Researchers from the Massachusetts Institute of Technology (MIT) in the United States have developed a relatively inexpensive and scalable technology for combining high-speed gallium nitride transistors with standard silicon chips.
A promising semiconductor material such as gallium nitride is expected to play a key role in the development of next-generation high-speed communication and power electronics systems. However, its widespread use will still be limited by its high cost and the need for special technologies.
In an effort to solve these problems, researchers at MIT have developed a new process that integrates high-performance gallium nitride transistors with standard silicon chips. This method involves creating a large number of tiny transistors on the surface of a gallium nitride chip. Each of them is cut out separately and only the necessary ones are combined with the silicon chip. This is done using a low-temperature technology that does not compromise the performance of either material.
Since the each chip a small amount of gallium nitride is added, and costs remain relatively low. At the same time, such chips become much more productive due to compact high-speed transistors. The distribution of gallium nitride transistors over the area of the silicon chip also reduces the overall system temperature.
Using this method, MIT researchers have created power amplifier, is critical for smartphones, delivering stronger signals and better efficiency than traditional silicon-based counterparts. In the case of a smartphone, this means a more stable connection, more reliable wireless communication, and longer battery life. The new method could also improve quantum computing and lead to quantum applications, as gallium nitride is more stable and efficient than silicon at low temperatures.
«If we can reduce the cost, improve scalability, and at the same time increase the performance of an electronic device, then we should definitely adopt this technology. We have combined the best of silicon with the best possible electronics based on gallium nitride. These hybrid chips have the potential to revolutionize many commercial markets, — says lead author of the study, MIT graduate student Pradyot Yadav.
Scientists have been working for a long time to combine gallium nitride chips with silicon chips. Some methods involve integrating gallium nitride transistors into a silicon chip by soldering of connections, which limits the size of transistors. The smaller the transistors, the higher the frequency at which they can operate.
Other methods integrate an entire gallium nitride wafer on top of a silicon wafer, but this is very costly. And gallium nitride is only needed in a small number of tiny transistors.
In their method, scientists from MIT first fabricates a tightly packed set of transistors across the surface of a gallium nitride wafer. Using a very thin laser, they trim each of the transistors to a size of 240 by 410 microns. Each transistor has tiny copper columns on top that are used to connect to copper columns on the surface of the silicon chip. These connections can be made at temperatures below 400 C°, which avoids damage to the materials.
To integrate gallium nitride transistors with silicon chips, scientists have created an innovative tool that can carefully place tiny GaN transistors on the surface of a silicon chip. This process uses a vacuum to hold the transistors while moving the tool across the surface of the silicon chip. The researchers used advanced microscopy to monitor the process. When the transistors are in the desired position, heat and pressure are used to attach them to the silicon chip.
After the researchers perfected the fabrication process, they demonstrated it by developing power amplifiers, which are radio frequency circuits that amplify wireless signals. Their devices have achieved higher bandwidth and better gain than devices made using traditional silicon transistors. Each compact chip has an area of less than half a square millimeter.
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