Browsing by Subject "microfabrication"

Now showing 1 - 2 of 2

Open Access
Design of GaN-based coplanar multi-octave band medium power power MMIC amplifiers
(2013) Eren, Gülesin
Wideband amplifiers are employed in many applications such as military radar, electronic warfare and electronic instrumentations and systems, etc. This thesis project aims to build a wideband medium power monolithic microwave integrated circuits (MMIC) amplifier which operates between 6 and 18 GHz by using 0.25 µm Gallium Nitride (GaN) based high electron mobility transistor (HEMT) technology. Fully monolithic microwave integrated circuits realized with gallium nitride (GaN) high electron mobility transistors are preferred for designing and implementing microwave and millimeter wave power amplifiers due to its superior properties like high breakdown voltage, high current density, high thermal conductivity and high saturation current. Large band gap energy and high saturation velocity of AlGaN/GaN high electron mobility transistors (HEMTs) are more attractive features for high power applications in comparison to the conventional material used in industry for power applications- gallium arsenide (GaAs). Besides the high power capability of GaN enables us to make devices with relatively smaller sizes than of GaAs based devices for the same output power. Device impedances in GaN technology are higher than the GaAs technology which makes broadband matching easier. Firstly, GaN material properties are overviewed by mentioning the design and characterization process of the AlGaN/GaN epitaxial layers grown by Bilkent NANOTAM. After the microfabrication process carried out by Bilkent NANOTAM is explained step by step. It is followed by characterization of the fabricated HEMTs. As a final step before going through the design phase, the small signal and large signal modeling considerations for GaN based HEMTs are presented. In the last part, designs of three different multi-octave MMIC amplifier realized with coplanar waveguide (CPW) elements are discussed. In order to extend the bandwidth and to obtain a flat gain response, two different design approaches are followed, the first one is realized with Chebyshev impedance matching technique without feedback circuit (CMwoFB) and the other one is utilized by Chebyshev Impedance matching technique with negative shunt feedback (CMwFB), respectively. To maximize the output power, two transistors in parallel (PT) are used by introducing Chebyshev matching circuit and negative feedback circuit. The design topology which consists of two parallel transistors (PT) is modified to fulfill all the design requirements and it is implemented by taking process variations and the previously obtained measurement results into account. The measurement and the simulation results match each other very well, the small signal gain is 7.9 ± 0.9 dB and the saturation output power in the bandwidth is higher than 27 dBm in this second iteration.
Open Access
Design, fabrication and characterization of liquid-solid microelectromechanical DC-contact switches
(2012) Çağatay, Engin
From critical applications such as life support systems and massive data communication centers to every day necessities like mobile phones and street lighting, people depend on the performance of electrical switches. Today, the vast majority of electrical switches are of solid-state semiconductor type. They are fast, with nanosecond response times, have the advantage of being produced by CMOS-compatible microfabrication processes, and unlike their major competitor counterparts, i.e., microelectromechanical systems (MEMS) switches, they do not suffer from mechanical contact issues like contact bounce, stiction, or contact degradation, due to the absence of solid-to-solid mechanical contacts. Therefore, electrical switches exhibit extremely long life times with superior reliability performance. However, they have a high ON-state resistance of 2-6 , low open-state impedance on the order of 105-107 , and show relatively low power-handling capabilities. In addition, their temperature and radiation-sensitive performance, limits their range of operating environment. The major counterpart switching technology, solid-to-solid DC-contact MEMS switches, on the other hand, transmit current when the two surfaces, namely dimple and contact pad, make contact. Although MEMS switches show very good RF performance, the required solid-to-solid contact is often quite non-ideal. This stems from the fact that the two contact surfaces have certain micro or nano-scale roughness including nano-scale asperities and thus cannot conform perfectly onto each other. Consequently, the actual contact area is only a small fraction of the apparent one. These devices suffer from mechanical problems such as switch bouncing, microwelding, adhesion and contact degradation, and as a result show degraded switching performance over time with long-term reliability issues. At this point, an alternative switching technology might be the proposal of liquid-to-solid MEMS (LS-MEMS) switches using movable liquid metal droplets. This promising concept enables electrical switches with higher isolation and lower insertion loss, much like conventional solid-solid MEMS switches. Moreover, since they do not have fragile moving solid parts, LS-MEMS switches potentially do not suffer from mechanical fatigue problems increased contact resistance and stiction/adhesion problems. Our aim in this study is to design and fabricate LS-MEMS switches, whereby we can characterize and examine the actuation of metallic liquid droplets, namely eutectic Ga-In (EGaIn), Gallium Indium Tin alloy (Galinstan), and mercury (Hg) using electrowetting on dielectric (EWOD) principle. We have investigated the effect of different actuation electrode geometries like rectangular, interdigitated fingers and crescent-shaped electrodes on the droplet actuation. With the application of 30-100 V voltage difference across the actuation electrode and the ground electrode, the metallic liquid droplets were observed to be actuated. With further optimization, LS-MEMS device structures demonstrated in this work might have potential applications as alternative high-performance electrical switches.