AlN FBAR Particle Sensor With a Thermophoretic Sampling Mechanism

Thermally Modulated CMOS-Compatible Particle Sensor for Air Quality Monitoring

“…Gravimetric particle sensors based on piezoelectric microelectromechanical systems (MEMS) attempt to resolve the highlighted issues [8], [14]- [21]. Gravimetric MEMS sensors commonly rely on measuring the change in resonant frequency caused by particles settling on the sensing area.…”

“…Frequency counter records shift in oscillation frequency caused by a change in collected particle mass [25], [26]. Lower sensitivity [8], [14]- [21] sensing [23]. One of the main drawbacks of cantilever sensors is their low operating resonant frequency (typically up to the medium frequency range (MF, < 3 MHz)), which causes limited mass sensitivity [22].…”

“…One of the main drawbacks of cantilever sensors is their low operating resonant frequency (typically up to the medium frequency range (MF, < 3 MHz)), which causes limited mass sensitivity [22]. Surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) sensors are other examples of MEMS sensors for particle sensing [8], [14]- [17], [19]- [21], [34]. In both types of sensors, a propagating or standing acoustic wave is excited in the piezoelectric material (zinc oxide or aluminium nitride, for example) by a voltage applied across metal electrodes.…”

“…Particle deposition increases the mass of the sensor and thus increases the wavelength of the acoustic wave. This leads to a decrease in the frequency of the same wave [8]. In 1959 the Sauerbrey Equation was developed to express this shift in the resonant frequency of a BAW quartz crystal microbalance (QCM), see Eq.…”

“…1. is Δ𝑚. Thus, the frequency shift of the device is proportional to the deposited particle mass, which in turn means that the particle sensitivity of the resonator is also proportional to its resonant frequency [8], [16].…”