Examensarbeten för masterexamen

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https://odr.chalmers.se/handle/20.500.12380/50

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Engineering of electrical contacts on 2D-semiconductor field-effect transistors
(2024) Ullman, Patrik; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Prasad Dash, Saroj; Prasad Dash, Saroj; Md Hoque, Anamul
Two-dimensional (2D) semiconductor materials, such as the transition metal dichalcogenides (TMDC), have attracted great attention in the last decade due to their excellent electronic properties, thin nature, free of surface dangling bonds, and ability to retain high carrier mobility down to atomic thickness. TMDCs such as Molybdenum disulfide (MoS2) have the potential to be integrated into and augment conventional silicon complementary metal-oxide semiconductor (Si-CMOS) technology for post-Moore’s law technology. However, the performance of 2D field-effect transistors (FETs) are largely limited by poor charge carrier injection at the metalsemiconductor (M-S) interface, owing to a large Schottky barrier due to metalinduced gap states (MIGS) and fermi-level pinning (FLP). In this work, exfoliated MoS2-FETs were fabricated and various contact engineering approaches were proposed to mitigate MIGS, to achieve efficient carrier injection. The M-S junction of gadolinium and bismuth has been investigated using state-of-the-art fabrication methods and electrical measurement techniques. Semi-metal Bi has the ability to suppress MIGS due to its near-zero density of states (DOS) near the chargeneutrality point (CNP), while gadolinium is in theory able to lower the Schottky barrier by work function tuning. Key parameters were extracted by performing temperature-dependent I-V measurements, as well as height profile analysis by AFM. It was found that both bismuth and gadolinium have the potential to be considered as good ohmic contacts to MoS2, owing to their low SBH of ϕ ≈ 43 meV and ϕ ≈ 56 meV, respectively. This thesis work sheds light on the challenges of contact en gineering and fabrication methods for 2D-FETs.
Large-angle deflection lens using supercell metasurfaces
(2024) Vahlin, Kerstin; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Haglund, Åsa; Strandberg, Erik
A metasurface is an ultra-thin flat optical component, containing nanostructures that scatter light. Due to the planar structure it can be monolithically integrated with a vertical cavity surface-emitting laser (VCSEL), which removes alignment issues. With metasurfaces, full control of the wavefront is possible and hence a light beam can be shaped in almost anyway. For instance focusing metalenses, lenses that deflect light or vortex generators can be made. In many applications, for example in bio-photonics, it is desirable to have a lens with high numerical aperture, which entails deflection of light with large angels. The conventional way of designing a metasurface is to use phase mapping, however that approach has a fundamental limitation when it comes to creating steep angles. Therefor another type of metasurface based on diffracting elements have been implemented in this project. More specifically, these metasurfaces are made in GaAs to enable integration with GaAs VCSELs and the diffracting elements (supercells) are structured by nano-holes to get the desired light shape and circumvent the issue of aspect ratio dependent etching (ARDE). The metasurfaces were first simulated in COMSOL, then fabricated using electronbeam lithography and dry etching, and finally characterized. Metalenses utilizing supercells that deflect light up to 85◦ have been achieved. The lenses deflect with the desired angle and show a focusing effect. However the focus of the lenses is not as tight as desired and calls for further investigation.
Text Classification with Cellular Automata Networks
(2024) Johansson, Oscar; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Konkoli, Zoran; Konkoli, Zoran
The thesis focuses on several options of exploiting reservoir computing ideas in the context of text classification, using cellular automata networks as the reservoir. The key innovative aspect of the study is related to finding options for computing with low-density networks, which should be easier to manufacture. The overarching idea is to extend Wolfram’s elementary cellular automata rules and implement them within the framework of random cellular automata networks. The primary objectives of this study are as follows: (i) To determine the optimal network topologies, (ii) to identify the most effective transition rules within these networks, and (iii) to develop a robust methodological framework for finding the best networks. By exploring various network configurations, the aim is to uncover the structural characteristics that facilitate efficient information propagation and decision-making within the cellular automata framework. Observations from the study indicate that there exist cellular automata network configurations which can function as efficient reservoirs. Moreover, all considered cellular automata networks are categorised into different groups based on their performance, providing a solid foundation for further research.
High frequency modeling of SMD resistors
(2024) Andersson, John; Fahd, Malik; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Kuylenstierna, Dan; Gustavsson, Per
Passive components, including resistors, capacitors, and inductors, are fundamental in electrical circuit design. Surface mount devices (SMDs) are extensively used in microwave hardware development at high frequencies and precise simulations of SMD components are crucial. This thesis highlights the unpredictability of SMD resistors and underscores the importance of accurate simulations for achieving expected performance and creates a 3D and equivalent circuit models of 0402 and 0201 SMD resistors to do this. 3D models are created and verified using real measurements of a SMD resistor up to 32 GHz, while the target is for the model to be valid in 42 GHz. This model is used to create an equivalent circuit model and a scalable model for ADS that can scale the substrate height, relative permittivity and the resistance of the resistor which can be used when developing microwave circuits such as attenuators. The film that is the resistive element of the SMD component is shown to be the biggest contributing factor to parasitics. The thickness and width of the film were studied, and it was concluded that the width affected the parasitics the most. Results show very good agreement between 3D model and real measurement as well as agreement between equivalent circuit models and 3D models. The scalability ranges between 0-500 Ohm with relative permittivity being adjustable between 2.6-5 and 4.7-13 Mil substrate height. Through optimization using the scalable model, a T-attenuator is created and compared with a 3D simulation which shows very good agreement in S11 with less agreement in S21 in terms of a small frequency shift. The methods of this thesis can be extended to creating models of SMD inductors and conductors.
On generating propagating grid states from superconducting circuits
(2024) Edenmyr, Albin; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Johansson, Göran; Khanahmadi, Maryam
Due to current advancements in quantum technologies, quantum processors are growing in size, and we enter into the distributed quantum computing era. Distributed quantum computing is based on sharing information between several spatially distributed processors. This is achieved by sending photons carrying the quantum information between two or more distant quantum processors. Since we want all communication to be secure and tolerant against unavoidable noise in the communication channel, one attractive possibility is to encode the quantum information in error correctable quantum states, e.g. GKP states, Schrödinger cat states. The goal with error correctable states is to compensate for errors and loss in our communication channels. Previously it has been shown that optional encoding of quantum information from a processor into a quantum propagating mode makes the output field multimode, i.e. it consists of a combination of single mode states with different temporal envelopes. As a solution to this problem, we study the generation of error correctable quantum states, specifically GKP states, in highly lossy quantum circuits to prepare it as a traveling state in a waveguide instead of in the system. In this thesis, we present the basic theory for the preparation protocol; optimal release and the necessary extensions to compensate for noise. We study the character of the output field, as well as restrictions of this methodology.

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