In recent years, the image of the MEMS based fiber-optic industry has been plagued by a wave of product launch delays and cancellations. Long been of great interest to the academic community, MEMS based solutions have suffered from a focus on the MEMS alone and an underestimation of the complexity of productization. What is needed for successful development is the implementation of the system approach in MEMS product development. The essence of this approach lies in developing a thorough understading of all the requirements and constraints at the product level, not just the MEMS level. This will reveal all the intricate design interdependencies and trade-offs between all the different technologies involved, from MEMS to manufacturing, and provide confidence in the development timeline and marketability of the final product. A variable optical attenuator is presented that was designed from the ground up using the system approach which has resulted in the smallest size, lowest cost, market accepted solution.
It is common to underestimate the challenges of integrating the at least four technologies in any MEMS product: the three technologies of any semiconductor device (electronics, packaging and testing) plus the MEMS microstructure. For some specific areas of application, for example for photonics, optics technology/components must also be integrated. While traditional semiconductor devices utilize standardized and inexpensive packaging and testing procedures and equipment, MEMS require custom solutions that introduce multiple physical domains, such as light in the case of photonics, directly to a potentially moving structure on the die. This heightened complexity coupled with nonstandard packaging, testing and other (optics) technologies has a dramatic impact on functionality, reliability and cost.
Being developed and successfully proven for a period of about twenty-five years the System Approach to MEMS Commercialization is based on three major principles:
A priori understanding of the interdependence of technologies integrated into MEMS products: micro-machining, IC technology, packaging, testing and other (optics) technologies.
Parallel development or implementation of these technologies within the MEMS product.
Redistribution of manufacturing complexity from individual to batch realm. Integrating packaging and testing and other (optics) components into the microstructure and including some of the testing and functional algorithms in the ASIC reduce cost by simplifying more expensive individual manufacturing steps.
The overall results of redistribution complexity from individual manufacturing technologies into batch manufacturing technologies are dramatic cost reduction, performance and quality improvement and shorter time to market.
Wafer-to-wafer bonding is the second, after wafer micromachining, most fundamental technology for MEMS. Independent on the specific application, bonding should provide certain level of bonding strength, which can be characterized by either pull or shear force required for delamination of the bonded wafers. It also should provide certain level of hermiticity or permability and some other characteristics such as level of induced stress during bonding, maximum temperature, thermo-mechanical stress due to the TCE difference, etc. The goal of presented novel class of bonding technologies is to decrease bonding area and increase mechanical strength and hermeticity of the bonding. This goal was achieved by a combination of the following: microprofiling the bonding area; making negative slope on the side walls of the trenches; making bridges; matching system of trenches and ridges; system of hooks; system of electrical outputs; spacers; barriers; system of capillaries for external true hermetization, etc. The common principle here is to use the third dimension - thickness of the wafer to achieve new quality, for example, to decrease bonding area on the surface of the wafer but increase total bonding surface and, therefore, increase mechanical strength and hermeticity.
The system approach considers a priori the interdependence of all technologies integrated into a MEMS product. Parallel development of these technologies and enabling wafer-level batch manufacturing through process integration is key to successful product development and meaningful cost reduction.