CCD resolutions in camera
Pixel size and the area that they are occupied is the key parameters of a CCD sensor Dynamic Range, the SNR, the Spacial Resolution and the Modulation Transfer Function (with a given optics).

However if pixel size is reduced, sensitivity to light reduced accordingly. So there is a clear tradeoff between spatial resolution and light sensitivity.
So be cautious when read pixel size. Some manufacturers also use the sub-sample pixel but this is done after some process.  

With the CMOS APS technology of 0.3μm (that was some years ago and I don’t know if it is changed), the optimal pixel size is 6.5μm.  That is 35 line pairs per mm Nyqist limit (i.e befor aliasing).
Technologies like 0.17μm may be allow down to about 4μ pixels.

High resolution industry standards -especially for medical applications- is 2.5k x 2.5k and 4k x4k. 

A good list is here