State-of-the-art transistors for the future of semiconductors


July 03, 2023

(Nanowerk News) Transistors that can change properties are an important element in the development of future semiconductors. With standard transistors approaching the limits of how small they can be, having more functionality on the same number of units has become increasingly important in enabling the development of small, energy-efficient circuits for increased memory and more powerful computers. Researchers at Lund University in Sweden have shown how to make new transistors configurable and take control to a new, more precise level.

Given the growing need for better, more powerful and efficient circuits, there is great interest in reconfigurable transistors. The advantage is that, in contrast to standard semiconductors, it is possible to change the properties of the transistor after it is manufactured.

Historically, the computing power and efficiency of computers have been increased by reducing the size of silicon transistors (also known as Moore’s Law). But now a stage has been reached where the cost of continuing development along those lines has become much higher, and quantum mechanics problems arise that slow down development.

Instead, the search for new materials, components and circuits is ongoing. Lund University is one of the world leaders in III-V materials, which are an alternative to silicon. It is a material with great potential in the development of high-frequency technologies (such as parts for future 6G and 7G networks), optical applications, and increasingly energy-efficient electronic components.

Ferroelectric materials are used to realize this potential. This is a special material that can change the polarization of its interior when exposed to an electric field. It can be compared to an ordinary magnet, but instead of the magnetic north and south poles, electric poles are formed with positive and negative charges on each side of the material. By changing the polarization, it is possible to control the transistor. Another advantage is that the material “remembers” its polarization, even if the current is turned off.

Through a new material combination, researchers have created ferroelectric “grains” that control tunnel junctions – the electrical coupling effect – inside transistors. This is on a very small scale – 10 nanometer grains. By measuring fluctuations in voltage or current, it is possible to identify when the polarization changes in individual grains and thereby understand how this affects the behavior of the transistor. millimeter-sized chip with ferroelectric tunnel field-effect transistors The millimeter-sized chip on which the transistors are located. (Image: Anton Persson)

New research published in Nature Communications (“Reconfigurable signal modulation in a tunnel ferroelectric field-effect transistor”) have examined a new ferroelectric memory in the form of a transistor with a tunnel barrier to create a new circuit architecture.

“The goal is to create neuromorphic circuits, that is, circuits that are adapted for artificial intelligence because they are similar in structure to the human brain with its synapses and neurons,” said Anton Eriksson, who recently completed his doctorate in nanoelectronics.

What is special about this new result is that it is possible to make tunnel junctions using ferroelectric grains located directly adjacent to the junctions. These nanograins can then be controlled at the individual level, where previously it was only possible to track entire groups of grains, known as ensembles. In this way, it is possible to identify and control the separate parts of the material.

“To create advanced applications, you must first understand the dynamics in individual grains down to the atomic level, as well as the defects present. Increased understanding of the material can be used to optimize functions. By controlling these ferroelectric grains, you can then create new semiconductors where you can change their properties. By changing the voltage, you can produce different functions within the same component,” said Lars-Erik Wernersson, professor of nanoelectronics.

The researchers have also examined how this knowledge can be used to create a variety of applications that can be reconfigured by manipulating the different ways the signal passes through the transistor. For example, it could be used for new memory cells or more energy efficient transistors.

This new type of transistor is called ferro-TFET and can be used in both digital and analog circuits.

“What’s exciting is that it is possible to modulate the input signal in various ways, for example by transistor phase shift, frequency doubling, and signal mixing. Because the transistor remembers its properties, even when the current is turned off, there is no need to reset it every time the circuit is used,” said Zhongyunshen Zho, doctoral student of nanoelectronics.

Another advantage of this transistor is that it can function at low voltages. This makes it energy efficient, which will be needed, for example, in future wireless communications, the Internet of Things and quantum computers.

“I consider this to be leading research with international standing. It is good that in Lund and Sweden we are at the forefront regarding semiconductors, especially given the Chips Act recently passed in the EU, which aims to strengthen the European position on semiconductors,” said Lars-Erik Wernersson.


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