a) During your KB5006 practical session Characterisation", you have shown how to characterize the sheet resistance of a few pieces of carbon coated paper which were cut from the same

original sheet:"Surface and Thin Film Coating A large plain carbon paper A few "carbon paper strips" with rectangular and serpentine shapes – squares marked on the backside of them. 1. Performing 4-point probe measurement on the large plain carbon paper to obtain sheet resistance values; 2. Using an electrical multi-meter to measure the resistance between two ends of each "carbon paper strips", before working out "number of squares", before calculating the sheet resistance values. The results from Method 1 are usually different to Method 2, discuss THREE potential reasons for this difference.(12 marks) b) In the above Question 3b, the Aluminium (Al) rectangular electrode coated the middle area of a square Glass (SIO2) substrate (Figure 1_Q3b, dark-field is aluminium material, white-field is exposed substrate). Sketch the photolithography mask required to pattern the above shape, using the following process: i) Assuming positive photo resist will be used, combined with lift-off process to form the shape. Please indicate which part of the mask is the light blocking chrome, and which part is the transparent glass. ii) Sketch the step-by-step process flow for the process described in (4b) –assuming positive photo resist and lift-off process, starting with a bare glass(SiO2) substrate, in standard cross-sectional view.