|Ph.D Student||Aharon Oren|
|Subject||Micro-Electro-Mechanical Systems (MEMS) for Communication|
|Department||Department of Electrical Engineering||Supervisor||Professor Emeritus Yael Nemirovsky|
|Full Thesis text|
RF MEMS (Micro-Electro-Mechanical-Systems) switches offer superior performance compared to solid-state switches in terms of switch isolation, insertion loss, linearity, and near-zero power consumption. Their most striking feature is the ability to operate over a broadband range of DC to mm-wave frequencies. The main electro-mechanical objectives of MEMS switches are low operating voltage and short switching time. The majority of RF MEMS switches are fabricated using surface micromachining technology.
This work presents the fundamentals of RF MEMS switches based on a relatively new hybrid approach. The term hybrid RF MEMS is used since the MEMS devices are fabricated separately before they are integrated with the RF wafer by vertical integration, using flip-chip bonding technology. The hybrid approach, based on bulk micromachining of SOI wafers (Silicon on Insulator), holds special considerations, derived mainly from the use of single-crystalline silicon as the structural material and the use of a multilayer structure.
One of the key advantages of the hybrid approach is the decoupling of the MEMS design from the RF design. The MEMS devices are fabricated and optimized separately from the RF circuits and the CPW (Coplanar Waveguide) type transmission lines. Thus, complex RF systems and circuits can be realized on a common RF or MIC (Microwave Integrated Circuit) substrate.
In the present study, a novel electro-mechanical design modeling methodology of the switch (bridge thickness and gap) is presented aimed at minimizing the STV (Switching Time Voltage) parameter which is the switching time and operating voltage product. The methodology is illustrated using shunt contact MEMS switches fabricated on top of an RF circuit in GaAs and tunable inductors in InP. This demonstrates one of the key advantages of the hybrid approach that enables the use of the same mechanical design with different RF technologies.
In this study, the RF devices were modeled and 3D electromagnetic simulation were performed. The devices fabrication process is described and special fabrication considerations of the hybrid approach are emphasized.
The electro-mechanical and RF performance of the devices were characterized. A very high isolation level of 34 dB up to 35 GHz and a very low insertion loss of 0.1 dB up to 35 GHz for the shunt switch were achieved. The high isolation value was achieved by using the zipping force technique applied to the switch contact. These results prove the superior performance of the RF MEMS technology over a broadband range of DC to mm-wave frequencies.