Flexural Plate Wave Piezoelectric MEMS Transducer for Cell Alignment in Aqueous Solution

In this work, the possibility to align cells dispersed in water by means of standing flexural plate waves (FPWs) in an underlying substrate has been explored by designing and fabricating a piezoelectric MEMS transducer. The MEMS exhibits a 6x6 mm2 cavity etched out in a silicon substrate forming a volume where cells dispersed in liquid can be steered under electronic control. The diaphragm of the cavity is composed of silicon (Si) and an aluminum nitride (AlN) layer. The generation of FPWs of the A0 mode in the diaphragm is achieved by applying proper excitation voltages to two metal interdigital transducers (IDTs). In turn, acoustic waves are transferred in the liquid, generating a one-dimensional acoustic field pattern thus steering and trapping the dispersed cells in distinct positions. The MEMS device has been fabricated by using the PiezoMUMPs process and experimentally tested by exploiting a tailored front-end circuit. The cavity has been loaded with inert fibroblasts cells with an approximate diameter of 15 μm dispersed in demineralized water with a concentration in the order of 105 cells/ml. By properly driving two IDTs, lines of cells spaced by half wavelength λ/2 = 56 μm have been achieved at 12.5 MHz, in good agreement with theoretical expectations.