Technology
High Electron Mobility Transistors for Millimeter-Wave Radar
Quick fact
HEMTs can switch at speeds exceeding 100 GHz, making them essential for the millimeter-wave radars used in autonomous vehicles and high-resolution security scanners.
Why this is interesting
Your car’s radar can detect a pedestrian at 200 meters, yet the transistor inside it is smaller than a grain of rice. How does such a tiny device generate the super-fast signals that make this possible?
Read the full explanation
Understanding High Electron Mobility Transistors for Millimeter-Wave Radar
Think of a HEMT as an ultra-fast switch for electrical signals. Traditional transistors work by controlling a flow of electrons through a semiconductor material, but they are limited by how easily electrons collide with atoms (scattering). A HEMT is constructed by layering two different semiconductor materials (a heterojunction) to create a very thin 'sheet' of electrons called a two-dimensional electron gas (2DEG). Because this gas is confined to a plane and separated from the doped region, electrons move with minimal scattering, resulting in extremely high mobility. For radar, this means the transistor can amplify and switch signals at frequencies in the millimeter-wave range (30–300 GHz), which are much higher than typical radio frequencies.
A deeper explanation
The key to HEMT performance is the heterojunction. When two materials with different band gaps (e.g., AlGaN and GaN) are brought together, electrons from the wider-bandgap material (AlGaN) fall into the lower-bandgap material (GaN), forming a conducting sheet at the interface. This electron gas has very high electron mobility because the electrons are spatially separated from the donor atoms, reducing impurity scattering. This allows the transistor to respond extremely quickly to voltage changes at the gate, enabling amplification of signals at millimeter-wave frequencies. In radar, high frequency allows for shorter wavelengths and thus finer angular resolution; higher power (achieved by GaN HEMTs) increases detection range. The combination of high speed, high power, and efficiency makes HEMTs the preferred choice for modern automotive radar, military radar, and even 5G communication systems.