整合機械式開關之微電容式振動-電能轉換器

Abstract

微機電系統是一個微系統與電子電路整合的科技平台。在無線感測網路等應用中，這些高度整合的可攜式元件都具有獨立電源的需求。拜先進的超大型積體電路技術所賜，這些微系統節點的電能需求已降至數十μW的程度。利用環境中的能源轉換成電能來供給這些可攜式元件使用已經成為一個可行的方法。 此論文呈現一個電容式振動-電能轉換器的設計、製作以及量測。在1 cm2的元件面積以及3.6 V 輔助電池電源的限制下，此元件的輸出功率可達31 μW (輸出電壓約40 V)。我們使用一個4克的外加質量塊來調整元件特性，使其在輸入振動下共振。元件整合了機械式開關，以提供準確的充電-放電能量轉換控制。元件是利用SOI晶圓並且搭配深蝕刻技術來製作，現階段已克服了所有的製程問題。此能量轉換器已經過量測。元件在有無承載外加質量塊的不同情形下，其共振頻率都符合設計值。元件的電容變化量比預期的還要小。利用背後基底部份掏空的技術，元件的寄生電容已被最小化。元件在無外加質量塊、5 Mohm負載以及1880 Hz振動頻率的情形下，量測到的交流輸出功率為1.2 μW。此情形的最大輸出功率預計為16 μW。有承載外加質量塊的元件之輸出功率量測仍在進行中。

Micro-Electro-Mechanical System (MEMS) is the technology platform that promotes the integration of various microsystems with circuit electronics on the same chip. When applied in fields such as wireless sensor networks, each one of these highly integrated portable devices needs an independent power supply. Due to recent advances in low power VLSI design technology, the power consumption is reduced to about a few tens of microwatts. Therefore, it becomes feasible to power the portable devices by scavenging the ambient energy. The design, fabrication and measurement of a capacitive vibration-to-electric energy converter are presented in this thesis. With a device area constraint of 1 cm2 and an auxiliary battery supply of 3.6 V, the device was designed to generate an output power of 31 μW with an output saturation voltage of 40 V. An external mass of 4 grams was needed to adjust the device resonance to match the input vibration. Mechanical switches are integrated onto the device transducer unit to provide accurate charge-discharge energy conversion timing. The device was fabricated in SOI (silicon-on-insulator) wafers by deep silicon etching technology. By overcoming all processing issues, the device can be successfully fabricated by a modified fabrication process. Measurements on the energy converter were also conducted. Resonant frequencies of the device with and without the external mass agreed with the designed values. Capacitance change was smaller than expected. Parasitic capacitance was minimized by partial back side substrate removal. Without the external mass, the measured AC output power was 1.2 μW with a load of 5 Mohm at 1880 Hz. The maximum output power in this condition is expected to be 16 μW. AC output power measurement of the devices with external mass attached is still in progress.