Leakage Current Characterization Research Articles

Characterization and Control of Carbon Nanotube Doping

Carbon nanotube FETs show great promise for beyond-Si and monolithic 3D electronics, however there are still fundamental questions to explore. In particular, controlled N- and P- doping is a fundamental process module which can be used to engineer semiconductor resistance in un-gated regions such as the contact or extension, as well as optimize band-to-band tunneling leakage [1-4]. To-date both N- and P- doping has been demonstrated for CNT, but the optimal strategies for doping control and carrier density quantification have not been determined. In this work, we present a study of N- and P- doping using solid-state dopants and doping control strategy using a dielectric barrier of tunable thickness. A TCAD evaluation reveals the tradeoffs between carrier density and mobility for increasing dielectric barrier thickness, and reveals the critical role of dielectric constant in optimizing performance of spacer doping [5]. Multiple characterization approaches under evaluation help to correlate doping strength to experimentally measurable quantities with insight into the doping mechanisms. Finally, we will summarize potential approaches for improving doping control and quantification, and progress towards integration of the doping in highly-scaled high-performance carbon nanotube FETs [6].[1] Z. Zhang, et al., “Complementary carbon nanotube metal-oxide-semiconductor field-effect transistors with localized solid-state extension doping,” Nature Electronics, 2023.[2] Q. Lin, et al., “Band-to-band Tunneling Leakage Current Characterization and Projection in Carbon Nanotube Transistors,” ACS Nano, 2023.[3] G. Zeevi, et al., “PN Junction and band to band tunneling in carbon nanotube transistors at room temperature,” Nanotechnology, 2021.[4] L. Liyanage, et al., “VLSI-compatible carbon nanotube doping technique with low work-function metal oxides,” Nano Letters, 2014.[5] C. Gilardi et al., “Barrier Booster for Remote Extension Doping and its DTCO for 1D & 2D FETs”, IEDM 2023[6] S.Li, et al., “High-performance and low parasitic capacitance CNT MOSFET: 1.2 mA/μm at VDS of 0.75 V by self-aligned doping in sub-20 nm spacer,” IEDM 2023.

Recent Fundamental Advances in Quality of High-Performance and Highly-Scaled Carbon Nanotube Transistors

Recently a number of breakthroughs have been reported by our team in the component qualities of transistors built on Carbon Nanotube (CNT) channels. However, any emerging channel material which seeks to outperform established semiconductors for transistor logic applications has a substantial hill to climb, given the incredible capabilities of advanced Si-based logic technology platforms. This talk will first aim to frame our progress on Carbon Nanotube CMOS technology in the broader context of the value proposition and desired component qualities needed to realize practical impact in computing applications. Next, we will share advances in the fundamental building blocks for Carbon Nanotube transistors towards these targets including channel, contact, doping, and gate-stack modules. Finally we will describe new record CNT MOSFET performance milestones achieved by integrating best available device components for first time, which gives insight into the remaining performance limiters and future directions.[1] G. Pitner, et al., "Building High Performance Transistors on Carbon Nanotube Channel," VLSI 2023.[2] S. Li, et al., "High-Performance and Low Parasitic Capacitance CNT MOSFET: 1.2 mA/um at Vds of 0.75 V by self-aligned doping in sub-20 nm spacer," IEDM 2023.[3] N. Safron, et al., "Low N-type Contact Resistance to Carbon Nanotubes in Highly Scaled Contacts through Dielectric Doping," IEDM 2023.[4] H.-Y. Chiu, et al., "Self-Aligned Contact Doping for Performance Enhancement of Low-Leakage Self-Alignment Method for High-Density Aligned CNT Array," Advanced Materials Interfaces, 2023.[5] T.A. Chao, et al., "Small Molecule Additives to Suppress Bundling in Dimensional-Liminted Self-Alignment Method for High-Density Aligned CNT Array," Advanced Materials Interfaces, 2023.[6] Q. Lin, et al., " Band-to-Band Tunneling Leakage Current Characterization and Projection in Carbon Nanotube Transistors," ACS Nano 2023.[7] Z. Zhang, et al., "Complementary Carbon Nanotube Metal-Oxide-Semicondcutor Field-Effect Transistors with Localized Solid-State Extension DOping," Nature Electronics, 2023.[8] S.K. Su, et al., " Perspective on Low-Dimensional Channel Materials for Extremely Scaled CMOS," VLSI 2022.[9] Z. Zhang, et al., "Sub-Nanometer Interfacial Oxides on Highly Oriented Pyrolytic Graphite and Carbon Nanotubes Enabled by Lateral Oxide Growth," ACS Applied aterials & Interfaces, 2022.[10] G. Pitner, et al., "Sub-0.5 nm Interfacial Dielectrics Enables Superior Electrostatics: 65 mV/dec top-gated Carbon Nanotube FETs at 15 nm gate length," IEDM 2020.

Band-to-Band Tunneling Leakage Current Characterization and Projection in Carbon Nanotube Transistors.

Carbon nanotube (CNT) transistors demonstrate high mobility but also experience off-state leakage due to the small effective mass and band gap. The lower limit of off-current (IMIN) was measured in electrostatically doped CNT metal-oxide-semiconductor field-effect transistors (MOSFETs) across a range of band gaps (0.37 to 1.19 eV), supply voltages (0.5 to 0.7 V), and extension doping levels (0.2 to 0.8 carriers/nm). A nonequilibrium Green's function (NEGF) model confirms the dependence of IMIN on CNT band gap, supply voltage, and extension doping level. A leakage current design space across CNT band gap, supply voltage, and extension doping is projected based on the validated NEGF model for long-channel CNT MOSFETs to identify the appropriate device design choices. The optimal extension doping and CNT band gap design choice for a target off-current density are identified by including on-current projection in the leakage current design space. An extension doping level >0.5 carrier/nm is required for optimized on-current.

Structural, magnetic, magneto-dielectric and magneto-electric properties of (1-x) Ba0.85Ca0.15Ti0.90Zr0.10O3 – (x) CoFe2O4 lead-free multiferroic composites sintered at higher temperature

Here in this article synthesis of lead-free magnetoelectric composites (1-x) Ba0.85Ca0.15 Ti0.9Zr0.1)O3 - xCoFe2O3 (BCTZ-CFO, x = 0.4, 0.5, and 0.6) is reported. Structural, magnetic, dielectric, magnetodielectric and magnetoelectric properties of lead-free BCTZ-CFO composites sintered at higher sintering temperature have been systematically investigated. The piezoelectric (ferroelectric) phase has been synthesized using the sol–gel route, while Metallo-organic decomposition (MOD) route was employed to prepare piezomagnetic (ferrite) phase. The structural and microstructural properties were studied using X-Ray diffraction and Scanning electron Microscope respectively acknowledged the presence of two distinct phases as ferrite and ferroelectric in composite samples. The dense microstructure and larger average grain size were observed for samples with higher ferrite phase content. Long-range magnetic order was observed under magnetic study for all-composites. The magnetic properties enhanced for composites prepared with higher ferrite phase content. Dielectric properties were studied at room temperature and enhanced dielectric constant has been observed for samples with higher ferroelectric phase content, while minimum dielectric loss was observed for sample with 50/50 ferrite/ferroelectric phase composition. The magnetodielectric response has been also investigated for all ME composites. Leakage current characterization has been also discussed at and above the room temperature. The magneto-electric coupling response was measured of all composites. The higher value of magneto-electric coupling coefficient has been observed for 0.5BCTZ-0.5CFO composite due to maximum possible ferrite-ferroelectric hetero-structure phase contact area.

Effect of Radiation on Reliability of Through-Silicon via for 3-D Packaging Systems

In this paper, radiation reliability of through-silicon via (TSV) was studied experimentally. Characterization of leakage current between adjacent TSVs and capacitance of an array of TSVs was used to evaluate the effects of radiation on reliability of TSVs. All samples were exposed to 60Co ${\gamma }$ radiation with a total radiation dose of 500 Gy. It was observed that leakage current increased and coupling capacitance decreased. The increase of leakage current was explained based on the percolation model for thin oxide layers. The decrease of capacitance was analyzed with the theory of coupling capacitance and equation of flat-band voltage and charge in the oxide layer. It is important and necessary to consider the effect of radiation on reliability of TSV for TSV-based applications under radiation conditions.

Highly tunable Mn-doped PZT thin films for integrated RF devices

Modern RF systems have triggered an important and urgent demand for inexpensive voltage controlled capacitors used for a wide range of applications such as tunable antennas or low-noise voltage-controlled oscillators (VCO). Ferroelectric materials have received considerable interest for electrically tunable dielectrics due to their high dielectric constant and large dielectric nonlinearity under dc bias field. Lead zirconate titanate (PZT) ceramics which have been under intense investigation for various industrial domains including micro-electro-mechanical systems (MEMS), non-volatile memories, and high-k capacitors, are especially well-known candidate materials due to their unequalled ferroelectric properties and stability in device operating ranges. However, reported voltage tunability of PZT films is relatively low (~35%@4GHz) and remains insufficient for microwave tunable devices. Therefore, much attention has been focused on the PZT modification by adding a small amount of dopants. Shao et al., studied strontium-doped PZT (PSZT) thin films and achieved a tunability of 48% @1MHz. More recently, Hu et al. reported a tunability of 65%@10kHz for lanthanum-modified PZT (PLZT) films. In the presented study, effect of manganese (Mn) doping on electrical properties of PZT (PMZT) thin films has been investigated. Metal/insulator/metal (MIM) capacitors using PZT-based thin films and ruthenium (Ru) top electrodes were processed on platinized (Pt) silicon wafers by a sol gel method. Dielectric properties of PMZT thin films were studied by varying the dopant amount and compared to those of pure PZT layers. At this end, on-wafer electrical measurements were conducted with a particular attention on leakage current characterization and RF measurements under DC bias voltage. We have shown that leakage current density decreased from 6.5 μA/cm2 to 1 μA/cm2 at 850kV/cm by doping PZT with Mn. Observed conduction mechanisms will be discussed in detail in the full-length paper. Moreover, developed PZT-based thin films exhibit high dielectric strengths achieving 2.1MV/cm and outstanding tunability as high as 85% (~7:1) @1GHz at bias voltage of 20V. Thus, PMZT tunability is among the highest ones reported in the literature for PZT-derived thin films but also for other piezoelectric materials. Indeed, in comparison, the tunability of BST-based materials, typically studied for voltage tunable applications, does not exceed 5:1. These remarkable results indicate that Mn-doped PZT thin films are promising candidates for RF tunable capacitors.

A Voltage-Based Leakage Current Calculation Scheme and its Application to Nanoscale MOSFET and FinFET Standard-Cell Designs

Logic-level estimators of leakage currents, in nanoscale standard-cell-based designs, are relevant for the dramatic speed advantage with respect to analog SPICE-level simulation. We propose a novel logic-level leakage estimation model based on the characterization of voltages at the internal nodes of digital cells, in conjunction with the characterization of leakage currents in a single field-effect transistor (FET) device and with the input-dependent Kirchhoff current law expression of the total current in the cell topology. The voltage-based nature of the approach simplifies the inclusion of supply voltage variation/scaling impact, as well as of output voltage drop (loading effect), on leakage currents. The method has been implemented in hardware description language models of a complete cell library. Exhaustive tests report average accuracy below 1% error in 22-nm CMOS and 20-nm FinFET technologies, when compared with SPICE BSIM simulation results.

Methods for rapid frequency-domain characterization of leakage currents in silicon nanowire-based field-effect transistors.

Silicon nanowire-based field-effect transistors (SiNW FETs) have demonstrated the ability of ultrasensitive detection of a wide range of biological and chemical targets. The detection is based on the variation of the conductance of a nanowire channel, which is caused by the target substance. This is seen in the voltage–current behavior between the drain and source. Some current, known as leakage current, flows between the gate and drain, and affects the current between the drain and source. Studies have shown that leakage current is frequency dependent. Measurements of such frequency characteristics can provide valuable tools in validating the functionality of the used transistor. The measurements can also be an advantage in developing new detection technologies utilizing SiNW FETs. The frequency-domain responses can be measured by using a commercial sine-sweep-based network analyzer. However, because the analyzer takes a long time, it effectively prevents the development of most practical applications. Another problem with the method is that in order to produce sinusoids the signal generator has to cope with a large number of signal levels. This may become challenging in developing low-cost applications. This paper presents fast, cost-effective frequency-domain methods with which to obtain the responses within seconds. The inverse-repeat binary sequence (IRS) is applied and the admittance spectroscopy between the drain and source is computed through Fourier methods. The methods is verified by experimental measurements from an n-type SiNW FET.

Leakage current characterization and compensation for piezoelectric actuator with charge drive

In this paper, the effects of leakage current on piezoelectric actuators with charge drive are presented, and a method to compensate it is proposed. Considering a piezoelectric stack driven by a switched capacitor charge pump as an example, the leakage current was found to be dependent on the voltage applied on the actuator but had a negligible relationship with the driving routes. The nonlinear relationship between the leakage current and the voltage was investigated, and a feedback circuit based on the applied voltage of the actuator was used for compensation. Experimental results showed that a displacement drift rate of lower than 0.033nm/s could be achieved with an applied voltage from 0V to 60V, whereas the drift rate was as large as 0.9nm/s without compensation.

The dielectric and leakage current behavior of CoFe 2O 4-BaTiO 3 composite films prepared by combining method of sol-gel and electrophoretic deposition

Composite CoFe 2O 4-BaTiO 3 films were prepared by combining method of sol-gel and electrophoretic deposition. CoFe 2O 4 thick films were prepared by electrophoretic deposition method and then BaTiO 3 precursor solution was spin-coated on these thick films to obtain dense structure. X-ray diffraction indicated that the films consisted of both spinel CoFe 2O 4 and perovskite BaTiO 3 phase. Dielectric properties and leakage current conduction of the films were studied. Leakage current characterization of the films exhibits an Ohmic conduction behavior at lower electric field and space charge limited conduction behavior at higher electric field, respectively.

Reliability study of TaON capacitors: From leakage current characterization to ESD robustness prediction

Electrostatic discharges are a permanent threaten for integrated metal–insulator–metal capacitors. Hence, the development of comprehensive models able to predict the capacitors robustness against ESD aggression is of major importance to adopt the adequate protection strategies. This work focuses more particularly on the failure mechanisms of TaON capacitors submitted to HBM ESD waves. From leakage current characterization to thermal dissipation effects, we propose a complete reliability model which accurately foresees not only ESD failure voltage, but also TDDB capacitors lifetime.

Characterization of leakage current on diamond Schottky barrier diodes using thermionic-field emission modeling

A diamond vertical Schottky barrier diode (SBD) with nonepitaxial crystallites (NCs) exhibits high leakage current in both its forward and its reverse characteristics. A shunt path current through the grain boundary of the NCs is the dominant mechanism. The defectless device shows a low leakage current of less than 10 − 11 A/cm 2, and the device yield corresponds to the density of the NCs. The reverse leakage current of the defectless device increases with the reverse field. The leakage current of the diamond SBD is in good agreement with the tunneling model described by thermionic-field emission (TFE) rather than the conventionally used barrier-lowering model. The TFE current dominates when the reverse electric field is larger than 1.2 MV/cm, and current density reaches 10 − 6 A/cm 2, even at 1.6 MV/cm, which is lower than the avalanche limit.

Dielectric Properties and Leakage Current Characterization of the Ba(SnxTi1-x)O3 Thin Films Prepared by Radio Frequency Magnetron Sputtering

Ba(SnxTi1-x)O3 (BSxT1-x, 0≤x≤0.15) thin films deposited by rf magnetron sputtering with platinum (Pt) top and silver (Ag) bottom electrodes have been characterized with respect to the dielectric properties and leakage current density as a function of composition and rf power. BSxT1-x thin films are amorphous when deposited at rf powers of 100 and 125 W, 5×10-3 Torr working pressure, an O2/(O2+Ar) ratio of 1/(1+9) and room temperature. The XRD result shows the presence of a single perovskite phase of BaTiO3, operated at a range of rf power increasing from 125 to 175 W. The maximum capacitance of Pt/BSxT1-x/Si/Ag capacitors increases with increasing Sn content. The ferroelectric characteristics of the capacitance–voltage hystersis loop in the BSxT1-x thin films are observed. The leakage current density of the Pt/BS0.15T0.85/Si/Ag capacitors at 100 kV/cm varies from mid 10-6 to about 10-8 A/cm2 with the rf power decreasing from 175 to 125 W. The dominant conduction mechanism of the BS0.15T0.85 thin films has shown to be related to Schottky emission (SE) and Poole–Frenkel (PF) mechanisms. The remnant polarization (Pr) and coercive electric field (Ec) of the above device appear to decrease with increasing Sn content.

Leakage current characterization for estimating the conditions of non-ceramic insulators’ surfaces

In this work both detection of the beginning of dry-band arcing and correlating the average value of leakage current (LC) with non-ceramic insulator surface damage have been investigated. Silicone rubber insulators were tested in salt-fog under different voltage and conductivity levels. The autocorrelation function (ACF) was calculated for both the fundamental and third harmonic components of LC during the early aging period (EAP). It has been observed that distinct differences exist in the behavior of both the fundamental and that of the third harmonic components of the LC during EAP. Although the fundamental component of the LC begins to grow immediately after starting the test, the third harmonic requires a much longer period of time to begin. Dry-band arcing is highly correlated with distortion in the LC and hence to its third harmonic component. But it has been observed that the level of the fundamental component of LC at which the third harmonic component started to increase is different from one case to another. As such, it is more appropriate to use the ACF of the third harmonic component of LC as an indication of dry-band arcing rather than a simple threshold value. Moreover, the average value of LC during late aging period (LAP) was correlated with the damage of non-ceramic insulators. It has been found that the average level of both the fundamental and third harmonic component of LC is well correlated with the different degrees of damage of non-ceramic insulators’ surface.

Leakage current characterization for estimating the conditions of ceramic and polymeric insulating surfaces

Leakage current produced on contaminated ceramic and polymeric insulating surfaces was analyzed using a wavelet transform technique providing time-frequency domain information. Salt-fog tests with and without the deposition of non-soluble contamination were conducted in a laboratory, during which the leakage current was separated into sinusoidal, local arc, or their transition components per halfwave of power frequency. The wavelet transform allowed the detection of the zero-cross point of the base current at 50 Hz without the need for voltage information. The source information regarding the distortion level (I/sub 150 Hz//I/sub 50 Hz/) of the current half-wave separated by the zero-cross point and a time lag to onset in current attributable to arcs are used in order to obtain the above three components. The time-integrated values (cumulative charges) of these components were found to correlate with hydrophobicity and contamination level. It was shown that time variations of the cumulative charges and of their component ratios were useful for estimating the conditions of ceramic and polymeric insulating surfaces.

Characterization of High-k Dielectric Films with Tunneling AFM

ABSTRACTIn this paper, we report the leakage current characterization of HfO2 high-k dielectric thin films by using tunneling AFM, which utilizes a conducting AFM probe to detect current passing through the sample and the probe while simultaneously acquiring a topographic image. We have studied tunneling current behavior of HfO2 films by characterizing the hot spots, which are characterized by excessive local leakage current, as well as the overall current distribution. Tunneling AFM results show sensitive dependence of tunneling current with variation of film thickness. The current distribution can be described approximately by a log-normal distribution, which is consistent with the characteristics of the thickness variation. Furthermore, the film structure and thickness were also characterized with TEM and spectroscopic ellipsometry.

Characterization of leakage currents in long-lifetime capacitors

The purpose of this paper is to present a new procedure that yields the material parameters characterizing leakage currents in MOS devices (generation lifetime in the depletion region τ g , recombination lifetime in the bulk τ r , interfacial generation velocity S) by means of the linear-sweep technique at different temperatures and at different depths of the depletion region. This characterization method is applied to long-lifetime MOS capacitors for which different contributions to the leakage current (generation in the depletion region, diffusion from the neutral bulk and interfacial generation) are of the same order of magnitude.