There is a growing number of videos showing how image sensors can be damaged by concert lasers:
One would expect the excessive energy to burn color filter first, while the underneath layers be able to withstand quite a significant heating. But it looks like the a whole column and/or row stops working, pointing to the electrical nature of the damage. The laser is green and should not cause the oxide charge accumulation in MOSFETs and STI. So, what can be the mechanism of such a damage?
My first guess was that a large photocurrent on the transistor diffusions in the array exceeds elecromigration limits blows some metal or via. Most CIS processes offer about 0.5mA per um of metal width for the array metals. Then, assuming the metal width in RED and Canon large sensors is 0.2um, the maximum allowed current should of order of 100uA. To get to this current, the photon flux should be about 2.0e15 ph/s per pixel. Seems way too much for these concert lasers.
And even if we managed to reach the electromigration limit of 100uA, the metal is supposed to last a long time at that current, such as 10,000 hours or more, assuming the sensor is colder than 70-80C. So, my next guess was that these large sensors get much hotter in video mode. If my memory serves me, the electromigration increases 3 times per 15C of temperature rise. Still, this does not sound enough to fit to the electromigration theory.
So, the next guess was that the laser heats the pixel locally, to 200-250C or so and then the electromigration limit gets exceeded. Currently, this seems to be my best guess. If true, the workaround should be to put the current limiters at each column and row, and also to the pixel VDD lines.
Anyone has a better explanation for the damage?
Update: Yet another Canon video of laser show published at Youtube on June 21, 2013, showing a similar column and row damage.
One would expect the excessive energy to burn color filter first, while the underneath layers be able to withstand quite a significant heating. But it looks like the a whole column and/or row stops working, pointing to the electrical nature of the damage. The laser is green and should not cause the oxide charge accumulation in MOSFETs and STI. So, what can be the mechanism of such a damage?
My first guess was that a large photocurrent on the transistor diffusions in the array exceeds elecromigration limits blows some metal or via. Most CIS processes offer about 0.5mA per um of metal width for the array metals. Then, assuming the metal width in RED and Canon large sensors is 0.2um, the maximum allowed current should of order of 100uA. To get to this current, the photon flux should be about 2.0e15 ph/s per pixel. Seems way too much for these concert lasers.
And even if we managed to reach the electromigration limit of 100uA, the metal is supposed to last a long time at that current, such as 10,000 hours or more, assuming the sensor is colder than 70-80C. So, my next guess was that these large sensors get much hotter in video mode. If my memory serves me, the electromigration increases 3 times per 15C of temperature rise. Still, this does not sound enough to fit to the electromigration theory.
So, the next guess was that the laser heats the pixel locally, to 200-250C or so and then the electromigration limit gets exceeded. Currently, this seems to be my best guess. If true, the workaround should be to put the current limiters at each column and row, and also to the pixel VDD lines.
Anyone has a better explanation for the damage?
Update: Yet another Canon video of laser show published at Youtube on June 21, 2013, showing a similar column and row damage.
