A comparison of pad metallization in miniaturized microfabricated silicon microcantilever-based wafer probes for low contact force low skate on-wafer measurements

Miniaturized, microfabricated microelectromechanical systems (MEMS)-based wafer probes are used here to evaluate different contact pad metallization at low tip forces (<mN) and low skate on the on-wafer pads. The target application is low force RF probes for on-wafer measurements which cause minimal damage to both probes and pads. Low force enables the use of softer, more conductive metallisation. We have studied four different thin film contact pad metals based on their thin film electrical resistivity and micro-hardness: gold, nickel, molybdenum, and chromium. The contact pads sizes were micrometre (1.9×1.9 µm2) and sub-micrometre (0.6×0.6 µm2). The contact resistance of Au-Au, Ni-Au, Mo-Au, and Cr-Au was measured as a function of tip deflection. The tip force (loading) of the contacts was evaluated from the deflection of the cantilever. It was observed that an overtravel of 300 nm resulting in a contact force of ~400 µN was sufficient to achieve a contact resistance <1 Ω for a sub-micrometre gold contact pad. Our results are compared with an analytical model of contact resistance in loaded metal-metal contacts—a reasonable fit was found. A larger contact resistance was observed for the other metals—but their hardness may be advantageous when probing other materials. Using a combination of a rigid silicon cantilever (>1000 Nm-1) and small contact pads enabled us to show that it is the length of the pad (in contact with the surface) which determines the contact resistivity rather than the total contact pad area.

Formation of the Energy Properties of the Surface of Clay Particles Modified by High Pressure

The article considers the issues of changing the energy activity of the surface of clay particles modified by pressure up to 800 MPa. The energy properties of the surface were evaluated by measuring the adhesion force between the surface of clay samples and the silicon cantilever of an atomic force microscope. It has been proved that when clay soils are modified by stress pressure, the adhesion force changes in different directions in clays with different mineral composition. So, in kaolin clay, with an increase in pressure from 25 to 800 MPa, the adhesion force increases, respectively, from 0.25 to 0.78 nN. In clays of montmorillonite composition, an increase in pressure to 150 MPa leads to an increase in the adhesive interaction, and a further increase in the load to 800 MPa leads to its decrease.