Gate Voltage Range Research Articles

Modeling of Quantum Confinement and Capacitance in III–V Gate-All-Around 1-D Transistors

In this paper, a physics-based compact model for calculating the semiconductor charges and gate capacitance of III–V nanowire (NW) MOS transistors is presented. The model calculates the subband energies and the semiconductor charges by considering the wave function penetration into the gate insulator, effective mass discontinuity at the semiconductor–oxide interface, 2-D confinement in the NW, and Fermi–Dirac statistics. The semiconductor charge expression proposed in this paper is completely explicit in terms of applied gate voltage, therefore, making it highly suitable for large circuit simulations. The model is also compared with the results from self-consistent Schrodinger–Poisson solver for different NW sizes and materials and found to be accurate over a wide range of gate voltages.

Performance Improvement of p-Channel Tin Monoxide Transistors With a Solution-Processed Zirconium Oxide Gate Dielectric

This letter reports the fabrication of p-channel tin monoxide (SnO) thin-film transistors (TFTs) with a high-permittivity zirconium oxide (ZrO2) gate insulator film, which were prepared by a low-cost spin-cast method. The spin-cast ZrO2 dielectrics exhibit a low leakage current density of $4.5 \times 10^{{\textsf {-8}}}$ A/cm2 at 1 MV/cm. Introducing the ZrO2 dielectric in top-type SnO TFTs allows for a reduction in the driving gate voltage range from 80 to 10 V, as compared with devices with a thermal SiO2 gate insulator. Additionally, a high field-effect mobility of 2.5 cm2/Vs and an $I_{{ \mathrm{\scriptscriptstyle ON} / \mathrm{\scriptscriptstyle OFF}}}$ of $3 \times 10^{{\textsf {3}}}$ were preserved.

Electric field controlled domain wall dynamics and magnetic easy axis switching in liquid gated CoFeB/MgO films

We present reversible electric (E) field driven switching of the magnetic easy axis in CoFeB/MgO/HfO2 heterostructures from perpendicular to in-plane using an ionic liquid gate. The modification of magnetic anisotropy reaches 0.108 mJ/m2 in a gate voltage range between −3 V and 3.5 V with an efficiency of 82 fJ (V m)–1. The influence of the E-field induced anisotropy changes on domain nucleation and propagation of magnetic domain walls has also been studied in the perpendicular anisotropy state. A significant modulation of the domain wall velocity is observed in both the creep and depinning regimes of domain wall motion consistent with the E-field induced anisotropy variation. In addition, we demonstrate voltage controlled magnetization switching under a constant magnetic field and voltage control of domain wall pinning.

Use of micro-photoluminescence as a contactless measure of the 2D electron density in a GaAs quantum well

We compare micro-photoluminescence (μPL) as a measure of the electron density in a clean, two-dimensional (2D) system confined in a GaAs quantum well (QW) to the standard magneto-transport technique. Our study explores the PL shape evolution across a number of molecular beam epitaxy-grown samples with different QW widths and 2D electron densities and notes its correspondence with the density obtained in magneto-transport measurements on these samples. We also measure the 2D density in a top-gated quantum well sample using both PL and transport and find that the two techniques agree to within a few percent over a wide range of gate voltages. We find that the PL measurements are sensitive to gate-induced 2D density changes on the order of 109 electrons/cm2. The spatial resolution of the PL density measurement in our experiments is 40 μm, which is already substantially better than the millimeter-scale resolution now possible in spatial density mapping using magneto-transport. Our results establish that μPL can be used as a reliable high spatial resolution technique for future contactless measurements of density variations in a 2D electron system.

Modeling of I-V characteristics in symmetric double-gate polysilicon thin-film transistors

A new closed-form approximation for surface potential and drain current (DC) in symmetric double-gate polysilicon thin-film transistors (DG poly-Si TFTs) is proposed. The solution of the surface potential is single-piece and suitable for a wide range of gate voltages under different conditions. A comparison with numerical results shows that this scheme gives an accurate description of surface potential. The development of surface-potential-based compact model for I-V characteristics is achieved based on this calculation. Finally, the validity of the model is verified by comparisons with various experimental data. It is showing that the model is accurate over a wide range of operation regions.

1200V SiC Trench-MOSFET Optimized for High Reliability and High Performance

A detailed analysis of the typical static and dynamic performance of the new developed Infineon 1200V CoolSiCTM MOSFET is shown which is designed for an on-resistance of 45 mΩ. In order to be compatible to various standard gate drivers the gate voltage range is designed for-5 V in off-state and +15 V in on-state. Long term gate oxide life time tests reveal that the extrinsic failure evolution follows the linear E-model which allows a confident prediction of the failure rate within the life time of the device of 0.2 ppm in 20 years under specified use condition.

Photogalvanic probing of helical edge channels in two-dimensional HgTe topological insulators

We report on the observation of a circular photogalvanic current excited by terahertz (THz) laser radiation in helical edge channels of HgTe-based 2D topological insulators (TIs). The direction of the photocurrent reverses by switching the radiation polarization from right-handed to left-handed one and, for fixed photon helicity, is opposite for the opposite edges. The photocurrent is detected in a wide range of gate voltages. With decreasing the Fermi level below the conduction band bottom, the current emerges, reaches a maximum, decreases, changes its sign close to the charge neutrality point (CNP), and again rises. Conductance measured over a 7 $\mu$m distance at CNP approaches 2e2/h, the value characteristic for ballistic transport in 2D TIs. The data reveal that the photocurrent is caused by photoionization of helical edge electrons to the conduction band. We discuss the microscopic model of this phenomenon and compare calculations with the experimental data.

Drain Extended Tunnel FET—A Novel Power Transistor for RF and Switching Applications

For the first time, a novel drain-extended tunnel FET (DeTFET) device is disclosed in this paper, while addressing the need for high-voltage/high-power devices for system-on-chip and automotive applications in beyond FinFET technology nodes. Operation of the proposed DeTFET device is presented with physics of band-to-band tunneling and associated carrier injection. Device’s intrinsic (dc/switching), analog, and RF performance is compared with the state-of-the-art drain-extended nMOS (DeNMOS) device. The proposed device for 11 V breakdown voltage offers $15\times $ better subthreshold slope, $8\times $ lower off-state leakage, $2\times $ higher ON current, and absence of channel length modulation and drain induced barrier lowering, while keeping $2.5\times $ lower threshold voltage. This results into significantly better ON resistance for a range of gate voltages, higher transconductance, orders of magnitude higher intrinsic transistor gain, and better RF characteristics, when compared with the DeNMOS device. Finally, device design guidelines are presented and scalability, without affecting breakdown voltage, of the proposed device is compared with the DeNMOS device.

Electrical Properties of Ultrathin Hf-Ti-O Higher k Gate Dielectric Films and Their Application in ETSOI MOSFET.

Ultrathin Hf-Ti-O higher k gate dielectric films (~2.55 nm) have been prepared by atomic layer deposition. Their electrical properties and application in ETSOI (fully depleted extremely thin SOI) PMOSFETs were studied. It is found that at the Ti concentration of Ti/(Ti + Hf) ~9.4%, low equivalent gate oxide thickness (EOT) of ~0.69 nm and acceptable gate leakage current density of 0.61 A/cm2 @ (V fb − 1)V could be obtained. The conduction mechanism through the gate dielectric is dominated by the F-N tunneling in the gate voltage range of −0.5 to −2 V. Under the same physical thickness and process flow, lower EOT and higher I on/I off ratio could be obtained while using Hf-Ti-O as gate dielectric compared with HfO2. With Hf-Ti-O as gate dielectric, two ETSOI PMOSFETs with gate width/gate length (W/L) of 0.5 μm/25 nm and 3 μm/40 nm show good performances such as high I on, I on/I off ratio in the magnitude of 105, and peak transconductance, as well as suitable threshold voltage (−0.3~−0.2 V). Particularly, ETSOI PMOSFETs show superior short-channel control capacity with DIBL <82 mV/V and subthreshold swing <70 mV/decade.

Universal Faraday Rotation in HgTe Wells with Critical Thickness.

The universal value of the Faraday rotation angle close to the fine structure constant (α≈1/137) is experimentally observed in thin HgTe quantum wells with a thickness on the border between trivial insulating and the topologically nontrivial Dirac phases. The quantized value of the Faraday angle remains robust in the broad range of magnetic fields and gate voltages. Dynamic Hall conductivity of the holelike carriers extracted from the analysis of the transmission data shows a theoretically predicted universal value of σ_{xy}=e^{2}/h, which is consistent with the doubly degenerate Dirac state. On shifting the Fermi level by the gate voltage, the effective sign of the charge carriers changes from positive (holes) to negative (electrons). The electronlike part of the dynamic response does not show quantum plateaus and is well described within the classical Drude model.

Strong Electrical Manipulation of Spin–Orbit Torque in Ferromagnetic Heterostructures

Electrical control of current‐induced spin–orbit effects in magnets is supposed to reduce the power consumption in high‐density memories to the utmost extent, but the efficient control in metallic magnets at a practical temperature remains elusive. Here, the electrical manipulation of spin–orbit torque is investigated in perpendicularly magnetized Pt/Co/HfOx heterostructures in a nonvolatile manner using an ionic liquid gate. The switching current of magnetization can be reversibly tuned by a factor of two within a small gate voltage range of 1.5 V. The modulation of effective spin Hall angle and the corresponding damping‐like torque mainly accounts for the strong electrical manipulation of switching current. Besides the fundamental significance, the findings here may advance the process toward the compatible memory and logic devices driven by dual electrical means, the electric field, and current.

Current transport mechanisms in mercury cadmium telluride diode

This paper reports the results of modelling of the current-voltage characteristics (I-V) of a planar mid-wave Mercury Cadmium Telluride photodiode in a gate controlled diode experiment. It is reported that the diode exhibits nearly ideal I-V characteristics under the optimum surface potential leading to the minimal surface leakage current. Deviations from the optimum surface potential lead to non ideal I–V characteristics, indicating a strong relationship between the ideality factor of the diode with its surface leakage current. Diode's I–V characteristics have been modelled over a range of gate voltages from −9 V to −2 V. This range of gate voltages includes accumulation, flat band, and depletion and inversion conditions below the gate structure of the diode. It is shown that the I–V characteristics of the diode can be very well described by (i) thermal diffusion current, (ii) ohmic shunt current, (iii) photo-current due to background illumination, and (iv) excess current that grows by the process of avalanche multiplication in the gate voltage range from −3 V to −5 V that corresponds to the optimum surface potential. Outside the optimum gate voltage range, the origin of the excess current of the diode is associated with its high surface leakage currents. It is reported that the ohmic shunt current model applies to small surface leakage currents. The higher surface leakage currents exhibit a nonlinear shunt behaviour. It is also shown that the observed zero-bias dynamic resistance of the diode over the entire gate voltage range is the sum of ohmic shunt resistance and estimated zero-bias dynamic resistance of the diode from its thermal saturation current.

Impact of carrier quantum confinement on the short channel effects of double-gate silicon-on-insulator FINFETs

In this work, we use a center potential based approach to determine the electrostatics viz. threshold voltage (Vth), Sub-Threshold Slope and Drain Induced Barrier Lowering (DIBL) for Fully Depleted (FD) Undoped Symmetric Double-Gate (DG) Silicon-on-Insulator (SOI) FINFETs over a wide range of Channel Lengths (Lg) and drain voltages (Vd). Based on this approach, a comparison of the electrostatics of Undoped Symmetric Double-Gate (DG) Silicon-on-Insulator (SOI) FINFETs is presented between the semi-classical and quantum confinement cases for two different SOI fin thicknesses of Tfin=2nm and Tfin=7nm, respectively. For both cases, it is observed that the threshold voltage roll-off and DIBL is greater in the quantum confinement case than in the semi-classical case. This seemingly counter-intuitive trend also implies that the channel length corresponding to the transition from long channel to short channel behavior (Lmin) is also lower in the semi-classical case compared to the quantum confinement case. This behavior is explained by comparing the Lateral Electric field (along the channel length) with the Electric Field along the thickness of the SOI fin for Tfin=2nm and Tfin=7nm over a wide range of gate and drain voltages. This analysis suggests that quantum confinement adversely affects the short channel effects and leads to an increase in the Lmin compared to the semi-classical case. These results for Lmin clearly illustrate the importance of the need to include the quantum confinement effects while evaluating the electrostatics performance and scalability of symmetric DG SOI FINFETs.

Improved memory characteristics of charge trap memory by employing double layered ZrO2 nanocrystals and inserted Al2O3

The charge trap memory capacitors incorporating a stacked charge trapping layer consisting of double layered ZrO2 nanocrystals (NCs) and inserted Al2O3 have been fabricated and investigated. It is observed that the memory capacitor with stacked trapping layer exhibits a hysteresis window as large as 14.3 V for ±10 V sweeping gate voltage range, faster program/erase speed, improved endurance performance, and good data retention characteristics with smaller extrapolated ten years charge loss at room temperature and 125 °C compared to single layered NCs. The special energy band alignment and the introduced additional traps of double layered ZrO2 NCs and inserted Al2O3 change the trapping and loss behavior of charges, and jointly contribute to the remarkable memory characteristics. Therefore, the memory capacitor with a stacked charge trapping layer is a promising candidate in future nonvolatile charge trap memory device design and application.

Anti-Ambipolar Field-Effect Transistors Based On Few-Layer 2D Transition Metal Dichalcogenides.

Two-dimensional (2D) materials and their related van der Waals heterostructures have attracted considerable interest for their fascinating new properties. There are still many challenges in realizing the potential of 2D semiconductors in practical (opto)electronics such as signal transmission and logic circuit, etc. Herein, we report the gate-tunable anti-ambipolar devices on the basis of few-layer transition metal dichalcogenides (TMDs) heterostructures to gain higher information storage density. Our study shows that carrier concentration regulated by the gate voltage plays a major role in the "anti-ambipolar" behavior, where the drain-source current can only pass through in specific range of gate voltage (Vg) and it will be restrained if the Vg goes beyond the range. Several improved strategies were theoretically discussed and experimentally adopted to obtain higher current on/off ratio for the anti-ambipolar devices, such as choosing suitable p-/n-pair, increasing carrier concentration by using thicker-layer TMDs, and so on. The modified SnS2/WSe2 device with the current on/off ratio exceeding 200 and on-state Vg ranging from -20 to 0 V was successfully achieved. On the basis of the anti-ambipolar field-effect transistors (FETs), we also reveal the potential of three-channel device unit for signal processing and information storage. With the equal quantity N of device units, 3(N) digital signals can be obtained from such three-channel devices, which are much larger than 2(N) ones obtained from traditional two-channel complementary metal oxide semiconductors (CMOS).

Two distinct regimes for the electrical control of the spin–orbit interaction in GaAs wells

We investigate the electrical control of the spin–orbit (SO) interaction in GaAs wells, involving both one- and two-subband electron occupations altered by a gate potential Vg, over a wide range of well widths w's. Through the self-consistent Schrödinger–Poisson calculation, we determine all the intrasubband Rashba αν(ν=1,2) and Dresselhaus βν, and also the intersubband Rashba η and Dresselhaus Γ couplings. We observe two distinct regimes marked off around w=wc=30−35nm. In the first regime with w<wc, we find the usual behavior of SO couplings, i.e., the intrasubband Rashba couplings α1 and α2 have the same sign and both change almost linearly with Vg, while the Dresselhaus couplings β1 and β2 obeying the relation β1<β2 are almost constant. In contrast, in the second regime with w>wc, we observe that α1 and α2 can either have the same sign or opposite signs depending on Vg. In addition, even though α1 sensitively depends on Vg, we find that α2 remains essentially constant within a certain gate voltage range. As for the Dresselhaus couplings in this second regime, the inequality β1<β2 (valid in the first regime) only holds near the symmetric configuration of our wells, but otherwise the inequality tends to be reversed. On the other hand, we find that both the intersubband Rashba η and Dresselhaus Γ couplings change almost linearly with Vg in the first regime while in the second one a maximum of |η| occurs near the symmetric configuration. We also determined the persistent-spin-helix symmetry points of the two subbands, where the Rashba and the renormalized (due to cubic corrections) Dressehaus couplings are matched. We find that the helix symmetry for the second subband retains over a broad range of Vg's, thus possibly facilitating its locking in practice. Our results should be essential for experiments pursuing an universal electrical control of the SO interaction in semiconductor nanostructures.

Electric-field control of spin-orbit torque in a magnetically doped topological insulator.

Electric-field manipulation of magnetic order has proved of both fundamental and technological importance in spintronic devices. So far, electric-field control of ferromagnetism, magnetization and magnetic anisotropy has been explored in various magnetic materials, but the efficient electric-field control of spin-orbit torque (SOT) still remains elusive. Here, we report the effective electric-field control of a giant SOT in a Cr-doped topological insulator (TI) thin film using a top-gate field-effect transistor structure. The SOT strength can be modulated by a factor of four within the accessible gate voltage range, and it shows strong correlation with the spin-polarized surface current in the film. Furthermore, we demonstrate the magnetization switching by scanning gate voltage with constant current and in-plane magnetic field applied in the film. The effective electric-field control of SOT and the giant spin-torque efficiency in Cr-doped TI may lead to the development of energy-efficient gate-controlled spin-torque devices compatible with modern field-effect semiconductor technologies.

Electrical Probing and Tuning of Molecular Physisorption on Graphene.

The ability to tune the molecular interaction electronically can have profound impact on wide-ranging scientific frontiers in catalysis, chemical and biological sensor development, and the understanding of key biological processes. Despite that electrochemistry is routinely used to probe redox reactions involving loss or gain of electrons, electrical probing and tuning of the weaker noncovalent interactions, such as molecular physisorption, have been challenging, primarily due to the inability to change the work function of conventional metal electrodes. To this end, we report electrical probing and tuning of the noncovalent physisorption of polar molecules on graphene surface by using graphene nanoelectronic heterodyne sensors. Temperature-dependent molecular desorptions for six different polar molecules were measured in real-time to study the desorption kinetics and extract the binding affinities. More importantly, we demonstrate electrical tuning of molecule-graphene binding kinetics through electrostatic gating of graphene; the molecular desorption can be slowed down nearly three times within a gate voltage range of 15 V. Our results provide insight into small molecule-nanomaterial interaction dynamics and signify the ability to electrically tailor interactions, which can lead to rational designs of complex chemical processes for catalysis and drug discovery.

A review of special gate coupling effects in long-channel SOI MOSFETs with lightly doped ultra-thin bodies and their compact analytical modeling

The charge coupling between the front and back gates is a fundamental property of any fully-depleted silicon-on-insulator (SOI) MOSFET. It is traditionally described by the classical Lim and Fossum model (Lim and Fossum, 1983). However, in the case of lightly-doped ultra-thin-body (UTB) SOI MOSFETs with ultra-thin gate dielectrics, significant deviations from this model have been observed and analyzed over the years. In this paper, we present a thorough review of special features of gate coupling in such devices, combining a large set of results from one-dimensional numerical simulations in classical and quantum–mechanical modes, experimental data and analytical modeling. We show that UTB SOI MOSFETs with ultra-thin gate dielectrics feature stronger modulation of the threshold voltage at the conduction side with opposite gate bias and much wider range of gate voltages for interface coupling than predicted by the Lim and Fossum model. These differences originate from both electrostatic and quantization effects. A simple analytical model taking into account these effects is presented. The model enables an easy assessment of the quantization-induced threshold voltage increase in a long-channel SOI MOSFET versus opposite gate bias and the electric field in the silicon film associated with gate decoupling.

Impact of Asymmetric Configurations on the Heterogate Germanium Electron&amp;#x2013;Hole Bilayer Tunnel FET Including Quantum Confinement

We investigate the effect of asymmetric configurations on the heterogate germanium electron–hole bilayer tunnel FET (TFET) and assess the improvement that they provide in terms of boosting the typically very low ON-current levels of TFET devices in the presence of field-induced quantum confinement. We show that when a very strong inversion for holes is induced at the bottom of the channel, the formation of the inversion layer for electrons is shifted to higher gate voltages, which in turn enhances the electrostatic control of the band bending at the top of the channel. As a result, the pinning of the quantized energy subbands is prevented for a wider range of gate voltages, and this allows vertical band-to-band tunneling distances to be further reduced compared with the conventional symmetric electron–hole bilayer configurations.