AlN films sputtered on iridium electrodes for bulk acoustic wave resonators

We report on the growth of highly c-axis-textured aluminum nitride (AlN) films sputtered on iridium layers for thin film bulk acoustic microresonator applications. Iridium films were evaporated on oxidized silicon covered with Ti or Mo/Ti seed layers to improve crystal quality and adhesion. The crystal quality of the AlN films as a function of the crystal structure of the iridium electrode and its pre-conditioning by Ar⁺ bombardment was analyzed by X-ray diffraction, atomic force microscopy and wet chemical etching. Solidly mounted resonators using a single low-impedance layer of silicon dioxide for acoustic isolation were fabricated for a preliminary assessment of the piezoelectric activity of AlN films and the influence of the AlN/Ir stack on the performance of the devices. The electromechanical coupling factor of the AlN films was derived by fitting the electrical response of the resonators to Mason's physical model. AlN films exhibited very high coupling factors (7.5%) barely dependent on the width of the rocking-curve around the AlN 00·2 reflection. The high acoustic impedance of iridium electrodes provided resonators with quality factors higher than those of similar resonators built on lighter electrodes, such as molybdenum.     

Optimization of the annealing process and nanoscale piezoelectric properties of (002) AlN thin films

In this paper, the effects of different annealing processes on the texture, surface morphology, and piezoelectric properties of aluminum nitride (AlN) thin films and the performance of AlN-based surface acoustic wave (SAW) devices were systematically investigated. Based on the crystallinity and the morphology results, it is evident that in-situ annealing method is superior to ex-situ annealing. For the AlN thin films, the crystallization and piezoelectricity were both enhanced and then receded as the annealing temperature increased from 300 to 600?°C. We demonstrated that good (002) orientation, excellent grain distribution and high relative piezoelectric coefficient of the AlN thin films were achieved via in-situ annealing at 500?°C. Meanwhile, the AlN thin films exhibited excellent polarization properties and polarization maintaining characteristics. Additionally, the uniform interdigital transducer (IDT) with 8 μm period (finger width?=?2 μm) were designed and the IDT/AlN/SiO₂/Si SAW devices with the center frequency f ₀ of 495 MHz and insert loss of ?24.1 dB were fabricated.     

AlN/FeCoSiB磁电复合薄膜的制备及其逆磁电效应研究

借助射频磁控溅射成功制备了AlN/FeCoSiB磁电复合薄膜, 探讨了退火条件对AlN薄膜压电性能和FeCoSiB薄膜磁性能的影响, 并研究了其逆磁电响应。结果显示, 500℃退火处理的AlN薄膜具有高度(002)择优取向和柱状生长结构; 经过300℃退火后FeCoSiB薄膜的磁场灵敏度提高。该磁电复合薄膜的逆磁电电压系数(α_CME)在偏置磁场(H_dc)为875 A/m时达到最大值62.5 A/(m·V); 且磁感应强度(B)随交变电压(V_ac)的变化呈现优异的线性响应(线性度达到1.3%)。这种AlN/FeCoSiB磁电复合薄膜在磁场或电场探测领域具有广阔的应用前景。     

热处理温度对铁电薄膜底电极Pt和Pt／Ti物相与形貌的影响

随着热处理温度上升，在ＳｉＯ２／Ｓｉ衬底上溅射的Ｐｔ、Ｐｔ／Ｔｉ电极中，构成Ｐｔ薄膜的晶粒由小变大，由分布均匀到晶粒局部聚集，最后分离成小岛。Ｔｉ层可提高Ｐｔ薄膜与基片间的粘附性和高温下的稳定性。快速热处理可提高Ｐｔ薄膜在高温下的连续性。并研究了Ｐｔ薄膜对ＰＬＴ铁电薄膜的成品率和分散性的影响。     

Influence of aluminum nitride interlayers on crystal orientation and piezoelectric property of aluminum nitride thin films prepared on titanium electrodes

Highly c-axis-oriented aluminum nitride (AlN) thin films have been prepared on titanium (Ti) bottom electrodes by using AlN interlayers. The AlN interlayers were deposited between Ti electrodes and silicon (Si) substrates, such as AlN/Ti/AlN/Si. The crystallinity and crystal orientation of the AlN films and Ti electrodes strongly depended on the thickness of the AlN interlayers. Although the sputtering conditions were the same, the X-ray diffraction intensity of AlN (0002) and Ti (0002) planes drastically increased, and the full-width at half-maximum (FWHM) of the X-ray rocking curves decreased from 5.1° to 2.6° and from 3.3° to 2.0°, respectively. Furthermore, the piezoelectric constant d₃₃ of the AlN films was significantly improved from − 0.2 to − 4.5 pC/N.     

Grain coarsening mechanism of Cu thin films by rapid annealing

Cu thin films have been produced by an electroplating method using nominal 9N anode and nominal 6N CuSO₄·5H₂O electrolyte. Film samples were heat-treated by two procedures: conventional isothermal annealing in hydrogen atmosphere (abbreviated as H₂ annealing) and rapid thermal annealing with an infrared lamp (abbreviated as RTA). After heat treatment, the average grain diameters and the grain orientation distributions were examined by electron backscattering pattern analysis. The RTA samples (400 °C for 5 min) have a larger average grain diameter, more uniform grain distribution and higher ratio of (111) orientation than H₂ annealed samples (400 °C for 30 min). This means that RTA can produce films with coarser and more uniformly distributed grains than H₂ annealing within a short time, i.e. only a few minutes. To clarify the grain coarsening mechanism, grain growth by RTA was simulated using the phase field method. The simulated grain diameter reaches its maximum at a heating rate which is the same order as that in the actual RTA experiment. The maximum grain diameter is larger than that obtained by H₂ annealing with the same annealing time at the isothermal stage as in RTA. The distribution of the misorientation was analyzed which led to a proposed grain growth model for the RTA method.     

利用前后处理技术改进钛／硅基板上的类金刚石场发射特性

采用微波等离子体化学气相沉积系统存钛/硅基板上沉积类金刚石薄膜,并利用拉曼光谱仪、扫瞄式电子显微镜及原子力显微镜研究了氢等离子体前处理及快速退火后处理对类金刚石薄膜场发射特性之影响.在沉积类金刚石薄膜之前,钛/硅基板使用了两种前处理技术:第一种为研磨金刚石粉末,第二种为研磨金刚石粉末后外加氢等离子体刻蚀处理.成长类金刚石薄膜后进行快速退火处理.发现不论是氢等离子体前处理还是快速退火后处理皆能改善场发射特性,其中经退火后处理的场发射特性比氢等离子体前处理的场发射特性改善更明显.其因之一在于快速退火后处理可在类金刚石薄膜表而形成sp2丛聚,提供了很多的场发射子,也同时增加了表面粗糙度;另一个原因可能是在快速退火后处理期间会使类金刚石薄膜进一步石墨化,因而提供了许多电子在通过类金刚石薄膜时的传输路径.研究结果表明:利用适当的前后处理技术可改进类金刚石薄膜的场发射特性,进而做为冷阴极材料之应用.     

Effects of rapid thermal annealing on nucleation, growth, and properties of lead zirconate titanate films

The nucleation and growth behavior of solgel-derived lead zirconate titanate (PZT) films was investigated at different rapid thermal annealing (RTA) processes. The effects of RTA on PZT film surface morphology, crystal orientation, residual stress, and properties were also studied and are discussed. PZT nucleation and growth behavior were found to be more sensitive to heating rate than to hold time during RTA. Higher heating rates were preferred for uniform PZT nucleation and grain growth, which resulted in dense microstructures, smooth surfaces, and better film ferroelectric properties. Lower heating rates led to strong PZT (100) orientation, better film piezoelectric properties, and low residual stress, but at the risk of film cracks caused by arbitrarily distributed large crystallites with diameters of approximately 300 nm among crystallites with diameters of approximately 30 nm. Furthermore, the residual stress of the PZT film was found to be effectively reduced by extending the hold time.     

Crystallization behavior and domain structure in textured Pb(Zr0.52Ti0.48)O3 thin films by different annealing processes

Amorphous Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were prepared on the Pt/Ti/SiO₂/Si substrates by radio-frequency magnetron sputtering at room temperature. After rapid thermal annealing (RTA) and conventional furnace annealing (CFA) at different temperatures, the films were transformed into polycrystalline PZT thin films with (111) and (100) orientation, respectively. The phase formation and ferroelectric domains correlated with different orientation were systematically investigated by X-ray diffraction and piezoresponse force microscopy. The results showed that the perovskite PZT crystal with [111] orientation hetero-nucleated preferentially on top of the PtPb intermetallic phase at the PZT/Pt interface during RTA process. It is of interest to find that the domain self-organized into a structure with rounded shape at the early stage of crystallization. While the nucleation of the films treated by CFA dominantly homo-nucleated, thus the (100) orientation grains with minimum surface energy were easy to grow. The texture effects on ferroelectric properties of PZT films were also discussed in relation to the domain structure.     

N掺杂Cu2O薄膜的低温沉积及快速热退火研究

采用氧化亚铜(Cu_2O)陶瓷靶,利用射频磁控溅射沉积法在氮气和氩气的混合气氛下制备了N掺杂Cu_2O(Cu_2O∶N)薄膜,并在N_2气氛下对薄膜进行了快速热退火处理,研究了N_2流量和退火温度对Cu_2O∶N薄膜的生长行为、物相结构、表面形貌及光电性能的影响。结果显示,在衬底温度300℃、N_2流量12sccm条件下生长的薄膜为纯相Cu_2O薄膜;在N_2气氛下对预沉积薄膜进行快速热退火处理不影响薄膜的物相结构,薄膜的结晶质量随退火温度(450℃)的升高而显著改善;快速热退火处理能改善薄膜的结晶质量和缺陷,降低光生载流子的散射,增强载流子的传输,预沉积Cu_2O∶N薄膜经400℃退火处理后展示出较好的电性能,薄膜的霍尔迁移率(μ)为27.8cm~2·V~(-1)·s~(-1)、电阻率(ρ)为2.47×10~3Ω·cm。研究表明低温溅射沉积和快速热退火处理能有效改善Cu_2O∶N薄膜的光电性能。     

Influence of the seed layer on structural and electro-acoustic properties of sputter-deposited AlN resonators

The growth of high-quality AlN films has been studied by reactive sputtering onto Mo electrodes with Ni, Ti, and TiW seed layers and subsequent integration into thin film bulk acoustic wave resonators. The crystalline structure and morphology of the Mo and c-axis oriented AlN films were found to vary strongly with seed layer material and thickness. The smoothest Mo electrodes were obtained on thin Ti films. Reactive sputtering of AlN on top of these optimized electrodes resulted in a dense columnar grain structure with a well-aligned (002) crystal orientation and good electro-acoustic properties, including an effective coupling coefficient of 6.89% and quality factor above 1000.     

Influence of rapid thermal annealing on the process of aluminum induced crystallization of amorphous Si

The effects of annealing methods on the crystallization process and microstructure of polycrystalline silicon (poly-Si) films obtained by aluminum-induced crystallization (AIC) of amorphous Si (a-Si) films were comparatively investigated. Glass/Al/a-Si structures were annealed by rapid thermal annealing (RTA) and conventional furnace at 500 °C for different times in Ar. As compared to furnace annealing, AIC of a-Si films annealed by RTA possesses a shorter period of nucleation time, a higher nucleation density and reduces the process time to form continuous poly-Si films. It is revealed that the continuous Si films obtained by both RTA and conventional furnace annealing are polycrystalline in nature, exhibiting good microstructures with Raman peaks at 518 cm^?1 and full-width at half-maximums of 6.43–6.48 cm^?1.     

Rapid thermal annealing of rare earth implanted ZnO epitaxial layers

Zinc oxide epilayers grown by metal organic vapour phase epitaxy on (0 0 0 1) sapphire substrates were doped with Praseodymium and Europium by ion implantation. The as-implanted samples were either annealed in air for 20 min in a tube furnace or rapid thermal annealing (RTA) was performed, for 2 min, in a nitrogen atmosphere. The samples were characterized by Rutherford Backscattering Spectrometry/Channelling and photoluminescence. The presented results indicate that in the as-implanted samples the majority of the rare earth (RE) ions are incorporated into substitutional Zn-sites. Furnace annealing at 1000 °C recovers the crystal quality of the samples but leads to an out-diffusion of the RE. RTA suppresses diffusion but lattice damage is not fully recovered at 1000 °C. More importantly, during RTA the RE ions are driven from the substitutional site and are now found mainly on random interstitial sites and no optical activation could be achieved.     

Influence of rapid thermal annealing (RTA) on the structural and electrical properties of SnS films

The performance of optoelectronic devices critically depends on the quality of active layer. An effective way to obtain a high quality layers is by creating excess of metal atoms through various heat treatments. Recently, rapid thermal annealing (RTA) has proved a versatile technique for the post-treatment of semiconductor materials as compared to other techniques due to its precise control over the resources. Thus, we carried out a set of experiments on SnS films to explore the influence of RTA treatment on their properties. From these experiments we noticed that the films treated at 400 °C for 1 min in N₂ atmosphere have a low electrical resistivity of ~5 Ωcm with relatively high Hall mobility and carrier density of 99 cm²/Vs and 1.3 × 10¹⁶ cm⁻³, respectively. The observed results, therefore, emphasise that it is possible to obtain good quality SnS films through RTA treatment without disturbing their crystal structure.     

Microwave annealing for preparation of crystalline hydroxyapatite thin films

A sol was spun on single crystal silicon substrates at a spin-rate of 3000–5000 rpm followed by a low temperature cure to form a stable sol–gel/silicon structure. Good quality crystalline HA films of thickness ∼300–400 nm were obtained by annealing the sol–gel/Si structure in a conventional cavity applicator microwave system with a magnetron power of 1300 W, frequency of 2.45 GHz, and at a low processing temperature of 425 °C for annealing times ranging from 2–60 min. X-ray Diffraction and FTIR analysis confirmed that the crystalline quality of the thin films were comparable or better than those heat-treated under the same processing conditions (temperature and time) in a Rapid Thermal Annealing (RTA) system. The RBS data suggests a composition corresponding to stoichiometric hydroxyapatite Ca₁₀(PO₄)₆(OH)₂, the major inorganic component of bone. The results showed that the HA film thickness decreases with increasing sol spin-rate. The HA films showed good biocompatibility because little monocyte adhesion occurred and hence no inflammatory response was activated in vitro. The potential of microwave annealing for rapid and low temperature processing of good crystalline quality HA thin films derived from sol–gel is demonstrated.     

Effect of AlN buffer layer on the microstructure and bandgap of AlN films deposited on sapphire substrates by pulsed laser deposition

AlN buffer layer is proposed to improve the growth of AlN films on the sapphire substrate by pulsed laser deposition. The buffer layers were pre-deposited under vacuum for different time, which was aimed to suppress the negative nitridation effect in the initial growth stage, and their effects on the surface morphology, crystal structure and bandgap of AlN films were characterized. It is found that AlN-buffered films exhibit a single (0002) preferred orientation and the crystallinity improves as the pre-deposition time increases from 5 to 20 min. Al-polarity AlN films are obtained at the pre-deposition time of 5 and 10 min, while the polarity inversion from the Al- to N-polarity is observed at 20 min. Based on the analysis of optical transmittance spectra, the bandgap of AlN films decreases with increasing pre-deposition time, which may be resulted from the decrease of axial ratio c/a.     

Properties of piezoelectric actuator on silicon membrane, prepared by screen printing method

Characteristics of piezoelectric actuator on Si membrane were investigated. Si membranes were fabricated as a function of size using bulk micromachining method. Bottom electrode Ag–Pd and piezoelectric thick films were fabricated using screen printing method, respectively. Piezoelectric thick films were sintered by rapid thermal annealing (RTA). Top electrodes Pt were deposited by DC sputtering system. We analyzed micro structure by scanning electron microscope (SEM) and investigated dynamic properties by MTI2000. Therefore, piezoelectric thick film on Si membrane had P_r of 15.7 μC cm⁻². The maximum displacement of micro actuator had 0.05 μm. We find the combination of thick film printing and MEMS process to form a Si membrane micro actuator.     

Characterization of dielectric and electro-optic properties of PLZT 9/65/35 films on sapphire for electro-optic applications

Lead lanthanum zirconate titanate (PLZT) thin films were deposited on r-plane sapphire at low temperatures by RF triode magnetron sputtering using lead compensated hot-pressed targets. To obtain fully perovskite phase in the films, two types of post-deposition processing were investigated: rapid thermal annealing (RTA) and furnace annealing (FA). Dielectric and electro-optic properties of PLZT films were found to be strongly dependent on annealing conditions. The peak dielectric constant of the films were 1200 and 2800 with Curie temperatures of 110 degrees C and 190 degrees C after RTA and FA processing, respectively. The dielectric losses in the films were fairly low; tan deltas were less than 0.02 after RTA and less than 0.04 after FA processing. The films showed good optical transmission characteristics after annealing and an anomalously large effective quadratic electro-optic effect was observed in one furnace annealed film.     

AlN薄膜体声波谐振器研究

采用一维Mason模型,研究了体声波谐振器的频率特性,探讨了压电薄膜AlN和上电极膜厚对谐振频率的影响,压电参数d33及压电薄膜与电极的厚度比率对机电耦合系数的影响,同时研究了谐振区域的面积和声能在衬底中的损耗对品质因数的影响.测量的体声波谐振器频率特性曲线与模拟结果吻合的较好.     

Effects of rapid thermal annealing on the morphology and electrical properties of ZnO/In films

Zinc oxide (ZnO) films were prepared by ultrasonic spray pyrolysis on indium (In) films deposited by evaporation and subsequently subjected to rapid thermal annealing (RTA) in air or vacuum. The crystallographic properties and surface morphology of the films were characterized before and after RTA by X-ray diffraction and scanning electron microscopy, respectively. The variation in resistivity of the films with RTA temperature and time was measured by the four-point probe method. Auger electron spectroscopy (AES) was carried out to determine the distribution of indium atoms in the ZnO films. The resistivity of the ZnO on In (ZnO/In) films decreased to 2×10⁻³ Ω cm by diffusion of the In. Indium diffusion into the ZnO films roughened the film surface. The results of depth profiling by AES showed a hump of In atoms around ZnO/In interface after RTA at 800 °C, which disappeared on RTA at 1000 °C. The effects of temperature, time and atmosphere during RTA on the structural and electrical properties of the ZnO/In films are discussed.