And, once again, these Nikon naysayers are very quickly forgetting that the Nikon orders pretty funded for many many years the development of the great sensor technology we see today in APS-C and FX bodies. I am fully aware that mobile phones were another key funding stream, but there is a difference between a mobile phone sensor and one for a DSLR.
Sorry for the late reply to this comment. I just wanted to clarify a point, there is no difference between making a mobile phone sensor or a full-frame one, it is exactly the same process. That it is due to the CMOS technology, the same one used to make nearly any chip inside any device, from cameras, to computers, to microwaves... well, there is one key difference, it is much cheaper to try new things in smaller sensors than big ones.
All CMOS technology it is build nowadays in wafers of pure Silicon (as pure as possible, any impurities can make a batch of sensors just a paperweight) of 300mm of diameter (some years ago they were using 200mm, and there was speculation of moving to 400mm for some years, but never happen). Each of these wafers can be used to build several sensors (or processors, or RAM memory...), if they chip chip is small, you can put more chips in the same wafer. This is done by a series of physical and chemical process... very precise one, since we are talking of few nanometres here for the precision of the process. Doing a quick search in Google, you can see here a wafer with several 35mm sensor chips:
https://www.google.com/search?q=sony+sensor+wafer&rlz=1C1GGRV_esES752__752&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjRm5_8xf7VAhUQsBQKHQhBCpYQ_AUICygC&biw=1920&bih=990#imgrc=POlZJr58ajWwhM:
Any impurity in the silicon in one of those chips, sensor to the waste, any error in the physical or chemical process for just impurity in the air, or the chemical, or whatever... chip to the waste... It is expected that not all the chips in a wafer work... the chip manufactures use what they call a yield rate, number of good chips / number of total chips in the wafer. They try to achive as close to 1 as possible. At the beginning of any technology introduction (new physical/chemical process... etc...) or new chip design, the yield rate tends to be low, it gets higher with the pass of time.
A way that the manufacturers have to get higher yield rates while trying new things, it is to do it with smaller chips, with smaller chips you have more chips per wafer, so even if 40% of the wafer produces bad chips, you still are getting enough chips to sell and compensate the costs... with bigger chips, maybe the majority are bad... and the good chips will be quite expensive. After fine tunning the process with smaller chips, you can feel confidente that you can scale up the technology to bigger chips.
New technologies that are comming to sensors in the lastest years, like Aptina-like amplifiers, BSI (both in the 850, A7r II), or stacked sensor (A9), first released in smartphones.
Here you have a nice paper of evolution of sensor technology:
https://semiengineering.com/cmos-image-sensors-cis-past-present-future/