Automotive Propels Consumer Sensors

May 1, 2006 By: Virgil LaBuda and Michelle A. Kelsey, Freescale Semiconductor Inc., Michelle A. Kelsey, Freescale Semiconductor Inc. Sensors

Building a bridge between automotive accelerometers and those designed for the consumer market means giving reconsideration to design, test, space, quality, time-to-market, front- and back-end assembly—and price.

The silicon micromachined inertial sensor that deploys your automotive airbags can't simply be dropped into your laptop for free-fall detection without some do-differentlys. The differences go well beyond the application spaces of medium/high-g and low-g that automotive sockets sport. In fact, the automotive and consumer markets present conflicting fundamental demands. Building a bridge between them means giving reconsideration to design, test, space, quality, time-to-market, front- and back-end assembly—and price.

Some Overlap, More Differences

Automotive and consumer inertial-sensing application domains overlap in the realm of single-digit g's. Automotive accelerometer sockets address safety requirements and range from ~1 g (e.g., tilt, dynamic suspension) to 250 g and above (impact or collision detection).

Consumer applications are designed for more benign acceleration environments; their value lies in product protection and feature enhancement.

As you can guess, the consumer OEM sector is more diversified and fragmented than the automotive arena. More and more consumer products, such as cell phones (in particular those supporting games and including digital video capability), portable hard-disk-drive devices, video games, car navigation systems, and digital cameras have begun adopting inertial sensors to monitor tilt, flag motion events, and detect shock, vibration, and position. GPS-based products, pedometers, and a host of devices that could benefit from anti-theft features can all take advantage of the capabilities provided by inertial sensors.

Moreover, the automotive and consumer markets differ in how they rank the relative importance of performance, reliability, and cost for low-g applications. Safety-critical automotive apps understandably demand the highest in quality and reliability; the most important consumer market constraints are typically cost, time-to-market, and low power consumption. Now let's look at some of the finer points of this distinction.

Price and Time-to-Market Call the Shots

In the consumer market, low price is usually second only to supplier selection—sometimes to the extent that features are slashed until the price can meet the customer's target cost. The conventional methods that semiconductor vendors rely on to reduce cost—smaller die size, shorter test time, improved yields, low-cost packaging, and high-volume production—are still used. But now heightened emphasis must be given to shrinking the time and costs of development, as well as rethinking design engineering and all facets associated with touch labor. Fortunately, it's possible to repurpose technologies developed for automotive products and still achieve shorter design cycles, high quality, and low cost.

The special case of inertial sensors with a two-chip (transducer and signal conditioning) approach is a good example. IC technology developed for products such as analog devices or microcontrollers can be reused for signal conditioning. A two-chip technique is also conducive to shorter design cycle times since transducer and IC design can be done in parallel, resulting in a shorter effective wafer process time.

Time is Always Money

Development, test, and burn-in during production are the three biggest cost contributors in inertial sensor qualification. In accordance with accepted practice, burn-in is removed from the consumer production flow. As for test, cost is further reduced by a judicious choice of parameters at which operational corners are tested. This is usually based on a vendor-customer agreed-upon list of critical parameters. The remaining electrical parameters are guaranteed by design, an approach justified by using enhanced characterizations with previously established very high parametric Cpk (process capability) values over extended qualification regimens. The high quality and reliability pedigree of automotive readily comes across.

Because consumer parts are usually specified with wider operational windows as compared to their automotive "cousins," the cost of this approach can be zero. In other cases, the cost is minimal when additional test intervals are folded into pre-existing characterization and qualification activities. This dramatically compresses new product introduction cycle time, as consumer product buyers usually accept the pre-existing data from the cousin parts or part components, while they look to their own module-level qualification and the qualification of record. This joint working relationship is mutually beneficial.

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