Page 28 - An Introduction to Microelectromechanical Systems Engineering

To MEMS or Not To MEMS? 7

To MEMS or Not To MEMS?

Like many other emerging technologies with significant future potential, MEMS is
subject to a rising level of excitement and publicity. As it evolves and end markets
develop, this excessive optimism is gradually moderated with a degree of realism
reflecting the technology’s strengths and capabilities.
Any end user considering developing a MEMS solution or incorporating one in
a design invariably reaches the difficult question of “why MEMS?” The question
strikes at the heart of the technology, particularly in view of competing methods
(e.g., conventional machining or plastic molding techniques, which do not have
recourse to micromachining). For applications that can benefit from existing com-
mercial MEMS products (e.g., pressure or acceleration sensors), the answer to this
question relies on the ability to meet required specifications and pricing. But the vast
majority of applications require unique solutions that often necessitate the funding
and completion of an evaluation or development program. In such situations, a
clear-cut answer is seldom easy to establish.
In practice, a MEMS solution becomes attractive if it enables a new function or
provides significant cost reduction or both. For instance, medical applications gener-
ally seem to focus on added or enabled functionality and improved performance,
whereas automotive applications often seek cost reduction. Size reduction can play
an important selling role but is seldom sufficient as the sole reason unless it
becomes enabling in itself. Naturally, reliability is always a dictated requirement.
The decision-making process is further complicated by the fact that MEMS is not
a single technology but rather a set of technologies (e.g., surface versus bulk
micromachining). At this point, it is beneficial for the end user to become familiar
with the capabilities and the limitations of any particular MEMS technology selected
for the application in mind. The active participation of the end user allows for the
application to drive the technology development rather than the frequent opposite.
Companies seeking MEMS solutions often contract a specialized facility for the
design and manufacture of the product. Others choose first to evaluate basic con-
ceptual designs through existing foundry services. A few decide to internally
develop a complete design. In the latter case, there is considerable risk that manufac-
turing considerations are not properly taken into account, resulting in significant
challenges in production.
Regardless of how exciting and promising a technology may be, its ultimate
realization is invariably dependent on economical success. The end user will justify
the technology on the basis of added value, increased productivity, or cost competi-
tiveness, and the manufacturer must show revenues and profits. On both tracks,
MEMS technology is able to deliver within a set of realistic expectations that may
vary with the end application. A key element to cost competitiveness is batch fabri-
cation (that is, the practice of simultaneously manufacturing hundreds or thousands
of identical parts, thus diluting the overall impact of fixed costs—including the cost
of maintaining expensive cleanroom and assembly facilities) (see Figure 1.1). This is
precisely the same approach that has resulted over the last few decades in a dramatic
decrease in the price of computer memory chips. Unfortunately, the argument
works in reverse too: Small manufacturing volumes will bear the full burden of
overhead expenses, regardless of how “enabling” the technology may be.