Hat-resistor

The base of a hat resistor can be considered as a rectangular resistor. The hat has minor influence on the untrimmed resistor. Therefore, the base resistor is designed according to the required start value of the trim range. The maximum resistance value of the hat is achieved when the resistor is cut in two halves (Equation 9.7) ... 

Hat resistors are not useful for radio-frequency designs because of selfresonance effects. In the process chain, thick-film resistors are always fired in the last 850°C sintering cycle to avoid resistance changes due to refirings. 

Ctirrent line distribution (a) untrimmed resistor (homogeneous ), (bl) Y-cut (white circle inhomogeneous, high density), (b2) L-cut (white circle fewer inhomogeneous, lower density), (c) hat resistor (white circle nearly homogeneous ). 

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