Progress in media compatible pressure sensors

摘要

The ability of MEMS devices to operate in potentially corrosive environments will be of the critical importance for the introduction of these devices into new markets. The most common MEMS devices, pressure sensors, have been traditionally specified for dry, non-corrosive gas environments. However, automotive, industrial, and medical applications require exposure of pressure sensors to a variety of liquids such as fuels, oils, acids, bases, and bodily fluids. When a pressure sensor is exposed to these environments, the metallic regions of a sensor die may corrode resulting in catastrophic failures and, in less drastic cases, in electrical output alteration. It is evident that MEMS pressure sensors can not operate in such environments without some form of protection or passivation. This ability of an electronic device, pressure sensor in this case, to perform its specified electromechanical function in chemical, electrical and thermal conditions is called media compatibility; and has evolved into a new MEMS packaging subeategory. The challenge for the pressure sensor media compatible package is to protect a device and, at the same time, enable its interaction with the environment to allow for the transmission of pressure. For this reason, the traditional IC packaging technologies can not be used or need to be modified. A variety of package-level media compatibility methods have emerged and some of them have been successfully employed in certain applications. The most commonly used methods are stainless steel diaphragm and barrier coatings including gels and thin, conformal coatings. Despite numerous proposed techniques, the realization of media compatible MEMS package for every application remains elusive. A partial reason for this is the lack of reliable testing techniques for rapid screening of coating candidates and processes, and early detection of corrosion failures. The development of such techniques is one of the key conditions for the further advancements or breakthroughs in media compatible pressure sensors.