SAW Devices Research Articles

Controlling the properties of surface acoustic waves using graphene

Abstract Surface acoustic waves (SAWs) are elastic waves that propagate on the surface of a solid, much like waves on the ocean, with SAW devices used widely in communication and sensing. The ability to dynamically control the properties of SAWs would allow the creation of devices with improved performance or new functionality. However, so far it has proved extremely difficult to develop a practical way of achieving this control. In this paper we demonstrate voltage control of SAWs in a hybrid graphene-lithium niobate device. The velocity shift of the SAWs was measured as the conductivity of the graphene was modulated using an ion-gel gate, with a 0.1% velocity shift achieved for a bias of approximately 1 V. This velocity shift is comparable to that previously achieved in much more complicated hybrid semiconductor devices, and optimization of this approach could therefore lead to a practical, cost-effective voltage-controlled velocity shifter. In addition, the piezoelectric fields associated with the SAW can also be used to trap and transport the charge carriers within the graphene. Uniquely to graphene, we show that the acoustoelectric current in the same device can be reversed, and switched off, using the gate voltage.

FEM simulation of AlN thin layers on diamond substrates for high frequency SAW devices

AlN/Diamond structure is very promising for high frequency acoustic wave devices. In this paper, a comprehensive investigation of AlN/Diamond structure is presented using finite element method. The phase velocity and the coupling coefficient of the first two modes of SAWs for the AlN/Diamond structure are numerically analyzed and compared to experimental data. Close agreement between experimental and numerical results is obtained. Results show that the mode 1 (Sezawa mode) exhibits the largest coupling coefficient of 1.28% associated with a phase velocity of 9500m/s. Additionally, the temperature coefficient of frequency (TCF) and the reflection coefficient (r) are studied. The simulation results show that for a zero TCF, a high phase velocity of 10,800m/s associated with a coupling coefficient of 0.5% can be obtained. These results demonstrate that the AlN/Diamond structure can be used to design wide-band and temperature-compensated SAW devices. The dependence of SAW devices performance with the electrode height, metallization ratio and mass-loading is also investigated.

Room temperature fabrication of ZnO/ST-cut quartz SAW UV photodetector with small temperature coefficient.

Room-temperature fabricated ZnO/ST-cut quartz is adopted for SAW ultraviolet (UV) photodetector. The ST-cut quartz substrate and ZnO layer are used for SAW excitation and photodetection, respectively. High resolution x-ray diffraction (XRD) and photoluminescence (PL) measurement indicate that high quality ZnO films can be deposited on ST-cut quartz using radio frequency (RF) sputtering. As the SAW devices under UV illumination (6 mW/cm(2)), a downshift in frequency of about 35 KHz can be observed. The observed small temperature coefficient of frequency (TCF) indicates that SAW devices exhibit good temperature stability. The results present feasibility of using ZnO/ST-cut quartz SAW photodetectors in ultraviolet region.

LiTaO3/Silicon Composite Wafers for the Fabrication of Low Loss Low TCF High Coupling Resonators for Filter Applications

SAW devices are widely used for radio-frequency (RF) telecommunication filtering and the number of SAW filters, resonators or duplexers is still increasing in RF stage of cellular phones. Therefore, a strong effort is still dedicated to reduce as much as possible their sensitivity to environmental parameter and more specifically to temperature. Bounding processes have been developed at FEMTO-ST and CEA-LETI using either Au/Au or direct bonding techniques for the fabrication of composite wafers combining materials with very different thermoelastic properties, yielding innovative solutions for about-zero temperature coefficient of frequency (TCF) bulk acoustic wave devices. In the present work, this approach has been applied to (YXl)/42∘ lithium tantalate plates, bounded onto (100) silicon wafers and thinned down to 25μm. The leading idea already explored by other groups as mentioned in introduction consists in impeding the thermal expansion of the piezoelectric material using silicon limited expansion. 2GHz resonators have been built on such plates and tested electrically and thermally, first by tip probing. A dramatic reduction of the TCF is observed for all the tested devices, allowing to reduce the thermal drift of the resonators down to a few ppm.K-1 within the standard temperature range. We then propose an analysis of the frequency-temperature behavior of the device to improve the resonator design to use these wafers for industrial applications.

2E3-3 Enhancement of Effective Electromechanical Coupling Factor by Mass Loading in Layered SAW Device Structures

2E3-3 Enhancement of Effective Electromechanical Coupling Factor by Mass Loading in Layered SAW Device Structures

超精密・微細切削加工技術の最新動向(OS3 先進製造技術(1)【基調講演】,研究討論セッション)

This paper describes the recent trends in ultra-precision and micro cutting technology and author's study cases. The ultra-precision and micro cutting technology is one of the most essential manufacturing processes in various fields such as IT, optical instrument and medical care. As one study case, the influence of the cutting atmosphere on the surface roughness and tool wear in CO_2-blow cutting of carbon steel with a diamond tool is demonstrated. As another case, the cutting properties of LiNbO_3 wafer in the direct cutting of micro grooves for the fabrication of SAW device in μ-TAS is demonstrated.

Modelling of SAW Devices for Gas Sensing Applications - A Comparison

SAW technology based devices are being widely used as gas sensors. This paper reports the modeling of SAW devices by comparing the results obtained using two different models. The devices were modeled for their responses in frequency & time domain. The results were used to calculate the insertion loss and bandwidth of SAW delay line at 400 MHz. The modeling study was carried out using MATLAB simulation tool and the results were used to design a photomask for device fabrication.

Design, fabrication and characterization of SAW pressure sensors for offshore oil and gas exploration

This work shows the design, development and measurements of an innovative pressure sensor for high pressure and high temperature environments for offshore oil and gas exploration. The proposed sensor is produced with a simple microfabrication process, which enables large-scale manufacturing, reducing production costs. The advantage of low cost production using these sensors is the ability to design distributed pressure sensors systems at affordable prices to monitor smart wells in oil and gas production. The proposed sensor consists of a two-port SAW device in contrast to the common BAW pressure sensors typically used in the oil and gas industry. A test capsule was designed to measure the device under pressure and the sensitivity obtained by the measurements was found to be 14.8Hz/psi. The operation range was 0–15,000psi and the device must operate on temperatures up to 150°C. Resolution was determined to be 1% of full scale. A capsule to package the sensor and circuits was designed and manufactured in 316L Stainless Steel. Results are very promising and expand the application of different kinds of sensors in the oil and gas industry.

SH-SAW sensor based microfluidic system for the detection of heavy metal compounds in liquid environments

In this work, a guided shear horizontal mode surface acoustic wave (SH-SAW) sensor, fabricated by patterning gold (Au) interdigitated electrodes (IDE) on a 64° YX-LiNbO3 based piezoelectric substrate, was used for the detection of heavy metal compounds. A flow cell, with a reservoir volume of 3μL, which employs inlet and outlet valves for the microfluidic chamber and polydimethylsiloxane (PDMS) based microfluidic channels, was also designed and fabricated using an acrylic material. The frequency based response of the SAW sensor toward varying concentrations of heavy metal compounds such as lead nitrate (PbNO3) and cadmium nitrate (CdNO3) were investigated. As the surface acoustic wave propagates on the substrate, between input and output IDEs, a shift in the resonant frequency of the SAW device was observed due to the change in velocity of the wave caused by the varying concentrations of the test analytes. The results obtained demonstrated the capability of the system to detect picomolar level concentrations. The response of the SAW sensor is analyzed and presented in this paper.

RF 고전력 스트레스에 의한 SAW Device의 고장메카니즘 분석

Abstract In this paper, the improved power durability test system and method for an reliability analysis of SAW device is proposed and the failure mechanism through failure analysis is analyzed. As a result of the failure analysis using microscope, SEM and EDX, the failure mechanism of the SAW device is electromigration due to joule heating under high current density and high temperature condition. The electromigration makes voids and hillocks in the IDT electrode and the voids and hillocks can lead to short circuit and open circuit faults, respectively, increasing the insertion loss of an SAW filter. The accelerated life testing of the SAW filter for 450MHz CDMA application using the proposed power durability test system and method is carried out. B 10 lifetime of the SAW filter using Eyring model and Weibull distribution is estimated as about 98,500 hours. Key Words : SAW Device, Reliability, Failure Mechanism, Power Durability, Life Test, SAW Filter * 정회원, 한국전자통신연구원 사업화본부 ** 정회원, 한국전자통신연구원 사업화본부 접수일자 : 2014년 9월 12일, 수정완료 : 2014년 10월 6일게재확정일자 : 2014년 10월 10일Received: 12 September, 2014 / Revised: 6 October, 2014 Accepted: 10 October, 2014

Automatic Test System for Frequency Response Characteristics of SAW Device

To solve complex measurement and difficult remote operation in the test for frequency response characteristic of SAW device, an automatic test system for frequency response characteristic of SAW device based on vector network analyzer is proposed. The system consists of the vector network analyzer, the crossover cable, the computer, the fixtures and the SAW device. The user interface of test system is developed with the VB language. By means of calling the VISA-COM library, the SCPI commands can send to the vector network analyzer. Many functions of the automatic test system for frequency response characteristic of SAW device include the settings of measurement parameters, the measurement calibration, the data storage, the data display, the data transmission, the marker analysis and the data output. By the actual measurement of a SAW device with the center frequency at 101.764MHz, the experimental results show that the transmission loss of SAW device is-27.532dB, and the reflection loss is-7.715 dB.

Harsh environment sensors: Aircraft and oil field applications of electromagnetic and acoustic technologies

There is an old saying that what can be measured can be improved. However, measuring the key parameters in aircraft engines that drive efficiency and emissions is very difficult. This is even more the case in oil field applications, where extremely high pressures and temperatures are commonly encountered. But the benefits to society of reduced emissions (carbon, pollutants, and noise) and improved oil and gas recovery are tremendous. The task for instrument manufacturers is to develop sensors that are both reliable and cost effective. Recent advances in the application of electromagnetic and acoustic technologies are described for measuring temperature, pressure, flow, and composition in harsh environments. The sensors range from inductively and optically coupled ceramic and silicon devices to ultrasonic and SAW devices packaged with high temperature electronics to fiber optic systems. These sensors are now being deployed on new airframes, engines, deep water wells, horizontal tight shale formations, and high temperature/high pressure wells.

Fabrication of AlN Films by RF Magnetron Sputtering for Surface Acoustic Wave Applications

Highly c-axis oriented AlN films were successfully deposited on SiO2/Si and sapphire substrates by RF magnetron sputtering. The optimum deposition conditions are nitrogen gas ratio (N2/Ar + N2) of 40%, RF power of 400 W, deposition pressure of 4 mTorr, and substrate temperature of 200°C. The full width at half maximum intensity of AlN(002) peak of AlN films on SiO2/Si and sapphire substrates sputtered at the optimum deposition conditions were about 0.26° and 0.2°, respectively. The phase velocity of the fabricated SAW device with AlN/SiO2/Si and AlN/sapphire layered structure was estimated to be about 4996 and 5589 m/s, respectively.

AlN/Sapphire: Promising Structure for High Temperature and High Frequency SAW Devices

In this paper, the performance of AlN/sapphire structure in high frequencies is investigated. Several SAW devices are fabricated with various designs (free-space delay, wavelength, metallization ratio, etc.) to study simultaneously different parameters (acoustic velocity, electromechanical coupling (K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), acoustic propagation loss (α), and temperature coefficient of frequency) versus frequency and temperature. Experimental results show that, as expected, α increases with temperature while K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is enhanced at high temperatures. Because of the antagonistic evolution of these two parameters, insertion loss decreases or increases as function of the free-space delay. We also demonstrate that this structure allows fabrication of devices operating up to 1.5 GHz and that the frequency varies linearly with temperature.

A Novel Closed-Loop Readout Topology for Monolithically Integrated Surface Acoustic Wave Sensors

A new frequency to voltage closed-loop integrated sensor circuit suitable for the read-out module of a monolithically integrated SAW sensor on Si is proposed. This closed-loop system consists of a voltage controlled oscillator, a peak detecting comparator, a finite state machine, and the monolithically integrated SAW sensor device. The output of the system is forced to oscillate within a narrow voltage range that correlates with the SAW pass-band response. The period of oscillation is of the order of the SAW phase delay. The output voltage range varies with changes in SAW center frequency, thus tracking mass sensing events in real time. The analysis and simulation of the system are presented for two SAW devices operating at 374 and 140 MHz, respectively. Experimental results for a test chip fabricated with AMIC5N 0.5 μm process are presented for comparison with simulation data of the 140 MHz design. Because of this frequency to voltage conversion, this approach is uniquely suitable for full monolithic integration of autonomous sensor systems and tags.

Super-high-frequency SAW transducer utilizing AIN/ultrananocrystalline diamond architectures.

SAW devices have been used in a variety of applications including high-volume telecommunications, electronic devices, and advanced sensors. Recently, high-bit-rate data processing in the gigahertz frequency range and ultrahigh-sensitivity sensors have called for the development of advanced SAW transducers. Because of its high acoustic velocity, ultrananocrystalline diamond (UNCD) with a crystal size of 3 to 5 nm, embedded in an amorphous carbon matrix with grain boundaries of 1 to 1.5 nm, is integrated with AlN to extend the operating frequency of SAW devices. We utilize this attractive property of UNCD through the facile synthesis of bilayer architectures consisting of sputtered AlN deposited on UNCD film. The UNCD films were synthesized using microwave plasma-enhanced chemical vapor deposition. The SAW devices were fabricated by electron beam lithography and lift off processes. The fabricated SAW nanodevices exhibit resonance frequencies up to 15.4 GHz. Multiple SAW transducers were fabricated with spatial periods ranging from 580 nm to 3.2 μm.

A Passive Wireless Multi-Sensor SAW Technology Device and System Perspectives

This paper will discuss a SAW passive, wireless multi-sensor system under development by our group for the past several years. The device focus is on orthogonal frequency coded (OFC) SAW sensors, which use both frequency diversity and pulse position reflectors to encode the device ID and will be briefly contrasted to other embodiments. A synchronous correlator transceiver is used for the hardware and post processing and correlation techniques of the received signal to extract the sensor information will be presented. Critical device and system parameters addressed include encoding, operational range, SAW device parameters, post-processing, and antenna-SAW device integration. A fully developed 915 MHz OFC SAW multi-sensor system is used to show experimental results. The system is based on a software radio approach that provides great flexibility for future enhancements and diverse sensor applications. Several different sensor types using the OFC SAW platform are shown.

Characterization and humidity sensing of ZnO/42° YX LiTaO3 Love wave devices with ZnO nanorods

Love mode surface acoustic wave devices based on ZnO/42° YX LiTaO3 were characterized with the thickness of the sputtered ZnO guiding layer varied from 250nm to 1.18μm. Phase velocity, temperature coefficient of resonant frequency, sensitivity, electromechanical coupling coefficient and humidity sensing of the Love mode SAW devices were studied as a function of the ZnO layer thickness. With increasing ZnO thickness over the range of thickness values we have examined, the sensitivity of 42° YX LiTaO3 to liquid loading increased and the values of electromechanical coupling coefficient decreased. The device with a thickness of 250nm showed the best humidity response. ZnO nanorods were grown on this device and its humidity sensing performance has been further improved due to their large surface-to-volume ratio of the ZnO nanorods.

Correlation between propagation loss and silicon dioxide film properties for surface acoustic wave devices

The correlation between the propagation loss and SiO2 film properties has been studied for temperature-compensated SAW devices using the SiO2/LiNbO3 structure. The SAW devices were prepared under different deposition temperatures for SiO2 film. Although they possessed excellent temperature coefficient of elasticity characteristics, devices prepared at lower temperature showed lower Q-factors. The SiO2 films were also deposited on a Si substrate under the same deposition conditions used for the SAW device preparation. Optical characterization was performed with Fourier transform infrared spectroscopy (FT-IR), spectrometer measurement, and Raman spectroscopy. IR absorbance spectra were almost same in the FT-IR measurement. However, optical attenuation in the UV region decreased with the deposition temperature in the spectrometer measurement. The optical attenuation is caused by the increase of the extinction coefficient in the SiO2 layer, and its optical wavelength dependence indicated that observed excess attenuation is caused by Rayleigh scattering. The Raman scattering also decreased with the deposition temperature in the Raman spectroscopy. The scattering is caused by the distortion of the SiO2 network. These results indicate that the Rayleigh scattering caused by the distortion of the SiO2 network is the main contributor to the excess SAW propagation loss in this case.

Low propagation loss in a one-port SAW resonator fabricated on single-crystal diamond for super-high-frequency applications

Diamond has the highest known SAW phase velocity, sufficient for applications in the gigahertz range. However, although numerous studies have demonstrated SAW devices on polycrystalline diamond thin films, all have had much larger propagation loss than single-crystal materials such as LiNbO3. Hence, in this study, we fabricated and characterized one-port SAW resonators on single-crystal diamond substrates synthesized using a high-pressure and high-temperature method to identify and minimize sources of propagation loss. A series of one-port resonators were fabricated with the interdigital transducer/ AlN/diamond structure and their characteristics were measured. The device with the best performance exhibited a resonance frequency f of 5.3 GHz, and the equivalent circuit model gave a quality factor Q of 5509. Thus, a large fQ product of approximately 2.9 × 10(13) was obtained, and the propagation loss was found to be only 0.006 dB/wavelength. These excellent properties are attributed mainly to the reduction of scattering loss in a substrate using a single-crystal diamond, which originated from the grain boundary of diamond and the surface roughness of the AlN thin film and the diamond substrate. These results show that single-crystal diamond SAW resonators have great potential for use in low-noise super-high-frequency oscillators.