Power gains

Advanced energy-efficient semiconductor devices with lower running costs are to be developed in a collaboration between a leading firm and UK universities.

Dynex Semiconductor — the UK subsidiary of Dynex Power — has received £530,000 of DTI funding to develop advanced, ultra-high power thyristor switches as part of the Newton project. A thyristor is a solid-state semiconductor device that is commonly used in high-voltage and high-current applications to switch an alternating current on and off.

Dynex is also developing high-power density transistor modules in the HIDRIVE project. Both devices can be used in high-power electronic applications such as power transmission systems and motor drives.

A small team from Loughborough University’s School of Mechanical and Manufacturing Engineering and its Institute of Polymer Technology will also work on the Newton project.

According to Paul Taylor, Dynex chief executive, the Newton project will help minimise power losses that are generated in a thyristor switch and could be useful in applications that deal with huge voltages such as at the distribution level of the National Grid.

‘The thyristor is quite a mature technology and in reality hasn’t benefited from recent advances. So we are applying new semiconductor technologies and innovations — such as new types of bonding and novel internal structures to protect it from high electric fields — to improve its performance,’ said Taylor.

Loughborough’s key area of expertise is in the packaging of electronics and semiconductors using the injection moulding of thermoplastics. The institute has been working with Dynex on similar technologies for a number of years. As part of the new project the university’s team will be looking at ways of encapsulating the new devices in plastic, a technique with a number of key advantages, according to Loughborough’s project leader Prof David Whalley.

‘Encapsulating in polymer reduces the cost of the device and also makes it more robust,’ he said. ‘It will greatly reduce assembly costs too by taking away all of the different packaging layers that are usually involved.

‘Quite often with electronics you have the semiconductor in a package, then put onto a circuit board, followed by another box which is then attached to something else. For some applications it is even then encased in a separate waterproofed box. Polymer packaging strips away all of these unnecessary and expensive layers.’

In the past the team has looked at using moulding in automotive applications, allowing electronic modules to be put directly into mechanical components, such as sensors in car bumpers, which can be moulded directly into the bumper rather than as a separate component.

For the Newton project the packaging of ultra-high power thyristors in polymer could work out far cheaper than existing processes, particularly as the semiconductors grow in size, said Whalley.

‘The real thing with these devices is that the current way of packaging is hermetic, which is an expensive process,’ he said. ‘The traditional packages for these types of devices are a mixture of ceramic and metal, which is totally impervious to atmospheric gases, whereas even the most resilient polymer will allow moisture through, which is why they’ve been avoided up until now.’

Whalley explained that for high-risk areas such as aerospace and defence the possibility of moisture contaminating the electronics made using polymers far too risky. However, advances in polymer production could soon change this, according to Whalley.

‘Modern high-purity polymers have not got ionic contamination so it is fine for them to be in close contact with semiconductors without having to worry too much about corrosion or other problems, if and when moisture does diffuse through,’ he said.

The Loughborough team has also patented a number of technologies related to polymer electronics. As well as developing soluble polymers for electronic packaging to make the products easier to recycle, Whalley and his team are also looking at ways of replacing printed circuit boards using textured polymers. These novel plastics would enable the electronic interconnections to be introduced through polymer moulding, an idea for which a patent application has just been submitted.

In the HIDRIVE project — also part of the DTI Technology Programme funding — Dynex is working with the Emerging Technologies Centre at De Montfort University. The project will look at the development of new, smaller transistor modules that could be used in high-power motor drive applications.

One of the project’s collaborators, Converteam, has been involved in developing high-power marine drives for the Royal Navy’s newest fleet of Type 45 all-electric propulsion destroyers.

Both projects are due to start early next year.

Niall Firth