Intrinsic Voltage Research Articles

The Impact of the Ge Concentration in the Source for Vertical Tunnel-FETs

The goal of this work is to study the influence of the germanium concentration in the source region of vertical TFETs for different temperatures. Vertical TFETs with the source region composed by Si(100%), Si0.73Ge0.27, Si0.56Ge0.44 and Ge(100%) were studied in the temperature range from room temperature to 150oC. The main analog parameters like transconductance, output conductance and intrinsic voltage gain were analyzed. With increasing Ge concentration the drive current, the subthreshold swing, the transconductance and the intrinsic voltage gain improves while the output conductance and 1/f noise degrades. The temperature increase impacts negatively the output conductance and the intrinsic voltage gain, in spite of improving the transconductance due to the higher band-to-band tunneling caused by the source bandgap lowering.

Proton Radiation Effects on the Analog Performance of Bulk n- and p-FinFETs

This paper presents an evaluation of the impact of 60 MeV Proton radiation on triple gate Bulk FinFETs, for both n and p types. The main focus is intrinsic voltage gain, threshold voltage and the OFF region drain current. The narrow nFinFET devices present an unexpected degradation of the drain current in the off-state region, which shows that the radiation affects severely the STI oxide resulting in a high parasitic conduction. The pFinFETs are more tolerant than the nFinFETs for environments that suffer from high-energy proton exposure.

Vertical Nanowire TFET Diameter Influence on Intrinsic Voltage Gain for Different Inversion Conditions

In this work, the impact of the nanowire TFET diameter on analog parameters in “weak” and “strong inversion” conditions is analyzed. Its relation with the current conduction mechanism is also studied. A comparison of the analog performance among TFETs doped with different source doping profile (abrupt and non-abrupt) and MOSFETs was experimentally realized for larger diameter nanowires. Additionally the TFET evaluation was extrapolated for smaller diameters by numerical simulation. The transistor efficiency and the Early voltage were considered in order to calculate the intrinsic voltage gain (AV). Both effects influence AV degradation for TFETs with smaller diameters biased in “weak inversion”. While larger TFET nanowires show better AV than MOSFETs under “strong inversion” bias, narrower nanowires present potentialities for low power and low voltage applications, since their AV is better than the corresponding values for larger diameters TFET nanowires under “weak inversion” bias.

Impact of Gate Stack Dielectric on Intrinsic Voltage Gain and Low Frequency Noise in Ge pMOSFETs

This paper presents an experimental analysis of the gate stack dielectric influence on low frequency noise and intrinsic voltage gain (AV) in planar germanium pMOSFETs with a HfO2/Al2O3 gate stack. The Av is studied not only at room temperature, but also from 25 to 150 °C. It is observed that neither the HfO2 - thickness nor the plasma oxidation power have a significant impact on the noise power spectral density and intrinsic voltage gain (AV). In contrast, the thinner Al2O3 - layer is more susceptible to any damage during the fabrication processes, which increases the interface state density (NIT) between the Ge surface and gate stack layer, resulting in a device performance degradation. Furthermore, from high temperature point of view, the AV is predominantly dominated by the carrier mobility degradation, which reduces the transconductance.

Analog performance of vertical nanowire TFETs as a function of temperature and transport mechanism

The goal of this work is to study the analog performance of tunnel field effect transistors (TFETs) and its susceptibility to temperature variation and to different dominant transport mechanisms. The experimental input characteristic of nanowire TFETs with different source compositions (100% Si and Si1−xGex) has been presented, leading to the extraction of the Activation Energy for each bias condition. These first results have been connected to the prevailing transport mechanism for each configuration, namely band-to-band tunneling (BTBT) or trap assisted tunneling (TAT). Afterward, this work analyzes the analog behavior, with the intrinsic voltage gain calculated in terms of Early voltage, transistor efficiency, transconductance and output conductance. Comparing the results for devices with different source compositions, it is interesting to note how the analog trends vary depending on the source characteristics and the prevailing transport mechanisms. This behavior results in a different suitability analysis depending on the working temperature. In other words, devices with full-Silicon source and non-abrupt junction profile present the worst intrinsic voltage gain at room temperature, but the best results for high temperatures. This was possible since, among the 4 studied devices, this configuration was the only one with a positive intrinsic voltage gain dependence on the temperature variation.

Dependence of the Lithiation/Delithiation Potentials of Silicon Microwire Anodes on Their State of Charge and Sizes

Cycle life and cycle stability are the crucial parameters when talking about batteries. The cycle life is affected when the operational voltage range is not correctly selected. In Si anodes, their intrinsic voltage limits are given by the phase transformation potentials. The voltage limits depend not only on external parameters like the voltage sweep rate, but mostly on internal parameters like the dimensions of the Si anode, and parameters of state like the state of charge. This is investigated in the present study, using Si microwires with different thicknesses and lengths. Additionally, the wires have been pre-lithiated to specific capacity limits. The analysis has been performed through cyclic voltammetry. It has been found that while short wires exhibit a lithiation limit at 50 % state of charge (SOC), the diffusion limitations are larger in long wires, which can be easily lithiated to a higher state of charge. The study showed that the optimal wire dimension has to be found to achieve better and stable cycling performance.

Block-Oxide Structure in Polycrystalline Silicon Thin-Film Transistor With Source/Drain Tie and Additional Polycrystalline Silicon Body for Analog Applications

In this paper, we for the first time demonstrate the analog performance of a block-oxide structure in polycrystalline silicon thin-film transistor with source/drain-tie and additional poly-Si body (BO-SDT-APSB TFT) experimentally and compared with the similar device with zero block-oxide structure (SDT-APSB TFT). The block-oxide in BOSDT-SDT-APSB TFT is fabricated to reduce the drain-induced barrier lowering and channel-length modulation. The source-drain tie and additional poly-silicon body region are fabricated in both devices to improve the device performance and reduce the self-heating effect. Experimental results show that the block-oxide structure can offer enhanced gate controllability over the channel, and the transconductance ( g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) of the BO-SDT-APSB TFT is therefore improved. In addition, although a higher drain conductance ( g d), implying a lower output resistance r o, is observed for a BO-SDT-APSB TFT, the enhanced gm still helps to achieve the desired intrinsic voltage gain ( A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</sub> = g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> /g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) behavior.

Long Josephson Junction in Ultralow-Noise Magnetometer Configuration

The magnetic field dependence of the Eck step voltage in long Josephson tunnel junctions (LJTJs) can be exploited for ultralownoise magnetic sensing. The magnetic flux to be measured is captured by a non-interrupted superconducting pickup loop in which a narrow constriction, forming the LJTJ wiring layer, produces a local high density circulating currents which, in turn, induces a magnetic field large enough to set a biased LJTJ at a finite voltage proportional to the field strength (flux-flow state). On this basis, an innovative and ultralow-noise superconducting device has been realized having a highly linear voltage responsivity and an intrinsic voltage spectral density down to few pV/√Hz. Being that the intrinsic voltage fluctuations of these all-Niobium sensors are very low (at T = 4.2 K), a double transformer superconducting quantum interference device (SQUID) amplifier has been used to determine the amplitude of its voltage spectral density obtaining a value as low as 10 pV/√Hz. In addition, the 1/f noise does not affect the sensor performance down to a few hertz. The corresponding magnetic field noise, equal to 10 fT/√Hz, together with highly linear and broadband voltage responsivity over a wide magnetic flux range, features performances that are comparable with those of a SQUID magnetometers having a comparable flux capture area.

Equilibrium Ion Selectivity of Human TPC2 Studied using a Plasma Membrane-Targeted Human TPC2 and Spermine Block

The permeation pathway of hTPC2 (two-pore channel 2) was studied using a plasma membrane-targeted hTPC2 (hTPC2PM) and the tetravalent cation spermine. We found that intracellular spermine blocks hTPC2PM (Kd=1.5mM) and displays intrinsic voltage sensitivity under zero extracellular Na+ condition. Extracellular Na+ decreases the observed binding energy of spermine, which allowed the determination of equilibrium dissociation constant of the responsible binding site. The contribution of extracellular ions to the effective valence of spermine block suggested that this binding site is located within the voltage field, likely at the selectivity filter external to the spermine-binding site. By analyzing the shifts in spermine binding energy, we arrived at the following sequence of equilibrium ion selectivity (Kd) of this binding site: Li+ (0.72mM) < Na+ (3.7mM) < Ca2+ (9.2mM) < K+ (26mM) < Cs+ (140mM), which suggests a linear decrease in ion binding energy as a function of ionic radius for the tested monovalent ions. This result is contrasted with the selectivity sequence determined using bi-ionic reversal potential, Na+ (1) ≥ Li+ (0.94) ≫ Ca2+ (0.04) ≥ K+ (0.03) ≥ Cs+ (0.02), and suggests that, in addition to equilibrium selectivity, kinetic factors may also be fundamental to the generation of Na+ selectivity in hTPC2.

Molecular Basis of Voltage-Dependent Gating in ClC Transporters

The CLC family encompasses Cl− channels and coupled Cl−/H+ exchangers. CLC channels and transporters both exhibit voltage-dependent gating, the physiological importance of which is illustrated by multiple disease-causing mutations that specifically result in altered voltage sensing. Despite a large body of available functional and structural data, the molecular mechanisms underlying voltage gating in CLCs still remain unclear. Using electrophysiological admittance measurements, we recently decomposed voltage-dependent activation of the human ClC-5 transporter into multiple discrete electrogenic transitions (Grieschat M & Alekov AK (2014) Biophys J 107, L13–L15). A key player of the gating machinery appears to be the so-called gating glutamate (Gluext; Glu148 in EcClC), which is thought to move upon changes in voltage. To better understand the basis of voltage-dependent gating, we conducted molecular dynamics simulations of the bacterial homologue EcClC. Using a double-bilayer system, we applied small ionic concentration gradients across the membrane that resulted in charge imbalances Δqion and we calculated the resulting potential differences Vm. Analysis of the dependence of Vm on Δqion for various conformations that differed in Cl− binding site occupancy and the protonation state of Gluext was used to determine charge displacements of the transporter along the electric field. Multiple processes, including protonation and conformational changes of Gluext, binding of Cl− ions and refocusing of the electric field triggered by changes in water accessibility are associated with charge transfer across the membrane and therefore exhibit intrinsic voltage dependence. We calculated gating charges that underlie these conformational transitions of the CLC transporter. Based on these calculations, gating charge recordings and capacitance measurements on ClC-5, we propose a molecular description of CLC voltage sensing which attributes fractional gating charges to these partial reactions of the transport cycle.

Influence of the Source Composition on the Analog Performance Parameters of Vertical Nanowire-TFETs

The goal of this paper is to study the analog performance parameters of tunnel field-effect transistors (TFETs) with different source compositions and process conditions. The experimental matrix included devices with either a 100% silicon or Si 1-x Ge x source, so that the germanium amount at the source/channel interface could be correlated with the prevailing transport mechanism and its impact on transconductance (gm), output conductance (gDS), and early voltage (V EA ) could be analyzed. The used process conditions were highlighted by comparing a reference split with no Si passivation to the cases with 12 and 18 Si monolayers to determine their influence on the interface trap density and eventual reduction of the traps in the gate oxide. All these process parameters enable to make conclusions on the intrinsic voltage gain (A V ) and the low-frequency noise. Based on these results, the suitability of each type of TFET has been discussed, revealing that 100% Si may still be considered

Can ClC-2 Chloride Channel be Activated by Hyperpolarization Alone in Cells Dialyzed with Non-Permeant Anions?

Open and closing of ion channels is driven by conformational changes triggered by either an intrinsic voltage sensor in voltage-gated channels or by ligand binding in ligand-gated channels. However, ClC-2, a two pore Cl− channel is activated by hyperpolarisations despite of lacking of an intrinsic voltage sensor. The structural information available to date strongly suggests that in the closed conformation each pore of ClC-2 is occluded by the negatively charged side chain of a glutamate residue. Although the gating mechanism is unknown, there is evidence which indicates that intracellular anions and extracellular protons regulate gating. The present work was aimed to determine the contribution of pore occupancy caused by intracellular anions in gating the mouse ClC-2 channel. In our experiments, ClC-2 was readily activated by hyperpolarisations when permeant anions such Cl−, SCN−, Br− and I− were present on either side of the membrane. However, ClC-2 was not activated in cells dialyzed with acetate (0 Cl−) and exposed to [H+]O=10−7.3 M. In contrast, the channels were opened by increasing [Cl−]i at [H+]O=10−10 M_a condition unlikely to protonate the glutamate's side chain. Importantly, voltage gating occurred when F− or glutamate were present in the cytosolic side. Since these two anions are non-permeant we propose that they must enter the pore and interact with the glutamate side chain from the inside in order to induce opening. Thus, we propose that a strong hyperpolarisation drives the intracellular anions into the permeation pathway and the subsequent electrostatic interaction between the anions and the negatively charged side chain opens the pore. Our data support the hypothesis that voltage-dependent gating in mouse ClC-2 requires intracellular anions. Supported by grant 219949 from CONACyT.

MnO/C nanocomposite prepared by one-pot hydrothermal reaction for high performance lithium-ion battery anodes

Among various candidates to replace the low capacity graphitic carbon anode in current lithium ion batteries (LIBs), manganese oxides possess the advantages of high lithium storage capacity, low cost, high intrinsic density, environmental friendliness and low lithium storage voltage, i.e., 0.5 V Li+/Li. Manganese oxides, however, have to be incorporated with conducting and porous matrix due to poor electrical conductivity and large volume expansions associated with conversion reaction upon cycling. In this study, a facile one-pot route was attempted for the synthesis of MnO/C nanocomposite for which Mn3O4 nanoparticles were grown in aqueous medium followed by carbon gel formation in a one-pot reactor. Thus obtained Mn3O4/C carbon gel was transformed into MnO/C nanocomposite by thermal annealing in an Ar flow. The MnO nanoparticles (60wt%) of 20–50 nm in diameter were well dispersed throughout the MnO/C composite. The MnO/C composite delivered reversible capacity of 541mAh g−1 with an excellent cycling stability over 100 cycles, while parent Mn3O4 lost most of its capacity in 10 cycles. The MnO/C composite also exhibited much higher rate capability than a commercial graphite anode. Hence, the MnO/C composite based on low cost materials and facile synthetic process could be an attractive candidate for large-scale energy storage applications.

Nanoscale ion sequestration to determine the polarity selectivity of ion conductance in carriers and channels.

The nanoscale spacing between a tethered lipid bilayer membrane (tBLM) and its supporting gold electrode can be utilized to determine the polarity selectivity of the conduction of ion channels and ion carriers embedded in a membrane. The technique relies upon a bias voltage sequestering or eliminating ions, of a particular polarity, into or out of the aqueous electrolyte region between the gold electrode and the tethered membrane. A demonstration is given, using ac swept frequency impedance spectrometry, of the bias polarity dependence of the ionophore conductance of gramicidin A, a cationic selective channel, and valinomycin, a potassium ion selective carrier. We further use pulsed amperometry to show that the intrinsic voltage dependence of the ion conduction is actually selective of the polarity of the transported ion and not simply of the direction of the ionic current flow.

Investigating antennas as ignition aid for automotive HID lamps

This paper considers the ignition of mercury-free high-intensity discharge (HID) lamps for car headlights. Due to safety reasons, these lamps need to have a fast run-up phase which is ensured, amongst other things, by a high Xe pressure of roughly 15 bar (cold) in the discharge vessel. The high Xe pressure causes an increased ignition voltage compared with former mercury-containing automotive HID lamps or low-pressure lamps used for general-lighting applications.The increase in ignition voltage can be limited if the electric field in front of the electrodes is raised by an uplifting of the electrical conductivity along the outer wall of the inner bulb either by a conductive layer on its surface or by a dielectric barrier discharge (DBD) within the outer bulb. This paper considers on the one hand conventional antennas deposited by physical vapour deposition (PVD) and on the other hand a combination of these antennas with a DBD within the outer-bulb operated in 100 mbar Ar as ignition aids. In both cases the antenna potential and antenna width are varied. Additionally, the effects of antenna thickness and antenna material are investigated.The ignition voltage, ignition current and light emission during ignition are measured on a nanosecond timescale. Furthermore, for the very first time, the ignition process is recorded in four consecutive intensified charge-coupled device images using a high-speed camera system with a time resolution in the range of nanoseconds.It was found that antennas strongly reduce the ignition voltage of automotive HID lamps. Active antennas reduce the ignition voltage significantly more than passive antennas, proportional to the conductance of the antenna. Combining conventional antennas with an outer-bulb discharge reduces the ignition voltage from 19 kV without any ignition aid to the intrinsic ignition voltage of the lamp below 10 kV, in the best case.

Extracting parameters in ambipolar organic transistors based on dicyanomethylene terthiophene

Ambipolar organic transistors based on dicyanomethylene terthiophene show electron and hole mobilities of up to 0.6 and 0.3 cm2 V−1 s−1, respectively, on tetratetracontane, which are thousands of times larger than the reported value. The intrinsic electron and hole threshold voltages are determined by analyzing the output and transfer characteristics, from which the ambipolar characteristics are quantitatively reproduced. Since the transistor is operated mostly in the unipolar region, the trap density of states is estimated from the temperature dependence of the transfer characteristics.

Impact of channel doping and spacer architecture on analog/RF performance of low power junctionless MOSFETs

This work reports on the significance of reducing channel doping and optimizing the spacer width to enhance analog/RF metrics of junctionless (JL) MOSFETs for operation at low current levels (∼30 μA μm−1). It is shown that optimally designed junctionless devices achieve 40–50% higher cut-off frequency (fT) and maximum oscillation frequency (fMAX), along with a 15% enhancement in intrinsic voltage gain (AVO) as compared to conventional junctionless (JL) transistors designed with a channel doping (Nd) of 1019 cm−3. The parasitic fringing capacitances are significantly reduced in optimized JL devices. The gain-bandwidth trade-off can be considerably improved around the analog ‘sweet spot’ as performance metrics are enhanced by 70–90%. Apart from the above benefits, the optimal JL design results in reduced sensitivity to variation in device parameters. Results will be useful for design and optimization of low power junctionless MOSFETs for analog/RF applications.

Pseudo-Ramp Current Balance (PRCB) Technique With Offset Cancellation Control (OCC) in Dual-Phase DC-DC Buck Converter

To cope with monolithic controller replicas and the current unbalance situation in multiphase converters, a pseudo-ramp current balance technique is proposed to achieve time-multiplexing current balance in voltage-mode multiphase DC-DC buck converter. With only one modulation controller, silicon area and power consumption caused by the replicas of controller can be reduced significantly. Current balance accuracy can be further enhanced since the mismatches between different controllers caused by process, voltage, and temperature variations are removed. Moreover, the offset cancellation control embedded in the current matching unit is used to eliminate intrinsic offset voltage existing at the operational transconductance amplifier for improved current balance. An explicit model, which contains both voltage and current balance loops with non-ideal effects, is derived for analyzing system stability. Experimental results show that current difference between each phase can be decreased by over 83% under both heavy and light load conditions.

Noise performance of superconductive magnetometers based on long Josephson tunnel junctions

The low-current fluctuations at cryogenic temperatures together with the low dynamical resistance in the resonant states of Josephson tunnel junctions allow for the realization of superconducting oscillators up to the THz range with ultra-low spectral linewidth. By virtue of the Josephson frequency-voltage relationship, we show that the same properties can be exploited for the practical realization of magnetic flux-to-voltage transducers based on the flux–flow in long Josephson tunnel junctions whose intrinsic low-frequency voltage fluctuations at amount to few , that is, too small to be measured by any present semiconductor electronics. Nevertheless, by using a double transformer SQUID amplifier we demonstrate that the (amplitude) voltage spectral density, , of an all-niobium sensor does not exceed the level of and is not affected by excess noise at least down to few hertz. Such ultra-low white noise, corresponding to a magnetic field noise , together with a highly linear and broadband voltage responsivity over a wide magnetic flux range, makes the flux–flow magnetometers potentially competitive with SQUID-based devices.

Invited: The Impact of a (Si)Ge Heterojunction on the Analog Performance of Vertical Tunnel FETs

Tunnel Field Effect Transistors (TFETs) have been appointed as one of the alternatives for future technologies due to their fast switching capability (1). In order to improve the on-state current, devices with different materials and architectures have been studied (2). In this work, the impact of the germanium content in the source of a silicon nanowire (NW) TFET is analyzed, focusing mainly on the analog performance of these devices. All analyzed vertical nanowire TFETs were fabricated at imec/Belgium with the following characteristics: a total channel length (LCH) of 220 nm, a physical gate length (LG) of 150 nm, a gate/drain underlap (LGD) of 100 nm, a gate/source overlap (LGS) of 30 nm and the gate dielectric is composed by 3nm HfO2 on top of 1nm interfacial SiO2 . The TFETs studied here have a diameter (D) of 200 nm, with 100 nanowires in parallel (NW=100). A layer of Si1-xGex (=source) is deposited prior to the nanowire (NW) etching on top of the undoped silicon channel layer in the case of SiGe hetero-TFETs. Three different source compositions are studied: 100% Si, Si0.73Ge0.27 and Si0.56Ge0.44. For the Si source devices, 2 different devices are evaluated: the first one has the source doped by ion implantation after gate stack etching (= self aligned), while for the second device the source was like for the SiGe source counterparts in situ B-doped epitaxial grown prior to the NW etching. As a result, the second case corresponds to a more abrupt junction profile. Considering the Si0.54Ge0.46 source composition, the studied splits have 3 different Si capping process conditions after NW etching: 12 Si Mono-Layers (MLs), 18 Si MLs and the reference that has no extra Si passivation. More details can be found in (3). The impact of the source composition on the TFET behavior can be evaluated through figure 1. By increasing the germanium amount in the source, the bandgap decreases which results in an increased BTBT and a higher on-state current (ION). However, an inversion on the off-state current (IOFF) trend was observed. When the different Si source devices (inset of fig.1) are considered, the abrupt junction device presents a higher ION, due to the higher BTBT. Focusing on the Si0.56Ge0.44 condition that presents the best TFET behavior at room temperature, 3 different Si capping conditions were analyzed (fig.2). When Si MLs are included in the process a smaller amount of germanium segregates at the oxide, reducing the charges into the gate oxide and consequently improving the low frequency noise (inset of fig.2). At the same time, devices with Si MLs present a hump in the off region due to the increase of interface traps. This interface traps increase also promotes a shift in the drain current (IDS) to higher gate voltages. In the output characteristics of TFET devices, there is a very flat plateau in a “like saturation” region due to the small drain voltage influence on the transport mechanism (4), showing that the TFET is a good alternative for analog applications. Based on these characteristics, the analog parameters were extracted and analyzed as a function of temperature. Table I shows the results obtained for the Early voltage and figure 3 presents the intrinsic voltage gain behavior for temperatures ranging from 25 º C to 150 º C. From table I it is possible to observe that in general with increasing the germanium amount in the source side, the Early Voltage (VEA) increases due to the smaller tunneling resistance near the source. However, when the VEA is evaluated at higher temperatures, it is possible to see that the higher the Ge amount in the source, the greater the VEA degradation. This degradation is a result of the dependence of the dominant transport mechanism on temperature. For Si non-abrupt source devices, the inverse trend is observed, because in this case the dominant transport mechanism is trap assisted tunneling (TAT), which is strongly influenced by a temperature increase. Since the intrinsic voltage gain (AV) can be calculated by AV=gm/IDS*VEA=gm/gD and VEA prevails over the gm/IDS ratio, the intrinsic voltage gain behavior as a function of temperature has the same trend as VEA. A more extensive discussion about the analog performance of TFETs with different source compositions will be presented. 1. W. Y. Choi et al., IEEE Electron Device Lett., 28, 743 (2007). 2. R. Rooyackers et al., IEDM, 92 (2013). 3. A. Vandooren et al., Solid-State Electronics, 78, 82 (2012). 4. P. G. D. Agopian et al., IEEE Trans. Electron Device, vol. 60, n. 8, 2493, (2013).