Investigation of Conduction Mechanism in Polymer Thick Film Resistors Trimmed by Multiple High Voltage Impulse Method
Busi Rambabu, B. Poornaiah, KV Subrahmanium and Y. Srinivasa Rao
The effect of high voltage impulses on the resistance of polymer thick film resistors is studied. The High resistivity materials have resistances in the range of Mega ohms and low resistivity materials have resistances in the range of Kilo ohms. It is found that the resistance decreases in the case of higher resistivity materials and the resistance increases in the case of lower resistivity materials with both the amplitude and duration of the high voltage impulses and with number of impulses. The change in resistance is attributed to the local heating produced in the resistive films when high voltage impulses are applied to polymer thick film resistors. A mechanism has been proposed through which the percentage change in resistance can be estimated in terms of the number of impulses, the duration of the impulses and the length of the impulses. Based on these investigations, we suggest a downward / upward trimming method for polymer thick film resistors through the application of high voltage impulses. This method of trimming is a clean and simple process. It is found that there is a considerable improvement in TCR and current noise of the trimmed resistors with high resistivity and a little degradation in TCR and current noise of the trimmed resistors with lower resistivity. These improvements are attributed to increase in the conductance paths in the trimmed resistors with higher resistivity and breaking of the conductive paths in the trimmed resistors with lower resistivity.
Keywords: Polymer resistors, Thick Films, Trimming, High Voltage Impulses