DC Current Measurement Research Articles

Atto-Farad Measurement and Modeling of On-Chip Coupling Capacitance

A first reported method of measuring coupling capacitance (both inter- and intralevel) between any two lines in the presence of any other lines in a very large scale integration (VLSI) chip, to an accuracy of atto-farad range, is discussed. The setup simply requires dc current measurement and the method has been tested for 180 nm and 130 nm technologies. Furthermore, the method can be easily implemented for on-wafer e-test measurement in a fab, to study die-to-die and wafer-to-wafer coupling capacitance variation due to manufacturing process variation. In one process, it has been observed that the coupling capacitance between parallel lines could vary as much as 17%.

Optical Fiber Current Transformer Applications on Railway Electric Power Supply Systems

The advances made in optical transmission and measurement technologies in recent years have expedited the development of optical networks and current sensors. This paper outlines the characteristics and special features of optical fiber sensors, describes the current measuring principles of optical current transformers (CTs) that utilize the Faraday (magneto-optic) effect, and introduces examples of their railway electric power system applications—the fault detection of Shinkansen changeover switches and the measurement of DC currents.

Robust technique for on-chip DC current measurements

A robust and highly scalable technique for measuring DC currents is described. The circuit consists largely of digital electronics except for a comparator and a passive RC filter. This simple structure is able to force a voltage at a circuit node while measuring the current that flows into it. The technique has been successfully demonstrated using a prototype constructed using a 0.35mm CMOS chip. The demand for highly integrated mixed-signal ICs has increased rapidly in recent years. This is mostly driven by the communications industry. However, as the level of integration increases, more and more analogue components are becoming buried deep inside the digital circuitry without external I/O access. Consequently, initial device character- isation and production testing of these components has become more challenging. An area of IC testing that is being affected by this high level of integration are the DC parametric tests. These tests are conducted to characterise a wide variety of mixed-signal circuits such as analogue-to-digital converters (ADCs), PLLs and bias networks. Also, these tests are needed in digital test applications such as pad current leakage and IDDQ tests. One type of DC parametric tests that is of focus involves forcing a voltage at a circuit node while measuring the current that flows into it. The traditional method for on- chip current measurements is by using a transimpedance amplifier (1, 2), an integrating network (3, 4) or a shunt resistance (5). However, all of these circuits involve the use of elaborate ADCs with trimmed components, which makes them more expensive and relatively nonscalable for on-chip implementation. This paper presents a novel technique for force-voltage current measurements. It makes use of simple ADCs and programmable voltage references (DACs) to capture the DC transfer characteristic of an internal load at different current levels. Once known, the transfer characteristic of the internal load can be used indirectly to determine the value of an unknown current level connected to the test circuit. The proposed method requires mostly digital logic with the exception of a comparator and several passive RC components. As a result, the circuit architecture will be able to take advantage of the down-scaling of digital integrated circuit technology and not be affected by the reduction in power supply voltages. Also, the system is programmable,

DC current and AC impedance measurements on boron-doped single crystalline diamond films

In this paper, we report the first measurement of impedance on boron-doped single crystalline diamond films from 0.1 Hz to 10 MHz with the temperature ranging from -100°C up to 300°C. The Cole-Cole (Z' via Z) plots are well fitted to a RC parallel circuit model and the equivalent Resistance and Capacitance for the diamond films have been estimated using the Zview curve fitting. The results show only one single semicircle response at each temperature measured. It was found that the resistance decreases from 70 GΩ at -100°C to 5 kΩ at 300°C. The linear curve fitting from -100°C to 150°C shows the sample has an activation energy of 0.37 eV, which is consistent with the theoretical value published of this kind of material. The equivalent capacitance is maintained at the level of pF up to 300°C suggesting that no grain boundaries are being involved, as expected from a single crystal diamond. The activation energy from the dc current-temperature curves is 0.36 eV, which is consistent with the value from ac impedance. The potential of this under-used technique for diamond film analysis will be discussed.

Study of an accurate dc busbar current measurement technique by using a transductor based network

The conventional single core or two core saturable reactor or transductor used for dc busbar current measurement may suffer from errors due to the magnetisation component of the dc flux and the asymmetry of the core materials. In the present paper a feedback technique of this type of dc current measurement has been developed. In this technique, the output signal has been used to send a feedback current through a feedback winding in order to nullify the magnetisation component of the dc flux and thus the measurement may be assumed to be more accurate with respect to other similar instruments. The developed network has been studied up to a dc busbar current of 50 A and the output characteristic has been found to be quite linear. The design of the network, its principle of operation and experimental data are reported in the present paper.

Temperature-compensated fiber-Bragg-grating-based magnetostrictive sensor for dc and ac currents

A compact and inexpensive optical fiber sensor for the measurement of dc and ac currents is demonstrated. The sensor consists of a fiber Bragg grating bonded on two joined pieces of metal alloys, one being Terfenol-D and the other MONEL 400. Because Terfenol-D has much stronger magnetostriction, a magnetic field applied along the two alloy bars stretches the two portions of the grating in different proportions and, thus, results in a split in the reflection spectrum of the grating, which can be measured with a simple technique using a single photodetector. On the other hand, because Terfenol-D and MONEL 400 have almost identical thermal expansion coefficients, a change in temperature does not cause the reflected spectrum of the grating to split and, therefore, does not affect the magnetic field measurement.

Micromachined low-finesse fabry-perot interferometer for the measurement of DC and AC electrical currents

A micromachined low finesse Fabry-Perot interferometer for measuring DC and AC electrical current is presented. Interrogation of the microcavity is achieved by a dual-wavelength fiber Bragg grating technique working in quadrature. A linear relation between the DC electrical current and the optical phase defined by the microcavity was detected. Large enhancement of the sensitivity of the microcavities is presented with the use of a planar coil instead of a power line. The sensitivity of the sensor with the planar coil configuration is 7.9 rad/A and resolution of /spl sim/0.18 mA//spl radic/Hz is achieved when the distance between the planar coil and the transducer head is 2 mm. The response of the sensor for AC measurements is 0.14 V/A with a resolution of 6 mA//spl radic/Hz when the distance between the power line and the transducer head is 5.5 cm.

Fabrication and optical characterization of the normal metal hot-electron microbolometer with Andreev mirrors

The normal metal hot-electron microbolometer (NHEB) is a direct detector for mm and sub-mm wavelengths. Theoretical estimations indicate that such a device should be able to achieve a sensitivity of around 10 −17 W/(Hz) 1/2 at 0.3 K and a time constant less than 1 μs. The temperature of the electron gas is monitored using superconductor–insulator–normal metal (SIN/NIS) tunnel junctions. We have fabricated such an NHEB where the normal metal strip is coupled to a double slot antenna for optical qualification (normal metal strip size (5.6×0.25×0.03) μm 3). The antenna is designed for 300 GHz and has an impedance of 30 Ω at the center frequency. The actual optical responsitivity and the response time of our NHEB has been measured at 0.5 K using a hot/cold load (black body radiation at room temperature and at liquid nitrogen temperature). DC-current measurements performed on other samples earlier indicate that our NHEB can achieve an electrical noise equivalent power (NEP) of at least 3×10 −16 W/(Hz) 1/2. We conclude that the optical responsitivity value obtained in the measurement is consistent with the electrical NEP value at the same temperature and in agreement with the estimated efficiency of the quasioptical coupling.

A simple low-dissipation amplifier for cryogenic STM

A current sensitive preamplifier designed for low-temperature scanning tunneling microscopy applications is presented. It combines the dc current measurement necessary for the feedback loop operation with a low noise ac measurement used for spectroscopy. The active device is a high electron mobility transistor which was chosen for its low input capacitance and excellent low-temperature performance. The power dissipation of the transistor can be kept at about 10 μW making it compatible with a variety of cryogenic systems. The ac current sensitivity is about 4 fA/√Hz at 4.2 K.

DC CONDUCTIVITY IN POLY-N-VINYLCARBAZOLE: A STUDY OF DIELECTRIC MEASUREMENTS

Dynamical dielectric measurements have been carried out on thin films of poly-N-vinylcarbazole. The dielectric response data were graphically represented in the conductivity complex plane, from which the values of the contribution of the DC conductivity were estimated. These values were in good agreement with the values obtained from DC current measurements, already reported in the literature. These results allow to conclude that the graphical representation of the complex conductivity in the complex plane represents a simple way for estimating the DC condctivity from dielectric data, without the experimental limitation to measure at very low frequencies, and without the difficulties appearing during DC current measurements.

DC CONDUCTIVITY IN POLY-N-VINYLCARBAZOLE: A STUDY OF DIELECTRIC MEASUREMENTS

Dynamical dielectric measurements have been carried out on thin films of poly-N-vinylcarbazole. The dielectric response data were graphically represented in the conductivity complex plane, from which the values of the contribution of the DC conductivity were estimated. These values were in good agreement with the values obtained from DC current measurements, already reported in the literature. These results allow to conclude that the graphical representation of the complex conductivity in the complex plane represents a simple way for estimating the DC condctivity from dielectric data, without the experimental limitation to measure at very low frequencies, and without the difficulties appearing during DC current measurements.

Do superconductors have zero resistance in a magnetic field?

We show that dc voltage versus current measurements of a YBa(2)Cu(3)O(7-delta) film in a magnetic field can be collapsed onto scaling functions proposed by Fisher et al. [Phys. Rev. B 43, 130 (1991)] as is widely reported in the literature. We find, however, that good data collapse is achieved for a wide range of critical exponents and temperatures. These results strongly suggest that agreement with scaling alone does not prove the existence of a phase transition. We propose a criterion to determine if the data collapse is valid, and thus if a phase transition occurs. To our knowledge, none of the data reported in the literature meet our criterion.

Energy relaxation process in a quantum dot studied by DC current and pulse-excited current measurements

Energy relaxation from an excited to a ground state in a quantum dot is studied by DC current and pulse-excited current measurements. We find that all the excited states can be classified as short-lived or long-lived excited states, although they are too short or too long for us to determine the actual lifetime with our method. The relaxation time is short (less than a few ns) if the transition takes place by means of electron–phonon interaction, while it is very long (more than a few μs) if the transition involves a spin-flip. The crossover between long and short relaxation time is studied at a particular level crossing.

Space charge behavior in low-density polyethylene

The space charge distribution in low-density polyethylene (LDPE) was measured with the pulsed electroacoustic (PEA) method. We used three types of LDPE: LDPE-L and LDPE-H were prepared by the high pressure process, and m-LDPE was polymerized with a metallocene catalyst. Space charge in LDPE strongly depended upon the electrode material. Semiconductive electrodes enhanced carrier injection into LDPE and, as a result, space charge. The density, polymerization process, applied field, temperature and so on also affected the space charge behavior. This space charge behavior was compared with the results of dc current measurements.

Vibration compensation technique for an optical current transducer

Details are presented on a technique for compensation of vibration-induced noise in an optical current transducer (OCT). The light intensity changes that result from vibration are reciprocal, i.e., their magnitude does not depend on the direction of light propagation. However, intensity changes that result from the Faraday rotation induced as the light travels through the OCT are dependent on the direction of propagation and hence, by using two counter-propagating beams, vibration- induced intensity noise can be canceled by applying simple signal processing. This solution also enables true dc current measurement to be made. The principles of operation of the compensation method an experimental evaluation of the system are presented and the limitations associated with the compensation scheme are discussed.

Precipitate formation in carbon-doped base of InGaP/GaAs heterojunction bipolar transistors grown by low-pressure metal organic chemical vapor deposition

The effect of intermediate temperature annealing on the carbon-doped base region of InGaP/GaAs heterojunction bipolar transistors (HBTs) was studied. This work shows that after annealing at only 600 °C a sample doped at 5.5×1019 cm−3 displays carbon precipitation. InGaP/GaAs HBT structures were grown for the annealing study. Hall measurements were used to measure hole concentration. Atomic force microscopy was employed to identify carbon precipitation. The annealing process not only removes hydrogen from the base but also creates carbon precipitates. The dc current gain measurements imply that the carbon precipitates increase base recombination. These results are very important in the growth and postgrowth annealing of high gain HBTs.

A novel wide range electrometer with quasilinear output

An electrometer using complementary metal–oxide–semiconductor bilateral switches for automatic range control is described. Based on a dual-switching configuration, the electrometer is capable of current measurement over eight orders of magnitude. Together with a voltage shifter, this circuit provides a quasilinear analog output for the measurement of input dc current between 10−3 and 10−12 A. The application of integrated circuits makes the whole system compact and extremely low cost.

Silicon nanocrystal formation in thin thermal-oxide films by very-low energy Si + ion implantation

Thin thermally grown silicon oxides are implanted with a high dose of silicon using very low energy ion implantation. After high temperature annealing, the oxides are observed by Transmission Electron Microscopy which reveals the existence of silicon nano-crystals. The electrical properties of metal-oxide-semiconductor devices are then investigated using dynamic conductance as well as dc current measurements.

Characteristics of SOI FET's under pulsed conditions

A system for measuring output characteristics of FET's using nanosecond pulses, instead of dc voltage and current measurement, is described. The measurement system is used to obtain the I-V characteristics of silicon-on-insulator (SOI) FET's without the degradation resulting from self heating. Use of the technique to study partially depleted SOI FET's with floating bodies shows that under pulsed conditions, their output curves have a history dependence. The physical mechanisms responsible for the history dependence are explained. Further understanding of the physical mechanisms is given by examination of single-shot pulse measurements. The role of transient and time-dependent phenomena in determining I-V curves is elucidated.

The noise-tee - a lightwave device for microwave noise measurements

An innovative lightwave method is proposed to insert noise in electronic circuits in favor of microwave noise measurements. The proposed noise-tee has attractive additional features compared to the use of 50 /spl Omega/ noise sources: 1) the inserted noise level and noise bandwidth is continuously variable over a wide dynamic range; 2) the wideband scaling accuracy of this level, relative to a pre-calibrated level, equals the accuracy of simple DC-current measurements; 3) level-induced impedance variations are negligible, compared to the 20% impedance variation of a commonly used microwave noise source; and 4) noise-tees enable the realization of 100% reflective noise sources, in favor of two-port noise-parameter measurements.