铌镁酸钡缓冲层对锆钛酸铅薄膜漏电流的抑制

将铌镁酸钡(Ba(Mg1/3Nb2/3)O3,BMN)作为缓冲层,通过溶胶-凝胶法制备了锆钛酸铅(Pb(Zr0.52Ti0.48)O3,PZT)铁电薄膜.探究BMN缓冲层对PZT铁电薄膜介电、铁电性能影响.研究发现:BMN缓冲层不仅可以改善PZT薄膜晶化生长,同时阻碍了PZT与Pt的互扩散而降低了漏电流.由于对漏电流的抑制作用,适当厚度BMN缓冲层的引入可改善PZT的铁电性能,但随着缓冲层厚度的增加,由于其分压作用,复合膜铁电性减弱.当厚度为10 nm时,薄膜的综合性能最好:介电常数εr=1612.03,介电损耗tanδ=0.024,剩余极化值Pr=31.65 μC/cm2,矫顽场Ec=71.5 kV/cm,漏电流密度J=4.4×10-6 A/cm2.     

(100)择优取向对0.935Bi_(1/2)Na_(1/2)TiO_3-0.065BaTiO_3-0.01Al_6Bi_2O_(12)无铅压电薄膜的结构和性能影响

通过激光脉冲沉积技术(PLD)在Pt(111)/Ti/SiO_2/Si(简称Pt)和具有LaNiO_3缓冲层的Pt(111)/Ti/SiO_2/Si(简称LNO/Pt)两种衬底上制备了0.935Bi_(1/2)Na_(1/2)TiO_3-0.065BaTiO_3-0.01Al_6Bi_2O_(12)(简称BNT-BT-AB)薄膜。利用X射线衍射仪、扫描电子显微镜、原子力显微镜和铁电分析仪等对薄膜的结构和性能进行了测试和表征。结果表明:Pt衬底上BNT-BT-AB薄膜为随机取向,晶粒形貌为立方块状,剩余极化强度2P_r=20.38μC/cm~2,介电可调为19%,局部有效压电系数d~*_(33)为130pm/V;LNO/Pt衬底上BNT-BT-AB薄膜呈现高度的(100)择优取向,薄膜表面平整,剩余极化强度2P_r=21.25μC/cm~2,介电常数(700)和介电可调性(23%)均大于随机取向薄膜,d~*_(33)提高到150pm/V。     

退火工艺对Pb(Zr_(0.55)Ti_(0.45))O_3铁电薄膜结晶取向的影响

用射频磁控溅射法在Pt(111)/Ti/SiO2/Si上成功的制备了Pb(zr0.55Ti0.45)O3(PZT)铁电薄膜,通过传统退火(CFA)和快速退火(RTA)不同的退火方式,获得了(100)和(111)择优取向的铁电薄膜。对薄膜电学特性的测试表明,薄膜的织构对其电学性能有很大影响,(111)取向的薄膜与(100)取向的薄膜相比,剩余极化Pr和矫顽场Ec较大,但抗疲劳特性却较差。     

钽镁酸钡缓冲层对锆钛酸铅铁电薄膜性能的影响

采用溶胶–凝胶工艺在Pt/Ti/Si O2/Si基片上,通过引入钽镁酸钡[Ba(Mg1/3Ta2/3)O3,BMT]缓冲层,制备了锆钛酸铅[Pb(Zr0.52Ti0.48)O3,PZT]铁电薄膜。研究了BMT缓冲层对PZT铁电薄膜结晶和性能的影响。结果表明:引入BMT缓冲层利于PZT薄膜的生长;PZT薄膜具有钙钛矿结构,且没有裂纹、结晶良好、致密性好;缓冲层的厚度对PZT铁电薄膜的微观结构和铁电性能有重要影响。随BMT缓冲层厚度增加,PZT晶粒增大,介电损耗tanδ逐渐减少,介电常数εr和剩余极化强度Pr先增大后减少,矫顽场Ec先减少后增大。当BMT缓冲层厚约为10 nm时,PZT薄膜具有最优的铁电性能:εr=1 850,Pr=20.2μC/cm2,Ec=43.9 k V/mm。这与BMT与PZT具有相似的晶格常数、较小的晶格失配度和相近的禁带宽度有关。     

BaTiO3铁电薄膜在硅基片上的取向生长

采用脉冲激光沉积方法,在硅基片上先沉积MgO或CeO2缓冲层后再制备BaTiO3(BTO)铁电薄膜.通过原位反射高能电子衍射来监测MgO,CeO2缓冲层在硅基片上的生长行为.用X射线衍射测定BTO薄膜的结晶取向.并利用压电响应力显微镜观察了铁电薄膜的自发极化形成的铁电畴.结果表明:BTO薄膜在不同的缓冲层硅基片上以不同的取向生长,在织构的MgO/Si(001)基片上为(001)择优,择优程度与MgO织构品质有关,其中在双轴织构MgO缓冲层上为(001)单一取向;在CeO2(111)缓冲层上为(011)单一取向.(001)取向的BTO薄膜具有更大的面外极化,而(011)取向的BTO薄膜具有更大的面内极化.     

异质界面个数对PbZr_(0.52)Ti_(0.48)O_3/Ba(Mg_(1/3)Ta_(2/3))O_3薄膜铁电性能的影响

采用溶胶-凝胶法制备PbZr_(0.52)Ti_(0.48)O_3(PZT)薄膜前驱体溶液,采用水溶液凝胶法制备Ba(Mg_1/_3Ta_2/_3)O_3(BMT)薄膜前驱体溶液。研究了异质界面个数对PZT/BMT薄膜微观形貌、铁电性能的影响。在PZT/BMT薄膜中,PZT薄膜没有裂纹、结晶良好,界面个数的增加有利于PZT薄膜结构的致密。界面个数的增加可降低PZT/BMT薄膜剩余极化值和矫顽场。PZT/BMT薄膜在适当偏置电场下存在一个介电峰值,且正负偏置电场下的介电峰值不同,介电偏压特性曲线呈现不对称分布。采用二极管等效界面势垒和对薄膜电滞回线求导可有效解释介电偏压特性曲线不对称和介电峰值的差异。     

底电极原位退火与沉积温度对PZT薄膜性能影响研究

采用磁控溅射工艺,在Pt/Ti底电极上沉积锆钛酸铅(PZT)薄膜,研究了原位退火温度与底电极沉积温度对溅射PZT薄膜结晶取向、微观结构、介电性能、铁电性能及疲劳性能的影响。X射线衍射(XRD)和扫描电子显微镜(SEM)分析结果表明,随着电极沉积温度升高,Pt晶粒尺寸增大,随着退火温度升高,PZT薄膜致密性变差。对室温制备的Pt/Ti底电极进行200 ℃原位退火30 min后,易于促进PZT薄膜沿(100)择优取向,而高温制备或经高温退火处理的Pt/Ti底电极更有利于PZT薄膜的(111)晶向生长。电学性能分析表明,室温制备的Pt/Ti底电极在经200 ℃原位退火30 min后,其PZT薄膜介电性能最优,同时展现较高的剩余极化强度和最小的矫顽场强,经历10⁸次极化翻转后,初始极化下降仅为11％。     

0.65BaTiO3-0.35Na0.5Bi0.5TiO3薄膜的制备及其电学性能研究

采用脉冲激光沉积法制备了0.65 BT-0.35NBT/SRO/STO异质结构薄膜.通过XRD、AFM和SEM分析了0.65BT-0.35NBT薄膜的微观结构.XRD结果表明:0.65BT-0.35NBT为钙钛矿结构,其薄膜为沿c轴择优取向生长结构.0.65BT-0.35NBT薄膜表现出优异的铁电和压电性能,剩余极化强度达到38.1 μC/cm2.0.65 BT-0.35NBT薄膜的居里温度(Tc ～ 223℃)明显高于BTO的居里温度,是一种具有优异电学性能和较高的居里温度的BTO基铁电材料.     

La~(3+)、Nd~(3+)掺杂对Bi_4Ti_3O_(12)纳米薄膜铁电和介电性能的优化（英文）

采用溶胶-凝胶法和快速热处理工艺,在Pt(111)/Ti/SiO_2/Si(100)衬底上制备出Bi_4Ti_3O_(12)及其La~(3+)、Nd~(3+)掺杂系列铁电薄膜Bi3.5(La/Nd)_(0.5)Ti_3O_(12),并对其相组成、微观结构、铁电和介电性能进行了研究。X射线衍射谱和SEM综合显示,薄膜均匀、致密,呈随机取向的多晶钙钛矿结构。铁电和介电性能研究表明:其掺杂系列较未掺杂薄膜具有更优异的极化行为和矩形度(剩余极化强度Pr从9.35μC/cm2增至15.53和26.24μC/cm2)、更低的漏电流密度(从10-4 A/cm2降至10-6 A/cm2甚至10-9 A/cm2)和更高的介电常数,但同时介电损耗也逐渐增加(高频段时tanδ从0.02增至0.10和0.25)。     

沉积温度对Na_(0.5)Bi_(0.5)TiO_3铁电薄膜结构与性能的影响

利用脉冲激光沉积法和磁控溅射法在(001)SrTiO_3单晶基片上构架了铁电异质结电容器Pt/La_(0.5)Sr_(0.5)CoO_3/Na_(0.5)Bi_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3/SrTiO3(LSCO/NBT/LSCO/STO)。利用原子力显微镜(AFM)、X射线衍射仪(XRD)、铁电测试仪和压电力显微镜(PFM)研究了沉积温度对Na_(0.5)Bi_(0.5)TiO_3(NBT)铁电薄膜的表面形貌、微结构和电学性能的影响。AFM结果表明,NBT薄膜晶粒尺寸随着沉积温度的增加先变小后增大。XRD结果显示,不同沉积温度下生长的NBT薄膜均为(00l)择优取向结构。铁电测试仪和PFM结果表明,NBT薄膜的铁电和压电性能随着沉积温度的增加先增大后减小,650℃生长的薄膜具有最高的剩余极化强度(19.6μC/cm2)和最大的有效压电系数(146 pm/V)。     

Fabrication of Pb(Zr,Ti)O3 thin films utilizing unconventional powder magnetron sputtering (PMS)

Pb(Zr,Ti)O3 (PZT) ferroelectric ceramic films exhibit highly superior ferroelectric, pyroelectric and piezoelectric properties which are promising for a number of applications including non-volatile random access memory devices, non-linear optics, motion and thermal sensors, tunable microwave systems and in energy harvesting (EH) use. In this research, a thin layer of PZT was deposited on two different substrates of Strontium Titanate (STO) and Strontium ruthenate (SRO) by powder magnetron sputtering (PMS) system. The preliminary powders, consisting of PbO, ZrO₂ and TiO_2, were manually mixed and placed into the target holder of the PMS. The deposition was performed at an elevated temperature reaching up to 600 °C via a ceramic heater. This high temperature is required for PZT thin film crystallinity, which is never achieved in conventional physical vapour deposition processes. The phase structure, crystallite size, stress-strain and surface morphology of deposited thin films were characterized using X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The composition of the PZT thin films were also analysed by X-ray photoelectron spectroscopy (XPS). The mechanical properties of the thin films were evaluated with micro-scratch adhesive strength and micro hardness equipment. FESEM results showed that the PZT thin films were successfully deposited on both SRO and STO substrates. The surfaces of the coated samples were free from cracks, relatively smooth, uniform and dense. The profile of X-ray diffraction confirmed the formation of single-c-domain/single crystal perovskite phase grown on both substrates. The XPS analysis have shown that the PZT thin film grown by this method and that a target of PZT+10% PbO is a proper target for growing nominal PZT thin films. The adhesion strength and micro hardness results have confirmed the stability and durability of the thin film on the substrates, although higher values have been reported for thin film of PZT deposited on SRO surfaces.     

Growth of Highly (100)‐Oriented SrTiO3 Thin Films on Si(111) Substrates Without Buffer Layer

The SrTiO₃ (STO) thin films were directly grown on Si(111) substrates without buffer layer by an electron‐cyclotron‐resonance ion beam sputter deposition. The growth temperature was varied from 700°C to 850°C, while other parameters were kept unchanged. X‐ray structural analysis demonstrates that the growth temperature has a strong influence in tuning degree of (100) orientation. The STO film grown at 800°C is found to be the highest degree of (100) orientation (98%) and a strong (100) fiber texture. For the surface morphology, the development of plate‐shaped grains reveals a good correlation with the change in the degree of (100) orientation. Moreover, the leakage current–voltage characteristics of the Au/STO/Si(111) metal‐insulator‐semiconductor capacitors are investigated and discussed in considerable detail.     

Role of the PbTiO3 Seed Layer on the Crystallization Behavior of PZT Thin Films

The role of a highly crystalline and oriented lead titanate (PTO) seed layer on the subsequent phase and texture evolution of lead zirconate titanate (PZT) thin films is investigated in situ using X‐ray diffraction (XRD) during crystallization. Crystalline PTO seed layers were first prepared via a 2‐methoxyethanol route. Amorphous PZT with a Zr/Ti ratio of 52/48 was then deposited on the seed layer using the same synthesis route and subsequently crystallized in situ during XRD. During heating, a tetragonal‐to‐cubic transformation of the seed layer occurs prior to the formation of perovskite PZT. Subsequent nucleation of the crystalline PZT occurs in the cubic phase. Simultaneous to nucleation of PZT, development of a dominant 100 texture component was observed in the PZT phase of the thin films. The results indicate that 100 textured PTO nucleates 100 texture of PZT thin films during crystallization.     

Optical properties of epitaxial BiFeO3 thin film grown on SrRuO3-buffered SrTiO3 substrate

The BiFeO₃ (BFO) thin film was deposited by pulsed-laser deposition on SrRuO₃ (SRO)-buffered (111) SrTiO₃ (STO) substrate. X-ray diffraction pattern reveals a well-grown epitaxial BFO thin film. Atomic force microscopy study indicates that the BFO film is rather dense with a smooth surface. The ellipsometric spectra of the STO substrate, the SRO buffer layer, and the BFO thin film were measured, respectively, in the photon energy range 1.55 to 5.40 eV. Following the dielectric functions of STO and SRO, the ones of BFO described by the Lorentz model are received by fitting the spectra data to a five-medium optical model consisting of a semi-infinite STO substrate/SRO layer/BFO film/surface roughness/air ambient structure. The thickness and the optical constants of the BFO film are obtained. Then a direct bandgap is calculated at 2.68 eV, which is believed to be influenced by near-bandgap transitions. Compared to BFO films on other substrates, the dependence of the bandgap for the BFO thin film on in-plane compressive strain from epitaxial structure is received. Moreover, the bandgap and the transition revealed by the Lorentz model also provide a ground for the assessment of the bandgap for BFO single crystals.     

Phase and Texture Evolution in Chemically Derived PZT Thin Films on Pt Substrates

The crystallization of lead zirconate titanate (PZT) thin films was evaluated on two different platinum‐coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO₂ adhesion layer. The Pt deposited on TiO₂ exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order (IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X‐ray diffraction at a synchrotron source. The intensity of the Pt₃Pb phase indicated that deposition on a highly oriented Pt/TiO₂ substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO₂ substrate than on the Pt/Ti substrate.     

Fabrication and properties of ZnO/GaN heterostructure nanocolumnar thin film on Si (111) substrate

Zinc oxide thin films have been obtained on bare and GaN buffer layer decorated Si (111) substrates by pulsed laser deposition (PLD), respectively. GaN buffer layer was achieved by a two-step method. The structure, surface morphology, composition, and optical properties of these thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, infrared absorption spectra, and photoluminiscence (PL) spectra, respectively. Scanning electron microscopy images indicate that the flower-like grains were presented on the surface of ZnO thin films grown on GaN/Si (111) substrate, while the ZnO thin films grown on Si (111) substrate show the morphology of inclination column. PL spectrum reveals that the ultraviolet emission efficiency of ZnO thin film on GaN buffer layer is high, and the defect emission of ZnO thin film derived from Zn_i and V_o is low. The results demonstrate that the existence of GaN buffer layer can greatly improve the ZnO thin film on the Si (111) substrate by PLD techniques.     

Fatigue-Free Lead Zirconate Titanate (Pb(Zr,Ti)O3)-Based Capacitors Co-modified by Lanthanum and Lithium for Nonvolatile Memories

Pb_0.98(La_{1− x} Li _x )_0.02(Zr_0.55Ti_0.45)O₃(PLLZT with 0.1 ≤ x ≤ 0.7) thin films were sol-gel-grown on Pt(111)/Ti/SiO₂/Si substrates, employing a thin lead zirconate titanate (PZT) template layer. Films annealed at >550°C showed a highly (111)-oriented preferential growth. Typical values of the switchable remanent polarization (2 P _r) and the coercive field ( E _c) of the PLLZT/PZT/Pt film capacitor for x = 0.3 were 50 μC/cm² and 39 kV/cm, respectively, at 5 V. All the PLLZT/PZT/Pt capacitors (for 0.1 ≤ x ≤ 0.7) exhibited fatigue-free behavior up to 6.5 × 10¹⁰ switching cycles, a quite stable charge retention profile with time, and high 2 P _rvalues, all which assure their suitability for nonvolatile ferroelectric memories.     

Hysteretic properties of Mn-doped Pb(Zr,Ti)O3 thin films

Pb(Zr,Ti)O₃ (PZT 30/70) and Mn-doped Pb(Zr,Ti)O₃ (PMZT 30/70) thin films have been fabricated on Pt/Ti/SiO₂/Si substrates by a chemical solution deposition technique. The experiments found that the addition of Mn in PZT thin films greatly improves the ferroelectric properties of thin films. It is demonstrated that the Mn-doped (1 mol%) PZT showed fatigue-free characteristics at least up to 10¹⁰ switching bipolar pulse cycles under 10 V and excellent retention properties. The Mn-doped PZT thin films also exhibited well-defined hysteresis loops with a remnant polarization (Pr) of 34 μC/cm² and a coercive field (Ec) of 100 kV/cm for the thickness of 300 nm. Dielectric constant and loss (tanδ) for Mn doped PZT thin films are 214 and 0.008, respectively. These figures compare well with or exceed the values reported previously. In this paper, the mechanism by which Mn influences on the ferroelectric properties of PZT thin films has also been discussed.     

Direct processing of PbZr0.53Ti0.47O3 films on glass and polymeric substrates

This work reports on direct crystallization of PbZr_0.53Ti_0.47O₃ (PZT) thin films on glass and polymeric substrates, using pulsed thermal processing (PTP). Specifically, xenon flash lamps deliver pulses of high intensity, short duration, broadband light to the surface of a chemical solution deposited thin film, resulting in the crystallization of the film. Structural analysis by X-ray diffraction (XRD) and transmission electron microscopy show the existence of perovskite structure in nano-sized grains (≤5 nm). Local functional analysis by band excitation piezoelectric spectroscopy and electrostatic force microscopy confirm the presence of a ferroelectric phase and retention of voltage-written polarization for multiple days. Based on structural and functional analyses, strategies are discussed for optimization of pulse voltage and duration for the realization of crystalline ferroelectric thin films. For ∼200 nm-thick PZT films on glass substrates, 500 μs-long pulses were required for crystallization, starting with 100 pulses at 350 V, 10 or 25 pulses at 400 V and in general lower number of pulses at higher voltages (resulting in higher radiant energy). Overall power densities of >6.4 kW/cm² were needed for appearance of peaks corresponding to the perovskite phase in the XRD. Films on glass processed at 350–400 V had a higher degree of 111-oriented perovskite grains. Higher applied radiant energy (through increased pulse voltage or count) resulted in more random and/or partially 001-oriented films. For ∼1 μm-thick PZT films on polymeric substrates, 10 to 25 250 μs-long pulses at voltages ranging between 200 to 250 V, corresponding to power densities of ∼2.8 kW/cm², were optimal for maximized perovskite phase crystallization, while avoiding substrate damage.