Terahertz responsivity of field-effect transistors under arbitrary biasing conditions

Current biased photoresponse model of long channel field-effect transistor (FET) detectors is introduced to describe the low frequency behavior in complex circuit environment. The model is applicable in all FET working regions, including subthreshold, linear, saturated modes, includes bulk potential variations, and handles the simultaneous gate-source and drain-source detection or source-driven topologies. The model is based on the phenomenological representation that links the photoresponse to the gate transconductance over drain current ratio (gm/ID) and circuit theory. A derived method is provided to analyze the detector behavior, to characterize existing antenna coupled detectors, and to predict the photoresponse in a complex circuit. The model is validated by measurements of 180 nm gate length silicon and GaAs high electron mobility FETs

APPLICATIONS OF PLASMONICS FOR TERAHERTZ DETECTION, MODULATION AND WAVEGUIDING

Ph.DDOCTOR OF PHILOSOPH

Characterization of Optimized Si-MOSFETs for Terahertz Detection

Research into components needed to utilize the THz region of the electromagnetic spectrum has recently gained more attention due to advances in semiconductor technology and materials science. These advances have led to the desire of create CMOS focal plane arrays (FPA) for THz imaging in a range of applications such as astronomy, security, earth science, industry, and communications. Si-MOSFETs are being investigated as the sensing node in THz FPAs due to their ability to detect THz and their ease of integration into the CMOS process facilitating the fabrication of large format arrays. To investigate the performance of devices fabricated at a commercial foundry, a test chip containing MOSFETs with appropriately sized dipole bowtie antennae were fabricated using a 0.35 micron CMOS process. A number of fabrication parameters were varied including both MOSFET geometry and antenna design to investigate optimizing detection for the 200 GHz atmospheric window. To test these devices an experimental low noise setup comprising of a lock-in amplifier, low noise current pre-amplifier, and various low noise techniques has been assembled. Different biasing conditions and temperature were used to analyze the mechanisms of detection and find the best operating parameters. The devices that implemented a 2 µm source extension, and antennae attached to the source and gate region yielded the largest response to 200 GHz incident radiation. The peak THz response varied little between room temperature and when cooled to 130K. Responsivities as high as 4.5 mA/W were measured and NEP as low as 6 nW/√Hz were achieved at room temperature. These results show agreement with other works regarding THz response to temperature and different biasing conditions

Journal of Telecommunications and Information Technology, 2004, nr 1

kwartalni

Photodetectors

In this book some recent advances in development of photodetectors and photodetection systems for specific applications are included. In the first section of the book nine different types of photodetectors and their characteristics are presented. Next, some theoretical aspects and simulations are discussed. The last eight chapters are devoted to the development of photodetection systems for imaging, particle size analysis, transfers of time, measurement of vibrations, magnetic field, polarization of light, and particle energy. The book is addressed to students, engineers, and researchers working in the field of photonics and advanced technologies

Evaluation of MOSFETs for Terahertz Detector Arrays

The terahertz (THz) region of the electromagnetic spectrum is one of the last remaining regions that has yet to be fully characterized. THz imaging is one of the foremost drivers of this technology gap and has the potential to push development in the near term to a similar capability level as infrared (IR). Properties of THz radiation are introduced, along with promising current applications. Interest in array based imaging of THz radiation (T-Rays) has gained traction lately, specifically using a CMOS process due to its ease of manufacturability and the use of MOSFETs as a detection mechanism. The theory outlined explains that incident terahertz radiation on to the gate channel region of a properly configured MOSFET can be related to plasmonic response waves, which change the electron density and potential across the channel producing a photoinduced response. This work utilizes a test chip fabricated to investigate these effects. The 0.35 um silicon CMOS MOSFETs tested contain varying structures, providing a range of detectors to analyze. Included are individual test MOSFETs for which various operating parameters and modes are studied and results presented. The focus on single transistor-antenna testing provides a path for discovering the most efficient combination for coupling 0.2 THz band energy. Specifically introduced, is a novel source region extension which is proven to improve MOSFET response. Sensitivity analysis and responsivity are described, in parallel with theoretical expectations of the plasmonic response in room temperature conditions. A maximum responsivity of 40 kV/W and corresponding NEP of 10 pW/Hz^(-1/2) (±10% uncertainty) is demonstrated

Journal of Telecommunications and Information Technology, 2009, nr 4

kwartalni

Wide Bandgap Based Devices

Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era. SiC- and GaN-based devices are starting to become more commercially available. Smaller, faster, and more efficient than their counterpart Si-based components, these WBG devices also offer greater expected reliability in tougher operating conditions. Furthermore, in this frame, a new class of microelectronic-grade semiconducting materials that have an even larger bandgap than the previously established wide bandgap semiconductors, such as GaN and SiC, have been created, and are thus referred to as “ultra-wide bandgap” materials. These materials, which include AlGaN, AlN, diamond, Ga2O3, and BN, offer theoretically superior properties, including a higher critical breakdown field, higher temperature operation, and potentially higher radiation tolerance. These attributes, in turn, make it possible to use revolutionary new devices for extreme environments, such as high-efficiency power transistors, because of the improved Baliga figure of merit, ultra-high voltage pulsed power switches, high-efficiency UV-LEDs, and electronics. This Special Issue aims to collect high quality research papers, short communications, and review articles that focus on wide bandgap device design, fabrication, and advanced characterization. The Special Issue will also publish selected papers from the 43rd Workshop on Compound Semiconductor Devices and Integrated Circuits, held in France (WOCSDICE 2019), which brings together scientists and engineers working in the area of III–V, and other compound semiconductor devices and integrated circuits

Electrical Characterisation of III-V Nanowire MOSFETs

The ever increasing demand for faster and more energy-efficient electricalcomputation and communication presents severe challenges for the semiconductor industry and particularly for the metal-oxidesemiconductorfield-effect transistor (MOSFET), which is the workhorse of modern electronics. III-V materials exhibit higher carrier mobilities than the most commonly used MOSFET material Si so that the realisation of III-V MOSFETs can enable higher operation speeds and lower drive voltages than that which is possible in Si electronics. A lowering of the transistor drive voltage can be further facilitated by employing gate-all-around nanowire geometries or novel operation principles. However, III-V materials bring about their own challenges related to material quality and to the quality of the gate oxide on top of a III-V MOSFET channel.This thesis presents detailed electrical characterisations of two types of (vertical) III-V nanowire transistors: MOSFETs based on conventional thermionic emission; and Tunnel FETs, which utilise quantum-mechanical tunnelling instead to control the device current and reach inverse subthreshold slopes below the thermal limit of 60 mV/decade. Transistor characterisations span over fourteen orders of magnitude in frequency/time constants and temperatures from 11 K to 370 K.The first part of the thesis focusses on the characterisation of electrically active material defects (‘traps’) related to the gate stack. Low-frequency noise measurements yielded border trap densities of 10^18 to 10^20 cm^-3 eV^-1 and hysteresis measurements yielded effective trap densities – projected to theoxide/semiconductor interface – of 2x10^12 to 3x10^13 cm^-2 eV^-1. Random telegraph noise measurements revealed that individual oxide traps can locally shift the channel energy bands by a few millielectronvolts and that such defects can be located at energies from inside the semiconductor band gap all the way into the conduction band.Small-signal radio frequency (RF) measurements revealed that parts of the wide oxide trap distribution can still interact with carriers in the MOSFET channel at gigahertz frequencies. This causes frequency hystereses in the small-signal transconductance and capacitances and can decrease the RF gains by a few decibels. A comprehensive small-signal model was developed, which takes into account these dispersions, and the model was applied to guide improvements of the physical structure of vertical RF MOSFETs. This resulted in values for the cutoff frequency fT and the maximum oscillation frequency fmax of about 150 GHz in vertical III-V nanowire MOSFETs.Bias temperature instability measurements and the integration of (lateral) III-V nanowire MOSFETs in a back end of line process were carried out as complements to the main focus of this thesis. The results of this thesis provide a broad perspective of the properties of gate oxide traps and of the RF performance of III-V nanowire transistors and can act as guidelines for further improvement and finally the integration of III-V nanowire MOSFETs in circuits