Investigation of layers' sheet resistance using the spread of mobile charge carriers

In this work, the insulating layer with a weakly conductive layer on its surface is charged with a needle electrode. The quantities that are measured and calculated are the transients of charging current and transferred charge. In addition, we calculate charge distribution in the weakly conductive layer at various moments of time, and potential kinetics. By comparing the calculation results with measurement data, it is possible to determine sheet resistance of the investigated weakly conductive layer. This sheet resistance can be also determined experimentally: during charging of the weakly conductive layer (deposited onto the insulating layer), the charging current and the deposited charge increase with decreasing sheet resistance of the weakly conductive material, hence its sheet resistance can be related to the measured charging current or to the deposited charge. The proposed method can be applied for measuring sheet resistances from 10+8 Ω/sq to 10+12 Ω/sq, and those measurements can be done in a second. It is also possible to use the contact-free method proposed in this work to measure various properties of the medium related to the material sheet resistance, e. g. relative air humidity, illumination, sample thickness, intensity of ionizing radiation, etc. This method is also suitable for measuring sheet resistance of island-type (discontinuous) layers, which is difficult to measure using usual methods. Results of this work make it possible to determine potential of a two-layer system consisting of a charged low-conductance layer and an insulator, as well as the radius of an electrographically developed area, which is important, for example, when the image is created using a needle electrode.

► Sheet resistance measurement method is proposed.
► This method relies on discharge in air from a needle top.
► Deposited charge spreads in weakly conductive layer which is placed upon isolator.
► Sheet resistance obtained on comparison current measurements and calculations.
►  Relative humidity, illumination, intensity of radiation also can be measured.