用有機金屬沉積法製作鐵電薄膜與介電薄膜之電性與物性研究

Abstract

本研究主要可分為兩部分,第一部分主要探討鐵電薄膜之電性與物性,第二部分是探討高介電薄膜之電性與物性,兩者皆是由化學製造法中的有機金屬沉積技術來製作鐵電性記憶體薄膜與高介電性薄膜。在鉭酸鍶鉍Sr0.8Bi2+xTa2O9+δ (SBT)鐵電薄膜中主要是探討鉍含量不同對薄膜電性、物性之影響。具有不同鉍含量之鉭酸鍶鉍鐵電薄膜除了組成成分x=0以外皆顯示含有優選(115)方向的SBT結晶相存在,除此之外, 鉭酸鍶鉍鐵電薄膜的微結構、極化對電場的遲滯迴路、漏電流密度皆與鉍含量有關, 而30% (x=0.6) 過量鉍之鉭酸鍶鉍鐵電薄膜無論在微結構、極化對電場的遲滯迴路、漏電流密度方面皆顯示了最佳的特性。 根據此結果,將鉭酸鍶鉍Sr0.8Bi2.6Ta2O9+δ (SBT)鐵電薄膜於不同的溫度下結晶成長,則鉭酸鍶鉍鐵電薄膜的極化對電場的特性顯示其隨結晶溫度增加而呈現出線性到非線性的系統性變化, 鉭酸鍶鉍鐵電薄膜的漏電密度與介電常數也明顯的與結晶溫度相關連,此結晶溫度主要決定了晶粒大小、平均表面粗糙度和介面層間的擴散,其漏電密度與介電常數會隨結晶溫度增加而上升。 將鉭酸鍶鉍Sr0.8Bi2.6Ta2O9+δ (SBT)鐵電薄膜沉積在Pt/Ti/SiO2/Si (MIM)和CeO2/Si (MFIS)的兩種記憶體結構中,然後於700℃結晶成長,而為了防止漏電流與介面層間之相互擴散,先於底材上長一層STO晶種層再鍍上鉭酸鍶鉍鐵電薄膜。在具有STO晶種層基材上沉積之鉭酸鍶鉍鐵電薄膜於700℃淬火後,無論在MIM和MFIS結構上皆可得完美(115)方向之SBT結晶相,而STO的種晶層在MIM結構中確實可以有效的阻止鉍原子擴散進入底電極,而降低漏電流,在MFIS結構中雖然得到一較小極化值,但由於鐵電層所分配到的電場值反而因介電常數值降低而增加,因而得到較大的記憶窗。 接下來以鈦酸鉍釹BNT (Bi3.25Nd0.75Ti3O12)作為記憶體鐵電薄膜,此薄膜旋镀於SrRuO3/SrTiO3/Si (MFMIS結構)基材上,然後於個種溫度下結晶成長。此薄膜在SrRuO3/SrTiO3/Si基材上顯示具有強的(104)優選BNT結晶方向。鈦酸鉍釹薄膜於MIM結構中顯現了較大的殘餘極化值58 μC/cm2與矯頑電場值104 kV/cm,而此薄膜於MFMIS結構亦顯示出其記憶窗比鉭酸緦鉍鐵電薄膜所得來的大。 第二部分的研究主要是以有機金屬沉積技術來製作高介電性薄膜,我們所選擇的高介電薄膜是鈦酸鍶加二氧化矽化合物SrTiO3-(x)SiO2 (SrTiSixO3±y), x值從0到0.45,此薄膜中的鈦酸鍶矽氧化晶粒隨矽含量增加而被細小化,此細小化之晶粒導致介電常數減低與漏電流降低。鈦酸鍶矽氧化合物薄膜的介電常數,隨結晶溫度的增加而增加,同一結晶溫度下介電常數隨矽的含量增加而降低。鈦酸鍶矽氧化合物薄膜的漏電流密度隨結晶溫度增加而增加,在同一結晶溫度下,則隨矽含量增加而降低至含量為0.25止。當鈦酸鍶矽氧化合物薄膜的矽含量為0.25於800℃結晶成長時,具有最適宜的介電常數與最低的漏電流值,分別是94.8與81.27×10-8 A/cm2。在此組成成份的鈦酸鍶矽氧化合物薄膜於700℃和800℃結晶成長後,其TDDB曲線顯示在0.6 Mv/cm電場下操作可維持十年以上。

This thesis is presented as two sections. One section is concerned with the electrical and physical characteristics of ferroelectric films, SBT and BNT, deposited by chemical solution method. Another section is the electrical and physical characteristics of high dielectric constant materials prepared by the same way. The Sr0.8Bi2+xTa2O9+δ (SBT) thin films are deposited on Ir/SiO2/Si substrate by using the metal-organic decomposition (MOD) technique. All the major peaks of the XRD pattern for Sr0.8Bi2+xTa2O9+δ thin films correspond to SBT phase excepted x equal to 0. The excess 30% Bi of Sr0.8Bi2+xTa2O9+δ thin films exhibit prefer oriented (115) phase, the microstructure, P-E hysteresis loops and leakage current are found to be dependent on the bismuth content. From above results, we find that Sr0.8Bi2.6Ta2O9+x (SBT) is the optimum compositions. The crystallization of the Sr0.8Bi2.6Ta2O9+x (SBT) thin films annealed at various temperatures is investigated. The polarization (P) versus electric field (E) characteristics exhibits systematic variation from linear to nonlinear polarization with increasing annealed temperature. The leakage current density and dielectric constant of Sr0.8Bi2.6Ta2O9+x thin films also are strongly dependent on annealed temperature, which are determined by the grain size, mean surface roughness and inter diffusion on interfacial layer. Both of the leakage current density and dielectric constant increase with increasing annealed temperature. The Sr0.8Bi2.6Ta2O9+x (SBT) thin films is deposited on Pt/Ti/SiO2/Si (MIM structure) and CeO2/Si (MFIS structure) substrates annealed at 700℃. In order to prevent the generation of higher leakage current and diffusion between two layers, the STO (SrTiO3) is also seeded on two substrates. The Sr0.8Bi2.6Ta2O9+x (SBT) thin films with a STO seeded layer on MIM structure show preferred (115) orientation, good crystallinity and lower crystallization temperature than those without STO seeding layer. The SBT thin films with STO seeded layer on MFIS structure also appear prefer (115), (006) orientation and good crystallinity. The seeded layer of STO effectively resists the diffusion of Bi into Ir bottom electrode on MIM structure. The remanent polarization and leakage current density of Sr0.8Bi2.6Ta2O9+x thin films with STO seeded layers are significantly improved. In MFIS structure, the Sr0.8Bi2.6Ta2O9+x thin films with STO seeded layer are improved memory window and lead to lower leakage current at low voltage. The Bi3.25Nd0.75Ti3O12 thin films are grown on SrRuO3/SrTiO3/Si substrates at 700℃annealed temperature by metal-organic deposition can obtain higher remanent polarization. The remanent polarization (Pr) and coercive field (Ec) of the BNT (Bi3.25Nd0.75Ti3O12) thin film are 58 μC/cm2 and 104 kV/cm, respectively. The memory window both of BNT and SBT thin films increases with increasing area ratios of MIS to MIM capacitor. The next section, we investigate the physical and electrical characteristics of SrTiO3-(x)SiO2 (SrTiSixO3±y) thin films varying x from 0 to 0.45. The 110 nm thicknesses of SrTiSixO3±y thin films have been prepared by chemical solution deposition (CSD) method at various annealed temperatures. Both of the leakage current density and dielectric constant of the thin films are obviously affected by crystallinity, annealed temperature and Si content. The Si content of SrTiSixO3±y thin film will depress the STO grain growth, produce lower dielectric constant and induce lower leakage current density. The dielectric constant of SrTiSixO3±y thin films increases with increasing annealed temperature and decreases with increasing Si content. The leakage current density of SrTiSixO3±y thin films decreases with increasing x value up to 0.25. The SrTiSixO3±y thin films with x equal to 0.25 have suitable dielectric constant and the lowest leakage current at 700℃annealed temperature. The TDDB (Time dependent dielectric breakdown) curve of the SrTiSixO3±y films with x equal to 0.25 operated at an electric field of 0.6 MV/cm have lifetime over 10 years at 700℃ and 800℃ annealed temperature.