Diamond extension for next generation microelectronics

The elongation of microfabricated diamonds paves the way for next-generation microelectronics applications. Credit: Dang Chaoqun / Hong Kong City University

Diamond is the hardest material in nature. But among many expectations, it has great potential as an excellent electronic material. A joint research team led by City University of Hong Kong (CityU) has demonstrated for the first time a uniform and uniform elastic traction of microfabricated diamond matrices through a nanomechanical approach. Their findings have shown that narrowed diamonds are the leading candidates for advanced functional devices in microelectronics, photonics, and quantum information technologies.

The research was led by Dr. Lu Yang, an associate professor in the CityU Department of Mechanical Engineering (MNE) and a researcher at the Massachusetts Institute of Technology.WITH ONE) and the Harbin Institute of Technology (HIT). Their findings have just been published in the prestigious scientific journal Science, entitled “Achieving High Uniform Traction Elasticity in Microfabricated Diamond”.

“This is the first time that a very high and uniform elasticity of diamond has been shown through tensile experiments. Our findings have shown that electronic devices can be developed through microfabricated diamond structures ‘through deep elastic stress engineering’,” said Dr. Lu.

Diamond: electronic material “Mount Everest”

Known for its hardness, the industrial applications of diamonds are usually cutting, drilling or grinding. But diamond is also considered a high-performance electronic and photonic material due to its very high thermal conductivity, exceptional mobility of the electric charge carrier, high fracture resistance, and very wide bandwidth. Bandgap is a key property of semiconductors, and broadbandgap allows the operation of high-power or high-frequency devices. “That’s why diamond can be said to be the‘ Mount Everest ’of electronic materials because it has all these excellent properties,” Dr. Lu said.

Traction filter for diamond bridges

Illustration of a microfabricated diamond bridge sample traction filter. Credit: Dang Chaoqun / Hong Kong City University

However, large bandwidths and narrow crystal structures of the diamond make it difficult to “drug”, a common way of modulating the electronic properties of semiconductors in production, and thus hinder the industrial application of diamonds in electronic and optoelectronic devices. A potential alternative is “deformation engineering”, which involves the application of high-voltage grid, changing the structure of the electronic band, and the associated functional properties. But it was considered “impossible” for diamond due to its very high hardness.

In 2018, Dr. Lu and his collaborators found, surprisingly, that a diamond with nanoscale scales can be elastically bent with unexpectedly high local stresses. This finding suggests that changes in the physical properties of diamond are possible through the engineering of elastic stresses. Based on this, recent research has shown how this phenomenon can be used to develop functional diamond devices.

Uniform voltage drop across the sample

The group first made microfabricated single-crystal diamond samples, single-crystal single-crystal. The samples were bridge-shaped – one micrometer long and 300 nanometers wide, to capture the two wider ends (see Figure 2). The diamond bridges were extended uniaxially in a well-controlled electron microscope. During the continuous and controlled load-discharge cycles of quantitative stress tests, diamond bridges showed a very uniform and high elastic deformation, with a stress of about 7.5%, across the sample section across the section, rather than deformed in a localized bending area. And after downloading they were restored to their original form.

By further optimizing the sample geometry using the American Society for Testing and Materials (ASTM) standard, they achieved a uniform tensile deformation of up to 9.7%, which also exceeded the local maximum value in the 2018 study and was close to theoretical. the elastic limit of the diamond. More importantly, to demonstrate the concept of a tightened diamond device, the team also performed an elastic filter of microfabricated diamond matrices.

Adjust the band gap by means of elastic tensions

The group then performed functional density theory (DFT) calculations to calculate the effect of elastic stress on the electronic properties of the 0-12% diamond. The results of the simulation indicated that the overall band gap of the diamond decreased as the tensile stress increased, reducing the maximum band gap reduction rate from 5 eV to 3 eV, a voltage of about 9%, during a specific crystalline orientation. The group performed an electron loss spectroscopy study on a predicted diamond sample and verified the downward trend of the band side.

Their calculation results showed, interestingly, that the bandwidth ranges from indirect to direct with a voltage range greater than 9% across a different crystalline orientation. This means that there is a direct band gap in a semiconductor and that electrons can emit photons directly, allowing a wide range of high-efficiency optoelectronic applications.

These discoveries are the first step towards deep elastic tensile engineering of microfabricated diamonds. From a nanomechanical point of view, the team demonstrated that the structure of the diamond band can change and, more importantly, that these changes can be continuous and reversible, allowing for different applications, from micro / nanoelectromechanical systems (MEMS / NEMS) to voltage transistors to novelty. optoelectronic and quantum technologies. “I think we have a new era of diamond ahead of us,” Dr. Lu said.

Reference: Chaoqun Dang, Jyh-Pin Chou, Bing Dai, Chang-Ti Chou, Yang Yang, Rong Fan, Weitong Lin, Fanling Meng, Alice Hu, Jiaqi Zhu, Jiecai Han, “Achieving high uniform elasticity in microfabricated diamond.” Andrew M. Minor, Ju Li and Yang Lu, January 1, 2021, Science.
DOI: 10.1126 / science.abc4174

Dr. Lu, Dr. Alice Hu, also from the CityU MNE, Professor Li Ju from MIT, and Professor Zhu Jiaqi from HIT are the authors of the article. The first authors are Dr. Dang Chaoqun with a degree and Dr. Chou Jyh-Pin, a former PhD from CityU MNE, Dr. Dai Bing from HIT and Chou Chang-Ti from Chou Chang National University. CityU Dr. Fan Rong and Dr. Lin Weitong are also part of the team. Other collaborating researchers are from the Lawrence Berkeley National Laboratory. University of California, Berkeley, and Southern University of Science and Technology.

CityU’s research is funded by the Hong Kong Research Grants Council and the National Foundation for Natural Sciences of China.

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