Honglang Li

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.

Low loss and high stopband rejection switchable SAW filter bank

The design and testing of low loss, high stopband rejection 16 channel switchable SAW filter bank using ST quartz as substrate is described. In order to decrease the insertion loss, the individual filters used for bank consisted of SPUDT with the insertion loss of less than 6 dB. Both input and output switches are used instead of input interconnection network and output switch to decrease the insertion loss of input interconnection network. The cascade-connected two stages are constructed to increase the stopband rejection. An amplifier is put between two stages to compensate loss of signal-to-noise. The experimental filter bank results in insertion loss of less than 13.5dB(include the insertion loss of four-stage switch), stopband rejection of more than 70 dB.

Optimal Design of an RSPUDT-Based SAW Filter with Constant Group Delay

This paper describes the application of resonant single-phase unidirectional transducers (RSPUDTs) to the development of low-loss SAW filters with constant group delay in transition bands as well as in the passband. A low-loss SAW filter with constant group delay was designed and fabricated on a 128degYX-LiNbO3 substrate. Experimental results were in good agreement with the design; the group delay deviation of 20 ns was realized over the range of plusmn8 MHz at the center frequency of 512 MHz. The minimum insertion loss and -3 dB bandwidth were 4.3 dB and 8.5 MHz, respectively. The application of this technique is also extended to develop high-performance wideband filters employing quasi-slanted interdigital transducers.

8 channel and 32 channel low loss switchable SAW filter banks

The design and testing of 8 channels and 32 channels low loss switchable SAW filter bank is described. Both input and output switches are used instead of input interconnection network and output switch to decrease the insertion loss of input interconnection network. In order to decrease the insertion loss, the individual filters used in 8 channels filter bank consists of longitudinally-coupled DMS filter on 64/spl deg/Y-X LiNbO/sub 3/ with the insertion of less than 2 dB. The experimental 8 channels filter bank results in insertion loss of less than 3 dB (include the insertion loss of two-stage switch), stopband rejection of more than 50 dB. In 32 channels filter bank, the individual filter consists of slanted-finger interdigital transducer (SIDT) including EWC/SPUDT on 128/spl deg/Y-X LiNbO/sub 3/ with the insertion loss of less than 10 dB. The experimental 32 channels filter bank results in insertion loss of less than 15dB (include the insertion loss of two-stage switch), volume less than 150cm/sup 3/.

Love-mode surface acoustic wave devices based on multilayers of TeO2/ZnO(112¯0)/Si(1 0 0) with high sensitivity and temperature stability

HighlightsLove wave mode of TeO2/ZnOSymbol/Si structure is proposed for biosensing applications.TeO2 film compensates the temperature effect and enhances the sensitivity of the Love mode device.K2, temperature coefficient and sensitivity are analyzed.Optimal design parameters are defined to achieve high sensitivity and temperature‐stable. ABSTRACT A multilayer structure of TeO2/interdigital transducers (IDTs)/ZnOSymbol/Si(1 0 0) was proposed and investigated to achieve both high sensitivity and temperature‐stability for bio‐sensing applications. Dispersions of phase velocities, electromechanical coupling coefficients K2, temperature coefficient of delay (TCD) and sensitivity in the multilayer structures were simulated as functions of normalized thicknesses of ZnO (hZnO/&lgr;) and TeO2 (hTeO2/&lgr;) films. The fundamental mode of Love mode (LM) ‐ surface acoustic wave (SAW) shows a larger value of K2 and higher sensitivity compared with those of the first mode. TeO2 film with a positive TCD not only compensates the temperature effect induced due to the negative TCD of ZnOSymbol/Si(1 0 0), but also enhances the sensitivity of the love mode device. The optimal normalized thickness ratios were identified to be hTeO2/&lgr; = 0.021 and hZnO/&lgr; = 0.304, and the devices with such structures can which generate a normalized sensitivity of −1.04 × 10−3 m3/kg, a TCD of 0.009 ppm/°C, and a K2 value of 2.76%.

Analysis of rayleigh surface acoustic waves propagation on piezoelectric phononic crystal with 3-D finite element model

In this paper, two surface acoustic wave (SAW) delay line structures respectively with and without phononic crystals (PCs) were applied to analyze the propagation of Rayleigh SAW in the 2D piezoelectric PCs in theory. Three-dimensional (3D) finite element method (FEM) was adopted to analyze the model using the commercial software COMSOL MULTIPHYSICS. Experiments were also designed to verify the theoretical results, which show good consistency with the theoretical results. Thus this model can be used to analyze more other structures of 2D piezoelectric PCs, which can be applied to improve the performance of SAW devices.

Finite difference time domain analysis of two-dimensional piezoelectric phononic crystals

Phononic crystals (PCs) have promising band gaps, in which Surface Acoustic Wave (SAW) propagating is prohibited. Several numerical methods have already been developed and applied to analyze piezoelectric PCs, most of them have various disadvantages, as they cannot calculate the transmission characteristic of the limited structure or cannot provide the propagation process for SAW in time domain. The finite-difference time-domain (FDTD) technique solving these problems is adopted to analyze the piezoelectric characteristics of PCs. Propagation in the PCs is studies by experience with direct generation and detection of SAW using interdigital transducers (IDTs). The simulation data agrees with the measurement data. Therefore the FDTD method is an effective method of simulating piezoelectric PCs structure in which a square array of parallel cylindrical aluminum placed on a 128°YX LiNbO3 substrate.

Controlled synthesis of brightly fluorescent CH3NH3PbBr3 perovskite nanocrystals employing Pb(C17H33COO)2 as the sole lead source

Organometal halide perovskite nanocrystals hold vast potential for application in photovoltaics, light emitting diodes, low-threshold lasers, and photodetectors due to their size-tunable bandgap energies and photoluminescence as well as excellent electron and hole mobilities. However, the synthesis of such nanocrystals typically suffers from poor structural stability in solution and the coexistence of lamellate nanocrystals (nanoplatelets) and spherical nanocrystals (nanoparticles). Here we show that the pure nanoparticle morphology of CH3NH3PbBr3 nanocrystals can be realized by employing lead oleate (Pb(C17H33COO)2) as the sole lead source and controlled using short- and long-chain mixed alkyl ammonium. These nanocrystals are monodispersed (2.2 ± 0.4 nm in diameter), highly fluorescent (with a quantum yield approaching 85%), and highly stable in the solution (for more than 30 days). Comparative studies reveal that the shape of CH3NH3PbBr3 nanocrystals is strongly dependent on the lead source, PbBr2 and Pb(C17H33COO)2, and evolves as a function of the ratio of short- and long-chain alkyl ammoniums in the precursors. At an optimal short to long-chain alkyl ammonium ratio of 4 : 6, the growth of CH3NH3PbBr3 nanoplatelets can be selectively suppressed with Pb(C17H33COO)2 as the sole lead source, enhancing the overall photoluminescence quantum yield of the produced CH3NH3PbBr3 nanocrystals. This work reveals important new insights for controlled synthesis of perovskite nanocrystals with pure crystal shape and significantly improved photoluminescence properties and stability.

Theoretical sensitivity evaluation of a shear-horizontal SAW based micro rate sensor

this paper presents a theoretical analysis on response mechanism of a micro rate sensor based on shear horizontal surface acoustic wave (SH-SAW) gyroscopic effect. The new SH-SAW propagating along the ST-90oX quartz substrate by composing heavy metal interdigital tranducers (IDTs) provides superior temperature stability, large acoustic velocity and higher electromechanical coupling factors. Using partial-wave analysis methods, the behavior of shear horizontal SAW propagating along pre-rotated ST-90°X quartz substrate was investigated. The angular detection sensitivity in the propagation path of SH-SAW was evaluated and the effect of the metal IDT electrode thickness on the sensor performance was also studied, optimal IDT electrode thickness was determined.

Extractions of reflection and velocity parameters for surface acoustic wave in two-dimensional piezoelectric phononic crystals

Two-dimensional (2D) piezoelectric phononic crystals (PnCs) have richer properties of band gaps than 1D PnCs but not enough study on the calculation of designing parameters such as reflection and velocity. This paper proposed a model to calculate these parameters of 2D piezoelectric PnCs with finite element method (FEM). In the model, by comparing two SAW delay line structures respectively with/without PnCs and using time domain window to wipe out triple reflection, reflection and velocity can be achieved. Through an example of 2D Nickel/128°YXLiNbO3, it shows that the transmission and reflection of 2D piezoelectric PnCs change rapidly in the frequency band, which is different from the 1D IDTs, and the velocity of the SAW in the 2D PnCs is slower than in the free surface of the piezoelectric substrate.