March 13, 2007
Asahi Kasei EMD Corp.
Asahi Kasei Microsystems Co., Ltd.

World's smallest and thinnest 3-axis electronic compass
- one-chip system with silicon monolithic Hall elements in chip-size packaging -

Asahi Kasei Microsystems (AKM), wholly owned subsidiary of Asahi Kasei EMD, has completed development of the AK8973S, the world's smallest and thinnest* 3-axis electronic compass with chip-size packaging of 2.5 × 2.5 × 0.5 mm. The small size is made possible by forming Si monolithic Hall elements together with amplifier and logic circuitry on a single chip. Samples of the AK8973S will be on display at Sensor Expo Japan 2007 from April 4 to 6 in Tokyo, as will applications and demonstrations of the AK8976A, at 4.5 × 4.5 × 0.9 (max 1.0) mm the world's smallest and thinnest* 6-axis electronic compass. Applications foreseen for the digital-interface AK8973S include pedestrian navigation systems in cell phones and personal navigation devices, and motion input in video game controllers.

* As of March 12, 2007, "smallest" in terms of volume, based on AKM research.

Development background
AKM is a world leader in the development of electronic compasses for portable applications, and its AK8970, the world's first 3-axis electronic compass developed for cell-phone use, began shipping in commercial volume in fiscal 2003. It and its successor the AK8970N have been employed in more than fifteen handset models throughout the world. Wide adoption of AKM's 3-axis electronic compasses for cell phones has been driven by the outstanding performance enabled by Asahi Kasei EMD's Dynamic Offset Estimation™ (DOE™) algorithm to automatically compensate for magnetic offset inside a handset. It is the extremely high sensing linearity and wide measurement range of the Hall elements, together with the exceptional AKM architecture for uniform sensitivity in all three axes, that ensures the effective performance of DOE™, resulting in a clearly superior electronic compass functionality that has been recognized by customers around the world.

While maintaining its hallmark performance, AKM has continued to miniaturize the electronic compass in anticipation of the needs of designers and developers of cellular handsets and other advanced portable electronics for successive size reductions. Following the AK8970, which at 5.9 × 6.3 × 1.0 mm was the world's smallest 3-axis electronic compass at the time of its introduction, AKM introduced the AK8970N in fiscal 2004, which at 5.0 × 5.0 × 1.0 mm has its volume reduced to 67% of that of its predecessor. In fiscal 2006 AKM introduced its then smallest electronic compass the AK8973 at 4.0 × 4.0 × 0.7 mm, with a volume reduced to 45% of that of the AK8970N. The AK8973S announced today, with chip-size packaging of 2.5 × 2.5 × 0.5 mm, has its volume reduced to 28% of that of the AK8973 and a mere 8% of the volume of the bellwether AK8970.

A succession of technological advances has enabled this extraordinary course of miniaturization. The first-generation products, the AK8970, AK8970N, and the AK8971N which included an accelerometer interface, were multi-chip modules comprising three compound semiconductor Hall elements from Asahi Kasei Electronics, one for each spatial axis, and an AKM signal processing LSI packaged together. The AK8970 and the AK8970N contained the same four component chips, with the size reduction in the latter obtained by a change in packaging technology. In order to attain even greater size reduction, the AK8976A and AK8973 introduced in fiscal 2006 are produced with Si monolithic Hall elements formed together with the amplifier and logic circuitry, resulting in a one-chip electronic compass. With the AK8973S, the potential size reduction of a one-chip conformation is taken to the limit by utilizing new technology for chip-size packaging.

Distinguishing features of the AK8973S, in depth
The development of Si monolithic Hall elements to serve as magnetic sensors, and their integration with amplifier and logic circuitry on a single chip, is itself a major advance both conceptually and in terms of applied technology. Any magnetic sensor, Hall element or otherwise, can only measure a magnetic field in a single axis. This is why conventional 3-axis sensors were of necessity multi-chip modules incorporating three separate magnetic sensors, emplaced in three different planar orientations corresponding to the spatial axes of X, Y, and Z. Because the Hall element, unlike other magnetic sensors, measures magnetic field in the axis perpendicular to the plane of the chip, many had considered it to be an unfavorable choice for 3-axis sensors, as two of the Hall elements needed to stand vertically with respect to the plane of the chip package. With the development of the Si monolithic Hall element, the perpendicular measurement direction of Hall elements becomes an advantage that enables sensors for all three spatial axes to be formed on a single wafer plane. The principles of magnetic field measurement using this technology will be presented on March 17 at a symposium of The Institute of Electrical Engineers of Japan.

Chip-size packaging (CSP), unlike QFN packaging, enables the 3-axis electronic compass to be used in circuit board designs with extremely high mounting density. For many portable electronics, cellular handsets in particular, recent years have seen a rapidly expanding adoption of CSP technology. The AK8973S uses wafer-level CSP, or WLCSP, in which LSIs are encapsulated in resin before the wafer is cut into individual chips.

Software compatibility with previous AKM electronic compasses enables customers to utilize existing software assets, including the patented DOET algorithm for automatic adjustment of magnetic offset and software for calculations to compensate for tilt. DOE™ has been provided to customers since before the beginning of volume shipment of AKM's first electronic compass product. With the AK8973S, as before, DOE™ enables greatly improved productivity by eliminating the need for adjustment to be performed individually for each handset before shipment, and makes it unnecessary for the consumer to perform adjustments when the ambient magnetic field changes.

Other features include:
  • Digital interface with internal A/D converter compatible with 2-line I2C bus
  • Internal oscillator circuitry – no clock input required
  • Low power consumption – 6.4 mA during sensor operation, 0.8 mA average with measurement at 100 ms intervals
  • Internal temperature sensor with 8-bit digital output
  • Internal EEPROM for recording geomagnetic sensor sensitivity adjustment data, etc.


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