A high-performance lab-on-a-chip liquid sensor employing surface acoustic wave resonance: part II

We recently introduced an in-liquid sensing concept based on surface acoustic resonance (SAR) in a lab-on-a-chip resonant device with one electrical port. The 185 MHz one-port SAR sensor has a sensitivity comparable to other surface acoustic wave (SAW) in-liquid sensors, while offering a high quality factor (Q) in water, low impedance, and fairly low susceptibility to viscous damping. In this work, we present significant design and performance enhancements of the original sensor presented in part I. A novel \u27lateral energy confinement\u27 (LEC) design is introduced, where the spatially varying reflectivity of the SAW reflectors enables strong SAW localization inside the sensing domain at resonance. An improvement in mass-sensitivity greater than 100% at resonance is achieved, while the measurement noise stays below 0.5 ppm. Sensing performance was evaluated through real-time measurements of the binding of 40 nm neutravidin-coated SiO2nanoparticles to a biotin-labeled lipid bilayer. Two complementary sensing parameters are studied, the shift of resonance frequency and the shift of conductance magnitude at resonance

Advances in Thin Piezoelectric Film based Resonant MEMS Technology

This work makes an overview of the progress made during the last decade with regard to a novel class of IC compatible piezoelectric devices employing plate-guided micro-acoustic waves in micromachined thin film membranes. This class of devices, originally proposed by the author in 2005, is referred to as either thin film Lamb wave resonators (LWR) or piezoelectric contour-mode resonators (CMR) both employing thin film AlN membranes. Their principle of operation is complementary to the so called thin film bulk acoustic resonators (FBAR), while employing the same technological platform. FBARs are currently widely employed in commercial filters and duplexers for telecom applications. Thin film Lamb wave resonators have shown unique performance in both frequency control and sensing applications. Here we demonstrate high quality factors Lamb wave resonators for low noise and thermally stable performance and discuss their application in high resolution gravimetric and pressure sensors. Ongoing research activities will be further outlined. These are focused on the development of RF Transformer-filters and duplexers with performance comparable to their FBAR counterparts. A specific emphasis is put on the ability of these devices to operate in contact with liquids in view of advanced Bio-sensor applications

A Four Parameter Microfluidic Tandem SAW-IS Bio-Sensor

Surface Acoustic Resonance (SAR) biosensing has recently been proposed as a highly compact and robust alternative to the conventional SAW delay-line based biosensing. The device can also be presented as a one-port high frequency alternative to the QCM, employing SAW resonance. It enables simple one-port measurements at low powers, while offering robust integration with microfluidics and implementation in integrated sensor arrays. Here we discuss the SAR approach as a key enabling and demonstrate its integration with the impedance spectroscopy (IS) concept in a single microfluidic device. The IS is integrated within a SAW reflector formed as interdigitated electrode (IDE) capacitor. A test fixture with SAW and IS ports is designed and fabricated. Four sensitive parameters are deduced from the tandem sensor readout and employed in a proof of principle study of liposome layers and their interaction with Ca2+ ions

Parametric study of the resonant TC-SAW piston-mode configurations

Recent trends in RF filter design has brought the necessity to design SAW resonators with boosted performance. Most importantly, improvements in both the resonators\u27 quality factors (Q) and temperature coefficient of frequency (TCF) are needed. TC-SAW concept employing 128 Y-cut LiNbO3 has attracted considerable practical interest in this view. Some excellent works from Qorvo have demonstrated the viability of this technology. Here we present some more detailed theoretical and experimental studies on the scaling rules regarding the design of TC-SAW resonators with suppressed spurious transverse mode responses

Design and characterization of surface acoustic wave resonance (SAR) system for in-liquid sensing

Sensors capable of in-liquid operation are of primary importance not only for biosensors applications, but also for liquid monitoring. Surface acoustic waves (SAW) have been employed for long time in various in-liquid sensors at relatively high frequencies. Unlike their QCM counterparts, SAW in-liquid sensors employ delay-line topology. Here, for the first time, we discuss a new concept for building a SAW in-liquid sensor employing surface acoustic wave resonance (SAR) in a one-port configuration. To demonstrate its utility, a SAR technological platform embedded in a polydimethylsiloxane (PDMS) microfluidic device was fabricated and characterized. Designs with suppressed spurious content were identified. Initial measurements in a liquid environment are performed. In comparison to a delay-line topology, the SAR concept features comparable sensitivity, while offering better electrical performance and smaller size

S-0 Lamb wave resonators for in-liquid sensing: promising alternative to shear bulk acoustic wave devices

Sensors capable of in-liquid operation are of primary importance not only for biosensors applications but also for liquid monitoring. Thin film electroacoustic (TEA) devices have emerged as promising choice for such applications. The most common TEA devices are the thin film bulk acoustic wave resonator (FBAR) and the Lamb wave resonator (LWR). FBAR operating on the shear mode have been widely studied in view of biosensors applications. A theoretical framework describing the in-liquid sensitivity features of LWR employing the S-0 mode (S-0-LWR) has been experimentally proven recently. However, a comparison between both devices has not been performed yet. Here we theoretically and experimentally compare AlN-based S-0-LWR and FBARs on their solidly mounted modality (SMR), in terms of their in-liquid sensitivity features at similar frequencies. S-0-LWR prove to be slightly more sensitive to the density and viscosity of the liquids. Moreover, if a metallic bottom electrode is not deposited on their backside they can also sense variations in the dielectric permittivity of the liquid, which cannot be done with common SMRs

COMSOL modeling of SAW Resonators

Here we demonstrate some generic 2D and 3D routines for SAW analysis employing the commercial COMSOL Multiphysics platform for finite element analysis (FEA). More specifically, we consider the analysis and optimization of high performance LSAW resonators for RF filters. The LSAW nature - being well studied and sufficiently complicated - is chosen as a suitable example for analysis and the results are compared to state-of-the-art knowledge. We found very good agreement between the results of the analytical scheme proposed here and the state-of-art findings. Finally, we demonstrate a TC-SAW piston-mode device simulated using SiO2/128 degrees Y-X LiNbO3

Influence of liquid properties on the performance of S-0-mode Lamb wave sensors II: Experimental validation

Electro-acoustic sensors proving an adequate operation in liquid media are appropriate candidates for biosensing or liquid monitoring applications. In this context, electro-acoustic devices based on Lamb waves have been widely used for such purpose during the last years. More particularly, S-0 mode Lamb wave resonators (S-0-LWRs) have shown promising in-liquid performance. However, a theoretical background describing their in-liquid sensing mechanisms has only been published recently. In this work we present the experimental verification of the previously developed theoretical background based on a finite element model. We discuss about similarities and discrepancies between model and experiments, stating a final model correctly describing the in-liquid sensitivity features of S-0-LWRs. These devices show appreciable different sensitivities of the resonant frequency to liquid viscosity and density, being more sensitive to the latter. Additionally, when they are not electrically isolated, the influence of the liquid electrical properties is superimposed to the mechanical ones and can be correctly extracted

High coupling phononic SH-SAW resonators for inliquid operation

In this communication we report on initial studies on the in-liquid operation of surface acoustic wave (SAW) phononic resonators employing shear (SH)-SAWs. The mode of operation is a SH-SAW with very high electromechanical coupling, propagating in the X-direction of Y-cut LiNbO3 substrates. Measurements of the resonators immersed in ethylene glycol - water mixtures are presented along with an analysis of the underlying phenomena that determine device sensitivity. We found that the change of electromechanical coupling due to variations in the dielectric permittivity of the liquid becomes a leading contributing factor to device sensitivity. The results of this study are expected to enable the design of a novel class of phononic bio-sensors for lab-on-a-chip applications

Bulk Acoustic Wave Transformer employing Periodically Polled array of Piezoelectric Rods

Multilayer bulk acoustic wave transformer employing a periodical array of piezoelectric rods with alternating polarization is experimentally demonstrated for the first time. Voltage transformation coefficient in excess of 6 was measured at a frequency of 150kHz, providing thus a solid experimental verification of the recently proposed principle of operation. Finite element analysis is used to reveal the underlying device physics