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Current AlGaN/GaN Heterojunction Field Effect Transistors (HFETs) make use of multiple sources, drains, and gates in parallel to maximize transconductance and effective gain while minimizing the current density through each channel. To connect the sources to a common ground, current practice prescribes the fabrication of air bridges above the gates and drains. This practice has the advantage of a low dielectric constant and low parasitic capacitance, but it is at the expense of manufacturability and robust device operation. In the study described below, the air bridges in AlGaN/GaN HFETs were replaced by a polymer supported metallization bridge with the intention of improving ease of fabrication and reliability. The DC, high frequency, and power performance for several polymer step heights were investigated. The resultant structures were functional and robust; however, their electrical performance was degraded due to high source resistance. The cause of the high source resistance was found to be thinning of the metallization at the polymer step. The effect was more pronounced for higher step heights. / Master of Science

Abstract ¡@¡@Biosensor chip has a lot of advantages, such as label-free, ultra-sensitive, highly selective, fast and real-time detection. Fabricating biosensor chip has great benefits for gene-detection, protein-detection, medical diagnosis and development of new medicine. This research will integrate the biomedical, chemistry, and physics, and also combined with biochemical technology and semiconductor technology to produce biosensor chip. ¡@¡@We use microelectronic semiconductor process technology to fabricate silicon nanowire field effect transistors (SiNW-FET). The source-drain current versus the voltage curve (Isd-Vsd) shows that the contact pad and the silicon nanowire form ohmic contact. And then we use chemical surface modification technologies to modified biotin on SiNW-FET to detect streptavidin. ¡@¡@In addition, we also grow AlGaN/GaN film by MBE, and fabricate nitride¡Vbased high electron mobility transistor (HEMT) by microelectronic semiconductor process technology. In this study, we apply HEMT in biosensor for pancreatic cancer marker CA19-9 antigen. And we modify pancreatic cancer marker CA19-9 antibody on the biosensor chip surface to detect pancreatic cancer marker CA19-9 antigen molecule. ¡@¡@Most of biomolecules are with weak charges, which can form chemical gating effect and change the conductance of p-type SiNW. And according to the streptavidin microfluidic measurement of biotin-modified SiNW-FET, the detection limit of streptavidin was 10-9 M. And the detection limit of pancreatic cancer marker CA19-9 antigen for N-HEMT biosensor was 150 U/mL.

Heterostructures of the materials system GaN/AlGaN/GaN were grown by molecular beam epitaxy on 6H-SiC substrates and high electron mobility transistors (HEMTs) were fabricated. For devices with large gate periphery an air bridge technology was developed for the drain contacts of the finger structure. The devices showed DC drain currents of more than 1 A/mm and values of the transconductance between 120 and 140 mS/mm. A power added efficiency of 41 % was measured on devices with a gate length of 1 µm at 2 GHz and 45 V drain bias. Power values of 8 W/mm were obtained. Devices with submicron gates exhibited power values of 6.1 W/mm (7 GHz) and 3.16 W/mm (25 GHz) respectively. The rf dispersion of the drain current is very low, although the devices were not passivated. / Heterostrukturen im Materialsystem GaN/AlGaN/GaN wurden mittels Molekularstrahlepitaxie auf 6H-SiC-Substraten gewachsen und High-Electron-Mobility-Transistoren (HEMTs) daraus hergestellt. Für Bauelemente mit großer Gateperipherie wurde eine Air-Bridge-Technik entwickelt, um die Drainkontakte der Fingerstruktur zu verbinden. Die Bauelemente zeigten Drainströme von mehr als 1 A/mm und Steilheiten zwischen 120 und 140 mS/mm. An Transistoren mit Gatelängen von 1 µm konnten Leistungswirkungsgrade (Power Added Efficiency) von 41 % (bei 2 GHz und 45 V Drain-Source-Spannung) sowie eine Leistung von 8 W/mm erzielt werden. Bauelemente mit Gatelängen im Submikrometerbereich zeigten Leistungswerte von 6,1 W/mm (7 GHz) bzw. 3,16 W/mm (25 GHz). Die Drainstromdispersion ist sehr gering, obwohl die Bauelemente nicht passiviert wurden.

The Square Kilometre Array (SKA) is a multibillion and a multinational science project to build the world’s largest and most sensitive radio telescope. For a very large field of view, the combined collecting area would be one square kilometre (or 1, 000, 000 square metre) and spread over more than 3,000 km wide which will require a massive count of antennas (thousands). Each of the antennas contains hundreds of low noise amplifier (LNA) circuits. The antenna arrays are divided into low, medium and high operational frequencies and located at different positions to boost up the telescope’s scanning sensitivity.The objective of this work was to develop and fabricate fully on-chip LNA circuits to meet the stringent requirements for the mid-frequency array from 0.4 GHz to 1.4 GHz of the SKA radio astronomy telescope using Monolithic Microwave Integrated Circuit technology (MMIC). Due to the number of LNA reaching figures of millions, the fabricated circuits were designed with the consideration for low cost fabrication and high reliability in the receiver chain. Therefore, a relaxed optical lithography with Lg = 1 µm was adopted for a high yield fabrication process.Towards the fulfilment of the device’s low noise characteristics, a large number of device designs, fabrication and characterisation of InGaAs/InAlAs/InP pHEMTs were undertaken. These include optimisations at each critical fabrication steps. The device’s high breakdown and very low gate leakage characteristics were further improved by a combination of judicious epitaxial growth and manipulation of materials’ energy gaps. An attempt to increase the device breakdown voltage was also employed by incorporating Field Plate structure at the gate terminal. This yielded the devices with improvements in the breakdown voltage up to 15 V and very low gate leakage of 1 µA/mm, in addition to high transconductance (gm) characteristic. Fully integrated double stage LNA had measured NF varying from 1.2 dB to 1.6 dB from 0.4 GHz to 1.4 GHz, compared with a slightly lower NF obtained from simulation (0.8 dB to 1.1 dB) across the same frequency band.These are amongst the attractive device properties for the implementation of a fully on-chip MMIC LNA circuits demonstrated in this work. The lower circuit’s low noise characteristic has been demonstrated using large gate width geometry pHEMTs, where the system’s noise resistance (Rn) has successfully reduced to a few ohms. The work reported here should facilitate the successful implementation of rugged low noise amplifiers as required by SKA receivers.

Gallium Nitride (GaN) high electron mobility transistors (HEMTs) are becoming increasingly popular in power amplifier systems as an alternative to bulkier vacuum tube technologies. GaN offers advantages over other III-V semiconductor heterostructures such as a large bandgap energy, a low dielectric constant, and a high critical breakdown field. The aforementioned qualities make GaN a prime candidate for high-power and radiation-hardened applications using a smaller form-factor. Several different types of semiconductor substrates have been considered for their thermal properties and cost-effectiveness, and Silicon (Si) has been of increasing interest due to a balance between both factors. In this thesis, the DC, RF, and thermal characteristics of GaN HEMTs grown on Si-substrates will be investigated through a series of accelerated lifetime experiments. A figure of merit known as the critical voltage is explored and used as the primary means by which the GaN-on-Si devices are electrically strained. The critical voltage is defined as the specific voltage bias by which a sudden change in device performance is experienced due to a deformation of the target GaN HEMT’s epitaxial structure. Literature on the topic details the inevitable formation of pits and cracks localized under the drain-side of the gate contact that promote electrical degradation of the devices via the inverse piezoelectric effect. Characteristic changes in device performance due to high field strain are recorded and physical mechanisms behind observed degraded performance are investigated. The study assesses the performance of roughly 60 GaN-on-Si HEMTs in four experimental settings. The first experiment investigates the critical voltage of the device in the off-state mode of operation and explores device recovery post-stress. The second experiment analyzes alterations in DC and RF performance under varying thermal loads and tracks the dependence of the critical voltage on temperature. The third experiment examines electron trapping within the HEMTs as well as detrapping methodologies. The final experiment links the changes in RF performance induced by high field strain to the small-signal parameters of the HEMT. Findings from the research conclude the existence of process-dependent defects that originate during the growth process and lead to inherent electron traps in unstressed devices. Electron detrapping due to high electric field stress applied to the HEMTs was observed, potentially localized within the AlGaN layer or GaN buffer of the HEMT. The electron detrapping in turn contributed to drain current recovery and increased unilateral performance of the transistor in the RF regime. Thermal experiments resulted in a positive shift in critical voltage, which enhanced gate leakage current at lower gate voltage drives.

In this thesis, the investigation focuses on the analysis of the high frequency characteristics and the nonlinearity of the transistors. In view of the III-V semiconductors which have excellent high frequency performance and the advantage for high frequency circuit design, the 0.15£gm InGaAs based pseudomorphic high electron mobility transistors provided by WIN semiconductor Corp. were used in this study. The high frequency measurement was utilized to extract both extrinsic and intrinsic components of the transistors, and further to establish the small signal equivalent model in each bias condition. According to the physical definition of the extracted gm, gds and the relationship with the output current, RF I-V curves could be determined through the integration procedure. The nonlinearity of the transistors can be attributed to the nonlinear input capacitance Cgs and Cgd, and the voltage dependent current source. The high frequency nonlinear models proposed in this thesis were based on classic Angelov model. For the high frequency application, the frequency dependent characteristics of the nonlinear sources would be taken into consideration through the combination of the RF I-V curves and extracted intrinsic components. Thus, the nonlinearities could be able to describe by nonlinear function through the fitting process and model the output performance completely. The accuracy of the models could be confirmed through the comparison between the simulation and the measurement result. Obviously, the high frequency models which include the high frequency effect and the nonlinear characteristics have excellent agreement with the experimental data.

Cette thèse s’inscrit dans le cadre du développement d’une filière de transistors de puissance à base de nitrure de Gallium au CEA-LETI. Ces transistors, en particulier les HEMT utilisant l’hétérostructure AlGaN/GaN, présentent des propriétés très utiles pour les applications de puissance. L’essor de cette technologie passe notamment par le développement de contacts ohmiques peu résistifs. Cette thèse a pour objectif d’approfondir la compréhension des mécanismes de formation du contact ohmique sur une structure AlGaN/GaN. Dans un premier temps, une étude thermodynamique sur une dizaine de métaux de transition utilisables comme base de l’empilement métallique du contact a été menée, ce qui a permis de retenir une métallisation Ti/Al. Puis, les différentes réactions physico-chimiques de cet empilement avec des substrats nitrurés ont été étudiées en faisant varier la composition et les températures de recuit de formation du contact ohmique. Enfin, plusieurs études sur structure AlGaN/GaN couplant caractérisations électriques et physico-chimiques ont permis d’identifier des paramètres décisifs pour la réalisation d’un contact ohmique, peu résistif et nécessitant une faible température de recuit. / This PhD is part of the development of Gallium nitride based power transistors at the CEA-LETI. These transistors, especially those based on AlGaN/GaN heterostructure, are very promising for power electronics applications. The goal of this PhD is to increase the knowledge of the mechanisms responsible for the ohmic contact formation on a AlGaN/GaN structure. First, a thermodynamic study of several transition metals has been performed, leading us to select Ti/Al metallization. Then, the multiple physico-chemical reactions of this stack with nitride substrates have been studied depending on the stack composition and the annealing temperature. Finally, several studies on AlGaN/GaN structure coupling both physico-chemical and electrical characterizations reveal different decisive parameters for the formation of an ohmic contact with a low-resistance and a low annealing temperature.