Title:
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Optical packaging of microlens over UV-LED array
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This thesis is part of a project entitled 'One thousand emitters per square millimetres',
an EPSRC project funded under the Basic Technology Programme. The project is
jointly run between Heriot-Watt University, The Institute of Photonics at the University
of Strathclyde, Imperial College London and the University of Sheffield. The overall
aim of the project is to design, manufacture and package a UV-LED array for a variety
ofbio-medical applications.
The objective of the research work presented here is the support to other partners in the
assembly of a microlens array on top of a UV-LED array.
This work focuses on the design, manufacture and characterisation of a packaging
structure that places a microlens array on top of a micro-UV-LED array. The required
lateral tolerance was defined to be less than 2/lm. Two approaches were considered and
systematically characterised. In the static approach, the microlens array is to be
accurately placed and fixed on the LED array. In the dynamic approach, the microlens
array is moveable in the vertical as well as lateral directions. Post processing of the lens
and LED arrays has been carried out using a modified UV-LIGA process. The
microlens array rests on four posts, to reduce lateral as well as vertical contact area for
the static approach, hence reducing the probability of misalignment. Using
electroplating of electrodes that are situated on the micro-UV-LED array structure,
vertical alignment of the microlens array with sub-micron accuracy has been
demonstrated.
The dynamic approach features a vertical electrostatic and a lateral magnetic actuator
that can be driven simultaneously. Both actuation methods exert a force on the
microlens array without the need of a physical contact, which eases the fabrication and
assembly process. As a restoring means, gel bumps are currently employed which
exhibit the necessary isotropic elasticity for the lateral and vertical movement. The
electrostatic actuator is able to achieve displacements of over 70/lm and shows good
repeatability with a standard deviation of 0.43/lm at a mean value of 24.75/lm. The
magnetic actuator achieves lateral movement exceeding 50/lm. Both actuation methods
have been demonstrated to offer sub-micron displacement accuracy. Due to the viscoelastic properties of the gel bumps and with appropriate equipment, accuracies in,
the order of tens ofnanometres are feasible.¬«
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