Canon Patent Application: Another stacked sensor patent application

After being quiet on the patent application front for a while, stacked sensors have made a comeback this week.

It's for certain that Canon is looking at stacked sensors, and I wouldn't be surprised if they come out with a stacked sensor sooner than later.

What does a stacked sensor allow Canon to do? You can greatly increase the efficiency of the sensor because the electronics are on the second substrate away from the light detection substrate.  The light detection substrate becomes very efficient because it no longer has to contain both the electronics and the photodetection circuits and thus is made much more simple.  Expect a dynamic range increase as well as a decrease in overall noise with such a sensor.  A stacked sensor allows Canon to also tailor the sensor for high-speed shooting, offloading AF operations, and a myriad of other features.  It opens an entire door do different processing Canon could do right on the sensor chip itself.

The biggest downside is expense, especially when we discuss full frame sensors.  Not only do you have to create one full frame substrate as you do now for full frame sensors, but you have to create two or more and put them together.  This increases the cost of the sensor by double or more.

Canon states in the application;

For solid-state image pickup devices, a configuration is known in which a photoelectric conversion unit and a peripheral circuit unit separately formed on different substrates are electrically connected through a micro bump. Patent Literature 1 discloses the following configuration. A photoelectric conversion unit is arranged on a first semiconductor substrate, whereas a peripheral circuit for reading out a signal from the photoelectric conversion unit, such as a vertical scanning unit and a horizontal scanning unit, is arranged on a second semiconductor substrate. Leakage current is less problematic for transistors arranged on the second semiconductor substrate than for a pixel unit. Accordingly, gate insulating films of the downsized transistors on the second semiconductor substrate are thinned with a CMOS process. 

As with all the patent applications, they simply show areas of Canon research and development and do not necessarily mean it will get turned into a product.  We do feel strongly that stacked sensors will be included in Canon cameras in the future.

US Patent Application 20190028663