Properties of the Thin Film TiNiCu Shape Memory Alloys Prepared by Sputtering Method
|Abstract:||本研究利用TiNi合金靶與銅靶在RF濺鍍系統中濺鍍TiNi非晶質薄膜與銅保護膜於銅基材或鍍銅之矽基材上。經熱處理促使銅擴散，轉換成TiNiCu形狀記憶合金晶質薄膜。探討濺鍍參數對薄膜沉積、結構與性質之影響。沉積之薄膜觀察其表面形貌、成份分佈、各元素之擴散情形、晶體結構之變化、相變化溫度、硬度及推導係數(Reduced modulus)等，依序藉由AFM與SEM 、EDS 、SIMS、XRD、DSC、奈米壓痕儀等等儀器，並利用特別設計的方法，測試薄膜記憶效應。
在薄膜製程方面：濺鍍完成的薄膜需經由熱處理使非晶質的薄膜晶質化；於熱處理前沉積銅保護膜以避免氧化並加速銅之擴散，因為Ti在一般真空度之下退火時非常容易氧化。基材施加負偏壓(-100 V)，發現薄膜奈米壓痕硬度由0.14 GPa提高到0.88 GPa，XRD繞射峰強度提高約三倍，且薄膜韌性明顯增加。不足的退火時間和溫度，薄膜往往具TiNi與TiNiCu兩相，但在600 ℃，120 min退火後，可得TiNiCu單相的XRD繞射峰。在濺鍍靶材Ti含量50.70 wt%條件下，薄膜熱處理前、後Ti含量分別為42.5~44.3 wt%之間和29.5~44.1 wt%之間。換言之，濺鍍與熱處理後，Ti含量比靶材低。
In this research, the TiNi amorphous films and then protective Cu films were deposited in sequence on Cu crystalline substrates or Si substrate coated with amorphous Cu films. The RF sputtering system with TiNi alloy and Cu targets was used for TiNi film and protective Cu film depositions, respectively. The specimens were then gone through a heat treatment process to enhance Cu diffusion and phase transformation to become TiNiCu thin film crystalline shape memory alloys. Effects of deposition and heat treatment parameters on film deposition, structures and properties were examined. The film morphologies, compositions, element diffusion, crystal structures, phase transformation temperatures, nano-hardness and reduced modulus were analyzed by AFM and SEM, EDS, SIMS, XRD, DSC, and nano-indentation techniques, respectively. A special method was developed to test the shape memory effect of the shape memory alloy films. In aspect of the film fabrication processes, the heat treatment process is required to transform the amorphous as-sputtered films to become crystalline films. For heat treatment, the protective Cu film deposition is critical to prevent the films from oxidation. This is due to the fact that Ti is very active to oxygen even under the general high vacuum atmosphere. The results also show that the substrate with a negative bias (-100 V) can rise the nano-hardness of the films from 0.14 GPa to 0.88 GPa, cause the XRD peak intensity up to three times stronger, and increase the toughness of the films quite obviously. If the annealing temperature and time are not sufficient, the crystal structures of the films at room temperature are generally consisting of two Phases (TiNi and TiNiCu). At annealing temperature and time of 600℃ and 120 minutes, the crystal structure of the films will become single TiNiCu phase at room temperature. It is also noted that the Ti contents of the films before and after heat treatment are 42.5~44.3 wt % and 29.5~44.1 wt %, respectively, by using a sputter target of 50.7 wt % Ti. In other words, after sputtering or heat treatment, the Ti contents of the films are deficient by comparing with that of the sputter target. The crystal structures of the present TiNiCu films are same as that of TiNi shape memory alloys with B2 martensite and B19 austenite structures. The present TiNiCu films had been successfully demonstrated their shape memory effect by using the specially designed method, which has the advantage of testing small film specimens (~200 mm2).
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