High Value Resistors with specified properties at small sizes. To analyze very low electronic signals, resistors with extremely high values are required. Microhm has succeeded in producing such components with stability better than the best measuring devices available on the market. It is possible to achieve also at very small sizes like 0402 (1×0.5mm) resistance values close to the range of insulators with specified properties for temperature and voltage dependency.
 
Resistor pastes for the high value range are much more sensitive to the firing conditions than the materials for the standard range. This is the main reason, that most of the chip resistor manufacturers’ don´t offer values much higher than 100 Megaohm in their program. It is an additional problem that at values in the Gigaohm range the measuring techniques from the standard resistance range are not more working satisfactory enough.

Thick film technology has proved to be the best technology to produce high resistance values with relatively good properties, as well as small sizes. For this technology thixotropic pastes are used, consisting of a mixture of metal/metal-oxide particles with glass and organic binders. The mixture is screen-printed on structured Aluminum-oxide ceramics and fired in the range of 850°C. During this firing process the printed material is transformed to a glassy structure with an electrical conductivity depending mainly on the amount and composition of the metal/metal-oxide particles. The electronic conduction mechanism in such structures is a combination of metallic and semiconductor conductivity.

 
Resistors higher than 100Megaohm are available as very small chip resistors like size 0402 (1.0×0.5 mm) as well as in big sizes with axial or radial lead wires. Because the reason that properties of resistors are better at low sheet resistances (resistance of a square area), the resistor design should use a very long and very small structure. With the big sizes of leaded resistors it is possible to get a length-to-width relation of more than 1000, so a very low resistive paste can be used. With the much smaller chip resistors it is only possible with the size 1206  to get a meander-structure with a length-to-width-relation higher than 10.