Fe81-yCoyGa19薄膜之結構與磁致伸縮研究

Abstract

本論文是藉由磁控濺鍍的方式製作Fe81-yCoyGa19薄膜，首先沉積於Corning 0211玻璃基板上，在本論文再次研究Co添加效應對於Fe81Ga19合金之影響:首先所添加Co之範圍是寬廣的可以到達２３%，其中Co原子的含量範圍(從y=0至y=２３); 第二，從添加Co原子去了解結構變化，經過量測及分析，得知Fe81-yCoyGa19薄膜結構以生長方向為<110>的織構為主，為BCC結構;第三，因為高頻率的性能，限制了渦流效應，在大多數鐵磁金屬，也很重要，我們研究了添加Co對電阻率ρ的效應，ρ大約是200μΩ-cm; 第四，隨著y從0增加到19 ％，飽和磁致伸縮λs穩定增加，由23增至70 ppm; 假如Co成分繼續增加從19增至23 %，結果造成λs下降。 接著，將Fe81-yCoyGa19薄膜沉積於矽(100)基板上，也是利用磁控濺鍍的方式製作Fe81-yCoyGa19薄膜，這次所添加Co之範圍也是寬廣的到達到23%，而且於各成分下沉積七種不同的厚度，薄膜厚度從30nm至400 nm，這篇論文主要的結論如下: 第一，隨著y成分增加從0％增至19 ％，λs也隨著增加，由36增至98 ppm;假如Co成分繼續增至23 %，結果造成λs下降; 這些結果顯示添加鈷原子到FeGa合金是有利於增加飽和磁致伸縮; 第二，比較Fe81-yCoyGa19薄膜/玻璃基板與Fe81-yCoyGa19薄膜/Si(100)之飽和磁致伸縮λs變化情況; 第三，了解Fe62Co19Ga19薄膜/Si(100)之結構性質由A2相與B2相組成; 第四，Fe62Co19Ga19薄膜分析隨著薄膜厚度與λs和矯頑磁力的關係; 第五，為了瞭解Fe62Co19Ga19薄膜/Si(100)上層與底層界面的關係，我們利用歐傑電子能譜儀測量了解各原子縱深分佈情形; 第六，Fe62Co19Ga19薄膜其他物理性質如下:飽和磁化量4πMs =1.8至2.0 T，矯頑磁力Hc=35至64 Oe，平均晶粒尺寸Dp=29.6 nm並且柱狀晶粒尺寸DL差不多接近薄膜厚度。 經實驗分析後發現，整體而言添加鈷於鐵鎵合金系統中都可以使飽和磁致伸縮量增加，而且飽和磁致伸縮量λS在鈷成份y=19時都比其他鈷成份來的大。 藉由不同溫度下VSM的量測Fe81-yCoyGa19薄膜/Si(100)之高溫磁性質從室溫增加至8000C如下: (1)所有Fe62Co19Ga19薄膜/Si(100)我們找到了兩個居里溫度點，一個是低溫相的居里點(Tc1)，另一個為高溫相的居里點(Tc2); (2)飽和磁化量4Ms是依賴溫度的變化，我們計算的方式藉由reduced hyperbolic Bessel function I5/2 (T); 並利用關係式λs(T)=λs (RT) × I5/2 (T)，我們比較高溫之飽和磁致伸縮λs(T)變化; (3)飽和磁致伸縮量λS隨著Co成分變化的關係我們所得知; (4) 當溫度增加時矯頑磁力稍微下降，但是溫度繼續增加矯頑磁力呈現最大值時近似為Tc1或Tc2;本論文的結論認為Fe62Co19Ga19薄膜這一個薄膜有最佳化高溫的磁性質，包含較大的λs (T)與較高的Tc1以及較好的Hc(T)。 一個良好的磁致伸縮薄膜致動器，傳感器，或者感知器應該掌握以下幾個特點，大的飽和磁致伸縮和低飽和磁場，使得磁致伸縮靈敏度是高的;在本篇論文成功製作出Fe62Co19Ga19/Si(100) 奈米晶薄膜共用直流磁控濺鍍技術改變製程參數如下:氬氣壓力工作壓力從 1到15 mTorr，濺射功率從10到120 watt，沉積溫度從室溫到3000C，我們將薄膜厚度固定在175 nm。 我們就FeCoGa薄膜進行以下各實驗： [1]原子力顯微鏡或磁力顯微鏡（AFM和MFM）。 [2]磁性質(VSM)。 [3]縱向與橫向的磁致伸縮(λ//orλ┴)。 [4]電阻率測量(ρ)。 [5] 飽和磁致伸縮靈敏測量(SH)。 Fe62Co19Ga19薄膜的優質化製程參數以及最佳性質如下表示: 例如PAr=5 mTorr，PW=80 watt，TS = RT，λS=80 ppm，HS=19.8 Oe，SH=6.1 ppm/Oe，ρ=57.0 μΩ-cm 。 其中Fe62Co19Ga19薄膜在室溫下以五種方式沉積於矽基板，分別是Ta/Fe62Co19Ga19(Tf)/Ta/Si(100)，Ta/Fe62Co19Ga19(Tf)/Si(100)，Fe62Co19Ga19(Tf)/Ta/Si(100)，Fe62Co19Ga19(Tf)/Si(100)，Ta/Fe62Co19Ga19(Tf)/Ta(X)/Si(100)，除了Ta(X)在濺鍍時不轉外，所有Fe62Co19Ga19 (Tf)和Ta在濺鍍時皆有旋轉，濺鍍時轉速設在12 r.p.m；Ta或Ta(X)當作覆蓋層或阻隔層時，膜厚固定在5nm；Fe62Co19Ga19 (Tf)的膜厚範圍介於5 nm至207nm之間。 量測所有樣品的飽和磁致伸縮量時，飽和磁致伸縮量和飽和磁場的定義分別是λS = (2/3)λ= (2/3)Δλ(λ?-λ┴)、HS，其中λ?為縱向磁致伸縮量，λ┴為橫向磁致伸縮量。 乃研究Ta做為覆蓋層或阻隔層，進一步探討隨著Fe62Co19Ga19膜厚的改變對飽和磁致伸縮量(λS)、飽和磁場(HS)的影響。 從實驗中發現，當Ta做為覆蓋層，隨著Fe62Co19Ga19膜厚遞減，飽和磁致伸縮量(λS)會顯著的增加。 假如Ta做為阻隔層，隨著Fe62Co19Ga19膜厚遞減，飽和磁場(HS)會遞增。當薄膜厚度tf=50 nm時，這一系列Ｔa/Fe62Co19Ga19/Ta (R)的飽和磁致伸縮靈敏度，其SH//=(Δλ///ΔH)為8.5 ppm/Oe、SH┴=(Δλ┴/ΔH) 為-5.7 ppm/Oe，SH=2/3(SH//-SH┴) 為9.4 ppm/Oe與沒有添加Ta層的Fe62Co19Ga19/Si(100)薄膜作比較其SH//=Δλ///ΔH)為9.2 ppm/Oe、SH┴=(Δλ┴/ΔH)為-7.7 ppm/Oe， SH=2/3(SH//-SH┴) 為11.2 ppm/Oe，由數據顯示在此膜厚時，沒有添加Ta層Fe62Co19Ga19/Si(100)薄膜的飽和磁致伸縮靈敏比較佳。 綜合所有磁致伸縮實驗及飽和磁致伸縮靈敏數據後，當tf=10 nm時，飽和磁致伸縮量(λS)的最大值在123ppm與當tf=50 nm時， 飽和磁致伸縮靈敏度的最大值在SH=11.2ppm/Oe，表示Fe62Co19Ga19薄膜有機會用於磁微機電的應用上。

In this research, Fe81-yCoyGa19 films were made by the dc magnetron sputtering method by depositing Fe81-yCoyGa19 thin films on Corning 0211 glass substrate. Herein we investigate the Co-substitution effect on the Fe81Ga19 alloy based on the following: (i) the Co-substitution range is wider, i.e., up to 19 at. %Co; (ii) the structural change from adding Co in the (110) textured Fe81-yCoyGa19 films; (iii) the high frequency performance limited by the eddy current effect electrical resistivity ρ of the FeCoGa films, ρ is about 200μΩ-cm; ( iv) λsincreases steadily from 23 to 56 ppm, as x increases from 0 to 19 at. % Co. Next, Fe81–yCoyGa19 films, with y=0-23 atom % Co, were deposited on Si(100) substrates, respectively, by the dc magnetron sputtering method. For each alloy target, we prepared six different thickness samples. Film thickness (tf) ranged from 30 to 400 nm. First, Our main finding is that as y increases from 0 to 19 atom % Co, λS increases from 36 to 98 ppm; as y increase for this, from 19 to 23 atom % Co, λS decreases. These results indicate that the addition of Co in the Fe81Ga19 alloy is advantageous in enhancing λS up to y~19% ; second, we that compare the λS of Fe81–yCoyGa19/glass with that of Fe81–yCoyGa19/Si(100); Third, from XRD, the Fe62Co19Ga19/Si(100) film reveals the A2 and B2 phases; Fourth, we analysis of the film thickness (tf) dependencies of λS and coercivity (Hc) of the Fe62Co19Ga19 film was by made; Fifth, the top and bottom interfaces, we performed Auger-depth (AES-DP) profile analysis on one Fe62Co19Ga19/Si(100) film. Sixth, Other physical properties of the Fe62Co19Ga19 films include the following:saturation magnetization 4πMS=1.8–2.0 T, coercivity HC=35–64 Oe, planar (mean) grain size DP=29.6 nm, and columnar grain size DL≈tf. After measuring and analyzing, we can know that the substitution of Co for Fe could give rise to increases in λS, and samples with composition y=19 have the largest magnetostriction. Furthermore, we measured the magnetic properties of Fe81-xCoxGa19 films at higher temperature. By the measurement of VSM at different temperature, Magnetic hysteresis loops of each film were measured from room temperature (RT) to 8000C. In terms of high temperature magnetic properties,(A) we find that for each film, there is one low-temperature-phase Curie point (TC1) and one high-temperature-phase Curie point (TC2); (B) based on the temperature dependence of 4πMS; (C) we calculated the reduced hyperbolic Bessel function &Icirc;5/2 (T); from the relationship λs (T) = λs (RT) × &Icirc;5/2 (T), we can compare the performances of λs (T) at higher temperatures; (D) Initially HC decreases slightly as T increases, but it turns around reaches a maximum value when either TC1 or TC2 is approached. It is concluded that the Fe62Co19Ga19 film has the optimal high-temperature magnetic properties, including a larger λs (T), higher TC1, and moderate HC (T). A good magnetostrictive thin film actuator, transducer, or sensor should acquire following characteristics,large saturation magnetostriction (λS) and low saturation (or anisotropy) field (HS), so that its magnetostriction susceptibility (SH ≡ Δλ/HS ≡ [λ//S - λ⊥S]/HS, where λ//S and λ⊥S are the longitudinal and transverse magnetostriction at HS) can be as large as possible. In this study, we have made Fe62Co19Ga19/Si(100) nano-crystalline films by using the dc magnetron sputtering technique under various fabrication conditions: Ar working gas pressure (pAr) varied from 1 to 15 mTorr, sputtering power (Pw) from 10 to 120 watt, deposition temperature (TS) from room temperature (RT) to 3000C, and film thickness (tf) fixed at 175 nm. The following experiments were performed on films: [1] the atomic force and magnetic force microscope (AFM and MFM), [2] the magnetic hysteresis-loop, [3] the longitudinal and transverse magnetostriction, [4] ferromagnetic resonance (FMR), and [5] the electrical resistivity (ρ) measurements. Each magnetic domain looks like a long leaf, with its long-axis being about 12 to 15 μm and short-axis about 1.5 μm. The optimal magnetic and electrical properties are collected from the Fe62Co19Ga19 film made with the following sputter deposition parameters, such as pAr= 5 mTorr, Pw= 80 watt, and TS = RT. Those optimal properties include λS = 80 ppm, HS = 19.8 Oe, SH = 6.1 ppm/Oe, and ρ = 57.0 μΩ-cm. Note that SH for the conventional magnetostrictive Terfenol-D film is, in general, equal to 1.5 ppm/Oe. Five series of Fe62Co19Ga19 films were deposited on Si(100) substrates at roomtemperature: they were (IR) Ta/Fe 62Co19Ga19(tf)/Ta/Si(100), (IIR) Ta/Fe62Co19Ga19(tf) /Si(100), (IIIR) Fe62Co19Ga19(tf)/Ta/Si(100), (IVR) Fe62Co19Ga19(tf)/Si(100), and (INR) Ta/Fe62Co19Ga19(tf)/Ta/Si(100), where R means the Si substrate was rotated at a speed of 12 rpm, while depositing Fe62Co19Ga19; NR means the Si substrate not rotated; the thickness of the Ta capping and/or barrier layer was 10 nm; and tf, ranging from 5 to 290 nm, is the thickness of Fe62Co19Ga19 film. We have measured the longitudinal and transverse magnetostriction (λ//S and λ⊥S) at the saturation field Hs for these films. The saturation magnetostriction is defined as λs≡ (2/3)Δλ= (2/3)(λ//s-λ⊥s), and the magnetostriction susceptibility (or sensitivity) as SH≡ (Δλ)/Hs. The main objective of this work is to study the Ta capping and/or barrier layer effect on λs or SH of Fe62Co19Ga19 films. The tf dependence of λs is similar to that of SH for each series of Fe62Co19Ga19 film: as tf decreases from 290nm, λs or SH first increases, reaches the maximum value λsm or SHm at tf= tf(K)m or tf= tf(K)M, where K≡IR to IVR and INR, and finally decreases if tf < tf(K)m or tf < tf (K)M. We found that if there is either a Ta capping or barrier layer, and if there are both, the tf(K)m or tf(K)M value is much reduced, but the λsm or SHm value is ,however, enhanced. The optimal value for λs is about 123 ppm obtained from the (IR)m film and that for SH is 6.1 ppm/Oe from the (IVR)M film, respectively.