Future work

The device fabrication must be improved in two ways. First of all, a modified shadow mask must be employed to prevent parasitic resistance between electrodes.

Second, the lateral contacts of the mechanical switches must be metallized as well. In oblique metal deposition as shown in Fig. 5.1, the device is fixed at a constant angle during the metal deposition. The process needs to be done twice to metallize both lateral contacts. In order to prevent the shortage between the two switch electrodes, the substrate beneath the switch gap also needs to be removed.

Fig. 5.1 Oblique metal deposition of the switch gaps

Vacuum packaging can be utilized to improve the device performance. The MEMS device is sealed away from environmental influence such as atmospheric pressure, temperature gradients and contamination. Vacuum packaging should

Fig. 5.2 Principle of electret-based generator [46]

m bm

k

xr(t)

xi(t)

C(xr)

Load

Polarized electret source

significantly improve the quality factor of the device by decreasing the squeeze film damping effect between the movable structures. Another benefit from the vacuum packaging is the slower oxidation of the metal contact surfaces of the mechanical switches. Thus, the life time of the device can be expanded.

The mechanical switches will only operate when the device reaches maximum displacement. In order to provide output power in lower displacement conditions, the AC output power circuitry should be utilized. The device design under this operation will be done in the future. The auxiliary battery supply can be replaced by a pre-charged electret. Fig. 5.2 shows the schematic of the electret-based energy converter [46]. Without the need of the auxiliary battery supply, the application potential of the capacitive energy converter is extended.

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Appendix A Detailed Simulink Models

Fig. A.1 “MEMS_structure” subsystem

Fig. A.2 “Qcontrol” subsystem

Fig. A.3 “Qmax_SW1” subsystem

Fig. A.4 “Qmax_SW1” subsystem

Fig. A.5 “SW2” subsystem