Cheaper home-grown power device

Scientists at the Indian Institute of Science, Bengaluru, have developed the country’s first High Electron Mobility Transistor (HEMT) using gallium nitride (GaN). These transistors are useful in electric cars, locomotives, power transmission and other areas requiring high-voltage and high-frequency switching. Commercialisation of this device, currently undergoing field testing, will save on import costs.

When you drive an electric car at full speed, you want the maximum voltage of the battery to be supplied to the engine. The power device should, therefore, offer least resistance to the flow of electricity. Conversely, when you brake, the power device must withstand the battery voltage supplied to it. Power electronic systems demand high ‘blocking voltage’ in OFF-state and high current in ON-state for efficient switching. Specific transistors called HEMT, made of aluminium gallium nitride/ gallium nitride (AlGaN/GaN), provides an edge over silicon-based transistors, as they allow the systems to operate at very high voltages, switch ON and OFF faster, and occupy less space.

Commercially available AlGaN/GaN HEMTs use techniques to keep the transistor in a normally OFF state, which affects the stability, performance and reliability of the device.

The HEMT developed by IISc is normally an ‘OFF device’ and can switch currents up to 4A and operates at 600V. This device will now be taken up for prototype development and field testing. The scientists used aluminium titanium oxide as the gate oxide, where the percentage of aluminium could be controlled during fabrication. Since aluminium titanium oxide is stable, it resulted in high reliability of the transistor.

The power device market was projected to cross the $18-billion mark by 2020, with the share of HEMTs being $5-plus billion. “GaN HEMTs will acquire a major share of the power device market,” says a press release from IISc.

Bacteria-resistant pacemaker

While the pacemaker or metal valve in your heart does a fine job of protecting you, it also runs the risk of infections from the microbial biofilms formed on its surface. Doctors generally treat this with a high dose of antibiotics. However, this does not help as the microbes become antibiotic resistant. In fact, the continuous release of antibiotics from the implants creates conditions for the growth of antibiotic-resistant strains of microbes.

Another disadvantage is the exhaustion of the antibiotic dose due to leaching. A study by a research group led by Sampa Saha, professor, Department of Materials Science and Engineering, IIT Delhi, has proposed a non-leachable antimicrobial coating. The team created a biodegradable 3D-printed polymeric implant, which is modified with anti-infective polymer brushes.

The implant itself is fabricated from a blend of biodegradable polyesters — polyester of tartaric acid, a

natural acid found in tomatoes, grapes and raw mangoes; and polylactic acid from corn starch. Using the polyester as a scaffold, infection-resistant polymer brushes are chemically bonded to its surface. The nano-sized brushes, fabricated from poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride], are antibacterial.