以低溫氣膠沉積法製作壓電微加工超音波傳感器的研究

Abstract

隨著智慧型手機與平板裝置之熱銷，觸控技術幾乎成為中小型移動裝置的必要功能。雖然觸控技術目前已漸趨成熟，但是3D面板上的觸控技術仍是一項需要突破發展的技術。不同於傳統的觸控面板，3D聲波面板為非直接接觸面板之觸控技術，目前主要的技術有電磁式、光學式和超音波式幾種技術，其中，超音波式具有低成本、可支援多點觸控、可輕易掛載於現有面板和可發展手勢觸控等優勢，相較於其他技術，超音波式的3D觸控為一項有潛力的重要技術。尤其在大尺寸螢幕的應用中，電容式觸控技術的製程良率過低且成本過高，而超音波3D觸控技術可有效解決此困境。由於國內研發觸控用的超音波收發器尚未成熟。關鍵的技術與製程皆掌握在國外廠商，使得價格在國際競爭上無法取得明顯優勢。若能設計出良好的超音波收發器，將可以有效提高解析度並簡化後端演算法的計算量，如此也將可以運用超音波元件的創新設計來作為取得大尺寸觸控螢幕競爭優勢的關鍵點。 本論文將針對新型的觸控感測器結構進行研究，透過微機電製程技術製作新型的壓電式微加工超音波傳感器(Piezoelectric Micromachined Ultrasonic Transducer , PMUT)，不同於以往溶膠-凝膠法(sol-gel)、網版印刷法(screen printing)與真空濺鍍法(sputtering)的PZT沉積技術，我們利用低溫氣膠沉積法(Aerosol)的方式沉積PZT，期望達到降低成本、快速沉積的目的；另外，我們嘗試使用不鏽鋼薄板取代過往矽基板的PMUT架構，量測其元件特性進行討論。最後透過反射性測試得到最適合皮膚感度的頻率範圍在55 kHz至65 kHz，未來期望將PMUT元件設計在此頻率範圍內，使其能應用於3D大尺寸聲波面板。

With smart phones and tablet devices getting ever more popular, touch panel technology is becoming an essential feature of small and medium mobile devices. Despite the advancement of touch panel technology over the years, 3D acoustic panel technology still awaits for some break through. Unlike conventional touch panel, 3D acoustic panel is a touch-less technology. Touch-less technology does require user to touch the surface of the screen, the possible mechasim includingelectromagnetic, optical (imaging), and the ultrasonic types to detect the movement and gesture of user figners and hands. The ultrasonic type has the combined characteristics of low cost, supporting multi-touch, mounted on the existing panels as an add-on, and compatible with touch gestures, etc. when compared to other available technologies. All these characteristics have made ultrasound-based 3D panel a technology with high potential. The advantages become even more significant for large panels. The current leading technology such as capacitive touch technology faces low yield and high cost in this application domain. On the other hand, the ultrasonic 3D acoustic panel technology can potentially solve this issue effectively. With ultrasound 3D acoustic sensor/actuator remains in early development stage and most of the key technologies controlled by foreign companies, our industry possess no price advantage when facing international competition. A good ultrasonic transducer that can effectively improve the resolution and simplify the calculation of the amount of back-end algorithms can thus potentially become the key competitive advantage for developing large-size 3D acousti panels. In this paper, we will focus on the structure of touch sensor, using MEMS technology to produce a new type of Piezoelectric Micromachined Ultrasonic Transducer (PMUT). Unlike previous PZT deposition techniques such as sol-gel, screen printing and sputtering, we used aerosol deposition method to deposite PZT to achieve lower costs and rapid deposition. In addition, we tried to use stainless steel shim to replace the traditional silicon substrate based PMUT. The characteristics of the components developed were measured. To further refine the design parameters, we attempted to develop the reflectivity experiments so as to confirm the most suitable frequency range of skin sensitivity is between 55 kHz ~ 65 kHz. This finding will be used to further improve the design and fabrication process of 3D ultrasound panel technology in the future.