Excellent High Frequency Performance Research Articles

Performance of the 100-μm Diameter High Conductivity CNT Fibers in MHz Frequencies

In the last few years there is an encouraging development in CNT-based wires. However, not a lot of fabrication technologies are able to produce a promising conductivity value. One of the most highly productive fabrication technologies to increase the electrical characteristics is the solution spinning technology. There are two kinds of high conductivity CNT-wires; one is CNTF yarn and the other is CNT fiber. This paper compares these two kinds of wires in high frequency MHz region. The CNTF yarn is proven to exhibit non-metallic characteristics and has excellent high frequency performance as compared to metals. The main focus of this paper is to investigate the high frequency performance focusing on the CNT fiber. One of the most conductive CNTF-yarn based wires is 500 μm in diameter with a conductivity of 2.7 ± 0.3 MS/m. Whereas, the CNT-fiber based wire is 100 μm in diameter with a conductivity of 8 ± 2 MS/m. Both wires are compared to solid copper wires. A bundle of these CNT fibers has been constructed to form the diameter similar to the other wires. Then, a spiral inductor was made for every wire with the same dimensions. The frequency and temperature measurement results prove that the CNTF yarn performs better than the bundled CNT fiber in high frequency. FEM analysis has been conducted to verify the measurement results. The analysis validated the measurement results and revealed that the CNT fiber displays quasi-metallic characteristics along with anisotropic effects. Both the measurement and the FEM results are discussed in the paper.

Impact of InGaN back barrier layer on performance of AIInN/AlN/GaN MOS-HEMTs

In the present work, we have discussed the effect of InGaN back barrier on device performances of 100 nm gate length AlInN/AlN/GaN metal oxide semiconductor high electron mobility transistor (MOS-HEMT) device and a wide comparison is made with respect to without considering the back barrier layer. The InGaN layer is introduced in the intension to raise the conduction band of GaN buffer with respect to GaN channel so that there is an improvement in the carrier confinement and at the same time witnessed excellent high frequency performance. The simulations are carried out using 2D Sentaurus TCAD simulator using Hydrodynamic mobility model by taking interface traps into consideration. Due to high value of two-dimensional electron gas (2DEG) density and mobility in AlInN/AlN/GaN MOS-HEMT device, higher drain current density is achieved. Simulation are carried out for different device parameters such as transfer characteristic (Id-Vg), transconductance factor (gm), drain induced barrier lowering (DIBL), Subthreshold slope (SS), conduction band energy, transconductance generation factor (gm/Id) and electric field. We have also examined the RF performance such as, total gate capacitance (Cgg), current gain cutoff frequency (fT) and power gain cutoff frequency (fmax) of the proposed devices. Use of InGaN back barrier tends to increase threshold voltage towards more positive value, reduced DIBL, and improves SS and significant growth in (gm/Id) by 5.5%. It also helps to achieve better frequency response like substantial increase in fT up to 91 GHz with current gain 60 dB as compare to 67 GHz with 56 dB for the device without considering back barrier and increase in fmax up to 112 GHz with respect 94 GHz. These results evident that use of InGaN back barrier in such devices can be better solution for future analog and RF applications.

CURRENT FEEDBACK OP-AMP UTILIZES NEW CURRENT CELL TO ENHANCE THE CMRR

Despite excellent high frequency and high speed performance, current-feedback operational amplifiers (CFOAs) generally exhibit poor common-mode rejection (CMRR) properties, which limit their utility [Analogue IC design: The current–mode approach, IEE Circuits and Systems Series, Peter peregrinus, 1990]. A novel current feedback operational amplifier (CFOA) with improved performance is presented. The proposed CFOA has a new current-cell [Novel current-feedback operational amplifier Design Based on a floating circuit technique, IEE Colloquium on Analogue Signal Processing, 1998], to bias the entire circuit, which achieves an incremental output resistance twice that of the well-known "Wilson" circuit. Simulation results of this new CFOA architecture indicate that the amplifier exhibits performance characteristics superior to those obtained with an established input architecture: in particular, the CMRR (common-mode rejection ratio) is 91 dB, and the d.c. offset voltage less than 26 μV.

High Performance RF FETs Using High-k Dielectrics on Wafer-Scale Quasi-Free-Standing Epitaxial Graphene

We explore the effect of processing on graphene/metal ohmic contact resistance, the integration of high-κ dielectric seeds and overlayers on carrier transport in epitaxial graphene, and directly demonstrate the importance of buffer elimination at the graphene/SiC(0001) interface for high frequency applications. We present a robust method for forming high quality ohmic contacts to graphene, which improves the contact resistance by nearly 6000x compared to untreated metal/graphene interfaces. Optimal specific contact resistance for treated Ti/Au contacts is found to average -7 Ohm-cm2. Additionally, we introduce a novel seeding technique for depositing dielectrics by ALD that utilizes direct deposition of high-κ seed layers and can lead to an increase in Hall mobility up to 70% from as-grown. Finally, we demonstrate that buffer elimination at the graphene/SiC(0001) results in excellent high frequency performance of graphene transistors with fT > 130 GHz at 75 nm gate lengths.

InAlAs/InGaAs Pseudomorphic High Eelectron Mobility Transistors Grown by Molecular Beam Epitaxy on the InP Substrate

A novel PMMA/PMGI/ZEP520 trilayer resist electron beam lithograph (EBL) technology is successfully developed and used to fabricate the 150 nm gate-length In0.7Ga0.3As/In0.52Al0.48As Pseudomorphic HEMT on an InP substrate, of which the material structure is successfully designed and optimized. A perfect profile of T-gate is successfully obtained. These fabricated devices demonstrate excellent dc and rf characteristics: the transconductance Gm, maximum saturation drain-to-source current IDSS, threshold voltage VT, maximum current gain frequency fT derived from h21, maximum frequency of oscillation derived from maximum available power gain/maximum stable gain and from unilateral power-gain of metamorphic InGaAs/InAlAs high electron mobility transistors (HEMTs) are 470 mS/mm, 560 mA/mm, −1.0 V, 76 GHz, 135 GHz and 436 GHz, respectively. The excellent high frequency performances promise the possibility of metamorphic HEMTs for millimeter-wave applications.

Design of a high performance mutually coupled circuit

A novel high performance transconductor-based mutually coupled circuit topology is presented, employing four active devices (six, if differential-output devices are not available) and only grounded passive elements. The primary and secondary self-inductances and the mutual inductance can be controlled independently. Being constructed with integrator and transconductor blocks, the circuit offers excellent sensitivity, stability and high frequency performances. The current-conveyor-based implementation is also presented to avail comparison with previous counterparts. Via measurements and simulations, theoretical predictions are verified and the comparisons are performed. As an RF application example, a tuned amplifier is built and simulated.

InGaP/InGaAs doped-channel direct-coupled field-effect transistors logic with low supply voltage

InGaP/InGaAs doped-channel direct-coupled field-effect transistor logic (DCFL) with relatively low supple voltage is demonstrated by two-dimensional analysis. In the integrated enhancement/depletion-mode transistors, subband and two-dimensional electron gas (2DEG) are formed in the InGaAs strain channels, which substantially increase the channel concentration and decrease the drain-to-source saturation voltage. The integrated devices show high turn-on voltage, high transconductance, broad gate voltage swing, and excellent high frequency performance, simultaneously. Furthermore, the integrated devices exhibit large noise margins for DCFL application with low supply voltage of 1.5 V attributed from the relatively small saturation voltages of the studied integrated devices.

The insulation performance of reactive parylene films in implantable electronic devices

Parylene-C (poly-chloro-p-xylylene) is an appropriate material for use in an implantable, microfabricated device. It is hydrophobic, conformally deposited, has a low dielectric constant, and superb biocompatibility. Yet for many bioelectrical applications, its poor wet adhesion may be an impassable shortcoming. This research contrasts parylene-C and poly(p-xylylene) functionalized with reactive group X (PPX-X) layers using long-term electrical soak and adhesion tests. The reactive parylene was made of complementary derivatives having aldehyde and aminomethyl side groups (PPX-CHO and PPX-CH 2NH 2 respectively). These functional groups have previously been shown to covalently react together after heating. Electrical testing was conducted in saline at 37 °C on interdigitated electrodes with either parylene-C or reactive parylene as the metal layer interface. Results showed that reactive parylene devices maintained the highest impedance. Heat-treated PPX-X device impedance was 800% greater at 10 kHz and 70% greater at 1 Hz relative to heated parylene-C controls after 60 days. Heat treatment proved to be critical for maintaining high impedance of both parylene-C and the reactive parylene. Adhesion measurements showed improved wet metal adhesion for PPX-X, which corresponds well with its excellent high frequency performance.

200 nm gate-length GaAs-based MHEMT devices by electron beam lithography

GaAs-based metamorphic HEMTs (MHEMT) consist of GaAs substrates and InP-based epitaxial structure, and have the advantages of both InP HEMT’s excellent performances and GaAs-based HEMT’s mature processes. GaAs-based MHEMTs were applied to millimeter-wave low-noise, high-power applications and systems. The current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) are important performance parameter of GaAs-based MHEMTs, and they are limited by the gate-length mainly. Electron beam lithography is one of the lithography technologies which can be used to realize the deep submicron gate-length. The 200 nm gate-length GaAs-based MHEMTs have been fabricated by electron beam lithography. In order to reduce the parasite gate capacitance and gate resistance, a trilayer resist structure was used to pattern the T-gate resist profile. Excellent DC, high frequency and power performances have been obtained. FT and fmax are 105 GHz, 70 GHz respectively. The research is very helpful to obtain higher performance GaAs-based MHEMTs.

Platform for Temporary Testing of Hybrid Microsystems at High Frequencies

In this paper, a platform based on the composite-IC concept that is optimized for high-frequency (HF) applications will be presented. Surface-micromachined microsprings are used for temporary connection and testing. This provides the system with an individual compensation of different contact heights due to production tolerances. In addition, self-alignment structures have been added to compensate lateral tolerances. The presented self-alignment structures were designed to compensate rising precision requirements in contrary to commonly used placing machines. Key elements of the HF platform are coplanar waveguides and microsprings that are processed using microelectromechanical-system technologies on alumina ceramic. Microsprings with outer dimensions between 2000 and 125 mum with different beamwidths, beam thicknesses, and beam lengths were designed, simulated, and fabricated. All structures were tested mechanically and electrically. As a further development, spiral microsprings are presented. These combine minimal space requirement with no preferred orientation. Positioning in an individual array is possible. Due to the design and the integration of the spiral microsprings as part of the flip-chip connection, the scattering parameters show excellent HF performance up to frequencies of 9 GHz. The same microsprings could also be used for onboard testing on multichip modules (MCMs). This provides the MCM with cheap and powerful testability and reworkability. This paper covers the mechanical and electrical design, simulation, optimization, production, and characterization of suitable microsprings.

有接点ＲＦ ＭＥＭＳスイッチ／リレー用静電駆動アクチュエータの開発

A compact switch/relay with excellent high frequency performance at around 2GHz is developed by adopting a novel non-linear spring structure and high frequency signal line structure.The non-linear spring system applied to an electrostatic actuator of RF MEMS switch/relay increases restoration force for switching reliability. The maximum restoration force can be three times higher than that of a linear spring system actuator. No failure due to restoration force shortage is observed during switching test up to 100 million cycles. The present RF MEMS switch/relay has been shown competitive RF performance over conventional RF switches such as PIN diodes and GaAs MMIC both by the experimental results.

EXPERIMENTAL STUDY OF CFOA-BASED INDUCTORLESS CHUA'S CIRCUIT

The current feedback op amps (CFOAs), with some significant advantages over the conventional op amps, have been used instead of voltage op amps (VOAs) in new implementations of Chua's circuit. In our previous study, after providing a comparative investigation of CFOA-based realizations of Chua's circuit in the literature, we have also presented an alternative inductorless CFOA-based realization of Chua's circuit, and the circuit's chaotic behavior by Pspice simulations. In this paper, we investigate CFOA-based Chua's circuit by constructing an experimental setup, and testing the performance of the proposed implementation at different frequencies. Its excellent high frequency performance was experimentally verified.

High CMRR current-feedback operational amplifier

Despite excellent high frequency and high speed performance, current-feedback operational amplifiers (CFOAs) generally exhibit poor common-mode rejection properties, which limits their utility. In this paper the authors analyse the conventional (CFOA) in terms of common-mode rejection ratio (CMRR) performance, and, having identified the mechanism primarily responsible for the CMRR, they present a modified CFOA input stage circuit design by introducing a combination of a bootstrapping technique and folded cascode transistors. Simulation results of this new CFOA architecture indicate that the amplifier has significantly improved both CMRR and gain accuracy. Other key characteristics are also improved, with the notable exception of slew rate, which is reduced as a consequence of the new topology.

Wider latitude for sophisticated devices by incorporating carbon into crystalline Si or SiGe

Research on highly supersaturated, carbon-containing alloys on silicon substrates started only a few years ago. Meanwhile, knowledge has been accumulated on growth, strain manipulation, thermal stability, carbon effects on band structure and charge carrier transport. We review basic mechanical and electrical material properties of Si 1− y C y and Si 1− x− y Ge x C y layers grown pseudomorphically on Si(001). Adding carbon alleviates some of the constraints for strained Si 1− x Ge x , and opens new possibilities for device application of heteroepitaxial Si-based systems. The incorporation of carbon is beneficial for: (i) improving SiGe layer properties; (ii) creating layers with new properties; and (iii) controlling dopant diffusion in microelectronic devices. A large variety of applications in microelectronic devices appears likely. The first device application ready for production is the npn–SiGe:C heterojunction bipolar transistor (HBT) with excellent static and high frequency performance.

The temperature dependence of the dc characteristics of silicon germanium bipolar transistors

Silicon germanium bipolar transistors provide excellent high frequency performance within the context of silicon, encroaching dramatically on III–V semiconductor’s territory. Applications of the technology, however, will require the performance specifications with regard to the temperature range of operation. Using devices accessible from a BiCMOS technology, adapted to incorporate SiGe, we have measured the temperature dependence of properties such as the dc gain, ideality factors, and VBE at various base current levels, from 100 to 450 K. The ideality factors are close to unity above 250 K but greater than 2.5 at 100 K. We suggest that tunneling at the emitter perimeter can account for the high base ideality factors at low current and low temperature. Our data show a decrease in the gain with increasing current and temperature in normal operating ranges—devices with “box” Ge profiles in the base layer do not have this feature. This is important in preventing thermal runaway in power transistors, and may remove the necessity of emitter ballast resistors and provide higher power-added-efficiency in an amplifier block. We also show that the gain-Early voltage product is roughly linear with 1/T above ambient temperature.

SiGe-HBTs for mobile communication

SiGe-HBTs are the most favored candidates for mobile communication systems. They demonstrated excellent high frequency and noise performances on research level, but now the production era of SiGe technologies is starting. First production-ready SiGe-DECT front-end will be presented including an LNA with a typical noise figure of 1.6 dB and a gain of 20 dB, and a power amplifier with 27.5 dBm output power and up to 47% on packaged devices at 1.9 GHz.

Growth of carbon doping Ga0.47In0.53As using CBr4 by gas source molecular beam epitaxy for InP/InGaAs heterojunction bipolar transistor applications

In this article, we present the comparison of material quality and device performance of gas-source molecular beam epitaxy (GSMBE)- and metal-organic molecular beam epitaxy (MOMBE)-grown C-doped InGaAs and npn InGaAs/InP heterojunction bipolar transistors (HBTs). The results indicate that the crystal quality of GSMBE-grown samples is comparable to that of MOMBE-grown samples. The GSMBE-grown HBTs show excellent dc and high frequency performance. The dc current gain (β) was 37 at a collector current of 21 mA and the emitter-base and base-collector junction ideality factors were 1.14 and 1.04 indicating good junction properties. For high frequency performance, the fT and fmax are around 108 and 128 GHz for a 4000 Å InGaAs collector with an emitter area of 3×10 μm2. Finally, the thermal stability of C-doped InGaAs and its effects on InP/InGaAs HBT device reliability will be discussed.

Advances in GaAs Mosfet's Using Ga2O3(Gd2O3) as Gate Oxide

ABSTRACTIn this article, we review the recent progress on GaAs MOSFET's using in-situ MBE-grown Ga2O3(Gd2O3) as the gate dielectric. Both depletion-mode (D-mode) and inversion-mode (I-mode) GaAs MOSFET's with negligible drain current drift and hysteresis are demostrated. The absence of drain current drift and hysteresis indicates that the excellent stability of the oxide and low oxide/GaAs interface state density have been achieved. The drain current density and transconductance are about one order of magnitude higher than the best previous reported data in the literature for an inversion-mode GaAs MOSFET. Excellent high frequency and power performances were also measured from the depletion-mode devices. These improvements are attributed to the excellent Ga2O3(Ga2O3) oxide properties and novel processing techniques.

A 70-GHz f/sub T/ low operating bias self-aligned p-type SiGe MODFET

A self-aligned process for the fabrication of SiGe p-type modulation-doped field-effect transistors (MODFETs) is described. Self-aligned devices with 0.1-μm gate-length have been fabricated and characterized. A maximum dc extrinsic transconductance of 258 mS/mm was obtained with a low turn-on resistance and very low knee voltage. Excellent high frequency performance with a unity current-gain cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of 70 GHz was obtained. This excellent high frequency performance was exhibited even at drain bias as low as 0.5 V.

Polypyrrole as a solid electrolyte for tantalum capacitors

Tantalum/tantalum pentoxide (Ta/Ta 2O 5)-based capacitors, in which polypyrrole (PP) is used as a solid electrolyte coating, have been studied. Aromatic sulfonate salts were used as the charge-compensating dopant ions due to their ability to impart good thermal and long-term stability. The capacitors prepared showed excellent high frequency performance up to 100 kHz and stability. The capacitors were prepared by two methods. In the first method the Ta 2O 5 dielectric layer was coated with chemically synthesized PP, followed by electrodeposition of a second layer of PP to increase the thickness and integrity of the PP layer. In the second method, chemical polymerization was used alone and the process repeated several times in order to obtain complete coverage of the Ta/Ta 2O 5, anodes. The redox properties of the PP synthesized chemically and electrochemically were studied by cyclic voltammetry and indicate that the polymers have similar electrochemical properties. Compositional analyses were carried out using X-ray photoelectron spectroscopy (XPS) before and after the re-anodization process used in the capacitor preparation to enhance the integrity of the TaTa 2O 5 dielectric. UV-Vis spectroscopy was used to check the stability of the PP to spontaneous ion exchange during the re-anodization process. The results indicate that aromatic sulfonates remain as the dopant ions when the reformation is carried out in the same aromatic sulfonate solution, but are partially substituted by H 2PO 4 - when the reformation is carried out in H 3PO 4. For the chemical polymerization, different synthetic conditions were used in order to improve the conductivity of PP; specifically, the use of low temperature and the addition of p-nitrophenol reduce the equivalent series resistance (ESR) of the capacitors.