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Identifier 000450092
Title Investigation of drain noise in high electron mobility transistors through On-Wafer characterization and modelling
Alternative Title Έρευνα θερμικού θορύβου στα τρανζίστορ υψιλής κινητικότητας ηλεκτρονίων ΗΕΜΤ χαρακτηρισμού σε πλακίδια ημιαγωγών και μοντελοποίησης
Author Gabritchidze, Bekari I.
Thesis advisor Ηλιόπουλος, Ελευθέριος
Reviewer Minnich, Austin
Cleary, Kieran
Δεληγιώργης, Γεώργιος
Παυλίδου, Βασιλική
Κομίνης, Ιωάννης
Γεωργακίλας, Αλέξανδρος
Abstract Noise in high electron mobility transistors (HEMTs) is generated by small current and voltage fluctuations, attributed to the discrete nature of electrical charge. These fluctuations determine the lower limit of the magnitude of the electrical signal that can be amplified by a HEMT without significant loss in the signal quality. Understanding and mitigating these fluctuations is therefore important; especially for fields such as radio astronomy and quantum computing, where HEMT based integrated circuits are constantly used to detect weak noise signals of similar magnitude and statistics as that introduce by the HEMTs themselves. The noise in HEMTs, at microwave and millimeter wave frequencies is studied as thermal or Johnson-Nyquist noise and in the presence of leakage currents as shot noise as well. These two noise sources are used in conjunction to a small signal model(SSM) to characterize and model the noise in terms of device resistances and their equivalent physical temperatures(Tph). In the late 1980s, Marian Pospieszalski introduced a noise model based on two uncorrelated thermal noise sources attributed to the gate resistance (Rg) and drain-source conductance(gds) of the HEMT. The Rg produces thermal noise that can be explained by its Tph; the gds, however, produces noise that is significantly larger than what would be expected for thermal noise source at Tph. A temperature, commonly referred to as drain temperature (Td) is assigned to gds to explain this discrepancy, is one or two orders of magnitude larger than Tph and is treated as a fitting parameter. Because Td ≫ Tph, the noise produced by gds is the limiting factor for the lowest achievable noise in HEMTs, at microwave and millimeter wave frequencies. Understanding the physical mechanism behind Td and then engineering HEMTs so that Td → Tph is central to the advancement of radio-astronomy. In this work we develop a microwave noise and S-parameter measurement system, based on a cryogenic probe station. First, we use this set-up to perform on-wafer characterization of S-parameters and microwave noise (T50) of discrete GaAs and GaN high electron mobility transistors (HEMTs) over a range of drain-source voltages (VDS) and physical temperatures (Tph) from 40 K to 300 K. Next, we develop SSM based on the data; to model the Sparameter characteristics of the HEMTs at each VDS and Tph, then we assign thermal noise source to the resistive elements of the SSM to create a noise model; Finally, we extract Td by fitting the noise model to the measured T50 at each VDS and Tph. The results of our investigation show that Td follows a super-linear and a sub-linear trend with VDS for GaAs and GaN HEMTs, respectively; while the dependence of Td on Tph is super-linear for both devices. In order to explain these data we developed a physical model for the drain noise, where Td arises due to a thermal component associated with the channel resistance and a component due to real-space transfer (RST) of electrons from the channel to the barrier. Based on this model we find that Td is dominated by electron physical temperatures Te at Tph below 100 K, while at 300 K the RST can account for over 60% of the total Td. Our model, indicates that Td can be reduced by improving the confinement of electrons in the quantum well and therefore decreasing the contribution of RST. Based on this finding; we expect to lower the noise temperature of room-temperature receivers by up to ∼ 50% for the GaAs devices and up to ∼ 40% for the GaN HEMTs.
Language English
Subject Cryogenic characterization
Cryogenics
Drain noise
HEMTs
Low noise amplifiers
Real-space transfer
Ενισχυτές χαμηλού θορύβου
Θερμικός θόρυβος
Κρυογενικά
Κρυογενικός χαρακτηρισμός
Φυσική μεταφορά ηλεκτρονίων
Issue date 2022-10-10
Collection   School/Department--School of Sciences and Engineering--Department of Physics--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/2/2/8/metadata-dlib-1658747189-535620-22715.tkl Bookmark and Share
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