A Fundamental Advantage in Technology: The Power of Synthetic Diamond

At the core of our RF Power Amplifiers (RFPAs) and small satellites (or CubeSats) is a pioneering new invention: Gallium Nitride (GaN)-on-Diamond wafer technology. In 2003, Akash co-founder, Felix Ejeckam (then at Group4 Labs, Inc.), invented the idea of lifting GaN thin films from its original growth substrate (for example, Silicon) and transferring it to a synthetic CVD diamond substrate [17, 9, and 2]. CVD diamond exhibits the highest thermal conductivity known to humans; at 1500+ W/mK, it is nearly four times that of copper or silicon carbide. This creative idea for the first time allows the power of diamond to be applied to high frequency (1 GHz+), high power (10W+) RF devices which are the basis of all radio telecommunications.

Figure 1: Conceptual process for making GaN-on-Diamond Wafers
Figure 2: 4-inch GaN-on-Diamond Wafers

GaN-on-Diamond RF Devices: Beat the Heat

Bringing the GaN active device layers – the sort used in our RFPAs – to within tens of nanometers from diamond helps whisk heat away from the devices almost at the instant that it is generated. Heat is a primary cause of failure or underperformance in modern wireless electronics; reducing or eliminating heat from a chip’s core will significantly and positively impact thermal efficiency, BOM costs, system costs, system lifetimes, and lifetime costs [4, 7, and 10].

Figure 3: Infrared images of operational GaN transistors on various substrates dissipating the same amount of power. GaN-on-Diamond is the coolest of the lot [12, 13 and 14]. Similarly, GaN-on-Diamond could be used to operate at a hotter ambient temperature due to the reduced thermal rise between substrate and gate.
Figure 4: A wafer of GaN-on-Diamond RF devices

GaN-on-Diamond MMICs and Amplifiers: How to Improve Size, Weight and Power

GaN-on-Diamond is the ultimate building block for an RF Power Amplifier; it gives the system designer a new thermal envelope to use for any number of product or system improvements. Performance benefits such as higher data transmission rates and greater picture resolution in a satellite are only part of the story: these Akash RFPAs can eliminate bulky heat sinks; enable smaller and more compact subsystem or system designs; enable greater system-wide efficiency by dissipating less thermal energy; or deliver previously unachievable levels of power from a power amplifier.

Figure 5: In a side-by-side Raman thermography tests [12], GaN-on-Diamond transistors showed a 40% (right box) and 80% (left box) reduction in gate temperature compared to GaN-on-SiC and GaN-on-Silicon respectively. This thermal reduction remained at 80% (blue vs. red line, left box) when compared to a GaN-on-Diamond with dislocation layers still embedded.
Figure 6: In this NRL work, GaN-on-Diamond (below) exhibits a tripling of the DC power density, while also reducing the GaN channel temperature by 50C, compared to GaN-on-Silicon (above) [4].

Intellectual Property

Akash Systems holds 80 patents related to GaN-on-Diamond materials, devices, and satellite communications systems.

Selected Published References

[1] Daniel Francis and Martin Kuball, “GaN-on-diamond materials and device technology: A review” in “Thermal Management of Gallium Nitride Electronics“, edited by Marko J. Tadjer and Travis J. Anderson, Woodhead Publishing, 2022.

[2] Daniel Francis, Brian Loran, Marty Yarborough, Larry Witkowski, Paul Saunier, Kris Kong, Ty Mitchell, and Felix Ejeckam, “Radiation-tested, High-Efficiency, GaN-on-Diamond Power Amplifiers and Satellite Radios” in 45th WOCSDICE EXAMTEC 2022, May 3-6, 2022, Ponta Delgada (Sao Miguel Island – Azores).

[3] “Proton Radiation Test on GaN-on-Diamond RF Power Amplifiers”, by Akash Systems, Inc. December, 2021.

[4] Marko J. Tadjer, Travis J. Anderson, Mario G. Ancona, Peter E. Raad, Pavel Komarov, Tingyu Bai, James C. Gallagher, Andrew D. Koehler, Mark S. Goorsky, Daniel A. Francis, Karl D. Hobart, and Fritz J. Kub, “GaN-on-Diamond HEMT Technology with TAVG = 176 °C at PDC,max = 56 W/mm Measured by Transient Thermoreflectance Imaging”, in IEEE Electron Device Letters, 11 April 2019.

[5] Felix Ejeckam, Ty Mitchell, Kris Kong and Paul Saunier, “Ultra-Cool GaN on Diamond Power Amplifiers for SATCOM”, in Microwave Journal, Diamond Anniversary Issue + Semiconductors & Packaging, June 2018, Vol. 61, 6th Edition.

[6] B. Alvarez, D. Francis, F. Faili, F. Lowe, D. Twitchen, K.B. Lee and P. Houston, “Elimination of Leakage in GaN-on-Diamond” in 38th IEEE CSIC Symposium, Austin, TX, Oct 23rd -26th 2016, Sec G.2. [Wafer maker: De Beers (Element Six)]

[7] L. Yates, A. Sood, Z. Cheng, T. Bougher, K. Malcom, J. Cho, M. Asheghi, K. Goodson, M. Goorsky, F. Faili, D. J. Twitchen, S. Graham, “Characterization of the Thermal Conductivity of CVD Diamond for GaN-on-Diamond Devices” in Compound Semiconductor Integrated Circuit Symposium (CSICS) 2016 IEEE, pp. 1-4, 2016. [Wafer maker: De Beers (Element Six)]. – This paper shows actual measurements of a GaN device channel temperature; an approximately 80C drop in temperature is shown (Table III). GaN-on-SiC shows a peak temperature of 232C, whereas GaN-on-Diamond shows a peak temperature of 152C.

[8] Felix Ejeckam, “Keeping Cool with Diamond”, in Compound Semiconductor Magazine, Vol. 20, Iss.7, October 2014 [Wafer maker: De Beers (Element Six)]

[9] F. Ejeckam, D. Francis, F. Faili, D.J. Twitchen, B. Bolliger, J. Felbinger, and D. Babic, “S2-T1: GaN-on-diamond: A brief history”, in Lester Eastman Conference on High Performance Devices (LEC), August 5-7 2014, DOI: 10.1109/LEC.2014.6951556. INSPEC Accession Number: 14775316

[10] D. Altman, M. Tyhach, J. McClymonds, S. Kim, S. Graham, J. Cho, K. Goodson, D. Francis, F. Faili, F. Ejeckam, and S. Bernstein, “Analysis and Characterization of Thermal Transport in GaN GEMTs on SiC and Diamond Substrates,” GOMACTech 2014, Charleston SC, April 2014, in press. [Wafer maker: De Beers (Element Six)]

[11] F. Ejeckam, D. Babic, F. Faili, D. Francis, F. Lowe, Q. Diduck, C. Khandavalli, D. Twitchen, B. Bolliger, “3,000+ Hours Continuous Operation of GaN-on-Diamond HEMTs at 350C Channel Temperature” in Semiconductor Thermal Measurement and Management Symposium (SEMI-THERM), 2014 30th Annual, March 9-13, 2014.

[12] J. Pomeroya , M. Bernardonia , A. Saruaa , A. Manoia , D.C.Dumkab , D.M. Fanningb , M. Kuball, “Achieving the Best Thermal Performance for GaN-on-Diamond,” in 35th IEEE Compound Semiconductor IC Symposium (CSICS) Oct13-16 2013, Monterey, CA, Section H.4. [Wafer maker: De Beers (Element Six)]

[13] D.C. Dumka, T.M. Chou, J.L. Jimenez, D.M. Fanning, D. Francis, F. Faili, F. Ejeckam, M. Bernardoni, J.W. Pomeroy, and M. Kuball, “Electrical and Thermal Performance of AlGaN/GaN HEMTs on Diamond Substrate for RF Applications” in 35th IEEE Compound Semiconductor IC Symposium (CSICS) Oct 13-16 2013, Monterey, CA, Section F.4. [Wafer maker: Group4 Labs, Inc.]

[14] G.D. Via, J.G. Felbinger, J. Blevins, K. Chabak, G. Jessen, J. Gillespie, R. Fitch, A. Crespo, K. Sutherlin, B. Poling, S. Tetlak, R. Gilbert, T. Cooper, R. Baranyai, J.W. Pomeroy, M. Kuball, J.J. Maurer, and A. Bar-Cohen, “Wafer-Scale GaN HEMT Performance Enhancement by Diamond Substrate Integration” in 10th International Conference on Nitride Semiconductors, ICNS-10, August 25-30, 2013, Washington DC, USA. [Wafer maker: Group4 Labs, Inc.]

[15] D.I. Babic, Q. Diduck, C.S. Khandavalli, D. Francis, F.N. Faili, and F. Ejeckam, “175,000 Device-Hours Operation of AlGaN/GaN HEMTs on Diamond at 200C Channel Temperature”, in MIPRO 2013, May 20-24, 2013 Opatija, Croatia.

[16] D. I. Babic, Q. Diduck, P. Yenigalla, A. Schreiber, D. Francis, F. Faili, F. Ejeckam, J.G. Felbinger and L.F. Eastman, “GaN-on-diamond Field-Effect Transistors: from Wafers to Amplifier Modules”, MIPRO, 2010 Proceedings of the 33rd International Convention, Opatija, Croatia, 24-29 May 2010, pp. 60-66 [Wafer maker: Group4 Labs, Inc.]

[17] “First GaN-on-Diamond transistor announced by Group4 Labs, Emcore, and AFRL” in Semiconductor Today, Aug 2, 2006. [Wafer maker: Group4 Labs, Inc.]