By: Norbert Lorenz
In recent years the interest in micro-devices, including Micro-Electro-Mechanical-Systems (MEMS), from research institutions, industry and the press has risen considerably. However one of the persisting challenges in the fabrication of such devices is the packaging process. A number of different bonding techniques have been developed but in general they require the entire device to be heated to high temperatures. In particular for direct bonding techniques like Si-fusion and anodic bonding, temperatures in excess of 1000°C and strong electric fields (1000-2000 V) are essential for successful packaging. As a consequence the use of temperature-sensitive materials within the package is restricted and problems are generated in multi-stage packaging processes where several heating cycles are carried out in sequence; parts joined in an earlier heating step can disassemble in a later one. Furthermore it is clearly important that the package should not affect the performance of the device or cause any damage. Often hermetic and/or vacuum packaging is required which makes the process application specific and expensive. Therefore it can easily account for up to 50% of the overall device cost and can even reach as much as 90%.