Ce travail de thèse explore l’excitation électrique de micro-OLEDs en régime d’impulsion afin d’évaluer la possibilité d’atteindre le seuil laser dans les diodes laser organiques qui restent encore à démontrer. Ils’agit d’identifier des solutions scientifiques et techniques ouvrant la voie vers des densités d’excitations électriques équivalentes aux seuils laser observés en pompage optique. Dans la littérature, les seuils les plus bas sont équivalents à des densités de courant entre 0.72 et 4kA/cm² si on suppose une efficacité quantique externe de 1%. De telles densités de courant imposent un régime d’excitation électrique impulsionnel pour s’affranchir des risques de destructions par effet thermique et des pertes par annihilation singulet-triplet dès lors que l’on travaille avec des durées d’impulsion de l’ordre de la nanoseconde. Et pour espérer des réponses électriques et optiques efficaces à de telles durées d’impulsions, il est proposé ici de combiner l’électronique hyperfréquence et l’optoélectronique organique. A cet effet, un modèle électrique équivalent de l’OLED permettant d’accéder à son temps de réponse en mode tout-ou-rien est développé. De plus, des électrodes spécifiques sont dimensionnées et structurées sous forme de lignes coplanaires d’impédance caractéristique 50Ω afin de maîtriser l’impédance du circuit d’excitation et d’assurer le transfert du maximum d’énergie de l’impulsion d’excitation vers celui-ci. Après dépôts de l’hétéro-structure organique basée sur le système hôte-dopant Alq3:DCM, les composants ainsi réalisés sont caractérisés électriquement et optiquement avec différentes techniques par analyse vectorielle, en régime continu et en régime d’impulsion. En régime d’impulsion de très courtes durées (2.5~20ns) et à faible taux de répétition (100Hz), des temps de réponse de 330ps etdes densités de courant maximales entre 4 et 6kA/cm² ont été mesurés alors que le maximum de luminance culmine à 4.11x10⁶ cd/m². / This thesis explores the pulsed electrical excitation of micro-OLEDs in order to evaluate the possibility of reaching the laser threshold in organic laser diodes that have not yet be demonstrated. The main goal is the identification of the scientific and technical solutions towards high electrical excitation current densities equivalent to the laser thresholds observed under optical pumping. In the literature, the lowest reported thresholds are equivalent to current densities between 0.72 and 4kA/cm², assuming an external quantum efficiency of 1%. Such current densities imply a pulsed electrical excitation regime to prevent the risks of device breakdown by Joule heating effects and to avoid losses by excitons annihilation processes, as long as the pulses duration are in nanosecond range. To expect efficient electrical and optical responses to such pulse durations, it is suggested to combine microwave electronics and organic optoelectronics. For this purpose, an equivalent electrical model of the organic light emitting device, allowing access to its on-off mode time response, is developed. Additionally, specific electrodes are designed and patterned in the coplanar waveguide configuration with characteristic impedance of 50Ω, inorder to control the impedance of the excitation circuit and to ensure the maximum energy transfer of the excitation pulse to the device. After deposition of organic hetero-structure based on the Alq3:DCM host-guest system, the device is characterized electrically and optically with different techniques by vector network analysis, in continuous mode and in pulse mode. In pulse excitation regime with very short pulses durations (2.5~20ns) and low repetition rate (100Hz), time response of 330ps and maximum current densities between 4 and 6kA/cm² are recorded while the maximum of luminance peaks at 4.11x10⁶ cd/m².

The immersive virtual reality (VR) and the optical see-through augmented reality (AR) are expected to revolutionize human lives in work, education, entertainment, healthcare, spatial computing, and digital twins, just to name a few. Next-generation VR/AR devices should exhibit a wide field-of-view (FoV), crisp image without screen-door effect, high dynamic range, compact form factor and lightweight, and low power consumption. Such demanding requirements pose a significant challenge to traditional direct-view display panels. To address these technical challenges, novel approaches need to be proposed. This dissertation is devoted to developing next-generation high-performance display light engines toward high resolution density, high optical efficiency, wide color gamut, and small form factor. These emerging solutions will fuel the growth and accelerate the widespread applications of VR/AR devices. In Chapter 2, we propose practical measurement methods to characterize the halo artifacts of miniature light-emitting diode (mini-LED) backlit liquid crystal displays (LCDs). After measuring and characterizing a high dynamic range (HDR) light engine, we propose and develop field sequential color (FSC) LCDs for high-end virtual reality (VR) devices in Chapter 3. Such an FSC LCD can triple the resolution density and optical efficiency via eliminating color filters. To further mitigate the color breakup (CBU), we also propose to combine mini-LEDs with FSC LCDs to enable progressive emission and achieve a higher frame rate (~ 600 Hz). To quantitatively compare the CBUs corresponding to simultaneous emission, progressive emission, and stencil algorithm, we adopt the CIEDE2000 color difference as a metric. Quantitative simulation results of the CBU indicate that a 600-Hz subframe rate can help mitigate the CBU dramatically. Micro organic light-emitting diode (micro-OLED) exhibiting high-resolution density and high contrast ratio is another type of display for high-end VR devices. More specifically, white micro-OLED is currently employed because it helps ease the manufacturing difficulty. In Chapter 4, we optimize the layer thicknesses to achieve a maximum efficiency while keeping a decent color gamut. We also push the limit of color gamut toward ~ 95% Rec. 2020. Lastly, liquid-crystal-on-silicon (LCoS) offers great potential for achieving high-efficiency and high-resolution waveguide-based AR displays. In Chapter 5, several strategies are proposed and developed to improve the performance of LCoS microdisplays and enable a small pixel size. In Chapter 6, we briefly summarize our major accomplishments.