Rethink the transistor at the material level！

Rethink the transistor at the material level

While many researchers focus on the miniaturization of transistors, others are looking to materials science to advance this building block of modern electronics.

Transistors have reached their physical limits in terms of size and speed. As transistors get smaller, the distance between source and drain decreases, resulting in a high drain current. And as transistors approach the atomic scale, it is harder to control the current, leading to a higher chance of miscalculation.

Smaller transistors mean slower switching speeds, which is particularly problematic in newer applications such as artificial intelligence, where large data sets need to be processed. More intensive integration is also a challenge due to stacking and thermal management issues.

This paper discusses recent advances that push the boundaries of existing transistor technology and how they are moving beyond current devices.

Two-dimensional materials are grown on silicon CMOS wafers

Current transistors are bulky and not easily stacked vertically to achieve high density. For this integration, the transistor must be made of an ultra-thin, two-dimensional material only a few atoms thick. However, growing two-dimensional material on silicon wafers is challenging because it typically requires temperatures of around 600°C, while circuits can only withstand 400°C at best.

To solve these problems, researchers at the Massachusetts Institute of Technology (MIT) have developed a cryogenic process that can grow two-dimensional materials on chips without damaging them. The new process reduces the time required to create a two-dimensional material and creates an even layer across the entire surface area. As a result, the new process can be used on larger surfaces than traditional processes.

The MIT researchers focused on molybdenum disulfide, a transparent flexible material with electron and photon properties, to demonstrate and validate their new process. Their process is placed in an oven with two chambers: a cold area at the front and a hot area at the back. The wafer is placed in the front, so it remains intact. The vaporized molybdenum and sulfur precursors are pumped into the furnace. Molybdenum remains in front and sulfur precursor flows and decomposes in high temperature region. After it breaks down, it flows back into the greenhouse, where it grows molybdenum disulfide.

The researchers placed the wafer vertically in the front chamber, so that neither edge was too close to the hot area. They also deposited a thin layer of passivating material on top of the chip to prevent vulcanization of metals such as aluminum and copper, which are commonly used to connect silicon circuits in packages or carriers. The passivation layer is then removed for connection. The researchers plan to fine-tune their technology and explore applications of the process on flexible surfaces such as polymers, textiles and paper.

New materials compete with silicon - based transistors

Researchers at Forschungszentrum Julich explored materials with more favorable electronic properties than silicon for use in circuits with better performance. They recently made a germanium-tin alloy that has many advantages over conventional silicon transistors.

Germanium exhibits higher electron mobility than silicon. The researchers added tin atoms to the germanium lattice to further optimize the material's electronic properties. The electron mobility of the new alloy is 2.5 times higher than that of pure germanium transistors and is compatible with current CMOS manufacturing processes.

The new transistors can operate at temperatures as low as 12 Kelvin - an important improvement over existing transistors, which require high voltages to switch at temperatures below 50 Kelvin and thus consume more power. With further improvements, the scientists claim, their alloy could even allow transistors to operate at temperatures below 12 Kelvin. The team believes their technology is a promising candidate for the next generation of low-power, high-performance chips, as well as future quantum computers.

Wood transistor

Researchers at Linkoping University and KTH Royal Institute of Technology have created a transistor out of wood. To do this, they used balsa wood, a non-textured, evenly structured wood. They removed the lignin, leaving only cellulose fibers with channels, and filled them with a conductive polymer called PEDOT:PSS.

The team found that their device could regulate the current and provide continuous operation at a selected output level. However, the switching time is very long. It takes about a second to close and about five seconds to open.

According to the researchers, these organic transistors can be used in high-power applications because they can withstand high currents. While the team has not yet created the device for any specific application, they hope their research will pave the way for organic electronics in the future.

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