Dwight C. Streit

A 108-GHz InP-HBT monolithic push-push VCO with low phase noise and wide tuning bandwidth

This paper reports on what is believed to be the highest frequency bipolar voltage-controlled oscillator (VCO) monolithic microwave integrated circuit (MMIC) so far reported. The W-band VCO is based on a push-push oscillator topology, which employs InP HBT technology with peak f/sub T/s and f/sub max/s of 75 and 200 GHz, respectively. The W-band VCO produces a maximum oscillating frequency of 108 GHz and delivers an output power of +0.92 dBm into 50 /spl Omega/. The VCO also obtains a tuning bandwidth of 2.73 GHz or 2.6% using a monolithic varactor. A phase noise of -88 dBc/Hz and -109 dBc/Hz is achieved at 1- and 10-MHz offsets, respectively, and is believed to be the lowest phase noise reported for a monolithic W-band VCO. The push-push VCO design approach demonstrated in this work enables higher VCO frequency operation, lower noise performance, and smaller size, which is attractive for millimeter-wave frequency source applications.

Two‐dimensional electron gas effects in the electromodulation spectra of a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation‐doped quantum well structure

We have studied the electroreflectance and photoreflectance spectra from a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation‐doped quantum well (MDQW) structure in the temperature range 79<T<304 K. The features from the InGaAs MDQW can be accounted for on the basis of a two‐dimensional density of states and a Fermi level filling factor. A detailed line shape fit makes it possible to evaluate the Fermi energy, and hence the two‐dimensional electron gas concentration (Ns), as well as other important parameters of the structure. Our value for Ns is in good agreement with a Hall measurement.

Doping of silicon in molecular beam epitaxy systems by solid phase epitaxy

Doped Si films were deposited by controlled coevaporation or Ga(u2009p) of Sb(n) and Si at room temperature on an atomically clean Si substrate in ultrahigh vacuum. The amorphous films were then crystallized at 230 A/min by heating the substrate to 575u2009°C. Good crystal quality results, judged by Rutherford backscattering and transmission electron microscopy. Advantages over normal evaporative doping during molecular beam epitaxial growth at ∼750u2009°C include (1) unity sticking coefficient of the dopant, (2) no smearing or carry‐over of the dopant, (3) better mobility (bulk values for n or p∼1018 cm−3), and (4) higher doping levels (>8×1018 cm−3 for Ga, 8×1019 cm−3 for Sb).

Thermal and Si‐beam assisted desorption of SiO2 from silicon in ultrahigh vacuum

We have measured the kinetic parameters for the removal of SiO2 films from silicon in ultrahigh vacuum using Auger electron spectroscopy and low‐energy electron diffraction, both with and without a beam of atomic silicon incident on the surface. Due to the very low vapor pressure of SiO2, it is removed only through reduction to SiO by excess silicon. We find that the activation energy for the rate limiting step in the thermal desorption of SiO2 is 3.54±0.2 eV, so that at temperatures below ∼900u2009°C, thick films (∼25u2009A) can scarcely be removed by thermal desorption alone, in agreement with earlier work. Very thin oxide films (∼5A) can be readily removed at lower temperatures, since SiO formed at the Si‐SiO2 interface encounters a negligible diffusion barrier and sublimes directly into vacuum. With a beam of silicon incident, SiO forms at the oxide surface and desorbs with an activation energy of only 0.84±0.2 eV. Oxide films on silicon can be removed at temperatures as low as 700u2009°C using an incident silico...

ROLE OF MISFIT DISLOCATIONS ON PSEUDOMORPHIC HIGH ELECTRON MOBILITY TRANSISTORS

The relationship between structural defects and device performance of In0.21Ga0.79As/(Al,Ga)As high electron mobility transistors with different In0.21Ga0.79As channel thicknesses (75–300 A) was analyzed. Using triple axis x‐ray diffraction and transmission electron microscopy, we determined that the presence of misfit dislocations along only one of the 〈110〉 directions did not impair device performance. In fact, the sample with the highest cutoff frequency possessed the misfit dislocations along one 〈110〉 direction. However, for thicker samples, with an orthogonal array of misfit dislocations, the device parameters were significantly degraded. We also determined that x‐ray diffuse scattering correlates strongly with device performance, making this nondestructive technique useful for device performance evaluation.

Diffuse X-ray scattering from misfit dislocations at semiconductor hetero-interfaces

X-ray diffuse scattering in (001) InGaAs/(AlGa)As transistor structures of high electron mobility was observed for structures whose InGaAs channel thickness substantially exceeded the critical thickness for misfit dislocation formation. The diffuse scattering was determined to originate from misfit dislocations, as confirmed by plan-view transmission electron microscopy. Diffuse scattering was measured using triple-axis X-ray diffraction, which showed that the diffuse scattering was sensitive to the density and direction of the misfit dislocations. Using transmission electron microscopy for calibration, we determined that the diffuse scattered intensity was directly proportional to the dislocation density. For samples with misfit dislocations along only (110), diffuse scattering was confined to a crystallographic direction that was perpendicular to the misfit segments, but for samples with thicker InGaAs layers (and with misfit segments in both (110) directions) diffuse scattering extended along all azimuthal directions. We also determined that observation of directional diffuse scattering provided a more sensitive means of detecting misfit segments than other commonly used techniques.

High reliability non-hermetic 0.15 /spl mu/m GaAs pseudomorphic HEMT MMIC amplifiers

High reliability performance of a Ka-band low-noise MMIC amplifier fabricated using a 0.15 /spl mu/m production AlGaAs-InGaAs-GaAs HEMT process technology is reported. Operating at an accelerated DC bias condition of Vds=5.2 V and Ids=250 mA/mm, two-stage balanced amplifiers were lifetested at three-temperatures (T/sub ambient/=235/spl deg/C, T/sub ambient/=250/spl deg/C, and T/sub ambient/=265/spl deg/C) in air ambient. Failure time for each temperature was determined using /spl Delta/S21=-1.0 dB measured at room temperature as the failure criteria. The activation energy (Ea) is 1.6 eV, achieving a projected median-time-to-failure (MTF) of 7/spl times/10/sup 9/ hours at a 125/spl deg/C junction temperature. This is the first report of 0.15 /spl mu/m HEMT reliability based on S21 failure criteria of MMIC amplifiers under DC stress at high junction temperature in air ambient. This result demonstrates a robust HEMT technology immune to the stress effects of high electric field under high temperature operation suitable for non-hermetic commercial Ka-band applications.

A 44-GHz-high IP3 InP HBT MMIC amplifier for low DC power millimeter-wave receiver applications

This paper reports on what is believed to be the highest IP3/P/sub dc/ power linearity figure of merit achieved from a monolithic microwave integrated circuit (MMIC) amplifier at millimeter-wave frequencies. The 44 GHz amplifier is based on an InP heterojunction bipolar transistor (HBT) technology with f/sub T/s and f/sub max/s of 70 and 200 GHz, respectively. The 44-GHz amplifier design consists of four prematched 1/spl times/l0/spl mu/m/sup 2/ four-finger (40-/spl mu/m/sup 2/) heterojunction bipolar transistor (HBT) cells combined in parallel using a compact /spl lambda//8 four-way microstrip combiner. Over a 44-50-GHz frequency band, the amplifier obtains a gain of 5.5-6 dB and a peak gain of 6.8-7.6 dB under optimum gain bias. At a low bias current of 48 mA and a total dc power of 120 mW, the amplifier obtains a peak IP3 of 34 dBm, which corresponds to an IP3/P/sub dc/ power ratio of 21:1, a factor of two better than previous state-of-the-art MMICs reported in this frequency range. By employing a thin, lightly doped HBT collector epitaxy design tailored for lower voltage and higher IP3, a record IP3/P/sub dc/, power ratio of 42.4:1 was also obtained and is believed to be the highest reported for an MMIC amplifier of any technology. The new high-linearity HBTs have strong implications for millimeter-wave receiver as well as low-voltage wireless applications.

Effect of rapid thermal annealing on planar‐doped pseudomorphic InGaAs high electron mobility transistor structures

We have investigated the effects of rapid thermal annealing on the electrical and optical properties of planar‐doped AlGaAs/InGaAs/GaAs high electron mobility transistor structures grown by molecular beam epitaxy. Hall effect and photoluminescence measurements on samples with In0.22Ga0.78As and In0.28Ga0.72As channels reveal a temperature‐dependent degradation in sheet charge density, Hall mobility, and photoluminescence response. The structures were essentially stable through the temperature range used in normal device processing. However, annealing temperatures greater than 700u2009°C resulted in strain relaxation and layer intermixing, especially for the In0.28Ga0.72As sample.

Monolithic 77- and 94-GHz InP-based HBT MMIC VCOs

This paper presents the development of 77- and 94-GHz monolithic fundamental mode VCOs using InP-based HBT MMIC technology. The InP-based HBT performance was improved by base mesa undercutting the base ohmic along two sides to reduce the base-collector junction capacitor by 40% which results in f/sub T/ and f/sub max/ of 70 and 170 GHz, respectively. By using this improved HBT device, the 77-GHz VCO exhibits a measured oscillation frequency of 77.6 GHz with a peak output power of -3 dBm, while the 94-GHz VCO demonstrates a measured oscillation frequency of 94.7 GHz with a peak output power of -3.5 dBm. The 94-GHz VCO is the highest frequency fundamental mode oscillator ever reported using bipolar device technology.