[IEDM 2017] Sony develops smartphone iris recognition CMOS sensor

Infrared, which is invisible to the human eye, has been introduced for biometric authentication in mobile devices

For iris recognition and face recognition in smartphones (smartphones) and media tablets, and for whole-body motion recognition in games , often using infrared rays. The object is irradiated with infrared rays and the reflected light is detected by an image sensor. Infrared is used because it is a wavelength that is not detectable by human vision (and is not annoying to users).

　However, silicon CMOS image sensors, which mainly detect visible light, are not very sensitive to infrared rays. For this reason, in order to add an infrared recognition function to the CMOS image sensor, a high-output infrared light emitting diode (IR LED) is adopted, or a CMOS image sensor with a thick silicon light absorption layer is used to increase infrared sensitivity. There is a need for countermeasures such as the use of sensors.

　These measures lead to an increase in parts costs. For example, it is only recently that small, high-output infrared LEDs that can be installed in smartphones have been commercialized. Naturally, the price rises compared to standard infrared LEDs. In addition, a CMOS image sensor with a thick silicon light absorption layer requires a long distance for implanting impurity ions in the manufacturing process, which makes the ion implanter, which is a manufacturing device, expensive. Therefore, manufacturing costs increase.

If the infrared sensitivity can be improved while maintaining the same thickness of the silicon light absorption layer as the conventional CMOS image sensor, the output required for the infrared LED will be reduced, and the manufacturing process of the CMOS image sensor will reduce the conventional The ion implanter can be used as it is. In addition to reducing the component cost of the infrared LED, it is possible to avoid increasing the manufacturing cost of the CMOS image sensor.

Sony Semiconductor Solutions (hereafter referred to as Sony), a major vendor of CMOS image sensors, has developed such a CMOS image sensor, and at the international academic conference IEDM 2017 held in San Francisco, USA in December, the technical overview was presented. (Lecture No. 16.4).