Generating the highest frequency ever attained by a microelectronic device, a tiny terahertz (THz) transmitter developed at the Technische Universität Darmstadt Institute for Microwave Technology and Photonics (Darmstadt, Germany) can operate at room temperature, opening up possibilities for many uses in medical applications. Because the electromagnetic radio wavelengths can nondestructively penetrate materials including plastics, ceramics, or fabrics, transmitters operating at THz frequencies have been widely used for testing workpieces, inspecting packages for hazardous substances, and other applications outside scientific and engineering fields, restricted mainly due to their expense and bulkiness.

But a resonance tunnel diode (RTD) developed by the TU Darmstadt team can generate THz electromagnetic radiation using relatively conventional semiconductor device fabrication technologies in a size of less than a square millimeter. A record-setting frequency for microelectronic devices of 1.111THz has also been achieved by this transmitter, and Dr. Michael Feiginov, leader of the development team, has theoretically proved that frequencies of up to 3THz could be possible with a similar tiny transmitter.

The diode was produced in collaboration with microelectronic circuit component fabricator ACST GmbH. In the RTD, the team used a thin layer of indium-gallium arsenide semiconductor with barrier layers of aluminum-arsenide semiconductors on either side to create a quantum well that is just a few nanometers thin. The dual-barrier structure o the semiconductors allow electromagnetic waves generated within a THz oscillator to be repeatedly amplified to emit continuous-wave electromagnetic radiation.

Feiginov will continue to work on the technology to achieve higher frequencies, which would lead to new applications in electronic equipment, mobile devices, and computers. Achieving higher frequencies would result in better spatial resolutions to recognize finer details. If substances that haven’t been available for spectroscopic analysis in the THz range could be examined, Feiginov notes that in medicine, it might allow for distinguishing healthy tissue from diseased tissue in vivo. A paper published in Applied Physics Letters describes the technology.