S. Kondratiev

Balanced bridge SAW impedance element filters (BBF's) developed recently have some important advantages such as wider passband, better suppression in the stopband, small size when compared with coupled resonator filters (CRF's). Compared to ladder type IEF's, a balanced bridge network gives lower insertion loss in passband, better suppression in the stopband and allows balanced input/output operation. The geometrical and COM

ABSTRACT Resonators with different designs and different resonance frequencies were fabricated on LGS. Resonators were studied at a temperature of 650°C. Annealing of LGS sensors was carried out in a furnace during 1000 hours. Dependences of the resonators behavior versus temperature were obtained. It was found that the first 100-300 hours of thermal annealing lead to the largest change in resonator properties, while further changes over the next hours are much smaller. Pt/Ti based resonators and Ir based resonators showed slow ageing trends, while Pt/Ti resonators passivated with an Al2O3 thin film with a thickness of 160 nm demonstrated steeper initial frequency changes. In spite of the obvious damage to electrodes, resonator properties remained reasonably robust to such kinds of degradation and clearly proved the possibility of long-term measurements with LGS based SAW sensor structures. The results showed that initial annealing of high temperature sensors is required to stabilize their ageing behavior. Using the XRD technique, we observed the process of oxidation of Ir and Pt electrodes of SAW-resonators during the first 100 hours of thermal annealing.

The research results of the influence of different technology parameters of crystal growth and device manufacturing process on SAW velocity variation on langasite (LGS) wafers Ø 3" are presented. The wafers were made from crystals grown by the Czochralski method along and directions. The paper also gives a technology process description of langasite crystal growth along direction and of making

We model the inductive and capacitive parasitic electromagnetic couplings in a packaged surface-acoustic wave (SAW) antenna duplexer. Theoretical estimates for self- and mutual inductances of the bond wires are computed in the presence of two ground planes. An equivalent circuit for the duplexer including the parasitic elements is presented. The frequency response of the duplexer is predicted with the help

The SAW Impedance Element Filters (IEFs) have some important advantages compared to Coupled Resonator Filters (CRFs). The losses in these filters can be made smaller because the effective propagation path of SAW is smaller and resistive losses are lower due to the greater number of short electrodes connected in parallel. The detailed analysis shows that the losses in IEFs due

A new class of filter is presented which works in a mode where there is a kind of mixture between Coupled Resonator Filters (CRFs) and ladder type SAW Impedance Element filters (IEFs). Long IDTs, working basically like resonators are used in a CRF type of operational mode. On substrates with high coupling coefficient and high finger reflectivity (as for example 36°-LiTaO3) a resonance condition imposed on the gap between long transducers must be satisfied in order to provide sufficient transfer of energy from one (input) transducer to another (output) transducer. Further, the relation between the transduction and reflection properties on strong coupling materials are such that unwanted longitudinal modes are strongly suppressed, and simulation shows that a nice flat passband can be realized. The bandwidth for this kind of filter is typically narrower than for conventional CRFs, but this is not a big disadvantage, because there are a lot of potential applications where these filters can be used and they are easy to design

ABSTRACT Photolithography together with ion beam etching was used for fabrication of high temperature SAW devices. Ir thin film of 0.3 μm thick was deposited by magnetron sputtering without additional adhesion layers and than Ir film was annealed after electrode patterning in different conditions. The resistivity of magnetron sputtered thick Ir films drops noticeably after annealing. However, this process requires special care in order to avoid delaminating of the film due to developing high stress during such procedures. We have annealed the substrates with Ir films in different regimes and in different gas/vacuum conditions. The results of these studies have shown that annealing in air up to about 500 °C decreases the Ir film resistivity 1.5-2 times. Vacuum annealing did not show much improvement in comparison to open air annealing. Magnetron sputtered thin Ir films have somewhat porous structure allowing oxygen to diffuse from the substrate surface through Ir films. Resonator structures with thick Ir electrodes were prepared and tested. Examples of the resonator structures show very promising properties, such as high conductance and high Q-factor.

ABSTRACT SAW resonators were patterned on CTGS wafers with different orientations at different propagation angles. Ir was used as a metal without additional adhesion layers. Resonator responses were acquired with a network analyzer. Resonance frequencies of the responses were measured and processed to obtain temperature behavior. For the cut with Euler angles (0, 90°, 0) almost linear behavior was observed with TCF close to -35 ppm/°C. The turnover point of the fitted parabolic curve gradually changed with propagation angle ψ (0, 90°, ψ) from negative temperatures up to about +550°C at (0, 90°, 90°). This also means that this material gives orientations (close to (0, 90°, 40°)) with the turnover point near the room temperature. Surrounding orientations should probably be same useful (the turnover point change is about 0.5°C with ψ angle change by 1' for these orientations). The coefficient at the quadratic term (with Ir metal) has a low value of about -30 ppb/°C2. This value is several times lower than that of most langasite cuts and is close to that of ST-quartz. The material seems to be chemically stable at high temperatures. CTGS shows great potential and useful properties for devices operating in a wide temperature range. Similar to ST-quartz, CTGS can serve for temperature compensated resonators and filters at room temperature. It can also work in devices operating at temperatures up to several hundred degrees C.

In this paper some alternative approaches to SAW tag design and coding are discussed. The first idea is to use chevron-type electrode reflectors (as in RAC devices) for reflecting “taps”. One of the advantages of the use of oblique reflectors is that there is no multiple reflection in such a system even if many reflectors are placed in the same acoustic channel. It is also important for the 2.5 GHz frequency range that the minimal size of electrode in oblique reflectors is roughly 1.4 larger than for normal reflectors. The small size of the device is another attractive feature. A further idea to be discussed is the possibility to code a tag device simply by the time positioning of the reflectors, which allows calibration problems to be avoided and simplifies the reading system since the phase of the pulses does not need to be measured. Measurements of propagation and reflection of SAW in the 2 GHz frequency range and tag prototype characteristics are presented

Surface acoustic wave (SAW) impedance element antenna duplexers provide compact, high performance, front-end components apt for industrial fabrication. We describe investigations on the design and modeling of a compact ISM antenna duplexer fabricated on a 36 degrees YX-cut LiTaO3 substrate based on SAW impedance elements. In particular, we have performed 3-D modeling of the inductive and capacitive electromagnetic couplings caused by the package parasitics for the duplexer. The use of a 1:3 IDT structure for the reduction of the passband width is discussed. The frequency response of the duplexer is predicted with the help of circuit simulation; the modeling is refined by optimization of the model parameters to improve the fit between the measured and simulated responses. We also report scanning optical imaging of the acoustic field within the resonator structures with the help of laser interferometry; this provides insight into the loss mechanisms beyond that attainable in mere electric measurements.