Micron moves to Mpixels
The MT9M011 uses a new sensor architecture and a next generation process to achieve best-in-class performance in key areas such as low-light sensitivity, signal-to-noise and ultra low power consumption.
Micron used its 150nm low leakage DRAM process. The company sees advantages in using DRAM processes over logic for this application. DRAMs and image sensors both use capacitance (electron storage) in their operation. By contrast, logic processes seek to minimise circuit capacitances.
Although the MT9M011 is the first mobile sensor to be based on the new architecture, many of Micron's future sensors will take advantage of the technology.
Micron's vice-president of Imaging Bob Gove reports "We achieve a lower dark current, low lag, higher quantum efficiency and higher sensitivity, thus providing a sensor that matches state-of-the-art CCDs yet requires less power than competing 1.3Mpixel sensors. We believe the process and architectural improvements incorporated into this product make it a best-in-class sensor, enabling our customers to improve the imaging performance of their mobile devices to levels beyond traditional digital still camera (DCS) solutions."
Features include programmable gain and exposure control and black-level calibration, a frame rate of up to 30fps at 50mW along with image decimation to any size while sustaining smooth, continuous motion.
The company has also produced two new VGA sensors (640x480pixels) – one a stand-alone device and the other a system-on-chip. The SoC includes a programmable image processor to perform functions such as auto-exposure, white balance and gamma colour correction. These VGA devices are produced at 180nm.
Micron’s CMOS imaging technology is called DigitalClarity. The process aims at a low dark current (15electrons/sec at 25degreesC), reduced cross-talk and lower temporal noise (less than 10electrons). Reduced cross-talk is achieved through a lower pixel height and a high quantum efficiency of 44%. The lower pixel height means that light focused by the microlens above the pixel is less likely to bleed through to an adjacent pixel. Another technical factor that improves performance is the company’s use of four transistors rather than three to make up a pixel.
Micron is gradually bringing all its CMOS imager production in-house. Two years ago, all production was sent out to foundries. In the past year, some imagers have been produced at Micron’s facilities.
The CMOS imaging capability came into Micron with the acquisition of Californian company Photobit. Manufacturing is carried out at Micron’s base in Boise, Idaho, using its DRAM process. Design activities cover the European, USA and Asian markets. In Oslo, Norway, design activities cover the mobile handset and medical market applications. Bracknell, UK, also produces designs for mobile handsets and DSCs.
The corporate business strategy for image sensing covers the mobile, consumer and emerging markets. One emerging application could be to gauge the necessary, safe force needed from an airbag deployment. Children can be injured by excessive force from an airbag designed for adults.
