| dc.description.abstract | In this study, low voltage operation and high photoelectric conversion capability of optical sensors, Current Active Optical Sensor (CAOS) and Voltage Active Optical Sensor (VAOS), were proposed and realized using a standard 0.35 μm Complementary Metal Oxide Semiconductor (CMOS) process technology .
In the design concept for CAOS, that is integrated conventional photodiode with standard Negative Metal Oxide Semiconductor (NMOS), gate bias voltage of NMOS can be reduced to maintain the amplification capability of NMOS by the existence of photo generation holes accumulated within the gate region of NMOS. The VAOS was consisted of a standard NMOS for enlarging photocurrent and a novel photodetector which can be realized by a modified Positive Metal Oxide Semiconductor (PMOS) for providing photo-voltage output above the gate electrode of NMOS to reduce the gate bias voltage. Therefore, the CMOS structure benefits design of VAOS. CAOS and VAOS not only provide low bias operation potentially but also differ from the conventional optical sensor on the photocurrent amplification for enhance photoelectric conversion further. Additionally, CAOS and VAOS own the pixel selection function intrinsically through the n-well bias of PMOS and drain voltage of NMOS as these devices are employed in the application of image sensing array.
Experimental results show that the output of the design elements in addition to the advantages of direct current amplification effect (can be increased by at least a hundred times), but also effectively increase the Photoresponsivity. The component designs can not only improve the photoelectric conversion efficiency, in which an operating voltage but also down to 0.25 V, the work is far less than the general bias 1 V, which is very suitable for handheld mobile products. And the photo-voltage was also measured in the novel optical sensor of VAOS to confirm the mechanism about converting photocurrent into photo-voltage without any resistance loading and external circuit like trans-impedance amplifier (TIA). At the same time, the measured photo-voltage provides strong evidence for low bias voltage operation in CAOS and VAOS benefiting the immunity of gate leakage and the reduction of power consumption.
CAOS and VAOS due to the unique structure of the more traditional elements can be combined area of small design , and have excellent optical characteristics and process steps without changing the standard design, in addition to having the advantages of low-cost mass production, but also make this paper design elements can be immediately supported with CMOS circuits smooth integration of peripheral and actually used in many applications need to detect the light intensity. | en_US |