Reorganization of A Computer Chip: Transistors Can Now Process and Use As Information Storage

A computer chip processes and stores information with two different devices. If engineers could combine these devices into one or place them side by side, there would be more space on a chip, making it faster and more powerful.

Purdue University engineers have developed a method that allows millions of tiny switches used to process information - called transistors - to store that information as one device.

The method described in an article published in Nature Electronics solves this problem by combining a transistor with memory technology that performs better than most computers called ferroelectric RAM.

Researchers have been trying to integrate the two for decades, but problems arise at the interface between a ferroelectric material and silicon, the semiconductor material that transistors are made of. Instead, ferroelectric RAM works as a separate on-chip unit, which limits its potential for increasing computing efficiency.

A team led by Peide Ye, Richard J., and Mary Jo Schwartz, professor of electrical engineering and information technology in Purdue, discovered how to overcome the hostile relationship between silicon and a ferroelectric material.

"We used a semiconductor with ferroelectric properties. This way, two materials become one material and you don't have to worry about the interfaces," said Ye.

The result is a so-called ferroelectric semiconductor field effect transistor, which is constructed in exactly the same way as the transistors currently used on computer chips.

The material, alpha-indium selenide, not only has ferroelectric properties, but also addresses the problem that a conventional ferroelectric material acts as an insulator rather than a semiconductor due to a so-called wide "band gap", which means that electricity does not can be let through and no arithmetic happens.

Alpha indium selenide has a much smaller band gap, so the material can be a semiconductor without losing the ferroelectric properties.

Mengwei Si, a Purdue postdoc in electrical and computer engineering, built and tested the transistor. He found that his performance was comparable to the existing ferroelectric field effect transistors and was able to exceed them with more optimization. Sumeet Gupta, a Purdue Assistant Professor of Electrical and Computer Engineering, and Ph.D. The candidate Atanu Saha supported the modeling.

The Si and Ye team also worked with researchers at the Georgia Institute of Technology to integrate alpha-indium selenide into a space on a chip, a ferroelectric tunnel junction, that engineers could use to improve a chip's capabilities. The team will present this work on December 9th at the IEEE International Electron Devices Meeting 2019.

In the past, researchers had failed to build a high-performance ferroelectric tunnel junction because the material was too thick due to its wide bandgap to allow electrical current to pass through. Because alpha indium selenide has a much smaller band gap, the material can only be 10 nanometers thick and more current can flow through it.

More current allows a device area to shrink to several nanometers, which makes chips denser and more energy-efficient, said Ye. A thinner material - even down to an atomic layer thickness - also means that the electrodes on either side of a tunnel junction can be much smaller, which would be useful for building circuits that mimic networks in the human brain.

This research was conducted at the Purdue Discovery Park Birck Nanotechnology Center and supported by the National Science Foundation, the Air Force Office for Scientific Research, the Semiconductor Research Corporation, the Defense Advanced Research Projects Agency and the US Office of Naval Research.

Journal Reference:

Mengwei Si, Atanu K. Saha, Shengjie Gao, Gang Qiu, Jingkai Qin, Yuqin Duan, Jie Jian, Chang Niu, Haiyan Wang, Wenzhuo Wu, Sumeet K. Gupta, Peide D. Ye. A ferroelectric semiconductor field-effect transistor. Nature Electronics, 2019; DOI: 10.1038/s41928-019-0338-7