Study of the impact of lithography techniques and the current fabrication processes on the design rules of tridimensional fabrication technologies

Working for the photolithography tool manufacturer leader sometimes gives me the impression of how complex and specific is the sector I am working on. This master thesis topic came with the goal of getting the overall picture of the state-of-the-art: stepping out and trying to get a helicopter view usually helps to understand where a process is in the productive chain, or what other firms and markets are doing to continue improvingUniversidad de sevilla.Máster Universitario en Microelectrónica: Diseño y Aplicaciones de Sistemas Micro/Nanométrico

3D Hybrid Integration for Silicon Photonics

Silicon photonics (SiPh) has emerged as a photonic integrated circuit (PIC) platform, especially for high volume applications. Integrated laser sources, however, remain a challenge. SiPh foundries have existed for more than 10 years but still don’t offer a qualified process with integrated lasers. Direct heteroepitaxy of group III-V materials on silicon is still immature and suffers from reliability issues. Heterogeneous and hybrid integration techniques, however, have been pursued in research and by industry and present a practical near-term solution for laser integration. Heterogenous approaches based on wafer bonding involve the bonding of bare III-V epitaxial material to silicon on insulator (SOI), co-fabrication, and evanescent light coupling. The laser active medium is thermally isolated from the silicon substrate by the buried oxide layer limiting the laser efficiency at high temperature. Hybrid integration approaches, such as the butt coupling of fabricated III-V lasers to SOI waveguides, may address the thermal issue. However, the main limitation for butt coupling is the significant mode mismatch of the waveguides that imposes a strict alignment requirement.In this thesis the novel 3D hybrid integration technique for SiPh, addressing the aspects of thermal performance and alignment tolerance, was proposed and demonstrated for the first time. This approach is based on the flip-chip integration of indium phosphide (InP) reflective semiconductor optical amplifiers (RSOAs) containing total internal reflection turning mirrors for surface emission. Light is coupled to the SOI waveguides through surface grating couplers. This technique yields increased alignment tolerance compared to butt coupling. Flip-chip integration also allows the RSOA chip to be bonded P-side down directly to the silicon substrate. In this way, the heat generated in the active region can dissipate more efficiently in the silicon. 3D hybrid integration can be carried out at wafer level in a backend step for high throughput manufacturing, and also allow for the integration of InP PICs on silicon interposers for large-scale electronic-photonic integration.A tunable laser was demonstrated with 3D hybrid integration demonstrating a side-mode suppression ratio up to 43 dB. Greater than 4 mW of optical power was coupled into SiPh waveguide and more than 20 nm wavelength tuning range was achieved. A linewidth of 1.5 MHz and relative intensity noise of -132 dB/Hz were demonstrated. A low thermal impedance of 6.2 ℃/W was extracted experimentally from a 3D hybrid laser that was bonded to the silicon substrate, demonstrating a factor of three improvement over a laser that was bonded above the SOI layer. To improve coupling efficiency, various advanced silicon surface grating couplers as well as dilute waveguide RSOAs were investigated. Coupling efficiency up to 85\% can be achieved while also maintaining an alignment tolerant implementation

In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon

Silicon is an excellent material for microelectronics and integrated photonics1–3 with untapped potential for mid-IR optics4. Despite broad recognition of the importance of the third dimension5,6, current lithography methods do not allow fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realised with techniques like reactive ion etching. Embedded optical elements, like in glass7, electronic devices, and better electronic-photonic integration are lacking8. Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1 µm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has a different optical index than unmodified parts, which enables numerous photonic devices. Optionally, these parts are chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface, i.e., “in-chip” microstructures for microfluidic cooling of chips, vias, MEMS, photovoltaic applications and photonic devices that match or surpass the corresponding state-of-the-art device performances

In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon

Silicon is an excellent material for microelectronics and integrated photonics 1-3, with untapped potential for mid-infrared optics 4 . Despite broad recognition of the importance of the third dimension 5,6, current lithography methods do not allow the fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realized with techniques like reactive ion etching. Embedded optical elements 7, electronic devices and better electronic-photonic integration are lacking 8 . Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1-μm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has an optical index different to that in unmodified parts, enabling the creation of numerous photonic devices. Optionally, these parts can be chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface - that is, 'in-chip' - microstructures for microfluidic cooling of chips, vias, micro-electro-mechanical systems, photovoltaic applications and photonic devices that match or surpass corresponding state-of-the-art device performances. © 2017 The Author(s)

Next Generation Silicon Photonic Transceiver: From Device Innovation to System Analysis

Silicon photonics is recognized as a disruptive technology that has the potential to reshape many application areas, for example, data center communication, telecommunications, high-performance computing, and sensing. The key capability that silicon photonics offers is to leverage CMOS-style design, fabrication, and test infrastructure to build compact, energy-efficient, and high-performance integrated photonic systems-on- chip at low cost. As the need to squeeze more data into a given bandwidth and a given footprint increases, silicon photonics becomes more and more promising. This work develops and demonstrates novel devices, methodologies, and architectures to resolve the challenges facing the next-generation silicon photonic transceivers. The first part of this thesis focuses on the topology optimization of passive silicon photonic devices. Specifically, a novel device optimization methodology - particle swarm optimization in conjunction with 3D finite-difference time-domain (FDTD), has been proposed and proven to be an effective way to design a wide range of passive silicon photonic devices. We demonstrate a polarization rotator and a 90◦ optical hybrid for polarization-diversity and phase-diversity communications - two important schemes to increase the communication capacity by increasing the spectral efficiency. The second part of this thesis focuses on the design and characterization of the next- generation silicon photonic transceivers. We demonstrate a polarization-insensitive WDM receiver with an aggregate data rate of 160 Gb/s. This receiver adopts a novel architecture which effectively reduces the polarization-dependent loss. In addition, we demonstrate a III-V/silicon hybrid external cavity laser with a tuning range larger than 60 nm in the C-band on a silicon-on-insulator platform. A III-V semiconductor gain chip is hybridized into the silicon chip by edge-coupling to the silicon chip. The demonstrated packaging method requires only passive alignment and is thus suitable for high-volume production. We also demonstrate all silicon-photonics-based transmission of 34 Gbaud (272 Gb/s) dual-polarization 16-QAM using our integrated laser and silicon photonic coherent transceiver. The results show no additional penalty compared to commercially available narrow linewidth tunable lasers. The last part of this thesis focuses on the chip-scale optical interconnect and presents two different types of reconfigurable memory interconnects for multi-core many-memory computing systems. These reconfigurable interconnects can effectively alleviate the memory access issues, such as non-uniform memory access, and Network-on-Chip (NoC) hot-spots that plague the many-memory computing systems by dynamically directing the available memory bandwidth to the required memory interface

Transfer printing based microassembly and colloidal quantum dot film integration

Micro / nanoscale manufacturing requires unique approaches to accommodate the immensely different characteristics of the miniscule objects due to their high surface area to volume ratio when compared with macroscale objects. Therefore, surface forces are much more dominating than body forces, which causes the significant difficulty of miniscule object manipulation. Because of this challenge, monolithic microfabrication relying on photolithography has been the primary method to manufacture micro / nanoscale structures and devices in place of microassembly. However, by virtue of the two-dimensional (2D) nature of photolithography, formation of complex 3D shape architectures via monolithic microfabrication is inherently limited, which would otherwise enable improvements in performance and novel functionalities of devices. Furthermore, monolithic microfabrication is compatible only with materials which survive in a wet condition during photolithography. Delicate nanomaterials such as colloidal quantum dots cannot be processed via monolithic microfabrication. In this context, transfer printing has emerged as a method to transfer heterogeneous material pieces from their mother substrates to a foreign substrate utilizing a polymeric stamp in a dry condition. In this thesis, advanced modes of transfer printing are studied and optimized to enable a 3D microassembly called ‘micro-Lego’ and a novel strategy of quantum dot film integration. Micro-Lego involves transfer printing for material piece pick-and-place and thermal joining for irreversible permanent bonding of placed material pieces. A microtip elastomeric stamp is designed to advance transfer printing and thermal joining processes are optimized to ensure subsequent material bonding. The mechanical joining strength between material pieces assembled by micro-Lego are characterized by means of blister tests and the nanoindentation. Moreover, the electrical contact between two conducting materials formed by micro-Lego are examined. Lastly, inspired from the subtractive transfer printing technique, protocols of quantum dot film patterning using polymeric stamps made of a shape memory polymer as well as a photoresist are established for the convenient integration of quantum dots in various geometries and configurations as desired. Transfer printing-based micro / nanoscale manufacturing presented in this thesis opens up new pathways to manufacture not only complex 3D functional micro devices but also high resolution nano devices for unparalleled performance or for an unusual functionality, which are unattainable through monolithic microfabrication

Next-generation single-photon sources using two-dimensional hexagonal boron nitride

With the second quantum revolution unfolding, the realization of optical quantum technologies will transform future information processing, communication, and sensing. One of the crucial building blocks of quantum information architectures is a single-photon source. Promising candidates for such quantum light sources are quantum dots, trapped ions, color centers in solid-state crystals, and sources based on heralded spontaneous parametric down-conversion. The recent discovery of optically active defects hosted by 2D materials has added yet another class to the solid-state quantum emitters. Stable quantum emitters have been reported in semiconducting transition metal dichalcogenides (TMDs) and in hexagonal boron nitride (hBN). Owing to the large band gap, the energy levels of defects in hBN are well isolated from the band edges. In contrast to TMDs, this allows for operation at room temperature and prevents non-radiative decay, resulting in a high quantum yield. Unlike NV centers in diamond and other solid-state quantum emitters in 3D systems, the 2D crystal lattice of hBN allows for an intrinsically ideal extraction efficiency. In this thesis, advances in developing this new type of emitter are described. In the first experiment, quantum emitters hosted by hBN are attached by van der Waals force to the core of multimode fibers. The system features a free space and fiber-coupled single-photon generation mode. The results can be generalized to waveguides and other on-chip photonic quantum information processing devices, thus providing a path toward integration with photonic networks. Next, the fabrication process, based on a microwave plasma etching technique, is substantially improved, achieving a narrow emission linewidth, high single-photon purity, and a significant reduction of the excited state lifetime. The defect formation probability is influenced by the plasma conditions, while the emitter brightness correlates with the annealing temperature. Due to their low size, weight and power requirements, the quantum emitters in hBN are promising candidates as light sources for long-distance satellite-based quantum communication. The next part of this thesis focuses on the feasibility of using these emitters as a light source for quantum key distribution. The necessary improvement in the photon quality is achieved by coupling an emitter with a microcavity in the Purcell regime. The device is characterized by a strong increase in spectral and single-photon purity and can be used for realistic quantum key distribution, thereby outperforming efficient state-of-the-art decoy state protocols. Moreover, the complete source is integrated on a 1U CubeSat, a picoclass satellite platform encapsulated within a cube of length 10cm. This makes the source among the smallest, fully self-contained, ready-to-operate single-photon sources in the world. The emitters are also space-qualified by exposure to ionizing radiation. After irradiation with gamma-rays, protons and electrons, the quantum emitters show negligible change in photophysics. The space certification study is also extended to other 2D materials, suggesting robust suitability for use of these nanomaterials for space instrumentation. Finally, since the nature of the single-photon emission is still debated and highly controversial, efforts are made to locate the defects with atomic precision. The positions at which the defects form correlate with the fabrication method. This allows one to engineer the emitters to be close to the surface, where high-resolution electron microscopy can be utilized to identify the chemical defect. The results so far prove that quantum emitters in hBN are well suited for quantum information applications and can also be integrated on satellite platforms. A device based around this technology would thus provide an excellent building block for a worldwide quantum internet, where metropolitan fiber networks are connected through satellite relay stations