A reconfigurable device based on 2D van der Waals heterostructures that functions as both a transistor and a memory

Schematic structure of the PFGFET created by the researchers, composed of graphene (purple, the partial floating gate), hexagonal boron nitride (green and purple) and tungsten diselenide (red and blue, the channel). The PFGFET can act as a memory with forward and reverse transfer characteristics and as a transistor. The device has a source electrode (S) and a drain electrode (D), and is controlled by two of the device terminals: the control gate (CG) and the top gate (TG). Credit: Sun et al, Natural electronics (2022). DOI: 10.1038/s41928-022-00858-z

One of the main goals of electronic engineering research is to develop computing devices that are both high performance and energy efficient, meaning they can calculate information quickly while consuming little power. One possible way to achieve this could be to combine units that perform logic operations and memory components in a single device.

Until now, most computing devices consisted of a processing unit and a physically separate memory component. Creating a device that can perform both of these functions efficiently, called an in-memory logic architecture, could help simplify devices dramatically and reduce their power consumption.

While a few of the in-memory logic architectures proposed so far have shown promising results, most existing solutions have practical limitations. For example, some devices have been found to be unstable, unreliable, or only applicable to specific use cases.

Researchers from Hunan University have recently developed a new reconfigurable in-memory logic architecture based on a 2D van der Waals heterostructure, structures consisting of isolated atomic layers linked together by the weak van der Waals interaction. Their device, presented in an article published in Natural electronicscan function both as a reconfigurable transistor (i.e. a device that can regulate, switch, and amplify electrical signals) and as a reconfigurable memory component.

“We report a two-dimensional van der Waals heterostructure device that can function as both a reconfigurable transistor and a reconfigurable non-volatile memory, as well as provide reconfigurable in-memory logic capabilities,” Xingxia Sun, Chenguang Zhu, Jiali Yi and colleagues write. in their diary. “The device architecture, called a partial floating-gate field-effect transistor, offers both charge trapping and field regulating units.”

The in-memory logic device created by Sun and his colleagues was called a partial floating-gate field-effect transistor (PFGFET). It was made using graphene (acting as the so-called floating gate), hexagonal boron nitride (hBN) and tungsten diselenide (WSe₂).

Due to its unique design, the device can be easily reconfigured and switched to perform memory or transistor functions. In initial tests, researchers have shown that it performs remarkably well in both of these functions.

“When operating as a transistor, the device can be switched between p- and n-type modes and exhibits sub-threshold oscillation of 64 mV dec^-1 and on/off current ratio close to 10⁸“, wrote Sun, Zhu, Yi and colleagues in their paper. “When operating as a memory, the device can be switched between p- and n-type memory and exhibits an erase/program ratio approaching 10⁸.”

In the future, the new logic memory architecture proposed by this team of researchers could be used to create a variety of high-performance electronic devices, significantly reducing their power consumption. So far, Sun and his colleagues have successfully used the PFGFETs they created to fabricate gates to perform linear and nonlinear binary operations, but they could eventually be applied to a wider range of computations and models. of operation.

“We use the devices to fabricate complementary metal-oxide-semiconductor circuits, linear and nonlinear logic gates with in-situ storage, and efficient half-adder circuits,” the researchers explain in their paper.

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