Periodic Reporting for period 2 - ATRONICS (Creating building blocks for atomic-scale electronics)
Reporting period: 2022-03-01 to 2023-08-31
Space and energy limitations of modern electronics have triggered the search for conceptually new approaches that allow us to go beyond the classical design of electronic components and integrated circuits in semiconductor technology. The growing demand has pushed the field of materials science towards a revolution in how materials and their specific electrical properties are designed. Of special interest are two-dimensional (2D) systems as they exhibit a wide variety of functional physical properties. Furthermore, the 2D nature facilitates atomic-scale feature sizes, which is crucial for the miniaturization of electronic devices and the lowering of their energy consumption.
Ferroelectric domain walls recently emerged as a new type of quasi-2D system, where the dynamic characteristics of ferroelectricity introduce the element of spatial mobility, allowing for the real-time adjustment of position, density and orientation of the walls. This mobility adds an additional degree of flexibility that enables domain walls to take an active role in future devices. Most application concepts, however, rely on injecting and deleting domain walls in micrometer-sized devices to control electric conductivity. While this approach achieves a step beyond conventional interfaces by utilizing the wall mobility, it does not break the mould of classical device architectures.
The goal of the ATRONICS projects is to enable the next-generation of domain-wall-based devices. At the length scale of only a few atoms, we use individual walls in improper ferroelectrics to emulate key electronic components such as diodes, transistors and logic gates. Crucially, as the functionality of the components is intrinsic to the domain walls, the walls themselves become the devices. Beyond demonstrating individual devices, we will integrate multiple domain-wall devices and develop quasi-2D circuitry and networks with a higher order of complexity then is currently achievable.
ATRONICS will represent a major advancement in 2D functional materials for future technologies and play an essential role in the transition from nano- to atomic-scale electronics.
Ferroelectric domain walls recently emerged as a new type of quasi-2D system, where the dynamic characteristics of ferroelectricity introduce the element of spatial mobility, allowing for the real-time adjustment of position, density and orientation of the walls. This mobility adds an additional degree of flexibility that enables domain walls to take an active role in future devices. Most application concepts, however, rely on injecting and deleting domain walls in micrometer-sized devices to control electric conductivity. While this approach achieves a step beyond conventional interfaces by utilizing the wall mobility, it does not break the mould of classical device architectures.
The goal of the ATRONICS projects is to enable the next-generation of domain-wall-based devices. At the length scale of only a few atoms, we use individual walls in improper ferroelectrics to emulate key electronic components such as diodes, transistors and logic gates. Crucially, as the functionality of the components is intrinsic to the domain walls, the walls themselves become the devices. Beyond demonstrating individual devices, we will integrate multiple domain-wall devices and develop quasi-2D circuitry and networks with a higher order of complexity then is currently achievable.
ATRONICS will represent a major advancement in 2D functional materials for future technologies and play an essential role in the transition from nano- to atomic-scale electronics.
ATRONICS explores how the behavior of key electronic components can be emulated based on individual improper ferroelectric domain walls and to what extend such functional units can be interconnected to realize more complex devices and networks, such as logic gates and combinatorial logic circuits.
A first important step was to learn how to nanostructure our materials and achieve device-relevant geometries without altering the electronic responses of the ferroelectric domain walls. The latter is highly non-trivial as energetic charged atoms are used for nanostructuring. As a consequence, this method can completely change the electronic structure, requiring careful control of the ablation process. In addition, whenever the size of a physical system is reduced, confinement effects come into play so that nano-sized systems do not necessarily exhibit the same properties as their macroscopic counterparts. Thus, it was a real breakthrough for us when we managed to reduce the thickness of our materials down to 10 – 100 nm without losing the functionality of the domain walls we are interested in. For example, we observe that the domain walls in our thin samples exhibit high and low resistance states between which we can switch by controlling the applied voltage, mimicking the behavior of a digital switch. To understand the atomic-scale physics of the walls, we combined different state-of-the-art microscopy techniques and also develop new experimental methodologies.
In order to progress towards the different envisioned device applications, we also established procedures to mount our nanostructured samples on biasing chips or electrically contact them in other ways. The latter is a crucial precondition to produce the two- and three-terminal device architectures on which we will focus our efforts in the second phase of ATRONICS. In addition, we successfully demonstrated a substantial impact of environmental conditions on the electronic conduction of the domain walls (e.g. gas atmosphere and temperature). Importantly, the domain wall responses are more pronounced than in the surrounding domains. For example, we managed to sense changes in oxygen partial pressure, which are detectable as a reversible change in the local conductivity, opening the door towards domain-wall-based environmental sensors.
The research activities showed the general possibility to achieve ultra-small electronic components and sensors based on individual domain walls. They represent the basis for the second project phase, during which we will explore pathways towards more complex devices, establishing novel concepts for the transition from nano- to atomic-scale electronics.
A first important step was to learn how to nanostructure our materials and achieve device-relevant geometries without altering the electronic responses of the ferroelectric domain walls. The latter is highly non-trivial as energetic charged atoms are used for nanostructuring. As a consequence, this method can completely change the electronic structure, requiring careful control of the ablation process. In addition, whenever the size of a physical system is reduced, confinement effects come into play so that nano-sized systems do not necessarily exhibit the same properties as their macroscopic counterparts. Thus, it was a real breakthrough for us when we managed to reduce the thickness of our materials down to 10 – 100 nm without losing the functionality of the domain walls we are interested in. For example, we observe that the domain walls in our thin samples exhibit high and low resistance states between which we can switch by controlling the applied voltage, mimicking the behavior of a digital switch. To understand the atomic-scale physics of the walls, we combined different state-of-the-art microscopy techniques and also develop new experimental methodologies.
In order to progress towards the different envisioned device applications, we also established procedures to mount our nanostructured samples on biasing chips or electrically contact them in other ways. The latter is a crucial precondition to produce the two- and three-terminal device architectures on which we will focus our efforts in the second phase of ATRONICS. In addition, we successfully demonstrated a substantial impact of environmental conditions on the electronic conduction of the domain walls (e.g. gas atmosphere and temperature). Importantly, the domain wall responses are more pronounced than in the surrounding domains. For example, we managed to sense changes in oxygen partial pressure, which are detectable as a reversible change in the local conductivity, opening the door towards domain-wall-based environmental sensors.
The research activities showed the general possibility to achieve ultra-small electronic components and sensors based on individual domain walls. They represent the basis for the second project phase, during which we will explore pathways towards more complex devices, establishing novel concepts for the transition from nano- to atomic-scale electronics.
In 2017, it was reported that the electronic transport at improper ferroelectric domain walls in ErMnO3 can be reversibly switched between high- and low-resistance states. This discovery triggered the idea to develop the domain walls themselves into ultra-small electronic components. The initial studies, however, were performed at the surface of millimeter-thick single crystals and it remained to be demonstrated that the physical dimensions can be reduced without compromising the functionality of the walls. By optimizing the preparation procedures, we now managed to downscale the sample thickness to a few nanometers while keeping the electronic integrity of the domain walls. We also succeeded in mounting such nanostructured specimens on biasing chips with customized electrodes, realizing first device-relevant geometries for the next project phase.
Another breakthrough is the level of control we have achieved in controlling local electronic conduction phenomena via oxygen defects. On the one hand, we can now precisely control the distribution of oxygen vacancies/interstitials in our samples and, hence, their local transport behavior. In the next step, this expertise will be used to interconnect different functional domain walls and emulate more complex electronic components, such as logical gates. On the other hand, we demonstrated that the domain walls can reversibly change their conductance as function of the local oxygen defect concentration. This sensitivity allows. e.g. for translating changes in oxygen partial pressure or temperature into electronic signals, demonstrating the general possibility to develop domain walls into ultra-small environmental sensors.
In summary, by successfully downscaling the physical dimensions of our model system, establishing procedures for contacting the domain walls, and gaining new insight into defect-driven electronic transport phenomena, we have reached important milestones that bring us an important step forward on our way towards domain-wall-based atomic-scale electronics.
Another breakthrough is the level of control we have achieved in controlling local electronic conduction phenomena via oxygen defects. On the one hand, we can now precisely control the distribution of oxygen vacancies/interstitials in our samples and, hence, their local transport behavior. In the next step, this expertise will be used to interconnect different functional domain walls and emulate more complex electronic components, such as logical gates. On the other hand, we demonstrated that the domain walls can reversibly change their conductance as function of the local oxygen defect concentration. This sensitivity allows. e.g. for translating changes in oxygen partial pressure or temperature into electronic signals, demonstrating the general possibility to develop domain walls into ultra-small environmental sensors.
In summary, by successfully downscaling the physical dimensions of our model system, establishing procedures for contacting the domain walls, and gaining new insight into defect-driven electronic transport phenomena, we have reached important milestones that bring us an important step forward on our way towards domain-wall-based atomic-scale electronics.