Carbon nanotube isolation layer enhancing in-liquid quality-factors of thin film bulk acoustic wave resonators for gravimetric sensing

Abstract

A thickness longitudinal mode (TLM) thin film bulk acoustic resonator biosensor is demonstrated to operate in water with a high quality-factor, Q. This is achieved using a layer of carbon nanotubes (CNTs) on top of the resonator which has a significantly different acoustic impedance to either the resonator or liquid whilst being susceptible to the binding of biological molecules. This allows the resonance to be decoupled from direct energy loss into the liquid, although still retaining mass sensitivity. AlN solidly mounted resonators (SMRs) having a thickness shear mode (TSM) at 1.1 GHz and TLM at 1.9 GHz are fabricated. CNTs with different forest densities are grown by chemical vapor deposition on the active area with Fe as catalyst and resulting devices compared. High forest density CNTs are shown to acoustically decouple the SMRs from the water and in-liquid TLM Q values higher than 150 are recorded even exceeding TSM SMRs without CNTs. The TLM Q in water is remarkably improved from 3 to 160

An Overview of High Frequency Acoustic Sensors—QCMs, SAWs and FBARs—Chemical and Biochemical Applications

“…Figure 3C shows packaged FBAR device connected with a network analyzer and integrated with customized PCB. There are two resonating modes [106] in FBARs devices i.e., thickness longitudinal mode (TLM) and thickness shear mode (TSM). In the first type, longitudinal waves are generated while in second type shear waves are produced.…”

Current trends in rapid tests for mycotoxins

“…Whilst biosensors based on thin film bulk acoustic resonators (FBAR) have not yet been used in mycotoxin analysis, literature highlights the potential of this technology as a highly sensitive technique that could be exploited for the detection of low molecular weight compounds like mycotoxins. An FBAR transducer is based on a similar principle to QCM, however, unlike QCM, the piezoelectric material used in FBAR transducers is generally a thin film (0.5-3μm thick) of aluminium nitride (AlN) or zinc oxide (ZnO) (Chen et al 2015;Rughoobur et al 2018). AIN is a popular choice due to its high values of chemical inertness, acoustic longitudinal wave velocity, electrical resistivity and its piezoelectric behaviour (García-Farrera et al 2017).…”

The deposition and wet etching of Mg-doped ZnO films and their applications for solidly mounted resonators

“…9,10 The SMR, with good mechanical strength and excellent acoustic properties, and being closer to CMOS integration, was therefore chosen in this work. 11,12 In recent decades, owing to excellent piezoelectric property, better quality factor, and high electromechanical coupling coefficient, ZnO is becoming a very promising candidate for FBAR devices as a piezoelectric material. [13][14][15][16] However, ZnO have the drawback of low longitudinal acoustic wave velocity and low resistance, which limits its application to high sensitivity acoustic sensors.…”