This thesis aimed to develop a novel micro thermal electric generator (£g-TEG) with a series-array bridge microstructure utilizing microelectromechanical systems (MEMS) technology. By integrating the tens of thousands of micro-thermocouple in a centimeter square area, the temperature difference between the hot plane and cold plane of the presented £g-TEG can be converted into a useful electrical power. The thermoelectrically transferred output electrical power is suitable for recharging various mobile communication products. There are two main configurations of the conventional £g-TEGs have been proposed, including the vertical and lateral structure types. The heat flow of the vertical-type £g-TEG can be directly transferred by the thermocouples and hence the energy loss through the substrate can be efficiently reduced and the thermoelectrical conversion efficiency is usually higher than vertical-type £g-TEG. However, to obtain a useful electrical power output, the height of the vertical-type £g-TEG usually more than 100 micrometers and this will increase the production difficulty and fabrication cost. In contrast, the height of the lateral-type £g-TEG is only about several micrometers and hence the production difficulty and fabrication cost are lower than vertical-type £g-TEG. The non-neglect energy loss through the substrate of lateral-type £g-TEG will constrain the efficiency of electrical power generation. Using the surface micromachining technology, tens of thousands of suspending micro polysilicon thermocouple are integrated and serially connected to increase the efficiency of electrical power generation and reduce the substrate energy loss. The main fabrication processes adopted in this research are including seven thin-film deposition processes and five photolithography processes. The implemented Poly-Si based £g-TEG demonstrates a maximum temperature difference of 1.29¢J between the hot plane and cold plane (under nine different substrate temperatures), a maximum output voltage of 4.47 V/cm2 and a maximum output power of 601.4 nW/cm2. The comparison and analysis of experimental and simulation (ANSYS) results under the nine different substrate temperatures are investigated and the influence of length of suspending micro thermocouples is also discussed in this work.

Abstract Compared with the other micro acoustic wave devices, the flexural plate-wave (FPW) device is more suitable for being used in liquid-sensing applications due to its higher mass sensitivity, lower phase velocity and lower operation frequency. However, conventional FPW devices usually present a high insertion loss and low fabrication yield. To reduce the insertion loss and enhance the fabrication yield of FPW device, a 1.5 £gm-thick silicon-trench reflective grating structure (RGS), a high electromechanical coupling coefficient ZnO thin-film and a 5 £gm-thick silicon oxide membrane substrate are adopted in this research. The influences of the amount of silicon trench and the distance between inter-digital transducer (IDT) and RGS on the insertion loss and quality factor of FPW device are investigated. The main fabrication technology adopted in the study is bulk micromachining technology and the main fabrication steps include six thin-film deposition and five photolithography processes. Under the optimized conditions of the sputtering deposition processes (200¢J substrate temperature, 200 W radio-frequency power and 75% gas flow ratio), a high C-axis (002) orientation ZnO piezoelectric thin-film with 31.33% electromechanical coupling coefficient can be demonstrated. The peak of XRD intensity of the standard ZnO film occurs at diffraction angle 2£c = 34.422¢X, which matches well with our results (2£c = 34.282¢X). By controlling the thickness of ZnO/Au/Cr/SiO2/Si3N4 sensing membrane less than 6.5 £gm-thick, the fabrication yield of FPW device can be improved and a low operation frequency (6.286 MHz) and high mass sensitivity (-113.63 cm2 / g) can be achieved. In addition, as the implemented FPW device with four silicon trenches RGS and 37.5 £gm distance between IDT and RGS, a low insertion loss (-40.854 dB) and very high quality factor (Q=206) can be obtained. Keywords¡Gflexural plate-wave; silicon-trench reflective grating structure; electromechanical coupling coefficient; ZnO; bulk micromachining technology

The conventional flexural plate-wave (FPW) device has advantages of high mass sensitivity, low phase velocity and low operation frequency. However, conventional FPW devices usually present a high insertion loss and low fabrication yield. This thesis aimed to reduce the insertion loss of conventional FPW devices. The influences of geometry of inter-digital transducers (IDTs), pair number of IDTs, depth of focus and length of delay line on the insertion loss of FPW device are investigated. This research utilizes bulk micromachining technique to develop a low insertion-loss FPW device and the main fabrication steps include seven thin-film deposition and four photolithography processes. As the wavelength is 100 £gm, pair number of IDTs is 20, depth of focus is 1000 £gm and length of delay line is 500 £gm, the measured insertion loss of the implemented FPW device with conventional parallel-type IDTs and novel focus-type IDTs are equal to -48 dB and -45.06 dB, respectively. On the other hand, the insertion loss of FPW device with focus-type 25-pairs IDTs (-43.69 dB) is smaller than that of FPW device with focus-type 20-pairs IDTs (-45.06 dB). Additional, the measured insertion loss of FPW device with 500 £gm focus depth (-41.47 dB) is smaller than that of FPW devices with 1000 £gm focus depth (-43.69 dB) or with 1500 £gm focus depth (-45.39 dB). Furthermore, the FPW device with 500 £gm delay line presents a smaller insertion loss (-40.46 dB) than that of FPW devices with 250 £gm delay line (-41.47 dB) or with 750 £gm delay line (-40.95 dB). Finally, under the optimized specifications (focus-type/25 pairs IDTs, 500 £gm focus depth and 500 £gm delay line), the FPW-based microsensor demonstrates a high sensitivity (91.53 cm2/g), high sensing linearity (99.18 %) and low insertion loss (-40.46 dB), hence it is very suitable for development of biomedical sensing microsystem.

This thesis presents a novel monolithic phased array implemented using the RF MEMS technology. The structure, which is designed at 15 GHz, consists of four linearly placed microstrip patch antennas, 3-bit distributed RF MEMS low-loss phase shifters, and a corporate feed network. The RF MEMS phase shifter employed in the system consists of three sections with a total of 28 unit cells, and it occupies an area of 22.4 mm &amp / #61620 / 2.1 mm. The performance of the phase shifters is improved using high-Q metal-air-metal capacitors in addition to MEMS switches as loading elements on a high-impedance coplanar waveguide transmission line. The phased array is fabricated monolithically using an in-house surface micromachining process, where a 1.2-&amp / #61549 / m thick gold structural layer is placed on a 500-&micro / m thick glass substrate with a capacitive gap of 2 &amp / #61549 / m. The fabrication process is simple, requires only 6 masks, and allows the implementation of various RF MEMS components on the same substrate, such as RF MEMS switches and phase shifters. The fabricated monolithic phased array occupies an area of only 6 cm &amp / #61620 / 5 cm. The measurement results show that the phase shifter can provide nearly 20&amp / #61616 / /50&amp / #61616 / /95&amp / #61616 / phase shifts and their eight combinations at the expense of 1.5 dB average insertion loss at 15 GHz. The phase shifters can be actuated with 16 V, while dissipating negligible power due to its capacitive operation. It is also shown by measurements that the main beam can be steered to 4&amp / #61616 / and 14&amp / #61616 / by suitable settings of the RF MEMS phase shifters.

In this thesis 10x10 reconfigurable reflectarray is designed at 26.5 GHz where the change in the progressive phase shift between elements is obtained with RF MEMS switches in the transmission lines of unit elements composed of aperture coupled microstrip patch antenna (ACMPA). The reflectarray is illuminated by a horn antenna, and the reflected beam is designed to switch between broadside and 40&deg / by considering the position of the horn antenna with respect to the reflectarray. In the design, the transmission line analysis is applied for matching the ACMPA to the free space. The full wave simulation techniques in HFSS are discussed to obtain the phase design curve which is used in determining two sets of transmission line lengths for each element, one for the broadside and the other for switching to the 40&deg / at 26.5 GHz. The switching between two sets of transmission line lengths is sustained by inserting RF MEMS switches into the transmission lines in each element. Two types of RF MEMS switches, series and shunt configurations, are designed for the switching purpose in the reflectarray. The phase errors due to nonideal phase design curve and type of the RF MEMS switch are reduced. The possible mutual coupling effects of the bias lines used to actuate the RF MEMS switches are also eliminated by the proper design. To show the validity of the design procedure, a prototype of 20x20 reflectarray composed of ACMPA elements is designed at 25GHz and produced using Printed Circuit Board (PCB) technology. The measurement results of the prototype reflectarray show that the main beam can be directed to the 40&deg / as desired. The process flow for the production of the reconfigurable reflectarray is suggested in terms of integration of the wafer bonding step with the in-house standard surface micromachined RF MEMS process.

This thesis presents fabrication of shunt, capacitive contact type RF MEMS switches which are designed according to given mm-wave performance specifications. The designed switches are modified for investigation in terms of reliability and lifetime. To observe the real-time performance of switches a time domain measurement setup is established and a CV (capacitance vs. voltage) curve measurement system is also included to measure CV curves, pull-in and hold-down voltages and the shifts of these due to actuations. By using the established setup reliability and lifetime measurements under different bias waveforms in different environments are performed. After investigation for the most suitable condition for improving lifetime long-term tests are performed and the outstanding result of more than 885 hours of operation under cycling bias waveform is obtained.

A reflective type Fresnel lens using an array of micromirrors is designed and fabricated using the MUMPs?? surface micromachining process. The focal length of the lens can be rapidly changed by controlling both the rotation and translation of electrostatically actuated micromirrors. The suspension spring, pedestal and electrodes are located under the mirror to maximize the optical efficiency. The micromirror translation and rotation are plotted versus the applied voltage. Relations are provided for the fill-factor and the numerical aperture as functions of the lens diameter, the mirror size, and the tolerances specified by the MUMPs?? design rules. Linnik interferometry is used to measure the translation, rotation, and flatness of a fabricated micromirror. The reflective type Fresnel lens is controlled by independent DC voltages of 16 channels with a 0 to 50V range, and translational and torsional stiffness are calibrated with measured data. The spot diameter of the point source by the fabricated and electrostatically controlled reflective type Fresnel lens is measured to test focusing quality of the lens.

For the application of 4G wireless communication system, this thesis aims to develop a high-quality-factor and low-power-dissipation suspending micro-inductor using electrochemical deposition and surface micromachining technologies. This research presents three technical points to improve the quality factor and reduce the power dissipation of micro inductor, including (i) to adopt a low resistivity material (copper) as the conducting layer to decrease the Eddy current due to the skin effect and reduce the total series resistance and energy loss, (ii) to utilize a suspending structure to diminish the power loss through the substrate and (iii) to replace the silicon wafer with a high resistance substrate (Corning 7740) to compress effectively the power dissipation in high frequency operation. The implemented suspending micro-inductors were characterized by a commercial network analyzer (Agilent E5071C) under 0.5~20 GHz testing frequency range. All the inductances and quality factors of the micro-inductors proposed in this thesis are extracted by the Agilent ADS software. The optimized value of the quality factor is around to 24.9 and the corresponding inductance is equal to 5.43 nH .

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.

Utilizing the bulk and surface micromachining technologies, this thesis designed and fabricated a piezoresistive pressure microsensor for developing an in-vivo and real-time biomedical detection microsystem to monitor the uric pressure in patients¡¦ bladder. In this study, the main processing steps include the implantation of a moderate boron ion concentration into the N-epitaxial silicon layer to form the piezoresistors, anisotropic etching the backside silicon substrate to create a cavity by 30% KOH solution in 80¢XC temperature, and anodic bonding of the silicon based pressure microsensor and the hole-drilled glass sustain. To obtain the optimum design specification of the piezoresistive pressure microsensor, this study compared the characterization of the four types of devices with three different pressure sensing area (As) and two different length/width ratios (L/W) of the N-epitaxial piezoresistors. Based on the measurement results, the highest sensitivity (0.0076mV/(V*kgf/cm2) can be achieved as the As and the L/W ratio are equal to 1050 ¡Ñ 1050 £gm2 and 90/9 £gm/£gm, respectively. Such sensitivity is suitable for the application of bladder pressure detection microsystem. A very high sensing linearity (99.6%) can also be demonstrated in this research and this value approach to that of the commercial pressure sensor. On the other hand, through cooperation with another laboratory, this work has established a prototype of the uric pressure detecting microsystem by assembled with the piezoresistive pressure microsensor, a control ASIC and a radio-frequency (RF) module.