Today’s mobile handsets need to fulfil a multitude of requirements – they need to be able to operate over an increasing number of frequency bands and across different countries, with each band having its own specific constraints. They also need to combine bands in order to meet data rate expectations in 4G LTE Advanced. The need for high-performance switching between different bands and between transmit and receive modes becomes crucially important.
This leads to many RF function requirements that will have to be imposed on the next generation RF switch:
- Low insertion loss switch>
- High linearity switch
- High isolation switch
- TX carrier aggregation (or Up-Link Carrier Aggregation) switch
- RX carrier aggregation (or Down-Link Carrier Aggregation) switch
- FDD TDD carrier aggregation switch
- 3.5 GHz and 5GHz RF switch
- Ohmic switch
- Multi throw RF switch
Such multi-band, multi-mode handsets contain multiple RF Front-End components and modules. This leads to component duplication and complex RF hardware as well as increased component count. In addition, the platform customization of each end application and regional variant requires advanced engineering, further escalating the development costs.
The radio frequency architecture therefore becomes more complex, consumes more power and generates an increase in the Bill of Materials (BoM) for LTE-Advanced applications.
While continued chip scaling has enabled size reduction and increased functionality per unit area in the device, the passive RF components (resistors, ferrites, high-Q inductors, capacitors, SAW filters, BAW filters and FBAR filters have become the limiting factor for volumetric scaling.
More than ever, new solutions for increased RF hardware integration (more compact) and improved RF performances are needed. For the antenna switch application, existing solid state Silicon-On-Insulator (SOI) and Silicon-On-Sapphire (SOS) technologies are facing challenges and limitations in terms of linearity, isolation and insertion loss.
As an alternative, RF MEMS (radio frequency micro-electro-mechanical systems) technologies have generated high expectations for such applications due to their enhanced technical features and promising electrical performances. However, cost, reliability and manufacturing yield issues have in the past prevented RF MEMS from achieving commercial success and extensive integration into microelectronics systems.
As demand for high performance data consumption increases, with 4G and 5G mobile networks, RF MEMS switching will become much more important as conventional SOI is becoming increasingly incapable of coping with high frequency bands – the best example being very fast SOI switch insertion loss performance deterioration for frequency bands above 2GHz, as well as SOI switch linearity performance limitation that reaches a peak for IIP3 at around 84dBm.