Four-inch rBN wafers support durable ferroelectric memory

Researchers have fabricated four-inch single-crystal rhombohedral boron nitride wafers and used the material to produce ferroelectric field-effect transistors with nanosecond switching and endurance beyond two billion cycles. Rhombohedral boron nitride, or rBN, consists of stacked atomic layers whose relative position gives the material a switchable electrical polarisation. That polarisation can represent a stored state without requiring power to maintain it. The work, published in Nature Nanotechnology , addresses the difficulty of producing the material uniformly over an area large enough for batch device fabrication. Reported memory performance The researchers fabricated FeFETs with channel lengths down to 30nm. They reported an on/off current ratio of 10 6 , a memory window of approximately 4V and switching on a nanosecond timescale. The devices completed more than 2 × 10 9 switching cycles. The team also projects ten-year non-volatile retention and reports operation at temperatures above 470K. Projected retention is not the same as a completed ten-year test. It is normally derived from shorter measurements performed at elevated temperatures or under accelerated conditions. The endurance, retention and device-to-device distributions would therefore need to be reproduced across production-scale arrays. Scaling the material Earlier rBN memory demonstrations generally used small flakes or limited-area films. Producing a four-inch single-crystal wafer allows multiple devices to be fabricated in repeatable batches and measured across the same substrate. The layered material could potentially be integrated with conventional semiconductor structures without requiring the same crystal-lattice match as a traditional epitaxial semiconductor. Its thin active region is also relevant to vertically stacked memory and logic. However, a laboratory wafer is not yet a manufacturing process. Transfer, patterning, contamination control, contact formation and integration with back-end interconnects remain important development stages. Memory and computing applications Ferroelectric transistors can combine a switching device and stored state in one structure. This has prompted research into non-volatile memory, in-memory computing and accelerator architectures in which stored weights or intermediate data are positioned close to the computing elements. The rBN work establishes a larger-area material platform with unusually strong experimental endurance. Further results will be needed to demonstrate array yield, error rates, peripheral circuitry and compatibility with existing wafer-processing equipment.