Product & Research in Focus


Product in Focus

Compact microwave plasma source – a versatile tool for various applications

Atmospheric plasmas offer a wide range of applications in the field of surface treatment and activation, including temperature-sensitive materials. The FBH has developed a very compact plasma source, sized only 114 x 33 x 25 mm³, that offers a 2.45 GHz microwave plasma in the 10…20 W range. The source only needs single 48 V DC supply, plus gas feeding and water cooling, which can also be replaced by air ventilation. Supply of the plasma medium, like air, argon, nitrogen, and oxygen, and the cooling medium is designed in such a way that the source can be used in a very flexible way. Applications range from the activation of surfaces (plastics, metals) in industrial production through cleaning and coating to medical applications.

The source comprises a microwave power oscillator, a resonator with plasma excitation, and the control circuit, integrated in a single, miniaturized package. An FBH gallium-nitride transistor is used for most efficient microwave power generation. The source is easy to handle, either as a stand-alone plasma tool or as part of equipment.

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Research in Focus

Deep UV LEDs with enhanced optical power

Within their Joint Lab GaN Optoelectronics, FBH and TU Berlin have considerably improved the performance of their deep-UV LEDs. LEDs emitting at wavelengths below 240 nm are of great interest for various applications including automotive (e.g. NOx and NH3 gas sensing), medical diagnostics, and space (e.g. photoionization of test masses). However, due to the very large bandgap energies of the AlxGa1-xN layers of up to 6 eV in the deep-UV LED heterostructures, the performance of these devices degrades rapidly with shorter UV wavelength. After optimizing the n-type AlGaN current spreading layer, the quantum wells, the electron blocking layer and the step-graded p-type AlGaN superlattice, the LED efficiency could be significantly improved. AlGaN heterostructures grown by epitaxial lateral overgrowth on (0001) AlN/sapphire substrates using metalorganic vapor phase epitaxy were processed to single chips, flip-chip mounted in 3.5 mm x 3.5 mm ceramic packages and capped by quartz glass lids. The LEDs emit at 233 nm with a total power of 0.3 mW when operated at 100 mA. This power is more than one order of magnitude higher than previously obtained values, and it opens the door to new applications of deep-UV LEDs.

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Towards terahertz transistors – transferred substrate InP/GaAsSb heterojunction bipolar transistor technology

InP-based semiconductor devices offer the highest cut-off frequencies and largest breakdown voltages. FBH has developed an InP MMIC transferred substrate process, offering better scaling capabilities towards THz frequencies. This process also allows for heterointegration with SiGe BiCMOS or CMOS process technology. Consequently, the power generation capability of InP DHBT technology can be combined with the circuit complexity of silicon technology on a single microchip, thus avoiding coupling losses and reducing integration costs. Full RF front ends for THz applications can be manufactured. Unnecessary InP material is replaced by a polymer with excellent high-frequency properties, thus reducing parasitic capacitances as compared to the standard triple mesa process. Therefore, high cut-off frequencies can be achieved even with relatively large transistor dimensions. FBH has applied epitaxial structures with a GaAsSb base grown at ETH Zurich to its unique transfer substrate process for the first time, reaching cut-off frequencies beyond 530 GHz. Further scaled transistors with projected values of 900 GHz are in production.

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