以氣膠沈積法建立鋯鈦酸鉛厚膜低溫微製程技術

Abstract

本研究發展一套鋯鈦酸鉛(PbTixZr1-xO3, PZT)低溫厚膜微製程技術。 首先建立用來沈積PZT厚膜的氣膠沈積法(aerosol deposition method)設備，此法可在室溫下沈積具有鈣鈦礦晶相(perovskite crystal phase)的PZT膜，在50 x 70 mm2的面積下可達2-10 μm/hr之高速沈積，所沈積之PZT膜在經過650 oC退火後，其材料性質約為其塊材的三分之ㄧ，相對介電常數ε33與壓電常數d31分別為420與-45 pm/V。 本研究以氣膠沈積法為核心，開發出一套於矽基材上製作PZT厚膜共振器的製程，其中最重要的技術在於PZT厚膜微結構的圖形定義，在此選擇負光阻THB-151N作為犧牲層，以舉離法(lift-off method)作為圖形定義方式，使13 μm厚的PZT結構具有最小線寬達30 μm，且可製作出多種微米級複雜結構，包含雙層PZT三維結構；另外利用石蠟作為犧牲層可製作出PZT半球殼微結構。 在實際製作PZT厚膜共振器方面，4 x 400 x 1000 μm3的PZT微懸臂樑與直徑1500 μm的彎曲型四支撐微壓電變壓器被製作出，懸臂樑利用390 oC、450 oC、550 oC以及650 oC進行退火並量測電訊號，在最低溫390 oC退火下仍可獲得具有壓電性的懸臂樑元件，使本技術具有與CMOS製程整合的可能性，最後在壓電變壓器製作方面，以四支撐樑的圓盤型彎曲變壓器做設計，得到最大升壓比為0.58。

This dissertation presents a low-temperature lead-zirconate-titanate (PZT) thick film microfabrication process using aerosol deposition method. The equipment of aerosol deposition has been constructed to deposit the PZT thick film for this research. The PZT film is deposited at room temperature and already has perovskite crystal phase. An ultra high deposition rate 2-10 μm/h can be achieved in a 50 x 70 mm2 deposition area. While the PZT film was annealed by 650 oC for 3 hours, the material quality of the PZT film was about 1/3 compared to its bulk sample. The relative dielectric constant ε33 and piezoelectric constant d31 were 420 and -45 pm/V, respectively. To set up a silicon-based fabrication process of PZT thick film resonators, a special lift-off pattern method has been developed for aerosol deposition method. The negative photoresist THB-151N was selected as the suitable sacrificial layer for lift-off method. In our process, the smallest line width of the PZT microstructure was limited to 30 μm when the thickness PZT film was 10 μm. Based on the developed techniques, PZT double-layer structures have also been fabricated by conducting twice lift-off processes. Besides, the hemisphere PZT shell structures can also be fabricated by paraffin wax. To realize the PZT transducer devices, the 4 x 400 x 1000 μm3 PZT micro-cantilever and the flexion piezoelectric transformer with 1500 μm in diameter have been fabricated. The cantilever was annealed by 4 different temperatures: 390 oC, 450 oC, 550 oC, and 650 oC. The cantilever still has piezoelectricity with the lowest annealing temperature 390 oC. This low temperature process is possible to combine with CMOS process. To improve the flexion transformer from a circumference fixed end bondary, a reduced constraint design with 4 legs was frabricated. The step up ratio is improved from 0.1 to 0.58.