低接觸阻值微慣性開關之研發

Abstract

運輸業常有偵測數十G碰撞發生的需求，若使用被動式慣性開關做為檢測元件，可具有安裝容易且不耗能的優點。而以往文獻中，被動式且以數十G為閾值的慣性開關，常有接觸阻值過高(數MΩ)，或體積較大的問題。 本研究重點即在研發被動式、體積小、低接觸阻值且加速度閾值在數十G範圍的微慣性碰撞開關。其作動機制是元件原為斷路，當受到某特定方向加速度閾值以上的碰撞時，慣性力可使內部卡榫機構形成通路。在結構設計上，是將加速度感測方向設定在出晶片平面向，再配合鎳基面型微加工技術，採用低電阻率的鎳製作可上下作動的懸浮結構，因此可加大卡榫寬度以增加卡榫接觸面積。利用這兩項特點，以使數十G微慣性開關元件可同時具有低接觸阻值且體積小的優點。另外，在此所提出的設計，也具有在僅改變懸浮彈簧厚度下，可提供不同加速度閾值的特點。 本慣性微開關已成功經電鍍製程完成，整體尺寸約2 mm x 2 mm x 40 um，其中彈簧、質量塊與卡榫結構的厚度分別為3.58 um、37.48 um與21.51 um。在測試方面，是以震動平台施加脈衝形式加速度於元件上，配合個人電腦截取加速度值與元件開關訊號；當受到17.22G加速度時，成功得到卡榫開關狀態切換的訊號，與模擬所得加速度值17.0G相比，約有1.3%誤差；接觸阻值為1.7KΩ，阻值低於100KΩ，易於被應用，非接觸阻值為100MΩ，與接觸阻值差距大，容易以電路判斷訊號。

In need of detecting the impact acceleration ranging in several tens of G during transportation, using passive sensors is more convenient to setup and power-efficient. However, the passive inertial switches with the threshold acceleration value in several tens of G are facing to the problems of high contact-resistance or large size. In this study, we develop a passive, small in size and low contact-resistance micro inertial switch with its threshold acceleration ranging in several tens of G. The latching mechanism in the inertial switch forms an open circuit just after been fabricated. If the inertial switch experienced the acceleration greater than the threshold value from its sensing direction, the latching mechanism would be locked and form a close circuit. Setting the sensing direction normal to the wafer plane and fabricating the suspension structures via nickel-based electro-plating technology, large contact area and low resistance ratio linkage can be achieved. With the two methods, the passive inertial switch with its threshold acceleration ranging in several tens of G can not only be small in size but also low in the contact resistance. The main structure is realized successfully with its overall size in 2 mm × 2 mm × 40 um. During the inertial switch experiencing the pulse acceleration induced by the shaker, the PC was simultaneously capturing the trigger signal and the acceleration value. The resistance was 100MΩ and 1.7 KΩ before and after applying 17.22G impact. From the analytical simulation, the threshold acceleration is 17.0 G with 1.3% difference compared with the experimental result.