Digital Theses Archive


Tesi etd-09292017-134940

Thesis type
Laser integration in Silicon-on-Insulator platform
Scientific disciplinary sector
Corso di studi
INGEGNERIA - Ph.D. Programme in Emerging Digital Technologies (EDT)
Presidente Prof. GIANNETTI Filippo
Parole chiave
  • Flip-chip bonding
  • Heterogeneous Integration
  • Laser Integration
  • Silicon Photonics
  • Transfer Printing
Data inizio appello
Riassunto analitico
Silicon photonics (SiPh) is defined as the application in photonics of silicon as optical medium. Using this technology a large group of devices has been developed and already put on the market. Silicon-on-Insulator (SOI) is one of the most used platforms for the development of SiPh devices. The crucial advantage of SOI is that its fabrication processes are CMOS compatible. On the other hand, silicon indirect bandgap properties hamper the achievement of an electrically pumped laser fabricated on chip and made of this material.<br><br>In order to overcome this limit several approaches have been proposed. A laser chip can be coupled with a SiPh integrated circuit (IC) by using a set of lenses that focuses the beam emitted by the laser on the circuit input coupler. Unfortunately, this approach has a high fabrication cost per chip and it is not power efficient. A second solution consists of bonding a stack of III-V layers on the top silicon of the SOI wafer. By properly processing the III-V stack it is possible to fabricate a laser directly on top of a silicon waveguide. Since there is no need of lenses for coupling, the fabrication cost is lower in this case than in the previous one. But using this solution the laser will be fabricated on top of a thick dielectric layer that would impede the dissipation of the laser heat towards the silicon substrate. This could limit the lifespan of the device itself.<br><br>In this work we developed and compared two novel approaches for the SiPh source integration issue. The first one, developed in Scuola Superiore Sant&#39;Anna, exploits a flip-chip bonding technique. The second one has been developed in collaboration with the Photonics Research Group of the University of Ghent. It exploits a new technique called &#34;transfer printing&#34;. In both cases the active device is bonded in direct contact with the silicon substrate in order to improve thermal dissipation. The light sources are fabricated before being transferred on the fully processed SOI. Both bonding processes are wafer scalable.<br><br>In the flip-chip approach we developed a novel and high efficient edge coupler that is used for coupling between the active device and the SOI circuit. The edge coupler was fabricated and tested obtaining coupling loss as low as 0.7dB. The same coupler has been used also for demonstrating an external cavity laser. This fabricated laser had a low threshold current of 8mA and a high maximum power of 5mW emitted in silicon waveguide. We designed and developed as well the processing of the SOI wafer, devoting particular attention to the deposition of the gold-tin solder alloy used for the device bonding.<br><br>For the integration process employing the transfer printing technique we designed and developed the fabrication process of both the III-V light source and the SOI circuit. Final test of the device showed emission at the SOI circuit output. This was the first electrically pumped III-V source butt-coupled with a silicon waveguide fabricated using this technique.