A comparison of low-frequency noise characteristics and noise sources in NPN and PNP InP-based heterojunction bipolar transistors

Low-frequency noise characteristics of NPN and PNP InP-based heterojunction bipolar transistors (HBTs) were investigated. NPN HBTs showed a lower base noise current level (3.85 /spl times/ 10/sup -17/ A/sup 2//Hz) than PNP HBTs (3.10 /spl times/ 10/sup -16/ A/sup 2//Hz), but higher collector noise current level (7.16 /spl times/ 10/sup -16/ A/sup 2//Hz) than PNP HBTs (1.48 /spl times/ 10/sup -16/ A/sup 2//Hz) at 10 Hz under I/sub C/=1 mA, V/sub C/=1 V. The NPN devices showed a weak dependence I/sub C//sup 0.77/ of the collector noise current, and a dependence I/sub B//sup 1.18/ of the base noise current, while the PNP devices showed dependences I/sub C//sup 1.92/ and I/sub B//sup 1.54/, respectively. The dominant noise sources and relative intrinsic noise strength were found in both NPN and PNP InP-based HBTs by comparing the noise spectral density with and without the emitter feedback resistor. Equivalent circuit models were employed and intrinsic noise sources were extracted. The high base noise current of PNP HBTs could be attributed to the exposed emitter periphery and higher electron surface recombination velocity in P-type InP materials, while the relatively high collector noise current of NPN HBTs may be due to the noise source originating from generation-recombination process in the bulk material between the emitter and the collector.     

Measured Noise Temperature Versus Theoretical Electron Temperature for Gas Discharge Noise Sources

In the past, measured noise temperatures T/sub n/ of a few commercially available gas discharge noise sources were indicated as agreeing with the predicted electron temperature T/sub e/ of the positive column based on the von Engel and Steenbeck relationship. Data were taken over the past 2 years on argon tubes over a pressure range of 5 to 40 mm and on neon tubes at 20 mm, with current variations from 100 to 300 mAdc. These data were compared against predicted electron temperatures. For the argon tubes at pressure-radius products greater than 20 mm/spl dot/cm there appeared to be reasonable correlation between the measured noise temperature and the predicted electron temperature although it is suggested that this correlation was fortuitous. For argon pressure-radius products less than 20 mm/spl dot/cm the measured noise temperature was as much as 15 percent lower than the predicted electron temperature. For neon tubes at 20-mm pressure, with the same variation in tube radius, and for pressure-radius products less than 24.0 mm/spl dot/cm, the measured noise temperature differed even more than for argon from the predicted electron temperature. A difference of as much as 30 percent at a pressure-radius product of 3.0 mm/spl dot/cm was observed. A qualitative explanation for argon is presented based mainly on the fact that these discharges do not have a Maxwellian distribution of electron velocities nor a velocity independent electron collision frequency. For neon the wide variation was not understood.     

On the theory of 1/f noise of semi-insulating materials

The 1/f noise phenomena associated with devices involving semi-insulating materials, for instance GaAs MESFET's on semi-insulating GaAs, has long been a perplexing problem. In this particular case the 1/f noise corner frequency can be up to 100 MHz before the mean square noise current at the drain is dominated by the Nyquist noise associated with the channel conductance. No reasonable explanation has ever been given, although there are many different theories. 1/f noise is a common phenomena in nature and other devices involving semi-insulating materials. We propose here that this 1/f noise is a bulk phenomena associated with localized high frequency variations and long range low frequency fluctuations, the lowest frequency being limited only by the volume of the material. Specifically the proposal here is that injection of a current I into a semi-insulating material will result in a mean square noise voltage at the point of injection given by v/sub n//sup 2/~=2(kT/q)q/spl Delta/fR(/spl omega//sub c///spl omega/) Volts/sup 2/ where /spl omega//sub c/=1/t/sub t/, for the radian frequencies, /spl omega/, larger than /spl omega//sub c/ which is the reciprocal of the transit time of the carriers. For a long sample and long transit times then this 1/f noise voltage due to current injection will be larger than the Nyquist mean square noise of the sample alone as long as the DC voltage developed across the semi-insulating sample exceeds ((2kT/q)l/sup 2/(/spl omega///spl mu/))/sup 1/2/. This theory then gives the 1/f or 1//spl omega/ frequency dependence. The dc current I might be injected for instance by the substrate current in a GaAs MESFET being injected into the semi-insulating substrate, or gate current in an IGET being injected into the gate insulator.<>     

High-speed photography, spectra, and temperature of optical discharge in silica-based fibers

The dynamics of fiber fuse effect including process of bubble formation in fiber core was investigated. Bubbles in the core were observed not later than 20/spl divide/70 /spl mu/s after the plasma forepart passed. For the first time, the temperature of optical discharge was measured for a wide range of laser radiation powers. For 40-W laser power, the temperature reached 10/sup 4/ K, the velocity of discharge propagation having increased to 10 m/s.     

High detectivity InGaN-GaN multiquantum well p-n junction photodiodes

InGaN-GaN multiquantum well (MQW) p-n junction photodiodes with semi-transparent Ni-Au electrodes were fabricated and characterized. It was found that the fabricated InGaN-GaN p-n junction photodiodes exhibit a 20-V breakdown voltage and a photocurrent to dark current contrast ratio of /spl sim/10/sup 5/ when a 0.4-V reverse bias was applied. The peak responsivity at 380 nm was 1.28 and 1.76 A/W with a 0.1- and 3-V applied reverse bias, respectively. Furthermore, an internal gain was found from our InGaN-GaN MQW p-n junction photodiodes possibly due to the long-lifetime of GaN based materials. Also, it was found that the low frequency noise of our photodiodes was dominated by the 1/f type noise. For a given bandwidth of 500 Hz, the corresponding noise equivalent power and normalized detectivity D/sup */ were found to be 6.34/spl times/10/sup -13/ W and 4.45/spl times/10/sup 11/ cm/spl middot/Hz/sup 0.5/ W/sup -1/, respectively.     

Low-frequency noise characteristics of p-n-p InAlAs/InGaAs HBTs

The low-frequency noise characteristics of p-n-p InAlAs/InGaAs heterojunction bipolar transistors (HBTs) were investigated. Devices with various geometries were measured under different bias conditions. The base noise current spectral density (3.11 /spl times/ 10/sup -16/ A/sup 2//Hz) was found to be higher than the collector noise current spectral density (1.48 /spl times/ 10/sup -16/ A/sup 2//Hz) at 10 Hz under low bias condition (I/sub C/=1 mA, V/sub EC/=1 V), while the base noise current spectral density (2.04 /spl times/ 10/sup -15/ A/sup 2//Hz) is lower than the collector noise current spectral density (7.87 /spl times/ 10/sup -15/ A/sup 2//Hz) under high bias condition (I/sub C/=10 mA, V/sub EC/=2 V). The low-frequency noise sources were identified using the emitter-feedback technique. The results suggest that the low-frequency noise is a surface-related process. In addition, the dominant noise sources varied with bias levels.     

Nitride-based p-i-n bandpass photodetectors

Nitride-based p-i-n bandpass photodetectors with semitransparent Ni-Au electrodes were successfully fabricated and characterized. The photodetectors exhibit a 20-V breakdown voltage and a small dark current of 40 pA at 4-V reverse bias. It was found that spectral responsivity shows a narrow bandpass characteristics from 337 to 365 nm. Moreover, the peak responsivity was estimated to be 0.13 A/W at 354 nm, corresponding to a quantum efficiency of 44%. The relatively high response at shorter wavelength is due to the unoptimized thickness of p-Al/sub 0.1/Ga/sub 0.9/N absorption layer. At low frequency, the noise of the photodetector is dominant by the 1/f-type noise. For our 330/spl times/330 /spl mu/m/sup 2/ device, given a bias of -3.18 V, the corresponding noise equivalent power and normalized detectivity D/sup */ are calculated to be 5.6/spl times/10/sup -12/ W and 3.34/spl times/10/sup 11/ cmHz/sup 0.5/ W/sup -1/, respectively.     

Flash ADC architecture

A 4-bit, 2.5 V modified flash analogue-to-digital converter (ADC) has been designed. In this design, the new flash topology only requires 2/sup (N-2)/+2 comparators. For comparison reasons, this new ADC architecture is operated at 400 MHz, consumes a total power of 1.68 mW and generates a total noise power of 4.86/spl times/10/sup -15/. /spl Delta/f(V/sup 2/) at this frequency.     

High-power P-i-N diode with local lifetime control using palladium diffusion controlled by radiation defects

We demonstrate for the first time a high-power P-i-N diode with local lifetime control using palladium (Pd) diffusion. Low-temperature (600/spl deg/C-700/spl deg/C) diffusion of Pd is stimulated by radiation defects resulting from alpha-particle irradiation (/sup 4/He/sup 2+/: 10 MeV, 10/sup 12/ cm/sup -2/). The region of maximal radiation damage of Gaussian shape is decorated by substitutional Pd after diffusion from a palladium silicide surface layer through the P/sup +/--P region into the N-base close to the anode junction. Significantly lower leakage current compared to that of standard /sup 4/He/sup 2+/ irradiation and very good ruggedness under fast recovery (di/dt/spl ap/500 A//spl mu/s, V/sub R//spl ap/2 kV) is demonstrated for Pd diffusion at 600/spl deg/C.     

10-gb/s operation of an In/sub 0.53/Ga/sub 0.47/As p-i-n photodiode on metamorphic InGaP buffered semi-insulating GaAs substrate

The SONET OC-192 receiving performance of In/sub 0.53/Ga/sub 0.47/As p-i-n photodiode grown on linearly graded metamorphic In/sub x/Ga/sub 1-x/P buffered GaAs substrate is reported. With a low-cost TO-46 package, such a device exhibits a frequency bandwidth up to 8 GHz, a bit-error rate (BER) of 10/sup -9/ at 10 Gb/s, a sensitivity of -17.8 dBm, and a noise equivalent power of 3.4/spl times/10/sup -15/ W/Hz/sup 1/2/ owing to its ultralow dark current of 3.6/spl times/10/sup -7/ A/cm/sup 2/. Eye diagram analysis at 10 Gb/s without transimpedance amplification reveals a statistically distributed Q-factor of 8.21, corresponding to a minimum BER of 1.1/spl times/10/sup -16/ at receiving power of -6 dBm.     

Measurement of far-infrared laser frequencies from optically pumped CHD/sub 2/OH

A three-laser heterodyne system was used to frequency measure 11 previously observed optically pumped far-infrared (FIR) laser emissions of CHD/sub 2/OH. These newly measured frequencies have fractional uncertainties of /spl plusmn/2/spl times/10/sup -7/ and correspond to laser wavelengths ranging from 47.8 to 238.0 /spl mu/m. The pump laser offset frequency was measured for 15 CHD/sub 2/OH FIR laser emissions.     

Low-frequency noise measurement-based reliability testing of VLSI interconnects with different geometry

Low-frequency noise measurements were performed on thin metallic very large-scale integration (VLSI) interconnects of three different geometries. These measurements were carried out under stressing current densities between 1.0/spl times/10/sup 5/ A/cm/sup 2/ and 2.2/spl times/10/sup 6/ A/cm/sup 2/ at different ambient temperatures up to 280/spl deg/C, in order to investigate the dependence of low-frequency noise on the geometrical shape of the VLSI interconnects. The behavior of these samples under these conditions is analyzed in this letter.     

Superconducting Tunnel Junctions As Mixers at 115 Ghz

Superconducting tunnel junctions have been used as the nonlinear element for mixing at a signal frequency of 115 GHz. The experimental results are compared with predictions of a theoretical analysis based on the quantum theory of mixing of J. R. Tucker. Qualitative agreement is obtained and suggestions are made for quantitative reconciliation. The junctions were small area (/spl equiv/0.4mu m/sup 2/) with normal resistances of 60 to 100 omega and capacitance approximately 20 fF. Measured sensitivity (T/ sup SSB/sub MXR/=62 K, L/sub c/=7.6 dB) implies receiver noise temperatures superior to the best receivers now in use at this frequency.     

Low-frequency noise in TaSiN/HfO/sub 2/ nMOSFETs and the effect of stress-relieved preoxide interfacial layer

Low-frequency noise characteristics are reported for TaSiN-gated n-channel MOSFETs with atomic-layer deposited HfO/sub 2/ on thermal SiO/sub 2/ with stress-relieved preoxide (SRPO) pretreatment. For comparison, control devices were also included with chemical SiO/sub 2/ resulting from standard Radio Corporation of America clean process. The normalized noise spectral density values for these devices are found to be lower when compared to reference poly Si gate stack with similar HfO/sub 2/ dielectric. Consequently, a lower oxide trap density of /spl sim/4/spl times/10/sup 17/ cm/sup -3/eV/sup -1/ is extracted compared to over 3/spl times/10/sup 18/ cm/sup -3/eV/sup -1/ values reported for poly Si devices indicating an improvement in the high-/spl kappa/ and interfacial layer quality. In fact, this represents the lowest trap density values reported to date on HfO/sub 2/ MOSFETs. The peak electron mobility measured on the SRPO devices is over 330 cm/sup 2//V/spl middot/s, much higher than those for equivalent poly Si or metal gate stacks. In addition, the devices with SRPO SiO/sub 2/ are found to exhibit at least /spl sim/10% higher effective mobility than RCA devices, notwithstanding the differences in the high-/spl kappa/ and interfacial layer thicknesses. The lower Coulomb scattering coefficient obtained from the noise data for the SRPO devices imply that channel carriers are better screened due to the presence of SRPO SiO/sub 2/, which, in part, contributes to the mobility improvement.     

Carrier synchronization for 3- and 4-bit-per-symbol optical transmission

We investigate carrier synchronization for coherent detection of optical signals encoding 3 and 4 bits/symbol. We consider the effects of laser phase noise and of additive white Gaussian noise (AWGN), which can arise from local oscillator (LO) shot noise or LO-spontaneous beat noise. We identify 8- and 16-ary quadrature amplitude modulation (QAM) schemes that perform well when the receiver phase-locked loop (PLL) tracks the instantaneous signal phase with moderate phase error. We propose implementations of 8- and 16-QAM transmitters using Mach-Zehnder (MZ) modulators. We outline a numerical method for computing the bit error rate (BER) of 8- and 16-QAM in the presence of AWGN and phase error. It is found that these schemes can tolerate phase-error standard deviations of 2.48/spl deg/ and 1.24/spl deg/, respectively, for a power penalty of 0.5 dB at a BER of 10/sup -9/. We propose a suitable PLL design and analyze its performance, taking account of laser phase noise, AWGN, and propagation delay within the PLL. Our analysis shows that the phase error depends on the constellation penalty, which is the mean power of constellation symbols times the mean inverse power. We establish a procedure for finding the optimal PLL natural frequency, and determine tolerable laser linewidths and PLL propagation delays. For zero propagation delay, 8- and 16-QAM can tolerate linewidth-to-bit-rate ratios of 1.8/spl times/10/sup -5/ and 1.4/spl times/10/sup -6/, respectively, assuming a total penalty of 1.0 dB.     

GaN MSM UV photodetectors with titanium tungsten transparent electrodes

GaN metal-semiconductor-metal (MSM) ultraviolet photodetectors with titanium tungsten (TiW) transparent electrodes were fabricated and characterized. It was found that the 10-nm-thick TiW film deposited with a 300-W RF power can still provide a reasonably high transmittance of 75.1% at 300 nm, a low resistivity of 1.7/spl times/10/sup -3/ /spl Omega//spl middot/cm and an effective Schottky barrier height of 0.773 eV on u-GaN. We also achieved a peak responsivity of 0.192 A/W and a quantum efficiency of 66.4% from the GaN ultraviolet MSM photodetector with TiW electrodes. With a 3-V applied bias, it was found that minimum noise equivalent power and maximum D/sup */ of our detector were 1.987/spl times/10/sup -10/ W and 6.365/spl times/10/sup 9/ cmHz/sup 0.5/W/sup -1/, respectively.     

Very High Sensitivity Heterodyne Detection of X-Band Radiation with Neon Indicator Lamps

Very high sensitivity with simple inexpensive commercial neon glow lamps designed for indicator-lamp applications is observed at X band in synchronous detection. Typical minimum detectable signals with 10-nW-order local-oscillator powers are 10/sup -17/ W /spl dot/ Hz/sup -1/ or lower. This is equivalent to 10/sup -22/ W /spl dot/Hz/spl -1/ with 1-mW local-oscillator power. As such lamps can be used without damage in high microwave fields, they can be used in principle with appropriate local-oscillator power levels to reach ideal microwave noise equivalent power (NEP) limits. The low NEP and noise figure result from the high responsivities of such devices which are due to high internal signal gain. Experimental results correlate well with the enhanced-ionization collision-rate detection model.     

Low-frequency noise in submicrometer MOSFETs with HfO/sub 2/, HfO/sub 2//Al/sub 2/O/sub 3/ and HfAlO/sub x/ gate stacks

Low-frequency noise measurements were performed on p- and n-channel MOSFETs with HfO/sub 2/, HfAlO/sub x/ and HfO/sub 2//Al/sub 2/O/sub 3/ as the gate dielectric materials. The gate length varied from 0.135 to 0.36 /spl mu/m with 10.02 /spl mu/m gate width. The equivalent oxide thicknesses were: HfO/sub 2/ 23 /spl Aring/, HfAlO/sub x/ 28.5 /spl Aring/ and HfO/sub 2//Al/sub 2/O/sub 3/ 33 /spl Aring/. In addition to the core structures with only about 10 /spl Aring/ of oxide between the high-/spl kappa/ dielectric and silicon substrate, there were "double-gate oxide" structures where an interfacial oxide layer of 40 /spl Aring/ was grown between the high-/spl kappa/ dielectric and Si. DC analysis showed low gate leakage currents in the order of 10/sup -12/A(2-5/spl times/10/sup -5/ A/cm/sup 2/) for the devices and, in general, yielded higher threshold voltages and lower mobility values when compared to the corresponding SiO/sub 2/ devices. The unified number-mobility fluctuation model was used to account for the observed 1/f noise and to extract the oxide trap density, which ranged from 1.8/spl times/10/sup 17/ cm/sup -3/eV/sup -1/ to 1.3/spl times/10/sup 19/ cm/sup -3/eV/sup -1/, somewhat higher compared to conventional SiO/sub 2/ MOSFETs with the similar device dimensions. There was no evidence of single electron switching events or random telegraph signals. The aim of this paper is to present a general discussion on low-frequency noise characteristics of the three different high-/spl kappa//gate stacks, relative comparison among them and to the Si--SiO/sub 2/ system.     

A 64-MHz clock-rate /spl Sigma//spl Delta/ ADC with 88-dB SNDR and -105-dB IM3 distortion at a 1.5-MHz signal frequency

A 64-MHz clock rate sigma-delta (/spl Sigma//spl Delta/) analog-to-digital converter (ADC) with -105-dB intermodulation distortion (IMD) at a 1.5-MHz signal frequency is reported. A linear replica bridge sampling network enables the ADC to achieve high linearity for high signal frequencies. Operating at an oversampling ratio of 29, a 2-1-1 cascade with a 2-b quantizer in the last stage reduces the quantization noise level well below that of the thermal noise. The measured signal-to-noise and distortion ratio (SNDR) in 1.1-MHz bandwidth is 88 dB, and the spurious-free-dynamic-range (SFDR) is 106 dB. The modulator and reference buffers occupy a 2.6-mm/sup 2/ die area and have been implemented with thick oxide devices, with minimum channel length of 0.35 /spl mu/m, in a dual-gate 0.18-/spl mu/m 1.8-V single-poly five-metal (SP5M) digital CMOS process. The power consumed by the ADC is 230 mW, including the decimation filters.     

As/sup +/-implanted AlGaAs oxide-confined VCSEL with enhanced oxidation rate and high performance uniformity

We report the utilization of an As/sup +/-implanted AlGaAs region and regrowth method to enhance and control the wet thermal oxidation rate for 850-nm oxide-confined vertical-cavity surface-emitting laser (VCSEL). The oxidation rate of the As/sup +/-implanted device showed a four-fold increase over the nonimplanted one at the As/sup +/ dosage of 1/spl times/10/sup 16/ cm/sup -3/ and the oxidation temperature of 400/spl deg/C. 50 side-by-side As/sup +/-implanted oxide-confined VCSELs fabricated using the method achieved very uniform performance with a deviation in threshold current of /spl Delta/I/sub th//spl sim/0.2 mA and slope-efficiency of /spl Delta/S.E./spl sim/3%.