Ferroelectric helps break transistor limits

Summary

Integrating an electronic material that exhibits a strange property called negative capacitance can help high-power gallium nitride transistors break through a performance barrier, say scientists in California. Research published in Science suggests that negative capacitance helps sidestep a physical limit that typically enforces trade-offs between how well a transistor performs in the “on” state versus how well it does in the “off” state. The researchers behind the project say this shows that negative capacitance, which has been extensively studied in silicon, may have broader applications than previously appreciated.Electronics based on GaN power 5G base stations and compact power adapters for cellphones. When trying to push the technology to higher frequency and higher power operations, engineers face trade-offs. In GaN devices used to amplify radio signals, called high-electron-mobility transistors (HEMTs), adding an insulating layer called a dielectric prevents them from wasting energy when they’re turned off, but it also suppresses the current flowing through them when they are on, compromising their performance.To maximize energy efficiency and switching speed, HEMTs use a metal component called a Schottky gate, which is set directly on top of a structure made up of layers of GaN and aluminum gallium nitride. When a voltage is applied by the Schottky gate, a 2D electron cloud forms inside the transistor. These electrons are zippy and help the transistor switch rapidly, but they also tend to travel up toward the gate and leak out. To prevent them from escaping, the device can be capped with a dielectric. But this additional layer increases the distance between the gate and the electron cloud. And that distance decreases the ability of the gate to control the transistor, hampering performance. This inverse relationship between the degree of gate control and the thickness of the device is called the Schottky limit.“Getting more current from the device by adding ...