Ultra-Low Power InAs/AlSb HEMTs for Cryogenic Low-Noise Applications
Abstract: The InAs/AlSb high electron mobility transistor (HEMT) is an emerging microwave device technology for ultra-low power and low noise applications. Due to the low bandgap (0.36 eV) and to the high mobility and peak velocity of electrons in the InAs channel, promising performance of InAs/AlSb HEMT-based circuits has been demonstrated at room temperature. However, the characterization of the cryogenic properties had not been reported prior to this work. The study of the device performance at cryogenic temperatures, which is of large importance in scientific instrumentation where lowest noise figure and power consumption are essential, was the initial objective of this work. Throughout this investigation, results advancing the state-of-the-art in InAs/AlSb HEMTs were found and are presented in this thesis. Anisotropic transport in the InAs/AlSb heterostructure grown on InP bulk substrate has been investigated. Significant differences in sheet resistance and electron mobility along the different crystal orientations were observed due to elongated pits in the channel. InAs/AlSb HEMTs fabricated along the favorable orientation delivered drain current and peak transconductance up to 25% higher. The electrical performance and stability against oxidation of shallow-mesa InAs/AlSb HEMTs have been improved through the development of a fabrication process based on in-situ passivation. Moreover, a true planar technology based on ion implantation has been demonstrated, with state-of-the-art performance and excellent stability against oxidation. This paves the way for reliable InAs/AlSb HEMT monolithic microwave integrated circuits (MMICs). The electrical properties InAs/AlSb HEMTs have been investigated as a function of temperature, showing an overall improvement of the device under cryogenic operation in the low-power regime. Significantly lower on-resistance and gate leakage as well as improved drain current saturation and up to 40% higher peak transconductance have been measured. At 6 K and for a drain bias of 0.1 V, the cut-off frequency and the maximum oscillation frequency increased by 72% and 100%, respectively, whereas the minimum noise figure at 8 GHz was reduced from 2.3 dB to 0.6 dB. The suitability of the InAs/AlSb HEMT for cryogenic and ultra low-power applications was demonstrated in a three-stage low noise amplifier operating in the 4-8 GHz frequency range. At 13 K, a minimum noise temperature of 19 K and a gain above 24 dB were measured at a total DC power consumption of only 6 mW. This corresponded to an ultra-low power consumption of only 600 μW in the HEMT device.
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