Flexible μLED-Based Optical Cochlear Implant for High-Resolution Stimulation : = Flexible [my]LED-Based Optical Cochlear Implant for High-Resolution Stimulation

Abstract: This thesis describes the first functional optical cochlear implant (oCI) based on integrated μLEDs successfully applied in vivo. In order to integrate the highest possible number of individually addressable μLEDs, different routing schemes implementing single- and multi-layer metallization have been evaluated. Based on conclusions drawn during the intense evaluation of the first oCI generation (oCI-1), a new single layer interconnection approach is developed, characterized, and found in a given range of complexity to be more efficient than the commonly used multilayer based multiplexing scheme commonly used for LED arrays. After comparing various light-emitting diode (LED) routing schemes such as common contact, multiplexing and tri-state switching, the most suitable approaches are transferred into two different optical cochlear implant (oCI) designs, namely oCI-1 and the second oCI generation (oCI-2) differing mainly in the way the μLEDs are interfaced. For both design generations a detailed process development is performed and analyzed. All relevant design and process parameters are evaluated in related parameter studies in order to extract the best parameter set. The key process steps developed for oCI-1 are (i) the homogeneous deposition of down to 5-μm-thin epoxy layers using spin-coating, (ii) the reliable wafer-level bonding based on indium used to transfer μLEDs with lateral dimensions down to 60_60 μm2 from the epitaxial sapphire substrate to the polymeric carrier, and (iii) the optimized laser lift-off (LLO) enabling the release of 6-μm-thin μLEDs embedded in a polymeric matrix from the sapphire wafer. The detailed process know-how acquired during the fabrication of oCI-1 implants is subsequently transferred into the layout and process design of the oCI-2 generation. Exemplarily, the epoxy deposition by spin-coating as developed in the case of oCI-1 is applied as well, but also transferred into a planarization step that is one of the key technological steps of oCI-2. The oCI-2 implants utilize the μLED sapphire growth-substrate not only to realize the μLEDs. The substrate also serves as the carrier substrate for the entire fabrication. The single-sided μLED process of the oCI-2 variant allows to implement both μLED contacts facing the same direction. This single-sided processing allows the epoxy substrate to be processed around the μLED mesas once they are realized by dry etching and metal layer deposition. The electroplated metal lines interfacing the μLEDs apply appropriate interconnection schemes and are sandwiched between planarized epoxy layers. For both design generations, a variety of process steps have been implemented in order to optimize the device performance. This includes (i) low-resistive and highly-reflective contacts to the gallium nitride (GaN) to increase the backside reflection in the case of oCI-1, (ii) side-mirrors integrated into the μLED passivation to reduce stray light, (iii) surface roughening of GaN using wet-chemical etching to increase the outcoupling efficiency of photons, (iv) the integration of micro lenses and conical concentrators to increase the peak intensity and confine the emission angle, and (v) the application of transparent, low-resistance n-contacts based on indium tin oxide to increase the emission surface and thus the optical power. In order to connect both types of oCIs several assembly methods are investigated. Based these tests it is concluded, that flip-chip bonding of polyimide-based ribbon cables enables the most reliable interfacing of the μLED arrays. A dedicated process is developed to bond contact pads of different height. This flip-chip bonding process is also identified as the process which is easiest to encapsulate by silicone underfill and provides the highest assembly yield. The complete encapsulation of the oCI and ribbon cable is done by a newly developed molding process which ensures that the sidewalls of the ultra-thin optical probes are encapsulated with a sufficient silicone thickness. The encapsulation procedure, including a preceding washing step applied prior to silicone deposition, is evaluated in a parameter study. Based on in vivo tests performed in cooperation with project partners, it is concluded that a single μLED is capable of efficiently stimulating optogenetically modified nerve cells in the cochlea. It is further demonstrated that the μLED arrays of the oCIs reduce the spectral spread, compared to a clinical style electrical cochlear implant, by up to 5 octaves

Angaben zum Objekt

• Weitere Titel: Flexible [my]LED-Based Optical Cochlear Implant for High-Resolution Stimulation
• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2023

Klassifikation und Themen

• Klassifikation: Ingenieurwissenschaften und Maschinenbau
• Schlagwort: Lumineszenzdiode ; Silicium ; Galliumnitrid

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2023
• Urheber: Klein, Eric
• Beteiligte Personen und Organisationen: Paul, Oliver ; Mathieson, Keith ; Albert-Ludwigs-Universität Freiburg. Institut für Mikrosystemtechnik ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Weitere Informationen

• DOI: 10.6094/UNIFR/242325
• URN: urn:nbn:de:bsz:25-freidok-2423256
• Rechteinformation: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 15.08.2025, 07:21 MESZ