h is by far the world leader in the MEMS sensor market. The automotive and consumer electronics industries are the biggest users of these sensors, and Bosch serves them via its Automotive Electronics division and its Sensortec and Akustica subsidiaries.
Basic research in the 1980s led to the ‘Bosch process’
Bosch is one of the most experienced players in the development and production of micromechanical sensors. It was Bosch researchers who developed the basic technology of bulk and surface micromachining from the middle of the 1980s onward; this is why one of the main production processes is known in the industry as the ‘Bosch process’. It is the key to high-volume production.
Economic success was quick to follow the start of production in 1995. The research was honoured with prestigious awards, including the European Patent Office’s European Inventor Award 2007, and the 2008 German Future Prize, Federal President’s Award for Technology and Innovation.
Bosch MEMS sensors are just as precise and reliable in measuring variables such as pressure, acceleration, yaw rate, or flow rate as they are in determining the direction of the Earth’s magnetic field. The sensors use microscopically small springs, bars, weights, or membranes to make their measurements. The structures etched into their silicon substrate are just thousandths of a millimetre across. Since micromechanical sensors produce only weak electrical signals, experts have integrated electronics either into the component housing beside the sensor or sometimes even directly on the same chip. These take the weak signal and either process it, amplify it, or convert it into digital data. In this way, MEMS sensors can provide measurements directly to control units.
MEMS for automotive technology
The first market for MEMS sensors was in automotive electronics. Here, the miniaturisation of sensors plays only a secondary role. Reliability and robustness are much more important. Bosch Automotive Electronics now produces several hundred vehicle-specific varieties of micromechanical sensor that make cars cleaner and safer, more economical and more comfortable. Each year sees an increase in the number of different varieties and in overall volumes. A modern car features up to 100 of these sensors – and the number is growing. For instance, they are the ‘senses’ for injection systems in petrol and diesel engines, they are what makes life-saving airbags deploy, and they are an essential part of the ESP anti-skid system.
MEMS for mobile consumer electronics
In consumer electronics, MEMS sensors make mobile devices such as smartphones or laptops safe, convenient, and user-friendly. The demands of this sector are fundamentally different from those of the automotive industry. For devices to be practical, the sensors they contain need to be tiny, and they must use very little power to conserve battery life. But most important of all, sensors must be cost-effective if many millions are to be used. Today’s smallest Bosch Sensortec MEMS sensors have an edge length of two millimetres and are less than one millimetre high, and their standby power consumption is even lower than the battery’s self-discharge rate.
In navigation devices and mobile phones with a navigation function, MEMS pressure sensors’ measurements of changes in altitude are accurate enough to allow for navigation even within a multi-story building. MEMS acceleration sensors make it possible to use hand movements to control devices, switch the display of content from portrait to landscape format, prevent the loss of data on hard drives when a notebook is dropped, and open up new worlds of experiences to users of new game consoles.
The latest development is a triaxial MEMS magnetic field sensor. By measuring the Earth’s magnetic field, it can determine the geographic direction. An integrated triaxial MEMS acceleration sensor compensates for errors caused by inclines, allowing this digital compass to maintain its accuracy whatever its position. The possible uses of this fusion of sensors extend far beyond those of a traditional compass and into the realm of augmented reality. A smartphone containing a digital compass could, for example, be used during a sightseeing tour of a city to display information about whichever sight users are pointing their phone at.
MEMS microphones for consumer applications are the specialty of Bosch’s Akustica subsidiary. These tiny microphones, measuring just a few millimetres, stand out for their small size, robustness and immunity to high-frequency signals from surrounding circuitry and displays, enabling consumer device manufacturers to integrate two or more microphones for enhanced noise suppression.
The potential for new developments in the consumer market is as high as ever, so we can expect further spectacular innovations based on MEMS components in the years to come.