One hundred nanometers is good! Optical chip alleviates chip bottleneck problem

Before the news that IBM has developed a 2-nanometer process chip spread, TSMC and its partners announced that they had made a technological breakthrough in the process chip below 1 nanometer. It is generally believed in the industry that with the rapid development of chip technology, it is approaching the limit of its physical theory step by step.

Recently, Tobias Kippenberg, a professor of EPFL in Lausanne, Switzerland, developed a technology for manufacturing integrated photonic circuits (photonic chips) using silicon nitride substrates, which achieved a record low optical loss and small chip size. Related research was published in Nature-Communication.

Catching up with photonic chips may help people break through the "ceiling" of Moore's Law and open up a new "track".

Silicon series and Damascus technology

Photonic chips are usually made of silicon rich in the earth's crust and have good optical properties, but it is difficult to meet all the requirements of integrated photonic chips, so many new materials have appeared to replace them, such as silicon nitride, silicon dioxide, aluminum nitride, lithium niobate and silicon carbide.

Tobias Kippenberg's team adopted silicon nitride photonic Damascus process (photonic mosaic process) technology. Damascus craft is a very old craft, which can be traced back to Arabs making colorful inlays and paintings on their weapons and decorations. In this process, we must first make the outline of the characters, and then embed the color materials into the outline and polish it, so that we can get colorful patterns.

"The idea of Damascus process was used in the manufacture of early copper electronic circuits. In the research process, we applied the silicon nitride Damascus process to the manufacture of integrated optical paths and achieved extremely low optical loss. " Dr. Liu, the first author of the paper and a doctor of micro-nano technology center, told China Science Journal, "With this technology, we have made an integrated optical path with an optical loss of only 1 dB/m, setting a record for all nonlinear photonic integrated materials."

Using this new technology, the researchers made a high quality micro resonator and a waveguide with a length of more than 1 meter on a 5 mm square chip. They also reported a manufacturing yield of 90%, which is very important for expanding the scale of industrial production in the future.

"Ultra-low-loss silicon nitride integrated photonic chips are very important for future communication, computing and 6G technology. This type of photonic chip can encode information into light and then transmit it through optical fiber, which becomes the core component of optical communication. " Liu said:

Photon integration, late, first come.

"When the electronic chip is working, it can be understood as inputting electrical signals into the chip for processing, such as storage, reading and operation. , and then output. Similarly, a photonic chip is a chip that inputs optical signals into the chip for data transmission, storage, calculation and output. " Liu said, "Compared with electronic chips, photonic chips have their own unique advantages, although they started late."

Scientists believe that light has natural parallel processing ability and mature wavelength division multiplexing technology, which greatly improves the data processing ability, capacity and bandwidth of photonic chips. Information such as wavelength, frequency, polarization state and phase of light wave can represent different data and can be used as a very effective communication seed source.

"Photonic chips have the characteristics of fast operation speed, low power consumption and low delay, and are not easily affected by temperature, electromagnetic field and noise changes." Zhang said, managing director of Zhongke Chuangxing, "Photonic chips can have more performance to improve the space, without the need to pursue extreme reduction of process size."

"Compared with electronic chips, optical chips have unique advantages in communication, lidar, sensing, image analysis and many other fields." Liu explained that the speed of the optical chip can reach 100G, which is much faster than that of the electric chip, so that more information can be encoded and carried on the optical channel, and the power consumption is smaller than that of the electric chip. Because light does not produce any thermal effect in propagation, which is different from electrons, and there is no interaction between light and light, and it will not be disturbed by background electromagnetic field.

Team Liu built an optical neural network with silicon nitride optical chips, solved the matrix with convolutional neural networks, and then applied it to relief filters. The related results were published in the journal Nature in June 5438+10 this year.

"We put an image signal into the system, and through the relief filter, it will strengthen the high-frequency signal and weaken the low-frequency signal, which is to achieve the purpose of strengthening the image edge. For example, a picture of a car, the internal structure of its original headlights you may not see. In the new image processed by the relief filter, the internal structure of the lamp has been strengthened. " Liu said, "This proves that silicon nitride photonic chips have good applications in optical neural networks and deep learning."

In addition to artificial intelligence, photonic chips are also widely used in lidar, microwave filter, millimeter wave generation, celestial spectrometer calibration, low noise microwave generation, and can also be used as mid-infrared double comb spectrum to measure the composition of gases. If applied to optical correlation tomography, we can see the structure of biological tissue. It can also be used as a data center switch for data conditioning.

Competition and cooperation between the two tracks

Liu said that it is generally understood that electronic chips are mainly used for information processing in mobile phones or computers, but information transmission requires optical fibers. Therefore, to this step, electro-optical conversion is needed. "At present, light and electricity are on two' tracks', each with its own application scenarios."

"The integrated semiconductor laser used in the Intel data center now converts electrical signals into optical signals, and then processes, encodes and transmits the data. Intel delivers tens of millions of such integrated semiconductor laser chips to the world every year. " Liu said, "Compared with the traditional discrete' optical-electrical-optical' processing method, photonic integrated circuits reduce complexity and improve reliability, and can build a brand-new network structure with more nodes at lower cost. Although it is still in the primary development stage, it has become the mainstream development trend of optical devices. "

"In the field of logic operation, the future trend is the combination of optoelectronic integration, and it will take a long time to realize all-optical computing." Zhang said, "Generally speaking, photonic chips can only replace electronic chips in individual computing and transmission fields."

Liu believes that from the architecture point of view, the whole photonic chip system is very complicated. Photonic chip system is composed of light source, processor and detector, and it also needs the integration and cooperation of various materials. Few single research units can build and prepare the whole system. In the manufacturing process, although the process and complexity of the two are similar, the structural requirements of photonic chips are not as strict as those of electrical chips, which are usually several hundred nanometers. Therefore, photonic chips do not need to use extreme ultraviolet lithography (EUV) like electronic chips.

"The wavelength of light is in the order of 100 nm to 1 micron, which limits the integration density of photonic devices. But at the same time, it also means that the optimal working conditions of optical chips do not depend on the most advanced semiconductor processes, such as extreme ultraviolet lithography. " Liu said, "This greatly reduces the dependence on advanced technology and relieves the bottleneck problem of chip development to some extent."

In addition, photonic chips provide a brand-new idea of chip design architecture, which completely subverts the original design concept and has more creative space for design.

"Light has the advantage of light, and electricity has the advantage of electricity. The advantage of light is that it is stable and not easily influenced by the outside world. At the same time, this is also the shortcoming of light, which means that people want to manipulate light and change the state of light, and the means are very limited. " Liu said, "In some application scenarios, the two also compete, such as neural networks. But more often, the two are cooperative. Optical chip technology is not as mature as electric chips at present, and there are many unknown factors. In the future, the two should be well connected. "

In this regard, Luo Jun, researcher of Institute of Microelectronics of Chinese Academy of Sciences and deputy director of R&D integrated circuit pilot technology center, holds the same view.

"There is a complementary relationship between electronic integrated circuits and photonic integrated circuits," Luo Jun told China Science News. "In the future, we can make full use of the advantages of high-speed transmission of photonic integrated circuits and multi-function and intelligence of electronic integrated circuits to run better on the new track."

Related paper information: https://doi.org/10.1038/s 41467-021-21973-z.

https://doi . org/ 10. 1038/s 4 1586-020-03070- 1