemical Vapor Deposition" (CVD), allows the addition of only one atomic layer of MoS2 Every time. The resulting final layer is only three atoms thick, but it requires a temperature of 850 degrees Celsius in order for it to function properly. For comparison, the familiar flexible substrate - which consists of polyimide (thin plastic) - would already lose its shape and deform at a temperature of 360 degrees Celsius, and even completely disintegrate as the temperature goes up and up.
By first creating these essential parts on a rigid silicon substrate and cooling the system, the researchers can get the flexible material in its required configuration without damaging it. With a simple bath of deionized water, the entire internal device peels away from the outer layer, and is now fully transferred to the flexible polyimide. After several additional manufacturing steps, the result is a flexible transistor capable of providing higher performance than any other semiconductor-based single-atom transistor. "In the end, the final structure is only five microns thick, including the flexible polyimide, explains the lead researcher. This size is ten times smaller than the thickness of a human hair."
After creating the prototype and applying for a patent for their product, the researchers move on to the next challenges they face, mainly to improve the device. They have already made similar transistors using other monoatomic semiconductor materials, MoSe2 and WSe2, this is in order to demonstrate the broad applicability of the method. Meanwhile, the lead researcher explains that he will try to integrate radio circuits into the device in the future, a result that will enable the development of miniaturized and flexible wireless communication in the future, especially in those devices intended for implantation inside the human body, for example a pacemaker. "The results of our research are much more than a promising manufacturing method - we were able to achieve flexibility, density, high performance and low stress - all the features together at the same time."
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