The use of yttrium-rare earth aluminium garnet solid solutions for bulk-acoustic-wave (BAW) devices

The isomorphic solid solution of yttrium-rare earth aluminium garnets is suggested as a dielectric material for acoustic waveguides with extremely low acoustic-wave absorption (AWA) at room temperature and for frequencies higher than 10 GHz. The two main mechanisms by which substitutional atoms decrease the bulk AWA are determined. The first one is the decrease in effective lifetime of the thermal phonons resulting in the corresponding reduction of the viscoelastic absorption-this mechanism is important for the shear acoustic waves. The second is more important for longitudinal waves. It is the reduction of Gruneisen constants for solid solution as compared to the crystal matrices.     

Microwave bulk-acoustic-wave reflection-grating resonators

A technique for fabrication of bulk-acoustic-wave (BAW) resonators operating at fundamental frequencies between 1 and 10 GHz is presented. The resonators utilize a reflection grating made by optical holographic methods in iron-doped lithium niobate. Q factors of 30000 at 1 GHz have been demonstrated. Extension to Q of 10000 at 10 GHz appears feasible. Projected limitations to performance are discussed. The high Q at the high fundamental frequency directly results in low-phase noise. Phase-noise measurements of BAW resonator-stabilized oscillators operating at 1.14 GHz are presented. The single-sideband noise floor of <-140 dBc/Hz is shown to be in agreement with an analytical model. Projected improvements in the devices and circuits promise performance of <-160 dBc/Hz.     

Theoretical analysis of planar bulk-acoustic-wave response

A detailed theoretical analysis for planar bulk-acoustic-wave (BAW) devices that results in a method for computing the bulk-acoustic-wave response for any orientation of any piezoelectric substrate is presented. The BAW responses for four devices is computed and are found to be in excellent agreement with published experimental results. The theory is used to optimize one of these devices by varying the thickness and interdigital transducer (IDT) separation so as to give minimum insertion loss. A similar optimization can be performed for other devices. The theory is also used to find a new BAW device with low insertion loss.     

Mode selection for a piezoelectric layer in a bulk-acoustic-wave composite acoustic resonator

An analysis is made of the mode selection for a thin piezoelectric layer in a bulk-acoustic-wave composite layered acoustic resonator by transformation of the impedance using a set of quarter-wave layers. Depending on the number of layers, the impedance of the substrate on which the piezoelectric layer is deposited may be abruptly increased or sharply reduced. This serves to simulate a “fixed” or “free” surface. As a result, a mechanically strong resonator structure is produced, operating at the natural frequencies of a thin piezoelectric layer. A numerical simulation is made of multilayer structures formed by alternating quarter-wave layers of LiNbO₃ and LiTaO₃. It is shown that if these layers are of micron thickness and there is a sufficiently large number of them, the acoustic properties of the substrate do not influence the frequency characteristics and Q factor of the thin piezoelectric vibrating layer in the microwave range. Pis’ma Zh. Tekh. Fiz. 23, 35–41 (October 12, 1997)     

New architectures for feedthrough SAW recursive devices

This paper presents an analysis of a new type of feedthrough recursive surface acoustic wave (SAW) device. The device combines a conventional SAW structure with positive feedback in a way that allows use of selective properties of the SAW structure, control of the central frequency and bandwidth, achieving significantly higher quality factors for given dimensions of the structure, and reduction of the sidelobe level. Several possible implementations are discussed from a simple one that uses external circuitry to the most advanced that includes digital supervisory control. Equations are presented that relate the central frequency, bandwidth, and sidelobe level to the parameters of the SAW structure and feedback loop. The simulation results were found to be in good agreement with experimental data. These data show the control of the central frequency within 1%, a 10-fold increase in the quality factor compared to the original SAW structure, and a reduction of the side-lobe level by 20 dB irrespective of the influence of second order effects and random manufacturing fluctuations.     

Ultra temperature-stable bulk-acoustic-wave resonators with SiO2 compensation layer

This paper describes temperature compensated bulk acoustic-wave resonators (BAR) with temperature coefficient of frequency (TCF) less than 1 ppm/degrees C at above 3 GHz. The temperature compensation is produced from the unique physical property of silicon dioxide's positive TCF, unlike most other materials that have negative TCF. Two types of resonators have been explored: film bulk acoustic resonator (FBAR) composed of Al/ZnO/Al/SiO2 on a surface micromachined cantilever that is released by XeF2 vapor etching and high-overtone acoustic resonator (HBAR) composed of an Al/ZnO/Al resonator on a bulk micromachined SiO2/Si/SiO2 supporting substrate.     

Analysis of piezoelectric bulk-acoustic-wave resonators as detectors in viscous conductive liquids

An analytical solution for the resonance condition of a piezoelectric quartz resonator with one surface in contact with a viscous conductive liquid is presented. The characteristic equation that describes the resonance condition and accounts for all interactions including acoustoelectric interactions with ions and dipoles in the solution is obtained in terms of the crystal and liquid parameters. A simple expression for the change in the resonance frequency is obtained. For viscous nonconductive solutions, the frequency change is reduced to a relationship in terms of the liquid density and viscosity. For dilute conductive liquid, the change in frequency is derived in terms of the solution conductivity and dielectric constant. The boundary conditions for the problem are defined with and without the electrical effects of electrodes. Experiments were conducted with various viscous and conductive chemical liquids using a fabricated miniature liquid flow cell containing an AT-cut quartz crystal resonator. The results, which show good agreement with the theory, on the use of quartz crystal resonators as conductivity and/or viscosity sensors are reported.     

New flexibilized diallyl phthalate resins for encapsulating electronic display devices

This research investigated diallyl phthalate encapsulating resins as a replacement for the moisture sensitive epoxies now used in light emitting diode (LED) displays. Consideration of display resin requirements led us to select for study the diallyl phthalate (DAP) polymer thermosetting system, which had most of the performance properties desired, but was excessively brittle. Flexibilizing co-monomers were evaluated including both vinyl and allylic types. A promising co-polymer of DAP with lauryl methacrylate (80/20) was defined that had most of the physical and performance characteristics desired, plus attractive inherent light diffusing properties. Allylic co-monomers such as diallyl adipate and triallyl citrate also formed interesting co-polymers and ter-polymers with DAP. DAP/ epoxy interpenetrating polymer networks were also explored and found to be most suitable for LED application.     

New PMMA-based composites for preparing spacer devices in prosthetic infections

Even though the systemic antibiotic therapy is usually applied after prosthetic infections surgical treatments, it is unable to reach the infection site in sufficient concentrations to eradicate bacteria. Delivering antibiotics locally with the use of custom made device (spacer or nail coating) might eradicate or reduce the infection and the risk of recolonization, providing a very high concentration of antibiotic. PMMA-based (Mendec Spine^®) composites with BaSO₄ were enriched with β-tricalcium phosphate (Porosectan-TCP) or only a slightly higher BaSO₄ concentration (Porosectan-BaSO₄) to obtain higher porosity. The aim of the study was to evaluate: (i) drug absorption capability and drug release kinetics in vitro soaking them with a combined solution of gentamicin and vancomycin, (ii) their in vitro and in vivo biocompatibility, and finally, (iii) they were tested preliminarily in an experimental model of bone infection. The simultaneous presence of β-TCP and BaSO₄ resulted in the formation of a texture of interconnecting channels with different diameters, from a few microns to several hundred microns, which totally filled the material. The porosity, determined by microcomputed tomography, was significantly higher in both tested plain composites (Porosectan-TCP: +17.3%; Porosectan-BaSO₄: +7.5%) in comparison to control composite material (Mendec Spine^®). The kinetics of antibiotic release from composites was rapid and complete, producing high drug concentrations for a short period of time. Both composites showed a good level of biocompatibility. The osteomyelitic model confirmed that both composites, soaked in antibiotic solution, were able to cure bone infection. These composites could be useful for preparing devices for prosthetic joint infections treatment also allowing the use of antibiotics solution at required concentrations.     

New oxadiazole complex with bipolar ligand for organic light-emitting devices

New oxadiazole complex with bipolar ligand, Zn(POTPA)₂, was designed and synthesized, and used as an emitter material in single-layer organic electroluminescent (EL) devices (OLED). The UV absorbance of Zn(POTPA)₂ is caused by electron π–π^? transition. Zn(POTPA)₂ exhibited strong blue luminescence in solution and film. Compared with triphenylamine and 2,5-diphenyl-1,3,4-oxadiazole, cyclic voltammograms exhibited that Zn(POTPA)₂ has bipolar properties, and the optical band gap energy, Eg, calculated based on the cyclic voltammograms is nearly equal to that deduced from the absorption spectrum. Single-layer device with the structure of ITO/Zn(POTPA)₂/Mg:Ag were fabricated and blue electroluminescence was observed with a maximum luminance of 271 cd/m² and efficiency of 0.46 cd/A.     

New design of active vibroprotection devices

A principally new design of active vibroprotection devices has been developed, which can overcome limitations with respect to the active frequency range and maximum vibration suppression coefficient, which are inherent in the existing devices. It is shown that these limitations are related to the parasitic signal of accelerometer inclination in the Earth’s gravity field. A method is proposed to compensate for this effect so that, even with simple electronic circuits, the lower frequency boundary of active vibroprotection decreases from 2 to 0.2 Hz and the maximum vibration suppression coefficient increases from 40 to 60 dB.     

New possibility on InZnO nano thin film for green emissive optoelectronic devices

Indium zinc oxide (InZnO) nano thin film was prepared from InZnO nanoparticles (NPs) by thermal evaporation technique. Fourier transform infrared spectroscopy showed the presence of metal-oxide bond. X-ray diffraction pattern revealed the mixed phase structure. The presence of elements In, Zn and O were identified from energy dispersive X-ray analysis. Size of the NPs was found to be 171 and 263 nm by transmission electron microscopy. Scanning electron microscopy image showed the spherical shape uniform morphology with uniform distribution grains. Photoluminescence spectrum exhibited a broad green emission for InZnO nano thin film. The acquired results of structure, smooth morphology and photoluminescence property suggested that the InZnO nano thin film to be a promising material for room temperature green emissive optoelectronic, laser diodes, solar cells and other optical devices.     

纳米 MOSFET/SOI器件新结构

重点介绍器件进入纳米尺度后出现的MOSFET／SOI器件的新结构，如超薄SOI器件、双栅MOSFET、FinFET和应变沟道等SOI器件，并对它们的性能进行了分析。