Local Electrical Conductivity Distribution in Micro-Electronic Components using Conductive AFM Techniques

Thick film resistors for surface mount technology are produced in billions every year and used in almost every electronic device on the planet. The electrical properties on nano-scale are crucial for performance and lifetime of the component and the devices they are used in. Conductive atomic force microscopy techniques can be used to characterize the distribution of electrical conductivity in the resistive layer of the component.

Introduction

Digitalization and miniaturization in the electronic industry are very important trends in the last years and one of the major driving forces for innovation of microelectronic components. Functional structures like dielectric layers or structures that conduct electrical current becoming progressively smaller, still must be capable of withstanding the same or increasing current, potential or power dissipation which increases the demand of detailed knowledge on the internal structure of the used materials. For instance, thickness deviation in dielectric layers in the nanometer range can create weak spots for dielectric break down and thus reduce the reliability of the whole film[1]. Therefore, the distribution of the electrical properties of components is getting more and more importance as concentration of current also means concentration of heat which has a direct impact on the lifetime of electrical components and consequently the devices, the components are used for. One of the most important components are resistors. The most common types of resistors are thin and thick film resistors. The structures consist of an isolating ceramic base material with a resistive layer deposited onto it. Thin and thick film resistors relate to the different layer thickness. While the thin films have a thickness in the order of 0.1 µm, thick film resistors exhibit a resistive layer of up to 100 µm. More than 80% of the market share in analog circuits is covered by thick film resistors. The resistive layer is made from a special paste that consists of a mixture of glassy frit as binder and different conductive oxides of ruthenium, iridium and rhenium. This paste is screen printed onto the ceramic base and fired at temperatures up to 850 °C, so that the glassy frit melts and solidification of the layer takes place. The solid glass forms a protective matrix for the conductive oxides, making this structure durable and stable[2]. The oxides are randomly distributed in the matrix and form a conductive network based on stochastic contact between the oxide particles. This forms the conductive tracks the current flows through during operation.

The aim of the following investigation is to identify the conductive areas within the resistive layer in a thick film resistor and to evaluate the local conductivity on nanometer scale.

References

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