Temperature Coefficient Of Delay Research Articles

Temperature stability of ZnO-based Love wave biosensor with SiO 2 buffer layer

Theoretical calculations have been performed for the temperature coefficient of delay (TCD) of Love wave biosensor with c-axis oriented ZnO thin film layered structures on SiO 2/Si substrate. The main interest of our paper is to optimize the SAW biosensor under the condition of temperature stability by considering the relations among electromechanical coupling coefficient, mass loading sensitivity and TCD. Some important results have been obtained by solving the coupled electromechanical field equations. It is found that the mass loading sensitivity can be further improved by adding a SiO 2 thin film, and a zero TCD device also can be obtained after integrating with a proper thickness of SiO 2 thin film. We try to obtain a device which possesses the mass loading sensitivity and coupling coefficient as high as possible and has zero TCD. The strategy of optimization is analyzed and a project is presented. We also find that though the interdigital transducers (IDTs) configurations and shorting metal arrangements influence the coupling coefficient a lot, they have few effects on TCD. This analysis is meaningful for the manufactures and applications of the ZnO/SiO 2/Si structure Love wave biosensor.

Analysis of the acoustoelectric behavior of microwave frequency, temperature-compensated AlN-based multilayer coupling configurations

Piezoelectric AlN films, 1.3–6.2 μm thick, have been grown on bare and metallized Al2O3(0001) substrates by reactive radio-frequency-sputtering technique at 180 °C. The films were uniform, stress-free, highly c-axis oriented normal to the surface, and extremely adhesive to the substrates. Surface acoustic wave (SAW) delay lines, showing harmonic modes with operating frequencies up to about 2.44 GHz, were obtained just using conventional optical lithography at 7.5 μm linewidth resolution. Four interdigital transducer (IDT)/counter electrode configurations were obtained locating the IDTs either on the AlN free surface or at the Al2O3/AlN interface, with and without an Al thin metal film opposite the IDTs. The temperature induced shift of the fundamental and harmonic operating frequencies of the four configurations was measured at different temperatures in the range from −25 to 70 °C. The first order temperature coefficient of delay (TCD) of the four structures was experimentally evaluated for different film thickness values and for SAWs propagating along and normal the Al2O3 a-axis. Eight AlN thicknesses, i.e., the temperature-compensated points (TCPs), were experimentally estimated at which the TCD is equal to 0 ppm/°C. These TCPs were found to be in good agreement with those theoretically evaluated. The SAW propagation along the four coupling structures was investigated in terms of phase and group velocity, electromechanical coupling coefficient, electrical potential, and IDT capacitance and radiation resistance for different film thickness values and SAW propagation directions. The numerical simulation of the mechanical and electrical behaviors of the coupling structures showed how the electroacoustic transduction efficiency, the IDT directivity, and bandwidth can benefit from having different electrical boundary conditions. The obtained results confirm the AlN feasibility to the implementation of SAW devices for application to gigahertz range, good electromechanical coupling, thermally stable electroacoustic devices.

Theoretical studies on a TeO2/ZnO/diamond-layered structure for zero TCD SAW devices

High-frequency surface acoustic wave (SAW) devices based on diamond substrate are useful because of their very high SAW velocity. In the present work, SAW propagation characteristics, such as phase velocity, coupling coefficient and temperature coefficient of delay (TCD) of a TeO2/ZnO/diamond-layered structure, are examined using theoretical calculations. The ZnO/diamond bi-layer structure is found to exhibit a high positive TCD value. A zero TCD device structure is obtained after integration with a TeO2 over layer having a negative TCD value. Introduction of a non-piezoelectric TeO2 over layer on the bi-layer structure (ZnO/diamond) increases the coupling coefficient. A relatively low thickness of TeO2 thin film (∼(1.6–3.1) × 10−3λ) is required to achieve temperature-stable SAW devices based on diamond.

Temperature stable amorphous-TeO2∕36°–46° Y-X LiTaO3 substrates for surface acoustic wave applications

This research investigated the temperature coefficient of delay (TCD) of the surface acoustic wave (SAW) on the amorphous TeO2∕36°–46° Y-X LiTaO3 layered substrates. The TCD can reach zero when the thickness of amorphous TeO2 film is much less than that of conventional SiO2 film, which means SAW devices on such substrates can be fabricated easily. Theoretical calculation showed that they have a very high K2 around 8%, a pure transverse surface wave mode, and a zero TCD simultaneously. They are therefore very appealing for a wide range of SAW applications.

Acousto-optical and SAW propagation characteristics of temperature stable multilayered structures based on LiNbO3 and diamond

Theoretical studies on the surface acoustic wave (SAW) properties of c-axis oriented LiNbO3/IDT/diamond and diamond/IDT/128° rotated Y–X cut LiNbO3 multilayered structures have been considered. Both layered structures exhibit a positive temperature coefficient of delay (TCD) characteristic, and a zero TCD device is obtained after integrating with an over-layer of either tellurium dioxide (TeO2) or silicon dioxide (SiO2). The presence of a TeO2 over-layer enhanced the electromechanical coupling coefficients of both multilayered structures, which acts as a better temperature compensation layer than SiO2. The temperature stable TeO2/LiNbO3/IDT/diamond layered structure exhibits good electromechanical coefficient and higher phase velocity for SAW device applications. On the other hand, a high acousto-optical (AO) figure of merit (30–37) × 10−15 s3 kg−1 has been obtained for the temperature stable SiO2/diamond/IDT/LiNbO3 layered structure indicating a promising device structure for AO applications.

Surface acoustic wave sensing system and method for measuring pressure and temperature

A surface acoustic wave (SAW) sensor and an interrogator that transmits a noise source to the sensor for receiving an interrogation signal that is processed and compared to the source signal provides pressure and temperature measurements. One SAW sensor a single interdigital transducer serving as both an input and an output transducer for generating and detecting a SAW, and coded reflectors in a mirrored arrangement opposing the single interdigital transducer. The piezoelectric substrate is supported in a hermetically sealed package such that pressure on the package causes distortion of the substrate transducer surface and thus SAW velocity changes that reflect changes in pressure. Characteristic temperature coefficients of delay for the substrate are directly translated into a temperature value.

Influence of temperature stability on the sensing properties of SAW NO x sensor

This paper presents the study on the influence of temperature stability of a SAW sensor on the NO x -sensing properties. A temperature-stable SAW sensor based on a 128° YX LiNbO 3 single crystal was developed after integrating with a rf-sputtered amorphous TeO 2+ y ( y = 0–1) thin film that acted as a temperature compensation over-layer. TeO 2+ y thin films possessing a negative temperature coefficient of delay (TCD) also served as a sensing layer for the detection of NO x gas. It was observed that the temperature-stable TeO 2+ y (0.045 λ)/128° Y– X LiNbO 3 SAW-layered structure with a TeO 2 over-layer deposited in a sputtering gas mixture (Ar + O 2) of 25% O 2 content exhibited the maximum sensitivity to a given concentration of NO x . The influence of the sensing layer thickness on the response characteristics was also studied after suppressing the contribution due to the temperature instability of the devices, and a thicker TeO 2 film was found to give enhanced sensitivity. The temperature-stable SAW devices are essentially desired to avoid the problem of false alarm, besides the enhancement in sensitivity and reliability.

New method of change in temperature coefficient delay of acoustic waves in thin piezoelectric plates

As is well-known, the development of high-effective and thermostable acoustic devices assumes using the acoustic waves with high coefficient of electromechanical coupling (K2) and low temperature coefficient of delay (TCD). At present, it also is well-known that fundamental shear horizontal (SH0) acoustic waves in thin piezoelectric plates possess by significantly more electromechanical coupling compared to surface acoustic waves (SAW) in the same material. However, although the value of TCD of SH0 waves is insignificantly less than for SAW, this is not enough for development of thermostable devices. This paper suggests a new way of decreasing TCD of SH0 waves in piezoelectric plates at a high level of electromechanical coupling. This way assumes to use the structure containing the piezoelectric plate and liquid with the special dependence of permittivity on temperature. Theoretical and experimental investigation showed that, for SH0 wave in YX LiNbO3 plate at hf = 700 m/s (h = plate thickness, f = wave frequency) the presence of butyl acetate can decrease the value of TCD by six times at K2 = 30%. In a whole the obtained results open the wide prospect of using SH0 wave in thin piezoelectric plate for development of high effective and thermo-stable acoustic devices.

Temperature-Compensated Devices Using Thin$hboxTeO_2$Layer With Negative TCD

This letter evaluates the applicability of TeO2 thin films as an attractive alternative over conventional SiO2 layers in the field of temperature compensation of various devices. It is reported that the processing environment during TeO2 growth plays an important role in defining its negative temperature coefficient of delay (TCD), and the magnitude of TCD increases continuously from -1.862times103 ppmmiddotdegC-1 to -9.883times103 ppmmiddotdegC-1 with an increase in the oxygen percentage from 25% to 100% in the processing gas mixture. A very low thickness of 0.008lambda for the TeO2 over layer (in comparison to the 0.32lambda-thick SiO 2 layer) is required for achieving a zero-TCD device without degrading its performance

Acoustic method of investigating the material properties and humidity sensing behavior of polymer coated piezoelectric substrates

The relative humidity (RH) sensing behavior of a polymeric film was investigated by means of polymer coated surface acoustic wave (SAW) delay lines implemented on single crystal piezoelectric substrates, such as quartz and LiNbO3, and on thin piezoelectric polycrystalline films, such as ZnO and AlN, on Si and GaAs. The same SAW delay line configuration was implemented on each substrate and the obtained devices’ operating frequency was in the range of 105–156MHz, depending on the type of the substrate, on its crystallographic orientation, and on the SAW propagation direction. The surface of each SAW device was covered by the same type RH sensitive film of the same thickness and the RH sensitivity of each polymer coated substrate, i.e., the SAW relative phase velocity shift per RH unit changes, was investigated in the 0%—80% RH range. The perturbational approach was used to relate the SAW sensor velocity response to the RH induced changes in the physical parameters of the sensitive polymer film: the incremental change in the mass density and shear modulus of the polymer film per unit RH change were estimated. The shift of the bare SAW delay lines operating frequency induced by the presence of the polymer film, at RH=0% and at T=−10°C, allowed the experimental estimation of the mass sensitivity values of each substrate. These values were in good accordance with those reported in the literature and with those theoretically evaluated by exact numerical calculation. The shift of the bare SAW delay lines propagation loss induced by the polymer coating of the device surface, at RH=0% and at ambient temperature, allowed the experimental estimation of the elastic sensitivity of each substrate. These values were found in good accordance with those available from the literature. The temperature coefficient of delay and the electromechanical coupling coefficient of the bare substrates were also estimated. The membrane sensitivity to ethanol, methanol and isopropylic alcohol was tested by means of a high-frequency (670MHz) high-sensitivity Si∕AlN resonator sensor.

Characteristics of fundamental acoustic wave modes in thin piezoelectric plates

The characteristics of the three lowest order plate waves (A 0, S 0, and SH 0) propagating in piezoelectric plates whose thickness h is much less than the acoustic wavelength λ are theoretically analyzed. It is found that these waves can provide much higher values of electromechanical coupling coefficient K 2 and lower values of temperature coefficient of delay (TCD) than is possible with surface acoustic waves (SAWs). For example, in 30 Y − X lithium niobate, the SH 0 mode has K 2 = 0.46 and TCD = 55 ppm/°C. The corresponding values for SAW in the widely used, strong coupling material of 128 Y − X lithium niobate are K 2 = 0.053 and TCD = 75 ppm/°C. Another important advantage of plate waves is that, unlike the case of SAWs, they can operate satisfactorily in contact with a liquid medium, thus making possible their use in liquid phase sensors.

Optimal pressure-sensitive cuts for surface acoustic waves on langasite

The crystal langasite manifests its unique advantages and potentials for high temperature applications due to a high electromechanical coupling coefficient, temperature compensated orientations for surface acoustic wave (SAW), and temperature stability. In order to analyze the pressure-induced frequency shift in SAW resonator type sensors at high temperature, this paper presents the electroelastic wave equations employing the effective material constants for small vibrations superimposed on biases originated from homogeneous temperature and external pressure fields in the Lagrangian description. Incorporated with the first-order perturbation integration, a model including both the mechanical and electrical perturbation items originating from thermal biases and small pressure fields is proposed. This universal model is suitable for substrate with high piezoelectricity and can be applied at either room temperature or high temperature circumstance. The criteria of optimal cuts for SAW pressure sensitivity, i.e., high electromechanical coupling coefficient and low temperature coefficient of delay, are proposed. A thorough investigation in trebly rotated cuts has shown that optimal pressure sensitive crystallographic areas can be obtained. The areas suitable for pressure sensors at room temperature are defined with Euler angles Ω 1: φ = 0°―0.6°, θ = 144.4°―145.8°, ψ = 23.2°―24.1°, Ω 2: φ =59.4°―61°, θ = 34.2°―36.2°, ψ = 24.1°―22.3°, Ω 3: φ =119°―120°, θ = 143.8°―145.5°, ψ = 22.3°―23.5°. The areas suitable for pressure sensors at high temperature are defined with Euler angles I: φ = 8°―30°, θ = 24°―36°, ψ = 4°―25°, II: φ = 30°―55°, θ = 144°―158°, ψ = 4°―28°. A set of experiments employing LGS (0, 150°, 22°) and (0, 90°, 0) has been performed to check the validity of the proposed calculation. The experimental relative sensitivity is in excellent agreement with the theoretical results.

Improved Temperature Stability of LiNbO3 Surface Acoustic Wave Devices with Sputtered SiO2 Over-Layers

SAW propagation characteristics, velocity and temperature coefficient of delay (TCD) of a 128° Y-X LiNbO 3 SAW device integrated with an over-layer of rf magnetron sputtered SiO2 film have been studied. A deviation in the experimental observations with respect to the theoretical calculations on the layered structure SiO 2 /LiNbO 3 are identified mainly due to the difference in the material parameters of the deposited SiO 2 film. Influence of deposition conditions on the materials parameters of SiO 2 thin film have been studied, and the representative values of density, dielectric constant, elastic constants (C 11 and C 44 and their temperature coefficients have been determined, required for the design of a temperature stable SAW device.

Investigation on SAW properties of LGS and optimal cuts for high-temperature applications

A promising perspective for surface acoustic wave (SAW) device applications at high temperature has been opened by langasite (LGS). The SAW properties of LGS in singly and doubly rotated cuts at 250 degrees C are investigated. Three noticeable regions for SAW-cut orientations and propagation directions at high temperature are put forward and are defined by Euler angles [0 degrees, 20 degrees --> 50 degrees, 35 degrees --> 45 degrees], [0 degrees, 85 degrees --> 110 degrees, 0 degrees --> 5 degrees], and [0 degrees, 138 degrees --> 145 degrees, 20 degrees --> 23 degrees], respectively. The first region includes zero or comparatively reduced temperature coefficient of delay (TCD) (<2 ppm) and smaller electromechanical coupling factor (K2) (0.2%-0.35%); the second one exhibits higher K2 (0.35%-0.45%) and moderate TCD (<5 ppm); and the highest K2 (>0.45%) and larger TCD (25-30 ppm) characterize the last region. For some typical orientations within the above-mentioned three regions, the temperature dependency of SAW characteristics (up to 1000 degrees C) is discussed. The second region [0 degrees, 85 degrees --> 110 degrees, 0 degrees --> 5 degrees], especially the orientation [0 degrees, 90 degrees, 0 degrees], has better comprehensive characteristics of SAW and is more suitable for high-temperature applications. Therefore, we should give a top priority to the orientation [0 degrees, 90 degrees, 0 degrees] in the design of SAW devices operating at high temperature. Comparison between published experimental results and numerical predictions based on LGS constants and their temperature coefficients available in the literature reveals that the theoretical results of TCD under 250 degrees C are in agreement with the experimental ones (the relative error of TCD is within 10%).

Temperature stability of ZnO thin film SAW device on fused quartz

Surface acoustic wave (SAW) filters for low-frequency (38-65 MHz) applications have been developed using a radio frequency (RF)-magnetron-sputtered ZnO film on fused-quartz substrates. SAW propagation characteristics such as electromechanical coupling coefficient (K/sup 2/), SAW phase velocity (v), insertion loss, and temperature coefficient of delay (TCD) have been measured. The intergidital transducer (IDT)/ZnO/fused-quartz device structure yields almost zero TCD (1 ppm/spl middot//spl deg/C/sup -1/) with 0.316 /spl lambda/ thick ZnO layer (for the device operating at 60 MHz). Alternately, an overlayer of positive TCD material (ZnO itself) has also been deposited on the IDT/ZnO(<0.316 /spl lambda/)/fused-quartz device at a low substrate temperature to reduce the TCD. A modified layered structure consisting of ZnO/IDT/ZnO/fused quartz yields almost zero TCD (-3 ppm/spl middot//spl deg/C/sup -1/) with a 5.3-/spl mu/m-thick ZnO overlayer and a 8.1-/spl mu/m-thick (0.183 /spl lambda/) ZnO bottom layer. Experimentally obtained SAW propagation characteristics have been compared with the theoretical results.

Propagation Characteristics of Surface Acoustic Waves on K3Li2Nb5O15

The contour maps of the phase velocity vf, the temperature coefficient of delay (TCD), the electromechanical coupling coefficient K2, and the power flow angle (PFA) of surface acoustic waves (SAWs) on K3Li2Nb5O15 are presented for Euler angles (φ, θ, ψ) with φ=0, 10°, 20°, 30°, and 40°, and -180° ≤φ, θ< 180°. These maps computed by Campbell and Jonnes' method reveal that SAWs on K3Li2Nb5O15 with Euler angles (4°, 49°, 92°), (33°, 76°, 126°), and (30°, 86°, 151°) have vf of 3255 m/s, 3383 m/s, and 3728 m/s, K2 of 0.0115, 0.0147, and 0.0045, the values of first-order TCD of 0.02 ppm/°C, 0.05 ppm/°C, and 0.04 ppm/°C, and PFAs of 0.005°, 4.7°, and 5.1°, respectively.

Propagation Characteristics of Shear-Horizontal-Type Surface Acoustic Wave on Langasite with Au or Ta2O5 Thin Film

The propagation characteristics, mainly the propagation loss and bulk wave radiation loss, of a pure shear-horizontal-type surface acoustic wave on (0°, θ, 90°)-cut langasite with a high-density thin film such as a gold (Au) film or a tantalum pentoxide (Ta2O5) dielectric film were investigated experimentally. The cut angles θ of 0°, 10° and 20° were chosen because a coupling factor of 1.0% and a zero temperature coefficient of delay (TCD) can both be expected at approximately these cut angles. For the Au film, the propagation loss and bulk wave radiation loss were small at θ=10°.

Temperature stable LiNbO3 surface acoustic wave device with diode sputtered amorphous TeO2 over-layer

Amorphous TeO2 thin film, sputtered in the O2+Ar(25%+75%) gas environment using a metallic tellurium target, has been identified as an attractive negative temperature coefficient of delay (TCD) material that can yield a temperature stable device when combined with a surface acoustic wave (SAW) device based on positive TCD material such as LiNbO3. The influence of amorphous TeO2 over-layer on the SAW propagation characteristics (velocity and temperature coefficient of delay) of the SAW filters (36 and 70 MHz) based on 128° rotated Y-cut X-propagating lithium niobate (128° Y-XLiNbO3) single crystal has been studied. It is found that 0.042λ thick TeO2 over-layer on a prefabricated SAW device operating at 36 MHz centre frequency, reduces the TCD of the device from 76ppm°C−1 to almost zero (∼1.4ppm°C−1) without deteriorating its efficiency and could be considered as a suitable alternative for temperature stable devices in comparison to conventional SiO2 over-layer.

LGX pure shear horizontal SAW for liquid sensor applications

This paper reports predicted and measured properties of the pure shear horizontal (SH) mode for the LGX family of crystals, which includes langasite (LGS), langanite (LGN), and langatate (LGT). These crystals are of the trigonal class 32 group, as quartz, and they exhibit the SH symmetry type uncoupling for the Euler angles (0/spl deg/, /spl theta/, 90/spl deg/). This surface acoustic mode, also known as surface transverse wave (STW), is especially attractive for liquid sensing due to the moderate damping observed in liquid or viscous environments. Numerical and experimental propagation data presented for the SH mode on LGX (0/spl deg/, /spl theta/, 90/spl deg/) includes phase velocity (v/sub p/), electromechanical coupling coefficient (K/sup 2/), temperature coefficient of delay (TCD), fractional change in frequency with respect to temperature (/spl Delta/f/fo), penetration depth, metal strip reflectivity, and excitation of spurious plate modes as a function of /spl theta/. High electromechanical coupling and zero temperature coefficient of delay (TCD) along LGX Euler angles (0/spl deg/, /spl theta/, 90/spl deg/), /spl theta/ between 10/spl deg/ and 25/spl deg/, with penetration depths comparable to surface acoustic wave (SAW) devices are disclosed. In particular, along LGT (0/spl deg/, 13.5/spl deg/, 90/spl deg/), the experimental results reported with resonators and delay line structures verify the high electromechanical coupling (0.8%) for a SH SAW mode, about 10 times stronger than the 36/spl deg/ Y rotated quartz SH orientation, and the existence of zero TCD around 140/spl deg/C. The phase velocity of 2660 m/s is within 0.2% of the calculated value, which is about 55% below the phase velocity of 36/spl deg/ Y quartz, thus leading to smaller STW devices. The penetration depth of 6.5 wavelengths is eight times more shallow than 36/spl deg/ Y quartz, thus providing significant SH mode energy trapping close to the surface. With such positive predicted and measured coupling and propagation characteristics, these orientations are appropriate for the fabrication of high coupling, zero TCD, smaller, and highly sensitive STW devices for filtering, frequency control, and liquid sensor applications.

Temperature coefficient of elastic constants of SiO2 over-layer on LiNbO3 for a temperature stable SAW device

The influence of sputtered SiO2 over-layer on the SAW propagation characteristics of a 128° rotated Y-cut X-propagating lithium niobate SAW filter has been studied. Experimentally measured SAW phase velocity and temperature coefficient of delay (TCD), with varying SiO2 over-layer thickness, show a significant deviation from the theoretically calculated values using the bulk material parameters of SiO2. The observed deviation is attributed to the differences in the material parameters (density, elastic and dielectric constants and their temperature coefficient) of the deposited SiO2 over-layer. The density and the dielectric constant of the deposited SiO2 layer were determined separately, and the elastic constants and their temperature coefficients were estimated by fitting the experimental velocity and TCD data, respectively. The deviation in the dielectric constant and the density in comparison to the bulk was insignificant, and the estimated values of the elastic constants (C11 = 0.75×1011 N m−2 and C44 = 0.225×1011 N m−2) were found to be lower, and the respective temperature coefficients (5.0×10−4 °C−1 and 2.0×10−4 °C−1) were high in comparison to the bulk material parameters.