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Cooking the Thanksgiving Turkey with GaN

by Eric Higham | Nov 30, 2015

I am just back from my Thanksgiving holiday. Thanksgiving traces its roots to a celebration of days of “special blessing”. In the US, the first Thanksgiving is commonly attributed to the Pilgrims celebrating their first harvest in the “New World” in 1621. Although there are some disputes, this celebration took place in Plymouth, MA, about 45 miles down the road from my office. “Thanksgiving” really encompasses the 4-day period from Thanksgiving Day on Thursday, through the weekend. It’s a great time to catch up with family and loved ones you don’t get to see or talk to very often and the traffic in the Northeast is a testimonial to the number of people that do travel to be with family. Since this holiday celebrates the Pilgrims’ first harvest, food figures prominently in the proceedings. Turkey is the centerpiece for a traditional Thanksgiving Day meal and I’ve been eating turkey, in various forms and consistencies all weekend…at just about every meal!

Watching the cooking process and the result on Thanksgiving got me thinking about the difficulties in cooking a turkey. They are oddly shaped, the thickness and density of the meat varies significantly and some people, like me, prefer stuffing that is cooked inside the turkey, which presents an entirely different cooking environment. While most turkeys are too large to fit into a microwave oven, the challenges of cooking a turkey illuminate some of the advantages of “RF Energy”, a new market segment that is, pardon the pun, really heating up!

I just wrote an Insight on applications and market forecasts for RF Energy (RFE)and the current state and future trends of the market are very interesting. If you make the rounds of the RF & Microwave industry trade shows, you’ve probably seen solid-state microwave oven demonstrations from either NXP or Freescale. Just before the European Microwave Conference in 2014, founding members E. G. O., Huber+Suhner, ITW, NXP Semiconductors, Rogers and Whirlpool R&D announced the RF Energy Alliance (RFEA). The RFEA aims to standardize, promote and educate target audiences about the advantages of using solid-state technologies to generate RF energy in a variety of consumer, industrial, medical, lighting and automotive applications. The incumbent technology for these applications is tube-based magnetrons and the founding members of the RFEA, along with new members MACOM, WIN Semiconductors and Anaren look to make use of the performance, efficiency, reliability and size benefits of LDMOS and GaN technology in this market segment.

This is a very compelling adjacent market opportunity for GaN/LDMOS, because the power and frequency requirements for RFE match current wireless applications very closely. One of the very big features of the solid-state technology is the fast response time that leads to a benefit of much more customization in the final application. Getting back to my turkey, a magnetron is prone to frequency and power variation on successive sweeps. This leads to cooking hot spots in a microwave that may be different from one use to another. Magnetron-based microwave ovens address this with a rotating platter and the idea that moving the food through the hot spots and heating gradients will “normalize” the process.

The RF Energy proponents propose microwave ovens with multiple, smaller size RF amplifiers located around the cooking cavity of the oven. The solid-state power amplifier can be controlled with a closed loop feedback network to intentionally vary frequency, power level and output phase to produce the optimum heating profile for a particular “load”, or piece of food. The simple block diagram from NXP shows the implementation of this idea.


The advantage of being able to control the power profile is shown in this video from NXP:


NXP Solid State Cooking Demonstration


About 2/3 of the way through, the presenter describes a program that allows the power, frequency and phase to vary. He then places a circuit board with red, green and yellow LEDs into the microwave and we see how the program can vary the heat distribution within the microwave cooking cavity. In addition to being a nice visual presentation, this starts to hint at the customization to a particular load that is possible.


Not to be outdone, the following video from Freescale shows a microwave oven outfitted with Freescale PAs and how it can cook a steak and vegetables at the same time:


Freescale’s  Solid-State RF Cooking Demonstration


My favorite video shows some examples of the broader range of RF Energy applications. It also shows a fish, encased in ice, cooked in a microwave without melting the ice. I’m not sure why you would want to do that, but it does indicate the high level of cooking precision that solid-state PAs can offer in microwave ovens.


NXP RF Energy Market Applications (cooking a fish in ice)


So, other than doggedly trying to figure out how I can cook my turkey in a microwave next Thanksgiving, why is this interesting? It really starts to get interesting when you consider all the potential market applications. In a webinar on the topic, MACOM stated that 70 million microwaves, globally and nearly 11 million dryers (US and EU) are sold every year. The microwaves range from about 600W – 1500W, so this puts the power opportunity at more than 42GW! Now, if the PAs can be distributed around the cooking cavity, the total power may drop, but the size of the opportunity is enormous. If you factor in some of the automotive, medical, lighting and industrial applications mentioned in the last NXP video, the total addressable market (TAM) goes well into the $billions.

The other interesting aspect of this market is that LDMOS or GaN PAs will power the “solid-state” amplifiers that RF Energy applications will use. MACOM has joined the RFEA and become such a big proponent of RF Energy because they see their GaN-on-silicon technology as fitting these opportunities perfectly. Some of the lighting and automotive opportunities could run the transistor quantities into the billions and they see this as a great driver to help them transition to 8” wafers, reduce the price of the devices and establish them as a leader in this market.

This sounds very promising for GaN manufacturers, but what’s the catch? As always, market acceptance will hinge strongly on price. The advantages of solid-state versus magnetrons are undeniable and GaN has a strong performance advantage versus LDMOS. The RFEA believes the price for a 300W solid-state power module must be no more than $12.00! This equates to $0.04/W and this is very challenging. Despite the challenge, the market opportunity is enormous and many of the GaN OEMs are working hard to address this opportunity.

I’ll be following this application closely, so check back to hear about the latest developments and whether I am cooking my turkey in a microwave oven next Thanksgiving!

  • Eric





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