Built-in self -test and self -repair for capacitive MEMS devices

With the rapid development of MEMS (microelectromechanical system) and its increasing applications to safety-critical applications, MEMS testing and fault-tolerant MEMS design are becoming more and more important. A robust and efficient MEMS testing solution is in urgent need for MEMS commercialization, and yield and reliability are also very important issues for MEMS devices. Unfortunately, research in these fields still remains in its infancy. In this thesis both built-in self-test (BIST) and built-in self-repair (BISR) of capacitive MEMS devices are studied.;First, we propose a dual-mode built-in self-test (BIST) technique for capacitive MEMS devices. The BIST technique partitions the fixed (instead of movable) capacitance plates. Due to this partition, the BIST technique can be extended to bulk micromachining and other MEMS technologies. Based on the partition, both sensitivity and symmetry BIST modes can be implemented. Since each of both modes has its own fault coverage, a combination of them ensures a more robust test solution. Three typical capacitive MEMS devices are used as examples to demonstrate the effectiveness of the dual-mode BIST method. Different defects are simulated for these devices. Simulation results prove the effectiveness of the dual-mode BIST technique.;Based on the dual-mode BIST technique, a built-in self-repair (BISR) technique for comb accelerometer devices is proposed. The BISR technique uses modularized design for each device. The device consists of several identical modules. Among them, some are connected as the main device, while others act as redundancy. If any of the working module is found faulty during BIST, the control circuit will replace it with a good module. In this way, the device can be self-repaired. Performance analysis shows that the device suffers sensitivity loss due to the modularized design. This can be compensated by adjusting the device parameters such as shrinking the beam width, etc. Electrostatic force can also be used as a powerful tool to compensate the sensitivity back to normal. The BISR scheme introduces 50% of area overhead. However, with this paid price, we gain great improvement in device yield as well as its reliability.;In order to evaluate the effectiveness of the BISR scheme on yield improvement, a yield model for MEMS redundancy repair is developed. The result demonstrates that a significant yield increase can be achieved for moderate initial yield. The defect fatal rates are also considered in the yield model. Monte Carlo simulation is performed and its result demonstrates an effective yield increase due to redundancy repair. The control circuit for the BISR implementation is also discussed, and the parasitic effects of the control and the BISR device are analyzed. In order to evaluate the reliability enhancement due to redundancy repair, a MEMS reliability model is also developed. Based on the reliability model, we evaluate the MEMS reliability in three different failure mechanisms: fatigue, shock and stiction. Analysis results prove that the BISR design leads to effective reliability enhancement for various failure mechanisms.