According to oilprice.com, scientists at the Lawrence Berkeley National Laboratory (BerkeleyLab) in the United States have developed microcapacitors with ultra-high energy and power density, paving the way for on-chip energy storage in electronic devices. Many readers have seen the number of capacitors installed on computer motherboards and other power-intensive silicon chip circuit boards.
The findings, published in the journal Nature, pave the way for on-chip energy storage and power delivery in next-generation electronics.
To make electronic devices smaller and more energy efficient, researchers want to bring energy storage directly to microchips to reduce the losses incurred when electricity is transmitted between different device components. To be efficient, on-chip energy storage must be able to store large amounts of energy in a small space and transmit it quickly when needed - requirements that existing technologies cannot meet.
To address this challenge, scientists at Lawrence Berkeley National Laboratory and UC Berkeley achieved record-high energy and power densities in microcapacitors made from engineered thin films of hafnium oxide and zirconium oxide, leveraging materials and fabrication techniques already widely used in chip manufacturing.
-------Microcapacitors made with engineered hafnium oxide/zirconium oxide thin films in a 3D trench capacitor structure—the same structure used in modern microelectronics—achieve record-high energy storage and power density, paving the way for on-chip energy storage. Image credit: Nirmaan Shanker/Suraj Cheema, Lawrence Berkeley National Laboratory.
“We have shown that it is possible to store large amounts of energy in microcapacitors made from engineered thin films, far exceeding the storage capabilities of common dielectrics,” explained Sayeef Salahuddin, a Berkeley Lab senior scientist and UC Berkeley professor who led the project. “What’s more, we are using a material that can be processed directly on a microprocessor.”
------Sayeef Salahuddin (left) and Nirmaan Shanker in the lab. Image credit: Marilyn Sargent/Berkeley Lab
The research is part of a broad effort at Berkeley Lab to develop new materials and technologies for smaller, faster and more energy-efficient microelectronics.
Capacitors are one of the basic components of circuits, but they can also be used to store energy. Unlike batteries that store energy through electrochemical reactions, capacitors store energy in an electric field established between two metal plates separated by a dielectric material. Capacitors can be discharged very quickly when needed, so that they can supply power quickly, and they will not be degraded by repeated charge and discharge cycles, so that their life is much longer than that of batteries. However, the energy density of capacitors is usually much lower than that of batteries, which means that they can store less energy per unit volume or weight, and this problem will only get worse when you try to reduce them to the size of micro-capacitors for energy storage on the chip.
In Lawrence Berkeley National Laboratory, researchers have carefully designed HFO _ 2-ZrO _ 2 thin films to achieve negative capacitance effect, thus achieving a record-breaking micro-capacitor. Usually, the superposition of one dielectric material on another will lead to the decrease of the overall capacitance. However, if one of the layers is a negative capacitance material, the overall capacitance will actually increase. In the early work, Salahuddin and his colleagues demonstrated the use of negative capacitance materials to produce transistors, which can work at much lower voltage than traditional MOSFET transistors. Here, they use negative capacitance to produce capacitors that can store a larger amount of charge, thus generating energy.
The crystalline thin film is made of a mixture of HfO2 _ 2 and ZrO2 _ 2, and is grown by atomic layer deposition, using standard materials and technologies for industrial chip manufacturing. Depending on the ratio of these two components, the thin film can be ferroelectric, in which the crystal structure has built-in polarization, or antiferroelectric, in which the structure can be pushed into a polar state by applying an electric field. When the composition is properly adjusted, the electric field generated by the charging capacitor balances the thin film at the critical point between ferroelectric and antiferroelectric order. This instability produces a negative capacitance effect, and even a small electric field can easily polarize the material.
Suraj Cheema, a postdoctoral fellow in Salahuddin research group, is one of the main authors of this paper. He explained: "During the phase change process, the unit cells really want to be polarized, which helps to generate extra charges under the action of electric field. This phenomenon is an example of negative capacitance effect, but you can think of it as a way to capture more charge than usual. "
In order to expand the energy storage capacity of the thin film, the research team needs to increase the thickness of the thin film without allowing it to relax from the frustrated antiferroelectric-ferroelectric state. They found that by adding atomic thin aluminum oxide layers after every few layers of HfO2-ZrO2, they could grow the thin film to 100 nanometers thick while still maintaining the required properties.
Finally, the researchers cooperated with the collaborators in Lincoln Laboratory of Massachusetts Institute of Technology to integrate the thin film into a three-dimensional micro-capacitor structure, and grow accurately layered thin films in deep trenches cut on silicon, with an aspect ratio as high as 100:1. These 3D trench capacitor structures are used in today's DRAM capacitors. Compared with planar capacitors, they can achieve higher capacitance per unit area, thus achieving greater miniaturization and design flexibility. The performance of the resulting devices is record-breaking: compared with the best electrostatic capacitors today, the energy density of these capacitors is 9 times higher and the power density is 170 times higher (80 mJ-cm-2 and 300 kW-cm-2 respectively).
"The energy and power density we got were much higher than we expected," Salahuddin pointed out. "We have been developing negative capacitance materials for many years, but these results are quite surprising."
These high-performance micro-capacitors can help meet the growing demand of micro-devices (such as Internet of Things sensors, edge computing systems and artificial intelligence processors) for efficient and miniaturized energy storage. Researchers are now committed to expanding the scale of this technology and integrating it into full-size microchips, while promoting the development of basic materials science to further improve the negative capacitance of these films.
Cheema added: "With this technology, we can finally start to realize the seamless integration of energy storage and power transmission on very small chips. It can open up a new energy technology field for microelectronics technology. "
Part of the work is carried out in the molecular foundry, which is the user facility of nanoscience in the Science Office of the U.S. Department of Energy at Berkeley Lab.
Source: New Micro Capacitors Break Energy Density and Power Barriers | OilPrice.com
