Channel Capacitance Research Articles

Components of channel capacitance in metal-insulator-semiconductor capacitors

In metal-insulator-semiconductor (MIS) capacitors, there are several components that influence the channel capacitance. Charges accumulate or deplete from the Γ, X, and L valleys for electrons and light, heavy and split-off bands for holes. Additionally dopants can change occupancy as a result of band-bending. A simple numerical method for calculating these components is presented along with potential implications for MIS capacitor characterization. Calculations for In0.53Ga0.47As indicate capacitance due to changes in dopant impurity ionization becomes significant around ND=1×1017 cm−3. The results also suggest that more detailed transient models are needed to verify the assumptions used in interface state characterization.

Timing optimization of a H-tree based digital silicon photomultiplier

This paper presents a compresensive analysis of timing resolution for a digital silicon photomultiplier (D-SiPM) using a SPICE simulator. Generally, digital silicon photomultipliers (D-SiPMs) have a full-width-half-maximum (FWHM) single-photon timing resolution (SPTR) of more than 100 ps, often of several hundreds picoseconds. This is primarily due to detector jitter, circuit noise, and routing skew. Circuit noise and skew, in turn, strongly depend on the SiPM design; this dependency has been investigated by varying transistor size and transistor channel length, wire resistance, and capacitance. The scalability of the method has been validated by considering D-SiPMs of different sizes and with a variety of signal distribution architectures.

Modeling Terahertz Plasmonic Si FETs With SPICE

As operating frequencies of Si FETs continue to grow, commercial circuit modeling tools must provide accurate simulations at very high frequencies with the ability to model plasmonic FETs in large and complex circuits. Traditional compact SPICE models used by commercial CAD tools model the channel resistance and capacitance and gate resistance as single lumped elements or use approximations to model the distributed nature of the FET channel. At high frequencies, these models become inaccurate and fail to model device physics properly. To describe plasmonic FETs, a THz SPICE model is developed for Si FETs. The THz SPICE model is validated experimentally to be in close agreement with measured results. The model is used to show predicted device response at different technology nodes.

Electrochemical impedance spectroscopy characterization of nanoporous alumina dengue virus biosensor

The Faradaic electrochemical impedance technique is employed to characterize the impedance change of a nanoporous alumina biosensor in response towards the specific binding of dengue serotype 2 (Denv2) viral particles to its serotype 2-specific immunoglobulin G antibody within the thin alumina layer. The optimal equivalent circuit model that matches the impedimetric responses of the sensor describes three distinct regions: the electrolyte solution (Rs), the porous alumina channels (including biomaterials) (Q1, R1) and the conductive electrode substrate layer (Q2, R2). Both channel resistance R1 and capacitance Q1 change in response to the increase of the Denv2 virus concentration. A linear relationship between R1 and Denv2 concentration from 1 to 900 plaque forming unit per mL (pfu mL−1) can be derived using Langmuir–Freundlich isotherm model. At 1pfu mL−1 Denv2 concentration, R1 can be distinguished from that of the cell culture control sample. Moreover, Q1 doubles when Denv2 is added but remains unchanged in the presence of two other non-specific viruses — West Nile virus and Chikungunya virus indicates biosensor specificity can be quantitatively measured using channel capacitance.

Parasitic capacitance removal of sub-100 nm p-MOSFETs using capacitance–voltage measurements

Capacitance–voltage measurements are performed on sub-100 nm high-k/metal gate p-MOSFETs to extract the intrinsic capacitance per gate length. This is then repeated on simulated devices using finite element modeling to compare to the experimental results. The intrinsic channel capacitance for the simulated devices is isolated from the parasitic capacitance, allowing for the comparison of analytic models of parasitic capacitances to the simulation.

A Program Disturb Model and Channel Leakage Current Study for Sub-20 nm nand Flash Cells

We have developed a program-disturb model to characterize the channel potential of the program-inhibited string during NAND flash cell programming. This model includes cell-to-cell capacitances from 3-D technology computer-aided design simulation and leakage currents associated with the boosted channel. We studied the program-disturb characteristics of sub-30-nm NAND cells using a delayed programming pulse method. The simulation results agree with the experimental data very well and show quantitative impacts of junction leakage current, band-to-band tunneling (BTBT) current, Fowler-Nordheim tunneling current, and channel capacitance on the program disturb. We further discuss the cell-scaling trend and identify that the BTBT current can be a dominant mechanism for the program disturb of sub-20-nm NAND cells.

Bias stress instability in organic transistors investigated by ac admittance measurements

In this paper, the bias stress effect (BSE) in organic field-effect transistors has been analyzed by an alternative experimental approach based on ac admittance (Y=G+jωC) measurements. conductance (C) and capacitance (G) curves have been recorded as a function of frequency at different times of the bias stress experiments and simultaneously fitted through a transmission line circuit, able to separately model the conducting properties of the channel and contact regions. The determination of the time behavior of the model fitting parameters is assumed as the starting point for a quantitative analysis of the BSE occurrence. This experimental procedure clarifies that both channel resistance (Rch) and contact resistance (Rc) are largely affected by the BSE, while the channel capacitance (Cch), related to the charge accumulation sheet, and the contact capacitance (Cc) result almost unchanged.

Non-metallic effects in silicided gate MOSFETs

Introducing metal or fully silicided gates in the semiconductor industry leads to improvements in MOSFET performance when compared to their polysilicon counterparts. However we will show, through Poisson–Schroedinger simulations, that when silicides are not treated as ideal metal contacts, the non-metallic effects such as accumulation and depletion regions in the gate, although partially suppressed, are still present, even if the actual electron density of a metal is taken into account. The role of the dark space hidden beneath highly doped gates is discussed, highlighting overestimation of C–V measurements in the extraction of the oxide thickness. In terms of insulator thickness, a 0.2 nm correction is suggested for silicided gates, due to quantum corrections in the gate contact. An error of up to 15% in the evaluation of gate to channel capacitance was found, due to the quantization of the holes in accumulation. Finally, the impact of a substoichiometric insulator layer and the band-gap narrowing of highly-doped polysilicon gates is also discussed.

Analysis of Fringing Effect on Resonant Plasma Frequency in Plasma Wave Devices

The effect of fringing electric field due to the nonideality of the gate two-dimensional electron gas (2DEG) channel capacitance on the fundamental resonant frequency of plasma waves in a high-electron-mobility transistor (HEMT) channel was investigated. The spatial distribution of sheet electron density in the fringed region of the 2DEG channel and the expression for the fundamental resonant frequency of plasma oscillation were obtained. A cascaded transmission line (TL) equivalent circuit model was developed to represent the gated and ungated fringed regions of the HEMT 2DEG channel. Results of calculation and IsSpice simulation show that fringing effects can be the cause of the fundamental plasma frequency reduction. Thus, the developed fringing effect model improves the deviation between theoretical and experimental data.

Harmonic-Balance Algorithms for the Circuit-Level Nonlinear Analysis of UWB Receivers in the Presence of Interfering Signals

This paper demonstrates, for the first time, a circuit-level approach to the analysis of pulse-ultrawideband (UWB) receiver front ends in the presence of interfering communication signals. The procedure is based on a model-order-reduction harmonic-balance technique based on Krylov subspaces. A sophisticated algorithm for performing matrix-vector multiplications has been particularly devised to handle signal spectra including very large numbers of arbitrarily spaced lines with very high numerical efficiency. The resulting simulation tool allows rigorous computation of interference effects on the nonlinear regime of UWB receivers and accurate circuit-level prediction of receiver sensitivity and channel capacitance. Simplifying assumptions typical of system-level approaches are overcome in this way, while keeping computational time at acceptable levels.

Bandstructure effects in ultra-thin-body double-gate field effect transistor: A fullband analysis

The properties of an n-channel ultra-thin-body (UTB) double-gate field effect transistor (DGFET), resulting from the bandstructure of the thin film Si channel, are discussed in this paper. The bandstructure has been calculated using a ten-orbital sp3d5s∗ tight-binding method. A number of intrinsic properties including band gap, density of states, intrinsic carrier concentration, and parabolic effective mass have been derived from the calculated bandstructure. The spatial distributions of intrinsic carrier concentration and ⟨100⟩ effective mass, resulting from the wave functions of different contributing subbands, are analyzed. A self-consistent solution of coupled Poisson-Schrödinger equations is obtained taking the full bandstructure into account, which is then applied to analyze volume inversion. The spatial distribution of carriers over the channel of a DGFET has been calculated and its effect on effective mass and channel capacitance is discussed.

Insights into the characterization of polymer-based organic thin-film transistors using capacitance-voltage analysis

Frequency dependent capacitance-voltage characteristics of organic thin-film transistors based on poly(3-hexylthiophene) as the active polymer layer are investigated. The frequency response of the channel capacitance in accumulation is examined through an analytical transmission line model, with the effect of contact resistances included in the model to account for deviations from ideal behavior. The model provides an excellent fit to the data. Furthermore, we show that the technique can be used to extract device parameters such as the mobility and the contact resistance and quantitative information on the influence of charge trapping on transport.

Measurement of Carrier Mobility in Silicon Nanowires

We report the first direct capacitance measurements of silicon nanowires (SiNWs) and the consequent determination of field carrier mobilities in undoped-channel SiNW field-effect transistors (FETs) at room temperature. We employ a two-FET method for accurate extraction of the intrinsic channel resistance and intrinsic channel capacitance of the SiNWs. The devices used in this study were fabricated using a top-down method to create SiNW FETs with up to 1000 wires in parallel for increasing the raw capacitance while maintaining excellent control on device dimensions and series resistance. We found that, compared with the universal mobility curves for bulk silicon, the electron and hole mobilities in nanowires are comparable to those of the surface orientation that offers a lower mobility.

Impact of Band Alignment on Line Electron Density and Channel Capacitance of Rectangular n-Channel Gate-All-Around Wire Field-Effect Transistor

In this paper, we apply a finite-difference-method-based mathematical scheme to simulate one-dimensional electron transport, where the parabolic band is assumed to be in the reciprocal lattice space, with arbitrary band orientation. In order to examine the validity of the theoretical scheme, we calculate wave functions of the one-dimensional electron system on a specific semiconductor surface, which has the nondiagonal component of the effective mass tensor in Schrödinger's equation. It is demonstrated that the anisotropic nature of the electron wave function is successfully reproduced with a negligibly small error in comparison with the exact analytical solutions. We characterize the surface orientation dependence of the line electron density and channel capacitance for various rectangular gate-all-around field-effect transistors (FETs). We also address the impact of the specific surface orientation of a semiconductor device on device performance.

Triple Gate FinFET Parameter Extraction Using High Frequency Capacitance - Voltage Curves

This work presents the characterization of triple Gate nMOS FinFET using high frequency Capacitance versus Voltage (CV) curves. Front channel capacitance as a function of the front and the back gate voltage is analyzed and used to determine Effective Oxide Thickness (EOT), fin height (Hfin) and the fin doping concentration (Nfin). Three-dimensional numerical simulations are performed to validate the proposed methods and also evaluated their sensitivity. The experimental results are in agreement with simulations results.

Accurate Multibias Equivalent-Circuit Extraction for GaN HEMTs

This paper focuses on the determination and analysis of an accurate small-signal equivalent circuit for gallium-nitride high electron-mobility transistors under different bias conditions. Our experimental results show that a channel capacitance has to be added to the conventional forward "cold" model for modeling the device-under-test. The validity of the proposed extraction procedure has been verified by the very good agreement between simulated and measured scattering parameters up to 50 GHz

Accurate extraction and analysis of intrinsic cutoff frequency of sub-0.1 µm MOSFETs

A new RF method based on the accurate extraction of the intrinsic transconductance and gate–source channel capacitance from measured S-parameters is proposed to determine the intrinsic cutoff frequency of sub-0.1 µm MOSFETs. Using the RF technique, the intrinsic cutoff frequency enhancement with the linear dependence on 1/Lpoly2 is observed in sub-0.1 µm bulk n-MOSFETs. It is also observed that the reduction of extrinsic charging time is the most important to increase the measured cutoff frequency in sub-0.1 µm CMOS devices.

A New Method to Extract Carrier Velocity in Sub-0.1-$mu$m MOSFETs Using RF Measurements

A novel RF method based on the accurate extraction of the gate–source channel capacitance and intrinsic transconductance from measured $S$ -parameters is proposed to determine the effective carrier velocity of sub-0.1- $mu$ m MOSFETs in the velocity saturation region. This method is developed to avoid the errors associated with underestimated charge in traditional ones. Using the RF technique, the electron velocity overshoot exceeding the bulk saturation velocity is observed along with the linear dependence of measured electron velocity on $1/L_ poly$ in bulk N-MOSFETs with a channel length of less than 0.085 $mu$ m. This extracted result is more accurate than that of previous methods, because $v_ eff$ is directly determined from the gate–source channel capacitance at high V $ ds$ instead of that at V $ ds=0$ .

Investigation of complex channel capacitance in C60 field effect transistor and evaluation of the effect of grain boundaries

Abstract Frequency and gate voltage dependences of capacitance in a C60 field effect transistor (FET) showed an intriguing power law (C ∝ f−p, p ∼ 0.3–0.35) irrespective of the gate voltage. In order to interpret this phenomenon, we formulated a complex impedance of the bottom contact FET based on a distributed constant circuit model in cases of both a single grain channel and a multi-grain channel. The power law could be well explained in terms of the complex impedance formula using only a small number of fitting parameters, the results of which indicate the validity of the model. This kind of analysis could usefully characterize the organic FETs consisting of grain boundaries, providing information on the resistance ratio of the grain interior to the grain boundary.

Longitudinal Power Distribution and Corresponding Temperature Distribution in a RF Waveguide CO2 Laser

The output power of a gas laser can not be increased by increasing the input power due to the increase of the gas temperature. As the temperature of the laser gas mixture increases up to 600K, the ampliflcation of the amplifying medium decreases rapidly and so the output power decreases. In this paper, longitudinal power distribution and corresponding temperature distribution along the CO2 waveguide laser are studied theoretically. Efiect of voltage and current distributions along and transverse to the electrode direction respectively are accounted for the studies. It is seen that the temperature decreases exponentially along the length of the electrodes on both sides of the feed point. DOI: 10.2529/PIERS060829221216 Several papers (1) have already described the huge potentiality of large area difiusion cooled RF capacitive discharges for the construction of medium | to high power CO2 lasers for materials processing. Indeed, some industrial sources based on this technology are presently appearing (2). However, there exist some open problems that limit the simple scaling of the above-mentioned technique to higher power segments. One of the major problem is certainly the attainment of a uniform gain medium excitation because of transmission line efiects (3) naturally determined by electrode dimensions comparable with the exciting RF wavelength. Typical counter measures to this di-culty are the adoption of sectioned discharges or the use of reactive elements along the electrodes. The principles for the correct design of systems based on these schemes are well established in the case of narrow channel devices (4{6), in which the equivalent-line characteristic impedance is mainly determined by the electrode structure. In (7) it is demonstrated that the same smoothing principals could be applied to wide channel high power discharges provided that the in∞uence of the discharge loading be taken into account. Indeed, from the analysis carried out in (7), it is possible to conclude that the main role played by the discharge loading is that of determining a new equivalent transmission line whose charac- teristic impedance is closer to that produced by the capacitance of the ion sheaths surrounding the electrodes rather than by the channel capacitance. This efiect determines the voltage and thus power distribution closer to a lossless-line rather than lossy-line models. Moreover (8,9), the typical impedances of sheaths and neutral plasma for the mixtures and pressure of the interests for CO2 laser construction produce distributions hardly distinguishable from uniform transmission line models (7,10,11). In this paper the temperature distribution along the longitudinal direction of the electrodes is studied theoretically by considering the longitudinal power distribution by applying the trans- mission line theory. Voltage distribution is considered along the longitudinal direction while the current in transverse direction of the electrodes. The voltage and current distributions along the electrodes are given by solving the simple transmission line difierential equations (2,7,10{12):