The thesis is composed of two topics: A SOC design for one-time implantable spinal cord stimulation system ¡]SCS¡^, and the design of an inter-chip capacitance coupling circuit. In the first topic, the SOC design using wireless power and data transmission techniques for the SCS system is presented in this work. The proposed SOC can control 4 electrodes to generate different patterns of stimulation waves. It has multiple modes to drive whole the SCS system. Notably, the SOC contains a novel ASK demodulator which converts the ASK signals into digital signals reliably. The SOC is implemented using a typical 0.18-£gm 1P6M CMOS process. The chip area is only 1.71 * 1.41 mm2. Besides, the volume of the implantable SCS pulse generator utilizing this SOC is less than 24 cm3, and the power consumption is only 59.4 mW. In the second topic, a high-speed inter-chip capacitance coupling circuit is presented. Digital signals between two chips can be transceived through capacitive coupling of the proposed circuit. Notably, the transceivers are designed below the capacitors to attain the area reduction. It is an advanced application for high-speed wafer testing and 3D IC communication. A prototype chip is presented to achieve 2 Gbps on silicon using a typical 0.18 £gm 1P6M CMOS process. The chip area is 1045 ¡Ñ 894 £gm2. Besides, it only costs 21.47 mW in terms of power consumption. This capacitive coupling technique for high-speed digital circuit has great potential in the coming future.

Polyimide thin films have been widely used in microelectronic and Micro-Electro-Mechanical System applications due to their many excellent characteristics including low dielectric constant, easy processing, good step coverage ability, high heat resistance and chemical resistance. This paper presents the design, fabrication and complete characterization of an innovative capacitive relative humidity (RH) microsensor. The double polyimide thin films adopted in this study function as a capacitance sensing layer and a protecting layer of top electrodes respectively. To improve the humidity sensitivity and responding speed, interlacing out-of-plane electrodes are designed in the RH microsensor. The higher sensitivity ( 1.25 pF/¢HRH ), optimized sensing linearity ( 99.968¢H ) , very low hysteresis ( 0.24 ¢HRH ), excellent stability ( 1.36 ¢HRH ) , high accuracy ( ¡Ó 1.12 ¢HRH ) and fast response ( within 1 seconds ) characteristics of the RH microsensor have been demonstrated in this thesis.

This thesis reports the development and analysis of high performance CMOS readout electronics for increasing the performance of MEMS gyroscopes developed at Middle East Technical University (METU). These readout electronics are based on unity gain buffers implemented with source followers. High impedance node biasing problem present in capacitive interfaces is solved with the implementation of a transistor operating in the subthreshold region. A generalized fully differential gyroscope model with force feedback electrodes has been developed in order to simulate the capacitive interfaces with the model of the gyroscope. This model is simplified for the single ended gyroscopes fabricated at METU, and simulations of resonance characteristics are done. Three gyroscope interfaces are designed by considering the problems faced in previous interface architectures. The first design is implemented using a single ended source follower biased with a subthreshold transistor. From the simulations, it is observed that biasing impedances up to several gigaohms can be achieved. The second design is the fully differential version of the first design with the addition of a self biasing scheme. In another interface, the second design is modified with an instrumentation amplifier which is used for fully differential to single ended conversion. All of these interfaces are fabricated in a standard 0.6 &micro / m CMOS process. Fabricated interfaces are characterized by measuring their ac responses, noise response and transient characteristics for a sinusoidal input. It is observed that, biasing impedances up to 60 gigaohms can be obtained with subthreshold transistors. Self biasing architecture eliminates the need for biasing the source of the subthreshold transistor to set the output dc point to 0 V. Single ended SOG gyroscopes are characterized with the single ended capacitive interfaces, and a 45 dB gain improvement is observed with the addition of capacitive interface to the drive mode. Minimum resolvable capacitance change and displacement that can be measured are found to be 58.31 zF and 38.87 Fermi, respectively. The scale factor of the gyroscope is found to be 1.97 mV/(&deg / /sec) with a nonlinearity of only 0.001% in &plusmn / 100 &deg / /sec measurement range. The bias instability and angle random walk of the gyroscope are determined using Allan variance method as 2.158 &deg / /&amp / #8730 / hr and 124.7 &deg / /hr, respectively.

This thesis presents the development and microfabrication of capacitive micromachined ultrasonic transducers (CMUT) with diamond membranes for the first time in the literature. Although silicon and silicon nitride (Si3N4) membranes have been generally used as the membrane material in CMUTs. These membrane materials have moderate properties that can cause damage during the operation of CMUTs. In this thesis, a new material for the membrane is introduced for CMUTs. Diamond has exceptional potential in the area of micro-nano technologies due to unrivalled stiffness and hardness, excellent tribological performance, highly tailorable and stable surface chemistry, high thermal conductivity and low thermal expansion, high acoustic velocity of propagating waves, and biocompatibility. Based on these excellent material properties, diamond is employed in the new generation CMUT structures for more robust and reliable operations. The microfabrication process of CMUT has been generally performed with either sacrificial release process or wafer bonding technique. High yield and low cost features of wafer bonding process makes it preferable for CMUT devices. In this thesis, plasma-activated direct wafer bonding process was developed for the microfabrication of 16-element 1-D CMUT arrays with diamond membranes. They were designed to operate at different resonance frequencies in the range of 1 MHz and 10 MHz with different cell diameters (120, 88, 72, 54, 44 &mu / m) and element spacing (250, 375 &mu / m). 1-D CMUT array devices can be used for focusing ultrasound applications. The electronic circuit for 1-D CMUT devices with diamond membranes was designed and implemented on PCB for the ultrasound focusing experiment. This electronic circuit generates continuous or burst AC signals of &plusmn / 15 V with different and adjustable phase shifting options at 3 MHz frequency. 16 elements of 72 &mu / m 1-D CMUT array were successfully tested. Fully functional 7 elements of 1-D CMUT array are focused at an axial distance of 5.81 mm on the normal to the CMUT center plane. The CMUT array was excited using 10 Vp&minus / p with 10 cycles sinusoidal signals at 3 MHz. The microfabrication process and focusing ultrasound of 1-D CMUT devices with diamond membranes are done successfully in this thesis.

People for long term exposed to an air-conditioned but highly humid environment are vulnerable to hyper-sensitivity or asthma triggered by fungi or dust mites. This thesis aims to develop a high-linearity and low-hysteresis capacitive relative humidity (RH) microsensor to more precisely accommodate the humidity of living spaces. To reduce the hysteresis and enhance the linearity, this research uses not only one polyimide (PI) thin film as a humidity sensing layer but also utilizes another PI thin film as a protecting layer of the top electrodes. To improve further the RH sensitivity and responding speed, interlacing out-of-plane electrodes are designed in the RH microsensor. The main processing steps of the RH sensor developed in this study involve at least five photolithographic and four thin film deposition processes. The influences of sensing area, number of electrode pairs and testing temperature on the sensitivity and sensing linearity of humidity microsensors were investigated. Based on the measurement results, the sensitivity apparently increase as well as the sensing area (2 mm ¡Ñ 2 mm: 0.12 pF/%RH, 3 mm ¡Ñ 3 mm: 0.48 pF/%RH, 5 mm ¡Ñ 5 mm: 1.09 pF/%RH), and decrease with the number of electrode pairs (40 pairs: 0.51 pF/%RH, 20 pairs: 0.4 pF/%RH) and increase with the testing temperature. The thesis has demonstrated that the capacitance of the RH sensor vary from the relative humidity with a very linear relationship (linearity: 98.8%~99.99%) over the range of 30~70%RH. Finally, to increase effectively the surface area and to reduce further the hysteresis, three-dimensional (3D) moisture entrances and exits were designed and a very low hysteresis value (0.5%RH) can be achieved.

To achieve the miniaturization and high performance of the mobile phone, notebook, hearing aid and personal digital assistant (PDA), many researchers focus on the developing a new-type microphone with very small dimension, high quality and low manufacturing cost utilizing MEMS technology. By using the surface and bulk micromachining technologies, this thesis designed and fabricated a capacitive MEMS microphone with a polyimide bcakplate microstructure. The main processing steps adopted in this study include five photolithoghaphies and seven thin-film depositions. A MEMS-based microphone with an only 2¡Ñ2 mm2 sensing area of the floating Si3N4/Poly-Si/Si3N4 membrane and a 2 £gm-height gap distance between the top and bottom electrodes was implemented and characterized. Measured in a special isolated-box and under 1 kHz audio frequency, a -60.3 dB/Pa sensitivity (deducted the 22.6 dB output gain of the pre-amplifier) and a 51 dB signal to noise ratio (SNR) of the implemented MEMS microphone can be obtained as the biasing voltage only about 3 volts. The very low driving voltage, moderate SNR and sensitivity demonstrated in this work keep abreast with the results of many outstanding research laboratories in the world.

The electrostatic actuation with its several advantages is the main principle for micro-electro-mechanical systems (MEMS). One major drawback is the nonlinear behavior, which results into instability, known as the electrostatic pull-in effect. This effect might also push a closed-loop configuration into instability and thus makes a linear time-invariant control inapplicable to the system. The paper investigates the stability of an acceleration sensor in closed-loop operation with this setting. A simplified controller adjustment gives a first insight into this topic. Practical implementations saturate on the quantizer's full-scale value, which is also considered in the stability analysis. Numerical phase-plane analysis verifies the stability and shows further surprising results.

The modern society uses more and more electronic devices needed to being able to function together. This put higher demands on the electrical grid together with that the typical load have changed from the past. Therefore utility companies are obliged to keep the voltage within certain limits for this to function. What exact these limits have been have not always been clear since they have not been gathered in one single document.  This thesis is a cooperation with Kraftringen who also has been the initiator. Kraftringen would like to become more proactive in their work regarding electric power quality. For becoming more proactive continuously measurements have to be done but the locations have to be carefully selected in the beginning to get a wider perspective of the grid. Energy markets inspectorate (EI) is supervisory of the electric power quality in Sweden and since 2011 they have published a code of statutes (EIFS 2011:2 later 2013:1) intended to summarize limits on voltage. Some of the electrical power quality aspects are not mentioned in EIFS 2013:1 and standards have to be used to find limited values. Flicker and interharmonics are not mentioned in EIFS 2013:1 and for values on flicker the standard SS-EN 50160 has to be used and for interharmonics the standard SS-EN 61000-2-2 state limit values. Besides all this there are standards with stricter limits than EIFS 2013:1 e.g. for total harmonic distortion on voltage were SS-EN 61000-2-2 suggest 6 % instead of 8 %. Three different field studies have been conducted in order to get some perception of the present situation regarding electric power quality. Two measurements were conducted on a typical office building because they represents a large part of the typical load in Lund. The third measurement was conducted on a substation in a rural area to get a perception of the situation outside urban areas.  These measurements shown that the overall electric power quality was within given limits according to EIFS 2013:1 and different standards. However, conducted measurements shown some interesting results. Both the typical office buildings have a slightly capacitive power factor which results in that the voltage inside the building is going to be slightly higher than at the substation. Since the voltage level at the measured urban substation was above nominal voltage level with about 2-5 % this could be problematic. Another eventual problem with a load with a capacitive power factor is resonance with the inductive parts of the grid like transformers leading to magnified harmonic levels. It is suggested that Kraftringen expand their number of permanent electric power quality measurement locations to get a better overview of the present situation. The best suited locations to start with are such that have received complaints earlier, preferably measured on the low voltage side of the transformer for also register the amount of zero sequence harmonics. Next step in the measurement expansion would be substations known to be under higher load than others or substations with a PEN-conductor in a smaller area than the phase conductors, supplying a typical office load with high amounts of third harmonics and unbalance. From this it would be appropriate to spread out the measurement locations geographically to better get to know the grids behaviour.

Carbon based materials, including porous carbons and carbon layer composites, are finding increased usage in latest environmental and energy related research. Among porous carbon materials, hierarchical porous carbons with multi-modal porosity are proving out to be an effective solution for applications where the traditional activated carbons fail. Thus, there has been a lot of recent interest in developing low-cost, facile, easy to scale-up, synthesis techniques for producing such multi-modal porous carbons. This dissertation offers two novel synthesis techniques: (i) ice templating integrated with hard templating, and (ii) salt templating coupled with hard templating, for producing such hierarchically porous carbons. The techniques offer tight control and tunability of porosity (macro- meso- and microscale) in terms of both size and extent. The synthesized multi-modal porous carbons are shown to be an effective solution for three important environment related applications – (i) Carbon dioxide capture using amine supported hierarchical porous carbons, (ii) Reduction in irreversible fouling of membranes used for wastewater reuse through a deposition of a layer of hierarchical porous carbons on the membrane surface, (iii) Electrode materials for electrosorptive applications. Finally, because of their tunability, the synthesized multi-modal porous carbons serve as excellent model systems for understanding the effect of different types of porosity on the performance of porous carbons for these applications. Also, recently, there has been a lot of interest in developing protective layer coatings for preventing photo-corrosion of semiconductor structures (in particular Cu2O) used for photoelectrochemical water splitting. Most of the developed protective strategies to date involve the use of metals or co-catalyst in the protective layer. Thus there is a big need for developing low-cost, facile and easy to scale protective coating strategies. Based on the expertise gained in synthesizing porous carbon materials, and owing to our group’s interest in developing suitable photoelectrode materials, this dissertation also proposes a novel carbon-Cu2O composite comprising of a carbon layer coated Cu2O nanowire array structure as a high performance and stable photoelectrode material for photoelectrochemical water splitting.

This thesis presents research of two novel magnetic materials, LiHoF4 and Tb2Ti2O7. Experiments were performed at low temperatures and in an applied magnetic field to study thermal expansion and magnetostriction using a capacitive dilatometer designed during this project. This thesis presents 3 distinct topics. This manuscript begins with a thermodynamic description of thermal expansion and magnetostriction. The design of a capacitive dilatometer suitable for use at ultra-low temperatures and in high magnetic fields is presented. The thermal expansion of oxygen free high conductivity copper is used as a test of the absolute accuracy of the dilatometer. The first material studied using this dilatometer was LiHoF4. Pure LiHoF4 is a dipolar coupled Ising ferromagnet and in an applied transverse magnetic field is a good representation of the transverse field Ising model. An ongoing discrepancy between theoretical and experimental work motivates further study of this textbook material. Presented here are thermal expansion and magnetostriction measurements of LiHoF4 in an applied transverse field. We find good agreement with existing experimental work. This suggests that there is some aspect of LiHoF4 or the effect of quantum mechanical fluctuations at finite temperatures which is not well understood. The second material studied is the spin liquid Tb2Ti2O7. Despite theoretical predictions that Tb2Ti2O7 will order at finite temperature, a large body of experimental evidence demonstrates that spins within Tb2Ti2O7 remain dynamic to the lowest temperatures studied. In addition Tb2Ti2O7 also exhibits anomalous thermal expansion below 20K, giant magnetostriction, and orders in an applied magnetic field. Thermal expansion and magnetostriction measurements of Tb2Ti2O7 are presented in applied longitudinal and transverse fields. Zero-field thermal expansion measurements do not repeat the previously observed anomalous thermal expansion. A large feature is observed in thermal expansion at 100mK, in rough agreement with existing experimental work. Longitudinal and transverse magnetic fields were applied to Tb2Ti2O7. Longitudinal magnetostriction measurements show qualitatively di erent behavior than previous observations. These measurements were taken along di erent crystal axes so direct comparison cannot be made. Thermal expansion measurements in an applied transverse field show evolution with the strength of the applied field. This evolution may relate to an ordering transition, however difficulties in repeatability in a transverse field require that these results be repeated in an improved setup.