Constant Current Injection Research Articles

Effects of junction temperature and its variations on the performance of GaN‐based high power flip‐chip LEDs

AbstractIn this paper, high power flip‐chip GaN‐based LEDs were fabricated, and then the effects of junction temperature and its variations were investigated. It was found that the optical output decreases seriously with rising temperature. The variations of junction temperature can be achieved to 9 °C at 350 mA in most regions of flip‐chip LED except for some hot regions around some electrodes. The combination of screening of quantum confined Stark effect (QCSE) and thermal effect surprisingly makes the peak wavelength constant from 300 mA to 800 mA in electroluminescence spectra. The full‐width at half‐maximum (FWHM) of emission peak was narrowed by thermal effect in constant current (CC) injection. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparison of Responses of Neurons in the Mouse Inferior Colliculus to Current Injections, Tones of Different Durations, and Sinusoidal Amplitude-Modulated Tones

We made in vivo whole cell patch-clamp recordings from the inferior colliculus of young-adult, anesthetized C57/Bl6 mice to compare the responses to constant-current injections with the responses to tones of different duration or to sinusoidal amplitude-modulated (SAM) tones. We observed that voltage-dependent ion channels contributed in several ways to the response to tones. A sustained response to long tones was observed only in cells showing little accommodation during current injection. Cells showing burst-onset firing during current injection showed a small response to SAM tones, whereas burst-sustained cells showed a good response to SAM tones. The hyperpolarization-activated nonselective cation channel I(h) had a special role in shaping the responses: I(h) was associated with an increased excitability, with chopper and pauser responses, and with an afterhyperpolarization following tones. Synaptic properties were more important in determining the responses to tones of different durations. A short-latency inhibitory response appeared to contribute to the long-pass response in some cells and short-pass and band-pass neurons were characterized by their slow recovery from synaptic adaptation. Cells that recovered slowly from synaptic adaptation showed a relatively small response to SAM tones. Our results show an important role for both intrinsic membrane properties -- most notably the presence of I(h) and the extent of accommodation -- and synaptic adaptation in shaping the response to tones in the inferior colliculus.

Point-Counterpoint: Heat-induced membrane depolarization of hypothalamic neurons: a putative/an unlikely mechanism of central thermosensitivity

heating and cooling various sites of the preoptic area and anterior hypothalamus (PO/AH) of mammals with fine thermodes reflexively evoke thermoregulatory responses, indicating that many central thermostats regulate temperature (T) of the brain ([16][1]). In PO/AH, heating- and cooling-activated

Instability analysis of charges trapped in the oxide of metal-ultra thin oxide-semiconductor structures

In this paper, we present the theoretical and experimental results of the influence of a charge trapped in ultra-thin oxide of metal/ultra-thin oxide/semiconductor structures (MOS) on the I(Vg) current-voltage characteristics when the conduction is of the Fowler-Nordheim (FN) tunneling type. The charge, which is negative, is trapped near the cathode (metal/oxide interface) after constant current injection by the metal ( Vg ). Of particular interest is the influence on the ( Vg ) shift over the whole I(Vg) characteristic at high field (greater than the injection field ( > 12.5 MV/cm)). It is shown that the charge centroid varies linearly with respect to the voltage Vg . The behavior at low field ( 12.5 MV/cm) is analyzed in reference A. Aziz, K. Kassmi, Ka. Kassmi, F. Olivie, Semicond. Sci. Technol. 19, 877 (2004) and considers that the trapped charge centroid is fixed. The results obtained make it possible to analyze the influence of the injected charge and the applied field on the centroid position of the trapped charge, and to highlight the charge instability in the ultra-thin oxide of MOS structures.

Plateau potentials and membrane oscillations in parasympathetic preganglionic neurones and intermediolateral neurones in the rat lumbosacral spinal cord.

Whole-cell patch recordings were made from parasympathetic preganglionic neurones (P-PGNs) and unidentified intermediolateral (IML) neurones in thick slices of the lower lumbar and sacral spinal cord of 14- to 21-day-old rats. The P-PGNs and IML neurones examined were similar in terms of soma sizes, input resistance and capacitance, and displayed a sag conductance as well as rebound firing. In the absence of drugs, the neurones responded with either tonic or adapting firing to depolarizing current steps. However, in the presence of the group I metabotropic glutamate receptor agonist (RS)-3,5-dihydroxyphenylglycine (DHPG), almost half of the neurones displayed accelerating firing rates during the constant current injection, followed by a sustained after-discharge. In the presence of TTX, plateau potentials were observed. The firing changes and plateaux were blocked by nifedipine, an L-type Ca2+ channel blocker, and (S)-(-)-Bay K8644 was able to produce these firing changes and plateaux in the absence of DHPG, demonstrating the involvement of an L-type Ca2+ conductance. Ca2+-activated nonspecific cationic conductances also appear to contribute to the firing changes. A few neurones displayed membrane oscillations and burst firing in the presence of DHPG. The results suggest that the firing characteristics of both P-PGNs and other neurones likely to be involved in caudal spinal reflex control are not static but, rather, quite dynamic and under metabotropic glutamate receptor modulatory control. Such changes in firing patterns may be involved in normal pelvic parasympathetic reflex function during micturition, defaecation and sexual reflexes, and may contribute to the abnormal output patterns seen with loss of descending brainstem input and visceral or perineal sensory disturbances.

Effects of gate material on Fowler-Nordheim stress induced thin silicon dioxide degradation under negative gate bias

An exhaustive theoretical investigation on the role of gate material as well as commonly used metal deposition processes [viz., electron beam (e-beam) evaporation and thermal evaporation] on high-field stress-induced dielectric breakdown and∕or degradation of identically thick (8–10nm) thermally grown silicon dioxide (SiO2) films used in memory devices has been reported. Gate materials studied here are n+-polycrystalline silicon (polySi) and aluminum (Al) with n-channel metal-oxide-semiconductor field effect transistor structures. Results will be shown here during constant current and constant field Fowler-Nordheim (FN) tunnel injection from the gate into SiO2. Our theoretical results establish that Al-gated structures exhibit poorer dielectric integrity compared to polySi-gated structures under both types of FN stressing technique. Furthermore, compared to thermally deposited Al-gated samples, e-beam evaporated Al-gated samples show slightly higher gate oxide deterioration in either mode of FN stressing studied here.

Modelling of the influence of charges trapped in the oxide on the I(Vg) characteristics of metal–ultra-thin oxide–semiconductor structures

This paper deals with the theoretical and experimental influences of the charge trapped in the oxide of metal/ultra-thin oxide/semiconductor structures. It focuses on the two characteristics current–voltage I(Vg) and voltage–charges injected Vg(Qinj) (Vg is the voltage applied, Qinj is the injected charge) when the conduction is of the Fowler–Nordheim type. The charge is trapped in the thin oxide after injection of a constant current at high field (>12 MV cm−1) from the metal (in accumulation regime: Vg < 0). This study considers that, after a given injection, the charge centroid is fixed during the acquisition of the I(Vg) characteristics.A method is proposed to determine the trapped charge characteristics (density and centroid) by analysing the theoretical and experimental I(Vg) and Vg(Qinj) characteristics. It is shown that the constant current injection creates a charge trapped in the oxide near the cathode. When the injected charge increases, the trapped charge density increases linearly and the charge centroid position shifts exponentially towards the injecting electrode. These results enable us to draw conclusions on the instability of the trapped charge. Indeed the increase in the charges injected causes the movement of the charge centroid towards the cathode.

Dissociation of retinal ganglion cells without enzymes

We describe here methods for dissociating retinal ganglion cells from adult goldfish and rat without proteolytic enzymes, and show responses of ganglion cells isolated this way to step-wise voltage changes and fluctuating current injections. Taking advantage of the laminar organization of vertebrate retinas, photoreceptors and other cells were lifted away from the distal side of freshly isolated goldfish retinas, after contact with pieces of membrane filter. Likewise, cells were sliced away from the distal side of freshly isolated rat retinas, after these adhered to a membrane filter. The remaining portions of retina were incubated in an enzyme-free, low Ca 2+ solution, and triturated. After aliquots of the resulting cell suspension were plated, ganglion cells could be identified by dye retrogradely transported via the optic nerve. These cells showed no obvious morphological degeneration for several days of culture. Perforated-patch whole-cell recordings showed that the goldfish ganglion cells spike tonically in response to depolarizing constant current injections, that these spikes are temporally precise in response to fluctuating current injections, and that the largest voltage-gated Na + currents of these cells were larger than those of ganglion cells isolated with a neutral protease.

Enhanced radiative efficiency in blue (In,Ga)N multiple-quantum-well light-emitting diodes with an electron reservoir layer

The temperature dependence of the electroluminescence (EL) spectral intensity of two blue (In,Ga)N/GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) without and with an additional n-doped (In,Ga)N electron reservoir layer is investigated between 20 and 300 K . The emission region of the LEDs, which have been prepared by metal-organic vapor-phase epitaxy, consists of three In 0.3Ga 0.7N QWs with a nominal width of 2.5 nm separated by 6.5 nm GaN barriers. The n-doped In 0.18Ga 0.82N electron reservoir layer has been inserted in order to exploit the effects of such additional layer on the carrier capture rates. We find that by adding the electron reservoir layer, the EL spectral intensity is significantly enhanced over a wide temperature range for a constant injection current. These results indicate the importance of the electron capture processes by radiative recombination centers in the (In,Ga)N MQW.

Ageing of metal/ultra-thin oxide/semiconductor structures under Fowler–Nordheimcurrent injection

In this paper, results of the ageing of metal/ultra-thin oxide/semiconductor structures underFowler–Nordheim constant current injections are presented. The oxide (silicon dioxide,SiO2) thickness layer of these structures varies from 3 to 12.5 nm for a p-type semiconductor. Itis shown that ageing induces trapped charges in the oxide layer (positive and negativenear the cathode and positive near the anode) and new interface states at theoxide/semiconductor interface.The positive charge created near the oxide/semiconductor interface,during current injection from the metal (accumulation regime,Vg<0), cannot be observed on current–voltage(I(Vg)) characteristics inthe inversion regime (Vg>0). It is shown that these charges can trap electrons injected from the semiconductor during acquisition of theI(Vg) characteristics(Vg>0). This inducesa shift in the I(Vg) characteristics as opposed to that what is obtained from capacity–voltage(C(Vg)) characteristics. So, the characteristics (density and centroid) of chargestrapped in the oxide layer cannot be obtained, as in the case of thicklayers (thickness greater than 20 nm), from the shift obtained from theI(Vg) characteristics in accumulation and inversion regimes. Also, it has been shown that thecapture of electrons by the positive charge at the oxide/semiconductor interface promotesthe creation of interface states.

Purinergic Modulation of Cochlear Partition Resistance and Its Effect on the Endocochlear Potential in the Guinea Pig

Introduction of adenosine 5'-triphosphate (ATP) into the endolymphatic compartment of the guinea-pig cochlea decreases the endocochlear potential (EP). To determine if this is due to an ATP-induced change in compartment resistance, the cochlear partition resistance (CoPR) was measured using constant current injections into scala media before, during, and after microinjection of ATP into the same compartment. The CoPR (mean = 3.13 +/- 0.13 kOmega) decreased with ATP in a dose-dependent manner (25.1 +/- 3.0% decrease in relation to baseline values) and this was linearly correlated ( R(2) = 0.91) to the magnitude of the ATP-induced decline in EP (41.6 +/- 7.0% decline in relation to the baseline). Pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, a P2X receptor antagonist) injected prior to ATP application blocked this ATP-induced reduction in EP and CoPR. This indicates that ATP-gated ion channels (P2X receptors) provide a latent shunt capable of regulating the majority of the electrical potential across the luminal surface of the sensory hair cells, which is necessary for sound transduction. The results suggest a novel sound transduction regulatory mechanism, which, via extracellular ATP, has the capability of adjusting hearing sensitivity.

Relationship between membrane potential oscillations and rhythmic discharges in identified hippocampal theta-related cells.

Intracellular recordings of cells, classified according to the criteria of Colom and Bland as phasic theta-ON or phasic theta-OFF cells, were carried out in the dorsal region of the hippocampal formation in urethan-anesthetized rats. Cells were studied during two spontaneously occurring hippocampal field conditions, asynchrony, termed large-amplitude irregular activity, and synchrony, termed theta. During the spontaneous cycling between these two field states, the effect of four levels of intracellular depolarizing and hyperpolarizing constant current injections on the amplitude and phase of membrane potential oscillations (MPOs) and the rate and pattern of cell discharges was assessed. Labeled CA1 pyramidal cells and bistratified cells met the criteria for classification as phasic theta-ON cells and labeled CA1 pyramidal layer basket cells, mossy hilar cells, and granule cells met the criteria for classification as phasic theta-OFF cells. MPOs were recorded in CA1 pyramidal cells, CA1 layer basket cells, mossy interneurons, and granule cells only during theta field activity, their onset in theta-ON cells signaled by a depolarizing shift of 5-10 mV and in theta-OFF cells by a hyperpolarizing shift of 5-10 mV, in membrane potential. The effect of current injections in phasic theta-ON and theta-OFF cells during the theta field condition revealed that MPO amplitude was voltage dependent and frequency was voltage independent. There were no phase changes observed in phasic theta-ON cells during current injections; however, amplitude analysis revealed an inverted U-shaped curve asymmetrically distributed around the average value of the membrane potential occurring during the spontaneous theta (no current) control condition. The occurrence and rate of rhythmical cell discharges in CA1 pyramidal phasic theta-ON cells during the theta condition was precisely controlled within a critical range of membrane potential values from approximately -57 to -68 mV, corresponding to a range of MPO amplitudes of approximately 4-7 mV. Outside the critical range, rhythmic cell discharges were abolished. Membrane potential oscillations in CA1 pyramidal layer basket cells underwent an approximate 180 degrees phase reversal when the membrane potential was depolarized above -65 mV. The occurrence and rate of rhythmic cell discharges in CA1 pyramidal layer basket cell phasic theta-OFF cells during the theta condition was precisely controlled within a critical range of membrane potential values from approximately -62 to -60 mV, corresponding to a range of MPO amplitudes of approximately 7-7.5 mV. Outside the critical range, cell discharges were absent or occurred singly.

Reciprocity-transposition-based sinusoidal pulsewidth modulation for diode-clamped multilevel converters

Modulation strategies for multilevel inverters have typically focused on synthesizing a desired set of three phase sinusoidal voltage waveforms using a fixed number of DC voltage levels. This results in the average current injection and hence the net power drawn from the multiple DC bus terminals to be unmatched and time varying. Subsequently, the DC-bus voltages are unregulated, requiring corrective control action to incorporated. In this paper, the principle of reciprocity transposition in introduced as a means for modeling the DC-bus current injection simultaneously as the modulation strategy is formulated. Furthermore, a new sinusoidal pulsewidth-modulation strategy that features constant and controllable current injection at the DC-bus terminals while maintaining output voltage waveform quality is introduced. The proposed strategy is general enough to be applied to converters with an even number of levels and an odd number of levels. Analytical results comparing the performance of the proposed modulator with a conventional multiple carrier modulator are presented for example multilevel converters with four and five levels. Computer simulation results verifying the analytical results are presented for a four-level converter.

Modification of metal-oxide-semiconductor devices by electron injection in high fields

The modification of metal-oxide-semiconductor (MOS) devices having Si/SiO 2/phosphosilicate glass/Al structure by Fowler–Nordheim (FN) tunnelling electron injection taking place in high fields is studied. The constant current FN electron injection from silicon substrate and metal electrode was used to modify the charge state of the MOS structure. The parameters characterizing the change of charge state in the MOS structures during the modification have been monitored by means of time dependence of voltage shift applied to a sample during the injection. It was found that the changes in the range of threshold voltage in MOS devices, which resulted from the electron injection, could reach values up to 6 V, while the range is extended with the growth of the concentration of phosphorus in the PSG layer. However, the value of the injected charge must not exceed the level of 0.1 mC/cm 2 during the adjustment of the threshold voltage, so as to provide acceptable surface state density.

Rate dependency of delayed rectifier currents during the guinea-pig ventricular action potential.

1. The action potential clamp technique was exploited to evaluate the rate dependency of delayed rectifier currents (I(Kr) and I(Ks)) during physiological electrical activity. I(Kr) and I(Ks) were measured in guinea-pig ventricular myocytes at pacing cycle lengths (CL) of 1000 and 250 ms. 2. A shorter CL, with the attendant changes in action potential shape, was associated with earlier activation and increased magnitude of both I(Kr) and I(Ks). Nonetheless, the relative contributions of I(Kr) and I(Ks) to total transmembrane current were independent of CL. 3. Shortening of diastolic interval only (constant action potential shape) enhanced I(Ks), but not I(Kr). 4. I(Kr) was increased by a change in the action potential shape only (constant diastolic interval). 5. In ramp clamp experiments, I(Kr) amplitude was directly proportional to repolarization rate at values within the low physiological range (< 1.0 V s(-1)); at higher repolarization rates proportionality became shallower and finally reversed. 6. When action potential duration (APD) was modulated by constant current injection (I-clamp), repolarization rates > 1.0 V s(-1) were associated with a reduced effect of I(Kr) block on APD. The effect of changes in repolarization rate was independent of CL and occurred in the presence of I(Ks) blockade. 7. In spite of its complexity, the behaviour of I(Kr) was accurately predicted by a numerical model based entirely on known kinetic properties of the current. 8. Both I(Kr) and I(Ks) may be increased at fast heart rates, but this may occur through completely different mechanisms. The mechanisms identified are such as to contribute to abnormal rate dependency of repolarization in prolonged repolarization syndromes.

Frequency dependence of spike timing reliability in cortical pyramidal cells and interneurons.

Pyramidal cells and interneurons in rat prefrontal cortical slices exhibit subthreshold oscillations when depolarized by constant current injection. For both types of neurons, the frequencies of these oscillations for current injection just below spike threshold were 2--10 Hz. Above spike threshold, however, the subthreshold oscillations in pyramidal cells remained low, but the frequency of oscillations in interneurons increased up to 50 Hz. To explore the interaction between these intrinsic oscillations and external inputs, the reliability of spiking in these cortical neurons was studied with sinusoidal current injection over a range of frequencies above and below the intrinsic frequency. Cortical neurons produced 1:1 phase locking for a limited range of driving frequencies for fixed amplitude. For low-input amplitude, 1:1 phase locking was obtained in the 5- to 10-Hz range. For higher-input amplitudes, pyramidal cells phase-locked in the 5- to 20-Hz range, whereas interneurons phase-locked in the 5- to 50-Hz range. For the amplitudes studied here, spike time reliability was always highest during 1:1 phase-locking, between 5 and 20 Hz for pyramidal cells and between 5 and 50 Hz for interneurons. The observed differences in the intrinsic frequency preference between pyramidal cells and interneurons have implications for rhythmogenesis and information transmission between populations of cortical neurons.

High field electron trap generation and oxide breakdown in thin silicon dioxide layers

Electrical breakdown of thin silicon oxide layers subject to high electric field during constant current injection is studied. The correlation between charge-to-breakdown and electron trap generated inside of the oxides during electron injection is verified. This correlation is described in terms of oxide thickness and field dependencies observed during thin oxide breakdown.

Distinct roles of CaMKII and PKA in regulation of firing patterns and K(+) currents in Drosophila neurons.

The Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and the cAMP-dependent protein kinase A (PKA) cascades have been implicated in neural mechanisms underlying learning and memory as supported by mutational analyses of the two enzymes in Drosophila. While there is mounting evidence for their roles in synaptic plasticity, less attention has been directed toward their regulation of neuronal membrane excitability and spike information coding. Here we report genetic and pharmacological analyses of the roles of PKA and CaMKII in the firing patterns and underlying K(+) currents in cultured Drosophila central neurons. Genetic perturbation of the catalytic subunit of PKA (DC0) did not alter the action potential duration but disrupted the frequency coding of spike-train responses to constant current injection in a subpopulation of neurons. In contrast, selective inhibition of CaMKII by the expression of an inhibitory peptide in ala transformants prolonged the spike duration but did not affect the spike frequency coding. Enhanced membrane excitability, indicated by spontaneous bursts of spikes, was observed in CaMKII-inhibited but not in PKA-diminished neurons. In wild-type neurons, the spike train firing patterns were highly reproducible under consistent stimulus conditions. However, disruption of either of these kinase pathways led to variable firing patterns in response to identical current stimuli delivered at a low frequency. Such variability in spike duration and frequency coding may impose problems for precision in signal processing in these protein kinase learning mutants. Pharmacological analyses of mutations that affect specific K(+) channel subunits demonstrated distinct effects of PKA and CaMKII in modulation of the kinetics and amplitude of different K(+) currents. The results suggest that PKA modulates Shaker A-type currents, whereas CaMKII modulates Shal-A type currents plus delayed rectifier Shab currents. Thus differential regulation of K(+) channels may influence the signal handling capability of neurons. This study provides support for the notion that, in addition to synaptic mechanisms, modulations in spike activity patterns may represent an important mechanism for learning and memory that should be explored more fully.

On the optimum thickness to test dielectric reliability, in an integrated technology of power devices

This paper deals with the extensive characterization of dielectric films with thicknesses from 20 to 65 nm. Thick dielectric reliability has been investigated with time dependent dielectric breakdown (TDDB). TDDB tests are conducted under constant current injection. Assuming that the logarithm of the median time-to-failure is described by a linear electric field dependence, a generalized empirical law for the long-term reliability of the dielectric is proposed. This law takes into account the applied electric field and the dielectric thickness. This reliability law is available for dielectric thicknesses greater than 10 nm. A procedure to test dielectrics of various thicknesses is given in order to predict their reliability in power integrated devices.

Effect of physical stress on the degradation of thin SiO/sub 2/ films under electrical stress

In this work, we demonstrate that for ultrathin MOS gate oxides, the reliability is closely related to the SiO/sub 2//Si interfacial physical stress for constant current gate injection (V/sub g//sup -/) in the Fowler-Nordheim tunneling regime. A physical stress-enhanced bond-breaking model is proposed to explain this. The oxide breakdown mechanism is very closely related to the Si-Si bond formation from the breakage of Si-O-Si bond, and that is influenced by the physical stress in the film. The interfacial stress is generated due to the volume expansion from Si to SiO/sub 2/ during the thermal oxidation, and it is a strong function of growth conditions, such as temperature, growth rate, and growth ambient. Higher temperatures, lower oxidation rates, and higher steam concentrations allow faster stress relaxation through viscous flow. Reduced disorder at the interface results in better reliability. Fourier transform infrared spectroscopy (FTIR) technique has been used to characterize stress in thin oxide films grown by both furnace and rapid thermal process (RTP). In conjunction with the Gibbs free energy theory, this model successfully predicts the trends of time-to-breakdown (t/sub bd/) as a function of oxide thickness and growth conditions. The trends of predicted t/sub bd/ values agree well with the experimental data from the electrical measurement.