Microwave multiple-state resonant tunneling bipolar transistors

Fabrication and microwave performance of a multiple-state resonant-tunneling bipolar transistor (RTBT) are presented. This transistor exhibits a maximum DC current gain of 60 at room temperature and a cutoff frequency of 24 GHz. Frequency multiplication by a factor of five has been demonstrated with a single transistor     

Microwave field-effect transistors from sulphur-implanted GaAs

Sulphur implanation into semi-insulating Cr doped GaAs has been used to fabricate MESFETs with 1.5 μm gatelength showing microwave gain equivalent to epitaxial FETs (MAG = 9 dB at 10 GHz) but higher noise. Room temperature implantation of S at an energy of 30 keV and a dose of 5 × 10¹² cm^?2, sputtered SiO₂ and Si₃N₄ as encapsulants and heat treatments from 820 to 900°C have been used. Electrical activation was found to depend critically on the substrate material. Si₃N₄-encapsulation gave slightly higher electrical activation than SiO₂.     

Theory of traveling-wave transistors

A distributed FET is treated as a problem of coupled active transmission lines over which the traveling waves grow by interaction. Models and equivalent circuits are proposed for evaluation of line parameters and propagation constants. Our calculations show that: 1) the gain increases with transistor width (or length of transmission line) up to about 2 cm, 2) at 15 GHz, a gain of 9 dB is achievable, and 3) the 3-dB bandwidth could be as large as 15 GHz. Possible applications of both types of traveling-wave transistors, unipolar and bipolar are discussed.     

Microwave field-effect transistors based on group-III nitrides

A concept for the design of experimental AlGaN/GaN/AlGaN double heterostructures with a two-dimensional electron channel are discussed, together with their main properties. The structures were formed by ammonia molecular-beam epitaxy on sapphire substrates. The foundations for postgrowth technology are developed for microwave field-effect transistors based on Group-III nitrides, including the formation of a mesa isolation and the preparation stage of nonrectifying contacts and the Schottky barrier. The first field-effect transistors fabricated based on the above heterostructures have a complete set of static characteristics and can operate in a mode of weak microwave signals at a frequency of 8.15 GHz.     

The emitter efficiency of bipolar transistors: Theory and experiments

A figure of merit (G_e) for the emitter is defined, which takes account of bandgap narrowing caused by high impurity concentrations, a doping-dependent lifetime, the built-in electric field and the recombination velocity at the emitter contact. A simple formula is given for G_e, based on computer simulations, and tested by several experiments.     

Microwave noise characterisation of poly-emitter bipolar junction transistors

The microwave noise characteristics of poly-emitter bipolar junction transistors have been evaluated in a 0.8 mu m silicon BiCMOS process, at frequencies between 1 and 5.6 GHz and for collector currents between 0.5 and 15 mA. Using a small-signal model for the poly-emitter bipolar junction transistors, very good agreement has been obtained between measurements and calculations of both noise figure (F/sub MIN/) against frequency, and F/sub MIN/ against collector current. It is found that F/sub MIN/ was 2.3 dB at 1 GHz and 8.3 dB at 5.6 GHz for a collector current of 5 mA.<>     

Pattern design of power transistors

The distribution of the emitter current density along the emitter stripe in the comb structure has been analytically obtained by taking into account the junction temperature and the sheet resistance of the diffused base layer, From this result the optimum length of the emitter stripe has been obtained.     

Microwave catheter design

A microwave antenna system for transcatheter ablation of cardiac tissue is investigated. A numerical model based on the finite-difference time-domain method incorporating a Gaussian pulse excitation has been constructed and frequency domain electric and magnetic fields are obtained through Fourier transformation. Results are presented for a coaxial line fed monopole catheter which is modified by the successive inclusion of a Teflon sheath outer coating, a terminating disk at the tip of the antenna, a sleeve choke, and a high dielectric constant cylinder surrounding the monopole antenna. The effects of these design features are characterized in terms of specific absorption rate (SAR) and return loss (RL). Numerical calculations are confirmed by comparing with the RL measurement of a Teflon-coated monopole containing a disk and choke     

Theory of four-terminal double-diffused field-effect transistors

Measurements on 4-terminal double-diffused field-effect transistors show considerable dissimilarity in the control characteristics of each gate, which can only be explained on the basis of a nonuniform channel doping. By using a linear approximation to the actual form of the channel doping, a theory of these devices in the pinchoff region is developed and compared with experimental observations. For the devices used, the agreement is extremely good in that it accurately predicts the ratios of the two transconductances and their variation with voltage. It is observed that the transconductance of the more heavily doped gate (gate 1) exhibits a nearly linear variation with voltage applied to the other gate and that the linearity is maintained over a wide range of gate 1 voltages. Such a property could be usefully exploited in automatic gain control systems.     

Theory of cylindrically symmetric unijunction transistors

A general theory for near-intrinsic homogenous semiconductor material is extended to the base region of an ideal cylindrical-geometry unijunction transistor. The theory predicts static emitter characteristics for planar geometries with cylindrical symmetry. These predicted characteristics include the effects of drift, diffusion, and simple recombination, and qualitatively agree with experimental data at high injection.     

Theory of organic field effect transistors

Field effect transistors with an organic material as active layer are at present essentially used to determine the mobilities in these materials. Until now, in analysing the measured current characteristics, only the simplest (Shockley) model has been used which accounts neither for this type of thin film transistor (TFT), which operates in depletion and accumulation, nor for the nature of the carriers. Starting from two-dimensional simulations for the analogous silicon TFT, we have developed an analytical model for the TFT that accounts for several peculiarities of the current characteristics of this type of transistor. In addition, a first modification has been developed which describes the situation when the charged states are polarons and bipolarons, as is the case in organic materials. Applications to published experimental current characteristics show that a general reanalysis is needed. Copyright © 1998 John Wiley & Sons, Ltd.     

Microwave CMOS-device physics and design

This paper discusses design issues and the microwave properties of CMOS devices. A qualitative understanding of the microwave characteristics of MOS transistors is provided. The paper is directed toward helping analog IC circuit designers create better front end radio-frequency CMOS circuits. The network properties of CMOS devices, the frequency response, and the microwave noise properties are reviewed, and a summary of the microwave scaling rules is presented     

Microwave operation of GaN/AlGaN-doped channel heterostructurefield effect transistors

We report on the microwave operation of 1 μm gate AlGaN/GaN doped channel heterostructure field effect transistors (DC-HFET's) with the cutoff frequency f_T of 18.3 GHz. These devices exhibit the cutoff frequency-gate length product in excess of 18 GHz·μm, comparable to that of the state-of-the-art GaAs MESFET's. We explain these improvements in the device performance by the increased sheet carrier density in the device channel and by a reduction in the parasitic series resistances, caused by doping the device channel     

Microwave phototube design considerations

The general behavior of the traveling-wave microwave phototube (TWP) as a broadband light demodulator has been described in previous publications. This paper presents specific theoretical and experimental analyses. It is shown that at low average currents the microwave power output of a TWP is given byP = frac{1}{2}i^{2} R_{eq}whereiis the peak value of the microwave current modulation at the cathode (i.e., the ac current) and Reqis an "equivalent interaction resistance" given byR_{eq} = pi^{2}N^{2}Z_{c}whereNis the helix length in electronic wavelengths and Zcis the longitudinal beam-circuit interaction impedance. Typical values of Reqare from 10⁵to 10⁷ohms. The bandwidth is determined by the productf^{2}Z_{c}, which can vary less than 3 db over an octave. The major noise contributions are found to be shot noise and thermal noise. The power output and signal-to-noise calculations are verified by experiments on an S-band TWP at low average current levels. Preliminary analysis of the TWP at high average currents shows that even higher values of Reqshould be obtainable. However, in that case the frequency-dependent microwave interactions in the gun region may provide a serious bandwidth limitation.     

Area-efficient layout design for CMOS output transistors

A novel layout design to effectively reduce the layout area of the thin-oxide NMOS and PMOS devices in CMOS output buffers with ESD consideration is proposed. With respect to the traditional finger-type layout, the large-dimension output NMOS and PMOS devices are realized by multiple octagonal cells. Without using extra ESD-optimization process, the output NMOS and PMOS devices in this octagon-type layout can provide higher driving/sinking current and better ESD robustness within a smaller layout area. The drain-to-bulk parasitic capacitance at the output node is also reduced by this octagon-type layout. Experimental results in a 0.6-μm CMOS process have shown that the output driving (sinking) current of CMOS output buffers in per unit layout area is increased 47.7% (34.3%) by this octagon-type layout. The HBM (MM) ESD robustness of this octagon-type output buffer in per unit layout area is also increased 41.5% (84.6%), as comparing to the traditional finger-type output buffer. This octagon-type layout design makes a substantial contribution to the submicron or deep-submicron CMOS IC's in high-density and high-speed applications     

Theory of intermediate and high injection noise in transistors

A theory is given of input, output, and cross-correlation of noise generators in transistors, operating at intermediate injection and at high injection. First, an approximate formula is derived for the carrier density spectra in a narrow quasi-neutral base. From this the noise sources in Z- and h-representation are derived, adding coherently the contributions of the junction voltages and the bulk drops. The open input noise voltage (for shorted collector) consists of ‘apparent junction noise’ which resembles in form the low injection result, plus current noise resulting from the conductivity-modulated impedance Z_bs in the longitudinal current path emitter-collector. This current noise has the form of amplified shot noise; it is partially correlated with the apparent junction noise. At the output the noise is represented by a short-circuit current generator (for open emitter) parallel to the collector admittance. It consists of a shot noise contribution which for intermediate injection is still close to the standard result, plus a quasi-thermal noise contribution due to the Early effect of the output admittance. A significant change is predicted for the cross correlation of the noise sources. This is caused by two effects; first there is no cancellation of thermal and shot noise contributions of the junction correlation noise, as for low injection and, secondly, input and output are related by the current noise of Z_bs. At very high injection only the latter remains and the correlation impedance is shown to be ≈ β_fZ_bs where β_f is the common emitter current gain. Several aspects of this theory are in fair agreement with intermediate injection noise measurements by Tong and van der Ziel.