微馬達設計與製作

Abstract

本文主要是研究微馬達的設計與製作。在製程考量方面，我們選擇了和半導體製程最為相容的表面微細加工技術，並採用類似Deng的幾何配置，設計製作了一個靜電側邊驅動、晃動式微馬達。我們並對此種設計提出改進之道，搭配上改進的製程，以期能提高微馬達製作的良率並使微馬達的效能提昇。其中有兩個主要的改進：其一是蝕刻阻擋（Etching stop）的製作使得中央固定軸不至於在結構釋放（Releasing）的過程中被破壞，此一蝕刻阻擋並可以形成轉子接地的通路，減低轉子與下方基材間的電位差和吸力。其二是採用混合層來構成軸承間隙（Bearing clearance）。我們利用濕氧化層（Wet oxidation）的高均勻性（Conformality）與電漿輔助化學氣相沈積（PECVD）氧化層不消耗矽之特性來得到厚度為一微米的軸承間隙，此間隙可以有效克服反應離子蝕刻（Reactive ion etching）造成的結構鎖死（Interlocking）並可能提供轉子一個向上的提昇力（Lift force）。在製程方面的努力與設計上的修正使我們製作出馬達主要的結構：分離且可動的轉子、定子、及聯結轉子與錨的軸承。但是由於機台的效能不佳，結構邊壁（Sidewall）的垂直度仍有待提昇。此外，我們亦依循Trimmer的推導，建立了適用於本身設計的力矩數學模型。而利用此數學模型可以估計出在理想操作條件下微馬達的輸出力矩。

This thesis focuses on the design and fabrication of micromotors. By using the surface micromachining technique, we designed and fabricated an electrostatic side-drive wobble micromotor based on Deng's geometric design.. Moreover, we also made improvement on her design and process. There are two major new ideas: the first is the fabrication of the etching stop which protects the bottom of the anchor from being damaged during releasing. With this etching stop, an additional electric path from the rotor to the substrate is also established. This electric path is always effective and would reduce the potential difference between the rotor and the substrate. The second is the 1 mm bearing clearance composed by a mixed-layer, a wet oxide and a PECVD oxide layer. The former has the advantage of high conformality while the latter consumes no polysilicon. This thick bearing clearance can solve the interlocking problem posed by the non-uniform RIE process and may induce a lift force on the rotor. Due to the efforts on process and the modified design, we fabricated a micromotor with the free moving and separated rotor, the stator, and the bearing connecting the rotor and the anchor. But because of the low performance of the RIE machine we've used, the sidewalls were not vertical as expected. Improvement on this process step is required. In addition to the design and the fabrication process, we also followed Trimmer's derivation and established the torque model for our micromotor geometry. By this model we can estimate the driving torque of the micromotor under ideal operation conditions.