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Estirant els límits de la fabricació additiva làser d’elements optoelectrònics
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[cat] L’optoelectrònica va sorgir al segle XX gràcies al desenvolupament de semiconductors capaços d’emetre i detectar llum, donant lloc a dispositius essencials avui en dia com són els LEDs, els làsers i fotodetectors en camps tan diversos com telecomunicacions i medicina. El seu avenç ha anat sempre lligat al desenvolupament de les tècniques de microfabricació. Durant dècades, la fotolitografia va ser la tècnica predominant per la seva gran resolució i rendiment industrial. A partir dels anys vuitanta, però, diversos mètodes de la indústria gràfica, com la serigrafia, es van adaptar per imprimir tintes funcionals. Aquestes tècniques, tot i oferir menor resolució, són econòmiques, compatibles amb substrats flexibles i són molt adequades per a la producció en massa. A inicis del segle XXI, la digitalització va impulsar l’aparició de tècniques d’escriptura directa, com la inkjet printing o la Laser Induced Forward Transfer (LIFT), que permeten dipositar volums micromètrics de tinta de manera selectiva. Les tècniques d’impressió, però, tenen un inconvenient: les gotes impreses s’acomoden segons la mullabilitat del substrat, la qual cosa limita el control sobre la geometria final. Els tractaments de superfície poden millorar-ho, però impliquen processos complexos, ús de químics i risc de degradació o contaminació del substrat. L’objectiu d’aquesta tesi és desenvolupar i estudiar un mètode de fabricació basat en l’ús de materials reconfigurables que anomenem Print-n-release. El principi de funcionament del mètode radica en estirar el substrat abans de la impressió i, una vegada feta la impressió, encongir-lo per a recuperar les seves dimensions originals, mentre la tinta es manté en estat líquid. Així, els patrons impresos experimentaran una miniaturització en superfície així com un increment en la seva alçada degut a la reducció de l’àrea de contacte. D’aquesta forma es pretén millorar la resolució de les tècniques d’impressió de líquids i assolir angles de contacte i geometries dels dipòsits més enllà del que permet la mullabilitat. En un dels capítols de la tesi es desenvolupa un model teòric amb les hipòtesis que l’adhesió del líquid és suficientment gran per a mantenir la línia de contacte sòlid-líquid durant l’encongiment, i que el volum del líquid es manté constant. Aquest model ha de permetre predir l’estat final i seleccionar la deformació d’estirament, 𝜀, per a obtenir els resultats d’impressió desitjats. Posteriorment, es presenten estudis de la implementació del Print-n-release combinat amb serigrafia i LIFT que analitzen els efectes que aquest mètode produeix en la morfologia i propietats funcionals de les impressions. En la seva aplicació sobre elèctrodes impresos amb serigrafia, el Print-n-release ha permès miniaturitzar les impressions un factor 0.37 respecte la seva mida inicial i incrementar l’alçada i la relació d’aspecte un factor 2.4 i 4.39 respectivament en comparació els valors obtinguts amb serigrafia aplicant un estirament ε de 1.1. Fabricant elèctrodes frontals de cèl·lules solars amb una ε de 0.53, aquest mètode permet reduir la resistència quadre en un ordre de magnitud i augmentar el pas de llum fins el medi fotovoltaic en un 56% respecte la serigrafia convencional. Combinat amb la LIFT, s’han fabricat microelèctrodes de plata amb amplades reduïdes de 95 μm a 45 μm i alçades i relacions d’aspecte que passen de 2.5 μm i 0.03 fins 11.5 μm i 0.26 respectivament aplicant una ε de 1.2. A més, aquests presenten resistències quadre quatre vegades inferiors a les de LIFT convencional. La seva funcionalitat es va validar en dues aplicacions, com a sensor de concentració d’un electròlit i com a sensor del volum de microgotes d’aigua, mostrant una sensibilitat un ordre de magnitud superior en aquesta última. Finalment, el Print-n-release aplicat a microlents impreses amb LIFT d’un prepolímer òptic ha permès incrementar l’angle de contacte un factor 4, fins 61º, reduir la distància focal un factor 0.88, fins 109 µm, i millorar l’obertura numèrica fins un valor de 0.44 amb una deformació 𝜀 de 0.83. A més, les microlents presenten unes aberracions òptiques negligibles, indicatiu d’una gran qualitat òptica que ha permès formar imatges múltiples d’alta qualitat i millorar la resolució de sistemes òptics de baixa obertura numèrica. En conjunt, el Print-n-release es presenta com una estratègia innovadora, universal i eficaç per superar les limitacions de resolució de les tècniques d’impressió líquida, oferint un alt potencial en la fabricació de microdispositius electrònics i òptics.
[eng] Optoelectronics emerged in the twentieth century thanks to the development of semiconductors capable of emitting and detecting light, giving rise to essential devices today such as LEDs, lasers and photodetectors in fields as diverse as telecommunications and medicine. Its progress has always been linked to the development of microfabrication techniques. For decades, photolithography was the predominant technique due to its high resolution and industrial performance. From the eighties, however, various methods in the graphic industry, such as screen printing, were adapted to print functional inks. These techniques, despite offering lower resolution, are economical, compatible with flexible substrates and are very suitable for mass production. At the beginning of the twenty-first century, digitization led to the emergence of direct writing techniques, such as inkjet printing or Laser Induced Forward Transfer (LIFT), which allow micrometric volumes of ink to be deposited selectively. Printing techniques, however, have a drawback: the printed droplets are arranged according to the wettability of the substrate, which limits control over the final geometry. Surface treatments can improve this, but they involve complex processes, the use of chemicals and the risk of degradation or contamination of the substrate. The aim of this thesis is to develop and study a manufacturing method based on the use of reconfigurable materials that we call Print-n-release. The principle of operation of the method lies in stretching the substrate before printing and, once printed, shrinking it to recover its original dimensions, while the ink remains in a liquid state. Thus, the printed patterns will experience a miniaturization on the surface as well as an increase in their height due to the reduction of the contact area. In this way, it is intended to improve the resolution of liquid printing techniques and achieve contact angles and tank geometries beyond what wettability allows. In one of the chapters of the thesis, a theoretical model is developed with the hypotheses that the adhesion of the liquid is large enough to maintain the solid-liquid contact line during shrinkage, and that the volume of the liquid remains constant. This model should allow predicting the final state and selecting the stretch deformation, ε, to obtain the desired printing results. Subsequently, studies of the implementation of Print-n-release combined with screen printing and LIFT are presented, which analyze the effects that this method produces on the morphology and functional properties of the prints. In its application on electrodes printed with screen printing, the Print-n-release has allowed the prints to be miniaturized by a factor of 0.37 with respect to their initial size and to increase the height and aspect ratio by a factor of 2.4 and 4.39 respectively compared to the values obtained with screen printing by applying a ε stretch of 1.1. By manufacturing solar cell front electrodes with a ε of 0.53, this method allows the frame resistance to be reduced by an order of magnitude and the passage of light to the photovoltaic medium to be increased by 56% compared to conventional screen printing. Combined with LIFT, silver microelectrodes have been manufactured with widths reduced from 95 μm to 45 μm and heights and aspect ratios ranging from 2.5 μm and 0.03 to 11.5 μm and 0.26 respectively by applying a ε of 1.2. In addition, these have frame resistors four times lower than those of conventional LIFT. Its functionality was validated in two applications, as an electrolyte concentration sensor and as a sensor of the volume of water microdroplets, showing a sensitivity an order of magnitude higher in the latter. Finally, the Print-n-release applied to microlenses printed with LIFT of an optical prepolymer has made it possible to increase the contact angle by a factor of 4, up to 61º, reduce the focal length by a factor of 0.88, up to 109 μm, and improve the numerical aperture to a value of 0.44 with a ε deformation of 0.83. In addition, microlenses have negligible optical aberrations, indicative of a high optical quality that has made it possible to form multiple high-quality images and improve the resolution of optical systems with low numerical aperture. Overall, Print-n-release is presented as an innovative, universal and effective strategy to overcome the resolution limitations of liquid printing techniques, offering a high potential in the manufacture of electronic and optical microdevices.
[eng] Optoelectronics emerged in the twentieth century thanks to the development of semiconductors capable of emitting and detecting light, giving rise to essential devices today such as LEDs, lasers and photodetectors in fields as diverse as telecommunications and medicine. Its progress has always been linked to the development of microfabrication techniques. For decades, photolithography was the predominant technique due to its high resolution and industrial performance. From the eighties, however, various methods in the graphic industry, such as screen printing, were adapted to print functional inks. These techniques, despite offering lower resolution, are economical, compatible with flexible substrates and are very suitable for mass production. At the beginning of the twenty-first century, digitization led to the emergence of direct writing techniques, such as inkjet printing or Laser Induced Forward Transfer (LIFT), which allow micrometric volumes of ink to be deposited selectively. Printing techniques, however, have a drawback: the printed droplets are arranged according to the wettability of the substrate, which limits control over the final geometry. Surface treatments can improve this, but they involve complex processes, the use of chemicals and the risk of degradation or contamination of the substrate. The aim of this thesis is to develop and study a manufacturing method based on the use of reconfigurable materials that we call Print-n-release. The principle of operation of the method lies in stretching the substrate before printing and, once printed, shrinking it to recover its original dimensions, while the ink remains in a liquid state. Thus, the printed patterns will experience a miniaturization on the surface as well as an increase in their height due to the reduction of the contact area. In this way, it is intended to improve the resolution of liquid printing techniques and achieve contact angles and tank geometries beyond what wettability allows. In one of the chapters of the thesis, a theoretical model is developed with the hypotheses that the adhesion of the liquid is large enough to maintain the solid-liquid contact line during shrinkage, and that the volume of the liquid remains constant. This model should allow predicting the final state and selecting the stretch deformation, ε, to obtain the desired printing results. Subsequently, studies of the implementation of Print-n-release combined with screen printing and LIFT are presented, which analyze the effects that this method produces on the morphology and functional properties of the prints. In its application on electrodes printed with screen printing, the Print-n-release has allowed the prints to be miniaturized by a factor of 0.37 with respect to their initial size and to increase the height and aspect ratio by a factor of 2.4 and 4.39 respectively compared to the values obtained with screen printing by applying a ε stretch of 1.1. By manufacturing solar cell front electrodes with a ε of 0.53, this method allows the frame resistance to be reduced by an order of magnitude and the passage of light to the photovoltaic medium to be increased by 56% compared to conventional screen printing. Combined with LIFT, silver microelectrodes have been manufactured with widths reduced from 95 μm to 45 μm and heights and aspect ratios ranging from 2.5 μm and 0.03 to 11.5 μm and 0.26 respectively by applying a ε of 1.2. In addition, these have frame resistors four times lower than those of conventional LIFT. Its functionality was validated in two applications, as an electrolyte concentration sensor and as a sensor of the volume of water microdroplets, showing a sensitivity an order of magnitude higher in the latter. Finally, the Print-n-release applied to microlenses printed with LIFT of an optical prepolymer has made it possible to increase the contact angle by a factor of 4, up to 61º, reduce the focal length by a factor of 0.88, up to 109 μm, and improve the numerical aperture to a value of 0.44 with a ε deformation of 0.83. In addition, microlenses have negligible optical aberrations, indicative of a high optical quality that has made it possible to form multiple high-quality images and improve the resolution of optical systems with low numerical aperture. Overall, Print-n-release is presented as an innovative, universal and effective strategy to overcome the resolution limitations of liquid printing techniques, offering a high potential in the manufacture of electronic and optical microdevices.
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MARTÍ JEREZ, Ernest. Estirant els límits de la fabricació additiva làser d’elements optoelectrònics. [consulted: 30 of September of 2026]. Available at: https://hdl.handle.net/2445/231644