Electromagnetic waves with frequencies between microwave and infrared light, also known as terahertz radiation, are leveraged by many existing technologies, including various imaging tools and wireless communication systems. Despite their widespread use, generating strong and continuous terahertz signals using existing electronics is known to be challenging.
To reliably generate terahertz signals, engineers often rely on frequency multipliers, electronic circuits that can distort an input signal, to generate an output signal with a desired frequency. Some of these circuits are based on Schottky barrier diodes, devices in which the junction between a metal and semiconductor form a one-way electrical contact.
While some frequency multipliers based on Schottky barrier diodes have achieved promising results, devices based on individual diodes can only handle a limited amount of energy. To increase the energy they can manage, engineers can use several diodes arranged in a chain. However, even this approach can have its limitations, as the distribution of the electromagnetic field between the diodes in a chain often becomes uneven.
Researchers at University of Electronic Science and Technology recently introduced a new diode chain design that could overcome this limitation, by reshaping local electromagnetic fields and distributing them more uniformly along the chain. The new asymmetric C-shaped diode chain, introduced in a paper published in Nature Electronics, was found to multiply frequencies more efficiently than most other diode-based frequency multipliers developed to date.
“Frequency multiplier devices based on Schottky barrier diodes can be used to generate terahertz radiation, offering high power output and potential integration into all-solid-state systems,” wrote Honji Zhou, Tianchi Zhou and their colleagues in their paper.
“However, the scaling of the output power of such devices is often limited by the power handling capacity of a single diode. A connected chain of Schottky barrier diodes, together with a power combining approach, can be used to increase the terahertz output power. Yet the uneven field distribution among the diodes—which is related to the similarity between the terahertz wavelength and the physical dimensions of the diodes themselves—leads to lower efficiency and premature breakdown.”
To overcome the limitations of previously introduced single diode-based and diode chain-based frequency amplifiers, the researchers introduced a new design in which diodes are arranged in a double-layer chain shaped like the letter C. The shape of the chain is asymmetric, as this can improve the flow of electromagnetic fields between diodes.
The researchers assessed the performance of their newly designed diode chain in both simulations and laboratory tests. Remarkably, they found that it achieved one of the highest terahertz frequency-doubling efficiencies reported to date, highlighting its potential as a frequency multiplier.
“We report an asymmetric double-layer C-shaped diode chain structure that can adjust the local electromagnetic field distribution and enhance the conversion efficiency of the diode chain,” wrote the authors. “Our resulting device has a frequency doubling efficiency of 38%, with an output exceeding 300 mW at 170 GHz.”
The C-shaped diode chain could soon be improved and used to develop a wide range of electronic devices. In the future, it could enable the introduction of more compact terahertz wave transmitters and generators, which could be used to create more advanced imaging, sensing and communication systems.
