September 10, 2012, Seoul — STMicroelectronics (ST), a global semiconductor company providing a wide range of electronic applications, the world's leading MEMS manufacturer, and a leader in MEMS sensors for mobile devices, has launched a new pressure sensor, the LPS331AP. This new product enables highly precise measurement of elevation relative to sea level in mobile devices such as mobile phones. This means it is possible to provide precise figures capable of determining "which step" one is on, rather than "which floor" one is currently on.

Accurate location determination on mobile devices is a core element of various location-based services that have recently gained popularity. Furthermore, these services are garnering high expectations as the next generation of "trending apps" in the mobile industry. The challenge is to provide a method to determine the location of mobile devices in three dimensions while overcoming constraints such as spatial resolution, reliability, physical size, durability, and cost.

Regarding latitude and longitude, GNSS (Global Navigation Satellite System) is a widely used solution worldwide, capable of measuring the horizontal position of a device with an error of within 1 meter under optimal conditions where signals can be received from four or more satellites. However, ST, together with CSR, developed and successfully demonstrated an indoor navigation solution that can determine the vertical and horizontal position of a mobile device even in areas with no satellite signals at all.

Barometric pressure measurement can provide a better solution than GNSS for verifying three-dimensional position (vertical elevation). This is because it utilizes the characteristic that pressure gradually decreases as altitude increases, making it useful even when four or fewer satellite signals are detected. ST's latest pressure sensor, recently released, can measure pressure very accurately between 260 millibars and 1,260 millibars. 260 millibars is the typical atmospheric pressure at an altitude of approximately 10 km, which is 1,500 meters higher than the summit of Mount Everest, while 1,260 millibars is the pressure found 1,800 meters below sea level, equivalent to half the depth of the deepest mine ever dug. Because this new product is manufactured in a 3x3mm package and guarantees low voltage and ultra-low power consumption, it is ideal not only for smartphones and sports watches but also for weather stations, automotive, and industrial applications. The LPS331AP is also featured in Samsung's most recently unveiled cutting-edge smartphone.

Benedetto Vigna, Vice President of STMicroelectronics’ Analog, MEMS, and Sensors Group, introduced the product, stating, “Since the integration of MEMS devices into consumer devices began, we have developed and provided products capable of detecting gravity, acceleration, angular velocity, and the Earth’s magnetic field. These sensors support the detection and response to the operation of smart devices, and the newly introduced device helps recognize whether a person or object is moving up or down by determining the weight of the atmosphere.”

The LPS331AP is manufactured using a MEMS-specific manufacturing technique called “VENSENS,” which fabricates pressure sensors on an integrated silicon chip. This method eliminates the need for wafer-to-wafer bonding and increases product reliability. The sensing element of the LPS331AP originates from a flexible silicon membrane positioned over an air cavity where the gap is controlled and internal pressure is verified. This membrane is not only much smaller than silicon membranes fabricated by conventional micromachines, but an embedded mechanical stopper prevents breakage. A piezoresistor is a very small structure in which the electrical resistance changes when this silicon film is bent according to external pressure. The piezoresistor is embedded in the silicon film, and the change in resistance is monitored. The electrical resistance changes as it bends according to changes in external pressure on the silicon. The piezoresistor is a small structure in which the electrical resistance changes, and the resistance change is monitored, compensates for temperature changes, and is converted into a digital pressure value that can be read through the industry standard I2C or SPI interface of the host processor.

Key Features of LPS331AP

• High resolution, low-noise sensor capable of detecting centimeter-level altitude differences
• Utilizes ST's exclusive VENSENS technology, providing high rupture resistance of up to 20 times.
• ODR selectable between 1Hz and 25Hz
• Low power consumption: Low resolution mode 5.5µA, High resolution mode 30µA
• Supply voltage: 1.71~ 3.6 V
• Temperature range from -40 °C to +85 °C
• Integrated temperature sensor that compensates for temperature differences
• Since temperature and pressure are calibrated at the factory, there is no need to recalibrate the shipped unit.
• 3x3x1mm plastic land grid array (HCLGA-16L) package. The package has holes to allow external pressure to reach the sensing element.

The LPS331AP is currently in mass production and is priced at $2.60 per unit for orders of 1,000. Samples and evaluation kits are also available for custom design and shortened product cycles. ST's pressure sensor evaluation kit consists of a motherboard (STEVAL-MKI109V2), a plug-in module, and a STEVALMKI120V1 adapter including an LPS331AP pressure sensor.