Understanding Smart Sensors - Nomads.usp

The Next Phase of Sensing Systems 329SensorMoresensorsSystemSmarterControllerFigure 14.9 The smart loop.14.8 SummarySmart sensors will mean more than the IEEE definition presented in Chapter 1.However, technology is not smart if it is not cost effective. The exciting prospectof merged MEMS and microelectronics is a sensor that adds very little costcompared to the cost of all the other electronics required to make the sensorfunction as expected in the final system. The level V sensor, as proposed inChapter 1, will use well-defined CMOS processing for all the microelectronicsand a CMOS-compatible micromachining process for the sensor(s).As noted in Chapter 1, semiconductor sensors originated as unwantedeffects on transistors. As the industry improves the ability to fabricatemicromachined sensors, especially surface micromachined sensors, the area ofthe sensor relative to circuitry that makes the sensor output useful and smarterbecomes a smaller and smaller portion of the overall area. Additional processingfor the sensor will increase the overall cost. Viewed from the perspective of asemiconductor manufacturer, the lion’s share of the cost is in everything exceptthe sensor. For all intents, the sensor is “free.” The cost increases, sometimessignificantly, as the specifications are defined for a specific sensor. Performance,especially accuracy, resolution, repeatability, and reliability, directly affectqualification efforts, test time, and yield—items that have a direct and significantimpact on cost.The cost is associated more with initial process, design, packaging, and, ofcourse, testing of the sensing system. The cost of the CMOS portion will be