Strained indium(0.52)aluminum(0.48)arsenide/indium(x)gallium(1-x)arsenide (x greater than 0.53) high electron mobility transistors (HEMT's) for microwave/millimeter -wave applications.

This thesis presents the design, fabrication and detailed characterization of strained \rm In\sb{0.52}Al\sb{0.48}As/In\sb{x}Ga\sb{1-x}As (x > 0.53) HEMT's for microwave/millimeter-wave applications. A set of theoretical criteria have been developed to allow the design of heterostructures for optimum device performance. Transport studies on these heterostructures show enhanced Hall mobilities and velocities when the channel Indium composition (x) increases from 0.53 to 0.65. A higher transconductance (g\sb{m}) and current gain cutoff frequency (f\sb{T}) is also obtained. 1$\mu$m long gate single-heterojunction HEMT's (SHHEMT's) with x = 0.65 have shown state-of-the-art extrinsic g\sb{m} of 590mS/mm and f\sb{T} of 45GHz. The device performance however degrades for x $\geq$ 0.7 and the output conductance (G\sb{ds}) increases considerably. To overcome this, 1$\mu$m double-heterojunction HEMT's (DHHEMT's) were investigated and showed low G\sb{ds} of $\sim$13mS/mm and high maximum oscillation frequency (f\sb{max}) of 65GHz. In addition to the theoretical, DC and microwave study of SHHEMT's and DHHEMT's, the devices were also characterized at low frequencies (LF) in order to investigate their 1/f noise, g\sb{m} and output-resistance (R\sb{ds}) dispersion properties. LF noise characteristics reveal shallow traps and high noise transition frequencies of $\sim$200-300 MHz. Dispersion in InAlAs/InGaAs HEMT's is attributed to the interface states of the heterointerfaces underneath the gate rather than the surface states of the ungated regions. The g\sb{m} and R\sb{ds} dispersion is small compared to GaAs MESFET's. Submicron (0.9 to 0.2 $\mu$m) HEMT's were also fabricated and characterized. As in the 1$\mu$m gate case, low G\sb{ds} values were found for the DHHEMT's even down to 0.25 $\mu$m; cutoff frequencies of these devices were f\sb{T} = 82GHz and f\sb{max} = 148GHz. Further device performance enhancement in the SHHEMT's was obtained by optimizing the submicron technology. Best results were obtained with 0.2$\mu$m mushroom-gate 65% In SHHEMT's (f\sb{T} = 160GHz and f\sb{max} = 220GHz). Finally, MMIC's using strained InAlAs/InGaAs HEMT's technology are reported for the first time and demonstrate their excellent potential for ultra-high frequency monolithic integrated circuit applications.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105250/1/9116260.pdfDescription of 9116260.pdf : Restricted to UM users only

Effective suppression of current collapse in both E- and D-mode AlGaN/GaN HEMTs on Si by [(NH4)2Sx] passivation

An effective suppression of drain current collapse was realized in both Enhancement (E)-mode and Depletion (D)-mode AlGaN/GaN High-electron-mobility-transistors (HEMTs) on 4-inch Silicon (111) by ammonium sulfide [(NH4)2Sx] passivation. The current collapse was studied using the pulsed current-voltage characteristics with the pulse width of 200 ns and pulse period of 1 ms. With reference to the AlGaN/GaN HEMTs without sulfur passivation, about 30% of the drain current collapse was suppressed for drain quiescent biases of 25 to 30 V. Obtaining low current collapse is essential to demonstrate high power GaN HEMTs

Are We There Yet ? – A Metamorphic HEMT and HBT Perspective

Metamorphic epitaxy technique offers the possibility of combining the advantages of low-cost and manufacturability of GaAs substrates and the high performance of InP-based devices. This paper will present the recent development of metamorphic HEMTs and HBTs and discuss their readiness for commercialization

Monolithic integration of heterojunction bipolar transistors and high electron mobility transistors

In this investigation, studies were undertaken for the possibility of monolithic integration of HEMTs and HBTs.RG 24/9

The end of traditional irrigation and the creation of trading companies for the sale of water: Riegos de Levante Company - Right Bank of the River Segura

Se analiza la actuación de Riegos de Levante en la margen derecha del río Segura, una empresa de venta de agua creada al calor de la política de la Restauración que generó unas desaforadas expectativas de riego en uno de los espacios de la península Ibérica con mayor déficit hidráulico. El espejismo se produjo con las obras de regulación realizadas en la cuenca del Segura y teniendo como estímulo el auge de la hortofruticultura. Los nuevos regadíos, fruto de una concesión establecida sobre los caudales del Segura en las proximidades de su desembocadura, ocuparon una extensión de alrededor de 4.000 hectáreas y fueron considerados inicialmente como «regadíos abusivos», al tiempo que la empresa que vendía el agua resultó ampliamente cuestionada por los usuarios. Los regantes se constituyeron en comunidad y sus regadíos fueron declarados «tradicionales», lo que supuso, primero, que se les reconociera el derecho preferente a los caudales regulados de la cuenca del Segura y, más tarde y como consecuencia de la insuficiencia de éstos, se les otorgó una asignación del trasvase Tajo-Segura. El regadío creado, no obstante, nunca contó con los recursos hídricos comprometidos, siendo la escasez de éstos particularmente acuciante en los numerosos períodos de sequía registrados, lo que incidió asimismo en una sustancial elevación del precio del agua.This paper analyses the activities of Riegos de Levante on the right bank of the River Segura, a water company created in the white heat of Restoration politics that raised exaggerated hopes for the irrigation of one of the areas of greatest hydraulic deficit on the Iberian Peninsula. The delusion came with the water control works carried out in the Segura basin stimulated by the rise in fruit and vegetable growing. The new irrigated land, the result of a concession established on the basis of the volume of flow of the River Segura close to its mouth, occupied approximately 4,000 hectares and was originally regarded as «abusive irrigation», while the company that sold the water was highly questioned by users. The irrigation users formed an organisation and their irrigated lands were declared to be «traditional». This meant, firstly, that their preferential right to the controlled volumes of flow from the Segura catchment area was recognised, and, later, as a consequence of the insufficiency of the latter, they were granted an allowance from the Tajo-Segura transfer. However, the irrigated area thus created never had access to the promised water resources, whose shortage was particularly pronounced in the numerous drought periods that occurred, something that also led to a considerable rise in the price of water.Este artículo ha recibido financiación del proyecto SEJ2004-08224/ECON del Ministerio de Educación y Ciencia

Temperature Dependent Characteristics of InAlN/GaN HEMTs for mm-Wave Applications

This work presents a 100 nm-gate InAlN/GaN HEMT with current-gain cutoff frequency (f[subscript T]) up to 120 GHz at room temperature (25 °C). Temperature dependent DC and RF characteristics are measured from 25 °C to 200 °C. The maximum drain current (I[subscript d−max]) decreases from 1247 mA/mm to 927 mA/mm as the temperature increases from 25 °C to 200 °C. For maximum f[subscript T], it drops to 87 GHz and 64 GHz at 100°C and 200°C respectively. These results show that although both DC and RF performances decrease with the increase in temperature, the device still exhibits high mm-wave performance at high temperatures. Thus, InAlN/GaN based HEMTs are very promising for high temperature mm-wave applications

Compact true time delay line with partially shielded coplanar waveguide transmission lines

This paper presents a method to attain a compact true time delay line with a partially shielded coplanar waveguide transmission line. Closely spaced air bridges were utilized to reduce the coupling effects between neighboring coplanar waveguide transmission lines. The proposed method is compatible with foundry's GaAs standard process and allows the transmission line to be compact and achieve a small sized true time delay line circuit. A true time delay line of approximately 85ps was fabricated and tested

High Johnson’s figure of merit (8.32 THz·V) in 0.15-µm conventional T-gate AlGaN/GaN HEMTs on silicon

AlGaN/GaN high-electron-mobility transistors (HEMTs) with a 0.15-µm gate were fabricated on a Si substrate with an 8-nm-thick AlGaN barrier. The device exhibited a unity current gain cutoff frequency fT of 63 GHz and maximum oscillation frequency fmax of 124 GHz. Its three-terminal OFF-state breakdown voltage BVgd is as high as 132 V. The estimated Johnson's figure of merit (=BVgd × fT) is 8.32 × 1012 V/s (8.32 THz·V), which is the highest value ever reported for a conventional SiN-passivated T-gate AlGaN/GaN HEMTs on a Si substrate without an additional field plate or gamma gate

Strategic research on RF and microwave

An introduction to the background, objectives and achievements of the project is given in chapter 1. This is followed by a detailed description of the microwave load pull measurement system in chapter 2. A brief introduction of the load pull concept is made. This is followed by a detailed characterization of the load pull system. With this set-up, several AlGaAs/InGaAs pHEMT and HBT devices fabricated at NTU have been measured to evaluate their power performance. The 6X100 // m PHEMT showed power density in excess of 500 mW/mm with a 16 dB gain at 5GHz when biased for maximum power and PAE of 61% under class AB operation at 3.5 V Vds. In the low voltage application this power density is shown to be comparable to state-of-the art performance The 3X15 //m2 self-aligned HBT demonstrated power density in excess of 2.5mW/um2 at 2.5GHz with PAE in excess of 67 % without harmonic tuning. These results are also comparable to existing technologies elsewhere. A large emitter area 160 //m2 HBT also demonstrated power in excess of 500 mW (power density of 3.3 mw//i m2) at 2.5 GHz

Investigation of self-heating effect on DC and RF performances in AlGaN/GaN HEMTs on CVD-Diamond

We have investigated the self-heating effect on DC and RF performances of identically fabricated AlGaN/GaN HEMTs on CVD-Diamond (GaN/Dia) and Si (GaN/Si) substrates. Self-heating induced device performances were extracted at different values drain bias voltage ( VD ) and dissipated DC power density ( PD ) in continuous wave (CW) operating condition. The effect of self-heating was observed much lesser in GaN/Dia HEMTs than GaN/Si HEMTs in terms of ID , IG , gm , fT and fmax reduction. Increased channel temperature caused by joule heating at high PD reduces the 2-DEG carrier mobility in the channel of the device. This behaviour was also confirmed by TCAD simulation which showed 3.9-times lower rising rate of maximum channel temperature and lowers thermal resistance ( Rth ) in GaN/Dia HEMTs than GaN/Si HEMTs. Small signal measurements and equivalent circuit parameter extraction were done to analyze the variation in performance of the devices. Our investigation reveals that the GaN/Dia HEMT is a promising candidate for high power density CW operation without significant reduction in electrical performance in a large drain bias range.Published versio