以氮化鋁為壓電薄膜之高頻薄膜體聲波濾波器研製

Abstract

隨著通訊系統以及無線感測網路系統的快速發展，體積小、成本低、更具效率的元件急需開發，為達到這個目的，系統單晶片以整合積體電路為目標。然而電路中，被動元件往往會因為矽基材，而損失大部分的能量，譬如說電感的Q值不易提高，而且所佔用的面積也很大。因此，開發適用於RF頻段的薄膜體聲波共振器(FBAR)，不但Q值高、面積小，同時也可以和積體電路製程整合。以薄膜體聲波濾波器過濾訊號，比以往表面聲波元件和陶瓷元件更小、更具效率。 此論文以薄膜體聲波濾波器(FBAR Filter)與CMOS積體電路整合電路為目的，利用氮化鋁壓電薄膜製作薄膜體聲波濾波器。壓電薄膜的成長在FBAR扮演極為重要的角色，使用濺鍍法(Sputtering)作為我們氮化鋁壓電薄膜成長的方法，其優點為低溫製程，在IC的製程當中溫度不能太高，以避免傷害到電路，而濺度法可以將溫度控制在300°C以下，是最好的選擇。為了濺鍍出具有良好的C軸擇優取向(C-axis Preferred Orientation)，須找出良好的製程參數，其製程的參數是決定薄膜的晶格方向重要因素，製程參數有晶片溫度、靶材到晶片的距離、氮氣與氬氣的比例、氣體流量、power、製程壓力、預鍍時間和濺鍍時間。不同的參數會造成不同的薄膜特性，如何控制準確的機台參數，為此研究的關鍵技術。 將濾波器與其他積體電路整合，是完成單晶片系統整合之前的必經之路。所以未來發展趨勢，必先奠基於面積小、低損耗、高Q值、可承受高功率的濾波器，接著則是把品質優良的濾波器與其他微波元件整合，以達成系統單晶片的最終目的。本研究即是將分析、設計優良的FBAR濾波器視為基礎工作，與其他通訊元件整合才是最終目標。

Due to the great demands posed by mobile communication systems and sensor network systems, smaller, cheaper, and more efficient devices are required. However, passive elements, such as inductors, usually suffer from great loss in silicon substrate. A thin film bulk acoustic wave resonator (FBAR) is a solution for this problem because of its high-Q, smaller volume, and integration compatibility. Meanwhile, it has been demonstrated that at higher frequencies a filter composed of FBARs is superior to a surface acoustic wave (SAW) filter and ceramic filter. The foci of this thesis are Film Bulk Acoustic Wave Filters (FBAW Filter) and CMOS integrated circuits. I will demonstrate that using AlN piezoelectric film produces Film Bulk Acoustic Wave Filters. Growing piezoelectric thin film plays a very important role in FBAR. We use sputtering method to grow AlN thin film. The advantage of a low temperature process, in which IC manufacturing is not performed at high temperature, is that it avoids harming the circuit. A sputtering temperature that can be controlled at 300 ° C below, is the best option. To sputtering with good C-axis Preferred Orientation, we must identify good manufacturing parameters. The parameters are very important factors in determining the direction of the lattice films. The parameters include chip temperature, chip to target distance, nitrogen and argon ratio of the gas flow, power, pressure, pre-sputtering and sputtering time. The means of accurately controlling the parameters are the key technologies in this study. Integrated filter and other circuit is complete single-chip system integration before the pass. Therefore, future development must first stem from the small size, low-loss, high Q-value, and affordable high-power filter. Subsequently, there can be further integration of the optimal quality of the filter with other microwave components, to achieve the final goal of a system on a chip (SOC).