Two-step sputtered ZnO piezoelectric films for film bulk acoustic resonators

This study investigates high-performance ZnO piezoelectric films used for thin film bulk acoustic resonators (TFBAR). The ZnO piezoelectric film was deposited on a Pt/Ti electrode using an RF magnetron sputter by a two-step method at room temperature. The Pt/Ti electrode was deposited by a DC sputtering system, on which, ZnO piezoelectric films were deposited in one step and in two steps to minimize roughness in the first step and produce the preferred orientation in the second. Both field-emission scanning electron microscopy (FESEM) and atom force microscopy (AFM) revealed that ZnO piezoelectric film deposited by two-step sputtering exhibited favorable characteristics, such as a rigidly precise surface structure with surface roughness of 7.37 nm, even better than in one-step sputtering. Examining the ZnO thin film by X-ray diffraction (XRD) showed a much higher c-axis-preferring orientation than in one-step sputtering. The reflection coefficient of the resonator device was measured using an HP8720 network analyzer. The frequency response of the FBAR device exhibited a return loss of -25 dB at a resonant frequency of 2212 MHz with a high coupling coefficient of 6.7%. PACS 68.55.Jk; 43.35.Ns; 81.15.-z     

ZnO-based film bulk acoustic resonator devices on a specially designed Bragg reflector

In this paper, we studied ZnO-based film bulk acoustic resonator (FBAR) device fabricated on a specially designed multilayered Bragg reflector part. Very thin chromium adhesion layers (0.03 μm thick) were additionally deposited to improve the quality of the Bragg reflector and some thermal treatments were performed to improve the resonant characteristics of the FBAR device. At the operating frequency of ∼2.7 GHz, excellent resonant characteristics were observed in terms of return loss and quality factor, and effective electromechanical coupling coefficient.     

An improvement of tilted AlN for shear and longitudinal acoustic wave

This study investigates c-axis tilted aluminum nitride (AlN) piezoelectric films for the improvement of both shear and longitudinal acoustic wave resonances. Solidly-mounted resonator (SMR) structure is adopted for the applications of high frequency wireless communications and high sensitivity sensors. As to the piezoelectric layer, c-axis tilted AlN has the capability to excite the dual-mode resonances, namely, the longitudinal and shear mode resonances. In this study, SMR devices made with a seven-layer molybdenum/silicon dioxide (Mo/SiO₂) Bragg reflector and the c-axis tilted AlN are carried out. A conventional off-axis sputtering technique is applied to grow the tilted AlN. The outcome frequency responses show dual resonant characteristics. However, the longitudinal resonance fades away with the AlN c-axis tilted angle, and the quality factor of the longitudinal resonance decreases. Consequently, we make an improvement by tilting the off-center substrates toward the sputtering source and successfully enhance the longitudinal resonance while preserving the shear resonance at the same time. Not only the shear resonance for the liquid-based sensing application, but also an outstanding longitudinal resonance could be obtained. The practicability of the dual-mode resonator is extended.     

Fabrication of piezoelectric AlN thin film for FBARs

This paper focuses on the fabrication of film bulk acoustic-wave resonator (FBAR) comprising an aluminum nitride (AlN) piezoelectric thin film sandwiched between two metal electrodes and located on a silicon substrate with a low-stress silicon nitride (Si₃N₄) support membrane for high frequency wireless applications, and analyzes the optimization of the thin AlN film deposition parameters on Mo electrodes using the reactive RF magnetron sputter system. Several critical parameters of the sputtering process such as RF power and Ar/N₂ flow rate ratio were studied to clarify their effects on different electrodes characteristics of the AlN films. The experiment indicated that the process for Mo electrode was easier compared with that of the Pt/Ti or Au/Cr bi-layer electrode as it entailed only one photo resist and metal deposition step. Besides, Pt/Ti or Au/Cr electrodes reduced the resonance frequency due to their high mass density and low bulk acoustic velocity. Compared with the case of the Al bottom electrode, there is no evident amorphous layer between the Mo bottom electrode and the deposited AlN film. The characteristics of the FBAR devices depend not only upon the thickness and quality of the AlN film, but also upon the thickness of the top electrode and the materials used. The results indicate that decreasing the thickness of either the AlN film or the top electrode increases the resonance frequency. This suggests the potential of tuning the performance of the FBAR device by carefully controlling AlN film thickness. Besides, increasing either the thickness of the AlN film or higher RF power has improved a stronger c-axis orientation and tended to promote a narrower rocking curve full-width at half-maximum (FWHM), but increased both the grain size and the surface roughness. An FBAR device fabricated under optimal AlN deposition parameters has demonstrated the effective electromechanical coupling coefficient (k _eff²) and the quality factor (Q _{f x} ) are about 1.5% and 332, respectively.     

Effects of reflecting layers on resonance characteristics of a solidly mounted resonator with ¼ λ mode configuration

The solidly mounted resonator (SMR) is composed of a piezoelectric thin film sandwiched between two electrodes and a Bragg reflector that comprises alternating high and low acoustic impedance with a thickness of a quarter wavelength. In this study, the combination Mo/SiO₂ is chosen as high/low acoustic impedance materials to form a Bragg reflector; aluminum nitride (AlN) is utilized as the piezoelectric layer. The purpose of this study is to investigate the resonance characteristics of solidly mounted resonators with various pairs of reflecting layers. The experimental results yield an electromechanical coupling (k_eff²)(k_{\mathrm{eff}}^{2}) of 1.926% and quality factor (Q) of 254 with three pairs of Mo/SiO₂ layers. The figure of merit (FOM), which is defined as the product of electromechanical coupling and quality factor, has a maximum of 489 with three pairs of Mo/SiO₂ layers.     

Orientation fluctuation trend of Pt and ZnO layers in film bulk acoustic resonator

ZnO-based film bulk acoustic resonator (FBAR) was fabricated with many ZnO/Pt layers by magnetron sputtering. All the layers are good crystallized and highly textured. By crystallographic test, the orientation fluctuation of Pt layer increases with increasing film thickness or stack layers, whereas that of ZnO layer decreases slightly. It is consistent with ZnO grain c-axis tilting observed using transmission electron microscopy. Due to these good quality layers, the device has a high resonate frequency of 3.94 GHz.     

Tunable Ba_0.5 Sr_0.5 TiO₃ film bulk acoustic resonators using SiO₂ /Mo Bragg reflectors

Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators(FBARs) based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3(BST) films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias(< 45 V) while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum(Mo) as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.     

Molybdenum thin films fabricated by rf and dc sputtering for Cu(In,Ga)Se_2 solar cell applications

Molybdenum(Mo) thin films, most commonly used as electrical back contacts in Cu(In?Ga)Se2(CIGS) solar cells, are deposited by rf and dc magnetron sputtering in identical systems to study the discrepancy and growth mechanisms of the two sputtering techniques. The results reveal that though different techniques generally de?posit films with different characteristic properties, Mo films with similar structural and physical properties can be obtained at respective suitable deposition conditions. Highly adhesive and conductive Mo films on soda lime glass are further optimized, and the as-fabricated solar cells reach efficiencies as high as 9.4% and 9.1% without an antireflective layer.     

Effect of sputtering power on surface topography of dc magnetron sputtered Ti thin films observed by AFM

Titanium films were deposited on glass substrates at room temperature by direct current (dc) magnetron sputtering at fixed Ar pressure of 1.7 Pa and sputtering time of 4 min with different sputtering power ranging from 100 to 300 W. Atomic force microscopy (AFM) was used to study topographic characteristics of the films, including crystalline feature, grain size, clustering and roughening. The amorphous-like microstructure feature has been observed at 100-150 W and the transition of crystal microstructure from amorphous-like to crystalline state occurs at 200 W. The increase in grain size of Ti films with the sputtering power (from 200 to 300 W) has been confirmed by AFM characterization. In addition, higher sputtering power (300 W) leads to the transformation of crystal texture from globular-like to hexagonal type. The study has shown that higher sputtering power results in the non-linear increase in deposition rate of Ti films. Good correlativity between the surface roughness parameters including root mean square (RMS) roughness, surface mean height (Ra) and maximum peak to valley height (P-V) for evaluating the lateral feature of the films has been manifested. Surface roughness has an increasing trend at 100-250 W, and then drops up to 300 W.     

基于MgxZn1−xO薄膜固体装配型体声波谐振器

本文研制了一种基于磁控溅射掺镁氧化锌(Mg_xZn_(1-x)O)压电薄膜的S波段固体装配型体声波谐振器(SMR-FBAR)。相比传统的氧化锌(ZnO)薄膜,Mg_xZn_(1-x)O具有高纵波声速,高电阻率优点,而且Mg原子以替位或填隙的方式进入晶格,没有改变ZnO的铅锌矿结构。通过优化磁控溅射参数的方法,获得了c轴方向生长良好的Mg_xZn_(1-x)O薄膜,并成功制得了串联谐振频率以及并联谐振频率分别在2.416 GHz和2.456 GHz的谐振器,测得其有效机电耦合系数为4.081%,回波损耗(S11)为-23.89 d B。这种SMR机械强度高、可靠性高、尺寸小,具有可立体集成到CMOS芯片表面的优势。     

高反射率Mo/B4C多层膜设计及制备

 运用遗传算法优化设计了Mo/B₄C多层膜结构。入射光入射角度取10°时,设计的理想多层膜膜对数为150,周期为3.59 nm,Gamma值（Mo膜厚与周期的比值）为0.41,峰值反射率为33.29%。采用恒功率模式直流磁控溅射方法制作Mo/B₄C多层膜。通过在Mo/B4C多层膜与基底之间增加15 nm厚的Cr粘附层,提高多层膜与基底的粘附力。另外,还采用调整多层膜Gamma值的方法减小其内应力,调整后多层膜结构周期为3.59 nm, Mo膜厚1.97 nm, B4C膜厚1.62 nm,峰值反射率26.34％。制备了膜对数为150的Mo/B₄C膜并测量了其反射率,在波长7.03 nm处,Mo/B₄C多层膜的近正入射反射率为21.0％。最后对测量结果进行了拟合,拟合得到Mo/B₄C多层膜的周期为3.60 nm,Gamma值0.60,界面粗糙度为0.30 nm。     

Fabrication and analysis of ZnO thin film bulk acoustic resonators

This study employs RF magnetron sputter technique to deposit high C-axis preferred orientation ZnO thin film on silicon substrate, which is then used as the piezoelectric thin film for a thin film bulk acoustic resonator (FBAR). Electrical properties of the FBAR component were investigated by sputtering a ZnO thin film on various bottom electrode materials, as well as varying sputter power, sputter pressure, substrate temperature, argon and oxygen flow rate ratio, so that structural parameters of each layer were changed. The experimental results show that when sputter power is 200 W, sputter pressure is 10 mTorr, substrate temperature is 300 °C, and argon to oxygen ratio is 4:6, the ZnO thin film has high C-axis preferred orientation. The FBAR component made in this experiment show that different bottom electrode materials have great impact on components. In the experiment, the Pt bottom electrode resonant frequency was clearly lower than the Mo bottom electrode resonant frequency, because Pt has higher mass density and lower acoustic wave rate. The component resonant frequency will decrease as ZnO thin film thickness increases; when top electrode thickness is higher, its resonant frequency also drops, due to top electrode mass loading effect and increased acoustic wave path. Therefore, ZnO thin film and top/bottom electrode thickness can be fine-tuned according to the required resonant frequency.     

Experimental study on Ti N coated racetrack-type ceramic pipe

Ti N film was coated on the internal surface of a racetrack-type ceramic pipe by three different methods:radio-frequency sputtering, DC sputtering and DC magnetron sputtering. The deposition rates of Ti N film under different coating methods were compared. The highest deposition rate was 156 nm/h, which was obtained by magnetron sputtering coating. Based on AFM, SEM and XPS test results, the properties of Ti N film, such as film roughness and surface morphology, were analyzed. Furthermore, the deposition rates were studied with two different cathode types, Ti wires and Ti plate. According to the SEM test results, the deposition rate of Ti N/Ti film was about 800 nm/h with Ti plate cathode by DC magnetron sputtering. Using Ti plate cathode rather than Ti wire cathode can greatly improve the film deposition rate.     

The pure-shear mode solidly mounted resonator based on c-axis oriented ZnO film

In this paper, we fabricate a pure-shear mode film bulk acoustic resonator based on c-axis oriented ZnO film. The resonator is consisted of an in-plane electrode, a highly c-axis oriented ZnO film and a SiO₂/W Bragg reflector. The shear mode wave is excited by the lateral electric field. The resonator works in a pure-shear mode with the resonance frequency near 1.5 GHz and the Q-factor of 479 in air. There is no obvious longitudinal mode resonance in the frequency response, which can be explained that the electric field component normal to the surface is very weak and the Bragg reflector has the effective frequency selectivity for the shear mode. Importantly for sensors, the immersion into de-ionized water and glycerol liquid still allows for a Q-factor up to 335 and 220, respectively. This resonator shows the potential as mass loading sensors for biochemical application.     

具有二氧化硅温度补偿层的薄膜体声波谐振器的建模与分析（英）

薄膜体声波谐振器(FBAR)的谐振频率会受到外界环境温度的影响而产生漂移,对于FBAR滤波器而言,这种温度-频率漂移特性会导致其中心频率、插入损耗、带内纹波等性能发生变化,降低其在电学应用中的可靠性。应用ANSYS有限元分析软件,对一个典型Mo-AlN-Mo三层结构的FBAR进行了温度-频率漂移特性的仿真,得到其在［－50 ℃, 150 ℃］温度范围内的频率温度系数(TCF)约为－3510－6/℃。在FBAR叠层薄膜结构中添加了一层具有正温度系数的二氧化硅温度补偿层,分析了该补偿层厚度对FBAR的温度-频率漂移特性、谐振频率和机电耦合特性的影响。设计了具有一层二氧化硅温度补偿层的FBAR叠层,由Mo/AlN/SiO2/Mo多层薄膜构成,仿真得到其频率温度系数为0.87210－6/℃;与没有温度补偿层的FBAR相比,温度稳定性得以显著改善。关键词: Abstract: Key words:     

Low-Temperature Synthesis of α-SiC Nanocrystals

Physics of the Solid State - Thick SiCx films have been deposited on a c-Si surface by radiofrequency (rf) magnetron sputtering (150 W, 13.56 MHz, Ar flow 2.4 L/h, 0.4 Pa) of graphite and silicon...     

Ti/Ti-类金刚石多层膜的制备与表征

采用电子回旋共振-化学气相沉积结合中频磁控溅射的真空镀膜技术, 以99.99%Ti为靶材, 乙炔为碳源制备了Ti/Ti-类金刚石(DLC)多层膜. 利用X射线衍射仪、扫描电子显微镜、X射线光电子能谱仪 对Ti/Ti-DLC多层膜进行了相结构、组织、成分及形态分析. 采用显微硬度仪、摩擦磨损仪、表面粗糙度仪对Ti/Ti-DLC多层膜进行了力学性能考察. 结果表明: Ti/Ti-DLC多层膜中主要含有TiC晶相; Ti层和Ti-DLC层中未出现柱状晶体生长模式, 分层中均以岛状模式生长; 当调制周期Λ≤ 50 nm时, 分层结构变模糊; 调制周期Λ对Ti/Ti-DLC多层膜的复合硬度、摩擦系数、表面形貌、表面粗糙度都有影响, 当调制周期Λ较小时表现出纳米增硬效应, 表面出现大颗粒, 表面粗糙度和摩擦系数均变大.     

UV detectors based on nanocrystalline ZnO films

Nanocrystalline films of zinc oxide deposited by rf magnetron sputtering are used as a working material of UV detectors. The photoelectric performance of UV detectors versus ZnO deposition conditions is studied. The influence of the surface topology of the UV detectors on their efficiency is examined with an atomic force microscope.     

用不同的Mo靶溅射功率制备Mo/Si多层膜

 用磁控溅射法制备了周期厚度和周期数均相同的Mo/Si多层膜，用原子力显微镜和小角X射线衍射分别研究了Mo靶溅射功率不相同时，Mo/Si多层膜表面形貌和晶相的变化。随后在国家同步辐射实验室测量了Mo/Si多层膜的软X射线反射率。研究发现，随着Mo靶溅射功率的增大，Mo/Si多层膜的表面粗糙度增加，Mo的特征X射线衍射峰也增强，Mo/Si多层膜的软X射线峰值反射率先增大后减小。     

Deposition of nanostructured crystalline and corrosion resistant alumina film on bell metal at low temperature by rf magnetron sputtering

Aluminium oxide films deposited by rf magnetron sputtering for protective coatings have been investigated. The alumina films are found to exhibit grainy surface microstructure. The grain size, structure and density depend on different system parameters such as argon and/or oxygen flow rate and applied rf power etc. The effect of transition of the discharge from metallic to reactive mode on the surface characteristics of the alumina film is studied. X-ray diffractometry reveals that in poisoned mode of sputtering and under optimized power and pressure, crystalline alumina film can be grown. Different system conditions are optimized for corrosion resistant aluminium oxide films with good adhesion properties. Nanostructured alumina film is obtained at lower pressure (8 × 10⁻⁴ to 9 × 10⁻⁴ Torr) by rf reactive magnetron sputtering.