New power semi structures enable sustainable energy

New power semi structures enable sustainable energy

Wide-bandgap semiconductors enable clean technologies

BY MARIANNE GERMAIN and HANNE DEGANS
Imec, Leuven, Belgium
http://www2.imec.be

According to recent estimations, by 2050 we may need twice as much energy as we have available today. The pernicious impact of fossil fuels and the looming shortage of the same have launched a recent acceleration in the search for an environmentally friendly and sustainable energy policy.

According to the International Energy Agency (IEA) we are on the right path and technological innovation is crucial. Today there are massive investments in cleantech, such as renewable energy, efficiency, and less-polluting technologies. Analysts expect this area to experience a real investment boom over the next 20 to 30 years.

The IMEC-SiN-AlGaN-GaN double heterostructure FET has demonstrated breakdown voltages up to 1,000 V.

A transition is underway

In the 20th century, when fossil fuel was the driver of a first industrial revolution, our economy was characterized by lots of manual labor, big factories, and the production of material goods. We acted as if the resources of the world were unlimited. Nowadays we are confronted with the depletion of our resources, the limits imposed by fossil fuels, and climate change problems that force us to reconsider our energy consumption and switch to more environmentally conscious methods.

Currently, our economy is driven by technological innovation, improving the quality of our lives through immaterial goods such as services and content. Technological innovation will also prove to be the key in tackling the energy challenges, where the only way to go is a dramatic switch to renewable energy combined with energy saving in all conceivable ways.

The electronics industry will play a prominent role in this transition. Technologies to generate renewable energy such as photovoltaic systems, non-food-based biofuels, wind energy, and hybrid cars have gained the interest of established chip companies.

Technological solutions

However, the introduction of renewable energy resources for electricity generation creates new additional challenges on the existing electricity network infrastructure:

How to face the increasing number of loads. How to integrate the various delocalized energy sources onto the same grid.How to face the fluctuations between different sources (think about wind farms). How to transport the electricity more efficiently. How to ensure a high reliability and a high stability of the electrical supply.

These challenges are pushing the development of the “smart grid.” The smart-grid network will help enable efficient integration of renewable and traditional energy resources, managing electricity distribution as a function of the availability of the resources and on the needs of the user. The deployment of the smart grid, like most of the new energy-efficient technologies that will appear, will be driven by advances in power conversion systems and more particularly in power electronics components. The result would be improved efficiency and reliability of the energy supply and a reduction in energy consumption.

Apart from a change in behavior and a call for energy-saving improvements in houses and office buildings, technological solutions such as efficient intelligent sensor-based ICT (information and communication technology) systems, more-efficient power conversion, and solid-state lighting will contribute to limiting energy consumption.

The role of power electronics

Power electronics for generating and converting energy is covering a large range of applications ranging from power supplies for ICT, to motor drives, solar converters, or hybrid electrical vehicles. Today, more than 60% of electrical energy passes through Si! Improving the performance of power electronics systems appears more and more as a key lever to significant electrical power consumption reduction.

More-efficient, faster, and more-reliable solid-state devices capable of operating at high-voltage, higher current density, and high temperatures must be developed. It’s a very challenging story for semiconductor developers. Power electronics components are reaching the intrinsic limits of the Si material.

Further innovation and improvement of energy-generating devices will require the use of wide-bandgap semiconductors that allow the production of devices with higher breakdown voltage. Among those, the best candidates appear to be the III-nitride wide bandgap materials, as they offer a combination of high voltage and high electron velocity, which significantly reduce the switching and conduction losses, at high voltages.

These wide-bandgap semiconductors will be enablers for newer cleaner technologies, such as in the hybrid automotive industry or solar converters. Indeed, although they only represent about 10% of the total semiconductor market, the power electronics industry has a higher combined aggregate growth rate (>11%) than the total semiconductor industry (~7%).

But a new technology for power electronics will only gain market acceptance as replacement of existing technologies or as enabler of new technology when its cost is competitive with existing solutions. It is therefore of key importance to find materials and processes that offer an optimal mix of performance and cost. Gallium nitride (GaN) has proven to be such a material.

At Imec, we have demonstrated GaN-on-Si switching devices with a breakdown voltage above 1,000 V and an order of magnitude less conduction loss, as compared to best Si power electronic component available. Higher switching frequency also allows us to dramatically reduce the size of the power converters, opening extremely interesting perspectives in terms of higher integration of power electronics. And, GaN has very promising cost-reduction perspectives.

Wide-bandgap semiconductors such as GaN are today being epitaxially grown on expensive and small-diameter substrates, such as sapphire and SiC. The use of Si (111) as a substrate for III-Nitride components offers not only a cheaper but also an excellent prospect for cost reduction through wafer diameter increase.

III-Nitrides are the sole wide-bandgap semiconductors that can be grown today on a 6-in. wafer diameter, with a very good perspective in a short time for larger wafer diameters. GaN growth on 200-mm silicon wafers has been demonstrated.

Last but not least, cost reduction in GaN-on-Si technology could be achieved by leveraging on the Si scale of economics, if processes compatible with standard Si process flow are being developed. These are today the key drivers of Imec research on GaN-on-Si technology.

And recently, imec combined high-breakdown voltage with low on-resistance and obtained e-mode device operation by growing a GaN-on-Si double heterostructure FET architecture. e-mode operation is typically required in applications for safety reasons. These results hold the promise of a huge market opportunity for GaN-on-Si power devices. ■