Integrated Piezoelectrics for Smart Microsystems - A Teamwork of Substrate and Piezo

Abstract

Microelectronic substrates like silicon, alumina and LTCC (Low Temperature Cofired Ceramics) allow for high robustness and reliability, 3D packaging (electrical connection, channels, cavities and membranes) as well as integration and application of electronic components whereas piezoceramic materials offer sensor and actuator operations. To combine the advantages of both, integrated solutions are of great interest. This paper deals with two approaches of monolithic integration, (i) screen printing of piezoceramic thick films on microelectronic substrates and subsequent post firing and (ii) integration of pre-fired piezoceramic components into green LTCC multilayer packages and subsequent sintering. Functionality of smart microsystems not only depends on the outer design and construction but to a great part on interaction of substrate and piezoceramic material properties. A thorough choice of materials as well as the understanding and prevention of chemical reactions are necessary to build effective systems.

Screen-printed ultrasonic 2-D matrix array transducers for microparticle manipulation

“…In the current fabrication process, the challenges existing in electrical interconnection still limited the number of the elements of the 2-D matrix array, one promising solution is to integrate 3-D electrode fan-out structures into multiple layers of ceramic [51,67], so that the concept of printing ultrasonic transducer arrays layer by layer can be fully extended to miniaturised arrays of large numbers of elements.…”

“…2 with the layer thicknesses and key material properties listed in Table 1. The piezoelectric material properties of PZT (IKTS-PZ5100 [51,58], Fraunhofer IKTS, Germany) are listed in Table 2, with a mechanical Q-factor of 76 at 1 MHz, and the other materials were assigned properties defined in the PZFlex material libraries. The FEA mesh size was 2.75 lm, approximately 1.38% of the wavelength in water, k w , at the 7.5 MHz frequency of interest, and the complete model was assigned a width four times the mesh size in the x-axis and with symmetry boundary conditions on both sides.…”

“…A series of net-shape patterned thick film layers was printed and sintered on a 100 mm  100 mm alumina substrate with 0.25 mm thickness (99.6%, Rubalit 710, CeramTec AG, Germany) in a sequence comprising bottom Au electrode, PZT thick film, top Au electrode, dielectric insulation layer and Au electrode fan-out tracks. High grade alumina was used as the substrate to prevent degradation of the piezoelectric properties of the PZT caused by interfusion and oxidation reactions between the PZT and possible silicon content in the substrate during the sintering process [51]. Screen-printing was carried out by means of a semi-automatic screen printer (EKRA M2-K, ASYS, Germany).…”

“…Furthermore, the substrates used in thick film techniques, e.g. platinised silicon [50] and alumina [51], can be directly used as fluid-cell carriers in USM devices because of their good biocompatibility [52][53][54][55].…”

2-D crossed-electrode transducer arrays for ultrasonic particle manipulation

“…The crossed-electrode array described here was fabricated from thick film PZT (IKTS-PZ5100 [5], Fraunhofer IKTS, Germany) using a screen-printing process reported elsewhere [4]. A 140-µm-thick 15 mm × 15 mm piezoelectric layer was printed and sintered on a 250-µm-thick 100 mm × 100 mm alumina substrate (99.6%, Rubalit 710, CeramTec AG, Germany).…”