TRANSISTOR TECHNOLOGY Magnetic transistor breakthrough could enable energy-efficient chips

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MIT engineers demonstrated a new type of magnetic transistor that performs the three-in-one action of current switching, amplification, and memory storage. The industry is continuously seeking silicon alternatives to enhance the operability and efficiency of end-products.

Transistors made from magnetic materials may be able to replace silicon-based transistors and prove to be more energy-efficient. The integration of magnetic materials in the semiconductor world has been actively researched.

Magnetic transistor

Between magnetics and electronics, spintronics is a sweet spot. Spintronics, or spin electronics, is an emerging technology that manipulates the intrinsic spin of electrons and their associated magnetic moments, along with electric charge, to store data.

The spin of an electron is a type of orientation related to the spin quantum number. There are only two spins, up and down. In the late nineties, spin transistors (spinFETs) were theorized. Modern spintronics could solve the memory wall problem, where memory performance lags significantly behind processor speed.

Hero of the experiment: Chromium sulfur bromide

Studies have shown that a change in the magnetic state of a material can affect the electronic band structure. The experiment published in a journal explores how magnetic transitions can also affect the movement of charge flow through the material. The newly developed transistor uses the magnetic semiconductor chromium sulfur bromide (CrSBr).

Mini-magnet

Chromium sulfur bromide is an air-stable semiconductor. The structure contains stacked layers weakly bonded by van der Waals forces. This means that chromium sulfur bromide can be transformed into a 2D semiconductor, which correlates to a smaller chip size. The bandgap energy of chromium sulfur bromide is slightly more than that of silicon.

Antiferromagnetism

Chromium sulfur bromide is an antiferromagnetic semiconductor, in which the magnetic moments/spins of neighboring atoms point in opposite directions, resulting in no overall magnetization. The benefit of choosing an antiferromagnetic material is the absence of stray magnetic fields, less interference between nearby devices, and ultra-fast switching in the THz range.

Using gum?

Electrodes are patterned, and a 2D van der Waals material is placed onto a silicon substrate using a gum/tape. The manufacturing process involved using a highly clean, contamination-free surface. The optimized process aims to reduce various types of defects in the end device.

On and off states

The experiment involved examining the properties of the antiferromagnetic transistor across a wide range of carrier densities, controlled using the gate voltage. Due to the structure, an external field can drive the transistor to switch between two magnetic states, similar to on and off processes in silicon transistors.

What is magnetoresistance?

The results demonstrated that chromium sulfur bromide exhibits a different magnetoresistance behavior at low and high densities, respectively. Magnetoresistance refers to the change in electrical resistance of a material when it is subjected to a magnetic field. The magnetic transistor merges conventional transistor operations of switching currents with storing information.

Results

Experimental results, simulation, and theoretical modeling focus on magnetically induced changes in carrier concentration at low densities and changes in carrier mobility at high densities. Through the experiment, MIT engineers demonstrated how antiferromagnetic semiconductors can open the doors for faster chips.

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Where can this discovery of magnetic transistors lead?

The transistor made from chromium sulfur bromide can function like a group of tiny magnets, offering optimal magnetic state control through external electric fields. As a result, the magnetic transistor can switch currents - switch between on and off states.

The magnetic transistor can also amplify currents with a gain of about 10. Better switching performance enables faster and more reliable readouts. The new development consumes significantly less energy than silicon.

Semiconductor memory

Semiconductor memory is where magnetism and semiconductors integrate. Chromium sulfur bromide exhibits an in-built memory to retain information. Dynamic random access memory (DRAM) is the modern “memory standard” used by all GPUs and AI accelerators in data centers and consumer devices, such as computers, laptops, and smartphones.

DRAM stores each bit in a small memory cell made from a single capacitor and a transistor. Capacitors leak charge over time. As a result, capacitors must be charged and discharged periodically to retain the information. The process is known as a refresh cycle or periodic refresh.

Refresh cycles need to be executed every 64 msec in DRAM cells to prevent data loss. As a result, refresh cycles consume a significant portion of power. Chip miniaturization is further complicating the situation and increasing power consumption, which in turn increases enterprise power budgets.

A spintronic-based memory, known as magnetoresistive random access memory (MRAM), stores data using electron spins, eliminating refresh cycles for energy efficiency. MRAM is a non-volatile memory. It means that MRAM can retain information even when the power supply is not present.

MRAM is a commercial technology and a part of volume production. The ability of the magnetic transistor made from CsSBr to switch magnetic states enables faster operations. It might improve MRAM functionality in commercial applications. The 2D structure of the material is atomically thin to manufacture smaller chips.

References

• https://news.mit.edu/2025/mit-engineers-develop-magnetic-transistor-more-energy-efficient-electronics-0923

• https://journals.aps.org/prl/abstract/10.1103/hpmq-rnh4

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