GaN-based HEMTs for Cryogenic Low-Noise Applications

Radio-astronomy deals with signals and radiations of extremely weak intensity. Also, it requires robust and rugged technologies able to sustain and prevent the Radio Frequency Interferences (RFI). Complying with the required high sensitivity, Low Noise Amplifiers (LNAs) operating at cryogenic temperatures are key elements in radio astronomy instrumentation. Thus far, advanced semiconductor technologies but with limited power-handling capabilities have been traditionally employed as LNAs. Over the past decades, Gallium Nitride (GaN)-based high electron mobility transistors (HEMTs) were demonstrated at room temperature to offer a combination of both excellent low-noise operation and a superior high-power handling performance compared to other materials. In addition, a number of studies indicated a promising potential for the GaN technology to operate at cryogenic temperatures. However, the cryogenic noise performance of the GaN-HEMTs remained unexplored so far.This thesis investigates the potential of GaN–based HEMTs for low-noise operation at these cryogenic temperatures. Established characterization and modeling approaches were employed for this purpose. As a main result, this work reveals a first estimation of the noise performance of GaN-HEMTs at cryogenic temperatures of ~10 K which compares to other more advanced technologies in this field. This was achieved through the extraction of a model, based on experimental noise measurements, describing the microwave noise behavior at cryogenic temperatures at the device level. The model predicts the noise contribution of GaN-HEMTs at cryogenic temperatures with respect to the frequency of operation, the dissipated power, and the total periphery of the device. Hence, it constitutes the basis for the design of future GaN-based LNAs which fulfill the different requirements set by the demanding cryogenic applications.The extracted cryogenic noise model was used to identify and analyze the role of the different physical parameters of the device, over which a technological control might be possible in the future in order to improve the assessed noise performance of the cryogenic GaN-HEMTs. From that perspective, GaN-HEMTs featuring superconducting Niobium (Nb)-gates were demonstrated for the first time. The successful integration of superconducting Nb-gates into AlGaN/GaN HEMTs was demonstrated on different samples, showing a suppression of the gate resistance independently of the width and length of the gate below a critical temperature \u1d447\u1d450 < 9.2 K. The superconductivity of the gate leads to the cancellation of the associated noise contribution. Comparing the noise performance of the resulting devices to that of the conventional Gold (Au)-gated GaN-HEMTs, it was concluded that further management of the device’s self-heating is required to enable the full potential of the Nb-gate by maintaining its superconductivity while operating at optimum-noise bias conditions

Feasibility study and design of a robust low-noise amplifier operating at millimeter-wave for high reliability applications

A feasibility study and the corresponding design flow for robust millimeter wave GaN LNAs is provided in this paper. Particular attention is devoted to the selection of the optimum geometry of the first stage active device. A trade-off is shown between noise performance and robustness requirements. The beneficial effects of source degenerative feedback are shown. The LNA's simulated performance are gain > 20B, NF < 1.7dB and power handling capability verified up to +20 dBm input power in CW operation. This design is well suited for operation in high reliability systems, such as space operation on airborne applications

Microwave Technologies for Satellite Systems: an ESA Perspective

Abstract -This paper intends to review the trends in solid-state microwave technologies and their impact on the anticipated performance enhancement expected for space applications

Characterization of Microwave Transistors for Robust Receivers and High Efficiency Transmitters

The next generation of integrated transceiver front-ends needs both robust low noise amplifiers and high power amplifiers on a single-chip. The Aluminium Gallium Nitride / Gallium Nitride (AlGaN/GaN) High Electron Mobility Transistors (HEMT) is a suitable semiconductor technology for this purpose due to its high breakdown voltage and high electron mobility. In this thesis the AlGaN/GaN HEMT’s thermal properties, noise and survivability have been characterized for the intended use in robust high power transceivers. Furthermore, a new characterization setup for load modulated high efficiency power amplifiers have been developed. The thermal properties of AlGaN/GaN HEMTs have been carefully investigated considering self-heating and its effect on small-signal parameters and high frequency noise. Self-heating is a severe problem for a high power transistor on any semiconductor material, including GaN. In addition to reliability problems, the performance of the operating HEMT degrades with temperature. The access resistances showed a large temperature dependence, which was also verified with TLM measurements. Due to the large self-heating, the temperature dependence of the access resistances has to be taken into account in the modeling of the AlGaN/GaN HEMT. A temperature dependent small-signal noise model was derived and verified through fabricated amplifiers. Design strategies for robust low noise amplifiers are discussed and implemented using the derived model. The new characterization setup gives new possibilities to characterize the performance of load modulated amplifiers. Recent results on load modulated amplifiers show promising efficiency improvements in back-off operation. Therefore a new measurement setup was developed that performs dynamic load modulation at the transistor terminals. This method should be useful to further improve the performance of load modulated amplifiers for high efficiency operation. The measurement setup is based on an active load-pull setup, where a modulated input signal is used to synthesize a time varying output power. The load impedance is dynamically controlled with the envelop of the input signal, following an optimum efficiency load trajectory. This gives better insight into device operation and possible improvements

Coherent Receiver Arrays for Astronomy and Remote Sensing

Monolithic Millimeter-wave Integrated Circuits (MMICs) provide a level of integration that makes possible the construction of large focal plane arrays of radio-frequency detectors—effectively the first “Radio Cameras”—and these will revolutionize radio-frequency observations with single dishes, interferometers, spectrometers, and spacecraft over the next two decades. The key technological advances have been made at the Jet Propulsion Laboratory (JPL) in collaboration with the Northrop Grumman Corporation (NGC). Although dramatic progress has been made in the last decade in several important areas, including (i) packaging that enables large coherent detector arrays, (ii) extending the performance of amplifiers to much higher frequencies, and (iii) reducing room-temperature noise at high frequencies, funding to develop MMIC performance at cryo-temperatures and at frequencies below 150GHz has dropped nearly to zero over the last five years. This has severely hampered the advance of the field. Moreover, because of the high visibility of < 150GHz cryogenic detectors in astrophysics and cosmology, lack of progress in this area has probably had a disproportionate impact on perceptions of the potential of coherent detectors in general. One of the prime objectives of the Keck Institute for Space Studies (KISS) is to select crucial areas of technological development in their embryonic stages, when relatively modest funding can have a highly significant impact by catalyzing collaborations between key institutions world-wide, supporting in-depth studies of the current state and potential of emerging technologies, and prototyping development of key components—all potentially leading to strong agency follow-on funding. The KISS large program “Coherent Instrumentation for Cosmic Microwave Background Observations” was initiated in order to investigate the scientific potential and technical feasibility of these “Radio Cameras.” This opens up the possibility of bringing support to this embryonic area of detector development at a critical phase during which KISS can catalyze and launch a coherent, coordinated, worldwide effort on the development of MMIC Arrays. A number of key questions, regarding (i) the importance and breadth of the scientific drivers, (ii) realistic limits on sensitivity, (iii) the potential of miniaturization into receiver “modules,” and (iv) digital signal processing, needed to be studied carefully before embarking on a major MMIC Array development effort led by Caltech/JPL/NGC and supported by KISS, in the hope of attracting adequate subsequent government funding. For this purpose a large study was undertaken under the sponsorship and aegis of KISS. The study began with a workshop in Pasadena on “MMIC Array Receivers and Spectrographs” (July 21–25, 2008)1, immediately after an international conference “CMB Component Separation and the Physics of Foregrounds” (July 14–18, 2008)2 that was organized in conjunction with the MMIC workshop. There was then an eight-month study period, culminating in a final “MMIC 2Workshop” (March 23–27, 2009).3 These workshops were very well attended, and brought together the major international groups and scientists in the field of coherent radio-frequency detector arrays. A notable aspect of the workshops is that they were well attended by young scientists—there are many graduate students and post-doctoral fellows coming into this area. The two workshops focused both on detailed discussions of key areas of interest and on the writing of this report. They were conducted in a spirit of full and impartial scrutiny of the pros and cons of MMICs, in order to make an objective assessment of their potential. It serves no useful purpose to pursue lines of technology development based on unrealistic and over-optimistic projections. This is crucially important for KISS, Caltech, and JPL which can only have real impact if they deliver on the promise of the technologies they develop. A broad range of opinions was evident at the start of the first workshop, but in the end a strong consensus was achieved on the most important questions that had emerged. This report reflects the workshop deliberations and that consensus. The key scientific drivers for the development of the MMIC technology are: (i) large angular-scale Bmode polarization observations of the cosmic microwave background—here MMICs are one of two key technologies under development at JPL, both of which are primary detectors on the recently-launched Planck mission; (ii) large-field spectroscopic surveys of the Galaxy and nearby galaxies at high spectral resolution, and of galaxy clusters at low resolution; (iii) wide-field imaging via deployment as focal plane arrays on interferometers; (iv) remote sensing of the atmosphere and Earth; and (v) wide-field imaging in planetary missions. These science drivers are discussed in the report. The most important single outcome of the workshops, and a sine qua non of this whole program, is that consensus was reached that it should be possible to reduce the noise of individual HEMTs or MMICs operating at cryogenic temperatures to less than three times the quantum limit at frequencies up to 150 GHz, by working closely with a foundry (in this case NGC) and providing rapid feedback on the performance of the devices they are fabricating, thus enabling tests of the effects of small changes in the design of these transistors. This kind of partnership has been very successful in the past, but can now be focused more intensively on cryogenic performance by carrying out tests of MMIC wafers, including tests on a cryogenic probe station. It was felt that a properly outfitted university laboratory dedicated to this testing and optimization would be an important element in this program, which would include MMIC designs, wafer runs, and a wide variety of tests of MMIC performance at cryogenic temperatures. This Study identified eight primary areas of technology development, including the one singled out above, which must be actively pursued in order to exploit the full potential of MMIC Arrays in a timely fashion: 1. Reduce the noise levels of individual transistors and MMICs to three times the quantum limit or lower at cryogenic temperatures at frequencies up to 150 GHz. 2. Integrate high-performing MMICs into the building blocks of large arrays without loss of performance. Currently factors of two in both noise and bandwidth are lost at this step. 3. Develop high performance, low mass, inexpensive feed arrays. 4. Develop robust interconnects and wiring that allow easy fabrication and integration of large arrays. 5. Develop mass production techniques suitable for arrays of differing sizes. 6. Reduce mass and power. (Requirements will differ widely with application. In the realm of planetary instruments, this is often the most important single requirement.) 7. Develop planar orthomode transducers with low crosstalk and broad bandwidth. 8. Develop high power and high efficiency MMIC amplifiers for LO chains, etc. Another important outcome of the two workshops was that a number of new collaborations were forged between leading groups worldwide with the object of focusing on the development of MMIC arrays

Ka-band High-linearity and Low-noise Gallium Nitride MMIC Amplifiers for Spaceborne Telecommunications

Gallium Nitride is becoming an interesting solution for low-noise applications in the lower part of the millimetre-wave spectrum and is gaining increasing attention in the space community for microwave receiver functionalities. Lately, its maturity level has increased and its performance in terms of noise figure and operating frequency is reaching other advanced III-V technologies such as Gallium Arsenide and Indium Phoshpide. Moreover, Gallium Nitride features higher power handling capability in comparison to the previously mentioned III-V technologies. In this context, we have designed and characterized two demonstrator circuits of critical microwave receiver functionalities: a Low-Noise Amplifier and a Low-Distortion Amplifier operating at Ka-band. It is shown that GaN circuits compare well in terms of noise figure, gain, and operating frequency with respect to other advanced III-V technologies, and most of all exhibit superior linearity in terms of intermodulation distortion. The designed Low-Noise Amplifier exhibits state-of-the-art 1.2 dB Noise Figure in the 27-31 GHz bandwidth thanks to a profitable combination of 60- and 100-nm gate length transistors on the same MMIC. On the other hand, the Low-Distortion Amplifier features state-of-the-art +30 dBm Output Third Order Intercept point in the same operating bandwidth while requiring only 216 mW dc power. The presented electrical performances are validated by comparing these designs to others available in open literature through figures of merit that normalize trade-offs by transistor length (therefore a fair comparison) aiming to highlight the merits of the proposed design methodologies