Investigation Of Inverted-Mesa Multi-QCM Intergration Based On Ion Beam Etching

As a trace weighing tool, Quartz crystal microbalance (QCM) is a thickness-shear mode (TSM) bulk acoustic wave transducer. The detection precision of QCM can reach to 10-9g in theory. The QCM has already shown some clear advantages over other micro-sensors in terms of relatively higher sensitivity, reliability, and easier to achieve real-time monitoring, and it has been generally extended to physical, biological and chemical sensing applications from a single application of films quality measurement since the Sauerbrey's Equation put forward in 1959. Currently, it is particularly important to achieve large resonance frequency and high sensitivity of QCM. Therefore, we introduced an inverted-mesa dual-QCM based on plasma etching, evaporation coating, magnetron sputtering and photolithography techniques in this work. The inverted-mesa QCM has a higher resonance frequency and sensing sensitivity compared to conventional QCM devices. The main points of this work can be summarized as follows.Firstly, we had introduced the background knowledge and properties of AT-cut quartz, and also summarized the bulk micromachining technologies consisting of chemical etching and physical etching. Then the dry etching method was chosen to fabricate the inverted-mesa structure and the ion beam etching technological parameters were investigated. The optimal process was obtained with the beam density of 0.497mA/cm2,the argonion energy of 300eV and the etching rate of 1.0?m/h. Moreover, the alignment device was also fabricated to assist the exposure process.Secondly, the film preparation and mask methods, micromachining process for fabrication of inverted-mesa dual-QCM were introduced. Three fabrication experimental schemes of inverted-mesa dual-QCM were established. The aluminum (Al) and gold (Au/Cr) electrodes were fabricated by evaporation coating and magnetron sputtering, respectively. In the process, the Al layer was employed for mask sacrificial layer as well as electrodes.Finally, we had fabricated the QCM measurement device and used the resonance frequency measurement instrument to measure the resonant frequency of inverted-mesa dual-QCM. The results indicate that the resonance frequencies of the QCM without etching and with one hour etching time on the same AT-cut quartz is 15.657830MHz and 15.753004MHz, respectively. Additionally, both the resonance frequencies of the QCMs without etching time and based three hour etching time are 15.754025MHz and 16.258001MHz. It is concluded that the resonance frequency of the inverted-mesa QCM is higher than that of the conventional QCM.