A Three-Terminal n plus -p-n plus Silicon CMOS Light-Emitting Device for the New Fully Integrated Optical-Type Fingerprint Recognition System

A new fully integrated CMOS optical-type fingerprint recognition system with silicon light-emitting devices (LEDs) and photodiodes is proposed. A three-terminal n+-p-n+ silicon CMOS LED is designed and implemented as a key block to replace the bulky optical light source and to realize a slim and integrated fingerprint sensor. The proposed LED employs injection-enhanced silicon in an avalanche mode, where E-field confinement with a wedge shape at a reverse biased p-n+ junction and hot-carrier injection from the adjacent forward biased p-n+ junction are applied to increase the quantum conversion efficiency of the LED. The developed LED was fabricated in a 0.18 mu m CMOS process. It emits 1.27 nW at a 600 nm wavelength consuming 2 mA at a 0.5 V reverse biased voltage and 2 V forward biased voltage. It provides an electrical-to-optical power conversion efficiency of 1.27 x 10(-6).