The challenges for conventional RF MEMS solutions
RF Front-End module architectures vary significantly from the receiver path to the transmitter path. In a 3G/4G handset, the minimum required receive signal level at the antenna port is -110 dBm and the maximum 3G/4G transmit signal level is +23 dBm (including compatibility with 2G which requires a maximum power level of +33 dBm).
With an RF MEMS ohmic switch, elevated switch power levels induce electrical arcing between the metal contacts, resulting in reliability issues. Hot switching (an RF signal is transmitting when the MEMS device switches off) generates stiction (the mechanical device remains stuck) and ohmic contact degradation.
For the above reasons, the classical RF MEMS structures (bridge and cantilever) are designed with a high level of mechanical 'stiffness'. Their main drawbacks are that they exhibit inadequate switching times and a high sensitivity to the assembly operation (induced stress during packaging and overmolding).
How DelfMEMS addresses the challenge
The challenge has been to define a structure which can overcome these limitations in the switched power level, switching time and integration. The DelfMEMS solution is an anchorless and push-pull mechanical device, which addresses these limitations. Deflected by electrostatic forces, this membrane is used to switch RF signals based on the principle of current electro-mechanical relays/ switches. The innovative microstructures enable:
- Ultra fast switch
- High reliability
- Very small size & cost switch
- Hot switching enabler
- High contact forces and high restoring forces
It is also necessary to have design flexibility to meet the requirements for handset talk time and cost. The integration of the digital and MEMS technologies is now addressed by the module makers through the use of simple die stacking. Currently, the both technologies present low cost, low power consumption and high integration with the recent use of flip-chip technology for MEMS switches.
The current performance of capped DelfMEMS switching technology on devices produced in industrial foundries is -0.2 dB < @ 2 GHz insertion loss, -45 dB @ 2 GHz isolation, and a very high typical linearity above 90 dBm for high throw count T/R switches. These specification requirements will drive MEMS switch technology 2-3 generations ahead of the best SOI technologies. Above all, these features allow RF Front-End module manufacturers to solve the problems inherent in LTE Advanced communication systems.