ABSTRACT
Microelectromechanical systems (MEMS) cantilevers can be used
to detect trace gas elements. The surface of a cantilever is
functionalized with a coating that preferentially bonds to the
substance that is to be detected. When the coating adsorbs this
substance, the cantilever will bend due to surface stresses, and
the resonant frequency of the cantilever will change. The change
is proportional to the additional mass of the adsorbed substance.
To construct an effective cantilever sensor, a sensitive technique
is required to read out the state of the cantilever. This chapter
describes the operation of MEMS cantilever sensors and the readout
techniques used to determine their state. The chapter also describes
a novel optical readout technique suitable for determining the state
of a cantilever sensor. A noise analysis is performed using theoretical
and computational models, and it is found that the readout system
is capable of a shot-noise-limited deflection noise density of
4.1 fm/ √ Hz. An implementation of the readout system has been
experimentally demonstrated, which has a noise floor of 1 pm/ √ Hz.
The rapid progress of the last few decades in electronics miniatur-
ization has led to a new class of devices known as microelectro-
mechanical systems (MEMS). These are characterized by having
mechanical moving parts that are typically in the range of a tenth
to a thousandth of a millimeter in size.
