Mite on MEMS
History

The fine sensory organs of technology – a review of sensory technology at Bosch

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Sensors are a product of the future. In the networked world, they determine temperature, pressure, light or acceleration. They help people find their way around, quickly summon the emergency services to an accident, or automatically close the skylights at home if it starts to rain.

The Bosch-Bell („Bosch-Glocke“), 1923
Making noise in case of tires losing air pressure. The Bosch-Bell („Bosch-Glocke“), 1923

The past

But they are actually also a product from the past. Measuring values has always been part of the history of technological development – providing a basis for prompting reactions, in other words changing conditions, or at least serving as a warning for such.
One example is the Bosch bell. This might not sound like a sensor, but it is. Launched by Bosch in the spring of 1923, it was an alarm device for automobiles that warned of falling pressure and the risk of a flat tire by ringing a loud bell.

If air escaping from the tire caused the rim to sink, the clapper attached to it would start dragging on the road surface with every turn of the wheel and, via a hinge, hit the top of a bell. This was an important idea at the time, as the shortage of natural rubber in Europe after the First World War (1914-18) made automobile tires expensive. Bosch recognized a gap in the market and offered five “Bosch bells” (one for the spare) for the price of one car tire.

Saving and reducing

The capabilities of sensors would come to play an increasingly important role at Bosch – but only many decades later. The next signs of their presence can be found in the pressure sensors that were used in the first electronically controlled fuel injection systems from 1967 on. The pressure reading, which was communicated to the control unit, determined the amount of fuel injected so as to ensure optimum combustion – in other words, achieving the lowest possible consumption and exhaust emissions.

After this came sensors for measuring air volume or the oxygen content in exhaust gas. The lambda sensor designed by Bosch and unveiled in 1976 was an intrinsic component for treating the exhaust gases from the three-way catalytic converters that had just become standard.

Smaller than a mite: modern mikromechanic sensors. Picture from 2001.
Smaller than a mite: In modern mikromechanic sensors, there are even mioving parts. Some moving structures have less cross section caliber than a single human hair. Picture from 2001.

Shrinking and improving

During the 1980s, the use of sensors at Bosch became a significant sales driver. Then as components in the automotive industry became smaller and smaller, this was bound to spark ideas of miniaturizing sensors, too. After all, they would need to fit into the housings of even the smallest control units. A Bosch engineering team started working on miniaturized successors to the mechanical sensors in 1987, but it was an extremely complex technical challenge. Consequently, it took about six years until they were ready for series production in 1993, and they eventually went into mass production at Bosch from 1995. There were good reasons for this.

A micromechanical construction eventually proved a feasible concept. But these sensors, known as “MEMS” (microelectromechanical systems), which were smaller than a pea, needed equipping with moving parts. One example is a “rocker”, which changes position in response to movement, such as in the event of a collision to indicate whether the airbag has to be deployed or not. A research team at Bosch succeeded in manufacturing these tiny structures at the start of the 1990s using a completely new process called plasma etching, which is standard for MEMS these days – and became known throughout the world of micromechanics as the “Bosch process”. This made it possible to produce MEMS in large quantities.

Not only for automobiles

These little helpers quickly caught on and appeared in almost all electronically controlled or supported functions in automobiles – in gasoline and diesel injection and in anti-lock braking and driver assistance systems, for instance in the ESP electronic stability program. But their small size – by ten years ago, the smallest sensors were just 2.5 millimeters long and wide – gave creative minds the idea of using them in entirely different devices, too.

So in 2005 Bosch founded the subsidiary Bosch Sensortec in order to further develop these micromechanical sensors for laptops, games consoles, and eventually also for smartphones and tablets, which were launched onto the market in subsequent years and soon manufactured in vast quantities. They notice when a tablet’s screen is rotated from landscape to portrait, or can halt the hard drive in the blink of an eye if a laptop falls off a table.

Assisted by video sensore, automatred driving becomes reality. This experimental car shows traffic sign detection. Picture from 2001
Assisted by video sensore, automatred driving becomes reality. This experimental car shows traffic sign detection. Picture from 2001

The future

MEMS sensors with integrated microcrontroller for Android smart phones
MEMS sensors with integrated microcrontroller for Android smart phones

Nowadays, Bosch manufactures approximately four millions of micromechanical sensors each day, making it the global market leader. And the annual production rate will undoubtedly continue to climb. Not only as a result of the growing demand for sensors in automobiles, but also because more and more everyday technology will function without human input. And this also calls for these little helpers. After all, before the heating can switch itself on or a skylight close automatically, a sensor has to register a sharp drop in temperature or raindrops.

Dietrich Kuhlgatz

Since 1998 I have been at Bosch. I’m working in the Historical Communications department as spokesperson and researcher, in charge of all product history requests. I also take care of contacts to technology and transportation museums.
Before joining Bosch, I studied in history and philosophy at Universities of Konstanz and Hamburg. After graduating, I was editor of a scientific journal and research associate at Deutsches Technikmuseum Berlin.

Picture of Dietrich Kuhlgatz

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