There are an incredible number of interrelated global values that need constant monitoring and control to keep society from coming unraveled. Consider that a few traffic light failures during rush hour-thanks to an aging sensor-mean chaos. Solid-state sensors are increasingly important as a revenue source for the IC assembly community and end users. But why address them in an optoelectronic column? Because while infrared (IR) sensors selectively monitor part of the electromagnetic spectrum, they are usually packaged in electronic modules. Typical Unit A typical IR unit includes a lens, mirrors (sometimes with an optoelectronic I/O conversion assembly), IR detector and necessary electronics that are packaged with a meter, indicator or some I/Os to pass along results. (That definition is courtesy of Frost & Sullivan's [frost.com] recent report, IR Sensors.) The broader solid-state industrial sensor market looks promising too.
IR sensors have been around for 100 years. However, they were not practical measuring instruments until the 1930s. Since then, they have gained wide acceptance in automotive, food and beverage, chemical, petrochemical and pharmaceutical applications. IR sensors, aka radiation detectors, generate an output signal corresponding to the amount of IR radiation striking the detector. Sensor makers can provide computer I/Os, software and communications capability, as well as other digital circuitry. A Fusion of Capabilities According to Frost & Sullivan's analysts, these next-generation digital/smart sensors, a fusion of rapidly evolving IR temperature measurement capabilities with high-speed digital interfaces, will broaden applications significantly. "Smart" instruments can use microprocessor transceivers for bi-directional communications between sensors on the manufacturing floor and process monitoring and control computers. Integrating smart sensors into process control applications offers an immediate advantage with a new level of sophistication in temperature monitoring and control. Expect Growth The industrial sensors markets should increase at an AAGR (average annual growth rate) of 6.2% between 2001 and 2006, reaching $6.8 billion in 2006. This overall pace is attributed to competitive pressures in process industries for improved performance and to new sensor technologies that are experiencing impressive success. The strongest growth arises from developments in the IC industry with the successful integration of microelectromechanical systems (MEMS) in sensing packages. MEMS can help integrate complex functions in a single package to meet user price/performance expectations. Sensors using semiconductor MEMS technologies are expected to grow at an average annual rate of 9.5%, reaching $2.1 billion in 2006, according to RGB-200R Industrial Sensor Technologies & Market, Business Communications Company Inc. [www.bccresearch.com] Gas Sensors A new sensor based on porous silicon (Figure 1) has been developed at Georgia Tech [prc.gatech.edu]. It employs a unique metallization process for enhanced sensitivity, reduced power demands and lower cost compared to existing technologies for detecting gaseous compounds. Made with silicon wafers and IC production techniques, these sensors operate at room temperature at relatively low voltages. They can be integrated into electronic equipment and used to build sensing arrays. Researchers described their devices in the February 15 issue of the Journal of Applied Physics. Rapid and Reversible Response The sensors have a rapid and reversible response to low concentrations of the gases at room temperature, said James L. Gole, a Georgia Tech physics professor (Figure 2).
Since the devices operate on a voltage much lower than those in a watch battery and are very small, they could be taken into the field by anyone concerned with harmful gases (soldiers?). The sensors are so simple that they could ultimately be mass-produced for pennies. Sensors based on porous silicon have been built before. However, they were impractical because of high electrode resistance interconnects to the porous silicon and they required up to 5 VDC. The new metallization process reduces silicon electrode resistance, allowing the sensors to operate at between 1 and 10 mV. The devices can detect ammonia, HCL and NO3 at concentrations of between 10 and 100 parts per million-if not lower-compared to 100 to 1,000 parts per million for the higher-voltage sensors. Because the chemical reaction used to detect the gases can be rapidly reversed, the devices are reusable. Peter Hesketh, the paper's co-author, and a professor at Georgia Tech's School of Mechanical Engineering, added that the sensors can be built at low cost in arrays, which opens up interesting opportunities for mixture analysis in water quality, environmental sensing, food toxin detection and agricultural uses. Caveats? Absolutely. Some solid-state sensors have been around for a long time, although not all have a trouble-free record. This suggests caution. Product designers need to keep wish lists in check, since, as the military knows all too well, a sensor can get very expensive when it becomes too complicated. Anecdotal reports in the 1990s about early U.S. weather bureau sensors suggest that considering environmental conditions is prudent. In polluted areas, thin-film deposition can occur on the sensor itself, its window or optics. This will most likely alter the readings. Mundane and Exotic Applications Many mundane and exotic sensor applications are possible now. With excess fab capacity still existing, now may be the time to experiment and develop some new product ideas. How about an affordable toaster that really matches the setting and toasts evenly? Medium should not mean clouds of smoke in the kitchen where another sensor, a smoke alarm, can really ruin your day.
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