Femtosecond laser micro-structuring of silicon wafer in water confinement

This thesis investigates the use of femtosecond laser induced surface morphology on silicon wafer surface in water confinement. Unlike irradiation of silicon surfaces in the air, there are no laser induced periodic structures, but irregular roughness is formed when the silicon wafer is ablated under water. Interestingly, a particular parameter combination enables a smooth surface, which can improve the surface quality of micro-machining products. This thesis first investigates the single ablation and multi-pulse ablation processes in order to study the effects of laser parameters on ablation morphology, as well as the basic physics and mechanism of the laser-material interaction process under water...Next femtosecond laser direct writing process in water confinement is investigated...The unique discovery of a smoothly processed silicon surface in water confinement under certain laser parameter combinations may help improve laser direct micro-machining surface quality in industrial application --Abstract, page iii

Phase noise effects on OFDM : analysis and mitigation

Orthogonal frequency division multiplexing (OFDM) is a promising technique which has high spectrum efficiency and the robustness against channel frequency selectivity. One drawback of OFDM is its sensitivity to phase noise. It has been shown that even small phase noise leads to significant performance loss of OFDM. Therefore, phase noise effects on OFDM systems need to be analyzed and methods be provided to its mitigation. Motivated by what have been proposed in the literature, the exact signal to interference plus noise ratio (SINR) is derived in this dissertation for arbitrary phase noise levels. In a multiple access environment with multiple phase noise, the closed form of bit error rate (BER) performance is derived as a function of phase noise parameters. Due to the detrimental effects of phase noise on OFDM, phase noise mitigation is quite necessary. Several schemes are proposed to mitigate both single and multiple phase noise. It is shown that, while outperforming conventional methods, these schemes have the performance close to no-phase-noise case. Two general approaches are presented which extend the conventional schemes proposed in the literature, making them special cases of these general approaches. Moreover, different implementation techniques are also presented. Analytical and numerical results are provided to compare the performance of these migitation approaches and implementation techniques. Similar to OFDM, an OFDM system with multiple antennas, i.e., Multiple Input. Multiple Output (MIMO)-OFDM, also suffer severe performance degradation due to phase noise, and what have been proposed in the literature may not be applicable to MIMO-OFDM. Therefore, a new scheme is proposed to mitigate phase noise for MIMO-OFDM, which provides significant performance gains over systems without phase noise mitigation. This scheme provides a very simple structure and achieves adequate performance with high spectrum efficiency, which makes it very attractive for practical implementations

Eliminating Via-Plane Coupling using Ground Vias for High-Speed Signal Transitions

When a high-speed signal transits through a via that penetrates a plane pair, parallel-plane resonances can cause additional insertion loss for the signal. To eliminate this via-plane coupling, ground vias are added adjacent to the signal via. This paper discusses the impact of the ground vias as a function of the number of the ground vias, their locations, and the size of the plane pair. A block-by-block physics-based equivalent circuit modeling approach is used in the study. The underlying physics of the phenomenon and the design implications are also discussed in the paper

A Practical Simulation Flow for Singing Capacitor based Acoustic Noise Analysis

Multilayer ceramic capacitors (MLCCs) are widely used in modern electronics. Due to the piezoelectric effect of the ceramic material, however, MLCCs subjected to electrical noise may vibrate and generate acoustic noise, as \u27singing\u27. Acoustic noise can be annoying for users, especially within mobile devices, so it becomes important to perform acoustic noise analysis before a product is released. In this paper, a practical simulation flow for singing capacitor based acoustic noise is presented. The simulation flow and analysis method are developed on Ansys Sherlock and Mechanical. In Ansys Sherlock, local library and Approved Vendor List (AVL) files were used to build the model efficiently. After the PCB and all parts were set correctly, the model was imported to Ansys Mechanical for further modal analysis and harmonic analysis. Using the proposed simulation flow the simulation model could be easily created, and the inherent vibration properties and frequency response of the structure could be estimated

Fast Impedance Prediction for Power Distribution Network using Deep Learning

Modeling and simulating a power distribution network (PDN) for printed circuit boards with irregular board shapes and multi-layer stackup is computationally inefficient using full-wave simulations. This paper presents a new concept of using deep learning for PDN impedance prediction. A boundary element method (BEM) is applied to efficiently calculate the impedance for arbitrary board shape and stackup. Then over one million boards with different shapes, stackup, integrated circuits (IC) location, and decap placement are randomly generated to train a deep neural network (DNN). The trained DNN can predict the impedance accurately for new board configurations that have not been used for training. The consumed time using the trained DNN is only 0.1 s, which is over 100 times faster than the BEM method and 10 000 times faster than full-wave simulations

A Methodology For Predicting Acoustic Noise From Singing Capacitors In Mobile Devices

Multilayer ceramic capacitors (MLCCs) connected to a power distribution network (PDN) can create acoustic noise through a combination of the power rail noise at the MLCCs and the piezoelectric effect of the capacitor\u27s ceramic material. The deformation of the MLCCs brought on by power supply noise creates vibrations which cause the printed circuit board (PCB) to vibrate and generate the audible acoustic noise. In the following paper, a simulation methodology is presented to analyze the acoustic noise created by MLCCs on a PCB. A simulation model for the PCB vibration modal response is built and the modal superposition method is used to analyze the harmonic response of the PCB excited by the capacitor. By multiplying the measured power noise spectrum on the MLCC with the simulated deformation of the PCB found from the harmonic response analysis, the total response is obtained. Simulated results show a good correlation with the measured acoustic noise. The proposed method shows promise for analyzing and predicting the acoustic noise from singing capacitors

Averaged Behavior Model of Current-Mode Buck Converters for Transient Power Noise Analysis

Accurate Evaluation and Simulation of Power Noise is Critical in the Development of Modern Electronic Devices. However, the Widely Used Target Impedance Fails to Predict the Low-Frequency Noise Generated in a Device Due to the Existence of the Dc–dc Converter, Whose Output Impedance Can Change under Different Loading Conditions. a Physical Circuit Model is Then Desired to Replicate the Behavior of a Voltage Regulator Module, and the Average Technique is an Efficient Method to Estimate the Noise of a Pulse Width-Modulated (PWM) Converter. with the Emergence of Converters with Adaptive On-Time (AOT) Controllers, More Complex Averaging Methods Are Required, But None of Them Supports Transient Simulation. a General, Efficient, and Accurate Modeling Technique is Presented in This Article, Whose Framework Supports Both Current-Mode PWM and AOT Controllers. in Addition, a Novel Two-Step Parameter Extraction Method is Proposed, Which Can Be Used to Evaluate the Equivalent Values of Internal Feedback Parameters of an Encrypted Simulation Model or from Measurement. the Modeling Method is Validated by Both Simulation and Measurement