Optical sensing, and the integration of sensors and electronics into Sensor on a Chip and Sensor on a Package systems are an approach to the creation of miniaturized, portable, customizable, low cost sensor systems for rapid health diagnostics, medical research, environmental monitoring, and security monitoring. To integrate optical sensing systems that are autonomous, it is essential to integrate the sensor, light source, and light detection into a single substrate or chip. The integration of this optical system with signal control and processing electronics enable discrimination with individually customized sensors in sensor arrays, and high sensitivity levels. Thin film optoelectronic active device integration with planar optical passive devices is a heterogeneous integration method for fabricating planar lightwave integrated circuits at the chip level and planar lightwave integrated systems at the substrate and package level.
Arrays of embedded bipolar junction transistor (BJT) photo detectors (PD) and a parallel mixed-signal processing system were fabricated as a silicon complementary metal oxide semiconductor (Si-CMOS) circuit for the integration optical sensors on the surface of the chip. The circuit was fabricated with AMI 1.5um n-well CMOS process and the embedded PNP BJT PD has a pixel size of 8um by 8um. BJT PD was chosen to take advantage of its higher gain amplification of photo current than that of PiN type detectors since the target application is a low-speed and high-sensitivity sensor. The photo current generated by BJT PD is manipulated by mixed-signal processing system, which consists of parallel first order low-pass delta-sigma oversampling analog-to-digital converters (ADC). There are 8 parallel ADCs on the chip and a group of 8 BJT PDs are selected with CMOS switches. An array of PD is composed of three or six groups of PDs depending on the number of rows.