Electronic Imaging: Digital Pixel Sensors and Systems

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Microsystems exploit micro-level technology to deliver system-level performance. Digital cameras are a good example of this concept, as tiny circuits in each pixel of an image sensor, and their support systems, are responsible for photographic capabilities. Digital cameras also provide a motivation for this research program. Because image sensors add billions of dollars in value to consumer, defence, industrial, and medical applications, research progress in pixel design could lead to a multi-million dollar impact. CCD and CMOS image sensors have enjoyed tremendous successes. Boyle and Smith shared a Nobel Prize for inventing the CCD technology and NASA invented the CMOS active pixel sensor (APS) technology that is now in every mobile phone. However, the dark limit with such image sensors is orders of magnitude worse than with the colour vision of the human retina, which is why digital cameras may need a flash when human eyes see clearly without one. If not impossible, it is very difficult to realize low dark limit with CCD or CMOS APS technology without sacrificing dynamic range, image quality, and/or frame rate. Consequently, a long-term objective of this research program is to break these barriers with new technology. Conventional CCD and CMOS image sensors use analog pixels. Because digital technology is robust to the noise and distortion that is inherent to analog technology, digital pixels are game changers. The main advantage of analog pixels is they are smaller but wider trends suggest this issue will become less significant. Vertically integrated CMOS technology, which is explored through an NSERC Partnership Grant, enables 3D stacking of two or more semiconductor tiers to achieve a more complex integrated circuit in the same area. By funding this Discovery Grant, NSERC supports the creativity and innovation that is at the heart of this research program on electronic imaging. In the short term, the spatial and bit resolution, power consumption, and colour matching of novel digital pixel sensor (DPS) technology will be improved, while training highly qualified personnel to design, build, and test microsystems of significant complexity, i.e., digital cameras.