Detecting frequency of quartz crystal microbalance sensors with high resolution

We propose a method for detecting the frequency of a quartz crystal microbalance (QCM) with high resolution to realize an inexpensive and easy-expanding array sensor system. The principle of proposed method is measuring the difference of the resonant frequency of a reference QCM and the QCM with sensory film (sensor probe) with a resolution of 0.1-0.2 Hz installed in a sensor array. This frequency counter was realized as an LSI along with an oscillation circuit and a data-transfer unit. We prepared a sensor unit with up to eight QCM sensors and the LSI. For a sensory film, we used a polymer film that was deposited by RF sputtering of organic solids (synthetic polymer and biological material). We demonstrated the detection of ppb-level volatile compound using the developed frequency counter and QCM sensor array. Also, the sensor system comprising of plural-number of sensor units is shown.