Separate Gate Research Articles

Hybrid architecture for shallow accumulation mode AlGaAs/GaAs heterostructures with epitaxial gates

Accumulation mode devices with epitaxially grown gates have excellent electrical stability due to the absence of dopant impurities and surface states. We overcome typical fabrication issues associated with epitaxially gated structures (e.g., gate leakage and high contact resistance) by using separate gates to control the electron densities in the Ohmic and Hall bar regions. This hybrid gate architecture opens up a way to make ultrastable nanoscale devices where the separation between the surface gates and the 2D electron gas is small. In this work, we demonstrate that the hybrid devices made from the same wafer have reproducible electrical characteristics, with identical mobility and density traces over a large range of 2D densities. In addition, thermal cycling does not influence the measured electrical characteristics. As a demonstration of concept, we have fabricated a hybrid single-electron transistor on a shallow (50 nm) AlGaAs/GaAs heterostructure that shows clear Coulomb blockade oscillations in the low temperature conductance.

Fetal Dual Doppler Echocardiography

ABSTRACT Dual Doppler echocardiography is a recently developed technique performed using an instrument with two separate sample gates, allowing simultaneous recording of signals from two locations. We describe the use of dual Doppler echocardiography to assess fetal cardiac rhythm. Fetal arrhythmias are common and encountered in 1 to 2% pregnancies. They often resolve spontaneously and do not require treatment, but sometimes lead to severe morbidity and mortality. Fetal arrhythmias are responsive to fetal therapy and require appropriate management through accurate diagnosis. Pulsed wave Doppler and M-mode echocardiography are widely used to assess fetal cardiac rhythm. Both methods have advantages and limitations, which are influenced by fetal position, image resolution, and the complexity of the arrhythmia. We developed a new technique that records pulsed wave Doppler signals in the hepatic vein (HV) and the descending aorta (DAo) simultaneously using dual Doppler. This method is less influenced by fetal position and the complexity of the arrhythmia, and the images have better resolution than those acquired using conventional Doppler methods in most cases. Although, electrical parameters, such as the QT interval cannot be evaluated, dual Doppler recording of flows in HV and DAo is an efficient and effective method for assessing fetal cardiac rhythms, allowing precise diagnosis of cardiac arrhythmias. How to cite this article Kaji T, Maeda K, Hichijo A, Takahashi Y, Nakayama S, Irahara M. Fetal Dual Doppler Echocardiography. Donald School J Ultrasound Obstet Gynecol 2014; 8(4):376-381.

A Novel Fin Electron–Hole Bilayer Tunnel Field-Effect Transistor

A novel fin electron-hole bilayer tunnel field-effect transistor (FinEHBTFET) is proposed and investigated by simulation. In this structure, a narrow fin is placed at the middle of a conventional p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -i-n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> tunnel field-effect transistor, and two separate gates formed on left and right sides of the fin are used to control the channel. The FinEHBTFET achieves drive current when band-to-band tunneling happens between the bias-induced electron-hole bilayer at the two sides of the fin. The FinEHBTFET shows a high I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</sub> ratio more than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> , and an average SS of 3 mV/dec over three decades of drain current.

Implementation of Fully Self-Aligned Homojunction Double-Gate a-IGZO TFTs

A simple method of fabricating fully self-aligned double-gate (SADG) homojunction a-IGZO TFTs is proposed and experimentally demonstrated for the first time. The self-alignment between the bottom- and top-gates is realized with one backside-illuminated photolithographic step; and that between the source/drain regions and the two gates is formed by both argon plasma treatment and hydrogen doping. The resulting overlap between the gate and source/drain regions is about 0.3 μm. Excellent symmetry between bidirectional transfer characteristics in the fabricated SADG TFTs is observed. Moreover, the dynamic threshold voltage operation is well demonstrated, and the driving capability, electrical stress effects under tied and separate gate biases are investigated.

Novel Electrostatically Doped Planar Field-Effect Transistor for High Temperature Applications

The dominating leakage path for OFF-state currents in today’s downscaled MOSFET devices originate from PN-junction and bulk leakage [refs. 1, 2]. These leakage currents increase severely with temperature. SOI technologies can reduce bulk-leakage currents significantly. However, PN-junction leakage is still present even in SOI FETs. Therefore, our device concept replaces conventional source/drain PN-junctions with Schottky-barrier contacts in a dopant-free CMOS environment. This adds a high temperature robustness as reported recently for fabricated silicon nanowire (SiNW) FETs [refs. 3, 4]. We have extended the SiNW-concept to planar, non nano-wire device structures.The combination of an ambipolar electrostatic doping back-gate (BG) configuration and a separated current flow control front-gate (FG) results in a superior on-to-off current ratio and leakage suppression at high temperatures, e.g. more than 3 decades at 700 K. This mainly results from the high front-gate barrier height of 0.57 eV (Fig. 2, 3). Depending on its polarity, the BG accumulates either holes or electrons at the interface between top silicon and buried oxide and at the same time facilitates carrier tunneling through the Schottky-barrier contacts at source/drain. In contrast, the FG can locally suppress the accumulation by the BG and control the flow of charge carriers (Fig. 2, 3).The simulations are backed by measurements on SiNW FETs (Fig. 4). Fabrication of planar devices based on our SiNW technology and electrical measurement are consistent with simulation. Detailed results will be presented at the meeting.So far, all ambipolar devices with a separate gate to control the current flow involve nanowire structures as, for example, silicon nanowires or carbon nanotubes. To the best of our knowledge, this is the first demonstration of a novel electrostatically doped planar field effect transistor for high temperature applications.Furthermore, the degree of freedom to select instantly n- and p-type behavior via the polarity of the BG allows designing reconfigurable circuits with increased functionality [5]. Additionally, as no classic doping process is required, the device does not suffer from dopant dependent reduction of carrier mobility and statistic dopant fluctuation that typically arise in modern aggressively scaled MOSFET devices.[1] J. Appenzeller et al., “Toward nanowire electronics”, IEEE Transactions On Electron Devices, vol. 55, pp. 2827–2845, 2008.[2] Koo et. al, “Silicon nanowires as enhancement-mode Schottky barrier field-effect transistors”, Nanotechnology, vol. 16, pp. 1482–1485, 2005.[3] F. Wessely, T. Krauss, U. Schwalke, “Reconfigurable CMOS with undoped silicon nanowire midgap Schottky-barrier FETs“, Microelectronics Journal 44 (12), pp. 1072-1076, 2013.[4] F. Wessely, T. Krauss, U. Schwalke, “Virtually dopant-free CMOS: midgap Schottky-barrier nanowire field-effect-transistors for high temperature applications“, Solid-State Electronics, vol. 74, pp. 91-96, 2012.[5] J. Trommer et al., “Elementary Aspects for Circuit Implementation of Reconfigurable Nanowire Transistors”, Electron Device Letters, vol. 35 (1), pp. 141-143, 2014.

RF characterization of 100‐nm separate gate InAlAs/InGaAs DG‐HEMT

ABSTRACTThis article presents a three port analysis for separate gate In0.52Al0.48As/In0.53Ga0.47As DG‐HEMT and a small signal equivalent circuit is developed using charge control model. The various intrinsic short circuit admittance parameters (Y‐parameters) are evaluated to extract scattering parameters, to determine the maximum transducer power gain of the device. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2796–2803, 2013

Gate 전하를 감소시키기 위해 Separate Gate Technique을 이용한 Trench Power MOSFET

이 논문에서 Trench Power MOSFET의 스위칭 성능을 향상시키기 위한 Separate Gate Technique(SGT)을 제안하였다. Trench Power MOSFET의 스위칭 성능을 개선시키기 위해서는 낮은 gate-to-drain 전하 (Miller 전하)가 요구된다. 이를 위하여 제안된 separate gate technique은 얇은(~500A)의 poly-si을 deposition하여 sidewall을 형성함으로서, 기존의 Trench MOSFET에 비해 얇은 gate를 형성하였다. 이 효과로 gate와 drain에 overlap 되는 면적을 줄일 수 있어 gate bottom에 쌓이는 Qgd를 감소시키는 효과를 얻었고, 이에 따른 전기적인 특성을 Silvaco T-CAD silmulation tool을 이용하여 일반적인 Trench MOSFET과 성능을 비교하였다. 그 결과 Ciss(input capacitance : Cgs+Cgd), Coss(output capacitance : Cgd+Cds) 및 Crss(reverse recovery capacitance : Cgd) 모두 개선되었으며, 각각 14.3%, 23%, 30%의 capacitance 감소 효과를 확인하였다. 또한 inverter circuit을 구성하여, Qgd와 capacitance 감소로 인한 24%의 reverse recovery time의 성능향상을 확인하였다. 또한 제안된 소자는 기존 소자와 비교하여 어떠한 전기적 특성저하 없이 공정이 가능하다. In this paper, We proposed Separate Gate Technique(SGT) to improve the switching characteristics of Trench power MOSFET. Low gate-to-drain 전하 (Miller 전하 : Qgd) has to be achieved to improve the switching characteristics of Trench power MOSFET. A thin poly-silicon deposition is processed to form side wall which is used as gate and thus, it has thinner gate compared to the gate of conventional Trench MOSFET. The reduction of the overlapped area between the gate and the drain decreases the overlapped charge, and the performance of the proposed device is compared to the conventional Trench MOSFET using Silvaco T-CAD. Ciss(input capacitance : Cgs+Cgd), Coss(output capacitance : Cgd+Cds) and Crss(reverse recovery capacitance : Cgd) are reduced to 14.3%, 23% and 30% respectively. To confirm the reduction effect of capacitance, the characteristics of inverter circuit is comprised. Consequently, the reverse recovery time is reduced by 28%. The proposed device can be fabricated with convetional processes without any electrical property degradation compare to conventional device.

Manifestation of chiral tunneling at a tilted graphenep-njunction

Electrons in graphene follow unconventional trajectories at $p$-$n$ junctions, driven by their pseudospintronic degree of freedom. The prominent angular dependence of transmission is significant, capturing the chiral nature of the electrons and culminating in unit transmission at normal incidence (Klein tunneling). We theoretically show that such chiral tunneling can be directly observed from the junction resistance of a tilted interface probed with separate split gates. The junction resistance is shown to increase with tilt, in agreement with recent experimental evidence. The tilt dependence arises because of the misalignment between modal density and the anisotropic transmission lobe oriented perpendicular to the tilt. A critical determinant is the presence of specular edge scattering events that can completely reverse the angle dependence. The absence of such reversals in the experiments indicates that these edge effects are not overwhelmingly deleterious, making the premise of transport governed by electron ``optics'' in graphene an exciting possibility.

Hybrid Porphyrin–Silicon Nanowire Field-Effect Transistor by Opto-Electrical Excitation

A porphyrin-silicon nanowire (Si-NW) hybrid field-effect transistor is introduced. The hybrid device has separate electrical and optical gates surrounding the Si-NW channel. Porphyrin, a component of chlorophyll, is employed as an optical gate to modulate the potential of the Si-NW channel. Due to the independently formed hybrid gates, both optical and electrical excitation can effectively modulate the device. The exposed porphyrin optical gate responds to the optical excitation, and independently formed electrical gates respond to the electrical excitation. Charge transfer characteristics between a semiconductor channel and the porphyrin optical gate are deeply investigated. Optical, electrical, and opto-electrical excitation methods are employed to analyze the charging and discharging behaviors. Of these methods, opto-electrical excitation enables the strongest charge transfer because the inversion electron formation by an electrical pulse and the photoinduced charge transfer by an optical stimulus are affected simultaneously. Discharging processes, such as rapid discharging, exponential detrapping, and the formation of metastable states are also analyzed.

Reproducibility of constituent time intervals of right and left fetal modified myocardial performance indices on pulsed Doppler echocardiography: a short report

To assess reproducibility of constituent time intervals measured by pulsed Doppler echocardiography for calculation of the right and left fetal myocardial performance indices (MPIs). This was a prospective study of 30 normal singleton pregnancies (19-36 weeks). In each, five different time intervals were measured from the Doppler waveform and four repeated measures were taken for each time interval. Three were from the left heart: isovolumetric contraction time (ICT), isovolumetric relaxation time (IRT) and ejection time (ET); two were from the right heart: 'a-interval' and 'b-interval'. The left and right modified MPIs (Mod-MPIs) generated by these constituent time intervals were also evaluated. Two operators evaluated the reproducibility of all measures. There was generally good intra- and interobserver reproducibility for all time intervals and resultant Mod-MPIs: ICT, range, 19-43 ms with intraclass correlation coefficient (ICC), 0.91 (95% CI, 0.85-0.95); ET, range, 160-184.8 ms with ICC, 0.90 (95% CI, 0.84-0.95); IRT, range, 35.8-48.5 ms with ICC, 0.67 (95% CI, 0.52-0.81); a-interval, range 208-265 ms with ICC, 0.89 (95% CI, 0.82-0.94); b-interval, range, 163.1-188.3 ms with ICC, 0.82 (95% CI, 0.71-0.90); left Mod-MPI, range, 0.33-0.48 with ICC, 0.84 (95% CI, 0.74-0.91); right Mod-MPI, range, 0.21-0.49 with ICC, 0.82 (95% CI, 0.71-0.90). The 95% limits of agreement showed no statistically significant difference in measurements between the two examiners for all time intervals. This is the first study to evaluate the reproducibility of the component time intervals of both right and left fetal Mod-MPIs in the second and third trimesters and supports the reproducibility of fetal functional cardiac assessment. The IRT is the main source of variation for the left Mod-MPI so should be the focus of further investigation. Even using two separate pulsed-wave Doppler gates and therefore separate cardiac cycles, the right Mod-MPI is reproducible.

Simultaneous recordings of pulsed wave Doppler signals in hepatic vein and descending aorta using dual Doppler: a novel method for evaluating fetal arrhythmias

Simultaneous recordings of pulsed wave Doppler signals in hepatic vein and descending aorta using dual Doppler: a novel method for evaluating fetal arrhythmias

Photoactive Memory by a Si-Nanowire Field-Effect Transistor

A photoactive memory is implemented on a n-type and p-type double-gate silicon nanowire (Si-NW) field-effect transistor (FET) through the grafting of solution-processable [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) in nanogaps. Despite integration with organic material, superior FET characteristics are observed. Lowered operation voltage is achieved through the use of an optical source and an efficient photon-absorbing structure. Due to the naturally separated gate structure for PCBM embedment, moreover, memory performances stemming from a photoactive property are notably improved by biasing asymmetric voltage to the separated gates, which are individually controlled. The development of photoactive Si-NW FET based on CMOS process can pave the way of optoelectronic applications with more degree of freedom in terms of overall device design.

Being Flexible: The Voltage-Controllable Activation Gate of Kv Channels

Kv channels form voltage-dependent potassium selective pores in the outer cell membrane and are composed out of four α-subunits, each having six membrane-spanning α-helices (S1–S6). The α-subunits tetramerize such that the S5–S6 pore domains co-assemble into a centrally located K+ pore which is surrounded by four operational voltage-sensing domains (VSD) that are each formed by the S1–S4 segments. Consequently, each subunit is capable of responding to changes in membrane potential and dictates whether the pore should be conductive or not. K+ permeation through the pore can be sealed off by two separate gates in series: (a) at the inner S6 bundle crossing (BC gate) and (b) at the level of the selectivity filter (SF gate) located at the extracellular entrance of the pore. Within the last years a general consensus emerged that a direct communication between the S4S5-linker and the bottom part of S6 (S6c) constitutes the coupling with the VSD thus making the BC gate the main voltage-controllable activation gate. While the BC gate listens to the VSD, the SF changes its conformation depending on the status of the BC gate. Through the eyes of an entering K+ ion, the operation of the BC gate apparatus can be compared with the iris-like motion of the diaphragm from a camera whereby its diameter widens. Two main gating motions have been proposed to create this BC gate widening: (1) tilting of the helix whereby the S6 converts from a straight α-helix to a tilted one or (2) swiveling of the S6c whereby the S6 remains bent. Such motions require a flexible hinge that decouples the pre- and post-hinge segment. Roughly at the middle of the S6 there exists a highly conserved glycine residue and a tandem proline motif that seem to fulfill the role of a gating hinge which allows for tilting/swiveling/rotations of the post-hinge S6 segment. In this review we delineate our current view on the operation of the BC gate for controlling K+ permeation in Kv channels.

A Novel 10-Transistor Encoder Design for Modified Booth Encoder to Optimize Power and Area

The aim of this paper is to reduce power and area of the Modified Booth Encoder. The encoders of the multiplier are implemented with Pass transistor XOR-XNOR block instead of two separate XOR and XNOR gates. The encoder consists of one XOR and XNOR with common inputs. The proposed encoder is designed with one XOR with two inputs and two outputs. Between two outputs, one is taken at before an inverter, the function is XNOR. Second is taken at after the inverter for XOR function. Due to this the proposed design eliminates two transistors. Hence this design consumes 47% and 77% less power than Pass Transistor XOR-XNOR [11] and CMOS XOR-XNOR respectively and also occupies less area. The results are obtained using H-spice at 2.0V for 180nm technology

Multibit Polycristalline Silicon–Oxide–Silicon Nitride–Oxide–Silicon Memory Cells with High Density Designed Utilizing a Separated Control Gate

Unique multibit NAND polycrystalline silicon–oxide–silicon nitride–oxide–silicon (SONOS) memory cells utilizing a separated control gate (SCG) were designed to increase memory density. The proposed NAND SONOS memory device based on a SCG structure was operated as two bits, resulting in an increase in the storage density of the NVM devices in comparison with conventional single-bit memories. The electrical properties of the SONOS memory cells with a SCG were investigated to clarify the charging effects in the SONOS memory cells. When the program voltage was supplied to each gate of the NAND SONOS flash memory cells, the electrons were trapped in the nitride region of the oxide–nitride–oxide layer under the gate to supply the program voltage. The electrons were accumulated without affecting the other gate during the programming operation, indicating the absence of cross-talk between two trap charge regions. It is expected that the inference effect will be suppressed by the lower program voltage than the program voltage of the conventional NAND flash memory. The simulation results indicate that the proposed unique NAND SONOS memory cells with a SCG can be used to increase memory density.

FinFACT—Fin Flip-Flop Actuated Channel Transistor

Nanoelectromechanical system technology is applied for a complementary metal-oxide-semiconductor device to provide a novel function. Based on an independently controlled double-gate FinFET, the fin of the proposed transistor is suspended by replacing the solid-state gate dielectric with a gas-state gate dielectric, which enables flip-flop actuation of the fin. Flip-flop actuation of the fin is accomplished via electrostatic force from two separated gates, representing a binary mechanical state of the fin. It is anticipated that the virtues of the reported device can be exploited in transformable circuit units and digital memory transistors.

Separate Gating Mechanisms Mediate the Regulation of K2P Potassium Channel TASK-2 by Intra- and Extracellular pH

TASK-2 (KCNK5 or K(2P)5.1) is a background K(+) channel that is opened by extracellular alkalinization and plays a role in renal bicarbonate reabsorption and central chemoreception. Here, we demonstrate that in addition to its regulation by extracellular protons (pH(o)) TASK-2 is gated open by intracellular alkalinization. The following pieces of evidence suggest that the gating process controlled by intracellular pH (pH(i)) is independent from that under the command of pH(o). It was not possible to overcome closure by extracellular acidification by means of intracellular alkalinization. The mutant TASK-2-R224A that lacks sensitivity to pH(o) had normal pH(i)-dependent gating. Increasing extracellular K(+) concentration acid shifts pH(o) activity curve of TASK-2 yet did not affect pH(i) gating of TASK-2. pH(o) modulation of TASK-2 is voltage-dependent, whereas pH(i) gating was not altered by membrane potential. These results suggest that pH(o), which controls a selectivity filter external gate, and pH(i) act at different gating processes to open and close TASK-2 channels. We speculate that pH(i) regulates an inner gate. We demonstrate that neutralization of a lysine residue (Lys(245)) located at the C-terminal end of transmembrane domain 4 by mutation to alanine abolishes gating by pH(i). We postulate that this lysine acts as an intracellular pH sensor as its mutation to histidine acid-shifts the pH(i)-dependence curve of TASK-2 as expected from its lower pK(a). We conclude that intracellular pH, together with pH(o), is a critical determinant of TASK-2 activity and therefore of its physiological function.

Gate adjustable coherent three and four level mixing in a vertical quantum dot molecule

We study level mixing in the single-particle energy spectrum of one of the constituent quantum dots in a vertical double quantum dot by performing magneto-resonant-tunneling spectroscopy. The device used in this study differs from previous vertical double quantum dot devices in that the single side gate is now split into four separate gates. Because of the presence of natural perturbations caused by anharmonicity and anisotropy, applying different combinations of voltages to these gates allows us to alter the effective potential landscape of the two dots and hence influence the level mixing. We present here preliminary results from one three level crossing and one four level crossing high up in the energy spectrum of one of the probed quantum dots, and demonstrate that we are able to change significantly the energy dispersions with magnetic field in the vicinity of the crossing regions.

Conformational Changes in the Nicotinic Acetylcholine Receptor during Gating and Desensitization

The nicotinic acetylcholine receptor (nAChR) is a member of the important Cys loop ligand-gated ion channel superfamily that modulates neuronal excitability. After they respond to their agonists, their actions are terminated either by removal of ligand or by fast and slow desensitization, processes that play an important role in modulating the duration of conducting states and hence of integrated neuronal behavior. We monitored structural changes occurring during fast and slow desensitization in the transmembrane domain of the Torpedo nAChR using time-resolved photolabeling with the hydrophobic probe 3-(trifluoromethyl)-3-(m-iodophenyl)diazirine (TID). After channel opening, TID photolabels a residue on the delta-subunit's M2-M3 loop and a cluster of four residues on deltaM1 and deltaM2, defining an open state pocket [Arevalo, E., et al. (2005) J. Biol. Chem. 280, 13631-13640]. We now find that photolabeling of this pocket persists during the transition to the fast desensitized state, the extent of photoincorporation decreasing only with the transition to the slow desensitized state. In contrast, the extent of photoincorporation in the channel lumen at the conserved 9'-leucines on the second transmembrane helix (M2-9') decreased successively during the resting to open and open to fast desensitized state transitions, implying that the local conformation is different in each state, a conclusion consistent with the hypothesis that there are separate gates for channel opening and desensitization. Thus, although during fast desensitization there is a conformation change in the channel lumen at the level of M2-9', there is none in the regions of the delta-subunit's M2-M3 loop and the interior of its M1-M4 helix bundle until slow desensitization occurs.

SODIUM AND POTASSIUM SENSORS BASED ON SEPARATED EXTENDED GATE FIELD EFFECT TRANSISTOR

A double potassium and sodium ions sensor based on separated extended gate field effect transistor (SEGFET) and a new entrapment method are proposed in this study. Having high sensitivity, reproducibility, and a simple manufacturing process, the sensors are quickly able to supply information and detect human blood within an abnormal range. The sensing membranes were fabricated using a Poly(vinyl chloride) carboxylated (PVC-COOH) matrix; sodium ionophore (B12C4) or potassium ionophore (valinomycin). The sensitivity of ion-selective biosensors is 42.55 mV/decade for Na+ between 1 M and 10-7 M, 42.75 mV/decade for K+ between 1 M and 10-6 M.