Quantum 1/f effect in piezoelectric sensors

Piezoelectric sensors used for the detection of chemical agents and for electronic nose instruments are based on BAW and SAW resonators. They are also useful in the detection of biological agents, and can be specific, particularly if the sensitive surface is activated with the right antigen. The BAW resonators are used for instance in the "quartz crystal microbalance" (QCM). This is usually a polymer-coated resonating quartz disk, a few mm in diameter, with smaller diameter metal electrodes on each side and with quality factor Q. The resonance frequency is usually in the 10-30 MHz range. Absorption of gas molecules with mass δm on the surface of the polymer coating gets detected by a reduction of the resonance frequency of the quartz disk, subject also to fundamental quantum 1/f frequency fluctuations. The quantum 1/f limit of detection is given by the quantum 1/f formula for quartz resonators. To optimize the device we must avoid closeness of the crystal volume to the phonon coherence length which corresponds to the maximum error and minimal sensitivity situation. Differential measurements that include a reference resonator without polymer coating can effectively eliminate temperature fluctuations, power supply instability, etc. Adsorbed masses below the pg range can be detected. Similarity, SAW resonators are used at about ten times higher frequencies in small sensors that operate best with sizes larger than the phonon coherence length. The discussion is similar, but applied to the surface and surface waves