Deep C. Dumka

Wideband high power GaN on SiC SPDT switch MMICs

The design and performance of three wideband SPDT switch MMICs utilizing GaN on SiC technology are presented. The circuits are designed to cover frequency ranges of DC-6 GHz, DC-12 GHz and DC-18 GHz with input power handling optimized over the specified bandwidth. Measured in-fixture s-parameter data demonstrates a maximum insertion loss of 0.7 dB, 1.0 dB and 1.5 dB, respectively for the 6 GHz, 12 GHz and 18 GHz designs. Measured continuous wave power data demonstrates typical input RF power handling of 40 W, 15 W and 10 W, respectively for the 6 GHz, 12 GHz and 18 GHz MMICs.

Low thermal resistance GaN-on-diamond transistors characterized by three-dimensional Raman thermography mapping

In order to achieve ultra-high radio frequency output power densities in GaN-based transistors new thermal management solutions must be developed for efficient heat extraction, including the use of high thermal conductivity substrates. Integration of GaN devices with the highest thermal conductivity material available, diamond, instead of the standard GaN-on-SiC, can lead to a substantial reduction in device thermal resistance. Current GaN-on-diamond transistors are shown to result in a 40% reduction in peak channel temperature when benchmarked against equivalent GaN-on-SiC transistors, with the potential for even further reductions through optimization. In order to understand the contribution of substrate and GaN/substrate interface to the device thermal resistance, a 3D Raman thermography mapping and modelling approach has been developed. The GaN/diamond interface thermal resistance is found to have the largest contribution to the thermal resistance of current GaN-on-diamond devices.

Progress in GaN Performances and Reliability

With the DARPA Wide Bandgap Semiconductor Technology RF Thrust Contract, TriQuint Semiconductor and its partners, BAE Systems, Lockheed Martin, IQE-RF, II-VI, Nitronex, M.I.T., and R.P.I, are achieving great progress towards the overall goal of making gallium nitride a revolutionary RF technology ready to be inserted in defense and commercial applications. Performance and reliability are two critical components of success (along with cost and manufacturability). In this paper we will discuss these two aspects.

High-performance double-recessed enhancement-mode metamorphic HEMTs on 4-in GaAs substrates

Enhancement-mode InAlAs/InGaAs/GaAs metamorphic HEMTs with a composite InGaAs channel and double-recessed 0.15-/spl mu/m gate length are presented. Epilayers with a room-temperature mobility of 10 000 cm/sup 2//V-s and a sheet charge of 3.5/spl times/10/sup 12/cm/sup -2/ are grown using molecular beam epitaxy on 4-in GaAs substrates. Fully selective double-recess and buried Pt-gate processes are employed to realize uniform and true enhancement-mode operation. Excellent dc and RF characteristics are achieved with threshold voltage, maximum drain current, extrinsic transconductance, and cutoff frequency of 0.3 V, 500 mA/mm, 850 mS/mm, and 128 GHz, respectively, as measured on 100-/spl mu/m gate width devices. The load pull measurements of 300-/spl mu/m gate width devices at 35 GHz yielded a 1-dB compression point output power density of 580 mW/mm, gain of 7.2 dB, and a power-added efficiency of 44% at 5 V of drain bias.

Electrical and Thermal Performance of AlGaN/GaN HEMTs on Diamond Substrate for RF Applications

Thermal conductivity of the substrate affects the performance of high power RF devices. It is a dominant limiting factor in current state-of- the-art GaN HEMTs on SiC substrate. Due to high thermal conductivity, diamond substrate is an attractive alternative for GaN HEMTs. We have developed device quality GaN-on-diamond wafers using CVD diamond and fabricated 0.25 μm gate length HEMTs. We present detailed electrical and thermal results of the fabricated devices, which show RF power comparable to standard GaN-on-SiC HEMTs. We demonstrate over 25 % lower channel temperature for these devices compared to GaN-on-SiC devices. Electrical results using DC and RF tests and thermal results using IR thermography and micro-Raman spectroscopy are included.

GaN Takes the Lead

Gallium nitride (GaN) technology is transforming RF monolithic microwave integrated circuits (MMICs) for power amplifiers (PAs), switches, low noise amplifiers, and more. Vendors are now producing GaN MMICs in volume and achieving outstanding performance. GaNs characteristics enable PA MMICs with 35 times the output power of GaAs alternatives or much smaller die sizes from L-band through Ka-band. High-power switches with low insertion loss up through 18 GHz have been developed. Low-noise amplifiers have been demonstrated with noise figures equivalent to gallium arsenide (GaAs) but with much higher input power survivability. The market for GaN RF MMICs spans commercial and military applications, including base station, cable television infrastructure, communications, radar and electronic warfare (EW), among others.

Achieving the Best Thermal Performance for GaN-on-Diamond

GaN-based RF transistors offer impressive power densities, although to achieve the maximum potential offered by GaN, thermal management must be improved beyond the current GaN-on-SiC devices. By using diamond, rather than SiC substrates, transistor thermal resistance can be significantly reduced. It is important to experimentally verify thermal resistance, rather than relying solely on simulation expectations, using measurement results to aid further optimization. The novel thermal characterization methodology presented here combines Raman thermography and simulation to determine the substrate thermal conductivity and GaN/substrate thermal resistance in GaN-on-diamond devices. Measured GaN-on-diamond interfacial thermal resistance is similar to reported values for GaN-on-SiC, whereas the diamond substrate thermal conductivity is substantially higher, resulting in a significantly improved thermal resistance with respect to GaN-on-SiC, with great potential for further improvement.

Design considerations for GaN based MMICs

Select considerations related to Gallium Nitride (GaN) based MMIC design are discussed. The unique properties of this material pose challenges to IC designers not typically encountered in Gallium Arsenide (GaAs) based technology. Specific examples of how some of these issues impact circuit design are discussed for wideband power amplifiers, high efficiency class-E power amplifiers and high power switching transistors.

AlGaN/GaN HEMTs on Diamond Substrate

In this paper AlGaN/GaN high electron mobility transistor (HEMT) fabricated on diamond substrate is presented. Epitaxial AlGaN/GaN layers were first grown on high resistivity Si (111) substrate and transferred to polycrystalline diamond substrate, which was separately grown by chemical vapor deposition (CVD). It is concluded that these are the best-reported results for a transistor using GaN on diamond material.

High Efficiency Ka-Band Power Amplifier MMIC Utilizing a High Voltage Dual Field Plate GaAs PHEMT Process

The design and performance of a high efficiency Ka-band power amplifier MMIC utilizing a 0.15um high voltage GaAs PHEMT process (HV15) is presented. Experimental continuous wave (CW) in-fixture results for the power amplifier MMIC demonstrate up to 5W of saturated output power and 30% associated power added efficiency at 35GHz.