Engineers in the University of Southampton School of Electronics and Computer Science have developed a method to make bipolar transistors twice as fast as current devices. Bipolar transistors are solid-state semiconductor devices used in mobile phones and various wireless systems. According to professor Peter Ashburn, who undertook this research in collaboration with STC Microelectronics, the team used a standard silicon bipolar technique with fluorine implants to deliver a record fT of 110 GHz -- twice as fast as the current record. Secondary ion mass spectroscopy and transmission electron microscopy were used to characterize the effect of the fluorine implantation energy and dose, the anneal temperature and ambient and the germanium pre-amorphisation implant on the fluorine profiles. The results showed that retention of fluorine in the silicon is maximized when a high-energy fluorine implant is combined with a low thermal budget inert anneal. "By using fluorine implants, the transistor can operate at a higher frequency, which means it will be twice as fast as it was before," said Ashburn. The fluorine implants are used to suppress boron diffusion in the base of the transistor, which means the base width is narrower, allowing electrons to travel across it faster. "This means that the electronics industry will be able to achieve better performance at little extra cost," Ashburn said. Ashburn and his team believe there is scope to reduce the boron diffusion 50 percent further, and they are currently monitoring how the fluorine behaves and looking at whether there are other materials that will also enable this diffusion. "We have already beaten the world record," Ashburn said. "We have just improved the performance of silicon to a level which was only previously possible with silicon geranium." For more information, visit: www.ecs.soton.ac.uk