Dissertations / Theses on the topic 'Surface wave microwave discharge'

碩士
中原大學
化學工程研究所
93
Reforming of methane and carbon dioxide via surface-wave microwave plasma was investigated. A series of experiments were conducted to determine methane with carbon dioxide conversion and product distributions over wide ranges of operation parameters. In the meanwhile, a mathematical model was also developed to characterize the chemical reactions taking place in methane/carbon dioxide plasmas. The model results were then compared with experimental measurements. Experimental result showed that methane could be effectively converted in methane/carbon dioxide plasma. The CH4/CO2 ratio has extremely large effect on H2/CO ratio in the effluent. An increase in microwave power resulted in increases of hydrogen, carbon monoxide and acetylene selectivity. Increasing the feed flow rate made the conversion to decrease but the energy consumption was improved. The conversion of CH4 and CO2 were also improved when adding argon or helium to the plasma. In the modeling studies, it was found that predictions of CH4/CO2 conversion and product flow rate agreed well with experimental data over a wide range of microwave power and CH4/CO2 flow rate. Sensitivity tests showed that the destruction of methane and carbon dioxide was not only caused by electron-impact but also by the radical induced reactions. Regarding to the product generation, hydrogen was not only formed by H-atom abstraction of hydrocarbons, but also by the recombination of H-atoms on the tube wall. Carbon monoxide was primarily formed by electron-impact dissociation of carbon dioxide, CHO+M®CO+H+M was also an important pathway.

博士
國立清華大學
工程與系統科學系
103
Surface plasma wave (SPW) is a surface wave, propagating along the interface of plasma and dielectric, determined by the free charges (electrons) in the plasma. For example, in the gas discharge, such as low temperature plasma, the SPW operates at the microwave frequency while the infrared and visible frequency would be employed to sustain the SPW as the wave exists on the interface of metal and dielectric. In the plasma based semiconductor processes, for decades, the microwave based plasma density sensor, according to the properties of sur-face plasma wave, has attracted plenty of interest in the monitoring of plasma condition be-cause of its minimal perturbation to the plasma. The plasma density can be measured by the variations of the phase of surface plasma wave due to the environmental plasma conditions. On the other hand, the same physical mechanism of surface plasma wave can be employed in the photonics. The surface plasma wave propagating along the interface of metal and dielectric is so-called surface plasmon polariton (SPP). For the photonics based on SPPs, the corre-sponding SPP devices have increased potential to nanoscale transmission due to breaking the diffraction criteria of light guiding. In this study, a novel sensor, ridged microstrip microwave interferometer (RMMI), based on the characteristics of SPW, is developed for monitoring of plasma density in plasma pro-cessing tools. The sensor is designed to operate at 2.4 GHz microwave frequency, with a compact size and materials that are compatible with most plasma processing tools. 3D EM simulations, where plasma is treated as a dielectric medium having a plasma permittivity de-termined by plasma density and microwave frequency, are employed to determine the phase shift/plasma density relation of this sensor. Measurement results show that plasma density measured by the sensor, although placed at the chamber wall, does reflect the variations of the plasma density near the chamber center. Compared with the measurement by plasma absorp-tion probe (PAP), the difference of plasma density measured by RMMI and PAP is due to the position of sensors. In real-time plasma based process, the temporal result shows that the plasma density obviously increases as the bias power is turned on and large enough, compara-ble to the source power. With this capability, the RMMI can be used for real-time feedback control of plasma density in plasma processing tools. The second topic in this study is to design SPP devices, such as SPP waveguides (SPPWGs), SPPWG based directional coupler / optical resonator / switch. We present low loss (rounded) top metal silicon (Si) hybrid dielectric-loaded plasmonic waveguides (TM-SiHDLW/ RTM-SiHDLW) and the associated compact high performance optical devices, e.g., directional coupler, optical disk resonator. Simulation analysis using finite element meth-od is employed for the design of the SPP based devices. For the design of the TM-SiHDLW, we investigate the effect of a thin (10 nm) silicon nitride (SiNx) layer covering the waveguide which was added for minimizing uncertainties on optical properties of SiHDLW resulting from high density of dangling bonds on Si surface. The resulting propagation length is 0.35 um and the mode area is around 0.029 um^2. In the case of the RTM-SiHDLW, it adopted rounded corners for reducing Ohmic loss around stripe edges/corners, and thus, a propagation length of 0.47 um is obtained by numerical simulation, an increase of ~ 30%, at a similar mode area, compared to conventional TM-SiHDLW. The directional couplers based on the two SPPWGs we proposed here show comparable coupling length, 2.66 and 2.42 um, which is only ~ 0.76% and ~ 0.69% of the propagation length, demonstrating high efficiencies of light coupling. The low loss TE021 optical disk resonators, also built by the two SPPWGs, are also designed to operate at the 1550 nm wavelength. A metal enclosure is employed for re-ducing the radiation loss. Simulation results show that, for both resonators, quality factors of > 1800, more than twice the results in previous works, could be obtained with a comparable resonator size. Finally, a compact high performance electro-optic (E-O) plasmonic switch con-structed in a “directional coupler” like structure, including a SPPWG (RTM-DLW), similar to RTM-SiHDLW proposed above, and an optical waveguide, is designed and operated around the 1550 nm wavelength. An organic crystal, DAST, is adopted to serve as both the E-O ma-terial of the switch and the dielectric in the SPPWG. The variation of phase matching between the two waveguides is achieved by applying a voltage as low as 22.5 V on the E-O material, so that the optical wave can be efficiently switched between the two output ports. For the op-timized dimensions, a transmittance up to 66% and an extinction ratio nearly 10 dB are achieved.

博士
臺灣大學
電信工程學研究所
98
In this dissertation, the designs and analysis of RF electrostatic discharging (ESD) protections in microwave and millimeter-wave (MMW) amplifiers and MMW multi-cascode low noise amplifiers (LNAs) are investigated. One goal of the dissertation is to design and implement the RF ESD protection circuit with impressive performance in modern compound semiconductor process, and apply to a 60-GHz LNA. Based on impedance isolation approach, the protection circuit incorporates with the ESD device to form a broadband band-pass filter structure at MMW frequencies in TSMC complementary metal-oxide-semiconductor (CMOS) 0.13-μm technology. Compared with conventional designs, this work presents better RF performance and higher ESD robustness. At the same time, it overcomes the design bottleneck of integrated circuits to operate at V-band frequency, and is the first RF ESD-protected LNA in MMW regime. Moreover, two novel RF ESD protection circuits applied to 5.8-GHz amplifiers in 2-μm GaAs based heterojunction bipolar transistor (HBT) process are also proposed. One incorporates with the ESD devices to form a band pass filter structure with good impedance matching, which has eight discharging paths. The other is fabricated with parasitic capacitance reduction technique for the ESD protection, and has four discharging paths. The two amplifiers feature much higher ESD robustness and better RF performance than the conventional design with bi-directional discharging paths. The multi-cascode amplified structure is also described and analyzed in the dissertation. The multi-cascode structure has the advantages of miniature size and high gain. However, since the multi-cascode structure will contribute excess noise at high frequency, only the cascode configuration with two transistors is utilized in recently years. Consequently, a low power multi-cascode structure with noise reduction technique, which incorporates with the high gain characteristic is proposed and employed to the design of millimeter-wave LNAs. For demonstration, a Q-band LNA in CMOS 0.13-μm process with triple-cascode structure and a V-band LNA in 65-nm technology with cascode device are fabricated. The two LNAs feature lower power consumption, better noise figure, higher gain, and more compact size than the conventional LNAs. To the best of our knowledge, the Q-band LNA is the first triple-cascode LNA implemented in MMW frequency.

碩士
國立清華大學
物理學系
88
Plasma has a specific oscillation called as Plasma Oscillation. When Plasma Oscillation and Electromagnetic wave have the same frequency, there exist a resonance between the plasma and the electromagnetic wave . In non-uniform Plasma, the electric field becomes a local maximum if the local plasma density is equal to the resonance density. In accordance with the theory, the measured maximum value of the resonance response is proportional to the plasma density gradient while the measured spatial width of the plasma resonance is inversely proportional to the plasma density gradient. In this thesis, we use Langmuir probe to measure the characteristic of Plasma and use short dipole antenna to measure the amplitude of electromagnetic wave.

碩士
國立清華大學
物理學系
85
Plasmas generated by microwave (2.45GHz) illustrate a higher plasma density and ionization ratio than radio frequency plasmas (RF plasma). It also shows that chemical radicals and molecule fragments can effectively be produced by microwave. Nevertheless, it is difficult to creat large volume homogeneous microwave plasmas serviceable for large area material processing due to the short microwave wavelength and small penetration depth of the microave into the plasma. Meanwhile, the appearance of the plasma can significantly change the transmission property of the microwave and can result in the failure of producing a large area plasma. In this study, two physical schemes are employed to overcome this issue. The first scheme is that the microwave power required for discharge is distributedly coupled over the desired plasma area. The second scheme is to separate the main microwave propagation structure from the plasma production region. As a result, a large area plasma with an area of 30cm X 60cm can be successfully produced. A 12-period vane-type slow wave structure is constructed to form a tunable surface wave cavity which is operated at pi-mode and resonant at 2.45GHz. This planar cavity is located by 3cm distance to the top of the vacuum chamber where two quartz plates (30cm X 30cm) are installed as coupling windows to the microwave power. With this arrangement, a surface wave mode is excited in the plasma. Measurements of plasma properties, i.e., plasma density, temperature, and spatial uniformity are undertaking by a Langmuir single probe. The source has been operated with a varity of pressure and power and this study focuses on argon. Microwave power up to 5kW have been applied andthe pressure varied between 0.005torr and 40torr. The plasma density inexcess of 1E12 #/cm^3 has been obtained. The electron temperature is 1.0eV. An uniform plasma source of 30cm X 60cm has been achieved. The results can be easily scaled up to commercial use.

博士
國立清華大學
物理學系
88
A new microwave plasma source has been successfully developed. This plasma source has high density and large area characteristics due to the excitation of plasma surface wave by a tunable surface wave cavity. The tunable surface wave cavity is composed of a vane type slow wave structure. It is operated in the p mode and resonant at 2.45 GHz. A linear theory is developed to design the cavity and analyze the waves in the plasma guided by a vane-type slow wave structure. It shows that by choosing a proper dimension of the cavity, the p mode resonant frequency will not change after the excitation of the plasma. In experimental aspect, good characteristics of this plasma source are verified. The plasma area is in access of 30cm’20cm with a uniformity ±5% and plasma density as high as 6’1012 cm-3. The plasma temperature is ~1.5eV. Above all, the number of the periods of the p mode cavity can be increased without changing the resonance frequency and the distribution of the microwave fields such that this plasma source is easy to up-scaled. In addition, the plasma resonance in a surface wave sustained plasma is first clearly characterized. The amplitude of the electric field of the microwave becomes a local maximum in the location where the local plasma density is equal to a critical value. In accordance with the theory, the measured maximum value of the resonance response is proportional to the plasma density gradient while the measured spatial width of the plasma resonance is inversely proportional to the plasma density gradient. High-energy electrons are observed in the plasma resonance.

This dissertation presents the research on a novel combination of well proven concepts for passive electromagnetic wave-guiding components. The goal of this work is to overcome and minimize losses occurring in frequency-selective structures. The work aims to contribute to an improvement in the application of conventional and Substrate Integrated Waveguide (SIW). It is proposed to mount conventional waveguide structures on the surface of printed circuit boards containing substrate integrated waveguides. The crossover technology is referred to as Surface Mounted Waveguide (SMW). Theoretical investigations are performed, proving the validity and superiority of the proposed structure focusing on the elimination of losses, while maintaining low space consumption and printed circuit board technology compatible manufacturing processes. Additionally, a mode matching technique is developed and successfully applied to prototype such components. The validation of this method reveals superior computational speed when compared to commercial available electromagnetic field solvers. The proposed structures are validated by measurements of several prototypes, including coupled SMW resonator filters, combined SMW and SIW resonator filters, a SMW triple-layer diplexer and single individual SMW resonator filters. The experimental verification shows good agreement between theory and measurements. Moreover, the comparison to other technologies proves the superiority of the proposed structures.
Graduate

This diploma thesis deals mainly with utilization of plasma in technological aplications. The introductory part is apllied to the theoretical description of plasma generated by the surfatron. This launcher works with the frequency of 2,45 GHz and it is able to excite the surface wave, that sustains plasma column in a quartz tube. Plasma generated by surfatron was used for modification of surface properties of polyethylen to change its surface energy. By changing of surface energy it was reached of higher hydrophilicity. Plasma generated by surfatron was diagnosed in detail during experiments in a continual regime as well as in a pulse one with a help of a single {--} probe and a double {--} probe Langmuir measurement. In this diploma thesis there is discussed influence of pressure, power and other experimental options.

L’objectif de ce mémoire de maîtrise est de caractériser la distribution axiale des plasmas tubulaires à la pression atmosphérique créés et entretenus par une onde électromagnétique de surface ainsi que d’explorer le potentiel de ces sources pour la synthèse de matériaux et de nanomatériaux. Un précédent travail de thèse, qui avait pour objectif de déterminer les mécanismes à l’origine de la contraction radiale du plasma créé dans des gaz rares, a mis en lumière un phénomène jusque-là inconnu dans les plasmas d’onde de surface (POS). En effet, la distribution axiale varie différemment selon la puissance incidente ce qui constitue une différence majeure par rapport aux plasmas à pression réduite. Dans ce contexte, nous avons réalisé une étude paramétrique des POS à la pression atmosphérique dans l’Ar. À partir de nos mesures de densité électronique, de température d’excitation et de densité d’atomes d’Ar dans un niveau métastable (Ar 3P2), résolues axialement, nous avons conclu que le comportement axial de l’intensité lumineuse avec la puissance n’est pas lié à un changement de la cinétique de la décharge (qui est dépendante de la température des électrons et de la densité d’atomes d’Ar métastables), mais plutôt à une distribution anormale de dissipation de puissance dans le plasma (reliée à la densité d’électrons). Plus précisément, nos résultats suggèrent que ce dépôt anormal de puissance provient d’une réflexion de l’onde dans le fort gradient de densité de charges en fin de colonne, un effet plus marqué pour de faibles longueurs de colonnes à plasma. Ensuite, nous avons effectué une étude spectroscopique du plasma en présence de précurseurs organiques, en particulier le HMDSO pour la synthèse de matériaux organosiliciés et l’IPT pour la synthèse de matériaux organotitaniques. Les POS à la PA sont caractérisés par des densités de charges très élevées (>10^13 cm^-3), permettant ainsi d’atteindre des degrés de dissociation des précurseurs nettement plus élevés que ceux d'autres plasmas froids à la pression atmosphérique comme les décharges à barrière diélectrique. Dans de tels cas, les matériaux synthétisés prennent la forme de nanopoudres organiques de taille inférieure à 100 nm. En présence de faibles quantités d’oxygène dans le plasma, nous obtenons plutôt des nanopoudres à base d’oxyde de silicium (HMDSO) ou à base de titanate de silicium (IPT), avec très peu de carbone.
The purpose of this master thesis is to characterize the axial distribution of tubular discharges at atmospheric pressure sustained by electromagnetic surface wave and to explore their potential for materials and nanomaterials synthesis. A previous doctoral thesis, aimed at determining the mechanisms driving radial plasma contraction in rare gas discharges shed light on a yet unknown phenomenon occurring in surface wave discharges (SWD). As a matter of fact, increasing the power injected into the system leads to a change of the axial distribution of the discharge, in sharp contrast with the behavior commonly observed in reduced-pressure plasmas. In this context, we have performed a parametric investigation of atmospheric pressure SWD sustained in Ar gas. Based on our axially-resolved measurements of the electron density, excitation temperature, and number density of Ar atoms in metastable state (Ar 3P2), we found that the peculiar change of the axial distribution of the light intensity with power is not linked to a modification in the discharge kinetics (linked to the electron temperature and metastable number density) but rather to an anomalous power deposition (linked to the electron density). More specifically, such anomalous power deposition can be attributed to a wave reflection in the high gradient of charged particle densities near the end of the plasma column; a behavior that is more apparent in short plasma columns. Then, we have realized a parametric investigation of the discharge with the addition of organic precursors. Particularly, we used HMDSO for organo-silicon material synthesis and TTIP for organo-titanium material synthesis. It is found that because SWD are characterized by high charged particle densities (>10^13 cm^-3), higher precursor dissociation rates can be achieved with respect to other cold, atmospheric-pressure plasmas such as low-density dielectric barrier discharges. In this case, powder-like nanomaterials with sizes below 100 nm are obtained. Moreover, the addition of small amounts of oxygen into the discharge leads to the formation of round-like silicon oxide or titanium oxide nanoparticles.