Extraction of DC base parasitic resistance of bipolar transistorsbased on impact-ionization-induced base current reversal

A method for the evaluation of the DC base parasitic resistance, R_B, of bipolar transistors is described. The method is based on impact-ionization-induced base current reversal and enables R_B to be evaluated independently from the emitter parasitic resistance in a wide range of emitter current and collector-base voltage, without requiring any special device structure. The method can also extract R_B in the impact-ionization regime, where current crowding due to negative base current induces an increase in R_B at increasing emitter current     

Ultradry annealing after polysilicon electrode formation forimproving the TDDB lifetime of ultrathin silicon oxide films in MOSdiodes

Effects of ultradry annealing on time-dependent dielectric breakdown (TDDB) lifetime (T_TDDB) were investigated for Si MOS diodes with 5-nm-thick silicon oxide and P-doped polysilicon gate electrode films. This annealing was performed at 800°C in ultradry N₂ of less than 1-ppm moisture concentration after the electrode formation. Under an accumulation-bias stress condition, T_TDDB for the ultradry-annealed n-type Si diodes was larger than that for the conventionally annealed ones, while such T _TDDB enhancement was not confirmed in the p-type ones. Since positive charges induced near anode-side oxide interfaces are closely related to T_TDDB, the T_TDDB enhancement for the ultradry-annealed n-type Si diodes probably reflects a qualitative improvement of the anode-side, i.e., gate-electrode-oxide, interfaces by ultradry annealing     

A new extrapolation algorithm for band-limited signals using theregularization method

The ill-posedness of the extrapolation problem in the presence of noise is considered. A stable algorithm is constructed by solving a Fredholm equation based on a regularization method. The algorithm appears relatively robust, since the noise η_δ(t ) is taken as a function in L²[-T,T](T>0) such that the error energy ∫|η_δ(t)|² dt⩽δ², where integration is from - T to T, and the constructed extrapolation uniformly converges to the desired signal over (-∞, +∞) as δ→0. An estimate for the error energy of the constructed extrapolation over (-∞, +∞) and for the absolute error between the constructed extrapolation and the desired signal over (-∞, +∞) are presented     

Modeling hot-carrier effects in polysilicon emitter bipolartransistors

In self-aligned polysilicon emitter transistors a large electric field existing at the periphery of the emitter-base junction under reverse bias can create hot-carrier-induced degradation. The degradation of polysilicon emitter transistor gain under DC stress conditions can be modelled by ΔI_B∝I_R ^m+ntⁿ where n≈0.5 and m ≈0.5. The more complex relationships of Δβ(I _C, I_R, t) and β(I _C, I_R, t) result naturally from the simple ΔI_B model. Using these relationships the device lifetime can be extrapolated over a wide range of reverse stress currents for a given technology     

The bandwidth performance of a two-element adaptive array withtapped delay-line processing

The bandwidth performance of a two-element adaptive array with a tapped delay line behind each element is examined. It is shown how the number of taps and the delay between taps affect the bandwidth performance of the array. An array with two weights and one delay behind each element is found to yield optimal performance (equal to that obtained with continuous-wave interference) for any value of intertap delay between zero and T₉₀/B, where T ₉₀ is a quarter-wavelength delay time and B is the fractional signal bandwidth. Delays less that T₉₀ yield optimal performance but result in large array weights. Delays larger than T₉₀/B yield suboptimal signal-to-interference-plus-noise ratio when each element has only two weights. For delays between T₉₀/B and 4T₉₀/B , the performance is suboptimal with only two taps but approaches the optimal if more taps are added to each element. Delays larger than T₉₀/B result in suboptimal performance regardless of the number of taps used     

Error probability of M-ary FSK with differential phasedetection in satellite mobile channel

Formulas are derived for the error probability of M-ary frequency shift keying (FSK) with differential phase detection in a satellite mobile channel. The received signal in this channel is composed of a specular signal, a diffuse signal, and white Gaussian noise; hence, the composite signal is fading and has a Rician envelope. The error probability is shown to depend on the following system parameters: (1) the signal-to-noise ratio; (2) the ratio of powers in the specular and diffuse signal components; (3) the normalized frequency deviation; (4) the normalized Doppler frequency; (5) the maximum normalized Doppler frequency; (6) the correlation function of the diffuse component, which depends on the normalized Doppler frequency and the type of the antenna; (7) the number of symbols; and (8) the normalized time delay between the specular and diffuse component (t _d/T) where 1/T is the symbol rate. Except for T_d/T, all normalized parameters are the ratios of the parameter value and symbol rate. The Doppler frequency depends on the velocity of the vehicle and the carrier frequency. The error probability is computed as a function of the various parameters. The bit error probability is plotted as a function of signal-to-noise ratio per bit and other system parameters     

Effect of conduction-band discontinuity on lasing characteristicsof 1.5 μm InGaAs/In(Ga)AlAs MQW-FP lasers

The characteristic temperature (T₀), relaxation frequency (f_r), differential gain (dg /dn) and nonlinear gain coefficient (ϵ) of 1.5-μm InGaAs/In(Ga)AlAs multiple-quantum-well (MQW) Fabry-Perot (FP) lasers grown by gas source molecular beam epitaxy (GSMBE) are reported. It is found that T₀ is little affected by the difference in the conduction band discontinuity. A maximum T₀ value of 86 K is obtained. The dg/dn and ϵ∈ were calculated from the slope of the f_r versus √ power plot and the damping K-factor. It is demonstrated that dg/dn and ϵ of InGaAs/In(Ga)AlAs MQW lasers increase with an increase in the conduction band discontinuity     

A model for fast switching transients in power systems: the nearzone concept

The author presents a simple time-domain model which makes it possible to predict the order of magnitude of the highest di/ dt values generated by closing switches in electrical power systems. The model is based on traveling-wave analysis. It is demonstrated that two different approaches must be applied, according to whether (a) the closing time, T_s, of the switch is faster than twice the traveling time to the first reflection point or (b) T_s is much slower. Under condition (b) the well-known quasistationary approach di/dt_max=U₀/L can be used, where U₀ is the switched voltage and L is the self-inductance of the line between the stray capacitances located to the left and the right of the switching device. Under condition (a) a new formula must be applied: di/dt _max≈2 U₀/ZT_s, where Z is the line impedance of the line in which the switching device is installed and T_s is the time during which the voltage across the switch collapses from U₀ to zero. Experimental results are given from both fast and slow closing switches     

High vibrational temperatures in optically-pumped CO2

A pulsed 4.3-μm CO₂ laser was used to optically pump mixtures of CO₂ and He, and create transient gain at 9 and 10 μm. A conventional continuous-wave CO₂ laser operating on both regular and sequence bands measures this transient gain, and determined the ν₃ (asymmetric stretching)-mode vibrational temperature T₃. The measured values of T ₃ are generally much higher than those attained in discharge-excited CO₂. It is shown that a Treanor distribution must be used to describe the populations in the ν₃ -mode when dilute mixtures of CO₂ in He are optically pumped to ν₃-mode temperatures of 3000 to 4000 K. Under these conditions the sequence-band gain coefficients are almost equal to those on the regular bands. The collisional relaxation of energy from the ν₃ mode shows evidence of fast V-T relaxation at high values of T₃, followed by a slower relaxation rate characteristic of the 00⁰1 population lifetime     

Tensile strain dependence of Brillouin frequency shift in silicaoptical fibers

Brillouin frequency shift in a single-mode optical fiber has been measured as a function of tensile strain. The strain coefficient of normalized Brillouin frequency shift C≡(dv_B/ dϵ)/v_B is found to be 4.4 for silica fibers. This result shows the potential of Brillouin spectroscopy to evaluate tensile strain in the fiber with the strain resolution of about 2×10^-4. The origin of the large strain coefficient is discussed     

Determination of carrier lifetime in p-i-n diodes by ramp recovery

The ramp recovery method for the measurement of carrier lifetime in p-i-n diodes is analyzed to show that B. Tien and C. Hu's (1988) formula τ=(t_A(t_A+t _B))^1/2, where t_A and t_B are the two intervals for the recovery, gives a good estimate of the lifetime. The recovery can be assumed to be complete at a time t₂ at which the reverse current has reduced to 10% of its peak value. This eliminates the necessity of assuming the ramp recovery waveform to be a triangle     

Maximum heat-sink temperature for CW operation of adouble-heterostructure semiconductor injection laser

Assuming that the temperature dependence of the threshold current for pulsed operation is known, an analytical expression for the maximum heat-sink temperature, T_hm, for CW operation of the laser can be derived. The maximum heat-sink temperature is expressed in terms of the characteristic temperature T₀, the room-temperature threshold current for pulsed operation I₀ , the equivalent effective thermal resistance &thetas;, and the equivalent effective series electrical resistance r of the device. It is shown that the values of T_hm can be enhanced by increasing the value of T₀ or by decreasing the values of I₀, &thetas;, and r     

Self-heating effects in basic semiconductor structures

Investigates the effects of self-heating on the high current I -V characteristics of semiconductor structures using a fully coupled electrothermal device simulator. It is shown that the breakdown in both resistors and diodes is caused by conductivity modulation due to minority carrier generation. In isothermal simulations with T=300 K, avalanche generation is the source of minority carriers. In simulations with self-heating, both avalanche and thermal generation of minority carriers can contribute to the breakdown mechanism. The voltage and current at breakdown are dependent on the structure of the device and the doping concentration in the region with lower doping. For all structures, except highly doped resistors with poor heating sinking at the contacts, the temperature at thermal breakdown ranged from 1.25T_i to 3T_i , where T_i is the temperature at which the semiconductor goes intrinsic. Hence, it is found that T=T_i is not a general condition for thermal (or second) breakdown. From these studies, an improved condition for thermal breakdown is proposed     

Performance analysis of disk allocation method usingerror-correcting codes

The problem of distributing a Cartesian product file on multiple disks to maximize the parallelism for partial match queries is addressed. C. Faloutsos et al. (1989) have proposed an allocation method for Cartesian product files on multiple disks by using linear error-correcting codes. The performance of the allocation method is analyzed. Some conditions under which the allocation method is strictly optimal for queries with a given number of unspecified attributes are presented. A necessary and sufficient condition for a linear code to give a strictly optimal allocation method is discussed. Formulas for the average response time on queries with w unspecified attributes, denoted T_w, in terms of the weight distribution of the code or its dual code, and formulas for the average response time Ton all queries, are given. Several examples whose average response times T_w or T are close to theoretical lower bounds are presented     

Transient stimulated Raman scattering in lead vapor

An investigation of stimulated Raman scattering (SRS) of short-pulse (6-ns) XeCl-laser radiation in Pb vapor is reported. Conversion efficiencies, based on peak power, up to 15% have been obtained for Pb-oven temperatures of 1260°C. The functional dependence of conversion efficiency, in the short-pulse regime, upon buffer-gas pressure and species differs significantly from that observed for long-pulse (>20-ns) pumping, corresponding to steady state behavior. Analysis of the data and comparison with transient SRS in H ₂ yield an estimate of T₂≈1ns for the transient response time T₂ of Pb vapor. The observed pressure effects are explained in terms of a reduction in T₂, and hence Raman gain, by collisions with buffer-gas atoms     

On-wafer microwave measurement setup for investigations on HEMTsand high-Tc superconductors at cryogenictemperatures down to 20 K

An on-wafer measurement setup for the microwave characterization of HEMTs and high-T_c superconductors at temperatures down to 20 K is presented. Both S-parameter and noise measurements can be performed in the frequency range from 45 MHz to 40 GHz and 2 GHz to 18 GHz, respectively, using standard calibration techniques and commercial microwave probe tips. Microwave measurements on a pseudomorphic FET and an AlGaAs-GaAs HEMT as well as investigations on a superconducting filter are presented to demonstrate the efficiency of the developed system     

A storage-efficient method for solving banded Toeplitz systems

A method is presented for solving the banded Toeplitz system Tx=y by decomposing T into its asymptotic upper and lower triangular factors (which are banded and Toeplitz) and a rank-p correction matrix, where p is the bandwidth of T. This way of representing T requires only O(p²) words of storage and allows computation of x in O(2Np) operations. A similar method is presented for the case in which T is bi-infinite and y is zero outside a finite region     

High-speed InP/InGaAs heterojunction bipolar transistors

Very-high-performance common-emitter InP/InGaAs single heterojunction bipolar transistors (HBTs) grown by metalorganic molecular beam epitaxy (MOMBE) are reported. They exhibit a maximum oscillation frequency (f_T) of 180 GHz at a current density of 1×10⁵ A/cm². this corresponds to an (R_BC_BC)_eff=f _T/(8πf²_max) delay time of 0.12 ps, which is the smallest value every reported for common-emitter InP/InGaAs HBTs. The devices have 11 μm² total emitter area and exhibit current gain values up to 100 at zero base-collector bias voltage. The breakdown voltage of these devices is high with measured BV_CEO and BV_CEO of 8 and 17 V, respectively     

A new system model for radar polarimeters

The validity of the 2×2 receive R and transmit T model for radar polarimeter systems, first proposed by H. Zebker et al. (1987), is questioned. The model is found to be invalid for many practical realizations of radar polarimeters, which can lead to significant errors in the calibration of polarimetric radar images. A more general model is put forward, which addresses the system defects which cause the 2×2 model to break down. By measuring one simple parameter from a polarimetric active radar calibration (PARC), it is possible to transform the scattering matrix measurements made by a radar polarimeter to a format compatible with a 2×2 R and T matrix model. Alternatively, the PARC can be used to verify the validity of the 2×2 model for any polarimetric radar system. Recommendations for the use of PARCs in polarimetric calibration and to measure the orientation angle of the horizontal (H) and vertical (V) coordinate system are also presented     

A temperature noise model for extrinsic FETs

A resistor temperature noise model for FETs has been successfully applied to extrinsic FETs to predict the frequency dependence of minimum noise figure F_min and associated gain G_Aopt. The model gives a fixed relationship between F_min and G_Aopt with one fitting parameter T_d. An extensive comparison to published results shows that the majority of FETs can be modeled with effective T_d values (the temperature of the output resistor) between 300 and 700 K for all of the frequencies (8 to 94 GHz), gate lengths (0.8 to 0.1 μm), and material types examined. The analysis shows that InP-based MODFETs exhibit significantly lower F_min and higher G_Aopt than conventional and pseudomorphic GaAs-based MODFETs of the same gate length. The results suggest a high F_max is a key factor for low noise figure