Radio frequency (RF) and analog/mixed-signal (AMS) integrated circuits (ICs) are key enabling components for mobile and wireless communications and their advancements continue to drive the growth of the related semiconductor market. The circuit and technology requirements for RF and AMS ICs in mobile and wireless communications are quite different in comparison to that for digital logic and memory applications. Many tradeoffs and unique considerations have to be applied for RF and analog/mixed-signal technology development and circuit implementations. This paper reviews the critical circuit and technology requirements for RF and analog/mixed-signal ICs for mobile and wireless communications and highlights future challenges and opportunities
A method is reported for capless annealing of ion-implanted GaAs which gives electrical activation of Se-implanted wafers nearly identical to that obtained with sputtered silicon nitride caps. State-of-the-art performance has been realized from Schottky-gate FET’s fabricated from this material.
High-speed microwave modulation is obtained by exploiting the intervalley electron transfer time in certain ternary III-V compounds. Saturation of the net carrier drift velocity due to intervalley electron transfer at threshold fields below 3 kV/cm is reported in GaA 1-x P x and Al x Ga 1-x As for x = 0.315 ± 0.01 and 0.38 ± 0.02, respectively. The equivalent circuit of a bulk device fabricated from such material is derived and verified through small-signal RF measurements which, in addition, directly yield the high-field differential mobility and electron diffusion coefficient of the material. Operated as a microwave switch, isolation levels in excess of 20 dB with 4-dB insertion loss are reported at X-band with GaAS 1-x P x devices. It is shown that contact resistance can present serious limitations, although refinements in contacting technology should result in improved performance, making devices useable through millimeter-wave frequencies. Switching speed, the measurement of which is limited by laboratory pulse generation and detection capabilities, is estimated to be well under 200 ps and a theoretical limit of 20 ps has been predicted. The importance of this work lies in the fact that these switching speeds can be obtained with no sacrifice of incident RF power-handling capability, since there is no minority-carrier charge storage in these majority-carrier devices. In addition, the devices are stable at their transit-time frequency due to the absence of negative differential mobility in the material.
A compact diagnostic pattern containing test structures for the measurement of key materials and device processing parameters is presented. The test devices have been used to study the correlation between the meterial and processing parameters and GaAs FET performance. This diagnostic tool has proven to be an invaluable aid in the development of ion-implanted FET's.
Abstract : This report presents the results of an investigation of technological problems associated with the growth and preparation of GaAs with emphasis on problems related to microwave devices. One of the most significant accomplishments of this program is the high uniformity and reproducibility of doping profiles achieved by ion implantation into semi-insulating substrates. Such results have brought GaAs ion implantation into maturity as a technique for preparation of device quality layers. These results are not only expected to lead to increased use of ion implantation for discrete FET device fabrication, but also to pave the way for the development of a planar GaAs IC technology. Experimental measurements of the low frequency noise of IMPATT diodes have been used to extract parameters useful for device design, such as intrinsic response time and multiplication factors under operating conditions. Measurements of ionization rates as functions of the electric field showed a strong dependence on doping concentration which has been qualitatively interpreted in terms of delays in promotion of the accelerated electrons into the higher conduction bands.
Abstract : This final report summarizes the results of a 4-year research effort; the first two years of which were on liquid phase epitaxial and MBE approaches and the last two years were on the plasma-enhanced CVD technique. The primary conclusions of this work are that: for the LPE technique, in spite of careful control of the kinetic factors, the thermodynamic instabilities at the melt-seed interface are dominant at the initiation of growth. This results in dissolution of a few monolayers of GaAs and subsequent autodoping in the Ge single crystal. However, the purity of the Ge layers was greatly improved by using the Plasma-Enhanced CVD technique. P-type layers with p approx 10 to the 16th power cu cm and p approx. 1500 sq cm/V-s have been achieved. Mirror smooth layers with sharp interfaces are routinely obtained. Doping with volatile hydride is compatible with the PECVD technique. P-type layers doped with B2H6 to up to p approx 4 x 10 to the 19th power cu cm has been obtained. In situ growth of multi-layer structures has also been demonstrated.
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.
An experiment in gallium arsenide liquid phase epitaxy (LPE) on a flight of the SPAR 6 is described. A general purpose LPE processor suitable for either SPAR or Space Transportation System flights was designed and built. The process was started before the launch, and only the final step, in which the epitaxial film is grown, was performed during the flight. The experiment achieved its objectives; epitaxial films of reasonably good quality and very nearly the thickness predicted for convection free diffusion limited growth were produced. The films were examined by conventional analytical techniques and compared with films grown in normal gravity.
