Thin film bulk acoustic wave filter

Thin film bulk acoustic wave (BAW) resonators (FBAR) are fabricated on a silicon nitride bridge using a ZnO piezolayer on a glass substrate and surface micromachining by standard thin film technology. These resonators exhibit a coupling constant k/sub t//sup 2/=7.8% at the first thickness extensional wave mode and are used as impedance elements in a ladder filter in the 1-GHz frequency band of mobile telecommunications. An electrical equivalent circuit is used to characterize the properties of the resonators and to show how the performance of the filter depends on the parameters of the resonators. 2.5% bandwidth, 2.8-dB insertion loss, and 35-dB selectivity are obtained in a filter with six resonators. The technology can be used to manufacture miniature microwave filters without any additional inductances.     

Determination of ZnO temperature coefficients using thin film bulk acoustic wave resonators

Thin film bulk acoustic wave (BAW) resonators have been the subject of research in RF microelectronics for some time. Much of the interest lay in utilizing the resonators to design filters for wireless applications. Some of the major advantages BAW devices present over other filter technologies in use today include size reduction and the possibility of on-chip integration. As the technology matures, the necessity to more fully characterize the performance of the devices and to develop more accurate models describing their behavior is apparent. In this investigation, the effects that temperature variations have on 1.8-2.0 GHz zinc oxide (ZnO)-based solidly mounted BAW resonators (SMRs) are studied. The average temperature coefficients of the series and parallel resonant frequencies of the fabricated devices are found to be -31.5 ppm//spl deg/C and -35.3 ppm//spl deg/C, respectively. The slight decrease in separation between the two resonant frequencies with temperature implies there is slightly less effective coupling with increased temperature. No definite trend is found describing the behavior of the quality factor (Q) of the resonator with temperature variations. With little temperature coefficient data for thin film ZnO available in the literature, the importance of an accurate model is evident. The resonator device performance is simulated using Ballato's electronic circuit model for acoustic devices on a SPICE-based platform. By virtue of the comparison between the predicted and measured device response, various material parameters are extracted.     

带隙可调的宽禁带半导体MgxZn1-xO薄膜研究进展

MgxZn1-xO薄膜是一种新型宽禁带半导体薄膜,在兼顾ZnO、MgO材料性能的同时,具有带隙连续可调的特点,近年来逐渐成为半导体光电功能材料与器件的研究热点之一。本文从MgxZn1-xO薄膜的基本特性、制备方法、应用研究等方面进行了分析和评述,并对其应用前景进行了展望。     

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.     

Beam-supported AlN thin film bulk acoustic resonators

A novel, suspended thin film bulk acoustic wave resonator (SFBAR) has been fabricated from an aluminum nitride film sputtered directly on a (100) silicon substrate. The suspended membrane design uses thin beams to support, as well as electrically connect, the resonator and has been fabricated using both thin film processing and bulk silicon micromachining. The quality factor and the effective electromechanical coupling coefficient were characterized as a function of the number and the length of the support beams. The length of the support beams was found to affect neither the quality factor at resonance nor the effective electromechanical coupling factor. However, longer support beams did facilitate better frequency pair response. Device performance varied with the number of support beams: 70% of the resonators tested showed a higher figure of merit with eight support beams than with four support beams.     

薄膜体声波谐振器应力负载效应摄动分析

薄膜体声波谐振器(FBAR)力学传感器有很大的应用潜力,但其敏感机理——应力负载效应尚不能被准确描述。为准确描述应力负载效应,预测FBAR力学传感器的频率灵敏度,提出一种摄动与有限元联合求解方法,并利用该方法计算FBAR微加速度计的频率-加速度灵敏度。首先,在COMSOL有限元软件中计算FBAR微加速度计在加速度下其压电层AlN的平均偏置应力;接着,在COMSOL中计算单个FBAR的谐振频率与相应的振型;最后,将有限元的计算数据和AlN的材料常数代入摄动积分公式中,得到FBAR微加速度计的频率-加速度灵敏度约为–98.879 kHz/g,与文献报道的实验结果–100 kHz/g相吻合,验证方法的可行性。     

偏场下薄膜体声波谐振器频率偏移的摄动分析

为准确预测测量力、热场的薄膜体声波谐振器(FBAR)传感器的灵敏度,采用叠加于有限偏场之上的小增量场理论描述,提出一种摄动与有限元联合求解方法。该方法利用COMSOL有限元软件计算FBAR传感器受外界载荷下其压电层AlN的平均偏置应力,进一步在COMSOL中计算FBAR的谐振频率与相应的振型,将有限元的计算数据代入摄动积分公式中,得到FBAR传感器的频率灵敏度。并以一个圆膜片FBAR为案例,介绍该方法用于计算圆膜片FBAR频率-集中力灵敏度的详细过程。采用摄动与有限元联合求解方法得到的频率灵敏度为41.3 MHz/N,与文献报道的实验结果 50 MHz/N接近,验证了方法的可行性。     

立方MgxZn1-xO晶体薄膜的制备和性能

采用低温物理沉积技术在二氧化硅衬底(SiO2/Si(100))和石英玻璃上生长出了MgxZn1-xO(x＞0.5)晶体薄膜,并用扫描电镜(SEM)、原子力显微镜(AFM)、X射线衍射(XRD)图谱和紫外-可见光透射光谱对其进行了表征.结果表明,在SiO2/Si(100)和石英玻璃衬底上沉积的MgxZn1-xO(x＞0.5)晶体薄膜表面平整,均呈立方结构,且具有高度的(001)择优取向.立方MgxZn1-xO薄膜具有从紫外到近红外波段良好的透明性,折射率为1.7～1.8,随着波长的增大或Mg组分的增大而降低.     

Fabrication and performance analysis of film bulk acoustic wave resonators

In this paper, a radio frequency reactive sputtering deposition technique for piezoelectric aluminum nitride (AlN) thin film formation on a gold (Au) bottom electrode and its successful application in a film bulk acoustic resonator (FBAR) are investigated. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements show that the AlN films were deposited onto an Au bottom electrode with highly c-axis-preferred orientation, well-textured columnar structure with a fairly uniform grain size of approximately 83 nm. The roughness is measured at a root-mean square (RMS) value of 5.4 nm and the average peak to valley of each grain column is 46.3 nm. The FBAR consists of an AlN piezoelectric thin film sandwiched between Au electrodes, all of which lie on a thin low-stress silicon nitride which serves as a support membrane on silicon. The performance of FBAR device exhibits a significant of the series quality factor (Q_s), the parallel quality factor (Q_p), the effective electromechanical coupling coefficient (k_eff²), and the bandwidths are 97, 120, 5.1%, and 24 MHz, respectively.     

High-Q AlN/SiO2 symmetric composite thin film bulk acoustic wave resonators

High-Q, bulk acoustic wave composite resonators based on a symmetric layer sequence of SiO₂-AlN-SiO₂ sandwiched between electrodes have been developed. Acoustic isolation was achieved by means of deep silicon etching to obtain membrane type thin film bulk acoustic wave resonators (TFBARs). Three different device versions were investigated. The SiO₂ film thicknesses were varied (0 nm, 70 nm, 310 nm, and 770 nm) while the piezoelectric AlN film had a constant thickness of 1.2 μm. The sputter-deposited AlN film grown on the amorphous, sputter-deposited SiO₂ layer exhibited a d_33,f of 4.0 pm/V. Experimental results of quality factors (Q) and coupling coefficients (k_t²) are in agreement with finite element calculations. A Q of 2000 is observed for the first harmonic of the 310 nm oxide devices. The most intense resonance of the 770 nm oxide device is the third harmonic reaching Q factors of 1450. The temperature drift reveals the impact of the SiO₂ layers, which is more pronounced on the first harmonic, reducing the TCF to 4 ppm/K for the 3rd harmonic of the 310 nm oxide devices.     

Deposition and characterization of reactive magnetron sputtered aluminum nitride thin films for film bulk acoustic wave resonator

This work studies the relationship between the deposition process parameters and the properties of sputtered c-axis-oriented aluminum nitride (AlN) thin films. AlN films were deposited on a Pt electrode by reactive magnetron sputtering under various deposition conditions. The films were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). A polycrystalline AlN film with highly c-axis-preferred orientation was achieved. The XRD rocking curve was 2.7°. The FESEM photographs also show that the AlN film has a dense hexagonal surface texture with uniform grain size and a highly ordered column structure.     

Growth of A1N piezoelectric film on diamond for high-frequency surface acoustic wave devices

Diamond films are very desirable for application to SAW devices because of their high acoustic wave velocity, which allows the extending of the frequency limit of operation at a given interdigital transducer line-width resolution. Use of high-quality AIN as the piezoelectric layer in conjunction with diamond is also desirable because of its high SAW velocity--the highest among all piezoelectric materials--together with its excellent electrical, mechanical, and chemical properties. The problems arising in the growth of A1N films on diamond have prevented, until now, the use of this combination of materials. In this paper we present recent results on the growth of highly oriented, low-stressed A1N films on diamond. SAW propagation on A1N/diamond has been theoretically investigated together with electromechanical coupling for both the Rayleigh and the Sezawa modes. The theoretical calculations show that high SAW velocities are achievable with good coupling efficiencies. Under proper conditions very large piezoelectric couplings are predicted--k2 = 2.2 and 4% for the Rayleigh and the Sezawa wave, respectively--comparable to those observed in strongly piezoelectric single crystals such as LiNbO3, but with SAW velocities approximately two-fold higher. Experiments performed on A1N/diamond/Si SAW test devices have shown good agreement between experimental results and theoretical predictions and demonstrate the feasibility of SAW devices based on this technology.     

Air gap type thin film bulk acoustic resonator fabrication using simplified process

In this study we propose a simplified process for making an air-gap-type film bulk acoustic resonator (FBAR) using the magnesium (Mg) sacrificial layer. The Mg sacrificial layer minimizes damage to other layers in the wet etching process because of its short etching time. Also the Mg sacrificial layer plays the role of etching aisle and air-gap simultaneous during the etching process. In addition, our proposed process can reduce the number of FBAR fabrication steps when compared with previous dry etching techniques. The FBAR's resonant frequency characteristics successfully show performance from 2.44 to 3.11 GHz.     

Surface acoustic wave characterization of a thin, rough polymer film

Laser generated surface acoustic waves (SAW) in a heterodyne diffraction scheme is a powerful technique for elastic characterization of thin films and it is frequently used on samples of high optical quality. We show that the method can also be effectively used in difficult conditions, on rough samples. Measurements are presented on a 3 µm thick film of polymer, spin-coated on steel, and on the same sample after addition of an aluminum coating. The experimental data are interpreted using a model assuming a stack of perfect layers. The analyses show good consistency within the SAW results for both configurations, and consistency with nano-indentation results, cross-validating both approaches.     

Si(111)衬底上生长的立方MgxZn1-xO晶体薄膜

在国际上第一次采用电子束反应蒸发法在Si(111)衬底上生长了MgxZn1-xO晶体薄膜.能量色散X射线(EDX)特征能谱及X射线衍射(XRD)分析表明薄膜呈立方结构,薄膜的晶面取向依赖于生长温度,在200C温度下生长得到高度(200)取向的立方MgxZn1-xO薄膜,温度过高时得到多晶薄膜.对高度(200)取向的立方MgxZn1-xO薄膜的光荧光激发谱(PLE)分析表明其光学带隙为4.20eV,相对于MgO的带隙红移量为3.50eV.XRD分析还表明立方MgxZn1-xO薄膜与MgO衬底之间的晶格失配仅为0.16%.这使得高质量立方MgxZn1-xO/MgO多量子阱材料的制备成为可能.     

CdxHg1−xTe thin film galvanomagnetic devices

The present paper concerns evaporated thin film Hall generators of Cd_xHg_1?xTe. We first give some information about the technology of Cd_xHg_1?xTe thin films and then we consider the construction and characteristics of these galvanomagnetic devices.     

Effects of H2O partial pressure on the crystallinity of ZnO thin film and electrical characteristics of film bulk acoustic wave resonators

We have improved electrical characteristics of a film bulk acoustic wave (BAW) resonator that features the injection of H₂O gas into a process chamber. The preferred crystallinity of piezoelectric ZnO film was obtained by RF sputtering at a high H₂O partial pressure 1.5×10⁻⁴ Pa. The effective electromechanical coupling coefficient () of the BAW resonator remarkably goes up from 1.8% to 4.7% for which the corresponding H₂O partial pressures are 2.7×10⁻⁵ and 1.5×10⁻⁴ Pa. Injection of H₂O during the deposition process contributes to the improvement of crystallinity of ZnO thin film and the electrical characteristics of the BAW resonator.     

Selective excitation of eigenmodes in a multilayer thin film resonator on bulk acoustic waves

We consider a method of control over the operating frequency of a resonator on bulk acoustic waves, which is based on the selective excitation of eigenmodes. The frequency switching is achieved by using several layers of a ferroelectric in the paraelectric state and applying a control voltage of appropriate magnitude and polarity to each layer. The principle of selectivity is formulated and the criterion function is defined, which ensure the most effective excitation of a selected eigenmode with the possible suppression of parasitic modes. An example of using this function for a resonator switched between four eigenmodes is presented.     

应用于体声波谐振器的ZnO薄膜结构和电学特性

采用直流磁控溅射的方法制备了ZnO压电薄膜,并在双面抛光的熔融石英基片上制备了高次谐波体声波谐振器.x射线衍射结果显示ZnO压电薄膜C轴择优取向明显,衍射峰半高宽为0.1624°,显示出较好的结晶质量;扫描电镜分析观察到ZnO垂直于基片表面的柱形晶粒结构和较平滑的薄膜表面.体声波器件的电学测试结果显示器件具有很好的多模谐振特性,说明ZnO压电薄膜很好地激发出了厚度方向的纵声波,可应用于体声波器件和声表面波器件中.另外采用间接的方法得到ZnO压电薄膜在870MHz时的介电常数约为5.24,介电损耗因子为1.07,进一步减小介电损耗因子,可以提高器件的Q值.