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Physical sensors drive MEMS consumerization wave (Part 2)

Posted: 08 Nov 2007 ?? ?Print Version ?Bookmark and Share

Keywords:accelerometers? MEMS? pressure sensors? micromachining? SiP?

ST's Benedetto Vigna notes that we are now living in the era of MEMS consumerization where mic, motion and pressure sensors are the main actors and he believes this trend will continue for the next five years. This is the second half of the article details with the growing number of applications employing MEMS.


Figure 3

Motion sensors for consumer apps
Currently, accelerometers and gyroscopes are widely adopted in the automotive market for active and passive safety systems. And they are used also in the medical market for pacemakers. Lately, they have started to penetrate the consumer market to address new applications.

The consumer market is looking for tiny, inexpensive, low voltage and low power consumption devices. Mobile phones, MP3 and MP4 players, and portable PCs are all battery operated and are becoming smaller and thinner. Moreover, the product life cycle of consumer devices is shorter than devices in automotive markets; therefore, MEMS suppliers have been tasked to develop new products much more quickly, while keeping the same level of reliability.

Traditional solutions for the automotive market use big, thick, and expensive packaging such as ceramic or cavity pre-molded packages with gel. On the other hand, the consumer market prefers surface mountable packages, small, thin and low cost (Figure 4). Full molded plastic packages (QFN and PLGA) for motion sensors were first introduced in 2002 by STMIcroelectronics and are now widely used in the industry, becoming a standard.


Figure 4

STMicroelectronics has been miniaturizing the three axis accelerometer family at very fast pace moving from 100mm3 to less than 10mm3 packages (Figure 3) in less than three years.

In the automotive market, power consumption and voltage supply do not represent a big technical hurdle since they sensors not battery operated. High shock resistance is important, but it's not the same as for portable devices that might drop on the floor almost everyday. Despite these differences, for the sake of clarity, we want to emphasize that the automotive market requires a higher level of reliability in products as well as a wider operating temperature range.

In the consumer market, the supply voltage goes down to 1.8V, and the electrical current has to be definitely lower than 1mA aiming to less than 100?A. Additionally, consumers have come to expect a power-down feature in their products and multiple interrupt pin functions to simplify product integration in the final equipment.

In the consumer market, multi-axis solutions are mandatory since consumers want to activate any function from any initial physical position because, in a handheld application, there is no constant frame of reference, like in a car. Analog output is no longer sufficient and digital output is preferred for easier integration in the final product and faster application software development. However, different markets require different features, and the solution must be flexible enough to accommodate varying customer needs. And, in any case, adequate applications development tools must be easily available to the final customer. ST may offer both two and three axis, analog and digital, products as shown in Figure 4 to accommodate customer requests. Each products comes with an evaluation kit and a reference design, with dedicated software for most relevant applications, is also available (Figure 5).


Figure 5

Currently, monolithic (single-chip, single-package) and hybrid (two-chips, single-package) solutions are available. Using today's technologies, it is possible to integrate the sensing element and interface together. But just because something is possible does not mean it is the best solution.

Practical systems have cost and time-to-market constraints, and sometimes it is more functional and less expensive to implement complex control circuits using standard CMOS technology. A multichip single-package solution is not only the most cost effective, but it can also provide the modularity and flexibility needed for fast time-to-market and time-to-volume, very important for the consumer market.

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