April S. Brown

50-nm self-aligned-gate pseudomorphic AlInAs/GaInAs high electron mobility transistors

The design and fabrication of a class of 50-nm self-aligned-gate pseudomorphic AlInAs/GaInAs high electron mobility transistors (HEMTs) with potential for ultra-high-frequency and ultra-low-noise applications are reported. These devices exhibit an extrinsic transconductance of 1740 mS/mm and an extrinsic current-gain cutoff frequency of 340 GHz at room temperature. The small-signal characteristics of a pseudomorphic and a lattice-matched AlInAs/GaInAs HEMT with similar gate length (50 nm) and gate-to-channel separation (17.5 nm) are compared. The former demonstrates a 16% higher transconductance and a 15% higher current-gain cutoff frequency, but exhibits a 38% poorer output conductance. An analysis of the high-field transport properties of ultra-short gate-length AlInAs/GaInAs HEMTs shows that a reduction of gate length from 150 to 50 nm neither enhances nor reduces their average velocity. In contrast, the addition of indium from 53% to 80% improves this parameter by 19%. >

Microwave performance of AlInAs-GaInAs HEMTs with 0.2- and 0.1- mu m gate length

The millimeter-wave performance is reported for Al/sub 0.48/In/sub 0.52/As-Ga/sub 0.47/In/sub 0.53/As high-electron-mobility transistors (HEMTs) with 0.2- mu m and 0.1- mu m-long gates on material grown by molecular-beam epitaxy on semi-insulating InP substrates. Devices of 50- mu m width exhibited extrinsic transconductances of 800 and 1080 mS/mm, respectively. External f/sub T/ (maximum frequency of oscillation) of 120 and 135 GHz, respectively, were measured. A maximum f/sub T/ of 170 GHz was obtained from a 0.1*200- mu m/sup 2/ device. A minimum noise figure of 0.8 dB and associated gain of 8.7 dB were obtained from a single-stage amplifier at frequencies near 63 GHz.<<ETX>>

High-performance submicrometer AlInAs-GaInAs HEMT's

The performance of long (1.3- mu m) and short (0.3- mu m) gate-length Al/sub 0.48/In/sub 0.52/ As-Ga/sub 0.47/In/sub 0.53/ high-electron-mobility transistors (HEMTs) is reported. Transconductances of 465 and 650 mS/mm, respectively, were achieved. The 0.3- mu m-long gate-length device exhibited an f/sub t/>80 GHz. These results are attributed to the excellent electronic properties of the AlInAs-GaInAs modulation-doped system.<<ETX>>

AlInAs-GaInAs HEMTs utilizing low-temperature AlInAs buffers grown by MBE

Low-temperature AlInAs buffer layers incorporated in AlInAs-GaInAs HEMT epitaxial layers grown by MBE are discussed. A growth temperature of 150 degrees C followed by a short anneal is shown to eliminate kinks in the device I-V characteristic and sidegating and to reduce the output conductance dramatically.<<ETX>>

Role of sapphire nitridation temperature on GaN growth by plasma assisted molecular beam epitaxy: Part I. Impact of the nitridation chemistry on material characteristics

The impact of the nitridation temperature on sapphire/GaN interface modifications and the structural, chemical, and optical properties of GaN epitaxial thin films with N plasma radicals is investigated. Based on ex situ spectroscopic ellipsometry and x-ray photoelectron spectroscopy analysis, it is found that the sapphire nitridation chemistry, specifically AlN versus oxynitride (NO) production, depends on the surface temperature. Nitridation at 200 °C produces a very thin AlN layer with 90% coverage, while high temperature nitridation leads to a 70% coverage of AlN layer containing NO. These initial stages of growth significantly impact the characteristics of the layers following the nitridation step, specifically the low temperature buffer, annealed buffer, and the GaN epitaxial layer. The annealed buffer on a 200 °C nitridation provides a homogeneous GaN thin layer covering most of the sapphire surface. This homogeneous GaN layer after annealing produces a superior template for subsequent growth, resul...

Shape matters: plasmonic nanoparticle shape enhances interaction with dielectric substrate.

Numerical analyses of the ultraviolet and visible plasmonic spectra measured from hemispherical gallium nanostructures on dielectric substrates reveal that resonance frequencies are quite sensitive to illumination angle and polarization in a way that depends on nanostructure size, shape, and substrate. Large, polarization-dependent splittings arise from the broken symmetry of hemispherical gallium nanoparticles on sapphire substrates, inducing strong interactions with the substrate that depend sensitively on the angle of illumination and the nanoparticle diameter.

The heterogeneous integration of optical interconnections into integrated microsystems

Emerging techniques for integrating optoelectronic (OE) devices, analog interface circuitry, RF circuitry, and digital logic into ultra-mixed signal systems offers approaches toward and demonstrations of integrated optical interconnections in electrical microsystems. As rising data rates dictate the use of optical interconnections and interfaces at increasingly smaller distances, optical interconnections stand at a threshold of opportunity for pervasive implementation if cost-effective integration process technology and performance can be implemented. Heterogeneous integration is one approach toward the integration of compound semiconductor OE devices, Si CMOS circuits, and organic materials. Heterogeneous integration approaches, which utilize dissimilar materials which can be independently grown and optimized, and are subsequently bonded together into an integrated system, are particularly attractive methods for creating high-performance microsystems. This paper describes a variety of optical interconnections integrated into microsystems using thin film heterogeneous integration. Thin film heterogeneous integration is attractive from the standpoint that the topography of the integrated microsystem can remain flat to within a few microns, substrates which are often optically absorbing are removed, both sides of the thin film devices can be processed (e.g., contacted, optically coated), and three-dimensionally stacked structures can be implemented. Demonstrations of interconnections using thin film heterogeneous integration technology include an integrated InGaAs/Si CMOS receiver circuit operating at 1 Gbps, an InGaAs thin film photodetector bonded onto a foundry Si CMOS microprocessor to demonstrate a single chip optically interconnected microprocessor, smart pixel emitter and detector arrays using resonant cavity enhanced P-i-N photodetectors bonded on top of per-pixel current controlled oscillators and resonant cavity enhanced light emitting diodes integrated onto digital to analog converter gray-scale per-pixel driver circuitry, and photodetectors embedded in waveguides on electrical interconnection substrates to demonstrate chip-to-chip embedded waveguide interconnections.

650-AA self-aligned-gate pseudomorphic Al/sub 0.48/In/sub 0.52/As/Ga/sub 0.2/In/sub 0.8/As high electron mobility transistors

The authors report on the design and fabrication of a 650-AA self-aligned-gate pseudomorphic Al/sub 0.48/In/sub 0.52/As/Ga/sub 0.2/In/sub 0.8/As high electron mobility transistor (HEMT) with a state-of-the-art current gain cutoff frequency of over 300 GHz. This work clearly demonstrates the potential of sub-0.1- mu m gate-length HEMTs for near-future microwave and millimeter-wave applications.<<ETX>>

Ultra-high-speed digital circuit performance in 0.2- mu m gate-length AlInAs/GaInAs HEMT technology

The fabrication of fifteen-stage ring oscillators and static flip-flop frequency dividers with 0.2- mu m gate-length AlInAs/GaInAs HEMT technology is described. The fabricated HEMT devices within the circuits demonstrated a g/sub m/ transconductance of 750 mS/mm and a full-channel current of 850 mA/mm. The measured cutoff frequency of the device is 120 GHz. The shortest gate delay measured for buffered-FET-logic (BFL) ring oscillators at 300 K was 9.3 ps at 66.7 mW/gate (fan-out=1); fan-out sensitivity was 1.5 ps per fanout. The shortest gate delay measured for capacitively enhanced logic (CEL) ring oscillators at 300 K was 6.0 ps at 23.8 mW/gate (fan-out=1) with a fan-out sensitivity of 2.7 ps per fan-out. The CEL gate delay reduced to less than 5.0 ps with 11.35-mW power dissipation when measured at 77 K. The highest operating frequency for the static dividers was 26.7 GHz at 73.1 mW and 300 K.<<ETX>>

Personalized diagnostics and biosensors: a review of the biology and technology needed for personalized medicine

Abstract Exploiting the burgeoning fields of genomics, proteomics and metabolomics improves understanding of human physiology and, critically, the mutations that signal disease susceptibility. Through these emerging fields, rational design approaches to diagnosis, drug development and ultimately personalized medicine are possible. Personalized medicine and point-of-care testing techniques must fulfill a host of constraints for real-world applicability. Point-of-care devices (POCDs) must ultimately provide a cost-effective alternative to expensive and time-consuming laboratory tests in order to assist health care personnel with disease diagnosis and treatment decisions. Sensor technologies are also expanding beyond the more traditional classes of biomarkers – nucleic acids and proteins – to metabolites and direct detection of pathogens, ultimately increasing the palette of available techniques for the use of personalized medicine. The technologies needed to perform such diagnostics have also been rapidly evolving, with each generation being increasingly sensitive and selective while being more resource conscious. Ultimately, the final hurdle for all such technologies is to be able to drive consumer adoption and achieve a meaningful medical outcome for the patient.