Further miniaturization of electret and MEMS component separation products

“As far as the current development trend is concerned, the size of Electronic products is getting smaller and smaller. In the coming era of the Internet of Things, micro sensors can develop technology applications that can only be found in fantasy novels. Naturally, the operation of special equipment for microelectronics technology still requires electrical energy, and its operating electrical power mainly comes from the collection of environmental energy such as mechanical vibrations by micro-electromechanical systems (MEMS).

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Experts from Tokyo Institute of Technology have developed a miniature energy harvester with a more flexible design process. Electricity is a MEMS vibration energy harvester provided by an external electret, which is very important for the development of future IoT applications.

As far as the current development trend is concerned, the size of electronic products is getting smaller and smaller. In the coming era of the Internet of Things, micro sensors can develop technology applications that can only be found in fantasy novels. Naturally, the operation of special equipment for microelectronics still requires electrical energy, and its operating electrical power mainly comes from the collection of environmental energy such as mechanical vibrations by micro-electromechanical systems (MEMS).

Figure 1 Traditional MEMS energy harvester (Image source: Tokyo Institute of Technology)

As shown in Figure 1, the traditional MEMS energy harvester places an electret (a dielectric that is polarized and can “permanently” maintain the electrical polarization under the action of a strong external electric field and other elements) in a MEMS capacitor. The capacitor has a moving electrode driven by environmental energy, which in turn causes the charge to move. However, the compatibility of the manufacturing process of electret and MEMS components is required to be high, which has great limitations on design and manufacturing.

Assistant Professor Daisuke Yamane of Tokyo Institute of Technology and his research team have developed a new MEMS energy harvester. It consists of two separate chips: one is a MEMS tunable capacitor, and the other is a capacitor made of electret and dielectric materials (Figure 1).

Yamane expert professor said: “This technology has completed the separation of electret and MEMS components for the first time.”

Figure 2 The collection principle of the new MEMS energy harvester (picture source: Tokyo Institute of Technology)

The basic principle of collection of the new MEMS energy harvester is shown in Figure 2. The resistance of the electret power circuit is fixed (Cfix), while the capacitor of the MEMS adjustable capacitor (CM) changes according to the tension of the spring (caused by external vibration).

Parameter CM and Cfix, if CM is higher, it will cause the charge to move, and the adjustable capacitor will get the charge. When Cfix is ​​higher, the charge moves in the opposite direction, and the capacitor in the electret circuit gets the charge.

Figure 3 System circuit diagram and output voltage (picture source: Tokyo Institute of Technology)

The movement of electric charge produces usable electricity. The left side of Figure 3 is a simplified diagram of the chip structure and device, and the right side shows the voltage generated by the collector.

Experts from Yamane said: “The new energy harvester separates the electret from the MEMS component, which improves compatibility and flexibility in design and manufacturing. This will promote the development of the Internet of Things era.”