42. High Volume Manufacturing and Field Stability of MEMS Products

Low-volume microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS) production is practical when an attractive concept is implemented with business, manufacturing, packaging, and test support. Moving beyond this to high-volume production adds requirements on design, process control, quality, product stability, market size, market maturity, internal capacity, and capital investment or transfer to foundry and business systems. In a broad sense, this chapter uses a case study approach: It describes and compares the silicon-based MEMS accelerometers and gyroscopes that are in high-volume production. What is described here also applies to other MEMS products such as pressure sensors, image projection systems, microphones, etc. Although they serve several markets, these businesses have common characteristics. For example, the manufacturing lines use automated semiconductor equipment and standard material sets to make consistent products in large quantities. Standard well-controlled processes are sometimes modified for a MEMS product. However, novel processes that cannot run with standard equipment and material sets are avoided when possible. When transferring to an external foundry, existing processes are modified to utilize the foundry equipment and processes where possible. This reliance on semiconductor tools, as well as the organizational practices required to manufacture clean, particle-free products, partially explains why the MEMS market leaders are integrated circuit manufacturers. There are other factors. MEMS and NEMS are enabling technologies, so it can take several years for high-volume applications to develop. Indeed, market size is usually a strong function of price. This becomes a vicious circle, because low price requires low cost – a result that is normally achieved only after a product is in high-volume production. During the early years, IC companies reduce cost and financial risk by using existing facilities for low-volume MEMS production. As a result, product architectures are partially determined by capabilities developed for previous products. This chapter includes a discussion of MEMS product architecture with particular attention to the impact of electronic integration, packaging, and surfaces. Packaging and testing are critical, because they are significant factors in MEMS product cost. MEMS devices have extremely high surface-to-volume ratio, so performance and stability may depend on the control of surface characteristics after packaging. Looking into the future, the competitive advantage of IC suppliers is decreasing because MEMS foundries are growing and small companies are learning to integrate MEMS/NEMS devices with die from CMOS foundries in one package. Packaging challenges still remain, because most MEMS/NEMS products must interact with the environment without degrading stability or reliability.