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Cellular telephones could be more secure in the future now that engineers at Fujitsu have completed development of a compact fingerprint sensor designed for use with handsets.

With growing use of services such as electric commerce and e-government, the company expects the demand for an authentication function on cell phones and other mobile devices to increase. But until now, fingerprint sensor devices have been too large and consumed too much power to be integrated into mobile devices, and there are issues of high cost and questionable reliability, says Chiaki Kuwahara, a spokesperson for Fujitsu.

Fujitsu engineers chose to use a capacitance-based sensor system, rejecting thermal and optical scanners, the other two main types of sensor. Those types of sensor are prone to incorrect readings because of interference from external sources of heat and light respectively.

Down to Size

The new capacitance-based scanner has a sensor array which is able to detect ridges and valleys in a fingerprint by measuring the difference in capacitance across the array when a finger is brought into contact with it, Kuwahara says. However, such sensors are usually too large to use in a cell phone and the main challenge has been making them smaller, Kuwahara says.

Fujitsu solved the problem by switching from a sensor that would scan the whole finger in one pass to a sensor over which the finger needs to be traced. By doing this, the sensor can be made small enough to fit into a cell phone.

"By adopting the tracing style, the size is reduced and so is the production cost," Kuwahara says.

The MBF 300 sensor has a surface area of 60.2 square millimeters, which is 10 times smaller than the existing Fujitsu sensor, and consumes less than 10 milliamperes, according to a company statement.

Sample shipments will start in April to customers worldwide at a unit price of $30 and the device will be unveiled at the Embedded Systems Conference in San Francisco between March 13 and 16, and CTIA Wireless 2002 in Orlando between March 18 and 20, the statement says.

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