The possibility of using new materials to replace silicon

The possibility of using new materials to replace silicon

In today's semiconductor industry, heat dissipation can almost be said to be the most important aspect that cannot be ignored except for PPA (power consumption, performance, and area). Taking mobile SoC as an example, the problem of chip overheating and frequency reduction affects any smartphone on the market.

But to greatly improve the heat dissipation performance of semiconductors themselves, almost all of them have to start from materials, which means we must overturn the stable position established by silicon for decades.

In the latest issue of the journal Science, two papers on cubic boron arsenide were published simultaneously, describing the possibility of this new material replacing silicon.

As mentioned at the beginning, excellent thermal conductivity has become a bottleneck for semiconductors to further improve their performance and be put into use in various scenarios. Therefore, people have started to develop semiconductor materials with high thermal conductivity,

That's why silicon carbide with a thermal conductivity of up to 500W/mK has gradually entered the automotive and aerospace markets, as its thermal conductivity is more than three times that of traditional silicon materials.

As early as 2018, researchers discovered that this boron arsenide material may have a higher thermal conductivity. Through testing of single crystal boron arsenide, its local room temperature thermal conductivity can exceed 1000W/mK, with an average value of around 900W/mK.

In subsequent studies, researchers found that if cubic boron arsenide structure is chosen, a thermal conductivity of 1200W/mK can be achieved, which is nearly ten times that of silicon materials and about three times that of materials such as silicon carbide and copper.

High carrier mobility is not just about high thermal conductivity, there is another important parameter, which is carrier mobility (electron mobility and hole mobility), which is also the focus of two papers.

Higher carrier mobility means faster logical operation speed in semiconductors, which enables higher performance in high-density semiconductor chips. This is precisely because materials such as silicon carbide and gallium nitride cannot compare to silicon in terms of electron mobility and hole mobility,

So it has not been widely used in the manufacturing of logic chips, mainly for power semiconductors.

In the paper published by the team of Academician Gang Chen from the Massachusetts Institute of Technology and Professor Zhifeng Ren from the University of Houston, they utilized the new technology of transient grating spectroscopy developed by MIT. With this ultrafast laser grating system, the electrical properties of materials can be measured simultaneously

Thermal performance. And another paper was published by the research team of Liu Xinfeng from the National Nanotechnology Center, in collaboration with the teams of Bao Jiming and Ren Zhifeng from the University of Houston in the United States. They built a "ultrafast carrier diffusion microscopy imaging system" for real-time in-situ observation.

These two papers found that the mobility of cubic boron arsenide is around 1600cm2/Vs, which is about 14% higher than silicon and surpasses third-generation semiconductor materials such as silicon carbide and gallium nitride. However, compared to gallium arsenide, which claims to have ultra-high electron mobility

There is still a considerable gap compared to the materials.

That being said, the superior conductivity and thermal conductivity have already set a good example for replacing silicon materials?

The performance may have reached the standard, but mass production is the challenge. As we mentioned in previous articles, silicon, as one of the most abundant elements, can be found almost everywhere. However, in order to be used as a semiconductor material, high-purity quartz sand of 5N or more is also required.

At present, cubic boron arsenide is not sufficient in reserves to compete with silicon, and purification and preparation are not only limited to laboratory scale, but also face many challenges. For example, ionizing impurities can lead to a decrease in carrier mobility, while neutral impurities can also reduce thermal conductivity.

Moreover, in order for cubic boron arsenide to replace silicon's dominant position, besides mobility and thermal conductivity, other material properties must also be sufficiently excellent, such as long-term stability.

In addition, with the rise of optoelectronic applications, currently three to five groups of semiconductors, such as gallium arsenide, gallium nitride, and boron nitride, are beginning to be applied in high-efficiency solar cells, solid-state lighting, and high-power, high-speed transistors,

However, the optical parameters of cubic boron arsenide still need to be explored. In 2020, there were also related research papers analyzing the optical properties of cubic boron arsenide, including the complex dielectric function, refractive index, and absorption coefficient in the ultraviolet, visible, and near-infrared wavelength ranges. Only after knowing these parameters can there be a reference for optoelectronic design using this material.

Although cubic boron arsenide has shown promising prospects in terms of thermal conductivity and mobility, there is still a long way to go before it can be officially put into commercial use. At present, the biggest advantage of cubic boron arsenide is still its thermal conductivity. In the future, it is likely to be used in some semiconductor scenarios with higher thermal requirements, and even as a thermal conductivity medium for traditional silicon-based semiconductors.