Achieving the Potential of Nano Gas SensorsSeptember 1, 2006 By: Zvi Yaniv, Prabhu Soundarrajan, H2Scan Corp. Sensors
Nanotechnology and a unique platform approach solve critical problems in gas sensing.
The demand for sensitive, low-power, low-cost gas sensors that respond quickly to appropriate stimuli is growing. Macro scale components and conventional manufacturing techniques cannot provide sensors that deliver the detection levels and low-power operation increasingly required by today's applications. And many of these sensors are prone to false alarms. However, manipulating sensing events at the molecular level avoids most problems associated with the more traditional sensor technologies.
Nanotechnology and Sensing
Nanotechnology offers a unique advantage to the sensor industry by manipulating materials at the molecular level, where sensing events occur. Potentially, the technology offers devices with greater sensitivity, selectivity, and reliability than conventional semiconductor, electrochemical, and optical sensors.
Attaining these advantages is not without challenges. Sensor manufacturers encounter difficulties in manufacturing nanostructures, controlling their behavior from the micro to the macro scale, reading reliable responses, and compensating for small signal drift. In short, the nanosensors business is extremely attractive, but it is fragmented and requires a flexible and robust commercialization strategy.
To overcome these obstacles, Applied Nanotech Inc. (ANI), a developer of nano gas sensors, is pursuing a multipurpose-platform approach. Conventional sensor manufacturers respond to a need and develop a technology adequate for a specific sensing event. This approach is one of the main reasons for the fragmentation the industry is encountering. By applying a multipurpose-platform approach, ANI customizes its basic sensor platform to produce a variety of gas sensors (i.e., each can detect different gases). The company has developed four platforms (Figure 1) that use the major gas sensor technologies: gated metal-oxide semiconductor (GMOS) sensors, metal nanoparticle sensors, enzyme-coated carbon nanotubes, and photoacoustic sensors. Each platform is based on existing core components and an understanding of the particular sensing mechanism at the molecular and nano levels. This enables the multipurpose platforms to respond to a variety of sensing events and offer the robustness and flexibility required for the commercialization of sensor products.
Figure 1. ANI sensor platforms
Gated Metal-Oxide Sensors. ANI's GMOS-based platform has replaced the thermal requirement of metal oxide semiconductor (MOS) sensors with an electronic gate bias (Figure 2). This platform offers enhanced environmental stability, low-power operation, and high sensitivity. Traditional MOS sensors operate with surface temperatures of 250°C–600°C, requiring the use of a heated substrate, which is often fragile. The sensors require high power (0.5–2 W) to operate the onchip heaters, limiting the robustness and battery life of the sensors in portable applications. The GMOS platform solves these problems, and because of its low power consumption (nW/sensor element) is well suited for wireless applications.
Figure 2. Gated metal-oxide semiconductor sensor architecture (A) and CO sensor response (B)
The immediate application for this platform is CO sensing. ANI has developed a GMOS CO sensor that requires no heating and has the potential for high selectivity, sensitivity, and specificity. The sensor operates on low power and has a demonstrated CO detection limit of 2 ppm (Figure 2). But the same device has the potential to reach much lower detection levels. The sensor also operates down to –60°C without a heater, a capability that is not available with MOS gas sensors. The GMOS-based platform has industrial and commercial applications in monitoring home safety, mines, vehicles, aircraft, and office and industrial buildings. The company is developing the CO sensor for military applications and intends to extend the platform to detect multiple gases in military and commercial applications.
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