Active feedback circuit for minimization of voltage transientsduring pulsed measurements of semiconductor devices

The operation of an active feedback circuit that minimizes voltage transients during pulsed-I-V measurements is presented. A field-effect transistor (FET) is used as the nominal device under test (DUT). The feedback circuit detects the sag in drain voltage that is caused by voltage drops produced across both the inductor in the drain bias tee and any series resistance in the drain-current path. The feedback signal consists of the current injected into the drain circuit that is sufficient to minimize the change in drain voltage. The feedback circuit actively synthesizes a small driving-point impedance that is seen by the drain of the DUT and is on the order of 10^-2 Ω. Larger voltages do not need to be applied to the drain circuit in order to overcome the nominal inductive and resistive voltage drops. Therefore, a low-current power supply can be used to set V_ds for low- or high-power FETs. Transient responses with and without the use of the feedback circuit are presented. Pulsed-I-V measurements using this feedback method (made less than 1 μs after the start of the gate pulse) of a high-power FET are also presented     

Coupled Ionic and Electronic Transport Model of Thin‐Film Semiconductor Memristive Behavior

The memristor, the fourth passive circuit element, was predicted theoretically nearly 40 years ago, but we just recently demonstrated both an intentional material system and an analytical model that exhibited the properties of such a device. Here we provide a more physical model based on numerical solutions of coupled drift‐diffusion equations for electrons and ions with appropriate boundary conditions. We simulate the dynamics of a two‐terminal memristive device based on a semiconductor thin film with mobile dopants that are partially compensated by a small amount of immobile acceptors. We examine the mobile ion distributions, zero‐bias potentials, and current–voltage characteristics of the model for both steady‐state bias conditions and for dynamical switching to obtain physical insight into the transport processes responsible for memristive behavior in semiconductor films.     

Flux-locked current source reference

The quantization of flux in a closed superconducting circuit is used to provide a stable reference current. A 10-mA current source is coupled through a toroidal transformer to a DC superconducting quantum interference device (SQUID) input, and the resulting signal is fed back as an error current. The result is a net flux linkage that exhibits short-term stability of 1 part in 10⁹/h. The net current is quantized with a step size of 59.4 nA, and it will exhibit the same stability as the flux provided the mutual inductance of the transformer remains constant. This current is passed through a precise 100-Ω resistor and compared against Zener diode references. The observed temperature coefficient for the flux transformer is 28.5±3 ppm/K at 4.2 K. Possible sources for the temperature dependence are discussed     

A New Device for Measurements of Pulses or High-Frequency Currents

Resistors are frequently used for measuring waveforms and magnitudes of pulse currents, assuming that the effect of residual inductance of the resistors is very small. However, when the very high-frequency components of the current must be taken into account, the effect of the residual inductance cannot be neglected. In this paper, a new current measuring device with a resistor of a special type is described. It is so constructed that the effect of residual inductance does not appear in the observing circuit of the device. Consequently, the voltage observed becomes exactly the product of the resistance of the device and the current to be measured, flowing through the device. As the effect of the residual inductance of the device does not appear in the observing circuit, the resistance of the device can be made very low, consequently, the circuit condition will be practically undisturbed by the connection of the device.     

Doping-free fabrication of carbon nanotube thin-film diodes and their photovoltaic characteristics

Random networks of single-walled carbon nanotubes (SWCNTs) were have been grown by chemical vapor deposition on silicon wafers and used for fabricating field-effect transistors (FETs) using symmetric Pd contacts and diodes using asymmetrical Pd and Sc contacts. For a short channel FET or diode with a channel length of about 1 μm or less, the device works in the direct transport regime, while for a longer channel device the transport mechanism changes to percolation. Detailed electronic and photovoltaic (PV) characterizations of these carbon nanotube (CNT) thin-film devices was carried out. While as-fabricated FETs exhibited typical p-type transfer characteristics, with a large current ON/OFF ratio of more than 10⁴ when metallic CNTs were removed via a controlled breakdown, it was found that the threshold voltage for the devices was typically very large, of the order of about 10 V. This situation was greatly improved when the device was coated with a passivation layer of 12 nm HfO₂, which effectively moved the threshold voltages of both FET and diode back to center around zero or turned these device to their OFF states when no bias was applied on the gate. PV measurements were then made on the short channel diodes under infrared laser illumination. It was shown that under an illumination power density of 1.5 kW/cm², the device resulted in an open circuit voltage V _OC = 0.21 V and a short circuit current I _SC = 3.74 nA. Furthermore, we compared PV characteristics of CNT film diodes with different channel lengths, and found that the power transform efficiency decreased significantly when the device changed from the direct transport to the percolation regime.     

三轴激光陀螺放电状态监控

对三轴激光陀螺的结构及串扰现象作了简要介绍,提出了放电状态监控电路的必要性.基于所设计的高压稳流电源电路,提出在高压电源每一稳流支路加入一路模拟开关,来控制稳流和状态监控的时序,从而通过监测采样电阻的端电压来实现放电状态的监控,并详细阐述了三轴放电状态监控电路的软硬件实现.最后对电路进行了实验测试,三轴激光陀螺在5s内的点燃率达到100%,电流的长期稳定度优于1×10-4,验证了状态监控电路的可行性和可靠性.     

A modified circuit topology for inductive pulsed power supply based on HTSPPTs

High temperature superconducting pulsed power transformer (HTSPPT) provides an efficient method for inductive energy storage and current multiplication. The primary inductor of HTSPPT used for energy storage is made of high temperature superconducting coils, and the secondary inductor used for current pulse generation is made of normal conductor coils. In the initial circuit, the secondary inductor generates current pulse by switching out the coupled primary superconducting inductor. However, during the switching period, the leakage flux caused by imperfect coupling and the sudden change in primary current induce a voltage across the opening switch which exceeds the affordability of modern solid-state switches. In previous studies, a half-cycle oscillatory discharge circuit is proposed to mitigate these problems by using a capacitor to recapture the energy in the leakage flux and to slow down the turnoff of current in the primary. However, there are still some problems should be settled. For example, the output pulse cannot be adjusted, the residual energy cannot be recovered and the capacitor branch circuit may have an impact on the charging process. In the paper, a modified discharge circuit topology is introduced to solve these problems. A multi-module system comprising of several HTSPPTs charging in series connection and discharging in parallel is also designed and simulated. This system can be used to power an electromagnetic emission device.     

A linear operational transconductance amplifier for instrumentationapplications

A linear operational transconductance amplifier (OTA) is described that consists of a linear transconductor and a translinear current gain cell followed by three current mirrors. The proposed circuit has superior linearity and temperature characteristic when compared with the commercially available OTA. A prototype circuit with a transconductance of 50 μS has been built with discrete bipolar transistors producing a linearity error of less than ±20% over an input voltage range from -0.8 to 0.8 V. The prototype OTA circuit also exhibits a transconductance that is linearly dependent on a bias current varying over four decades with a sensitivity of 1 S/A     

Visible-infrared spectral response of microcrystalline hydrogenated silicon hetero-junctions

Microcrystalline p–i–n devices with an increased infrared sensitivity infrared sensitivity are prepared by the closed-chamber cyclic technique.The spectral response for different applied bias, the current–voltage characteristics at different wavelengths and the photocurrent delivered by the device are analysed. The spectral response is extended far beyond the amorphous limit of about 750 nm and even at a wavelength of 1000 nm, the response is still at a level of about 5% of the maximum. The good near infrared sensitivity is considered to be a result of the large optical absorption ascribed to the crystalline phase. Under reverse bias, the spectral response is high and essentially unchanged, reflecting a good collection efficiency. Under increasing forward bias, up to values near the open-circuit voltage, it decreases continuously, but even at much higher bias (up to about 0.8 V), the device produces a photocurrent.A heterojunction model based on the growth mechanism of the device and supported by a numerical simulation is presented to explain this behaviour.     

Off-diagonal impedance in amorphous wires and its application to linear magnetic sensors

We investigated the magnetic-field behavior of the off-diagonal impedance in Co-based amorphous wires under sinusoidal (50 MHz) and pulsed (5 ns rise time) current excitations. For comparison, we measured the field characteristics of the diagonal impedance as well. In general, when an alternating current is applied to a magnetic wire, the voltage signal is generated not only across the wire but also in a pickup coil wound on it. These voltages are related to the diagonal and off-diagonal impedances, respectively. We demonstrate that these impedances have a different behavior as functions of axial magnetic field: the diagonal impedance is symmetrical, whereas the off-diagonal one is antisymmetrical with a near-linear portion within a certain field interval. For the off-diagonal response, the dc bias current is necessary to eliminate circular domains. In the case of the sinusoidal excitation without a dc bias current, the off-diagonal response is very small and irregular. In contrast, the pulsed excitation, combining both high- and low-frequency harmonics, produces the off-diagonal voltage response without additional biasing. This behavior is ideal for a practical sensor circuit design. We discuss the principles of operation of a linear magnetic sensor based on a complementary metal-oxide-semiconductor transistor circuit.     

Longitudinal and transverse magnetoelectric voltage coefficients of magnetostrictive/piezoelectric laminate composite: theory

This paper presents a novel, long-type of magnetostrictive and piezoelectric laminate composite design in which the layers are, respectively, magnetized/poled along their length axes, and a theory for modeling its behavior. Using piezoelectric and magnetostrictive constitutive equations, and an equation of motion, a magneto-elasto-electric bieffect equivalent circuit is developed. The circuit is used to predict the longitudinal and transverse magnetoelectric (ME) voltage coefficients of our Terfenol-D/Pb(Zr/sub 1-x/Ti/sub x/)O/sub 3/ laminate design. It is found that the longitudinal ME voltage coefficient is significantly higher (/spl sim/5x) than the transverse one, and that our new laminate design has significantly higher ME voltage coefficients under small applied direct current (DC) magnetic bias fields than designs reported previously by other groups. Experimental values were found to be coincidental with predicted ones.     

A new type of balanced-bridge controlled oscillator

A novel bridge-controlled crystal oscillator circuit with exceptional temperature stability is described. The contribution to the oscillator temperature coefficient of frequency (tempco) from the circuit components (exclusive of the crystal) is reduced to about 10(-11)/ degrees C, which is several orders of magnitude better than conventional oscillator circuits. This avoids a situation in which the overall tempco is limited by circuit component drift rather than crystal stability, which can easily occur with conventional circuits when the crystal is ovenized at a turnover point. Previous attempts to use a bridge in an oscillator were made by Meacham (1938), who used an imperfectly balanced bridge, and Sulzer (1955), who used a balanced pseudo-bridge. The reasons why these are unsatisfactory are discussed. Although the bridge greatly reduces reactive frequency pulling, it does not address directly the additional issue of pulling caused by variations in crystal drive current amplitude. However, it is an enabling technology for a novel ALC circuit with greatly improved stability. The new bridge-controlled oscillator is also much less sensitive to other environmental effects such as humidity (2x10 (-11), 5%/25% R.H. @70 degrees C), power supply voltage, load impedance, and stray capacitance.     

Device based on the coupling of an organic light-emitting diode with a photoconductive material

We have realized a device based on the coupling of an organic light-emitting diode (with tri(8-hydroxyquinoline)aluminium for light emission) as an input unit with a photoconductive material as an output unit. Various photoconductive materials like pentacene, Cu-phtalocyanine and fullerene were investigated under green light illumination with an emission peak at 550 nm. Photocurrent measurements versus light intensity and bias voltage (applied between two 50 μm distant indium-tin oxide bottom electrodes for the current to flow through the materials) were realized at room temperature a photocurrent gain around 4 is obtained when the materials are subjected to a luminance of about 5000 cd/m² and for bias voltage of − 50 V. Besides, it was shown that to obtain a device with a fast photocurrent response by switching the light off and on, it is necessary to apply a bias voltage higher than − 200 V in these conditions, the gain is multiplied by a factor of 3.     

Effect of hafnium addition on the electrical properties of indium zinc oxide thin film transistors

This study reports the performance and stability of hafnium-indium zinc oxide (HfInZnO) thin film transistors (TFTs) with thermally grown SiO2. The HfInZnO channel layer was deposited at room temperature by a co-sputtering system. We examined the effects of hafnium addition on the X-ray photoelectron spectroscopy properties and on the electrical characteristics of the TFTs varying the concentration of the added hafnium. We found that the transistor on-off currents were greatly influenced by the composition of hafnium addition, which suppressed the formation of oxygen vacancies. The field-effect mobility of optimized HfInZnO TFT was 1.34 cm² V⁻¹ s⁻¹, along with an on-off current ratio of 10⁸ and a threshold voltage of 4.54 V. We also investigated the effects of bias stress on HfInZnO TFTs with passivated and non-passivated layers. The threshold voltage change in the passivated device after positive gate bias stress was lower than that in the non-passivated device. This result indicates that HfInZnO TFTs are sensitive to the ambient conditions of the back surface.     

Interaction between magnetoresistor and magnetotransistor in the longitudinal and folded vertical Hall devices

This study investigates the one-dimensional longitudinal and folded vertical Hall devices, fabricated in a standard 0.35-/spl mu/m CMOS process. The smallest nonlinearity error 0.18%, the minimum offset 0.29 mV, and the maximum supply-current-related sensitivity S/sub RI/=3.837 V/A/spl middot/T, are obtained with a 10-mA bias current excited by the supply voltage of 0.6 V. The main magnetic mechanism is that the filament current of the vertical magnetoresistor is directly injected into the base region of the bulk magnetotransistor (BMT) to increase the density of minority carriers and then enhance the magnetosensitivity. Furthermore, the induced Hall voltage of the longitudinal vertical Hall device is proportional to the bias current, but the folded vertical Hall device is inversely impacted. This advantage makes it possible to get a low-power folded vertical Hall device. The folded style not only reduces the nonlinearity error but also minimizes the offset. Unfortunately, the tradeoff is a fall in sensitivity. The BMT is applied to increase magnetic sensitivity and to compensate for this negative impact.     

Modeling novel double-in-plane gate electric-double-layer thin-film and nanoscale transistors

A novel double-in-plane gate oxide-based electric-double-layer (EDL) transistor structure applicable to thin-film transistors (TFTs) and nanoscale transistors (nanoFETs) is proposed. An equivalent circuit model is provided to illustrate the operation mechanism. The double-in-plane gate structure can simplify device fabrication effectively and provide unique tunability of threshold. Specifically, the gate bias modulates the threshold voltage of TFT and nanoFET and effectively controls the transistor subthreshold swing and leakage current. Moreover, the EDL gate dielectric can lead to a high gate dielectric capacitance (>1 μF/cm(2)). These simulation results provide basic understanding needed to use and control EDL TFTs and nanoFETs in a novel manner.     

An Active-Filter Device for Extreme Selective Measurements at Low Frequencies

This paper describes the systematic development of an active filter destined for the extreme selective balancing of a low-frequency ac bridge. The power voltage with the frequency of 50 Hz and its higher harmonics were to be suppressed, the measurement voltage with the frequency of 190 Hz was to be amplified. The filter device makes use of the twin-T RC network in connection with operational amplifiers in a manifold way. A theoretical consideration of the stability of an elementary filter circuit is given. The signal (190 Hz) to noise (50 Hz) ratio of the whole filter device is greater than 160 dB.     

偏置电压极性对力反馈电容式微加速度计特性的影响分析

对电容式加速度计,为测量其电容的变化,通常需要带直流偏置的交流电压信号来驱动。驱动信号产生的静电力有时会干扰器件的测量和正常工作。文章中定量分析了带有电压反馈的双边驱动信号对器件特性的影响。对于这种驱动方式,正-负和正-正的直流电压偏置可以改善器件的测量线性度,基本消除由驱动信号导致的吸合效应,而负-负和负．正的直流电压偏置会使驱动信号引起的吸合效应增大,从而大大缩小了器件的安全工作范围。     

Boosting efficiency and stability of perovskite solar cells with nickel phthalocyanine as a low-cost hole transporting layer material

The efficiency of perovskite solar cells(PSCs) has increased from around 4% to over 22% following a few years of intensive investigation. For most PSCs, organic materials such as 2,2',7,7'-tetrakis(N,Npdimethoxyphenylamino)-9,9'-spirobifluorene(spiro-OMeTAD) are used as the hole transporting materials(HTMs), which are thermally and chemically unstable and also expensive. Here, we explored nickel phthalocyanine(NiPc) as a stable and cost-effective HTM to replace the conventionally used spiroOMeTAD. Because of its high carrier mobility and proper band alignments, we achieved a PCE of 12.1% on NiPc based planar device with short-circuit current density(Jsc) of 17.64 mAcm~(-2), open circuit voltage(Voc) of 0.94 V, and fill factor(FF) of 73%, outperforming the planar device based on copper phthalocyanine(CuPc) that is an outstanding representative of metal phthalocyanines(MPcs) reported. Moreover,the device with NiPc shows much improved stability compared to that based on the conventional spiroOMeTAD as a result of NiPc's high stability. Photoluminescence(PL) and Impedance spectroscopy analysis results show that thermally deposited NiPc has good hole-extraction ability. Our results suggest that NiPc is a promising HTM for the large area, low cost and stable PSCs.     

Current noise measured in the dc SQUID

Measurements are presented of the current noise in a dc superconducting quantum interference device (SQUID) and of its correlation with the voltage noise across the SQUID. The measured spectral densities are in good agreement with analog simulations. When a resonant circuit is connected across the output of the SQUID, there is a reduction in the current noise for frequencies at which the impedance of the circuit is low. This effect is also in good agreement with predictions.