Packaging of Transducers

Abstract

Packaging is one of the key problems, whose solution determines whether a Micro Electro Mechanical System (MEMS) can become a successful product. Moreover, not only the technical requirements have to be fulfilled but also the price of the packaging must be taken into account. This chapter describes important requirements for the packaging of a micromachined ultrasound system. The first Section gives an overview of packaging demands for the silicon resonators. Section 5.2 focuses on the low-stress mounting technique of the transducer element on the substrate. The housing which encapsulates the mounted resonator is investigated in the last Section. Two particular housing designs are reported. While the resonator emits ultrasound from the front side of the membrane in the first design, the ultrasound is radiated from the rear side through the etch cavity in the second design. An acoustic horn is integrated in the second housing design to increase the impedance of the transducer element and to focus the emitted sound waves (Section 5.4). A housing with an acoustic horn can not be applied in the first design because the horn throat has to be in direct contact with the surface of the resonator chip which results in large mechanical stress acting on the vibrating membrane. Therefore, an air column in the housing acting like an organ pipe increases the impedance in the first design (Section 5.3). The focusing of the sound waves is achieved using either a grid of one large opening or 9 small openings.