Defects analysis and a self-repairable strategy for tunable RF MEMS filter

Radio frequency (RF) Micro-Electro-Mechanical Systems (MEMS) is currently a developing field. In order to make RF MEMS devices more applicable and marketable, the reliability and testability of the device are critical. In this thesis, a testing methodology to be applied onto the RF MEMS devices is proposed. The RF MEMS device under test is the tunable filter with RF MEMS switches. First, the layout of the tunable MEMS filter is determined. Then electromagnetic simulation is carried out on the filter. Faults are introduced into the layouts of the filters and the frequency output responses of the faulty filter are simulated using the Sonnet EM simulation software. The faults that are simulated are broken structures, parametric variation, stuck-at-on and stuck-at-off for switch faulty condition, and a combination of stuck-at-on and stuck-at-off faults. From the simulation analysis two classifications of the faults are made: one is made according to the effect on the output frequency response, another one is made according to the fault on the filter. Using this testing methodology, the fault that occurs during fabrication process can be quickly identified from measuring the frequency output response of the tunable filter. With the quick identification of the fault, this fault can be corrected during fabrication process so that less faulty filter will be fabricated. Once the list of faults and their effects is available, the tunable filter can be quickly tested to determine the fault. The limitation of this method is that the change of the filter design will require the repetition of the whole procedure to obtain a whole new list of the fault and effect. Admittedly, only a single fault and the combination of the stuck-at-on fault can be detected from the list, but future work will address this issue. Knowing the importance of the MEMS switches, a filter with built-in self repair function is proposed. This filter is designed using “redundant structures” method. This is done by redesigning the MEMS switch biasing circuit into separate control biasing circuit. Then each of the resonators is designed separately for the required tuning center frequency by elongating the narrow line segments. Lastly, all three resonators are put together as one filter. The location of the MEMS switches and switch grounding pads will move according to the narrow line segments. Then this design method is simplified to obtain another similar filter with the built-in self-repair function. This simplified method is easier and requires shorter time to implement the built-in self-repair function on the filter.