Researchers at Fraunhofer IAF have succeeded in developing a new type of transistor with extremely high cut-off frequencies: Metal Oxide Semiconductor HEMTs, or MOSHEMTs, in short. For this purpose, they replaced the Schottky barrier of the conventional HEMT with an oxide. The result is a transistor that enables even smaller and more powerful components and that has already reached a record frequency of 640 GHz.
In recent years, the high-frequency properties of high electron mobility transistors (HEMTs) have been continuously improved. The transistors have become faster and faster by scaling down the gate length to 20 nm. However, the HEMT encounters a problem with these small structure sizes: the thinner the barrier material made of indium aluminum arsenide (InAlAs) becomes, the more electrons dissipate from the current-carrying channel to the gate. These unwanted gate leakage currents have a negative impact on the performance and lifetime of the transistor. The current transistor geometry of a conventional HEMT has reached its scaling limit. This problem also occurs with silicon MOSFETs (metal oxide semiconductor field effect transistors). However, they have an oxide layer that can prevent unwanted leakage currents for longer than it is the case with HEMTs.
Source: “MOSHEMT – novel transistor technology reaches record frequencies”, Jennifer Funk, Fraunhofer Group for Microelectronics