Two compact modules from Lite-on Semiconductor, the FLB8100 (for wireless handsets and PDAs) and the FLB8200 (for notebook computers), are optical fingerprint sensors that will provide an additional layer of security for those devices. Another series, the FLB6000, which includes the FLB6100, presently performs the same function for pen drives and computer mice.
These fingerprint sensor modules leverage the development of Lite-on’s contact image sensor (CIS) technology and combine a CMOS image sensor with onboard data processing to reconstruct the fingerprint of a fingertip moving over its narrow rectangular optical sensor window of 9.34 mm x 1.5 mm. The sensor captures images of 500 dpi. at swipe speeds up to 20 cm/s. Both FLB8000 parts have recognition times of less than 1 s.
In addition to functioning as a fingerprint sensor, the module can also function as a virtual joystick. Finger motions and taps can be detected and translated into equivalent joystick movements to navigate through wireless handset menus.
According to R.J. Hong, president of Lite-on’s Image Business Group, these first modules feature a straightforward design in which an infrared LED transmits light onto the surface of the finger. Due to light scattering within the tissue of the finger and reflection effects at the sensor window, the epidermal ridges of the finger create an optical contrast pattern of the fingerprint that can be detected by the module’s CMOS image sensor.
The electrical isolation made possible with the optical technology in the FLB8000 series provides ±15 kV ESD immunity. The wavelength of the radiated light is in the infrared region. This wavelength is highly compatible with human skin and allows interference from ambient light to be blocked with an optical filter.
The FLB8100 operates at 1.8 V and consumes less than 18 mA when operating and less than 50 μA when in standby. For the FLB8200 these figures are 3.3 V, 45 mA and 200 μA, respectively. Both parts are available in LGA or Flex cable packages. The modules also use chip-on-board packaging technology.
The modules already have features to enhance security, such as the option that requires two different fingers to be swiped in rapid succession. Future versions of this product might include advanced features, such as a way to verify that an image has been created by living tissue by checking for a pulse or correct body temperature.
Lite-on is still approaching potential OEMs about these fingerprint sensors. Because wireless service providers often provide replacement phones to their subscribers on a regular basis, they also provide a direct path for new technology to reach consumers. The enthusiasm with which fingerprint sensors are received by users of wireless handsets will probably influence whether or not the technology is adopted for other applications. By the same token, designers who first introduce fingerprint sensors into wireless handsets may actually foster widespread acceptance of the technology.