Sony back-illuminated CMOS image sensor with global shutter function

Sony has developed a 1.46 effective megapixel back-illuminated CMOS image sensor equipped with a Global Shutter function.

Sony Corporation press release

Sony develops back-illuminated CMOS image sensor with pixel-to-parallel A/D converter that enables global shutter function*1

Tokyo, Japan—Sony Corporation today announced that it has developed a 1.46 effective megapixel back-illuminated CMOS image sensor equipped with a Global Shutter function*1. Newly developed pixel-parallel analog-to-digital converters provide the function of instantly converting the analog signal of all pixels, exposed simultaneously, into a digital signal in parallel. This new technology was announced at the International Solid-State Circuits Conference (ISSCC) on February 11, 2018 in San Francisco, USA.

CMOS image sensors using the conventional column A/D conversion method*2 read analog signals photoelectrically converted from pixels line by line, resulting in image distortion (focal plane distortion) caused by time lag due to line-by-line reading.

The new Sony sensor comes with new compact low current A/D converters positioned below each pixel. These A/D converters instantaneously convert the analog signal of all the pixels exposed simultaneously in parallel into a digital signal to store it temporarily in a digital memory. This architecture eliminates focal plane distortion due to readout time lag, enabling a Global Shutter function to be provided.*1an industry first for a high-sensitivity back-illuminated CMOS sensor with parallel pixel A/D converter of more than one megapixel*3.

The inclusion of nearly 1,000 times more A/D converters compared to the traditional column A/D conversion method*2 means an increase in current demand. Sony has solved this problem by developing a compact 14-bit A/D converter that offers the best performance in the industry.*4 in low current operation.

The A/D converter and digital memory spaces are secured in a stacked configuration with these elements integrated into the lower die. The connection between each pixel on the top chip uses a Cu-Cu (copper-copper) connection*5a technology that Sony put into mass production as a world premiere in January 2016.

Additionally, a newly developed data transfer mechanism is implemented in the sensor to enable high-speed massively parallel read data required for the A/D conversion process.

  • *1:A feature that mitigates image distortion (focal plane distortion) typical of CMOS image sensors that read pixel signals line by line.
  • *2:A method where the A/D converter is provided for each vertical row of pixels in a parallel configuration.
  • *3:From the announcement of February 13, 2018.
  • *4:At the time of announcement on February 13, 2018. FoM (Figure of Merit): 0.24e-・nJ/step. (power consumption x noise) / {no. pixels x frame rate x 2 ^(ADC resolution)}.
  • *5:Technology that provides electrical continuity through Cu (copper) pads connected when stacking the back-illuminated CMOS image sensor section (upper chip) and logic circuitry (lower chip). Compared to through-silicon via (TSV) wiring, where the connection is made by penetrating electrodes around the circumference of the pixel area, this method gives more design freedom, improves productivity, allows for a more compact size and increases performance. Sony announced this technology in December 2016 at the International Electron Devices Meeting (IEDM) in San Francisco.

main Features

Global shutter function*1 obtained in a high-sensitivity back-illuminated CMOS image sensor using the following key technologies:

  1. Compact, low-current pixel-to-parallel A/D converter
    To reduce power consumption, the new converter uses comparators that operate with sub-threshold currents, resulting in the best efficiency in the industry.*4, compact, low-current 14-bit A/D converter. This solves the problem of increased current demand due to the inclusion of nearly 1,000 times more A/D converters compared to the traditional column A/D conversion method.*2.
  2. Cu-Cu (copper-copper) connection*5
    To achieve parallel A/D conversion for all pixels, Sony has developed a technology that allows the inclusion of approximately three million Cu-Cu (copper-copper) connections*5 in a single sensor. The Cu-Cu connection provides electrical continuity between the pixel and the logic substrate, while securing space to implement up to 1.46 million A/D converters, the same number as effective megapixels, as well than digital memory.
  3. High-speed data transfer construction
    Sony has developed a new read circuit to support the massively parallel digital signal transfer required in the A/D conversion process using 1.46 million A/D converters, allowing read and write all high-speed pixel signals.

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Michael C. Garrison