Effect Of Charge Injection Research Articles

Effects of signal-dependant errors on the performance of switched-current Viterbi decoders

Analog current-mode circuits including switched-current (SI) methods can he employed beneficially to implement high-speed, low-power Viterbi decoders for convolutional codes. Unfortunately, signal-dependent errors due to charge injection tend to limit the application of these methods to relatively small constraint-length decoders. This paper presents a technique for reducing the effects of charge injection on system performance. As a result, the use of SI techniques can be extended to the realization of larger Viterbi decoders, including the type conventionally employed in satellite communications.

Time-delayed charge-injection effects on photocurrent shape in a double layer

Transient photocurrents of double-layer structures were simulated by a random walk through a cubic lattice in this work. The canonical technique of time of flight was simulated to find the characteristics of the photocurrents shape when each layer had a different mobility. The results reproduce the main features of the experimental data from similar real experiments reported in the literature. Also, the origin of the peak shape of photocurrents is discussed and it is shown that it is related to a stochastic process which forces the out-of-equilibrium charge carriers to be injected from one layer to the other within a period of time $(t,t+dt)$ as given by a time-dependent probability $\ensuremath{\varphi}(t)\mathrm{dt}.$

Reduction of effects of signal-dependent errorsin current-mode analogue Viterbi decoders

Current-mode analogue techniques can be employed to realise high-speed, low-power Viterbi decoders. However, signal dependent errors due to charge injection tend to limit the application of these methods to small decoders. A technique is presented for reducing the effects of charge injection on the system performance.

Charge injection and trapping effects in DPOP–PPV polymer films

We report on the measurement of the Kerr electro-optic susceptibility in DPOP-poly-phenylene-vinylene films sandwiched between indium tin oxide and metal electrodes. Such a polymer was designed and used for the application in third-order non-linear optical integrated devices. The results, obtained by means of non-linear reflectance ellipsometry, indicate the presence of charge injected and trapped in the polymer films under application of a dc voltage. The values of the Kerr χ (3) susceptibility and of the total voltage drop on the film are evaluated.

A design and implementation of fully programmable switched-current IIR filters

An approach to switched-current filter design based on digital multiply-accumulator and delay blocks is presented. The characteristics of the filter are made fully programmable by simply changing the ratios of the coefficient transistors. To reduce the effect of switch charge injection and channel-length modulation, a high-performance, single-ended differential, switched-current memory cell is developed and used as a basic building block. To reduce the chip area and to maintain the required accuracy of the coefficients, an array consisting of three different sizes of transistors is designed instead of using a unit transistor array as coefficient transistors. An experimental prototype infinite impulse response filter array consisting of six second-order switched-current sections is designed and fabricated with a standard 1.2-/spl mu/ CMOS process technology. A hard-wiring technique is used to program the filters. The test results show that the characteristics of the filters satisfy the design requirements.

Current memory based differentiator with protectionof storage node

A time-domain differentiator based on current memory is presented. To ensure processing accuracy, a MOS charge divider is used to reduce the effect of charge injection and a well (n or p type) is used to protect the storage device from minority carrier diffusion in the substrate. The circuit operates at low current levels. A single-poly CMOS technology can be used for circuit implementation.

Device model investigation of single layer organic light emitting diodes

We present calculations of single layer organic light emitting diode (LED) characteristics using a device model which includes charge injection, transport, recombination, and space charge effects in the organic material. Contact limited and ohmic contacts, high and low carrier mobilities, and device thicknesses from 5 to 200 nm are considered. The scaling of device current with applied voltage bias and organic film thickness is described for contact limited and ohmic contacts. Calculated device current, light output, and quantum and power efficiency are presented for representative cases of material and device parameters. These results are interpreted using the calculated spatial variation of the electric field, charge density, and recombination rate density in the devices. We find that efficient single layer organic LEDs are possible for a wide range of organic material and contact parameters.

Reflection electro-optical measurements on electroluminescent polymer films: A good tool for investigating charge injection and space charge effects

We present experimental results on the electro-optic response of electroluminescent polymer films, pertaining to the family of the poly-phenylene-vinylenes. The samples used in the experiments were obtained by sandwiching polymer films between chromium-gold and indium tin oxide electrodes. The technique that was adopted is based on the Teng and Man setup, that is usually adopted for the determination of the electro-optic Pockels coefficient in poled polymers. As the structure of the polymer used is not provided with polar groups and, moreover, is completely disordered and therefore centrosymmetric, as expected, only quadratic electro-optical effects were observed (Kerr), which are connected to the presence of third-order optical nonlinearities (χ(2)≡0, χ(3)≠0). The existence of charge injection and trapping in the samples, giving rise to built-in static electric fields in the polymer layers, is put into evidence. The experimental data show the presence of a third-order susceptibility for Kerr electro-optic effect which is comparable to values reported in literature, namely χ(3)(−ω;ω,0,0)=7.9×10−21 m2/V2 at the wavelength λ=0.6328 μm. The possibility that the measured signals are due to a mechanical compression of the films is taken into account and discarded on the basis of the experimental results. The technique can be usefully applied in order to perform charge injection and trapping measurements in electroluminescent devices. Moreover, the results show that in the case of measurements performed on poled polymers for χ(2) applications, the measured values for the electro-optic coefficient can be offset by a third-order contribution, even in those cases when usually one assumes it may be neglected. In the article, the main models reported in literature, describing the effects contributing to the electro-optic response, are critically reviewed. The measurement on the centrosymmetric polymer films were used in order to check those models and permit us to evaluate.

Device model for single carrier organic diodes

We present a unified device model for single layer organic light emitting diodes (LEDs) which includes charge injection, transport, and space charge effects in the organic material. The model can describe both injection limited and space charge limited current flow and the transition between them. We specifically considered cases in which the energy barrier to injection of electrons is much larger than that for holes so that holes dominate the current flow in the device. Charge injection into the organic material occurs by thermionic emission and by tunneling. For Schottky energy barriers less than about 0.3–0.4 eV, for typical organic LED device parameters, the current flow is space charge limited and the electric field in the structure is highly nonuniform. For larger energy barriers the current flow is injection limited. In the injection limited regime, the net injected charge is relatively small, the electric field is nearly uniform, and space charge effects are not important. At smaller bias in the injection limited regime, thermionic emission is the dominant injection mechanism. For this case the thermionic emission injection current and a backward flowing interface recombination current, which is the time reversed process of thermionic emission, combine to establish a quasi-equilibrium carrier density. The quasi-equilibrium density is bias dependent because of image force lowering of the injection barrier. The net device current is determined by the drift of these carriers in the nearly constant electric field. The net device current is much smaller than either the thermionic emission or interface recombination current which nearly cancel. At higher bias, injection is dominated by tunneling. The bias at which tunneling exceeds thermionic emission depends on the size of the Schottky energy barrier. When tunneling is the dominant injection mechanism, a combination of tunneling injection current and the backflowing interface recombination current combine to establish the carrier density. We compare the model results with experimental measurements on devices fabricated using the electroluminescent conjugated polymer poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] which by changing the contacts can show either injection limited behavior or space charge limited behavior.

Effects of non-uniform charge injection on gain, threshold current, and linewidth enhancement factor for a 1.55 μm InP-based multiple quantum well laser

In laser structures where the active region consists of several quantum wells, non-uniform charge injection can occur. We examine the consequences of non-uniform charge injection on gain, threshold current, and linewidth enhancement factor. Non-uniform charge injection in a InP-based multiple quantum well laser was considered in order to analyze effects on gain, threshold current, and linewidth enhancement factor. We find that although the best values for gain, threshold current and linewidth enhancement factor occur under uniform charge injection conditions, these parameters do not suffer significant degradation under even highly non-uniform charge injection.

Initial velocity effect on space-charge-limited currents

The characteristics of a monopolar space-charge region under the effect of charge injection with a uniform initial velocity are studied. Poisson’s equation has been solved as a Dirichlet boundary-value problem, other than by conventional serial integrations, to yield exact analytical expressions for the potential, field, charge density, and current. The structure of the space-charge region is characterized by a potential well and an effective diode gap, and can be explained in terms of the initial kinetic energy of the charge. The Child–Langmuir limit, when calculated by using the effective diode gap, is a firm limit.

A low-power, CMOS peak detect and hold circuit for nuclear pulse spectroscopy

A low-power CMOS peak detecting track and hold circuit optimized for nuclear pulse spectroscopy is presented. The circuit topology eliminates the need for a rectifying diode, reducing the effect of charge injection into the hold capacitor, incorporates a linear gate at the input to prevent pulse pileup, and uses dynamic bias control that minimizes both pedestal and droop. Both positive-going and negative-going pulses are accommodated using a complementary set of track and hold circuits. Full characterization of the design fabricated in 1.2 /spl mu/m CMOS including dynamic range, integral nonlinearity, droop rate, pedestal, and power measurements is presented. The circuit operates with only 250 /spl mu/w for input pulses with 7 /spl mu/s peaking time. Power consumption was increased to 750 /spl mu/w for driving off-chip and test system capacitances. Analysis and design approaches for optimization of operational characteristics are also discussed. >

Relaxation of Second-Harmonic Generation in Guest/Host Polymers Poled by Indium-Tin Oxide Sandwich Electrodes

Second-harmonic generation (SHG) is used to monitor reorientation dynamics of 4-(dimethylamino)-4'-nitrostilbene doped at 1 wt % in poly(ethyl methacrylate) within a temperature range of T g ±30 K. Special emphasis is put on a systematic analysis of experiments conditions and their severe impact on SHG data for samples which are poled in an indium-tin oxide (ITO)-sandwich-electrode configuration. These effects include thermal history, local heating effects due to laser focus, importance of dopant concentration, physical aging, details of the poling procedure, and charge-injection effects. The fast initial response of the SHG signal upon field switching is attributed to space charge effects. We show how the problem of SHG reproducibility can be overcome with appropriate experimental conditions

PIMOD processing and properties of a LiNbO3-based MFSFET for nonvolatile memories

Abstract The photo-induced metallo-organic decomposition (PIMOD) process has been successfully used to deposit a lithium niobate thin film acting as the gate oxide of the conventional MFSFET structure. The use of the low-temperature PIMOD process for thin film deposition has increased the device yields of the molybdenum liftoff for small area isolation. The electronic alteration of the properties of the ferroelectric gate transistor was previously shown to be caused by charges in the semiconductor being injected into the ferroelectric film. To prevent this problem, a thin SiO2 buffer layer was thermally grown on the silicon substrate immediately before lithium niobate deposition. The silicon-lithium niobate interface was stabilized and the charge injection effect was eliminated due to the formation of the buffer layer. The channel current was shown to be greatly altered by the application of voltage pulses between the gate of the device and the substrate. Upon switching, the change in surface conductivity...

Highly sensitive capacitance measurement for sensors

Very small capacitance changes from a capacitive transducer can be measured using a custom-designed signal-processing chip. The chip features a switched-capacitor integrator with chopper stabilisation to remove the effects of offset, 1/f noise and switch charge injection; the circuit is insensitive to stray capacitance. The achievement of high resolution and low drift is demonstrated.

Orientational decay in poled second-order nonlinear optical guest-host polymers: Temperature dependence and effects of poling geometry

The orientational decay of chemically and thermally stable high-temperature chromophores doped into thin films made from polyimides and a variety of other polymeric hosts has been investigated. The chromophores are aligned using electric field poling and second-harmonic generation (SHG) is used to probe the decay of the electric field poling induced alignment. The decay rate of the SHG signal from films poled using both a corona discharge and side-by-side in-plane electrodes was measured. When electrodes are chosen so that the effects of charge injection are minimized, little difference has been observed between the orientational decays from films poled using the two methods for either an amorphous preimidized polyimide host or a highly anisotropic film poled during imidization. The films imidized during poling showed significant orientational stability at 250 °C for over 15 h after a fast initial partial decay. In addition, the decay of the SHG signal was measured as a function of temperature below the glass transition in a wide variety of different polymer host systems. The temperature dependence of the decay was found to be non-Arrhenius, but could be strongly correlated with the glass transition temperature of the guest-host system using an empirical relationship similar to the Williams–Landel–Ferry or Vogel–Tamann–Fulcher equation.

An optimized bit cell design for a pipelined current-mode algorithmic A/D converter

The design of a current-mode algorithmic bit cell for use in a pipelined A/D converter is presented. Design issues such as power supply rejection, charge-injection effects, the op-amp's gain/bandwidth tradeoff and the circuit's stability are considered. The circuit was implemented using a 1.2-µm CMOS process and required an area of 0.066 mm2. The bit cell features a 10-bit resolution at an 83-kHz sampling rate and a 1.6-mW power dissipation.

A digital readout technique for capacitive sensor applications

The difference between two capacitors is measured digitally using a charge redistribution technique incorporating a comparator, MOS switches, a successive approximation register, and a digital-to-analog converter. The technique is insensitive to comparator offset and parasitic capacitance, and the effect of MOS switch charge injection is measured and canceled. Extensive measurements have been made from test chips fabricated in 3- mu m CMOS technology. Detection of percent differences of <0.5% on 20-100-fF capacitors has been successfully demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling of charge-injection effects in metal-oxide-semiconductor structures

A recently published dynamic balance model which describes gate-oxide degradation following prolonged charge injection is modified. This modification replaces the average electric field in the oxide with the electric field spatial distribution. It is shown that a very close interchangeable relationship exists between the electric field spatial distribution and the spatial distributions of the trapped charge and generated trapping sites. The validity of the new modified model is confirmed for different oxide thicknesses (130–720 Å), injection techniques (hot-electron injection and constant current-tunneling injection), and gate electrode material (aluminum versus polycrystalline silicon). The most attractive feature of the modified dynamic balance model is its ability to describe the steady-state occupation level changes for any given electric field following any oxide stress injection. Furthermore, the modified model is used to propose a new breakdown model which is described in a companion paper.

Temperature effects on electron trap generation and occupation in SiO2

The effects of charge injection under constant tunneling current through gate oxides of metal-oxide-silicon transistors are studied at different temperatures. For this study, a recently introduced novel characterization method for enduring charge injection effects in SiO2 is used. Results show that trapping–detrapping sites and saturation of surface state generation are independent of the temperature. It is shown that in the temperature range of −120–20 °C, the steady-state field-dependent occupation function is independent of the temperature. On the other hand, the rates for filling repulsive traps, generating new trapping sites, and generating surface states increase with increasing temperature.