The objective of the microsystems work within the project, led by MISEC at Heriot-Watt University, is to issue a fully integrated packaging solution, that permits the static and active alignment of a microlens array placed on top of a micro-UV-LED array. The packaging structure is processed by UV-LIGA, using the photoresist SU8.

The microlens array rests on four posts on top of the micro-UV-LED array, in order to reduce the contact area and hence reducing the probability of vertical misalignment. The cavities, where the posts fit in, are situated on the micro-UV-LED array structure. Each of these cavities features two electrodes made of titanium. By electroplating the electrodes with a certain thickness, the distance between microlens and micro-LEDs can be fine adjusted and possible tilting due to uneven post heights, compensated.

This concept is, with minimal modification, transferred into a microactuator, which enables the movement of the microlens array in the vertical direction. For that purpose a special electrostatic actuation method is applied, which features a floating-electrode on the microlens-array, that does not need to be connected to any potential. Therefore, no electrical wire is attached to the microlens array which would disturb its free movement. The posts and holes then serve as a guidance to limit the lateral movement.

A further possibility is the lateral actuation using magnetic force simultaneously with the electrostatic vertical movement. The device featuring the magnetic flux necessary for the actuation is either MEMS based or a macrostructure which can be temporarily or permanently attached to the micro-UV-LED array chip.

Furthermore a method to manufacture two-dimensional bundles of single mode optical fibres of highly accurate pitch has been developed. Electrostatic actuation of metal-clad optical fibres is performed to align the fibres with sub-micron translational alignment accuracy. The manufacturing and alignment performance characteristics of the fibre holder have been fully investigated. The sensitivity of the active alignment procedure is between 0.25 and 1 micrometer per volt depending on the clamping distance. The combination of the electrostatic actuation with the optical monitoring of the fibre pitch in a closed-loop feedback system provides a highly accurate and sensitive alignment system.

The MISEC group is also working on development of cost and time effective, “direct-writing” processes of fabricating metallic patterns on non-conductive substrates. The current focus is direct UV patterning of polyimide with a simple chemical surface modification pretreatment.

Silver ions are embedded in the polyimide surface within a thin depth by immersion of KOH and AgNO 3 solutions. Subsequent UV irradiation reduces the silver ions into silver metal, which can then serve as a seed for further selective electroless plating (e.g. Cu, Au) on the irradiated areas. This simple metallization process on a flexible substrate can be adopted into spin-, spray- and mould- coating of liquid polyimide precursor on various materials and non-planar surfaces. In addition, complex, 3-D metallic structures may be fabricated by integration of this method. Characterisations of the photon input (wavelength, dose) and its correlation to the final metal deposit in this process are underway. It is envisaged that this process would make a promising application for the Micro-UV-LED-Array