I need 4 accurately matched resistors for my circuit, I heard resistor arrays have better matching quality. but I don't know what parameter to look for in the datasheets. all I see is Tolerance. I don't mind if the resistors have 10% tolerance but if one of them(for example 10k nominal) is 10.91k all others be exactly 10.91k. is there any specific parameter in datasheet of resistor arrays that refers to this kind of accuracy? also, what is the difference between thick film and thin film?
When applied to the resistance, the parameter you want is 'matching'. However, most don't specify that, but only the initial tolerance of the individual resistors.
When applied to the temperature coefficient of resistance (tempco), the parameter you want is 'tracking'. The problem of testing individual resistors for a match in resistance is that the initial tolerance can quickly be overwhelmed by a change in temperature affecting the resistors differently.
Search for 'matched resistor networks'. They will be more expensive than an equivalent bunch of non-matched resistors. You will be unlikely to find low tolerance resistors matched to a high tolerance.
Something like the LT5400 gives an idea of what's possible. It has 4 resistors each to a 0.01% tolerance, 1ppm/C tempco, claims CMRR matching of 0.005% over a wide temperature range, and comes at an eye-watering price. I wonder should you just buy a complete in-amp?