Integration techniques of pHEMTs and planar Gunn diodes on GaAs substrates

This work presents two different approaches for the implementation of pseudomorphic high electron mobility transistors (pHEMTs) and planar Gunn diodes on the same gallium arsenide substrate. In the first approach, a combined wafer is used where a buffer layer separates the active layers of the two devices. A second approach was also examined using a single wafer where the AlGaAs/InGaAs/GaAs heterostructures were designed for the realisation of pHEMTs. The comparison between the two techniques showed that the devices fabricated on the single pHEMT wafer presented superior performance over the combined wafer technique. The DC and small-signal characteristics of the pHEMTs on the single wafer were enhanced after the use of T-gates with 70 nm length. The maximum transconductance of the transistors was equal to 780 mS/mm with 200 GHz maximum frequency of oscillation (fmax). Planar Gunn diodes fabricated in the pHEMT wafer, with 1.3 μm anode-to-cathode separation (LAC) presented oscillations at 87.6 GHz with maximum power of oscillation equal to -40 dBm

GaN HEMT Low Frequency Noise Characterization for Low Phase Noise Oscillator Design

The thesis presents low frequency noise (LFN) characterization of Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) for low phase noise oscillator design. First, GaN HEMT technology is benchmarked versus other transistor technologies, e.g., GaAs-InGaP Heterojunction Bipolar Transistor (HBT) and GaAs pHEMT, in terms of noise and power. In the comparison, LFN at given frequency normalized to DC power is used as a benchmark parameter. It is verified that InGaP HBT technology provides better performance in terms of both absolute noise level and normalized values compared to other technologies. However, at higher frequencies where flicker noise is less critical, GaN HEMT has an advantage of higher power. For this reason, GaN HEMT is considered to have good potential for design of oscillators for communication systems with large channel bandwidth. Then, some factors which influence the LFN of two types of GaN HEMTs: AlGaN/GaN based HEMT and AlInN/AlN/GaN based HEMT such as surface passivation methods and variations in transistor geometry are studied. It is seen that the surface passivation has a major impact on the noise level while the effect of transistor geometry (e.g. gate length, gate width and source-drain distance) is insignificant. The best surface passivation, with respect to LFN, is Al2O3 deposited with thermal Atomic Layer Deposition (ALD). Finally, two monolithic integrated circuit (MMIC) oscillators based on GaN HEMT technology are demonstrated. A fixed frequency GaN HEMT oscillator is designed at about 10 GHz with the best achieved phase noise of -100 dBc/Hz @ 100 kHz offset. Another GaN HEMT voltage controlled oscillator (VCO) is also designed with medium (15%) tuning range between 6.45-7.55 GHz, high tuning linearity, average output power about 1 dBm and low phase noise. For a bias of Vd /Id = = 6 V/33 mA, the measured phase noise is -98 dBc/Hz @ 100 kHz and -132 dBc/Hz @ 1 MHz offset frequencies, respectively. This is the lowest phase noise reported for a GaN HEMT based VCO with comparable tuning range and oscillation frequency. Its 1 MHz phase noise performance is comparable to state-of-the-art VCOs based on InGaP-HBT technology with similar tuning range

28 GHz balanced pHEMT VCO with low phase noise and high output power performance for 5G mm-Wave systems

This paper presents the study and design of a balanced voltage controlled oscillator VCO for 5G wireless communication systems. This circuit is designed in monolithic microwave integrated circuit (MMIC) technology using PH15 process from UMS foundry. The VCO ensures an adequate tuning range by a single-ended pHEMT varactors configuration. The simulation results show that this circuit delivers a sinusoidal signal of output power around 9 dBm with a second harmonic rejection between 25.87 and 33.83 dB, the oscillation frequency varies between 26.46 and 28.90 GHz, the phase noise is -113.155 and -133.167 dBc/Hz respectively at 1 MHz and 10 MHz offset and the Figure of Merit is -181.06 dBc/Hz. The power consumed by the VCO is 122 mW. The oscillator layout with bias and RF output pads occupies an area of 0.515 mm2

Boundary layer flow and heat transfer over a permeable shrinking sheet with partial slip

The steady, laminar flow of an incompressible viscous fluid over a shrinking permeable sheet is investigated. The governing partial differential equations are transformed into ordinary differential equations using similarity transformation, before being solved numerically by the shooting method. The features of the flow and heat transfer characteristics for different values of the slip parameter and Prandtl number are analyzed and discussed. The results indicate that both the skin friction coefficient and the heat transfer rate at the surface increase as the slip parameter increases

Integration of planar Gunn diodes and HEMTs for high-power MMIC oscillators

This work has as main objective the integration of planar Gunn diodes and high electron mobility transistors (HEMTs) on the same chip for the realisation of high-power oscillators in the millimeter-wave regime. By integrating the two devices, we can reinforce the high frequency oscillations generated by the diode using a transistor-based amplifier. The integration of the planar Gunn diode and the pseudomorphic HEMT was initially attempted on a combined gallium arsenide (GaAs) wafer. In this approach, the active layers of the two devices were separated by a thick buffer layer. A second technique was examined afterwards where both devices were fabricated on the same wafer that included AlGaAs/InGaAs/GaAs heterostructures optimised for the fabrication of pHEMTs. The second approach demonstrated the successful implementation of both devices on the same substrate. Planar Gunn diodes with 1.3 μm anode-to-cathode separation (Lac) presented oscillations up to 87.6 GHz with a maximum power equal to -40 dBm. A new technique was developed for the fabrication of 70 nm long T-gates, improving the gain and the high frequency performance of the transistor. The pHEMT presented cut-off frequency (fT) equal to 90 GHz and 200 GHz maximum frequency of oscillation (fmax). The same side-by-side approach was applied afterwards for the implementation of both devices on an indium phosphide (InP) HEMT wafer for the first time. Planar Gunn diodes with Lac equal to 1 μm generated oscillations up to 204 GHz with -7.1 dBm maximum power. The developed 70 nm T-gate technology was applied for the fabrication of HEMTs with fT equal to 220 GHz and fmax equal to 330 GHz. In the end of this work, the two devices were combined in the same monolithic microwave integrated circuit (MMIC), where the diode was connected to the transistor based amplifier. The amplifier demonstrated a very promising performance with 10 dB of stable gain at 43 GHz. However, imperfections of the material caused large variations at the current density of the devices. As a consequence, no signals were detected at the output of the complete MMIC oscillators

MMIC-based Low Phase Noise Millimetre-wave Signal Source Design

Wireless technology for future communication systems has been continuously evolving to meet society’s increasing demand on network capacity. The millimetre-wave frequency band has a large amount of bandwidth available, which is a key factor in enabling the capability of carrying higher data rates. However, a challenge with wideband systems is that the capacity of these systems is limited by the noise floor of the local oscillator (LO). The LO in today’s communication systems is traditionally generated at low frequency and subsequently multiplied using frequency multipliers, leading to a significant degradation of the LO noise floor at millimetre-wave frequencies. For this reason, the thesis considers low phase noise millimetre-wave signal source design optimised for future wideband millimetre-wave communications.In an oscillator, low frequency noise (LFN) is up-converted into phase noise around the microwave signal. Thus, aiming for low phase noise oscillator design, LFN characterisations and comparisons of several common III-V transistor technologies, e.g. GaAs-InGaP HBTs, GaAs pHEMTs, and GaN HEMTs, are carried out. It is shown that GaN HEMTs have good potential for oscillator applications where far-carrier phase noise performance is critical, e.g. wideband millimetre-wave communications. Since GaN HEMT is identified as an attractive technology for low noise floor oscillator applications, an in-depth study of some factors which affects LFN characteristics of III-N GaN HEMTs such as surface passivation methods and variations in transistor geometry are also investigated. It is found that the best surface passivation and deposition method can improve the LFN level of GaN HEMT devices significantly, resulting in a lower oscillator phase noise. Several MMIC GaN HEMT based oscillators including X-band Colpitts voltage-controlled-oscillators (VCOs) and Ka-band reflection type oscillators are demonstrated. It is verified that GaN HEMT based oscillators can reach a low noise floor. For instance, X-band GaN HEMT VCOs and a Ka-band GaN HEMT reflection type oscillator with 1 MHz phase noise performance of -135 dBc/Hz and -129 dBc/Hz, respectively, are demonstrated. These results are not only state-of-the-art for GaN HEMT oscillators, but also in-line with the best performance reported for GaAs-InGaP HBT based oscillators. Further, the MMIC oscillator designs are combined with accurate phase noise calculations based on a cyclostationary method and experimental LFN data. It has been seen that the measured and calculated phase noise agree well.The final part of this thesis covers low phase noise millimetre-wave signal source design and a comparison of different architectures and technological approaches. Specifically, a fundamental frequency 220 GHz oscillator is designed in advanced 130 nm InP DHBT process and a D-band signal source is based on the Ka-band GaN HEMT oscillator presented above and followed by a SiGe BiCMOS MMIC including a sixtupler and an amplifier. The Ka-band GaN HEMT oscillator is used to reach the critical low noise floor. The 220 GHz signal source presents an output power around 5 dBm, phase noise of -110 dBc/Hz at 10 MHz offset and a dc-to-RF efficiency in excess of 10% which is the highest number reported in open literature for a fundamental frequency signal source beyond 200 GHz. The D-band signal source, on the other hand, presents an output power of 5 dBm and phase noise of -128 dBc/Hz at 10 MHz offset from a 135 GHz carrier signal. Commenting on the performance of these two different millimetre-wave signal sources, the GaN HEMT/SiGe HBT source presents the best normalized phase noise at 10 MHz, while the integrated InP HBT oscillator demonstrates significantly better conversion efficiency and still a decent phase noise

Design and characterization of GaAs multilayer CPW components and circuits for advanced MMICs

With the demand of modern wireless communications, monolithic microwave integrated circuit (MMIC) has become a very promising technique as it is mass-productive, low loss and highly integrated. Microstrip and Coplanar Waveguide (CPW) are both widely used in MMIC. Particularly, CPW has seen a rapid increase on research works recent years due to its unique capability including having less parasitic contribution to the circuit. In this thesis, a novel 3-D multilayer CPW technique is presented. Semi-insulating (S.I.) GaAs substrate, polyimide dielectric layers and Titanium/Gold metal layers are employed in this five-layer structure. The active devices are based on GaAs pHEMTs technology provided by Filtronic Compound Semiconductor Ltd. The fabricated components are simulated and characterized by Agilent Advanced Design System (ADS) and Momentum E.M simulator. A novel Open-short-through de-embedding technique is developed and applied to the passive circuits in order to reduce the impact of pads on probing. A new library of components and circuits are built in this work. Various structures of 3-D CPW transmission lines are designed and characterized to demonstrate the low-loss and highly compact characters. Meanwhile, the influence of various combinations of metal and dielectric layers is studied in order to provide designers with great flexibility for the realization of novel compact transmission lines for 3D MMICs. The effect of temperature on the performance of the transmission lines has also been investigated. Moreover, a set of compact capacitors are designed and proven to have high capacitance density with low parasitics. Finally, based on the extraction of pHEMT parameters from circuit characterization and analysis program (IC-CAP), RF switch and active filter MMICs have been designed and simulated to provide references for further development of 3-D multilayer CPW circuits.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Innovative Design and Realization of Microwave and Millimeter-Wave Integrated circuits

Ph.DDOCTOR OF PHILOSOPH

High efficiency and high frequency resonant tunneling diode sources

Terahertz (THz) technology has been generating a lot of interest due to the numerous potential applications for systems working in this previously unexplored frequency range. THz radiation has unique properties suited for high capacity communication systems and non-invasive, non-ionizing properties that when coupled with a fairly good spatial resolution are unparalleled in its sensing capabilities for use in biomedical, industrial and security fields. However, in order to achieve this potential, effective and efficient ways of generating THz radiation are required. Devices which exhibit negative differential resistance (NDR) in their current-voltage (I – V) characteristics can be used for the generation of these radio frequency (RF) signals. Among them, the resonant tunnelling diode (RTD) is considered to be one of the most promising solid-state sources for millimeter and submillimeter wave radiation, which can operate at room temperature. However, the main limitations of RTD oscillators are producing high output power and increasing the DC-to-RF conversion efficiency. Although oscillation frequencies of up to 1.98 THz have been already reported, the output power is in the range of micro-Watts and conversion efficiencies are under 1 %. This thesis describes the systematic work done on the design, fabrication, and characterization of RTD-based oscillators in monolithic microwave/millimeter-wave integrated circuits (MMIC) that can produce high output power and have a high conversion efficiency at the same time. At the device level, parasitic oscillations caused by the biasing line inductance when the diode is biased in the NDR region prevents accurate characterization and compromises the maximum RF power output. In order to stabilise the NDR devices, a common method is the use of a suitable resistor connected across the device, to make the differential resistance in the NDR region positive. However, this approach severely hinders the diode’s performance in terms of DC-to-RF conversion efficiency. In this work, a new DC bias decoupling circuit topology has been developed to enable accurate, direct measurements of the device’s NDR characteristic and when implemented in an oscillator design provides over a 10-fold improvement in DC-to-RF conversion efficiency. The proposed method can be adapted for higher frequency and higher power devices and could have a major impact with regards to the adoption of RTD technology, especially for portable devices where power consumption must be taken into consideration. RF and DC characterization of the device were used in the realization on an accurate large-signal model of the RTD. S-parameter measurements were used to determine an accurate small-signal model for the device’s capacitance and inductance, while the extracted DC characteristics where used to replicate the I-V characteristics. The model is able to replicate the non-stable behavior of RTD devices when biased in the NDR region and the RF characteristics seen in oscillator circuits. It is expected that the developed model will serve in future optimization processes of RTD devices in millimeter and submillimeter wave applications. Finally, a wireless data transmission link operating in the Ka-band (26.5 GHz – – 40 GHz) using two RTDs operating as a transmitter and receiver is presented in this thesis. Wireless error-free data transfer of up to 2 gigabits per second (Gbit/s) was achieved at a transmission distance of 15 cm. In summary, this work makes important contributions to the accurate characterization, and modeling of RTDs and demonstrates the feasibility of this technology for use in future portable wireless communication systems and imaging setups