Understanding Smart Sensors - Nomads.usp

The Next Phase of Sensing Systems 321Taking the next step using MEMS may be a logical extension of thistechnology.14.4.5 Microangular Rate SensorsSmall cost-effective angular rate sensors are being developed for vehicle stability,adaptive cruise control, and vehicle navigation systems. One approach usesa plating mold for a metal structure for sensing angular rate [15]. As shown inFigure 14.4(a), the initial surface micromachined sensor used a ring structure.The center is held in place by four spring support arms attached to four mountingposts. The sensor measures rotation around the X- and Y-axes. The morerecent ring-comb combination increases the signal and improves the temperatureperformance. The signal conditioning is performed by CMOS circuitrythat can be integrated on the same chip as the angular rate sensor. This combinationof micromachining and microelectronics allows the angular rate sensorto be embedded in a vehicle control system for use by consumers. This sensorwill also be connected to a vehicle communication bus for use in other systems.As with other CMOS MEMS, the possibility of monolithically integrating thecircuitry with the structure should be both possible and cost effective in thefuture.14.4.6 MCU With Integrated Pressure SensorA monolithic microcontroller with a micromachined pressure sensor has beendemonstrated [16]. Figure 14.5 shows the key elements of the design. TheMCU-sensor combination is based on a widely available MCU architecture,with an integral bulk-micromachined sensor. Fabricating the chip is only oneaspect of taking it from concept to reality. The packaging and testing challengesdiscussed in Chapter 10 also must be addressed [17]. Currently, a separateMCU and sensor packaged at a module level provides a more cost-effectivesolution. However, a specific application may require the space savings or performanceadvantages that the monolithic solution can provide. At that point,the level V sensor shown in Figure 1.7, the fully integrated sensing system, willbecome a reality.An example of an application for this might be that of a side airbag sensor[18]. A pressure sensor inside the door panel of a car could be used to sense thechange in pressure when the panel crumples under an impact. The ability toprogram the on-chip microcontroller will enable the auto manufacturer toembed the control algorithm inside the chip. To complete an entire system,only a mechanism for actuating the airbag needs to be added. That actuation