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The conformality of thin films grown by atomic layer deposition (ALD) is studied using all-silicon test structures with long narrow lateral channels. A diffusion model, developed in this work, is used for studying the propagation of ALD growth in narrow channels. The diffusion model takes into account the gas transportation at low pressures, the dynamic Langmuir adsorption model for the film growth and the effect of channel narrowing due to film growth. The film growth is calculated by solving the diffusion equation with surface reactions. An efficient analytic approximate solution of the diffusion equation is developed for fitting the model to the measured thickness profile. The fitting gives the equilibrium constant of adsorption and the sticking coefficient. This model and Gordon's plug flow model are compared. The simulations predict the experimental measurement results quite well for Al2O3 and TiO2 ALD processes.

A 2-D model is developed for calculating lateral acoustical coupling between adjacent thin film BAW resonators forming an electrical N-port. The model is based on solution and superposition of lateral eigenmodes and eigenfrequencies in a structure consisting of adjacent regions with known plate wave dispersion properties. Mechanical and electrical response of the device are calculated as a superposition of eigenmodes according to voltage drive at one electrical port at a time while extracting current induced in the other ports, leading to a full Y-parameter description of the device. Exemplary cases are simulated to show the usefulness of the model in the study of the basic design rules of laterally coupled thin film BAW resonator filters. Model predictions are compared to an experimental 1.9-GHz band-pass filter based on aluminum nitride thin film technology and lateral acoustical coupling. Good agreement is obtained in prediction of passband behavior. The eigenmode-based model forms a useful tool for fast simulation of laterally coupled acoustic devices. It allows one to gain insight into basic device physics in a very intuitive fashion compared with more detailed but heavier finite element method. Shortcomings of this model and possible improvements are discussed.

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.

High permittivity oxide thin film capacitors for RF components should be integrated on the chip to form a complete miniaturized module, with other semiconductor or thin film components such as inductors, isolation capacitors, and bias resistors. The quality factor (Q) values of the RF capacitors are strongly dependent on electrode conductivity. Alas the best conducting metals (e.g. Ag, Cu, Al) are not thermodynamically stable during deposition of high permittivity oxide films with high temperature and oxygen atmosphere. On the other hand, refractory metals (e.g. Mo, W) endure high temperatures, but are prone to oxidation. Therefore, a diffusion barrier is a prerequisite for integrating refractory metals to achieve a stable electrode structure.In this study both non-reactive and sacrificial diffusion barriers with Mo metallization were investigated on Si/SiO2 substrates. Also, noble metals (Au and Pt) as oxidation resistant materials were examined. Annealing at 650 °C was performed to the electrode stacks in an open-end air furnace and in vacuum with protective gas.The chemically inert materials Au and Pt failed to endure the high annealing temperature. Au became extremely rough and cracks appeared. Massive grain growth and adhesion loss occurred with Pt film. Mo electrode withstood the oxidizing ambient conditions with a sacrificial Si or Al–Ti diffusion barrier. Moderate increase in surface roughness was observed after the annealing due to oxidation. Also, thermally stable AlN, Si3N4, and SiO2 diffusion barriers were able to block oxygen from the Mo electrode.

We present a computational study of spontaneous polarization and piezoelectricity in Sc(x)Al(1-x)N alloys in the compositional range from x = 0 to x = 0.5, obtained in the context of density functional theory and the Berry-phase theory of electric polarization using large periodic supercells. We report composition-dependent values of piezoelectric coefficients e(ij), piezoelectric moduli d(ij) and elastic constants C(ij). The theoretical findings are complemented with experimental measurement of e33 for a series of sputtered ScAlN films carried out with a piezoelectric resonator. The rapid increase with Sc content of the piezoelectric response reported in previous studies is confirmed for the available data. A detailed description of the full methodology required to calculate the piezoelectric properties of ScAlN, with application to other complex alloys, is presented. In particular, we find that the large amount of internal strain present in ScAlN and its intricate relation with electric polarization make configurational sampling and the use of large supercells at different compositions necessary in order to accurately derive the piezoelectric response of the material.

In the first edition of "The Nano-Micro Interface," we discussed the piezoelectric quality of zinc oxide (ZnO) thin films. In this second edition's chapter, we have extended our view and included other piezoelectric materials like AlN, Sc-alloyed AlN, PZT (lead zirconate titanate) {Pb(ZrTi)O3}, and leadfree compounds. The focus of applying these thin piezoelectric films is in BAW (thin film bulk acoustic wave resonator) technology, which is used in all smart mobile devices from phones to tablets for wellness, health, and entertainment. BAW technology is based on the venerable crystal oscillator principle (such as quartz resonator) extended to the GHz frequency range by utilizing thin film technology to shrink the dimensions of the oscillator to the micrometer-scale. The main application of BAW is in telecommunications. The BAW filters show promise to be even smaller and have higher performance than SAW (surface acoustic wave) filters. Two different approaches of BAW filters are reviewed and compared: bridge-type technology and acoustic-mirror-based technology. Piezoelectric materials in thin film form using microelectronics fabrication methods and nanolevel control of piezoelectric film growth will be emphasized.

Piezoelectric zinc oxide films are used in microelectromechanical systems (MEMS) applications, where they can be used in sensors to detect, e.g., pressure or acceleration. Beside sensors, ZnO films are applied in activation devices, where force is needed. Conductive-doped zinc oxide (most often with aluminum) is also used in optoelectronics. Piezoelectric films including AlN and ZnO are more difficult to produce than the corresponding conductive materials. In order to achieve good piezoelectricity in ZnO films, they have to possess high purity, a (0 0 1) orientation (ZnO has hexagonal crystal structure), high resistivity, and fine columnar microstructure perpendicular to the substrate. We have used r.f. magnetron (13.56 MHz) sputtering from a ZnO target in an oxygen atmosphere to achieve the piezoelectric ZnO. The aim of this work has been to develop an r.f. sputtering process for ZnO to achieve highly piezoelectric thin films. As a test vehicle to measure the piezoelectricity of the ZnO films we have fabricated resonators and passband filters in the 1–2 GHz range using standard microelectronics photolithography, deposition, and etching techniques on 100-mm diameter Corning glass or silicon wafers. The influence of the sputtering-process parameters on the film properties has been studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and electrical measurements. In this study, the effects of the process parameters on the final material properties of the ZnO film are discussed in detail.

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 kt2 = 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.

We study the pressure sensitivity of AlN thin-film resonators on a poly-Si membrane sublayer. The studied resonators operate on the S 0 -mode Lamb wave at 750 MHz. The resonators are fabricated on a released membrane which consists of a polysilicon sublayer, molybdenum electrodes, and AlN as the piezoelectric layer. Operation of the test structures is simulated using 2D and 3D finite element method models. Simulated pressure sensitivity at pressures below 1 Pa is 0.035 ppm/Pa. Pressure sensitivity of the fabricated test devices was measured by probing the devices on-wafer and measuring their electric frequency response while applying a variable differential pressure over the wafer. To remove the noise and the outliers, the data was filtered with a 3-point median filter prior to analysis. The linearized pressure sensitivity of frequency below 1 Pa is around 1 ppm/Pa. With minimized residual stress, optimal materials and modified membrane design, the pressure sensitivity can be improved.

The mechanical nonlinearity due to high power level in zinc oxide thin film bulk acoustic wave resonators has been studied in this work. The nonlinear behavior of these resonators was investigated using transmission response measurements. The resonator was decoupled from the 50 Ohm line impedance by 20 pF shunting capacitors in order to allow the excitation of high mechanical vibration levels at the series resonance frequency. The power levels ranged from +5 dBm to +29 dBm at the resonator input. At low excitation power (+5 dBm) the measured series and parallel resonance frequencies of the studied device were 941 MHz and 969 MHz, respectively. When increasing the excitation power level the transmission response exhibits a Duffing-behavior with tilting direction towards lower frequencies. The transmission shows a two-valued response starting at +15 dBm. (5 refs.)

A simple model is developed for calculating lateral acoustical coupling between adjacent thin film BAW resonators forming an electrical N-port. The model is based on plate wave dispersion properties of different regions of the device and solution of lateral eigenmodes and eigenfrequencies. Mechanical and electrical response of the device is calculated as a superposition of eigenmodes according to voltage drive at one electrical port at a time while extracting current induced in the other ports, leading to a full Y-parameter description of the device. Comparison of model prediction with experimental results from adjacent large square resonators and narrow finger-like resonators is performed. Large resonators exhibit comb-shaped oscillating transmission characteristics over wide frequency band, while narrow finger create a single pass-band. Fair qualitative agreement is obtained.

Size dependence of resonator performance is studied in AlN and ZnO resonators with FEM simulation, electrical measurements, and laser interferometry. Eigenmode spectrum compression due to increased size of the resonator leads to smoothening of the electrical response and flattening of the vibrational at-resonance response as several modes can be simultaneously excited near the device resonance frequency. This is seen both in simulations and in measurements.

The main application of FBAR (thin film bulk acoustic wave resonator) is in telecommunications. These new FBAR filters with their light weight and small size will replace the currently used bulky ceramic filters in mobile telephone handsets. FBAR filters show promise to be even smaller and have higher performance than SAW (surface acoustic wave) filters. Two different approaches of FBAR filters are reviewed and compared; bridge type technology and acoustic mirror based technology. The idea of using CMP (chemical mechanical polishing) smoothening to improve the quality of FBAR will be presented as well as the preliminary results achieved.

As a test vehicle to measure the piezoelectricity of zinc oxide films, bulk acoustic wave (BAW) re-sonators were fabricated using standard microelectronics deposition, photolithography, and etching tech-niques on 100 mm Corning glass or silicon wafers. Resonators and filters were of solidly mounted re-sonator (SMR) type. The acoustic quarter wavelength mirror consisted of high and low acoustic impe-dance materials, which were either three pairs of molybdenum and silicon dioxide or two pairs of tungs-ten and silicon dioxide, respectively. Mirrors were designed for 1 and 2 GHz frequencies. Material pro-perties of the zinc oxide films have been studied by x-ray diffraction (including rocking curve), scanning electron microscopy and atomic force microscopy. Resonators were measured from 0.5 to 6 GHz using network analyzer. The highest acoustic coupling coefficient, K2 = 10.4% at 1.6 GHz, for thin film zinc oxide was achieved. Also a passband filter, fulfilling the complete E-GSM specifications, was fabricated using zinc oxide piezoelectric in the resonators.

Spurious resonance suppression in ZnO based thin film BAW resonators by the boundary ring method of (1) is studied. Electrical responses of resonators with varying width of the boundary ring structure are measured. Very clean resonator response is reached with optimum dimensions. Emergence of the piston mode and simultaneous spurious resonance suppression is demonstrated by 2D FEM simulation with a model corresponding to the measured devices. Good correlation between measurement and simulation is found. I. INTRODUCTION Thin film bulk acoustic wave resonators and filters for the GHz range have been intensively developed during the last ca. 10 years due to great demand in the mobile communications industry. Main application of the thin film BAW devices is in the band pass filters of the antenna circuit of mobile phones. With the thin film BAW technology, low insertion loss, high power handling, steep pass band skirts and small footprint are sought together with low manufacturing cost. The BAW filters are also inherently better applicable for higher frequencies (> 2 GHz) than SAW filters due to the lack of critical dimensions. Also as BAW resonators do not rely on a special crystalline substrate, possibility to integrate them with silicon IC:s exists. In order to create high performance filters, the BAW resonators they consist of, must fulfill certain performance criteria. Most importantly the effective coupling coefficient K 2 determines the attainable bandwidth of the filter and the Q- values affect the insertion loss and pass band skirt steepness. In addition, the resonator should not have ripple in or near the inductive region of its electrical response. In a low insertion loss filter this is only attained by suppressing the spurious resonances in some manner.

We have probed ultrasonic vibrations of a piezoelectric thin film utilizing a scanning laser interferometric technique. The vibrations are also simulated using a "toy" model of a membrane of zero thickness, and applying 2D FEM modeling for the solution of the eigenmodes. Despite the strong truncations used in the modeling, the agreement between our simulations and the measurements for several of the modes is striking. The samples were fabricated by patterning thin films photolithographically.

Insulating films consisting of thin layers of tantalum oxide and aluminum oxide were deposited using the atomic layer epitaxy technique at a temperature of 300 °C from metallic chlorides and H2O. The average film composition can be modified between pure aluminum oxide and pure tantalum oxide by varying the pulsing ratio. The effective refractive index is adjustable between 1.67 and 2.23 and the relative permittivity between 8.4 and 24. The leakage current of tantalum oxide is significantly reduced by thin interposed layers of aluminum oxide. These multilayers will potentially be useful, for example for applications in future memory integrated circuit and large-area display technologies.

We present results for a ZnO based filters for the mobile Extended GSM (EGSM) Rx band centered at 942.5 MHz. Our devices are of the SMR type. The acoustical isolation from the glass substrate is achieved by a tungsten-silicon dioxide quarter wavelength mirror. Resonators with an effective coupling coefficient of 0.236 and Q/spl sim/800 have been achieved. The filters are realized as either 3-section ladder or 2-section lattice connected FBARs without any external components. The ladder filters achieve a 3.5 dB absolute bandwidth of 39 MHz with minimum insertion loss of 1.3 dB, stop band rejection at 23 dB and VSWR of 2.2 in the pass band. The balanced filter design has a slightly larger bandwidth of 46 MHz and improved stop band behavior characteristic for this type of device.

— The luminance, contrast ratio, CIE color coordinates, viewing-angle range, and luminous efficacy of an ACTFEL display are all affected by the multilayer structure of the device. A model incorporating absorption and reflection in the metal electrode, interference in the thin-film stack, and transmission in the thick layers is developed and used to predict the visual performance. Especially important are the effects of various metallization schemes and color and gray-shade filters. Also, the effect of viewing angle on the contrast and perceived color is discussed.

Tantalum oxide is a widely used insulator in electronic applications requiring high permittivity. When deposited at low temperature, tantalum oxide films, however, often exhibit large leakage current. A common way to reduce leakage is to anneal the films in an ambient containing extremely reactive oxygen species, or at high temperature in dry oxygen. A different approach is to use composite oxide materials. We have studied layered tantalum based oxide films deposited by Atomic Layer Epitaxy, and observed that the leakage current is decreased by several orders of magnitude when a fraction of tantalum oxide is replaced by another oxide, such as aluminum or hafnium oxide. Leakage current density of 40 nA/cm2 in the electric field of 1 MV/cm is attained for unannealed Ta-Hf-O film deposited at 300°C. Layered composite insulators are an interesting new class of materials, and ALE proves to be a useful method for depositing them.