MQEC Mimix Broadband Abstract

The recent success of smart-phones such as the iPhone and the transition from voice to mobile video, gaming and other data-hungry applications is driving unprecedented growth in wireless data traffic worldwide. A recent survey predicts that by 2014 there will be 5 billion personal devices connected to mobile networks generating 3.6 exabytes of data traffic per month, a 39-fold increase in four years. Network operators will accommodate this growth through equipment upgrades and new base-station installations requiring additional backhaul capacity, much of it in the form of microwave and millimetre-wave links using existing radio bands and new frequency allocations. Efficient use of the available spectrum for wireless backhaul requires the use of high-order modulation schemes which in turn demand high linearity and low noise front-end components operating up to 80 GHz. All components must be carefully designed for excellent reliability in harsh operating environments to minimise on-going maintenance costs and network down-time. Compound semiconductors based on gallium arsenide (GaAs) remain the preferred technology for point-to-point microwave and millimetre-wave applications due to physical properties of the material system such as high electron mobility and a proven track record in commercial, military and space applications. The Pseudomorphic High Electron Mobility Transistor (PHEMT) with gate features defined by electron-beam lithography is the most common workhorse for amplifiers and frequency converters in this frequency range. Despite the high cost of electron-beam GaAs wafers relative to optical lithography silicon they remain competitive in low and medium volume markets due to very low mask costs and mature fabrication technology. Much of the compound semiconductor technology applied to commercial products today is the result of defence related research and funding, while high volume markets such as handset power amplifiers and front-end modules have helped to reduce GaAs wafer prices across the industry. Pure-play semiconductor foundries have emerged alongside fabless (and fab-lite) semiconductor companies to drive efficiencies and competition in the marketplace. Mimix Broadband is a fabless semiconductor company addressing the microwave and millimetre-wave radio markets with a broad product range of compound semiconductor ICs. Recent product designs at Mimix Broadband illustrate the challenges associated with millimetre-wave circuit design and demonstrate the technological advances that will support data traffic demands in the next few years with particular emphasis on cost reduction, linearity, efficiency and reliability. These examples show how high levels of integration and the transition to lower cost packaging solutions create new challenges for electrical, electromagnetic and thermal design. New measurement techniques, CAD tool improvements and the steady growth in computing power continually open up new possibilities for device modelling and circuit simulation, however the designer must be prepared to constantly adapt and innovate to make best use of current and future technologies. New foundry processes continue to emerge. These offer interesting possibilities for future millimetre-wave applications. Semiconductors based on gallium nitride (GaN), indium phosphide, silicon on insulating substrates and short gate length optical lithography PHEMTs in GaAs and GaN will compete against electron-beam GaAs PHEMT for front-end IC applications in wireless backhaul. In high volume consumer markets cheap RF CMOS has proven capable of adequate performance for consumer 60 GHz wireless links but it remains to be seen whether it can provide the linearity, efficiency, power and noise performance required in the more demanding cellular backhaul environment. Many interesting challenges remain for both foundry technology and circuit design in meeting the expected growth in data traffic against a relentless drive to reduce costs.