Enhancement of Temperature Sensitivity for Metal–Oxide–Semiconductor (MOS) Tunneling Temperature Sensors by Utilizing Hafnium Oxide (HfO2) Film Added on Silicon Dioxide (SiO2)

In this paper, metal-oxide-semiconductor (MOS) capacitors fabricated on p-type silicon substrate with hafnium oxide (HfO₂ ) film added on silicon dioxide (SiO₂) were demonstrated as reliable temperature-detecting devices. The saturation current of MOS (p) capacitor with added HfO₂ film is easy to saturate within 0.5 V. From 40 degC to 90degC, each increase of 10degC almost doubles the saturation current. The C-V curves show that the interface properties of Si/SiO₂ and SiO₂/HfO ₂ are good. It was also shown that these devices are reliable even though they had been electrically stressed at various temperatures (30degC~90degC) for 15 000 s. They have the potential to be integrated into the circuits as temperature detectors in the era of ultralarge-scale-integration technology     

Electric characterization of HfO2 thin films prepared by chemical solution deposition

Hafnium dioxide (HfO₂) thin films were prepared on Si substrates using the chemical solution deposition (CSD) method. The Au/HfO₂/n-Si/Ag structures were characterized by X-ray diffraction (XRD), C–V curves and leakage current measurements. A relative dielectric constant of about 13.5 was obtained for the 65 nm HfO₂ film. Atomic force microscopy (AFM) measurements show uniform surfaces of the films. C–V hysteresis was found for the metal-oxide-semiconductor (MOS) structures with HfO₂ films of 52 and 65 nm thick. It is found that the width of C–V windows is related with the thickness of the HfO₂ films. Furthermore, the C–V hysteresis reveals the possibility of stress-effect, suggesting that it is possible to use HfO₂ to build an MOS structure with controllable C–V windows for memory devices. The leakage current decreases as the film thickness increases and a relatively low leakage current density has been achieved with the HfO₂ film of 65 nm.     

Chemical vapour deposition of praseodymium oxide films on silicon: influence of temperature and oxygen pressure

Metal-organic chemical vapour deposition (MOCVD) of various phases in PrO_x system has been studied in relation with deposition temperature (450–750 °C) and oxygen partial pressure (0.027–100 Pa or 0.2–750 mTorr). Depositions were carried out by pulsed liquid injection MOCVD using Pr(thd)₃ (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) precursor dissolved in toluene or monoglyme. By varying deposition temperature and oxygen partial pressure amorphous films or various crystalline PrO_x phases (Pr₂O₃, Pr₇O₁₂, Pr₆O₁₁) and their mixtures can be grown. The pure crystalline Pr₂O₃ phase grows only in a narrow range of partial oxygen pressure and temperature, while high oxygen pressure (40–100 Pa) always leads to the most stable Pr₆O₁₁ phase. The influence of annealing under vacuum at 750 °C on film phase composition was also studied. Near 90% step coverage conformity was achieved for PrO_x films on structured silicon substrates with aspect ratio 1:10. In air degradation of Pr₂O₃ films with transformation to Pr(OH)₃ was observed in contrast to Pr₆O₁₁ films.     

Deposition of HfO2 thin films on ZnS substrates

HfO₂ thin films with columnar microstructure were deposited directly on ZnS substrates by electron beam evaporation process. SiO₂ thin films, deposited by reactive magnetron sputtering, were used as buffer layers, HfO₂ thin films of granular microstructure were obtained on SiO₂ interlayer by this process. X-ray diffraction patterns demonstrate that the as-deposited HfO₂ films are in an amorphous-like state with small amount of crystalline phase while the HfO₂ films annealed at 450 °C in O₂ for 30 min and in Ar for 150 min underwent a phase transformation from amorphous-like to monoclinic phase. Antireflection effect in certain infrared wave band, such as 3–6 μm, 4–12 μm, 4–8 μm and 3–10 μm, can be observed, which was dependent on the thickness of thin films. The cross-sectional images of HfO₂ films, obtained by field emission scanning electron microscopy, revealed that there was no distinct morphological change upon annealing.     

Direct liquid injection metal-organic chemical vapor deposition of HfO2 thin films using Hf(dimethylaminoethoxide)4

Hf(OCH₂CH₂NMe₂)₄, [Hf(dmae)₄] (dmae=dimethylaminoethoxide) was synthesized and used as a chemical vapor deposition precursor for depositing Hf oxide (HfO₂). Hf(dmae)₄ is a liquid at room temperature and has a moderate vapor pressure (4.5 Torr at 80 °C). It was found that HfO₂ film could be deposited as low as 150 °C with carbon level not detected by X-ray photoelectron spectroscopy. As deposited film was amorphous but when the deposition temperature was raised to 400 °C, X-ray diffraction pattern showed that the film was polycrystalline with weak peak of monoclinic (020). Scanning electron microscope analysis indicated that the grain size was not significantly changed with the increase of the annealing temperature. Capacitance–voltage measurement showed that with the increase of annealing temperature, the effective dielectric constant was increased, but above 900 °C, the effective dielectric constant was decreased due to the formation of interface oxide. For 500 Å thin film, the dielectric constant of HfO₂ film annealed at 800 °C was 20.1 and the current–voltage measurements showed that the leakage current density of the HfO₂ thin film annealed at 800 °C was 2.2×10⁻⁶ A/cm² at 5 V.     

氟化镁基底上HfO2中间层对Al2O3薄膜微观组织和力学性能的影响

采用电子束蒸镀技术在氟化镁基底上制备了单层Al₂O₃薄膜和含有HfO₂中间层的HfO₂/Al₂O₃双层薄膜。在空气中对所制备的薄膜进行1 h 600℃的退火处理。通过掠入角X射线衍射仪(GIXRD)、场发射扫描电镜(FE-SEM)、傅里叶变换红外光谱仪(FTIR)、纳米压痕和划痕法对薄膜的微观结构、红外透过率和力学性能进行了表征。结果表明: 退火处理后HfO₂/Al₂O₃双层薄膜中形成了一层树枝状的新层, 这种新层的硬度大于17.5 GPa。这种高硬度的新层能够保护氟化镁基底不被划伤。从GIXRD图谱中只能找到单斜相HfO₂的衍射峰, 而Al₂O₃薄膜仍然保持非晶态。从这些结果中可以推断出HfO₂从非晶态向单斜相的转变促进了这种树枝状新层的产生, 也正是这种新层提高了保护薄膜的力学性能。     

The use of Ce(fod)4 as a precursor for the growth of ceria films by metal-organic chemical vapour deposition

We report the growth of thin films of cerium oxide using the metal-organic chemical vapour deposition (MOCVD) technique. The homoleptic complex, Ce(fod)₄, where fod-H is 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione, was used as a precursor. Silicon wafers with a (100) orientation were used as substrates. This work can be considered a feasibility study of this precursor as a potential source of ceria for the eventual production of solid solutions with a stoichiometry of Ce_0.9Gd_0.1O_1.95. These ceramic films are intended for use as electrolytes in solid oxide fuel cells (SOFCs). In this paper, the difficulties associated with CVD growth of oxide films using solid phase precursors such as Ce(fod)₄ which contain fluorinated ligands are discussed as well as the methods used to eliminate such problems. The variation of important CVD parameters such as moist oxygen flow rate are discussed in terms of their effect on the growth rate and the elemental composition of the deposited films. Analysis was carried out using techniques such as scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray fluorescence.     

Deposition of BaTiO3 thin films by plasma MOCVD

Barium titanium trioxide (BaTiO₃) thin films were deposited on fused silica or silicon wafer substrate from barium dipivaloylmethanate (II) (Ba(dpm)₂) and titanium tetraisopropoxide (IV) (TTIP) used as precursors in an oxygen microwave plasma. The substrates were dielectrically heated and the substrate temperatures were around 900 K during the film deposition. The deposition was performed for 15 min and the deposits were identified as BaTiO₃ by means of X-ray diffraction, X-ray photoelectron spectroscopy, infrared spectroscopy, and ellipsometry. Oxygen and barium atoms and TiO and CO molecules were identified in the plasma. These species would produce higher deposition rates at lower substrate temperatures than those did in the usual thermal metalorganic chemical vapor deposition (MOCVD). The dielectric constant of the BaTiO₃ thin film that was directly deposited on the silicon wafer substrate was as low as 10¹ order of magnitude. Because the deposit reacted with the substrate and an interdiffusional layer was formed, the platinum layer was coated on the silicon wafer substrate in order to prevent the formation of an interdiffusional layer. The dielectric constant then increased to 10³ order of magnitude.     

Study of HfO2 films prepared by ion-assisted deposition using a gridless end-hall ion source

HfO₂ thin films were deposited using e-beam gun evaporation with ion assisted deposition (IAD) of low energy oxygen ions (40–100 eV) from an end-Hall ion source. A comparison was made using Hf and HfO₂ starting materials. The index of refraction was measured as a function of the ion source voltage and compared to results without IAD. Application to high power laser mirrors was verified by measurements of laser damage thresholds at 1.06 μm.     

Pulsed Laser Deposition of Superhard Nitride Coatings

Nitrides coatings have a large number of applications in high-technology industries due to many unique physical, chemical, and mechanical properties. Thin films of aluminum nitride (AIN), silicon nitride (Si₃N₄), and carbon nitride (CN_x) were deposited on Si (100) substrates using the pulsed laser deposition (PLD) method. The seeding of titanium nitride (TiN) before the CN_x deposition has promoted the growth of the predominantly crystalline CN_x films. The laser deposition parameters and substrate temperature play an important role in fabricating high quality films. The structural and microstructural properties of these films have been characterized using x-ray diffraction, and scanning electron microscope techniques. The Fourier Transform Infrared (FTIR) and x-ray photoelectron spectroscopy (XPS) have been used to investigate the bonding properties in CN_x films. The mechanical properties of the films were evaluated to correlate with the processing parameters of the deposited films. It has been shown that the films with crystalline quality structure have higher hardness and modulus values.     

Lattice Expansion by Adding Oxygen to Control Crystallographic Orientations in Chemically Ordered L10 FePt Films

We fabricated L1₀ FePt thin films by sputtering in reactive oxygen on polycrystalline glass substrates, and we investigated the magnetic properties and crystallographic orientations of the films. Oxygen addition during the FePt deposition promoted heteoroepitaxial growth by decreasing the lattice misfit with the Ag underlayer. In an oxygen/argon ratio of 1.5-3.0 vol.%, the in-plane lattice parameter of the FePt films expanded, and the lattice misfit with the Ag underlayer decreased from 6.3 to 3.9% in the as-deposited state, as determined by grazing incidence X-ray diffraction (GIXRD). Annealing at 700degC for 1 min produced a heteroepitaxially grown L1₀ (001) texture with a large out-of-plane coercivity of 8.8 kOe and a nucleation field of kOe. Transmission electron microscopy showed that average grain size in the as-deposited films was about 4-5 nm and was in the range of 10-15 nm in the annealed films, indicating that there was some grain growth.     

Characterization of the surface of bio-ceramic thin films

The biocompatibility and corrosion resistance of orthopaedic and dental implants are determined by their material composition and surface microstructural properties such as surface roughness, grain size, etc. Thin films of bio-inert materials such as oxides of Ti, Al, Zr, and bio-active materials such as hydroxy-apatite (Ca₁₀(PO₄)₆(OH)₂), compounds of calcium and phosphorous oxides are more attractive as bio-ceramic films because of their biocompatibility being higher, and toxicity being lower than those of the other materials. In this study, we mainly focused on characterization of the surface of bio-ceramics using atomic force microscopy (AFM). These films having a thickness of about 500 nm, had been processed using ion-beam sputter deposition, and ion-beam-assisted sputter deposition methods. Investigation of the surface of the films by AFM shows that irradiation with oxygen ions in the energy range of 3 keV increases the surface roughness. A detailed study of the grain size and roughness of several experimental cases of TiO₂ thin films showed that the films contained columnar grains with mean size of about 100 × 100 nm² grown in the z direction with a height of a few nanometers.     

离子源偏压对PIA-EB-Hf法制备的HfO2激光薄膜性能的影响

探究HfO₂薄膜的激光损伤特性以进一步提高激光损伤阈值(Laser Induced Damage Threshold, 简称LIDT), 对其在高功率激光系统中的广泛应用具有重要的意义。在不同的离子源偏压下, 采用等离子体辅助电子束蒸发金属铪(Hf)并充氧(O₂)进行反应沉积法制备了中心波长为1064 nm, 光学厚度为4H的HfO₂薄膜样品。测试了薄膜组分和残余应力; 根据透射谱拟合了薄膜的折射率; 通过XRD谱图和SEM表面形貌图分析了薄膜的微观结构; 对激光损伤阈值、损伤特性和机理进行了论述。结果表明: 偏压100 V时制备的薄膜具有最佳O/Hf配比; 薄膜压应力和折射率均随偏压降低而减小。薄膜内存在结晶, 激光能量在晶界缺陷处被强烈聚集和吸收, 加速了膜层的破坏, 形成由几百纳米的烧灼坑聚集而成的海绵状损伤结构。随着偏压降低, 膜结晶取向由(\stackrel{\text{?}}{1}11)晶面向(002)晶面转变, 界面能降低; 晶粒减小, 结构更均匀, 缓解了激光能量在晶界处的局部聚集与吸收, 表现出较大的激光损伤阈值。     

In situ investigation of thermally influenced phase transformations in (pb0.92sr0.08) (zr0.65ti0.35)o3 thin films using micro-raman spectroscopy and x-ray diffraction

Thin films of ferroelectric strontium-doped lead zirconate titanate [PSZT, (Pb_0.92Sr_0.08)(Zr_0.65Ti_0.35)O₃] deposited by RF magnetron sputtering have been analyzed by in situ analysis techniques. The in situ techniques employed for this study include micro-Raman spectroscopy and X-ray diffraction (XRD), and variations in thin film structure and orientations for temperatures up to 350degC and 750degC for the respective techniques have been studied. The samples analyzed were PSZT thin films deposited on platinum-coated silicon substrates at either room temperature or at 750degC. In situ measurements using micro-Raman spectroscopy and XRD techniques have been used to identify the Curie point for poly-crystalline PSZT thin films and to determine the temperature-activating significant grain growth for room-temperature-deposited PSZT thin films. To study the presence of hysteresis, analysis was carried out during both temperature ramp-up and ramp-down cycles. Raman measurements showed expected bands (albeit weak), and the in situ measurements have detected variations in the crystal structure of the thin film samples, with negligible variations between the heating and cooling cycles. A combination of the Raman and XRD results has shown that the temperature activating significant grain growth for the room-temperature deposited films is about 275degC and the Curie point lies between 325 and 400degC. This relatively high Curie point makes these films suitable for wide temperature range applications.     

Excitons in self-organized layered perovskite films prepared by the two-step growth process

Thin films of microcrystalline (C₈H₁₇NH₃)₂PbBr₄ were prepared by a two-step growth process as follows: (1) deposition of PbBr₂ films on substrates and (2) self-organized growth of layered perovskite compounds by exposing the PbBr₂ film to C₈H₁₇NH₃Br vapor in a vacuum chamber. As-synthesized (C₈H₁₇NH₃)₂PbBr₄ films were characterized by using X-ray diffraction, temperature dependence in optical absorption and photoluminescence spectra. (C₈H₁₇NH₃)₂PbBr₄ films created by this synthesis approach were found to microcrystalline form, single phase and highly oriented with a c-axis perpendicular to the substrate surface. (C₈H₁₇NH₃)₂PbBr₄ films showed clear exciton absorption and photoluminescence even at room temperature in the near-ultraviolet region. Exciton binding energy of (C₈H₁₇NH₃)₂PbBr₄ was estimated about 200 meV.     

TaN薄膜的等离子体增强原子层沉积及其抗Cu扩散性能

使用Ta[N(CH₃)₂]₅和NH₃等离子体作为反物用等离子体增强原子层沉积工艺生长了TaN薄膜,借助原子力显微镜、X射线光电子能谱、四探针和X射线反射等手段研究了薄膜的性能与工艺条件之间的关系。结果表明,TaN薄膜主要由Ta、N和少量的C、O组成。当衬底温度由250℃提高到325℃时Ta与N的原子比由46:41升高到55:35,C的原子分数由6%降低到2%。同时,薄膜的密度由10.9 g/cm³提高到11.6 g/cm³,电阻率由0.18 Ω?cm降低到0.044 Ω?cm。与未退火的薄膜相比,在400℃退火30 min后TaN薄膜的密度平均提高了~0.28 g/cm³,电阻率降低到0.12~0.029 Ω?cm。在250℃生长的3 nm超薄TaN阻挡层在500℃退火30 min后仍保持良好的抗Cu扩散性能。     

Deposition of Sm2O3 doped CeO2 thin films from Ce(DPM)4 and Sm(DPM)3 (DPM=2,2,6,6-tetramethyl-3,5-heptanedionato) by aerosol-assisted metal–organic chemical vapor deposition

Samarium-doped ceria (SDC) thin films were prepared from Sm(DPM)₃ (DPM = 2,2,6,6-tetramethyl-3,5-heptanedionato) and Ce(DPM)₄ using the aerosol-assisted metal–organic chemical vapor deposition method. -Al₂O₃ and NiO-YSZ (YSZ = Y₂O₃-stabilized ZrO₂) disks were chosen as substrates in order to investigate the difference in the growth process on the two substrates. Single cubic structure could be obtained on either -Al₂O₃ or NiO-YSZ substrates at deposition temperatures above 450 °C; the similar structure between YSZ and SDC results in matching growth compared with the deposition on -Al₂O₃ substrate. A typical columnar structure could be obtained at 650 °C on -Al₂O₃ substrate and a more uniform surface was produced on NiO-YSZ substrate at 500 °C. The composition of SDC film deposited at 450 °C is close to that of precursor solution (Sm : Ce = 1 : 4), higher or lower deposition temperature will both lead to sharp deviation from this elemental ratio. The different thermal properties of Sm(DPM)₃ and Ce(DPM)₄ may be the key reason for the variation in composition with the increase of deposition temperature.     

Nonlinear pyroelectric energy harvesting from relaxor single crystals

Energy harvesting from temperature variations in a Pb(Zn_1/3Nb_2/3)_0.955Ti_0.045O₃ single crystal was studied and evaluated using the Ericsson thermodynamic cycle. The efficiency of this cycle related to Carnot cycle is 100 times higher than direct pyroelectric energy harvesting, and it can be as high as 5.5% for a 10degC temperature variation and 2 kV/mm electric field. The amount of harvested energy for a 60degC temperature variation and 2 kV/mm electric field is 242.7 mJmiddotcm^-3. The influence of ferroelectric phase transitions on the energy harvesting performance is discussed and illustrated with experimental results.     

Piezoelectric properties in (K0.5Bi0.5)TiO 3-(Na0.5Bi0.5)TiO3-BaTiO 3 lead-free ceramics

Lead-free piezoelectric ceramics with compositions around the morphotropic phase boundary (MPB) x(Na_0.5Bi_0.5)TiO _3-y(K_0.5Bi_0.5)TiO₃-zBaTiO ₃ [x + y + z = 1; y:z = 2:1] were synthesized using conventional, solid-state processing. Dielectric maximum temperatures of 280degC and 262degC were found for tetragonal 0.79(Na_0.5Bi_0.5)TiO₃-0.14(K_0.5 Bi_0.5)TiO₃-0.07BaTiO$ d3 (BNBK79) and MPB composition 0.88(Na_0.5Bi_0.5)TiO₃-0.08(K _0.5Bi_0.5)TiO₃-0.04BaTiO$ d3 (BNBK88), with depolarization temperatures of 224degC and 162degC, respectively. Piezoelectric coefficients d₃₃ were found to be 135 pC/N and 170 pC/N for BNBK79 and BNBK88, and the piezoelectric d₃₁ was determined to be -37 pC/N and -51 pC/N, demonstrating strong anisotropy. Coercive field values were found to be 37 kV/cm and 29 kV/cm for BNBK79 and BNBK88, respectively. The remanent polarization of BNBK88 (~40 muC/cm²) was larger than that of BNBK79 (~29 muC/cm²). The piezoelectric, electromechanical, and high-field strain behaviors also were studied as a function of temperature and discussed     

Atomic layer deposition of calcium oxide and calcium hafnium oxide films using calcium cyclopentadienyl precursor

Calcium oxide and calcium hafnium oxide thin films were grown by atomic layer deposition on borosilicate glass and silicon substrates in the temperature range of 205–300 °C. The calcium oxide films were grown from novel calcium cyclopentadienyl precursor and water. Calcium oxide films possessed refractive index 1.75–1.80. Calcium oxide films grown without Al₂O₃ capping layer occurred hygroscopic and converted to Ca(OH)₂ after exposure to air. As-deposited CaO films were (200)-oriented. CaO covered with Al₂O₃ capping layers contained relatively low amounts of hydrogen and re-oriented into (111) direction upon annealing at 900 °C. In order to examine the application of CaO in high-permittivity dielectric layers, mixtures of Ca and Hf oxides were grown by alternate CaO and HfO₂ growth cycles at 230 and 300 °C. HfCl₄ was used as a hafnium precursor. When grown at 230 °C, the films were amorphous with equal amounts of Ca and Hf constituents (15 at.%). These films crystallized upon annealing at 750 °C, showing X-ray diffraction peaks characteristic of hafnium-rich phases such as Ca₂Hf₇O₁₆ or Ca₆Hf₁₉O₄₄. At 300 °C, the relative Ca content remained below 8 at.%. The crystallized phase well matched with rhombohedral Ca₂Hf₇O₁₆. The dielectric films grown on Si(100) substrates possessed effective permittivity values in the range of 12.8–14.2.