Creating Changeable Transistors with Ferroelectric Grains: Cutting-Edge Research for Future Semiconductors

Transistors that can change properties are important parts in the development of future semiconductors. As ordinary transistors approach their limit of how small they can be, more functions on the same number of devices becomes increasingly important to be able to develop small and energy-efficient circuits for ever better memories and more powerful computers.
In two articles in Science Advances and Nature Communications, researchers at LTH have shown both how to create new changeable transistors and, on a new detailed level, check how the control works.

Given the ever-increasing need for better, more powerful and efficient circuits, there is a great deal of interest in so-called reconfigurable field-effect transistors (FETs). The advantage of these is that it is possible to change the transistor’s properties after they are manufactured, unlike ordinary semiconductors.

Historically, computing power and efficiency of computers has been improved by scaling down the size of silicon transistors (also known as Moore’s Law). But now they have reached such a point that the costs of continuing that development have become increasingly high, while at the same time quantum mechanical problems have arisen which have caused development to slow down.

Ferroelectric materials

Instead, they look for new materials, components and circuits. In Lund, they are among the world leaders in so-called III-V material, which is an alternative to silicon. It is a material with great potential for developing high-frequency technology (such as parts of the future 6G and 7G networks), optical applications and increasingly energy-efficient electronic components.

To create this, so-called ferroelectric materials are used, special materials that can change their internal polarization when exposed to electric fields. You can compare it to a normal magnet, but instead of a magnetic north pole and south pole respectively, electric poles are formed with a positive and a negative charge on the respective side of the material. By changing the polarization you control the transistor. Another advantage is that the material “remembers” its polarization even if the voltage is interrupted.

Extremely small scale

Through a new combination of materials, the researchers have created ferroelectric “grains” that control a tunnel junction – an electrical junction – in the transistor. This on an extremely small scale, the grains are 10 nanometers in size. By measuring changes in the electrical voltage or current, it has been possible to identify when the polarization changes in the individual grains and thus understand how this affects the behavior of the transistor.

In the research now published, new ferroelectric memories in the form of transistors with tunneling barriers have been investigated in order to create new circuit architectures.

– The goal is to be able to create so-called neuromorphic circuits, i.e. circuits that are adapted for artificial intelligence in that their structure mimics the human brain with its synapses and neurons, says Anton Eriksson, recently PhD student in nanoelectronics and one of the authors to the articles.

Semiconductors that can change properties

The special thing about the new results is that they have succeeded in creating thin transitions with ferroelectric grains that sit right next to the transition. These nanoparticles can then be controlled on an individual level – and not as before when you only had control over entire groups of grains, so-called ensembles. In this way, individual parts of the material can be detected and controlled.

– In order to be able to make advanced applications, one must understand the dynamics of individual grains down to the atomic level and also which defects exist. The increased understanding of the material can be used to optimize the functions. By controlling its ferroelectric grains, one can then create new semiconductors where one can change properties. By changing the electrical voltage, different functions can be achieved in one and the same component, says Lars-Erik Wernersson, professor of nanoelectronics and also supervisor and co-author of the article.

Can become new memory cells

The researchers have also looked at how this knowledge can be used precisely to create various reconfigurable applications by manipulating the signal passing through the transistor in different ways. It could, for example, be used for new memory cells or even more energy-efficient transistors.

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

– The interesting thing is that it is possible to change the input signal in different ways, for example by changing the phase of the transistor, doubling the frequency or mixing signals. Because the transistor remembers its properties even when the power is turned off, you don’t have to set them up again every time the circuit is used, says Zhongyunshen Zho, PhD student in nanoelectronics and one of the article’s authors.

Cutting edge research

Another advantage of these transistors is that they can operate with low voltage, which makes them energy-efficient, which is needed, for example, for future wireless communication, the Internet of Things and quantum computers.

– I consider this to be cutting-edge research of international class. It is good that we in Lund and Sweden are far ahead when it comes to semiconductors, especially considering that the EU recently adopted the chips act, which aims to strengthen Europe’s position regarding semiconductors, says Lars-Erik Wernersson.

Artikeln i Science Advances

The article in Nature Communications

EU Chips ACT

The regulation on semiconductors should strengthen the EU’s competitiveness and resilience in semiconductor technology and contribute to both the digital and the green transition. It will also strengthen the EU’s technical leadership in the field.
The European Commission has carried out a survey on chips which shows that the industry expects the demand for chips to double by 2030. This shows the increasing importance of semiconductors for industry and society in the EU. It will be difficult to meet the growing demand, especially in light of the current semiconductor crisis if nothing is done.

Transistors

Transistors are building blocks in all modern electronics. The transistor acts as a voltage-controlled switch that can turn on or off. Transistors are getting smaller and smaller and the smallest ones are produced using nanotechnology.

Transistors are the most important component in all modern electronics. The data chip can be said to be the “brain” of electronic products and systems.

III-V technology platform

III-V refers to materials found within groups three and five of the periodic table. These are characterized by very good transport and optical properties.

For more information contact: Lars-Erik Wernersson, professor of nanoelectronics

E-mail: lars-erik.wernersson@eit.lth.se
Phone: 046-222 90 03

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