Takaki Niwa

50-GHz bandwidth base-band amplifiers using GaAs-based HBTs

Base-band amplifiers have been demonstrated using AlGaAs/InGaAs HBTs with regrown base contacts. The transimpedance amplifier achieved a bandwidth of 49.3 GHz and a transimpedance gain of 43.7 dB /spl Omega/. The Darlington feedback amplifier achieved a bandwidth of 54.7 GHz and a gain of 8.2 dB. These are the widest bandwidths yet reported for lumped-circuit-design amplifiers. These performances suggest the great potential of these amplifiers for use in future optical communication and millimeter-wave applications.

A low phase-noise 38-GHz HBT MMIC oscillator utilizing a novel transmission line resonator

This paper reports on a low phase noise 38 GHz-band HBT MMIC oscillator employing a newly proposed transmission line resonator. The achieved phase noise of -114 dBc/Hz at 1 MHz offset is believed to be the lowest reported for millimeter-wave oscillators without a dielectric resonator.

RF HBT oscillators with low-phase noise and high-power performance utilizing a (/spl lambda//4/spl plusmn//spl delta/) open-stubs resonator

This paper presents a new type of transmission-line resonator and its application to RF (microwave and millimeter-wave) heterojunction bipolar transistor (HBT) oscillators. The resonator is a parallel combination of two open stubs having length of lambda/4plusmndelta(deltaLtlambda), where lambda is a wavelength at a resonant frequency. The most important feature of this resonator is that the coupling coefficient (betaC) can be controlled by changing delta while maintaining unloaded Q-factor (Q u) constant. Choosing a small value of delta allows us to reduce betaC or equivalently to increase loaded Q-factor (Q L). Since coupling elements such as capacitors or electromagnetic gaps are not needed, betaC and QL can be precisely controlled based on mature lithography technology. This feature of the resonator proves useful in reducing phase noise and also in enhancing output power of microwave oscillators. The proposed resonator is applied to 18-GHz and 38-GHz HBT oscillators, leading to the phase noise of -96-dBc/Hz at 100-kHz offset with 10.3-dBm output power (18-GHz oscillator) and -104-dBc/Hz at 1-MHz offset with 11.9 dBm (38-GHz oscillator). These performances are comparable to or better than state-of-the-art values for GaAs- or InP-based planar-circuit fundamental-frequency oscillators at the same frequency bands

A high-sensitivity 40-Gbit/s optical receiver using packaged GaAs HBT-ICs

Summary form only given. In this paper, we report the development of 40-Gbit/s optical receiver that employs three packaged AlGaAs-InGaAs HBT ICs: a preamplifier, a distributed amplifier, and a D-type flip-flop circuit. Approaches have been applied in packaged IC design for high-speed operation, which resulted in a very high receiver sensitivity at 40 Gbit/s.

A 38 GHz Low Phase Noise Monolithic VCO for FM MOD Using an AlGaAs/InGaAs HBT with p+/p Regrown Base Contacts

A 38 GHz-band Monolithic Microwave IC (MIMIC) voltage controlled oscillator (VCO) using an AlGaAs/InGaAs HBT with p+/p regrown base contacts has been designed. The HBT MIMIC VCO has exhibited a phase noise of 85 dBc/Hz at 100 kHz offset and an output power of +8.4 dBm at 38.1 GHz.

A composite-collector InGaP/GaAs HBT with high ruggedness for GSM power amplifiers

This paper reports on an InGaP/GaAs HBT with a GaAs/InGaP composite collector for a GSM power amplifier. The GaAs/InGaP composite collector enables the device to pass a ruggedness test with SWR=10:1 at V/sub CE/ >5 V, keeping the total collector thickness of around 900 nm and with a high power added efficiency (PAE). The load-pull measurement results for multi-cell HBTs with total emitter size of 7200 /spl mu/m/sup 2/ reveals a PAE of 74% at Pout=35 dBm and V/sub CE/=3.5 V for the composite collector.

Microwave low-noise GaAs HBTs

In this paper we present our approach to improving microwave noise performance of HBTs. A minimum noise figure of 0.83 dB was obtained at 2 GHz by using an emitter guardring structure which improves the DC current gain particularly at low current densities. We also fabricated HBTs with regrown extrinsic base layers and InGaAs graded base layers which drastically reduce base contact resistance and base transit time, respectively. It is shown that this type of HBTs not only improve the noise-figure at X-band or Ku-band but also make the noise impedance matching easier.

40-GHz frequency dividers with reduced power dissipation fabricated using high-speed small-emitter-area AlGaAs/InGaAs HBTs

This paper reports low power dissipation 40-GHz frequency dividers fabricated using high-performance AlGaAs/InGaAs HBTs. The high-speed performance of small-emitter-area HBTs was markedly improved by analyzing the device delay time and reducing the emitter resistance R/sub E/. An f/sub T/ of above 110 GHz and an f/sub max/ of 250 GHz were achieved with a small emitter area of 2.8 /spl mu/m/sup 2/. A frequency divider fabricated using these high-speed small-emitter-area HBTs operated at 40 GHz with an output voltage of 0.6 V/sub P-P/ and a low power dissipation of 0.9 W. The power dissipation is reduced by 43% compared with that for a frequency divider using conventional size HBTs.

A Ka-band HBT MMIC power amplifier

This paper reports on the fully matched, HBT MMIC power amplifier operating at the Ka-band with >1W CW output power. At 30 GHz, the power amplifier delivered maximum output power of 1.59 W with peak PAE of 35% and 6.5-dB linear gain. The achieved performance indicates that HBTs are strong candidate as cost-effective MMICs for Ka-band wireless applications.

Formation of an n-GaAs/n-GaAs regrowth interface without carrier depletion using electron cyclotron resonance hydrogen plasma

We report on the formation of a GaAs MBE regrowth interface without carrier depletion and contaminants using electron cyclotron resonance (ECR) hydrogen plasma. The mechanism for removing GaAs surface-contaminants such as Si, O, and C has been investigated to realize a contaminant-free regrowth-interface. Secondary ion mass spectroscopy (SIMS) analysis shows that Si and O contaminants result not only from adsorption when exposed to air prior to regrowth but also from the sputtering of the quartz liner in the ECR chamber during plasma treatment. These can be reduced to a level below the SIMS detection limit by lowering the hydrogen pressure to below 10 -3 Torr, because sputtering can be suppressed. SIMS also reveals that the C contaminant can be removed at substrate temperatures above 400°C to a level below the SIMS detection limit. This was verified through thermal desorption spectroscopy (TDS) analysis. This is because the C contaminant is removed through transformation into CH3 at substrate temperatures above 400°C. Furthermore, reflection high-energy electron diffraction (RHEED) observation, atomic force microscopy (AFM) and capacitance-voltage (C-V) measurements indicate that both structural and electrical damage induced by ECR plasma is completely eliminated at 500°C. Based on these methods, we are able to produce an undamaged and contaminant-free MBE regrowth interface on n-GaAs/n-GaAs for the first time.