Breakthrough transmitter sets frequency record

The device operates at room temperature, which could lead to it paving the way for new applications such as nondestructive testing or medical diagnostics. Terahertz (THz) electromagnetic radiation has yet to establish a reputation for itself in scientific and engineering fields, partly due to the fact that transmitters and receivers operating at THz frequencies were bulky and expensive. A team of physicists and engineers led by Dr Michael Feiginov at the TU Darmstadt's Institute for Microwave Technology and Photonics has developed a resonance tunnel diode (RTD) for generating terahertz electromag¬netic radiation that takes up less than 1mm² and may be produced using conventional semiconductor device fabrication technologies. The team notes that the innovative transmitter has set a new frequency record, 1.111THz, for microelectronic devices - the highest frequency ever generated by an active semiconductor device. At the heart of the RTD is a dual barrier structure, within which a quantum well (QW) is embedded. A QW is a very thin layer of indium gallium arsenide semiconductor sandwiched between a pair of ultrathin barrier layers of aluminum arsenide semiconductor. Every one of the layers is approximately 1nm thin. This dual barrier structure, plus a quantum mechanical effect, means electromagnetic waves generated within a terahertz oscillator will be repeatedly amplified, rather than attenuated. This results in an oscillator that emits continuous wave electromagnetic radiation at terahertz frequencies. Feiginov believes he has been able to theoretically prove that a minuscule transmitter such as this should be capable of generating much higher frequencies extending up to 3THz. "That was formerly regarded as impossible by those involved in terahertz research," he said. Achieving such higher frequencies would mean attaining better spatial resolutions, recognising finer details, and employing terahertz electromagnetic radiation in materials testing and analysis. The fact the technology operates at room temperature makes it even more attractive for use in engineering applications. "It might, for example, be utilised in spectroscopic analyses of molecules that have transitions falling within the THz range," noted Feiginov. This, he believes, would mean that substances that have so far escaped spectroscopic analysis in the THz range could be investigated employing the widely practiced, scientific method in fields such as medicine, where it might allow distinguishing diseased body tissues from healthy body tissues. "Extracting higher frequencies from the device would [also] lead to new applications, or application areas, in the fields of computers, mobile telephones, and other types of electronic equipment," Feiginov stated. To produce the diode, the researchers collaborated with ACST, a local fabricator of microelectronic circuit components.