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    Power Semiconductors; the Next Big Revolution in the Chip Industry

    Power Management systems is always in charge of the reliability, performance, time and breakage of the electronic systems. These systems consist of integrated circuits which ultimately put the load to the type of semiconductor used. Power Semiconductor GaN is replacing the standards of using semiconductors in an integrated circuit. They maximize power density, high breakdown strength, faster switching speed, lower on resistance and more reliability.

    Talking with Sheeba Chauhan, Sub Editor of ELE Times on next big innovations in the wide-band gap semiconductors, Dr. Dinesh Ramanathan, Co-CEO, NexGen Power Systems shed quite a light on few of the important talk points.

    Excerpt:

    , Dr. Dinesh Ramanathan, Co-CEO, NexGen Power Systems

    Q1. What could be the new, more advanced kind of power semiconductor other than GaN (Gallium Nitride)?

    Today’s gallium nitride (GaN) is what people call GaN-on-silicon. This is made by taking a silicon wafer and growing gallium nitride on it. The next and more advanced kind of power semiconductor is based on a technology called GaN-on GaN. This is what NexGen Power Systems develops. This means we do not use a silicon wafer, but grow GaN on a GaN wafer – a single material system which is purely GaN. We have n-type Gallium Nitride, p-type Gallium Nitride, and we make our devices with p-n junctions. This is proven to be exceedingly efficient and the right way to make power transistors.

    Q2. How GaN is exceptionally reliable in comparison to Silicon?

    To answer this, I would like to talk specifically about Gallium Nitride on Gallium Nitride as the structure we touched upon about using p-n junctions is the same as what a silicon does – that is, using p-n junctions to make its power transistors. The Vertical Gallium Nitride devices that NexGen Power Systems makes has the following properties:

    • Our Vertical Gallium Nitride devices avalanche – a built in self-protection mechanism essential for power devices. It is a way by which the devices can absorb significantly high amounts of energy (when the AC line voltage fluctuates) and then come back to operating per specification. This is a very important function and feature which shows reliability.
    • Vertical GaN devices can operate at very high temperatures. NexGen’s Vertical GaN devices can operate at roughly 300 degrees Celsius. The thermal coefficient of the resistance of these transistors is significantly lower than that of silicon. This indicates that when the devices get hot, the resistance of these devices does not increase much. When we compare how much the resistance of silicon devices increases or decreases with that of gallium nitride, we can see it is an order of magnitude lesser than that of silicon.
    • Short-circuit behaviour of our Vertical Gallium Nitride devices are very robust. These devices run through the standard reliability tests and have higher bandgap compared to silicon. This is why Vertical Gallium Nitride is reliable.

    Q3. Why are automotive applications ranging from on-board chargers and DC/DC converters are switching to GaN technology?

    Applications such as Automotive on-board charges and DC/DC converters need two things to improve performance – a high switching frequency and high voltages. In order to get the high switching frequency, automotive applications are trying to move towards GaN-on-Si solutions. However, GaN-on-Si solutions have not been able to go past roughly 650 volts. These applications have also tried to work with silicon carbide (SiC) which can give you high voltages, but they do not switch at high switching frequencies.

    The GaN solution these applications are moving towards is NexGen’s Vertical GaN technology. NexGen offers both high voltages as well as the ability to switch fast (1+MHz). We need high voltages because batteries are moving from 400-volt output to 800-volt output. A battery system that runs at 800-volts needs a 1,200-volt device in order to be able to push power into (charge) that battery.

    We are the only company that makes Vertical GaN devices that can operate at 1200-volts and switch at a 1+MHz switching frequency. This is why automotive applications are moving towards the Vertical GaN solutions that we are bringing to the table.

    Q4. Are wide band gap semiconductors successful in lowering the CO2 emission? If so, what is the base process helping?

    Yes, let me state an example to explain this better. Wide bandgap semiconductors such as Vertical GaN that we make at NexGen can withstand high voltages and can switch these high voltages and high currents at very high switching frequencies. These devices have significantly smaller output capacitance and allow us to make systems a lot more efficient than those built with silicon.

    NexGen has built a 240-watt power supply which is 94% efficient today. The efficiency of existing silicon solutions in the marketplace is roughly 88%, which would dissipate (waste) 28.8-watts worth of power and a 94% efficient power supply with 240-watts will dissipate waste) 14.4-watts worth of power. We are essentially saving 14.4-watts worth of power by being more efficiency. If we multiply 14.4-watts of power saved by roughly 35 million units of 240W power supplies in the marketplace, then we are saving roughly 450 million watts, which is 450 megawatts! 450MW is typically the size of either two coal plants or one nuclear plant. If all 240W power supplies switched to using NexGen technology, we’d save 450MW. Since we do not need it, it helps with reducing carbon emissions. This is how Vertical GaN contributes to the lowering of carbon dioxide emissions.

    Q5. In the near future, what could be the possible enhancement in the present technology of GaN?

    The new future is what we at NexGen are working on, which is Vertical GaN technology. As I said before, our technology is based on pure GaN devices and no other material system that goes with it, such as silicon, aluminium nitride or aluminium gallium nitride. We only have n-type GaN and P-type GaN and our devices are made of p-n junctions. This is the enhancement to the current technology. From a voltage perspective, this technology scales all the way from a 100 volts to 4,000+ volts and can conduct current ranging from 0.5A to 800 amps pulsed in a single device.

    Q6. Please share some focus points of Gallium-nitride technology and solutions.

    Our Vertical GaN technology solutions go into high-end gaming laptops that run on 240-watt power supply. Because of the scalable nature of this 240W design, our technology solutions also go into data centers. The advantage with data centers is that we can reduce the size of the power supply by roughly 50% and increase the overall compute density of one rack in a data center. There are typically a million such racks that go into the data centers that are getting created every year.

    In addition to this, we also work in the automotive space. Besides making automotive systems a lot more efficient, we also reduce their weight which helps in the reduction of their overall costs. Our GaN technology allows automotive to run a lot further on a given battery value. Overall, this reduces the cost of electric vehicles. It also makes these electric vehicles significantly more efficient and improves their performance significantly.

    In addition to these, we also enhance the power supplies of standard laptops and make them more efficient and smaller. This means the amount of power needed to charge batteries inside the laptops and cell phones come down dramatically. We have over a hundred patents to our Vertical GaN technology and device architecture which we manufacture in our fabrication facility in upstate New York, we also have about 30 patents on the system-level solutions that we are putting together based on the Vertical GaN device that we use to make these systems work.

    Q7. NexGen Power system is doing great in its vertical. Shed some light on the challenges you faced to make it reach this height.

    Any new technology that companies work on always comes with a set of challenges. Our biggest challenge has been to make the devices cost-competitive, very high performing and to make sure that we can put systems around these power transistors that can operate at very high switching frequencies.

    The key challenge has been making these devices and getting these devices qualified. In addition to that, we also had to make sure that the systems that we can build with these devices can be optimized and provide the maximum value to our customers in the shortest period of time.

    Sheeba Chauhan | Sub Editor | ELE Times

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