Imagine a world where your smartphones never run out of battery, your fitness trackers are more accurate, and your smart home devices communicate seamlessly. The common challenge behind these technologies is battery performance, which is often limited by size and efficiency. Fortunately, researchers in Sayeef Salahuddin’s lab at UC Berkeley are addressing these limitations by achieving record energy and power density in a new type of energy storage device: microcapacitors.

Capacitors consist of two metal plates separated by an insulating material. They store energy in an electric field that forms when opposite charges accumulate on the plates. Unlike batteries, which involve slow chemical reactions, capacitors instantaneously store and release energy, making them effective for powering devices. Their performance is measured as capacitance, which is how much charge can be stored at a given voltage.

Typically, capacitance is positive—the charge stored in a capacitor is directly proportional to the applied voltage across the plates. Instead, the researchers harnessed negative capacitance, where a decrease in voltage leads to an increase in charge. Negative capacitance allows capacitors to store more charge with less voltage, enabling devices to be more energy efficient. The team achieved negative capacitance using ferroelectrics—materials with aligned electric charges that switch directions when a voltage is applied. As charges rapidly build up during this switch, the internal electric field temporarily decreases, causing a drop in the applied voltage and resulting in negative capacitance. Usually, negative capacitance is a temporary effect, so the researchers stabilized it by layering an insulating material that exhibits positive capacitance, thus optimizing the system for an overall negative capacitance effect.

The microcapacitors boast nine times higher energy density and 170 times higher power density than current technologies. Since the required materials are widely available, this advancement is poised to revolutionize on-chip energy storage and improve the performance of compact, powerful microelectronics.