PA MMIC Leverages GaN-On-SiC HEMT Technology

MODERN ELECTRONIC-WARFARE (EW) systems require amplifiers with high power, wide bandwidth, and high efficiency. One way to increase output power for high-bandwidth applications is to use a highvoltage transistor technology. Today's galliumnitride (GaN) transistors operate with nearly an order-of-magnitude increase in power-supply voltage while delivering gain and efficiency that rival gallium-arsenide (GaAs) PHEMT devices. At TriQuint Semiconductor, the design and measured continuous-wave (CW) performance of a GaNon- silicon-carbide (SiC), nonuniform-distributedpower- amplifier (NDPA) monolithic microwave integrated circuit (MMIC) has been presented by Charles Campbell, Cathy Lee, Victoria Williams, Ming-Yih Kao, Hua-Quen Tserng, Paul Saunier, and Tony Balisteri.

This amplifier covers 1.5 to 17 GHz. From a 30-V supply, experimental results credit the PA with more than 10 dB small signal gain, 9 to 15 W saturated output power, and 20 to 38 percent peak power-added efficiency. The amplifier utilizes dual field-plate, 0.25-m GaN-on-SiC device technology integrated into TriQuint's three-metal-interconnect (3MI) process technology. That technology features high-density capacitors (1200 pF/mm2), thick plated lines (6.77 m), and capacitors that are constructed directly over substrate vias.

The PA's epitaxial structure has a Si GaN buffer with advanced Fe doping to improve isolation. An AlN spacer is inserted between the buffer and AlGaN Schottky barrier layer. To provide better leakage performance, the surface is terminated by a GaN cap layer. The active device epitaxial layers are isolated by performing a mesa etch to the GaN buffer. See "A Wideband Power Amplifier MMIC Utilizing GaN on SiC HEMT Technology," IEEE Journal Of Solid-State Circuits, October 2009, p. 2640.

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