- Membrane-Type Surface Stress Sensor
The membrane-type surface stress Sensor (MSS) is an optimized nanomechanical sensor platform designed for the so-called “static mode” operation. MSS consists of an “adsorbate membrane” supported with four constricted “sensing beams,” on which piezoresistors are embedded for electrical read-out of analyte-induced surface stress on the adsorbate membrane. With this configuration, each sensing beam experiences the cumulative deformation of the membrane, and thus, piezoresistors embedded at these sensing beams can efficiently detect the whole surface stress applied on the adsorbate membrane. The MSS design offers several advantages including high sensitivity (limit of detection ~0.1 mN/m), high stability (without free-ends), low drift (with self-compensation of full Wheatstone bridge), easy coating of receptors (with double-side coating method), low
cost, compact system, and the capability of mass production (with CMOS compatibility). In this chapter, the properties of MSS are discussed along with recent results. 6.1 Introduction
Nanomechanical sensors detect volume-or mass-induced mechanical changes of a sensing structure by means of socalled static or dynamic mode operations, respectively. Since all substances have these basic properties, nanomechanical sensors can be used for detecting almost any kind of samples as demonstrated in various examples.1-6 Thus, nanomechanical sensors have been expected as a versatile sensor in various fields, including medicine, security, and environmental science. There is, however, still no nanomechanical sensor actually working in industry or in our daily life even after the decades of studies since their first reports.7,8 It is important to develop a platform for practical applications in which nanomechanical sensors can contribute exclusively. For this purpose, each component of a nanomechanical sensor has to be optimized for fulfilling the practical requirements, such as small, simple, and low-cost, in addition to enhancing fundamental properties, including sensitivity, stability, and reproducibility.