Nanocrystalline diamond (NCD) due its outstanding thermal, mechanical and tribological properties is an ideal candidate for MEMS/NEMS devices. NCD offers the possibility to increase the reliability and life time of RF-MEMS switches and by mitigating the problems of stiction, charge trapping, surface wear and cold welding found in traditional all metal MEMS devices. In this work, nanocrystalline diamond cantilever beams and bridges have been fabricated on a low resistive silicon substrate by using standard micromachining techniques. The diamond structures are then integrated onto alumina and aluminium nitride substrates upon which microwave transmission lines in the microstrip and coplanar waveguide (CPW) topology have been fabricated. The diamond actuators are integrated using a combined soldering and flip chip technique. The NCD bridges are thermally actuated wherein the difference in coefficient of thermal expansion between copper and diamond bends the diamond bridge thus moving the bridges to the actuated state. In the CPW topology, RF-MEMS switches and tunable planar inductors are realized using the micromachined devices. These devices are mounted on a 650 micrometer thick alumina substrate and the microwave characteristics are analyzed in the frequency range of 5-30 GHz. The switches yield a return loss of 15 dB and an insertion loss of 0.2 dB at 20GHz. An inductance ratio of 2.2 is achieved by the tunable inductors at 30 GHz. High power measurements are performed on the diamond actuators which utilize a dual actuation scheme which comprises of thermal and electrostatic actuation. The measurements are performed on the diamond actuators in the power range of 24-47 dBm for the mechanically actuated switches, and 24-40 dBm for electrically actuated switches. The measurements show an insertion loss of 0.2-03 dB in the entire power spectrum. NCD based RF-MEMS capacitive switches is also designed, fabricated and tested. The switches are fabricated on a high resistive silicon substrate and are electrostatically actuated. Small signal measurements are presented in the frequency range of 1-65 GHz. The measured insertion loss in the up-state is 1.1 dB at 50 GHz with 30 dB isolation in the down-state. Dielectric characterization is performed using the Corona-Kelvin technique and the standard I-V and C-V stress tests for nitride and diamond films. The leaky nature of the diamond films provides a potential solution to reliability issues related to dielectric charging.

This dissertation presents a systematic design and demonstration of a novel solid-state DC circuit breaker. The mechanical circuit breaker is widely used in power systems to protect industrial equipment during fault or abnormal conditions. Compared with the slow and high-maintenance mechanical circuit breaker, the solid-state circuit breaker is capable of high-speed interruption of high currents without generating an arc, hence it is maintenance-free. Both the switch and the tripping unit are solid-state, which meet the requirements of precise protection and high reliability. The major challenge in developing and adopting a solid-state circuit breaker has been the lack of power semiconductor switches that have adequate current-carrying capability and interruption capability. The high-speed, high-current solid-state DC circuit breaker proposed and demonstrated here uses a newly-emerging power semiconductor switch, the emitter turn-off (ETO) thyristor as the main interruption switch. In order to meet the requirement of being a high-current circuit breaker, ETO parallel operation is needed. Therefore the major effort of this dissertation is dedicated to the development of a high-current (5000A) DC switch module that utilizes multiple ETOs in parallel. This work can also be used to develop an AC switch module by changing the asymmetrical ETOs used to symmetrical ETOs. An accurate device model of the ETO is needed for the development of the high-current DC switch module. In this dissertation a novel physics-base lumped charge model is developed for the ETO thyristor for the first time. This model is verified experimentally and used for the research and development of the emitter turn-off (ETO) thyristor as well as the DC switch module discussed in this dissertation. With the aid of the developed device model, the device current sharing between paralleled multiple ETO thyristors is investigated. Current sharing is difficult to achieve for a thyristor-type device due to the large device parameter variations and strong positive feedback mechanism in a latched thyristor. The author proposes the "DirectETO" concept that directly benefits from the high-speed capability of the ETO and strong thermal couplings among ETOs. A high-current DC switch module based on the DirectETO can be realized by directly connecting ETOs in parallel without the bulky current sharing inductors used in other current-sharing solutions. In order to achieve voltage stress suppression under high current conditions, the parasitic parameters, especially parasitic inductance in a high-current ETO switch module are studied. The Partial Element Equivalent Circuit (PEEC) method is used to extract the parasitics. Combined with the developed device model, the electrical interactions among multiple ETOs are investigated which results in structural modification for the solid-state DC switch module. The electro-thermal model of the DC switch module and the heatsink subsystem is used to identify the "thermal runaway" phenomenon in the module that is caused by the negative temperature coefficient of the ETO's conduction drop. The comparative study of the electro-thermal coupling identifies a strongly-coupled thermal network that increases the stability of the thermal subsystem. The electro-thermal model is also used to calculate the DC and transient thermal limit of the DC switch module. The high-current (5000A) DC switch module coupled with a solid state tripping unit is successfully applied as a high-speed, high-current solid-state DC circuit breaker. The experimental demonstration of a 5000A current interruption shows an interruption time of about 5 microseconds. This high-speed, high-current DC switch module can therefore be used in DC circuit breaker applications as well as other types of application, such as AC circuit breakers, transfer switches and fault current limiters. Since the novel solid-state DC circuit breaker is able to extinguish the fault current even before it reaches an uncontrollable level, this feature provides a fast-acting, current-limiting protection scheme for power systems that is not possible with traditional circuit breakers. The potential impact on the power system is also discussed in this dissertation. / Ph. D.