Annealing of linear birefringence in single-mode fiber coils:application to optical fiber current sensors

Annealing procedures that greatly reduce linear birefringence in single-mode fiber coils are described. These procedures have been successfully applied to coils ranging from 5 mm to 10 cm in diameter and up to 200 or more turns. They involve temperature cycles that last 3-4 days and reach maximum temperatures of about 850°C. The residual birefringence and induced loss, are minimized by proper selection of fiber. The primary application of these coils is optical fiber current sensors, where they yield small sensors that are more stable than those achieved by other techniques. A current sensor with a temperature stability of +8.4×10^-5/K over the range from -75 to +145°C has been demonstrated. This is approximately 20% greater than the temperature dependence of the Verdet constant. Packaging degrades the stability, but a packaged sensor coil with a temperature stability of about +1.6+10^-4/K over the range from -20 to +120°C has also been demonstrated     

Experimental determination of electron drift velocity in 4H-SiC p+-n-n+ avalanche diodes

4H-SiC p⁺-n-n⁺ diodes of low series resistivity (<1×10^-4 Ω·cm²) were fabricated and packaged. The diodes exhibited homogeneous avalanche breakdown at voltages U_b=250-270 V according to the doping level of the n layer. The temperature coefficient of the breakdown voltage was measured to be 2.6×10^-4 k^-1 in the temperature range 300 to 573 K. These diodes were capable of dissipating a pulsed power density of 3.7 MW/cm² under avalanche current conditions. The transient thermal resistance of the diode was measured to be 0.6 K/W for a 100-ns pulse width, An experimental determination of the electron saturated drift velocity along the c-axis in 4H-SIC was performed for the first time, It was estimated to be 0.8×10⁷ cm/s at room temperature and 0.75×10⁷ cm/s at approximately 360 K     

Development of prototype fiber-optic-based Fizeau pressure sensorswith temperature compensation and signal recovery by coherence reading

A range of prototype fiber-optic-based Fizeau interferometric pressure sensors with temperature compensation and signal recovery by dual-wavelength coherence reading have been developed. A separate fiber-optic-based Fizeau temperature sensor with similar cavity length was incorporated into the pressure sensor to allow the pressure measurement to be corrected for the temperature dependence of the pressure probe. The pressure and temperature probes were multiplexed spatially. For the low-pressure sensor, the obtained range to resolution ratio and the accuracy were ~6.7×10³:1 and better than ±1 percent over a pressure range of 0-0.48 bar, respectively. For the medium pressure sensor, the achieved range to resolution ratio and the overall accuracy were 3.6×10⁴:1 and ±0.15 percent over a full-pressure range of ~10 bar. For the high pressure sensor, a range to resolute ratio of ~1.67×10⁴:1 and an overall measurement accuracy of ±0.69 percent over a pressure range of ~1000 bar have been achieved. Due to the universality of the signal-processing scheme based on the dual-wavelength coherence-reading technique, the signal-processing box can be compatible with a range of sensors illuminated by the sources with similar central wavelengths. This study would be readily used to develop a range of commercial fiber-optic pressure sensors with similar optical path differences, interrogated by a universal signal-processing box, for different applications     

A simple, inexpensive electrometer used to measure currents of individual silicon vidicon diodes in the 10-16to 10-15ampere range

A simple, inexpensive, essentially noiseless current-measuring device has been devised with a sensitivity of 10^-16to 10^-15ampere. Its operation relies on a measurement of the voltage decay of the device under test, the current being proportional to the rate of change of the voltage. Individual diodes of silicon vidicon targets (10^-15ampere) and high resistivity layers (10¹⁵ohms/square) have been measured. In addition to its simplicity, this technique lends itself to nondestructive in-line testing.     

Flicker noise in GaN/Al0.15Ga0.85N dopedchannel heterostructure field effect transistors

We have investigated noise characteristics of novel GaN/Al_0.15Ga_0.85N doped channel heterostructure field effect transistors designed for high-power density applications. The measurements were carried out for various gate bias voltages V_GS and with the drain voltage V_DS varying from the linear to the saturation regions of operation V_DS>5 V. Our results show that flicker, e.g., 1/f noise, is the dominant limiting noise of these devices; and the Hooge parameter is of the order of 10 ^-5-10^-4. The gate voltage dependence of 1/f noise was observed in the linear region for all examined V_GS and in the saturation region for V_GS>0. These results indicating low values of the Hooge parameter are important for microwave applications     

Temperature and vibration insensitive fiber-optic current sensor

A robust interferometric fiber-optic current sensor with inherent temperature compensation of the Faraday effect is presented. Sensor configurations based on Sagnac and polarization-rotated reflection interferometers are considered. The sensing fiber is residing and thermally annealed in a coiled capillary of fused silica. The capillary is embedded in silicone within a ring-shaped housing. It is theoretically and experimentally shown that the temperature dependence of the birefringent fiber-optic phase retarders of the interferometers can be employed to balance the temperature dependence of the Faraday effect (0.7×10^-4/°C). Insensitivity of the sensor to temperature within 0.2% is demonstrated between -35°C and 85°C. The influence of the phase retarders on the linearity of the sensor is also addressed. Furthermore, the sensitivity to vibration of the two configurations at frequencies up to 500 Hz and accelerations up to 10 g is compared. High immunity of the reflective sensor to mechanical perturbations is verified     

Highly linear GaAs hall devices fabricated by ion implantation

Gallium arsenide Hall devices have been fabricated with very thin active layers formed by silicon implantation. The variation of Hall voltage with calibrated magnetic-flux density shows that the linearity error is better than ±0.03 percent in the magnetic-flux-density range below 10 kG at room temperature. Measurements in a superconducting magnet at 4.2 K shows that the linearity error is within ± 0.6 percent at the range below 68 kG. When this device is used as a magnetic sensor, magnetic-flux meters with an accuracy of 0.1 percent (B< 10 kG) at room temperature and 0.6 percent (B< 68 kG) at 4.2 K can be achieved.     

Fundamental characteristics of a magnetoresistive sensor using Y1Ba2Cu3O7-x ceramicsuperconducting films

The fundamental characteristics of a magnetic sensor fabricated from a Y₁Ba₂Cu₃O_7-x ceramic superconducting film are investigated. The operation principle of the sensor is based on the magnetoresistive properties of the material. The Y₁Ba₂Cu₃O_7-x ceramic film was prepared by the spray pyrolysis method. An element of the magnetic sensor consists of the film patterned to a meander shape. the sensitivity is discussed in connection with the noise measurement of the element. A magnetic field resolution of 2×10^-6 G/(Hz) ^1/2 at 100 Hz was obtained in the 0.1-100 G range. The sensitivity is much higher than that of a conventional semiconductor magnetic sensor. With an AC modulation provided by a magnetic field, phase detection of the magnetic field can be performed using a lock-in amplifier. An improvement in the low-frequency (<1 Hz) magnetic field resolution of about one order of magnitude was obtained using this method     

Some new FIR laser lines of optically pumped12CH316OH,12CH316OD, and12CH3I,12CH3Br,12CD2Cl2absorption spectroscopy of water and acetonitrile

The wavelength, polarization, and output power of several lines of the optically pumped CW FIR¹²CH3¹⁶OH (methanol) and¹²CH3¹⁶OD (1-D deuterated methanol), methyl iodide, methyl bromide, and deuterated methylene chloride lasers have been determined. In addition to lines already reported in the literature, seven strong lines have been observed. Optimum performance of the laser system is achieved by means of an improved coupling of the CO2pump power into the resonator and extraction of the FIR power from the resonator. Measurements on the power absorption coefficient of water using the laser indicate thatalpha(bar{nu})rises to almost 1100 Np ċ cm^-1at 170 cm^-1, and then shows a gradual fall with an increase in frequency. A strong temperature dependence of the 200 cm^-1peak inalpha(bar{nu})is predicted, with a decrease in the frequency of maximum power absorption coefficient with an increase in temperature. The range of measurements for acetonitrile is extended to lower frequencies so as to overlap with those determined from other millimeter wave techniques. For highly power-absorbing liquids,alpha(bar{nu})is estimated to be within ± 5 percent.     

Leakage mechanisms in the heavily doped gated diode structures

A leakage current model is presented which shows very good agreement with reported experimental results on gated diode structures with contemporary ULSI dimensions. The leakage current is modeled as the Shockley-Read-Hall generation current, enhanced by the Poole-Frenkel effect and trap-assisted tunneling. The model shows very good agreement on gate voltage, temperature, and oxide thickness dependence for the normal operating voltage range. It is found from the model that the doping range from 2×10¹⁸ to 1×10¹⁹ cm ^-3 gives the most significant degradation to the leakage characteristics in trench-type DRAM cells and the drain of MOSFETs     

Electrical properties of nickel-low-doped n-type gallium arsenide Schottky-barrier diodes

The forward current characteristics of nickel-low-doped n-type gallium arsenide Schottky-barrier diodes are measured over the temperature range 90.5-434 K. The ideality factor and its temperature dependence is determined and found to decrease with increasing temperature according to the relationshipn(T) = 11.4T^{-1/2}+0.444 to within ±4 percent. This is in agreement with the theoretical analysis of Strikha, who predicted a temperature dependence law between T^-1andT^{-1/2}. The barrier height is determined from both the saturation current and the capacitance methods. A modification is made to the forward current expression, which results in good agreement between the values of the barrier height obtained from both methods over a wide temperature range. The barrier height is found to decrease with increasing temperature at a rate of 5.8 × 10-4V/K. Comparison with the dependence of the energy gap on temperature in GaAs suggests that the observed change in the barrier height is equal to that of Eg.     

High performance 0.35 μm gate-length monolithicenhancement/depletion-mode metamorphicIn0.52Al0.48As/In0.53Ga0.47As HEMTs on GaAs substrates

Monolithic integration of enhancement (E)- and depletion (D)-mode metamorphic In_0.52Al_0.48As/In_0.53Ga_0.47 As/GaAs HEMTs with 0.35 μm gate-length is presented for the first time. Epilayers are grown on 3-inch SI GaAs substrates using molecular beam epitaxy. A mobility of 9550 cm²/V-s and a sheet density of 1.12×10^{12 -2} are achieved at room temperature. Buried Pt-gate was employed for E-mode devices to achieve a positive shift in the threshold voltage. Excellent characteristics are achieved with threshold voltage, maximum drain current, and extrinsic transconductance of 100 mV, 370 mA/mm and 660 mS/mm, respectively for E-mode devices, and -550 mV, 390 mA/mm and 510 mS/mm, respectively for D-mode devices. The unity current gain cutoff frequencies of 75 GHz for E-mode and 80 GHz for D-mode are reported     

Characteristics of a 1.2-µm CMOS technology fabricated on an RF-heated zone-melting recrystallized SOI

0.7-5-µm CMOSFET's were fabricated on SOI which was recrystallized using an RF-heated zone-melting recrystallization (RFZMR) method. The leakage currents of n-channel MOSFET's having gate lengths between 5- and 0.7-µm range between 10^-14and 10^-12A/µm and show no dependence on channel length. Those of the p-channel MOSFET's were 10^-14-10^-12A/µm when the gate lengths were longer than 1.2 µm, and increased when the gate lengths were shorter than 1.0 µm. The propagation delay time of the CMOSFET inverter was 0.13 ns per stage at a supply voltage of 3.5 V.     

Controlled noise generation with avalanche diodes II. High pulse rate design

The low pulse rate design of an avalanche noise diode described by Haitz¹is modified in order to obtain a Gaussian probability distribution. The essential modification is an increase of the avalanche pulse rate from less than 10⁴sec^-1to more than 10⁶sec^-1. This high pulse rate is achieved, in a controlled way, by reducing the breakdown voltage from about 30 volts to 12 volts. As with the low pulse rate design of Haitz [1], the avalanche pulse rate is determined by trigger carriers generated by internal field emission. Spectral voltage density and temperature coefficient are estimated and found to be in good agreement with the experimental results of 0.5 mV per c/s^1/2and -8.10^-3/°C, respectively. The spectral voltage density is fiat within ±1 dB over the frequency range from 10 c/s to 200 kc/s. After passing the noise through a low pass filter with a cutoff frequency of 200 kc/s the probability distribution of the noise voltage is Gaussian. The spectral voltage density is practically insensitive to variations of the supply voltage between 15 volts and 25 volts, corresponding to a current variation from 30 µA to 130 µA.     

A monolithic1 x 10array of InGaAsP/InP photodiodes with small dark current and uniform responsivities

We fabricated a monolithic 1 × 10 array of InGaAsP/InP double-heterostructure photodiodes by liquid-phase epitaxy, which has highly uniform characteristics in breakdown voltages and responsivities and whose deviations in an array are ±1 percent and ±6 percent, respectively. The dark current of the elemental photodiode at low bias voltage, which is attributed mainly to the generation-recombination process in the depletion layer, is smaller than that of the germanium avalanche photodiode by one order at room temperature. The elemental photodiodes in the array have high quantum efficiency of more than 60 percent with SiOxfilm for antireflection in a wavelength range of1.0-1.2 mum, fast response time shorter than 1 ns, and very high cutoff frequency of about 800 MHz with the load resistance of 50 Ω.     

Buried-guarded layer ion-implanted resistors

Megohm silicon monolithic resistors have been fabricated with sheet resistances up to 120 kΩ/□ using an implanted p-layer resistor which is buried under an implanted n-guard layer. The n-guard layer protects against slice-to-slice variations of the fixed surface charge, and was made using phosphorus doses and energy of 1.5-5 × 10¹²/cm²and 30 keV. Resistors have been fabricated up to 20 MΩ; sheet resistances were in the range of 7-120 kΩ/□ using boron doses and energies of 1-3 × 10^:12/cm²and 30-300 keV. The sheet resistance, voltage dependence of resistance, temperature coefficients, junction leakage, and parasitic capacitance have been measured for different implantation parameters. This process has been used to fabricate two matched 8-MΩ resistors for use in a high input impedance differential preamplifier integrated circuit. A match of 2 percent and a magnitude tolerance of ±10 percent has been achieved. The temperature coefficient of resistance (TCR) is about 4000 ppm/°C and tracks within 400 ppm/ °C. These resistors are linear up to ∼1 V, about 50 times higher bias voltage than required in the application. The structure and fabrication are compatible with present monolithic silicon integrated circuit processing.     

InP MISFET's with plasma anodic Al2O3and interlayed native Oxide gate insulators

InP MISFET's, with native oxide film interlayed between plasma anodic Al2O3film and the InP substrate, has been fabricated and showed the instability of the drain current reduced less than ± 4 percent for the period of 5 µs ∼ 5 × 10⁴s. The effective electron mobility is 2100 ∼ 2600 cm²/V.s at room temperature. The CV characteristics of MIS diodes and AES in-depth profiles are also discussed with respect to effects of interlaying native oxide film on device characteristics.     

X-ray imaging camera tube using sputter-deposited CdTe/CdSheterojunction

CdTe heterojunction devices have been fabricated for the first time by an RF sputter deposition method for application to X-ray imaging sensors. The electrical resistivities of sputter-deposited polycrystalline CdS and CdTe films are greater than 10⁶ Ω-cm and 10⁹ Ω-cm, respectively. The fabricated CdS/CdTe heterojunction sensor shows a good diode characteristic and a high sensitivity to X-ray radiation. An X-ray imaging camera tube consisting of CdS/CdTe heterojunction photoconductive target shows three times larger responsivity to X-rays than the conventional PbO X-ray tube. The dark current density of the device is observed to be lower than 10 nA/cm² at 20 V target voltage at room temperature     

Detailed performance characteristics of hybrid InP-InGaAsP APD's

Detailed performance characteristics of hybrid InP-InGaAsP APD's having negligible dark current (ID< 6 nA at M = 30) are reported. The excess noise factor F is found to be given by F/M ≈ const ≈ 0.42 ± 0.10 for gains in the range 5 ≤ M ≤ 35. The breakdown voltage increases with temperature according to ΔV_{BD}/V_{BD}/ΔT = 1.0 × 10^-3/°C. The dark current near breakdown doubles every 15°C. Sub-nanosecond rise times are observed, however, fall times are extended to ∼3 nsec by a diffusion tail that will be difficult to completely eliminate.     

Photoresponses in In2O3transparent gate MOS capacitors

In this paper electrical and photoelectronic properties of sputtered In2O3films including 5 wt % SnO2and transparent gate MOS capacitors employing this film were discussed. In order to improve the characteristics of the sputtered films and to recover the radiation damage generated during the sputtering process, high-temperature annealing of the film in nitrogen was important. In the present experiment, the best post-annealing temperature was about 850°C, and the minimum resistivity ρ and the interface-state density Nsswhich resulted from this annealing were 1.1 × 10^-3Ω . cm and 6.5 × 10¹⁰cm^-2. eV^-1, respectively. The dark current was comparable to that of conventional Al-gate MOS capacitors. Moreover, it became clear that the recombination loss of photogenerated carriers due to the interface states caused the degradation of the spectral response in the short wavelength range, when the surface of the MOS substrate was maintained in the vicinity of mid-gap potential. However, the transparent gate MOS capacitors biased in weak or strong inversion could be usable as high-sensitivity, photosensors in the blue region of the spectrum, because the interface states could not act as effective recombination centers for these bias conditions.