Single-phase Unidirectional Transducers Research Articles

On Low-Power Droplet Manipulator Employing High-Frequency Surface Acoustic Waves

A droplet manipulator working with low driving power was developed by using the surface acoustic wave (SAW) technology. The manipulator was driven at a relatively high frequency of 350MHz to increase the SAW power density. First, a single phase unidirectional transducer (SPUDT) was designed. Because of its low insertion loss of 1.5 dB and high directivity of 10 dB, the SPUDT successfully conveyed a 100 nl water droplet with RF input power of 18 dBm (60 mW). Second, the SPUDT design was extended to a curved transducer to focus and launch the SAW energy into the narrow waveguide. Owing to the increased SAW power density, the required SAW power was reduced to 15 dBm (30 mW) for the 100 nl droplet manipulation. In addition, fabrication of liquid injectors was discussed for the formation of tiny droplet.

Optimization of unidirectional interdigital transducers via the scanning window technique

An original procedure for optimization of single-phase unidirectional interdigital transducers of surface acoustic waves (SAWs) is described. These transducers are designed for RF filters with low levels of the insertion loss and the triple-transit signal. The optimization algorithm is based on the so-called scanning window technique. Unlike most methods published in the literature, this technique optimizes not continuous (analog) weighting functions of the SAW sources and reflectors but the sequence of base electrode cells; i.e., the technique directly optimizes the transducer topology.

Optimal design on SAW sensor for wireless pressure measurement based on reflective delay line

This paper presents optimal design on wireless pressure micro-sensor based on surface acoustic wave (SAW) reflective delay line. Using the coupling-of-modes (COM) analysis, the device was simulated, and the effect of reflector configuration and interdigital transducer (IDT) structure on the performance of the devices was studied. From the COM simulation results, a 440 MHz SAW-based pressure sensor based on a reflective delay line on 41° YX LiNbO 3 with shorted circuit grating reflectors and single-phase unidirectional transducers (SPUDT) structure was developed experimentally. Using the network analyzer, the SAW sensor was wirelessly characterized, and the experiment results were well matched with simulation data. Sharp reflection peaks, low insertion loss and few spurious signals between the peaks were observed. Obtained pressure sensitivity was 2.67°/kPa.

High frequency stability oscillator for surface acoustic wave-based gas sensor

This paper presents a 158 MHz surface acoustic wave (SAW) oscillator used for a gas sensor. Asthe oscillator element, a SAW delay line on ST-X quartz substrate with low insertion loss(<8 dB) and single mode selection capability was developed. Low insertion loss wasachieved by an electrode width control single phase unidirectional transducer(EWC/SPUDT) configuration. Single mode selection was simply accomplished by acomb transducer which is a means of combining the frequency selectivity of twointerdigital transducers (IDTs). Coupling of modes (COM) simulation was performed topredict device performance prior to fabrication. The measured frequency responseS12 showed a good agreement with simulated results. The effect of the oscillator circuitsystem temperature shift upon frequency stability was observed in detail.The experimental results showed that the baseline noise was typically up to∼0.7 × 10−7 in a laboratory environment with temperature control. The oscillatorwas successfully applied to a gas sensor coated self-assembled compositemonolayer as a sensor material for dimethyl-methyl-phosphonate (DMMP).The sensitivity for low DMMP concentration detection was evaluated as∼25 Hz mg−1 m−3, and the threshold detection limit was up to0.5 mg m−3.

Surface Acoustic Wave Based Pressure Sensor with Ground Shielding over Cavity on 41° YX LiNbO3

A surface acoustic wave (SAW)-based pressure sensor was fabricated for stable mechanical compression force measurement. A single phase unidirectional transducer (SPUDT) and two acoustic tracks were employed to minimize inherent insertion loss and improve reflectivity from the reflectors. The coupling of modes (COM) theory and finite element methods (FEMs) were used to determine optimal design parameters. A LiNbO3 diaphragm was bonded to a heavily doped silicon substrate with a cavity of ∼250 µm deep, in which gold was lined all over the inner cavity to reduce the coupling loss of SAW energy to the surrounding atmosphere. As a mechanical compression force was applied to the diaphragm, the diaphragm bent, resulting in phase shifts of the reflected peaks. The phase shifts were modulated depending on the amount of mechanical compression applied. The measured reflection coefficient S11 showed good agreement with simulated results.

Low-Loss and Constant-Group-Delay Surface Acoustic Wave Filters Employing Cu-Based Resonant Single-Phase Unidirectional Transducers

This paper aims at reducing the insertion loss of surface acoustic wave (SAW) filters with constant group delay using Cu electrodes based on resonant single-phase unidirectional transducers (RSPUDTs). Theoretical analysis indicates that the reflectivity of a Cu-electrode/128°YX-LiNbO3 structure is about two times larger than that of an Al-electrode/128°YX-LiNbO3 structure of the same thickness. The high reflectivity of Cu electrodes is effective in increasing the variable range in the reflectivity, which provides more degrees of freedom in the optimization of RSPUDT. A constant-group-delay filter is designed and fabricated. Experimental results are in fairly good agreement with the design; group delay deviation of 30 ns is realized over the range of ±6.5 MHz at the center frequency of 490 MHz where the minimum insertion loss is 6.1 dB.

A New Configuration of Surface Acoustic Wave Intermediate-Frequency Filter with Compact Size and Improved Insertion Loss

Size reduction is always a major challenge to surface acoustic wave (SAW) manufacturers. For some years, commercial SAW filter designers have been developing various configurations of SAW filters just to fit into a smaller package. In this work, a new single-phase unidirectional transducer (SPUDT) based intermediate-frequency (IF) filter with improved insertion loss and compact size is proposed. This filter has an architecture that combines electrode-width controlled single-phase unidirectional transducer (EWC-SPUDT) and comb-type SPUDT. As a result of this improvement, a filter for IF-filtering of Digital European Cordless Telephone (DECT) system can be squeezed into a surface-mount device (SMD) 7.0×5.0 mm2 package. The performance of this filter even excels most commercial available IF filters in the same application.

An iterative approach to design a SAW filter having desired response

Present work proposes an iterative technique to estimate reflection weighting function and transduction weighting function simultaneously to achieve a desired single-phase unidirectional transducer (SPUDT) response. The technique uses the p-matrix formulation in order to describe characteristics of a SPUDT. Simulation results are presented to show the validity of the approach.

Ultra Low-Insertion-Loss Surface Acoustic Wave Filters Using Unidirectional Interdigital Transducers with Grating SAW Substrates

Surface acoustic wave (SAW) filters employing unidirectional interdigital transducers (UIDT) exhibit low-loss properties. We propose a new single-phase unidirectional transducer (SPUIDT) with an electrode width of approximately λ/4 of the best transducer efficiency. The new UDTs are obtained by fabricating an IDT on a very thin dielectric grating with λ/8 shifts. The electromechanical couplings (k2) of electrodes on SiO2 films decrease rapidly with film thickness. Therefore, good UIDT properties are obtained for a very thin SiO2 grating (about 0.03 µm at 2 GHz with an Al electrode thickness of 0.07 µm). In this paper we describe the experimental results of wide-band and very low-loss filters with an insertion loss of less than 1 dB in the 2 GHz-range.

SPUDT filters for the 2.45 GHz ISM band

Filters based on using single-phase, unidirectional transducers (SPUDT) consisting of lambda/4 and wider electrodes are presented. The design variants exploit the significant difference between the reflectivity of short-circuited lambda/4 electrodes and that of floating wide electrodes on 128 degree lithium niobate (LiNbO3). The surface acoustic wave (SAW) devices operating at 2.45 GHz have critical dimensions of about 0.3-0.4 microm, accessible to standard optical lithography. When matched, the fabricated SPUDT filters exhibit minimum insertion losses of 5.5-7.9 dB together with 3 dB passbands of 89-102 MHz. The majority of the insertion loss can be attributed to the attenuation on free surface and inside the grating, and to the resistivity of the electrodes.

New SPUDT cell structures

The present paper describes single-phase unidirectional transducers (SPUDT) cells with all fingers wider than lambda/8 while maintaining the unidirectional effect. The first solution is related to a SPUDT consisting of lambda/4 and lambda/2 wide fingers arranged in two tracks. Each track has no significant unidirectional effect. Both tracks form a waveguide, and the waveguide coupling generates the interaction of the tracks. As a result of that interaction, a unidirectional effect arises as verified by experiment. This transducer type is called double-track (DT) SPUDT. A second solution is suggested that includes, in contrast to distributed acoustic reflection transducer (DART), electrode width control (EWC), and Hunsinger cells, SPUDT cell fingers with one and the same width only. Cell types with lambda/6, lambda/5, and lambda/3 wide fingers called uniform width electrode (UWE) cells are considered. One of these cell types, including exclusively lambda/5 wide fingers, is experimentally investigated and a unidirectional effect is found. Moreover, a filter example using the lambda/5 cell type has been designed for reducing SPUDT reflections. The echo suppression expected could be verified experimentally. No waveguide coupling is required for this cell type.

Surface Acoustic Wave Unidirectional Transducers Using Grating Substrates and Resonators Using λ-Period Reflectors

Surface acoustic wave (SAW) filters employing a unidirectional interdigital transducer (UIDT) show low loss, wide band properties. In this paper we describe a new single phase unidirectional transducer (UDT) of about λ/4 electrode width with the best transducer efficiency. The new UDTs are fabricated on the very thin dielectric grating or very shallow groove grating SAW substrates. The electromechanical couplings (k2) of electrodes on SiO2 gratings decrease rapidly for film thickness. Therefore the good properties of UDT are obtained for very thin SiO2 (about 0.3 µm and 0.03 µm at 100 MHz and 1 GHz, respectively). The calculation results show wide-band, low-loss filters with various k2 materials. Also, the electrodes of λ/2 width have large reflection coefficients of SAW. The calculation and experimental results of SAW resonators with λ/2 electrode width and λ-period using susceptance changes are described.

Single-Phase Unidirectional Surface Acoustic Wave Transducer Using Cu Electrode

This paper proposes the application of Cu electrodes to surface acoustic wave single-phase unidirectional transducers (SAW SPUDTs). Since SPUDTs require large and widely variable reflectivity obtained by relatively thin electrodes, Cu with large mass density is one of the candidate materials. First, SAW reflection characteristics of a Cu electrode on 128°YX-LiNbO3 were theoretically investigated. It is shown that Cu electrodes offer much larger reflectivity than Al electrodes. In addition, SAW velocity change with electrode width is quite moderate compared with other materials having large mass density such as Au. An SPUDT was fabricated employing Cu electrodes to discuss how effectively SAW reflectivity contributes, for example, to its unidirectionality. As a result, the obtained directivity for the Cu-SPUDT was about 16 dB, which was 10 dB larger than that for an SPUDT employing conventional Al electrodes.

Small and Low-Loss Intermediate Frequency Surface Acoustic Wave Filters Using Zinc Oxide Film on Quartz Substrate

A ZnO/quartz substrate is expected to be applied to a intermediate frequency (IF) surface acoustic wave (SAW) filter for which a small size, a low insertion loss, and a good temperature coefficient of frequency (TCF) are necessary because it has a large ks and an excellent TCF. However it was clarified that the SAW filter consisting of a single solid electrode or single-phase unidirectional transducer (SPUDT) on ZnO/quartz substrate often has a large spurious response due to the Love wave. The new cutting angle and the propagating direction (26–27°Y-X) for quartz were developed in order to suppress the spurious response. The developed W-CDMA IF 380 MHz filter was mounted on a small package of 3.2×5.0 mm2. It had a low loss of 5.8 dB, and high adjacent channel selectivity (ACS) of 36.1 dB/35.0 dB. Then, the developed N-CDMA IF 183 MHz filter was mounted on a small package of 5×7 mm2. It had a low loss of 4.3 dB. In both cases, the frequency shift per 1°C was less than 0.37 ppm/°C.

Comparison between ST-cut quartz 25 degrees and -60 degrees NSPUDT propagation directions.

This paper discusses directivity and other propagation properties of natural single phase unidirectional transducer (NSPUDT) propagation directions on ST-cut quartz. The work focuses on the comparison of surface acoustic wave (SAW) directivity and propagation properties between the ST-cut quartz -60 degrees, Euler angles: (0 degrees, 132.75 degrees, -60 degrees), and the ST-cut quartz 25 degrees, Euler angles: (0 degrees, 132.75 degrees, 25 degrees), NSPUDT propagation directions, including predicted and measured directivity responses for both propagation directions. The well-known SAW 25 degrees propagation direction is used for low loss, high performance SAW filter designs for consumer products and communications applications. The ST-cut quartz -60 degrees propagation direction has been predicted to have a reflection coefficient 2.5 times larger than ST-cut quartz 25 degrees. In addition the ST-cut quartz -60 degrees satisfied the NSPUDT 90 degrees reflection coefficient phase condition much more closely, resulting in an improved directivity response. For the delay line structures used in the experiments, the measured directivity is 10.1 dB for the -60 degrees propagation direction. For the same structures, the measured directivity along the 25 degrees propagation direction is about 5.0 dB. The experimental results given in this paper verify that indeed ST-cut quartz -60 degrees has a higher directivity than ST-cut quartz 25 degrees, confirming the theoretical predictions. In addition, this work compares other propagation properties for both directions, namely, phase velocities, electromechanical couplings, temperature coefficients of delay, power flow angles, and metallic strip reflection coefficient amplitudes and phases.

Metal strip reflectivity and NSPUDT orientations in langanite, langasite, and gallium phosphate.

New materials of the trigonal 32 class have received much attention recently, due to their quartz-like temperature behavior and the promise of higher electromechanical coupling coefficients. The magnitude and phase of the reflection coefficient of the metal strips that form the SAW transducers and reflector structures is a critical parameter that allows proper device designs and optimal material surface orientation. This paper describes an investigation of the magnitude and phase of the SAW metal strip reflectivity in some new materials and along new orientations. The materials are langanite, langasite, and gallium phosphate. The results are presented as contour plots of the magnitude and phase of the reflection coefficient. In addition, the phase velocity, temperature coefficient of delay, electromechanical coupling coefficient, and power flow angle are given, thus allowing proper orientation selection for SAW device designs. The results presented highlight the reflection coefficient calculations in the selection of natural single-phase unidirectional transducer orientations (NSPUDT) for these new materials. As a result of the present work, reflection coefficient magnitudes five times larger than those of the well-known quartz NSPUDT orientation (Euler angles: 0 degrees 132.75 degrees 25 degrees) can be obtained with the new materials, for orientations where the optimum NSPUDT reflection coefficient phase criterion is met. The new materials discussed here provide an opportunity to design shorter- and higher-bandwidth devices due to: the increased electromechanical coupling coefficient; the higher reflection coefficient; and the lower phase velocities; while maintaining the excellent temperature insensitivity characteristic of quartz. The orientation regions suggested in this paper for the new materials are thus very promising for low-loss, high-performance consumer and communications SAW designs, such as NSPUDT filters, resonator-based filters, and other devices that can benefit from a high metal strip reflectivity.

Parameters of Coupled-Mode Equations for a Natural Single Phase Unidirectional Transducer on a La3Ga5.5Ta0.5O14 Substrate

The computed parameters of coupled-mode equations are presented for natural single phase unidirectional transducers (NSPUDTs) on La3Ga5.5Ta0.5O14 substrates with Euler angles (0°, 140°, 23°) and (12.7°, 150.1°, 36.3°). The aluminum electrode width and height dependences of the coefficients of coupled-mode equations are investigated in detail. Numerical results show that the amplitude of mutual-coupling coefficient κ12 for an NSPUDT on a (0°, 140°, 23°) La3Ga5.5Ta0.5O14 substrate is larger than that on a (12.7°, 150.1°, 36.3°) La3Ga5.5Ta0.5O14 substrate for the same electrode width and height within the range of 0.5≤w/p and 0.04 ≤h/p. Our results of the insertion loss for a filter which consists of an NSPUDT and two split interdigital transducers on a (0°, 140°, 23°) La3Ga5.5Ta0.5O14 substrate agree well with previous experimental results.

Coefficients of Coupled-Mode Equations for Interdigital Transducers with Solid Electrodes of Gold, Silver, Tantalum, or Tungsten Alloy on a 50°Y-25°X La3Ga5SiO14 Substrate

Computed results of all the coefficients of coupled-mode equations are presented for interdigital transducers with solid electrodes of gold, silver, tantalum, or tungsten alloy on a 50° Y-25° X La3Ga5SiO14 substrate. The electrode thickness and width dependences of the coefficients for tantalum or tungsten electrodes are investigated in detail. Numerical results show that the phase of the mutual-coupling coefficient for natural single phase unidirectional transducers (NSPUDTs) with tantalum or tungsten electrodes do not increase monotonically with increasing electrode height. Our results of the effective velocity and the difference between the phase of the mutual-coupling coefficient and two times the phase of the transduction coefficient agree well with the earlier experimental results.

Effects of Electrode Materials on Natural Unidirectionality of Langasite

In this study, we carried out experimental research on the directivity of surface acoustic wave (SAW) filters with Al, W and Ta electrodes formed on langasite single-crystal wafers, in order to find electrode materials that make the natural unidirectionality disappear. The results proved that by using W and Ta, the natural unidirectionality disappears at the normalized thickness (h/λ) of 0.033–0.037. This suggests a potential application of these metals as electrode materials for langasite-based SAW filters so that the design process of the single-phase unidirectional transducer (SPUDT) filter can be simplified by using tools for conventional SPUDT filters.

A new design concept for low-loss SAW filters based on different-width split-finger SPUDT

A new design concept of a single-phase unidirectional transducer (SPUDT) has been investigated in this paper. The concept has been realized by using a newly developed different-width split-finger-SPUDT structure, in which the adjacent electrode fingers are given different widths. A symmetrical radiation conductance is obtained by adjusting the electrode finger positions. Computer simulations have confirmed that the electrical 1/Q factor and the directivity have a tradeoff relationship with regard to the finger-width ratio, depending on the metallization thickness used. From the simulation results, the optimum finger-width ratio for achieving a low insertion loss has been obtained. An experimental filter was constructed, which shows good performance, with the insertion loss improved by 1 dB when compared to a conventional electrode-width-controlled-SPUDT filter on an ST-cut quartz substrate.