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Digital archive of theses discussed at the University of Pisa


Thesis etd-01102017-161326

Thesis type
Tesi di dottorato di ricerca
Thesis title
Advanced Microstructuring of Silicon and Polymer
Academic discipline
Course of study
tutor Prof. Barillaro, Giuseppe
tutor Prof. Bruschi, Paolo
  • Accelerometer
  • Conjugated Polymers
  • Electrochemical Micromachining
  • Microstructuring
  • PDMS
  • Photoluminescence
  • Polymer
  • Replica Moulding
  • Sensing
  • Silicon
  • Silicon Microparticles
  • SU-8
Graduation session start date
Release date
The field of material structuring is wide and diverse. Historically, this blooming ample field first sparked with the emergence of man, who has evolved over the ages of civilization through shaping materials. Today, this field encompasses processes and techniques capable of providing products of high quality that meet both the simplest and the most complex needs of our modern daily life. Through all stages of technological progress, man sought the way to make best use of materials by structuring them to emphasize their properties, as nature itself did to evolve its self-ordered structure.
In the last decades, a new great range of structuring technologies have been developed to provide and to exploit combinations of properties, enabling for entirely new devices to be made or quite new effects to be achieved. This colorful scenario of potential applications is further widened by remarkable and, sometimes, unpredictable phenomena arising from scaling down structuring technologies to the micrometer and nanometer scale. Micro and nanofabrication, in fact, are increasingly central in modern science, industry and technology for reasons spanning from empowering Microelectronics mass-production, to providing fast and portable diagnostic tools, to allowing multifunctionality integration into the same device.
In this work, the integration of novel and avant-garde polymer, silicon and composite materials microstructuring technologies is used for the fabrication of microstructures and microsystems suitable for a wide range of applications, ranging from the fields of Microfluidics and Biosensing, to Micro Electromechanical Systems (MEMS), to Microtagging, and Sensing.
In particular, the design, fabrication, characterization, and preliminary testing of an SU-8 on-glass microfluidic platform for multi-analyte optical detection is reported. SU-8 is a photosensitive polymer that has recently gained prominence for its easy processing by standard photolithography, allowing for the fabrication of high-aspect-ratio structures with nearly vertical sidewall. Upon definition and optimization of a proper structuring protocol with resolution of ~5μm, on both silicon and glass, the designed microfluidic platform was successfully fabricated and tested.
Silicon is the most used substrate for MEMS fabrication by standard photolithographic techniques. In this work, the design, simulation and fabrication of a high-aspect-ratio all-silicon in-plane optical accelerometer by silicon Electrochemical Micromachining (ECM) technology is reported. Electrochemical Micromachining (ECM) is a novel wet etching technology based on the controlled electrochemical dissolution of silicon in Hydrofluoric Acid (HF)-based aqueous solutions allowing for high-aspect-ratio and for high-complexity microsystem fabrication in any lab at low cost.
In the reference frame of silicon microstructuring technologies, moreover, the fabrication by back-side illumination electrochemical etching (BIEE) at high anodic voltage of ordered macropore arrays featuring spatial periods of 2 μm and submicrometric size is successfully achieved and reported. This result could represent the first step toward low-doped n-type silicon nanofabrication at low HF concentration by BIEE.
Integrating both silicon and polymer microstructuring technologies, a high-yield (> 95%) top-down parallel and facile polymer structuring technique for the fabrication of two-dimensional (2D) arrays of micrometric-sized (down to ~3μm2) polymeric freestanding membranes integrated into microstructured silicon is demonstrated by drop-casting technology. The technique versatility is proved by reporting the successful fabrication of 2D membrane arrays arranged in either regular or non-regular patterns, using both conjugated and non-conjugated polymers, and their application for Microtagging is detailed. Conjugated polymers have been widely investigated over the last decades for their unique optical and semiconducting properties, although their use for hybrid polymer/silicon microstructured platforms has been somehow overlooked.
Finally, the design, fabrication, characterization, and preliminary testing of luminescent porous silicon-polydimethylsiloxane (PDMS) composite micropillar arrays for oxygen sensing applications is reported in the last section. Luminescent porous silicon is shown to quench upon exposure to molecular oxygen, though suffering from permanent loss of sensing capabilities and drift in the baseline due to photo-oxidation. The concept of this work relies upon the use of a composite material embedding luminescent porous silicon in a PDMS matrix in order to exploit quenching of porous silicon luminescence for oxygen sensing, PDMS as both a baseline-drift-stabilizer and an oxygen-permeable substrate, and micropillar array structure for the high surface area and the sensitivity-enhancing waveguide effect.