R. W. Ryan

AT&T Labs, Austin, Texas, United States

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Publications (31)40.39 Total impact

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    ABSTRACT: A broadband amplifier using InP-InGaAs single heterojunction bipolar transistors (HBTs) is presented. This modified Darlington amplifier exhibits a low-frequency gain of 6.2 dB with -3 dB bandwidth of 90 GHz. This wide bandwidth performance is compatible, or superior to, other lumped or distributed amplifiers based on HEMT and HBT technologies reported in the literature
    Electronics Letters 11/2000; · 1.04 Impact Factor
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    ABSTRACT: We have fabricated reduced area InGaAs/InP DHBTs for high speed circuit applications. To produce the small dimensions required, a process involving both wet chemical and ECR plasma etching was developed. Optical emission spectroscopy was used for end-point detection during plasma etching. With this improved process, an ft of 170 and fmax of 200 GHz were achieved for 1.2 × 3 µm2 emitter size devices with a 500 Å base.
    Journal of Electronic Materials 01/2000; 29(2):222-224. · 1.64 Impact Factor
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    ABSTRACT: An InP HBT technology developed at Lucent Technologies Bell laboratories, with peak f<sub>t</sub>-100 GHz is used to design and fabricate a limiting amplifier with high gain and bandwidth margin at 10 Gbps. Feedback techniques are used to obtain >30 dB differential gain with >10 GHz bandwidth for the packaged chip. The design reduces current density with standard cell transistors to improve circuit reliability (at the expense of performance). Stable operating conditions are found by adjusting the DC bias tail currents. The limiting output is set by the current in the output stage. Open eyes are obtained even with >2 V differential output. Depending on the required output swing, the power consumption is 200-500 mW (at V<sub>ee</sub>~-3.5 to -4.5 V)
    Indium Phosphide and Related Materials, 1999. IPRM. 1999 Eleventh International Conference on; 02/1999
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    ABSTRACT: We have developed a method for producing alignment marks on a wafer using exposed photoresist. Alignment to the exposed pattern is possible without having to develop out the pattern, provided that there is enough contrast between the exposed and unexposed areas. The exposed pattern was easily found for alignment using the He–Ne laser alignment system in our stepper. Although the contrast between the exposed and unexposed resist was rather faint to the human eye, the contrast was greatly improved using a commercially available contrast enhancement layer, so this method can be used in contact lithography where multiple mask levels must be exposed prior to development. The ability to align to the exposed pattern prior to development is especially useful in stepper-based lithography. For example, wafers may be aligned using the stepper for multiple mask exposures or for multilevel resist schemes prior to pattern development. In addition, very thick resist can be exposed using multiple exposures and changing the depth of focus. © 1999 American Vacuum Society.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/1999; 17(3). · 1.36 Impact Factor
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    ABSTRACT: We have optimized the base electrode for InGaAs/InP based double heterojunction bipolar transistors with a buried emitter-base junction. For the buried emitter-base structure, the base metal is diffused through a thin graded quaternary region, which is doped lightly n-type, to make ohmic contact to the p+InGaAs base region. The metal diffusion depth must be controlled, or contact will also be made to the collector region. Several metal schemes were evaluated. An alloy of Pd/Pt/Au was the best choice for the base metal, since it had the lowest contact resistance and a sufficient diffusion depth after annealing. The Pd diffusion depth was easily controlled by limiting the thickness to 50Å, and using ample Pt, at least 350Å, as a barrier metal to the top layer of Au. Devices with a 500Å base region show no degradation in dc characteristics after operation at an emitter current density of 90 kA/cm2 and a collector bias, VCE, of 2V at room temperature for over 500 h. Typical common emitter current gain was 120. An ft of 95 GHz and fmax, of 131 GHz were achieved for 2×4 µm2 emitter size devices.
    Journal of Electronic Materials 10/1998; 27(11):1244-1247. · 1.64 Impact Factor
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    ABSTRACT: Device encapsulation and passivation are critical for long-term reliability and stability. Several encapsulation techniques were evaluated in terms of degradation of electrical characteristics, gap filling under the mesa structures, and adhesion to the semiconductor and metal surfaces. These included plasma enhanced chemical vapor deposited (PECVD) SiO2, electron cyclotron resonance CVD SiNx, spin-on glass, benzocyclobutene, and polyimide. Damage from plasma exposure caused gain degradation in the devices. Spin-on coatings cause little to no gain degradation, provided that there is minimal stress in the cured film. SOG and BCB films have acceptable adhesion properties and were excellent for gap filling. Polyimide films have excellent adhesion properties, however, they were poor at gap filling and had a great deal of shrinkage during curing. Device passivation was evaluated using double heterojunction bipolar transistor structures with either an abrupt or graded emitter-base junction. Abrupt junction devices had the self-aligned base metal directly on the p+ InGaAs base. Graded junction devices had the base metal on top of graded InGaAsP layers, which the metal was diffused through, to make contact to the base region. Abrupt junction devices stressed at an initial JE of 90 kA/cm2 at a VCE of 2V at 25°C degraded 20% within 70 h of operation, whereas, the graded junction devices show no degradation in dc characteristics after operation for over 500 h. Typical common emitter current gain was 50. An ft of 80 and fmax of 155 GHz were achieved for 2×4 µm2 emitter size devices.
    Journal of Electronic Materials 07/1998; 27(8):954-960. · 1.64 Impact Factor
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    ABSTRACT: We compare ECR plasma etch fabrication of self-aligned thin emitter carbondoped base InGaAs/InP DHBT structures using either CH4/H2/Ar or BCl3/N2 etch chemistries. Detrimental hydrogen passivation of the carbon doping in the base region of our structure during CH4/H2/Ar dry etching of the emitter region is observed. Initial conductivity is not recovered with annealing up to a temperature of 500°C. This passivation is not due to damage from the dry etching or from the MOMBE growth process, since DHBT structures which are ECR plasma etched in BCl3/N2 have the same electrical characteristics as wet etched controls. It is due to hydrogen implantation from the plasma exposure. This is supported with secondary ion mass spectroscopy profiles of structures which are etched in CH4/D2/Ar showing an accumulation of deuterium in the C-doped base region.
    Journal of Electronic Materials 01/1998; 27(2):69-72. · 1.64 Impact Factor
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    ABSTRACT: We have developed a simple technique for wafer bonding for use with stepper-based lithography. The technique involves side-by-side bonding of two or more pieces of a wafer together with epoxy. A bonded wafer with the same dimensions, such as thickness, flatness, and position of the large flat, as a whole wafer can be run on a stepper. Since a stepper can align each field independently, all of the area without the actual bond may be patterned. This technique is quite useful for salvaging a broken wafer in the middle of processing. In addition, it may be used for bonding several substrates of different materials together for monolithic integration. © 1998 American Vacuum Society.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/1998; 16:2110-2112. · 1.36 Impact Factor
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    ABSTRACT: We have developed a simple, trilayer lift-off process for obtaining metal of various thickness while retaining good feature definition down to 1 μm, using only standard photoresist and developer, and e-beam evaporated dielectric. This process has been implemented for fabrication of high speed circuits using InP/InGaAs/InP double heterojunction bipolar transistor devices. This structure is nonplanar, with a topography of about 1.3 μm from the top of the emitter to the substrate level for interconnects. Clean edges are obtained for all of the metallization steps. Metal lift-off with our trilayer process is easily accomplished by gentle rinsing with acetone, and does not require the use of high pressure spray or any heat treatment, such as boiling in a solvent to aid lift-off. This new process has greatly improved our circuit yield. © 1998 American Vacuum Society.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/1998; 16:2759-2762. · 1.36 Impact Factor
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    ABSTRACT: We have fabricated InGaAs/InP based DHBTs for high speed circuit applications. A process involving both wet chemical and ECR plasma etching was developed. Carbon was employed as the p-type dopant of the base layer for excellent device stability. Both the emitter–base and base–collector regions were graded using quaternary InGaAsP alloys. The extrinsic emitter–base junction is buried for junction passivation to improve device reliability. The use of an InP collector structure with the graded region results in high breakdown voltages of 8-10 V, with no current blocking. The entire structure is encapsulated with spin-on-glass. These devices show no degradation in d.c. characteristics after operation at an emitter current density of 90 kA cm−2 and a collector bias, VCE, of 2 V at room temperature for over 500 h. Typical common emitter current gain was 50. An ft of 80 and fmax of 155 GHz were achieved for 2×4 μm2 emitter size devices.
    Solid-State Electronics 01/1998; 42(12):2239-2250. · 1.48 Impact Factor
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    ABSTRACT: InP based HBT's for circuit applications were fabricated on MOMBE grown HBT layers. The layer structure included an InP emitter, InGaAs base, and InP collector. A C-doped base was employed for excellent device stability. The emitter-base and base-collector heterojunctions were both graded with InGaAsP layers for better electrical characteristics. An emitter-base self-aligned process was employed with dry etch and wet chemical etch mesa isolations. For base contacts, Pd/Zn/Pt/Au ohmic contacts were placed on top of the InGaAsP graded layer between the emitter and base, and made to diffuse into the base layer using rapid thermal annealing. This method produces an emitter-base junction buried under the InGaAsP graded layer and helps increase device reliability and life time. The device showed about 3% degradation in DC characteristics when stressed at a collector current density (J<sub>c</sub>) of 100 kA/cm<sup>2</sup> and collector bias of 2 V at room temperature for 360 hours. Typical common emitter current gain was 40. f<sub>t</sub> of 78 GHz and f<sub>max</sub> of 129 GHz were achieved for 3×5 μm<sup>2</sup> emitter size devices. Maximum f <sub>t</sub> was achieved at 70 kA/cm<sup>2</sup> collector current density and 2.25 V collector bias. f<sub>t</sub> decreased to 70 GHz at 130 kA/cm<sup>2</sup> collector current density. F<sub>max</sub> decreased for longer emitter size devices (3×10 and 3×15 μm<sup>2</sup>) while f<sub>t</sub> maintained comparable values
    High Speed Semiconductor Devices and Circuits, 1997. Proceedings., 1997 IEEE/Cornell Conference on Advanced Concepts in; 09/1997
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    ABSTRACT: Power transistors with a low d.c. supply voltage were demonstrated with pseudomorphic InGaP/In0.2Ga0.8As/GaAs heterostructure field effect transistors on GaAs substrates and 1 μm gate length technology. A current density of 200 mA mm−1 and an extrinsic transconductance of 300 mS mm−1 were exhibited on a 400 μm gate width process control monitor device. For a 1 cm gate width device measured at 850 MHz and Vds = 1.3 V, state-of-the-art results, 57.4% for the PAE, 12.7 dB for the linear gain and 21.5 dBm for the output power, were obtained.
    Solid-State Electronics 01/1997; 41(12):1913-1915. · 1.48 Impact Factor
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    ABSTRACT: Summary form only given. We have developed a new self-aligned thin emitter HBT process technology to fabricate high performance InP/InGaAs/InP DHBTs for digital and microwave IC applications. The epistructure which is grown by MOMBE features a C-doped base using a CBr <sub>4</sub> gas dopant source for stable device operation at high emitter current densities. The process technology uses combined ECR-RIE and wet etching and incorporates self-aligned emitter-base metallizations and spin-on-glass dielectric passivation. The 0.5 μm InP collector structure results in much improved common emitter I-V characteristics (compared to InGaAs collectors) with low output conductance and high collector breakdown voltages (8-10 V). The insertion of thin n-doped 30 nm InGaAsP quaternary layers between the InP collector and InGaAs base allows high current density operation (J <sub>c</sub>=100 kA/cm<sup>2</sup>) of the DHBT without current blocking. The use of a chirped InP/InGaAs superlattice emitter structure reduces the V<sub>be</sub> of the devices with ideality factors very close to n=1.00. On-wafer s-parameter measurements demonstrated peak values (@J<sub>c</sub>=80 kA/cm<sup>2</sup>, V<sub>be</sub>=2 V) of f <sub>t</sub>=100 GHz and f<sub>max</sub>=60 GHz for 2.4×9.4 μm <sup>2</sup> transistors
    Device Research Conference, 1996. Digest. 54th Annual; 07/1996
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    ABSTRACT: We have built 10 and 26 GHz differential VCOs using InP HBTs. Both oscillators use a 3 stage emitter coupled pair ring section. The 10 GHz VCO is connected in the well known fashion but the 26 GHz circuit uses a patented summed output from each of the three ECP (Emitter Coupled Pair) stages. The circuits are powered from a single 5 V supply consuming 250 mW. The chip size is 870×975 μm<sup>2</sup>. The phase noise at a 100 kHz offset for the 10 and 26 GHz oscillators is 83 dBc/Hz and -70 dBc/Hz respectively
    Microwave Symposium Digest, 1996., IEEE MTT-S International; 07/1996
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    ABSTRACT: Metalorganic molecular beam epitaxy (MOMBE) growth of C-doped Ga0.47In0.53As heterostructures and Ga0.47In0.53AsInP heterostructure bipolar transistors (HBT) using carbontetrabromide (CBr4) as the dopant source is reported. Hall, secondary ion mass spectrometry (SIMS), and X-ray data were used to characterize the bulk CGa0.47In0.53As material. The incorporation of C showed a power dependence on the group V beam flux of −0.29 and −0.75 for solid arsenic and AsH3 sources, respectively. This may be related to the change in group V vacancy concentration as the group V beam flux is varied. X-ray measurements of C-doped layers indicated a contraction in the lattice parameter larger than would be calculated using Vegard's law. Doping levels from 2 × 1017 to 7 × 1019cm−3 were measured with mobilities ranging from 105 to 40 cm2/V · s, respectively. SIMS data showed very abrupt profiles with no apparent memory effects. Hydrogen was also measured in the layers and annealing of samples in vacuum showed an increase in doping, of at most 50%, only for samples grown at lower temperatures, about 450°C. For most samples, however, an increase in the mobility was measured after annealing, indicating that the neutral CH complexes most likely contribute to the majority carrier scattering. Large area devices with varying base thickness, WB, and base doping, p, were fabricated. Devices showed good Gummel characteristics with nc = 1.15 and nb = 1.17. The gain variation for different devices was found to be proportional to 1(WBp)2, which is consistent with a diffusive base transport and Auger-dominated recombination in the heavily doped base region. A comparison with Be-doped devices showed the same trend with slightly higher gains. It was also observed that in devices where the C-doped base was grown at temperatures 500°C the gain was shifted to much lower values. Small devices were also fabricated and measured with fT and fmax values of 70 and 50 GHz, respectively.
    Journal of Crystal Growth 07/1996; 164(1):362-370. · 1.55 Impact Factor
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    ABSTRACT: The metallurgical stability of ohmic contacts: Pt, Pt/Ti, Au/Ti, Au/Pt/Ti, and Au/Pt/Ti/W, on a 500 /spl Aring/ thick p/sup +/-InGaAs base of InP/InGaAs/InP HBTs have been investigated as a function of anneal temperature. All contacts were stable after a 300/spl deg/C-30 s anneal. Pt contact failed at 350/spl deg/C whereas Pt/Ti, Au/Ti, and Au/Pt/Ti contacts failed at 400/spl deg/C. The failure mechanism was a collector leakage short owing to the penetration of Pt or Ti through the thin base. Only HBTs with Au/Pt/Ti/W contact were still functional after a 400/spl deg/C anneal with no apparent shift in the turn-on voltage for the emitter and collector junctions.
    IEEE Electron Device Letters 03/1996; · 2.79 Impact Factor
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    ABSTRACT: Two Ka-band monolithic voltage controlled oscillators (VCO's) designed in a coplanar waveguide (CPW) structure are described. Each VCO utilizes an InGaAs/InP heterojunction bipolar transistor (HBT) as the active device and an HBT base-collector junction as the tuning varactor. These two VCO's are biased at a very low voltage of V<sub>CE</sub>=1.5 V and the emitter current is less than 10 mA. Under this low dc power dissipation, the VCO's with center frequencies of 26.5 and 33.5 GHz show high dc-to-rf conversion efficiencies over 10% and 5% within the frequency tuning ranges of 1.6 and 1.2 GHz, respectively. The measured phase noise at 1 MHz offset frequency is -110 dBc/Hz
    IEEE Microwave and Guided Wave Letters 12/1995;
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    ABSTRACT: Metalorganic molecular beam epitaxy of carbon‐doped heterostructures and InP/Ga 0.47 In 0.53 As heterostructure bipolar transistors using carbontetrabromide (CBr 4 ) as the dopant source is reported. Secondary ion mass spectrometry show H incorporation associated with the carbon doping. Hall data for as‐grown and postgrowth annealed samples showed a clear increase in doping only for samples grown at the lowest temperature, 450 °C, and higher doping levels. An increase in the mobility, however, was measured for nearly all samples after annealing, indicating that the neutral C–H complexes most likely contribute to majority carrier scattering. The gain variation for various devices with base thickness, W B , and base doping, p, was found to be nearly proportional to 1/(W B ×p)<sup>2</sup> consistent with diffusive base transport and Auger dominated recombination in the heavily doped base region. It was also observed that in devices where the C‐doped base was grown at temperatures ≳500 °C, the gain was shifted to much lower values possibly indicating a reduced electron carrier lifetime. © 1995 American Institute of Physics.
    Applied Physics Letters 11/1995; · 3.52 Impact Factor
  • Ultrafast Electronics and Optoelectronics; 03/1995
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    ABSTRACT: Significant improvements in the reliability as well as yield and reproducibility of GaAs planar doped barrier (PDB) microwave detector diodes have been achieved by substituting carbon-doped acceptor regions in place of conventional beryllium acceptor dopant. The superior characteristics of the C-doped PDB diodes are thought to be related to the hyperabrupt and stable carbon acceptor doping spikes (10-60 A) obtained in the n<sup>+</sup>-i-p<sup>+</sup>-i-n<sup>+</sup> doping profile grown by molecular beam epitaxy (MBE). Mesa geometry PDB diodes (10-20 micron diameter) in micropill packages were RF tested at 10 and 35 GHz. Excellent tangential sensitivity up to -58 dBm was measured with a detector video impedance of 2-50 kohms depending upon barrier height. The electrostatic discharge (ESD) failure threshold voltages were found to be much higher for the PDB diodes (3500 V) in comparison to Schottky detector diodes (300 V)
    High Speed Semiconductor Devices and Circuits, 1993. Proceedings., IEEE/Cornell Conference on Advanced Concepts in; 09/1993