Asymmetrically Recessed 50-nm Gate-Length Metamorphic High Electron-Mobility Transistor With Enhanced Gain Performance

We report the design, fabrication and characterization of ultrahigh gain metamorphic high electron-mobility transistors. In this letter, a high-yield 50-nm T-gate process was successfully developed and applied to epitaxial layers containing high indium mole fraction InGaAs channels grown on GaAs substrates. A unique gate recess process was adopted to significantly increase device gain by effectively suppressing output conductance and feedback capacitance. Coupled with extremely small 10 mum times 25 mum via holes on substrates thinned to 1 mil, we achieved a 13.5 dB maximum stable gain (MSG) at 110 GHz for a 30-mum gate-width device. To our knowledge, this is the highest gain performance reported for microwave high electron-mobility transistor devices of similar gate periphery at this frequency, and equivalent circuit modeling indicates that this device will operate at frequencies beyond 300 GHz.     

Design and performance of octave S/C band MMICT/R modules for multi-function phased arrays

A complex wideband transmit/receive module that achieves performance levels superior to any MMIC module is described. Peak performance within the octave 3.0 to 6.0 GHz band includes a power output of 21 W at S-band and 19 W at C-band, a noise figure of 3.9 to 5.0 dB, 30 to 38 dB of receive gain, 25 to 26 dBm output IP₃, 40 dB of gain control in 256 steps, dual receive channels with independent amplitude and phase control, and an 8-bit phase shifter with less than 1 degree calibrated RMS phase error. Total GaAs area is 146 mm² with 170 mm of total gate periphery. The module incorporates a compact digital interface, requires only three supply voltages, and utilizes advanced packaging techniques, resulting in a size compatible with a grating lobe free grid spacing     

Wideband HEMT balanced amplifier

The high electron mobility transistor (HEMT) has demonstrated great potential for high-gain and low-noise applications, achieving a noise figure and current gain cutoff frequency fT superior to that of the GaAs MESFET. The letter presents the practical use of an HEMT in a hybrid wideband balanced amplifier covering 8.5 to 16 GHz producing 9.7 ± 0.5 dB gain and 2.6 dB midband noise figure. The performance is also compared to a GaAs MESFET stage.     

Understanding Customer Trust in Agent-Mediated Electronic Commerce, Web-Mediated Electronic Commerce, and Traditional Commerce

Customer trust is important in agent-mediated electronic commerce, web-mediated electronic commerce, and traditional commerce. However, the meaning of customer trust in these contexts has not been clearly defined or fully delineated. This paper proposes a new trust model that differentiates between cognitive trust and emotional trust, defines customer trust in each type of commerce as cognitive trust and emotional trust in the various entities (e.g., website, computer agent) that make up a commerce context, and then compares customer trust across the three types of commerce. We propose that, first, emotional trust merits research, particularly in e-commerce. Second, both awareness of the known and awareness of the unknown will be higher in e-commerce than in traditional commerce; this will lead to lower cognitive trust and emotional trust in e-commerce. Third, the key to increase customer trust in e-commerce is to design and develop technologies to reduce the distance between a customer and each entity, thereby increasing awareness of the known and decreasing awareness of the unknown. Fourth, cognitive trust and emotional trust fall along a continuum with potentially asymmetric effects on customer dependence on entities in e-commerce (e.g., computer agent adoption). Finally, future research on customer trust in e-commerce is outlined.     

AlGaN/GaN high electron mobility transistors on Si(111) substrates

AlGaN/GaN high electron mobility transistors (HEMTs) on silicon substrates have for the first time been realized using organometallic vapor phase epitaxy (OMVPE). Using 1 Ω-cm p-Si(111), these devices exhibited static output characteristics with low output conductance and isolation approaching 80 V. Under microwave rf operation, the substrate charge becomes capacitively coupled and parasitically loads these devices thereby limiting their performance. As a result, typical 0.3 μm gate length devices show a 25 GHz cutoff frequency, with near unity f_max/f_T ratio and 0.55 W/mm output power. A small-signal equivalent circuit incorporating elements representing the parasitic substrate loading accurately models the measured S-parameters. Removal of the conductive substrate is one way to effectively eliminate this parasitic loading. Through backside processing, freestanding 0.4-mm HEMT membranes with no thermal management were demonstrated and exhibited a significant improvement in their f_max/f_T ratio up to 2.5 at the cost of lower f_T and f_max along with an almost four-fold reduction of I_dss