MEMS-fabricated electrical contacts are commonly used in MEMS relays. These electrical contacts can be as simple as two flat surfaces coming into contact [1]. Modeling their contact force/resistance relationship can be difficult because much of the theory on contact resistance was developed for macro-scale contacts [2], and contact properties for MEMS-scale contacts do not always agree with those predicted by this theory [3]. One contribution to this disagreement is that when the dimensions of the contact thickness are on the order of the a-spot dimensions, the spreading resistance is affected [4]. In order to determine the relationship between contact force and resistance for a wide range of parameters, we have developed a two-coupon test system which allows the properties of these contacts to be empirically determined. The design of the two-coupon system allows for the rapid fabrication of multiple contact materials and geometries. The two-coupon system was used to test the contact resistance properties of sputtered and electroplated Au films in thicknesses of 0.1 μm, 0.3 μm, and 0.5 μm. Contact force was measured using a custom flexural force gauge and the 4-point contact resistance was measured using an integrated Kelvin Structure [5]. The results are compared to traditional Holm theory to determine the effects of film thickness on spreading resistance.

The dependence of contact resistance on force between flat, thin-films is thought to be different than that in bulk materials [1]. Multiple mathematical and finite element models have attempted to model this dependence but have been limited in the ranges over which they are valid [1,2]. Experimental results have shown that the contact resistance between flat, thin films is greater than that predicted by Holm theory when the Holm equivalent radius is greater than the film thickness for gold films of thicknesses between 0.1 and 0.5 μm [3]. This paper fits an equation to the FEM results presented in [2] and the experimental results presented in [3]. New experimental results between gold sphere-on-flat contacts of film thickness 1 μm and contact radii of 20 and 40 μm are presented and the results are compared to those predicted by the equation fitted to the previous FEM and experimental flat-on-flat contact results. As with the thin film flat-on-flat contacts, the thin film sphere-onflat contacts also have a contact resistance higher than that predicted by Holm in the region where the Holm equivalent radius is greater than the film thickness. Also examined is the transition in the force v. contact resistance relationship at the point where the Hertz radius of contact becomes greater than the Holm equivalent radius of contact.

The terminal and repeater equipments described are development prototype models for use on the British Post Office trunk TE0 mode waveguide field trials programme over a 15 km route in East Anglia. The equipment is entirely solid state and, as far as practical, has been designed to be electrically and physically representative of future service equipment.Whilst the band branching networks have been designed from the outset to encompass the usable bandwidth of a 50 mm diameter circular waveguide, the existing transmitter, receiver and channelling units are intended only for operation up to 50 GHz. QPSK modulation techniques are adopted to provide 16, both-way, channels of 500 Mbit/s capacity within allocated total bandwidths of 0.5 GHz over the frequency range 32-50 GHz. Modulation is implemented at an i.f. of 1.25 GHz; likewise demodulation, which is accomplished by a composite loop configuration affording simultaneous recovery of carrier information and coherent detection, prior to regeneration of the two separate 250 Mbit/s binary data streams.The overall performance of the terminal and repeater equipment is discussed, together with the salient design features of the transmitter -receiver equipment. System AspectsIt is required that the current term6nal and repeater equipment should operate at an error rate of at least 1 x 10 when the circular waveguide transmission path has a loss value of 62 dB at 32 GHz, falling to 54 dB at 50 GHz. This performance level can be achieved with various equipment configurations and designs, but, irrespective of the particular arrangement selected, the optimum performance in terms of operating margin and reliability, is inevitably conducive upon a low loss frequency division multiplexing network to connect the numerous transmitter and receiver units to the circular waveguide transmission path.To comply with the above, a centre-excited band branching unit and comnutating filter channelling network have been selected.