A system for determining the thickness of an oxide deposit on a conductive surface by applying a voltage across the deposit while measuring the dielectric breakdown of the layer at various points. An electrode mechanism containing a first electrode can be positioned at any point on the surface of the deposit with a high degree of accuracy. A second electrode is defined by a contact which is electrically coupled to the conductive surface. With the first electrode positioned at a point on the deposit, a ramped voltage is applied across the electrodes. An analog dielectric breakdown detection circuit monitors electrode voltage until dielectric breakdown occurs. At the point in time of dielectric breakdown of a deposit, the voltage across the deposit decreases sharply, approaching a short circuit condition. The dielectric breakdown detection circuit, however, maintains the maximum voltage attained, which is represented as the true breakdown voltage for the point being tested. The dielectric breakdown detection circuit comprises comparitor circuitry for determining if the particular point being tested exhibits normal dielectric breakdown characteristics or if the point represents a region of electrical conductivity. The data obtained is then stored and is subsequently processed to obtain an indication of the thickness of the deposit.
James G. Barbee