What is the relationship between sheet resistance and resistivity
Many people asked: what do you mean by writing “ohm/sq” or “Ω/□” for the sheet resistance of ITO coated glass, FTO coated glass…
For the meanings of ohm/sq, maybe we can know about it from the relationship between sheet resistance R□ and resistivity ρ.
Usually, we use sheet resistance to measure the conductive properties of the conductive layer of ITO coated glass, FTO coated glass, AZO coated glass, et al.
For the conductive layer with length L1, width L2, thickness d, the resistance between the cross sections (the left side and the right side) is R = ρ L1/(dL2)
For a certain kind of the conductive layer material with thickness d, we can consider that it with a certain resistivity value ρ, When L1= L2, no matter what is the size of the conductive layer, such as L1=100mm, L2=100mm or L1=1m, L2=1m, the value of R will remain the same, so we call it sheet resistance R□ .
For example, for ITO Glass with ITO layer resistivity ρ = 5×10-4Ω•cm, ITO layer thickness d=500 Å, its sheet resistance is
R□ = ρ/d = 5×10-4Ω•cm / 500×10-8cm = 100 Ω/□ = 100 ohm/sq