Semiconductors of the future using cutting edge transistors

As traditional transistors reach the threshold of their miniaturisation potential, the ability to incorporate multiple functionalities within a limited number of units becomes crucial for facilitating the creation of compact, energy-efficient circuits. This, in turn, paves the way for enhanced memory capabilities and the realisation of more potent computing systems.

Researchers at Lund University in Sweden have shown how to create new configurable transistors and exert control on a new, more precise level.

Given the ever-growing demand for superior, high-performance circuits, there exists a significant enthusiasm surrounding reconfigurable transistors. These transistors possess a distinct advantage over conventional semiconductors as they allow for the alteration of their properties even after the manufacturing process has been completed. This flexibility and adaptability make reconfigurable transistors highly desirable in the pursuit of more powerful and efficient electronic systems.

Throughout history, advancements in the computational power and efficiency of computers have been achieved through the reduction in size of silicon transistors, often referred to as Moore's Law. However, we have now reached a point where the costs associated with further developments in this direction have significantly escalated, and challenges rooted in quantum mechanics have emerged, impeding progress.

Consequently, the focus has shifted towards exploring novel materials, components, and circuits as alternatives. Lund University is at the forefront of pioneering research in III-V materials, which offer a viable alternative to silicon. These materials hold immense potential in the advancement of high-frequency technology, including the development of components for future 6G and 7G networks. Additionally, they find applications in optics and contribute to the creation of increasingly energy-efficient electronic components.

To harness this potential, the utilisation of ferroelectric materials is imperative. These unique materials possess the ability to alter their internal polarisation when subjected to an electric field. Similar to an ordinary magnet having north and south poles, ferroelectric materials develop electric poles with positive and negative charges on opposite sides. By manipulating the polarisation, it becomes feasible to regulate the behaviour of the transistor. Additionally, one notable advantage is that the material retains its polarisation even when the current is switched off, exhibiting a ‘memory’ of its previous state.

By employing a novel amalgamation of materials, the researchers have successfully engineered ferroelectric ‘grains’ that govern a tunnel junction within the transistor, inducing an electrical bridging effect. Remarkably, these grains are of minuscule proportions, measuring just 10 nanometres in size. Through meticulous measurements of voltage or current fluctuations, the scientists have been able to detect and comprehend the polarisation shifts occurring within individual grains, thereby unravelling the influence of such changes on the transistor's functionality.

The newly published research has examined new ferroelectric memory in the form of transistors with tunnel barriers in order to create new circuit architectures.

“The aim is to create neuromorphic circuits, i.e., circuits that are adapted for artificial intelligence in that their structure is similar to the human brain with its synapses and neurons,” says Anton Eriksson, who recently completed his doctoral degree in nanoelectronics.

The novelty of the recent findings lies in the successful creation of tunnel junctions utilising ferroelectric grains positioned in immediate proximity to the junction itself. These nanoscale grains can now be individually controlled, unlike previous limitations where monitoring was restricted to entire ensembles of grains. This breakthrough enables the identification and manipulation of specific components within the material, paving the way for enhanced precision and control in future applications.

“In order to create advanced applications, you must first understand the dynamics in individual grains down to the atomic level, as well as the defects that exist. The increased understanding of the material can be used to optimise the functions. By controlling these ferroelectric grains, you can then create new semiconductors in which you can alter properties. By changing the voltage, you can thus produce different functions in one and the same component,” says Lars-Erik Wernersson, professor of nanoelectronics.

Additionally, the researchers have explored the potential applications of this knowledge in creating diverse reconfigurable functionalities by manipulating the signal passing through the transistor in various ways. This understanding opens avenues for the development of novel memory cells or the realisation of more energy-efficient transistors, among other possibilities. By leveraging these findings, innovative solutions can be devised to enhance memory technologies and contribute to the advancement of energy-efficient electronic systems.

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

“What’s interesting is that it’s possible to modulate the input signal in various ways, for example by the transistor shifting phase, frequency doubling, and signal mixing. As 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,” says Zhongyunshen Zho, doctoral student in nanoelectronics.

These transistors offer an additional advantage of operating at low voltage levels, rendering them highly energy-efficient. This characteristic proves invaluable for the future of wireless communication, Internet of Things (IoT), and quantum computing applications. The demand for energy-efficient solutions in these domains necessitates the use of transistors capable of operating efficiently at low voltage, and the newfound capability of these transistors aligns perfectly with those requirements.

“I consider this to be leading-edge research of international standing. It’s good that in Lund and Sweden we are at the forefront regarding semiconductors, especially in view of the EU’s recently enacted Chips Act, which aims to strengthen Europe’s position regarding semiconductors,” says Wernersson.