Silicon-based Microsensor Research Articles

Microcantilever sensing arrays from biodegradable, pH-responsive hydrogels

Biodegradable, pH-responsive hydrogels composed of poly(methacrylic acid) crosslinked with varying molar percentages of polycaprolactone diacrylate were synthesized. The equilibrium swelling properties of these pH-responsive materials were studied. Methods were developed to incorporate these novel hydrogels as sensing components in silicon-based microsensors. Extremely thin layers of hydrogels were prepared by photopolymerization atop silicon microcantilever arrays that served to transduce the pH-responsive volume change of the hydrogel into an optical signal. Organosilane chemistry allowed covalent adhesion of the hydrogel to the silicon beam. As the hydrogel swelled, the stress generated at the surface between the hydrogel and the silicon caused a beam deflection downward. The resulting sensor demonstrated a maximum sensitivity of 1nm/5.7×10(-5) pH unit. Sensors were tested in protein-rich solutions to mimic biological conditions and found to retain their high sensitivity. The existing theory was evaluated and developed to predict deflection of these composite cantilever beams.

Electrochemical multiphase microsensor for detection of organophosphates

A simple, miniaturized and very sensitive electrochemical microsensor has been designed, fabricated and tested to detect trace levels of organophosphorus (OP) compounds. The device is a silicon-based microsensor with a Teflon nanoporous membrane supported on silicon. It uses the reaction of a hydroxamic acid with OP to yield cyanide ions that can be detected electrochemically. The microsensor developed here shows a very sensitive response to an ultra-low level of OP simulant. The inertness of a silicon substrate and also the reduced diffusion time of cyanide ions to the electrode with the nanoporous gas–liquid interface are the factors that tremendously enhance the sensitivity of our detector.

Silicon-Based Microchemical Systems: Characteristics and Applications

AbstractMicrofabrication techniques and scale-up by replication promise to transform classical batch-wise chemical laboratory procedures into integrated systems capable of providing new understanding and control of fundamental processes. Such integrated microchemical systems would enable rapid, continuous discovery and development of new products with the use of fewer resources and the generation of less waste. Additional opportunities exist for on-demand and on-site synthesis, with perhaps the first applications emerging in portable energy sources based on the conversion of hydrocarbons to hydrogen for miniaturized fuel cells.Microchemical systems can be realized in a wide range of materials including stainless steel, glass, ceramics, silicon, and polymers. The high mechanical strength, excellent temperature characteristics, and good chemical compatibility of silicon combined with the existing fabrication infrastructure for microelectromechanical systems (MEMS) offer advantages in fabricating chemical microsystems that are compatible with strong solvents and operate at elevated temperatures and pressures. Furthermore, silicon-based microsensors for flow, pressure, and temperature can readily be integrated into the systems.Microsystems for broad chemical applications should be discovery tools that can easily be applied by chemists and materials scientists while also having a convincing “scale-out” to at least small production levels. The interplay of both these capabilities is important in making microreaction technology successful. Perhaps the largest impact of microchemical systems will ultimately be the ability to explore reaction conditions and chemistry at conditions that are otherwise difficult to establish in the laboratory. Case studies are selected to illustrate microfluidic applications in which silicon adds advantages, specifically, integration of physical sensors and infrared spectroscopy, highthroughput experimentation in moisture-sensitive organic synthesis, controlled synthesis of nanoparticles (quantum dots), multiphase and heterogeneous catalytic reactions at elevated temperatures and pressures, and thermal management in the conversion of hydrocarbons to hydrogen.

Design of a silicon microsensor array device for gas analysis

This paper describes the design of a silicon-based microsensor array for application in gas or odour monitoring. Individual sensor cells consist of both lateral and vertical electrode pairs to measure film conductance and/or capacitance. The fabrication process involves standard silicon technologies to integrate a platinum or nickel-iron heater below the sensor cells. A simulation of the device gives a thermal response time of only 60 ms and an ultra low power loss of about 50 mW at 400°C per sensor. This compares well with experimental values observed on a similar device. The process technology is suitable for both the deposition of organic materials (e.g. conducting polymers) and inorganic materials (e.g. semiconducting oxides). A scheme of the tranducer interface circuity is also provided, and could be used in a portable battery-powered instrument.

Solid-state integrated microsensors

The development of integrated sensors based on solid-state technology has become an important goal for many application areas. These devices are an important link for gathering, processing, and communicating information between many electronic systems and users, and the nonelectronic world in areas such as health, care, transportation, manufacturing, avionics, environmental monitoring, and many others. Significant advances have been made in developing new integrated sensors and microsystems: sensors for measuring pressure, acceleration, flow, image, vibration, strain, sound, and many others have been developed. This paper will review the state-of-the-art in integrated sensors and microsystems. It will briefly review the application of integrated circuit technology to micromachining and microsensors, and will provide examples of a few solid-state, silicon-based microsensors. Finally, the paper will discuss the impact that these devices have had on measurement and control systems, and will review future applications.