Silicon transistors, used for signal amplification and switching, are critical components in most electronic devices, from smartphones to cars. However, silicon semiconductor technology is hampered by fundamental physical limitations that prevent transistors from operating below a certain voltage.
This limitation, known as “Boltzmann’s tyranny,” hinders the energy efficiency of computers and other electronic devices, especially with the rapid development of artificial intelligence technologies that require faster calculations.
To overcome this fundamental limitation of silicon, MIT researchers used a unique set of ultrathin semiconductor materials to fabricate a different type of three-dimensional transistor.
Featuring vertical nanowires just a few nanometers wide, the company’s devices can achieve performance comparable to state-of-the-art silicon transistors while efficiently operating at much lower voltages than traditional devices.
“This is a technology that has the potential to replace silicon, so it has all the functionality that silicon currently has, but with much more energy efficiency,” said Dr. said Yangji Xiao, lead author of the technology paper. transistor.
This transistor uses quantum mechanical properties to simultaneously achieve low voltage operation and high performance within an area of just a few square nanometers. Their extremely small size allows more 3D transistors to be packed on a computer chip, resulting in more energy-efficient, faster, and more powerful electronics.
“Traditional physics can only do so much. Yanjie’s work shows we can do better than that, but we need to use a different physics.” Many challenges still need to be overcome for this approach to be commercialized in the future, but conceptually, this is truly a breakthrough,” said lead author, Massachusetts Institute of Technology Electrical Engineering・Jesus del Alamo, Donner Professor of Engineering in the Department of Computer Science. (EECS).
Zhu Li, professor of nuclear engineering at Tokyo Electric Power Company and professor of materials science and engineering at Massachusetts Institute of Technology, also contributed to this paper. EECS graduate student Hao Tang. MIT Postdoctoral Fellow Baoming Wang; Professors Marco Parra and David Esseni of the University of Udine, Italy; The study is published today in Nature Electronics.
More than silicon
In electronic devices, silicon transistors often act as switches. When voltage is applied to a transistor, electrons move across the energy barrier from one side to the other, switching the transistor from “off” to “on”. By switching transistors, binary numbers are expressed and calculations are performed.
The switching slope of a transistor reflects the sharpness of the “off” to “on” transition. The steeper the slope, the less voltage is required to turn on the transistor and the more energy efficient it is.
However, because of the way electrons move across energy barriers, Boltzmann tyranny requires a certain minimum voltage to switch a transistor at room temperature.
To overcome the physical limitations of silicon, MIT researchers used a different set of semiconductor materials, gallium antimony and indium arsenide, and engineered their devices to take advantage of a unique phenomenon in quantum mechanics called quantum tunneling. I designed it.
Quantum tunneling is the ability of electrons to pass through barriers. The researchers took advantage of this property to create tunnel transistors that encourage electrons to penetrate energy barriers rather than cross them.
“Now you can turn the device on and off very easily,” Shao says.
However, although tunnel transistors enable steep switching slopes, they typically operate at low currents, which hinders the performance of electronic devices. Higher currents are required to create powerful transistor switches for demanding applications.
Fine-grained manufacturing
Using tools at MIT.nano, MIT’s state-of-the-art nanoscale research facility, engineers were able to carefully control the 3D shape of the transistor and create vertical nanowire heterostructures just 6 nanometers in diameter. Ta. They believe this is the smallest 3D transistor ever reported.
This precision engineering allows us to simultaneously achieve steep switching slopes and high currents. This is made possible by a phenomenon called quantum confinement.
Quantum confinement occurs when electrons are confined in a space so small that they cannot move. When this happens, the effective mass of the electrons and the properties of the material change, allowing for stronger tunneling of electrons through the barrier.
Because transistors are so small, researchers can engineer very strong quantum confinement effects while creating very thin barriers.
“We have so much flexibility in designing these material heterostructures that we can achieve very thin tunnel barriers, which allow us to obtain very high currents,” Shao says.
Precisely manufacturing a device large enough to accomplish this was a major challenge.
“We are really interested in the single nanometer dimension with this research. There are very few groups in the world that can make good transistors in this range.” They are very good at making transistors,” Del Alamo said.
When the researchers tested the device, the switching slope steepness was below the fundamental limit achievable with traditional silicon transistors. Their device performed about 20 times better than similar tunnel transistors.
“This is the first time we have been able to achieve such sharp switching steepness with this design,” adds Shao.
Researchers are currently working to enhance manufacturing methods to make transistors more uniform across the chip. In such small devices, even a nanometer difference can change the behavior of the electrons and affect the operation of the device. In addition to vertical nanowire transistors, they are also investigating vertical fin structures that could improve the uniformity of devices on a chip.
“This work is definitely in the right direction and significantly improves the performance of break-gap tunneling field-effect transistors (TFETs), which exhibit a steep slope with record drive currents. “We highlight the importance of small dimensions, extreme confinement, and low-defect materials and interfaces in TFETs. These features have been achieved through well-mastered and nanometer-sized controlled processes.” said Aryan Afzarian, a key member of the technical staff at electronics research organization imec, who was not involved in the research.
This research received funding in part from Intel Corporation.
