Frederic Sarry

Modelling of SAW filter based on ZnO/diamond/Si layered structure including velocity dispersion

Abstract A simulator based on the coupling of mode (COM) theory, previously developed for modelling the bulk substrate surface acoustic wave (SAW) devices, was modified to be adapted for layered structures. The frequency response of ZnO/diamond/Si SAW filter was calculated and the results were compared with experimental ones extracted from the literature. A good agreement is obtained for the frequencies within and close to the pass-band of the filter. Outside of this pass-band, the experimental frequency response exhibits an asymmetry, which is not reproduced by the simulation. This asymmetry is attributed to the dispersion, as a function of frequency, of SAW velocity (VP) and electromechanical coupling coefficient (K2), which cannot be neglected in the case of layered structures. In the original program developed for bulk structures, K2 and V were assumed to be constant. To take into account the effect of dispersion, the program was modified by the introduction of a dispersive model. The confrontation between the results obtained by simulation, including the dispersive model, and by experimental measurements shows a good agreement.

Sezawa mode SAW pressure sensors based on ZnO/Si structure

Surface acoustic wave (SAW) devices have been shown to be suitable for many sensor applications. One of these applications is pressure sensor. In this study we investigate the performance of SAW pressure sensors formed with ZnO/Si(001) structure. The pressure sensitivities of Rayleigh mode as well as the Sezawa mode are studied as a function of normalized thickness (kh=2/spl pi/h/sub ZnO///spl lambda/). The experimental results show an opposite strain effect in the ZnO layer and Si substrate. A theoretical approach based on the perturbation method has been developed for the evaluation of pressure sensitivity in the Sezawa mode. Experimental and theoretical results obtained for the ZnO/Si SAW sensor prepared with kh=1.18 are in good agreement. For kh/spl les/1.2, the ZnO contribution to the sensor sensitivity can be neglected in the Sezawa mode in which ZnO acts mainly as an electromechanical conversion layer.

Enhanced Sensitivity of SAW-Based Pirani Vacuum Pressure Sensor

The authors have already presented a novel surface acoustic wave device for vacuum pressure measurement by employing a piezoelectric substrate that has a high value of temperature coefficient of frequency. Frequency-shift measurements as a function of vacuum pressure can be used to extract information about the pressure sensitivity of the device. In this paper, we report that the deposition of an aluminum thin-film layer and rise in the sensors operating temperature significantly improve the sensitivity of the device. The results are crucial for improving the lower limit of the vacuum pressure measurement, which currently stands around 10-3 Pa.

AlN/ZnO/diamond waveguiding layer acoustic wave structure: Theoretical and experimental results

We present a theoretical calculation and experimental results for a waveguiding layer acoustic wave (WLAW). The experimental device is modeled by the finite element method (FEM) for the AlN/ZnO/diamond structure. It was found that the AlN thickness must be at least larger than 3λ/2 to obtain negligible surface displacement. In the same way, the ZnO thickness for a fixed value of AlN thickness at 2λ must be larger than λ/4 to confine the acoustic wave. The electromechanical coupling of the wave presents an optimum around λ/2 for the ZnO layer thickness. A first experimental AlN/ZnO/diamond device has been developed and shows the WLAW at 412 MHz.

Rayleigh surface acoustic wave as an efficient heating system for biological reactions: investigation of microdroplet temperature uniformity

When a microdroplet is put on the Rayleigh surface acoustic wave path, longitudinal waves are radiated into the liquid and induce several phenomena such as the wellknown surface acoustic wave streaming. At the same time, the temperature of the microdroplet increases as it has been shown. In this paper, we study the temperature uniformity of a microdroplet heated by Rayleigh surface acoustic wave for discrete microfluidic applications such as biological reactions. To precisely ascertain the temperature uniformity and not interfere with the biological reaction, we used an infrared camera. We then tested the temperature uniformity as a function of three parameters: the microdroplet volume, the Rayleigh surface acoustic wave frequency, and the continuous applied radio frequency power. Based on these results, we propose a new device structure to develop a future lab on a chip based on reaction temperatures.

Numerical Development of ZnO/Quartz Love Wave Structure for Gas Contamination Detection

Love wave structures are encouraging devices for sensing applications in gaseous or liquid media because of their high sensitivity. In this paper, we first investigate basic properties of a ZnO/quartz Love wave device by the use of theoretical considerations in order to get a good gas sensor. Second, experimental results of the developed structure, ZnO(2.1 mum)/90deg ST-cut quartz, confirm the suitable characteristics, including temperature compensation, high electromechanical coupling coefficient, and good sensitivity to mass loading effect. We finally characterize the gas effect on the photoresist Shipley S1805 with the above structure, and thus we confirm our approach

Wide vacuum pressure range monitoring by pirani SAW sensor

A new kind of surface acoustic wave (SAW) sensor has been developed to measure sub-atmospheric pressure below 100 mtorr with accuracy better than 0.1 mtorr. It provides an efficient measuring solution in the pressure range inaccessible in past by conventional diaphragm-based SAW sensors. Indeed, because of the small bending force in lower pressure and limited sensitivity, diaphragm-based SAW sensors are only suited to monitor relatively high pressure with a precision hardly better than 0.5 torr. To reach precision level better than 1 mtorr at sub-atmospheric pressure for vacuum technology applications, a radically different SAW-based solution is necessary. Our device aims to measure sub-atmospheric pressure less than 100 mtorr with a threshold resolution better than 0.1 mtorr. The concept is similar to the one used by Pirani pressure gauges. However, it is claimed that a heated and suspended SAW device should have better sensitivity. A theoretical model based on the basic concepts of gas kinetic theory and thermodynamics is presented. The validity of the model is checked by comparison between theoretical and experimental results.

New measurement method to characterize piezoelectric saw substrates at very high temperature

In this paper we present a new experimental set-up leading to characterize SAW sensor properties in high temperature up to 900degC. The characterization method consists in hanging a small piece of self-warming piezoelectric SAW device in a vacuum chamber. The device is made of the piezoelectric material to be tested equipped with its IDT plus a heating resistance, both in Platinum. The whole system is suspended from a PCB by mean of classical bonding wires. It is therefore thermally isolated from the rest of the experimental set-up. This allows using standard low-cost circuitry, to connect the SAW device to the measurement apparatus (standard coaxial feed-lines and SMA connectors). The warming being localised on the piezoelectric substrate, it also becomes possible to reach very high temperature, quickly and at low energy cost. This allows easy making of temperature cycles to test the aging of materials. In a first step, TCF values for Quartz ST and LiNbO3 Y-128deg were measured in the range [20-500degC], then compared to calculated ones in order to validate the method. In a second step, one LGS Y-X SAW Delay-Line with Pt/Ta IDT was characterized using this test method in the range [20-900degC].

Growth and toxic gas sensing properties of poly(urethaneimide) thin films

In this work we present a study on the growth and the gas sensing properties of poly(urethane imide) thin films. We first deeply characterized by atomic force microscopy (AFM) the nanostructuration of the poly(urethane imide) holding different amine groups. We further studied the interaction between highly toxic gases such as hexamethyleneimine (HMI) and pyridine and the polymer by using an unconventional method based on Quartz Crystal Microbalance (QCM) measurement. We showed for the first time that weak interactions, i.e. hydrogen bonding between the gas molecules and the polymer film allow the diffusion of the gas molecule deep in the polymeric film and the recovery of the film once the gas molecules leave the sensor. This first work paves a new way for the design of a completely recoverable sensor able to detect highly toxic gases for environmental concern.

Temperature uniformity of microdroplet heated by buried surface acoustic wave device

In this paper, we have studied the uniformity of temperature of microdroplet heated by an original device based on Rayleigh surface acoustic wave in view of discrete microfluidic applications such as biological and chemical reactions. The new device consists to place the microdroplets directly on the transducer to avoid various losses such as wave propagation losses. The other major advantage of this device is that the self-heating of the transducer allows to increase the temperature of the droplets and to improve the temperature uniformity. To precisely ascertain the temperature uniformity, we have used a non-contact method based on infrared thermography so as not to interfere with the system. We then have tested the temperature uniformity as a function of several parameters and compare with a classical Rayleigh surface acoustic wave device.