Design and Fabrication of a Novel T-Shaped Piezoelectric ZnO Cantilever Sensor

A novel T-shaped piezoelectric ZnO cantilever sensor for chem/bio-detection is designed and fabricated with MEMS technology. By using Rayleigh-Ritz method, the fundamental resonant frequency formula of T-shaped cantilevers is deduced for the first time and is validated by simulation results and experimental results. From this formula, we can easily find the superiority of adopting T-shape for the cantilevers. The complete process of the cantilever sensor is then successfully developed. The cantilever sensor is actuated by a layer of high-quality ZnO film with preferred (002) orientation, which is evaluated by SEM and XRD. The key step of the process is protecting the ZnO film from KOH etching by a novel and effective method, which has rarely appeared in the literature. Finally, this cantilever sensor is measured by a network analyzer, and it has a fundamental resonant frequency of 24.60？kHz. The cantilever sensor developed in this study illustrates the feasibility and potential for many miniaturized sensor applications. 1. Introduction There is a dramatic and urgent demand to develop inexpensive, microfabricated, and extremely sensitive sensors for chem/bio-sensing. As mass sensitive sensors, microcantilever sensors have many advantages over other transducers. For example, these sensors have been shown to exhibit over two orders of magnitude greater absolute sensitivity such as quartz crystal microbalance (QCM), surface acoustic wave (SAW) devices, acoustic plate mode (APM) devices, chemiresistors, and flexural plate wave (FPW) oscillators [1]. So far, one of the most common ways to detect frequency shift or static deflection of cantilever-based sensors is optical inspection by means of a laser and position sensitive diode (PSD). However, laser and PSD are quite complex and bulky and almost impossible to minimize. Another popular method without huge optical systems is by using piezoresistive layer on the cantilever itself. Any changes in the surface stress due to bending will cause an electrical output from the piezoresistive electrodes. The disadvantage of piezoresistive technique is that it requires passing a current through the cantilever for displacement measurements. This results in electronic noises and thermal drift in cantilever deflection. In this study, we choose piezoelectric method for the purpose of simplifying and minimizing the sensors. To date, lead zirconate titanate (PZT) is one of the most widely exploited and extensively used piezoelectric materials. For example, Lee et al. [2] developed a PZT microcantilever biosensor for using in a