Fabricating of Stable Thin Film Microdevices with UV Laser

Abstract

Short-term and long-term stability remains a limiting factor in the practical deployment of micro-scale sensors and actuators, where small structural, thermal, or material changes can produce disproportionate performance drift over time. This thesis investigates drift mitigation strategies in two ultraviolet (UV) laser–fabricated micro-devices that operate in distinct but complementary domains: NiCr thin-film strain sensors for mechanical sensing and laser-induced graphene (LIG) microheaters for thermal actuation. Although these devices serve different functions, both exhibit degradation mechanisms rooted in microstructural instability, insufficient mechanical constraint, or poorly controlled thermal boundary conditions.

For NiCr strain sensors, short-term resistance drift under constant mechanical load is addressed through the introduction of post-fabrication infill materials that mechanically encapsulate the laser-ablated traces. A systematic comparison of infill chemistries and viscosities demonstrates substantial reductions in noise, hysteresis, and short-term drift, supporting mechanical stabilization as the dominant mitigation mechanism. For LIG microheaters, long-term thermal stability is improved by incorporating an aluminum backing layer during fabrication, which fundamentally alters heat dissipation during UV laser processing. This substrate-mediated thermal boundary control produces denser LIG microstructures and enables stable Joule heating with minimal drift over 1000 thermal cycles and extended continuous operation.

Across both device classes, this work demonstrates that stability can be engineered through deliberate control of mechanical constraint and boundary conditions, rather than relying solely on material substitution or complex control electronics. The results establish practical, fabrication-compatible strategies for improving short-term and long-term reliability in UV-laser-fabricated micro-devices and provide experimentally grounded hypotheses to guide future stability-oriented micro-device design.