A low-noise microwave oscillator employing a self-alignedAlGaAs/GaAs HBT

A study is made of the application of heterojunction bipolar transistors (HBTs) to low-noise microwave circuits. Design considerations and the low-noise performance of a Ku-band free-running oscillator using a self-aligned AlGaAs/GaAs HBT are described. The device has a novel structure in which, by utilizing SiO ₂ sidewalls, the base surface area, which is the main cause of low-frequency noise, is drastically reduced. For a collector current of 1 mA, the fabricated device has base current noise power densities of 4×10^-20, 6×10^-21, and 2.5×10^-21 A²/Hz at baseband frequencies of 1, 10, and 100 kHz, respectively. A prototype oscillator operating at 15.5 GHz has a measured output power of 6 dBm and SSB FM noise power densities of -34 dBc/Hz at 1 kHz, -65 dBc/Hz at 10 kHz, and -96 dBc/Hz at 100 kHz off-carrier, without using high-Q elements such as a dielectric resonator. The results of this study demonstrate the suitability of HBTs for low-phase-noise microwave and millimeter-wave oscillator applications     

A low-noise K-Ka band oscillator AlGaAs/GaAsheterojunction bipolar transistors

The design considerations, fabrication process, and performance of the first K-Ka-band oscillator implemented using a self-aligned AlGaAs/GaAs heterojunction bipolar transistor (HBT) are described. A large-signal time-domain-based design approach has been used which applies a SPICE-F simulator for optimization of the oscillator circuit parameters for maximum output power. The oscillator employs a 2×10-μm² emitter AlGaAs/GaAs HBT that was fabricated using a pattern inversion technology. The HBT has a base current 1/f noise power density lower than 1×10^-20 A²/Hz at 1 kHz and lower than 1×10^-22 A/²/Hz at 100 kHz for a collector current of 1 mA. The oscillator, which is composed of only low-Q microstrip transmission lines, has a phase noise of -80 dBc/Hz at 100 kHz off carrier when operated at 26.6 GHz. These results indicate the applicability of the HBTs to low-phase-noise monolithic oscillators at microwave and millimeter-wave frequencies, where both Si bipolar transistors and GaAs FETs are absent     

Suppression of the intensity noise in a diode-pumped neodymium:YAGnonplanar ring laser

We investigate the intensity noise properties of a continuous-wave diode pumped Nd:YAG ring-laser system and present results for an active feedback loop that suppresses the relaxation oscillation noise. This system reduces the intensity noise to within 6.1 dB of the quantum noise equivalent level (which is at 1.5×10^-8/√Hz for 1.5 mA) for frequencies between 10 kHz to 300 kHz and to less than 1×10^-7/√Hz for frequencies between 300 Hz and 10 kHz. The technical properties of the optimized feedback system are presented. The theoretical limits of performance for the system are discussed and it is shown that the performance is within 3.1 dB of these limits. We also present data from an optical beat experiment demonstrating that the intensity control system does not introduce any new features into the frequency noise spectrum     

Low frequency noise in 6H-SiC MOSFET's

The noise spectra for n-channel, depletion-mode MOSFETs fabricated in 6H-SiC material were measured from 1-10⁵ Hz at room temperature. Devices were biased in the linear regime, where the noise spectra was found to be dependent upon the drain-to-source bias current density. At a drain-to-source current of 50 μA for MOSFETs with a W/L of 400 μm/4 μm, the measured drain-to-source noise power spectral density was found to be A/(f^λ), with A being 2.6×10^-12 V², and λ being between 0.73 and 0.85, indicating a nonuniform spatial trap density skewed towards the oxide-semiconductor interface. The measured Hooge parameter (α_H) was 2×10^-5. This letter represents the first reported noise characterization of 6H-SiC MOSFET's     

Low-noise single-photon detection at wavelength 1.55 μm

The photon-counting performance of commercially available InGaAs/InP avalanche photodiodes operated in Geiger mode was investigated at temperatures between 77 and 260 K. In particular, their noise equivalent power was measured to be 4×10^-17 WHz ^-1/2 at 77 K. The implications of these results in the context of a quantum cryptography application are discussed     

Low-noise back-illuminated AlxGa1-xN-basedp-i-n solar-blind ultraviolet photodetectors

We report the growth, fabrication and characterization of Al_0.4Ga_0.6N-Al_0.6Ga_0.4N back-illuminated, solar-blind p-i-n photodiodes. The peak responsivity of the photodiodes is 27 and 79 mA/W at λ≈280 nm for bias voltages of 0 V and -60 V, respectively, with a UV-to-visible rejection ratio of more than three decades (at 400 nm). These devices exhibit very low dark current densities (~5 nA/cm² at -10 V). At low frequencies, the noise exhibits a 1/f-type behavior. The noise power density is S₀≈5×10^-25 A²/Hz at -12.7 V and the detectivity (D*) at 0 V is estimated to be in the range of 4×10¹¹-5×10¹³ cm·Hz^1/2 /W. Time-domain pulse response measurements in a front-illumination configuration indicate that the devices are RC-time limited and show a strong spatial dependence with respect to the position of the incident excitation, which is mainly due to the high resistivity of the p-type Al_0.4Ga_0.6 N layer     

Effect of laser phase noise in Sagnac interferometers

A theoretical analysis of the responsivity and the noise caused by backscattering in a Sagnac interferometer used as a sensor for reciprocal measurands, such as acoustic waves, is presented. Both Rayleigh backscattering and reflections from splices are taken into account. The noise power is found to increase proportionally to the source coherence time, and a noise equivalent phase shift in the range of 0.1×10^-6 rad r.m.s./Hz^1/2 is predicted for typical fibers and diode lasers. Experimentally, a noise equivalent phase shift of 2.5×10^-7 rad r.m.s./Hz^1/2 at 10 kHz was observed, with a detector current of 3 μA     

Lasing mode behavior of a single-mode MQW laser injected with TMpolarized light

The lasing mode behavior of a multiple quantum well (MQW) distributed feedback (DFB) laser was measured when intensity-modulated orthogonally polarized transverse magnetic (TM) mode light was injected. The 3-dB bandwidth of the frequency response shows a trend different from that observed with conventional bias current modulation: at high bias currents, it decreases with increasing bias current. The maximum bandwidth of 3 dB was observed when the normalized bias current was 4, and it reached 16 GHz at this bias current. The gain saturation coefficients for the transverse electric (TE) and TM modes estimated from these results were ∈_p^E; 2.5×10^-17 cm³ and ∈_q^E 5.7×10^-18 cm³ for the TE mode, and ∈_p^M: 6.0×10^-17 cm³ and ∈_q^M: 2.0×10^-14 cm³ for the TM mode     

Diamond grit-based field emission cathodes

This letter describes the fabrication and operation of diamond grit gated cathodes. The structure is similar to Spindt-type cathode, but the field emission cone is replaced with a more planar diamond grit layer 50 to 200 nm thick. Although the minimum lithographic dimension of these cathodes is from 1 to 5 μm, these devices have exceptionally low turn-on voltages, 5 to 7 V. Cathode current noise is less than 2.5% rms with a maximum absolute current variation of 6.7% over a 6 h period. These devices can operate in pressures of nitrogen above 133 Pa (1 Torr). Although operation in 6.6×10^-2 Pa (5×10 ^-4 Torr) with more reactive gasses, O₂ or H₂ S, degrades performance, the cathodes recover when the pressure is reduced to ⩽1.3×10^-4 Pa (1×10^-6 Torr). Gate current varies from 0.2 to 100 times the emitted current and depends on the technique used to deposit the diamond grit. High current densities (>10 A cm^-2), low gate voltages (<50 V), low emission noise, excellent longevity, temporal uniformity, and ease of fabrication make these devices potential cathodes for flat panel displays. However, excessive gate current and unsatisfactory processing reproducibility at present limit their general application     

Diamond cold cathode

Diamond cold cathodes have been formed by fabricating mesa-etched diodes using carbon ion implantation into p-type diamond substrates. When these diodes are forward biased, current is emitted into vacuum. The cathode efficiency (emitted current divided by diode current) varies from 2×10^-4 to 1×10^-10 and increases with the addition of 10^-2-torr partial pressure of O₂ into the vacuum system. Current densities of 0.1 to 1 A-cm^-2 are estimated for a diode current of 10 mA. This compares favorably with Si cold cathodes (not coated with Cs), which have efficiencies of ~2×10^-5 and current densities of ~2×10^-2 A-cm^-2. It is believed that higher current densities and efficiencies can be obtained with more efficient cathode designs and an ultrahigh-vacuum environment     

Photorefractive effects in proton exchanged LiTaO3optical waveguides

A circuit model is proposed to describe photorefractive effects in LiNbO₃/LiTaO₃ channel waveguides at any intensity level. Capacitive charge storage at the waveguide boundaries is assumed to be provided by trapping states associated with photoconductivity. A consequence of this model is that photoconductive transients are independent of optical intensity at low intensity levels. Photovoltaic and photoconductive effects in proton exchange LiTaO₃ channel waveguides were experimentally investigated. Dark conductivities of 2×10^-15 to 2 ×10^-14(Ω-cm)^-1 were extrapolated from photoconductivities up to 2×10^-13 (Ω-cm)^-1 for power levels of 0.1 to 3 mW. Large DC voltage dependent effects on the conductivity were observed. Straight channel waveguides were observed to be free of photovoltaic effects for output power levels below 35-75 mW     

Low-resistance bandgap-engineeredW/Si1-xGex/Si contacts

Bandgap-engineered W/Si_1-xGe_x/Si junctions (p⁺ and n⁺) with ultra-low contact resistivity and low leakage have been fabricated and characterized. The junctions are formed via outdiffusion from a selectively deposited Si_0.7Ge _0.3 layer which is implanted and annealed using RTA. The Si _1-xGe_x layer can then be selectively thinned using NH₄OH/H₂O₂/H₂O at 75°C with little change in characteristics or left as-deposited. Leakage currents were better than 1.6×10^-9 A/cm² (areal), 7.45×10^-12 A/cm (peripheral) for p⁺/n and 3.5×10^-10 A/cm² (peripheral) for n⁺/p. W contacts were formed using selective LPCVD on Si_1-xGe_x. A specific contact resistivity of better than 3.2×10^-8 Ω cm² for p ⁺/n and 2.2×10^-8 Ω cm² for n⁺/p is demonstrated-an order of magnitude n⁺ better than current TiSi₂ technology. W/Si_1-xGe _x/Si junctions show great potential for ULSI applications     

FM noise reduction and subkilohertz linewidth of an AlGaAs laser bynegative electrical feedback

Negative electrical feedback was applied to a CSP-type AlGaAs laser, reducing its FM noise at the Fourier frequency range of f⩽40 MHz. The magnitude of the FM noise was far lower than the quantum noise level of the free-running laser at 100 Hz⩽f ⩽4.4 MHz. It was as low as 1×10^-7~1×10 ^-6 that of the free-running laser at 100 Hz⩽f⩽1 kHz. The full width at half maximum of the field spectrum was reduced to 560 Hz. The major factors necessary for realizing the very low FM noise level were: (1) the laser had almost constant FM response characteristics for a wide Fourier frequency range; (2) a high-finesse Fabry-Perot interferometer was employed for highly-sensitive FM noise detection and to get higher feedback gain; (3) the reflection mode of the Fabry-Perot interferometer was employed to increase the bandwidth and efficiency of the FM noise detection; and (4) a computer simulation was utilized for optimum design of the feedback loop     

Modeling the variation of the low-frequency noise in polysiliconemitter bipolar junction transistors

The variation of the low-frequency noise in polysilicon emitter bipolar junction transistors (BJTs) was investigated as a function of emitter area (A_E). For individual BJTs with submicron-sized A _E, the low-frequency noise strongly deviated from a 1/f-dependence. The averaged noise varied as 1/f, with a magnitude proportional to A_E^-1, while the variation in the noise level was found to vary as A_E^-1.5. A new expression that takes into account this deviation is proposed for SPICE modeling of the low-frequency noise. The traps responsible for the noise were located at the thin SiO₂ interface between the polysilicon and monosilicon emitter. The traps' energy level, areal concentration and capture cross-section were estimated to 0.31 eV, 6×10⁸ cm^-2 and 2×10^-19 cm ², respectively     

A compact fiber-optic magnetometer employing an amorphous metalwire transducer

A compact fiber-optic magnetometer constructed using a short piece of amorphous metal wire (5-cm long×100-μm diameter) as the magnetostrictive transducer is discussed. The inherently large ratio of length to cross-sectional area results in a low demagnetization along the axial direction. A magnetostrictive constant of 5×10^-5 /Oe², which is 10-50 times larger than the reported values for transducers made from Metglas ribbons, was measured. Minimum detectable magnetic fields on the order of 10^-5 Oe/Hz^1/2 at 1 Hz were achieved using a 5-cm-long sensing fiber     

Deep cryogenic noise and electrical characterization of thecomplementary heterojunction field-effect transistor (CHFET)

This paper discusses a characterization at 4 K of the complementary heterojunction field-effect transistor (CHFET), to examine its suitability for deep cryogenic (<10 K) readout electronics applications. The CHFET is a GaAs-based transistor analogous in structure and operation to silicon CMOS. The electrical properties including the gate leakage current, subthreshold transconductance, and input-referred noise voltage were examined. It is shown that both n-channel and p-channel CHFET's are fully functional at 4 K, with no anomalous behavior, such as hysteresis or kinks. Complementary circuit designs are possible, and a simple CHFET-based multiplexed op-amp is presented and characterized at 4 K. The noise and gate leakage current of the CHFET are presently several orders of magnitude too large for readout applications, however. The input-referred noise is on the order of 1 μV/√(Hz) at 100 Hz for a 50×50 μm n-channel CHFET. The gate current is strongly dependent on the doping at the gate edge, and is on the order of 10^-14 A for a 10×10 μm ² n-channel CHFET with light gate-edge region doping     

Hooge fluctuation parameter of semiconductor microstructures

The Hooge 1/f fluctuation parameter α_H of a mesoscopic n-GaAs filament is studied experimentally and compared with that derived from the quantum model. The minimum value of the Hooge parameter α_H was 2×10^-6 and 1×10 ^-8 at room temperature and 60 K, respectively. The temperature dependence of α_H below 100 K and the electric field dependence at 77 K are favorably compared with those obtained for the impurity scattering fluctuation of the quantum 1/f noise theory     

Frequency stabilization of a novel 1.5-μm Er-Yb bulk laser to a39K sub-Doppler line at 770.1 nm

The second harmonic output at 770.1 nm of a novel and compact Er-Yb:glass laser was frequency stabilized against the sub-Doppler linewidth of a crossover line in the ³⁹K 4S_1/2-4P _1/2 transition as obtained by saturation spectroscopy. Efficient frequency doubling, with a conversion efficiency of ~220% W ^-1, and with second harmonic power in excess of 15 μW, was achieved in a waveguide made in a periodically poled lithium niobate crystal. As measured through the analysis of the closed-loop error signal, a laser frequency instability of ~200 Hz was obtained; the Allan standard deviation of the frequency samples was below 4×10^-12 for integration times τ between 100 ms and 100 s, and reached a lowest floor level of 8×10^-13 for 20 s⩽τ⩽100 s. The measured frequency noise spectral density was in good agreement with the analysis performed in the time domain. Compared to previously published data for stabilized solid-state laser sources in this wavelength region, these results represent a significant improvement in the frequency stability     

1/f noise reduction in PMOSFETs by an additional preoxidationcleaning with an ammonia hydrogen peroxide mixture

1/f noise magnitude in a 15 μm×0.5 μm PMOSFET was remarkably reduced by simply adding a cleaning step using an ammonia hydrogen peroxide mixture (APM) prior to gate oxidation. Gate input-referred noise level for APM-finished PMOSFETs at f=10 Hz was around -128 dBV²/Hz whereas for standard, HF-finished devices, the level was around -114 dBV²/Hz. Flat-band voltages (V_FBs) determined by a capacitance-voltage (C-V) measurement were -0.19 V for an APM-finished PMOS and -0.34 V for a HF-finished PMOS. Based on the V_FB values, interface state densities were determined to be N_it=3.02×10¹¹ cm^-2 for APM-finished PMOS and N_it=6.47×10¹¹ cm^-2 for HF-finished PMOS. Lower interface state density obtained by the APM preoxidation cleaning is consistent with the remarkable reduction in the 1/f noise magnitude     

一种宽温高精度温补晶振的研制

介绍了一种新型宽温微机补偿晶体振荡器。文中使用微处理器对专用集成电路芯片设计了温补晶振,分别在高低温区段对输出频率进行分段补偿;增加了噪声处理电路,滤除补偿电压跳变引入的噪声,避免相噪恶化;用二次分段补偿的方法,将补偿温度范围拓展到-55~+105 ℃。试验结果表明,使用该方法研制的10 MHz温补晶振,其频率温度稳定性在-55~+105 ℃范围内,优于±1.0×10^-6,相位噪声优于-140 dBc/Hz@1 kHz。