K. Nosaeva¹, T. Al-Sawaf¹, W. John¹, D. Stoppel¹, M. Rudolph², F.-J. Schmückle¹, B. Janke¹, O. Krüger¹, V. Krozer¹, W. Heinrich¹, and N.G. Weimann¹

Published in:

IEEE Trans. Electron Devices, vol. 63, no. 5, pp. 1846-1852 (2016).

Abstract:

The RF power output of scaled subterahertz and terahertz indium phosphide double-heterostructure bipolar transistors (InP DHBTs) is limited by the thermal device resistance, which increases with the geometrical frequency scaling of these devices. We present a diamond thin-film heat sink process aimed at the efficient removal of the heat generated in submicrometer InP HBTs. The thin-film diamond is integrated in a wafer bond process. Vertical connections are facilitated by plasma-processed contact holes through the diamond layer, metallized with electroplated gold. The process is suitable for monolithic circuit integration, amenable to the realization of high-power analog circuits in the millimeter-wave region and beyond. The thermal resistance of double-finger transistors with a 0.8-µm emitter width could be reduced to 0.7 K/mW, while reaching the gain cutoff frequencies of f_T = 360 GHz and f_max = 350 GHz. An integrated two-stage power amplifier with four-way power combining fabricated in this technology exhibited 20-dBm power output at 90 GHz with a bandwidth of 10 GHz.

Index Terms:

Diamond, heterobipolar transistor (HBT), indium phosphide (InP), millimeter wave, subterahertz, terahertz, thermal conductivity.

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