We have successfully commercialized the Micro-cantilever and Micro-heater technologies for various micro/nano scale sensing applications. A detailed description of these technologies is given below.
MEMS and NEMS Cantilevers
A Cantilever is a diving board like structure that is anchored at one end and the rest is suspended. It can bend both downwards as well as upwards due to compressive and tensile stresses causing strain in the whole structure.The structure is capable of transducing a nano-mechanical motion into an electrical signal.
MEMS (Micro Electro Mechanical System) and NEMS (Nano Electro Mechanical System) Cantilevers are structures with dimensions of the order of microns (10-6 meters) and capable of measuring nano-mechanical(10-9 meters) motion. At such a small scale, very small physical factors such as surface stresses are enough to substantially bend the cantilever structure. This bending of cantilevers can be further measured to determine surface activity.
Hence, Cantilevers can be used as sensors when the surface activity is selective in nature. For selectivity, the surface of the cantilever is functionalized and specifically activated to respond to certain chemicals or compounds only. These nano-mechanical cantilevers sensors are known to have sensitivity higher than the order of parts per trillion.
Piezo-resistive MEMS and NEMS Cantilevers are electrically conducting structures that show change in electrical resistance due to upward or downward bending. The structure is made of a piezo-resistive compound sandwiched between layers of electrically insulating materials. The cantilever stack bends due to compressive and tensile surface stresses which cause strain in the piezo structure. This stain is measured in the form of change in resistance between two conducting contact points on the anchored base of the cantilever.
Cantilevers for Bio/Chemical Sensing
Piezoresistive MEMS and NEMS cantilevers can be functionalized as sensors and used for various applications. The key is to selectively activate one surface of the cantilever by coating it with a compound which shows specific affinity to the target molecules also called analyte molecules.
Passivation is performed on the other side of the cantilever by coating it with chemically passive compounds so that it does not react with the analyte.
In the presence of analyte molecules, the cantilever is subjected to differential surface stress due to the active and passive sides and bends accordingly. This bending causes a change in the resistance of the cantilever structure this change in the resistance is electrically measured and recorded.
This opens up the scope of using this generic cantilever platform for numerous applications as sensors and for detection, analysis and characterization studies on surface chemical interaction.
Micro-heaters, designed and fabricated by NanoSniff Technologies, are conducting MEMS structures, suspended like a bridge from a silicon substrate and acting like a miniature hot plate when connected to a current source due to resistive heating (I2R). The silicon under the bridge is completely etched out to release a thin resistive wafer with a serpentine conductor and very low thermal mass that can be heated up to several hundreds of degrees within milliseconds by currents as low as 10 mA.
These micro-heaters incorporate another thermally coupled resistor to act as a RTD based temperature sensor for real-time thermal monitoring and control. The hotplate is electrically insulated with SiO2 from top and bottom for use in different applications.
Micro-heaters find their use in various applications such as small volume gas heating, sources for generation of wide band IR, ignition etc.